Ejector mixing of solutions in electroplating

Drill for mixing mortar

Hi all! Construction or major repairs are almost never complete without work that requires preparing a working mixture of dry components and water. And for mixing the solution in large portions (from 8 liters), it is very convenient to use a special tool - a construction mixer. This is exactly what we will talk about today, and we will look at how to choose a high-quality construction mixer.

Model rating

The following brands of drill-mixers are the most popular among consumers.

• Fiolent is a Russian-made product that is optimal for mixing the thickest and most viscous compositions. The power of the device is 1100 W, and the speed is 600 rpm.
• Rebir - the most popular low-speed drills are produced under this brand. Some models from this manufacturer have exceptional performance characteristics: power up to 2000 W and rotation speed up to 500 rpm.

Main types of mixers

The choice of a construction mixer primarily depends on the volume of work and frequency of use.

By type of drive, the tool differs into:

• Manual. The device has a special attachment and is driven by human muscle power. Suitable for mixing small portions of the working mixture.
• Electric. This can be a drill or hammer drill with a special attachment, or a specialized device with a set of attachments.

It is used during large-scale construction and repair work.

The tool comes with either one or two screws. Twin screw models are characterized by higher power and increased productivity. The nozzles of a twin-screw mixer rotate in different directions, due to which the position of the mixer is stabilized and it is more convenient for them to work.

Based on power, construction mixers are divided into household models (mostly hammer drills and drills, as well as low-power mixers) - up to 1 kW, and professional tools - these include hammer drills and specialized mixers with a power of over 1 kW. The power of specialized units designed to work with heavy solutions is 2.5 - 3 kW.

What to look for when choosing

To choose the right construction mixer, pay attention to the characteristics and functionality of the models.

Weight. From 2 kg (for a drill with an attachment) to 15 kg (professional tool). Semi-professional models weigh about 7 - 9 kg.

Speed ​​adjustment. The mixer is designed for preparing suspensions of various viscosities, in order to cope with the work regardless of the characteristics of the composition, it must be equipped with a built-in electronic mechanism that regulates the engine speed. Without a regulator, the operating mode of the device during the mixing process will be disrupted due to changes in viscosity.

Torque. The higher the number, the denser the mixture it can work with. A household tool with a power of up to 1 kW and a torque of up to 20 Nm allows you to prepare primers, putties, painting compounds, tile adhesive, and plaster mixture. Semi-professional and professional tools with a torque of 50 - 100 Nm can handle concrete mixtures.

Speed. Low-power models are single-speed. The powerful tool is equipped with a gearbox - the second speed is intended for preparing liquid solutions.

When deciding which construction mixer to choose, pay attention to additional model options, in particular:

• Smooth start. In this mode, the engine starts without jerking, so that the components of the mixture do not splash or scatter to the sides. By reducing the peak load, the service life of the power tool is extended.
• Electronic motor protection system. Automatically turns off the motor when the brushes wear out, when overheating occurs, and stops operation if the loads have reached critical values.
• Hand protection. The handles are arranged in such a way that it is convenient and safe to work with the mixer.

Special mixers

Anchor or frame mixers with blades curved to the shape of the walls and bottom of the vessel are considered one of the types of blade mixers and are used for mixing viscous liquids and pasty materials (Figure 4). Anchor and frame mixers, the shape of which is close to the internal shape and diameter of the container or apparatus, clean the walls of the apparatus from material adhering to them, thereby improving heat transfer and preventing local overheating of the mixed substances. They are durable and suitable for mixing viscous liquids, as well as for mixing low-viscosity liquids in containers heated using heating jackets or coils, when precipitation may occur or the mixing product may adhere to the heated walls of the container or apparatus. In these cases, an anchor or frame stirrer is used so that the edges and underside of the stirrer clean the walls and bottom of the apparatus from settled mixing products. Typically, these mixers are driven by a geared motor at a low speed, such as 15–40 rpm.

Figure 4. Anchor (left) and frame agitators

A sheet mixer consists of an approximately square blade mounted on a vertical shaft (Figure 5). These mixers are especially suitable for processes that require uniform distribution of the substance throughout the volume, such as dissolution, dilution or chemical reactions. Sheet mixers are sometimes classified as turbine mixers without a stator based on the type of flow they produce. In addition to the purely tangential flow, which is predominant, vortex flows are created by the upper and lower edges of the mixer, similar to the flows formed when mixing with a paddle mixer.

Figure 5. Sheet agitator

At a high number of revolutions, the tangential flow becomes radial. There are very simple designs of sheet mixers used in various industries. They are especially widely used to accelerate chemical reactions, dissolution and processes occurring during heat exchange. Creating jets in a liquid to promote dissolution can be achieved by drilling holes in the stirrer blade.

Sheet mixers are very durable and suitable for heavy-duty mixing, but are not suitable for mixing slurries and viscous mixtures.

The drum mixer is a paddle drum in the form of a so-called squirrel wheel (Fig. 6). Mixers of this design create a large lifting force and are therefore very effective in carrying out reactions between gas and liquid, as well as in obtaining emulsions, processing rapidly separating suspensions and stirring up heavy sediments. Recommended conditions for using drum mixers: ratio of drum diameter to vessel diameter from 1:4 to 1:6, ratio of liquid height to drum diameter of at least 10.

Figure 6. Drum mixer

Pendulum mixers. Mechanical stirrers are usually rigidly mounted on the lid or on the edge of the container. However, if it is necessary for the flow of liquid caused by the stirrer to reach places behind some partition, or if it is necessary to protect the stirrer from damage when striking pieces of loaded material, it is secured to an elastic pad, which allows some freedom of movement of the stirrer in the container. To do this, the support of a conventional propeller mixer with an electric motor is mounted on a rubber lining, securing it to the lid of the container. Thus, the stirrer is able to move in the vessel within the elasticity of this lining, and, in addition to rotational motion, also performs oscillatory motion. Sometimes, instead of a rubber lining, springs are used, onto which a support with a transmission, an electric motor and a stirrer are attached. In both cases, the elasticity of the lining must be calculated so that the stirrer cannot hit the walls of the vessel. .

Preparation of concrete manually and using a drill mixer.

Household models are equipped with handles in the form of brackets - a ring version. For professional models for working with heavy mixtures, the handle has a T-shaped design. If the coating is anti-vibration and anti-slip, this makes the operation of the device more comfortable.

The configuration also influences the choice of the appropriate model. The kit includes a nozzle along with a device for fixing it. The nozzle is attached in different ways.

Threaded connection. The nozzle is screwed into the spindle with its threaded upper part. Used in professional tools, as it provides reliable fixation.

Jaw chuck. Suitable for drills - mixers and household electric drills. A special key is used to secure it in the chuck. Suitable for liquid, light and medium viscosity solutions.

SDS connection. Designed for hammer drills. The nozzle must have an appropriate design. It is used for mixing adhesives, plaster and putty solutions.

FastFix keyless chuck. The system allows you to quickly change attachments, similar to a screwdriver, but is not designed for frequent work with concrete mixtures - the edges of the chuck are erased. If reverse is used, there is a danger of the attachment becoming loose.

Morse cone. The most reliable option, allows you to work with any type of composition. Used on professional instrument models.

In addition to purchasing the construction mixer itself, you need to take care of choosing attachments. The propeller stirrer is suitable for liquid formulations. The nozzle is a cross with vertical blades used for mixing viscous and heavy mixtures.

The left-handed spiral (moves the mixture down) and right-handed (moves the mixture up) is used for gypsum- or cement-based compositions and “lightweight” concrete. The double-sided screw is designed for liquid and non-viscous mixtures. The universal screw is suitable for working with all types of mixtures.

Conclusion

When choosing a construction mixer, proceed from the range and volume of work to be performed. For repairs, a household model is usually enough; for construction, it is recommended to purchase a semi-professional mixer, choosing a tool with the optimal price-quality ratio.

Video on the topic “how to choose a construction mixer”:

When carrying out
repair work, it is very often necessary to use a wide variety of manual, automatic or semi-automatic operations: chiselling, drilling, polishing, grinding, cutting, welding, etc. It is known that for each repair operation there is its own specialized tool.
It is not always necessary to perform these operations equally often: sometimes it happens that a repair operation occurs relatively rarely or even once. What to do then? Should I run out and buy the necessary construction tools for one-time use? Borrow from neighbors, acquaintances or friends “for a couple of days”? Of course, there is a desire to use a tool that is already in use to replace the missing one.

The most common tool used in repair and construction work is a hammer drill. Almost everyone who has encountered repairs at least once in their life has this power tool. On the other hand, one of the most rarely used tools today is a construction mixer , designed for mixing various construction and repair mortars. The reason for its rare use in repairs is the usually small amount of solution (varnish, glue, etc.) stirred at a time, in which it is quite possible to do without mechanization: stir by hand.

However, there are cases when it is simply necessary to use electromechanical stirring: a very viscous medium, a large volume, a harmful environment, a large mass of one batch, specificity of the process (uniformity, very fast or very slow shaft rotation speeds, a combination of them), short terms , requiring high performance, etc.

In all of the above methods, they try to replace the mixer with a puncher when mixing. How justified is this? Is the hammer drill capable of performing a function that is not typical for its main application? We will try to answer all these questions in this article.

As you know, modern hammer drills are capable of operating in at least two modes: drilling and hammer drilling. It is also known that to carry out drilling, an adapter (additional chuck) for drills is inserted SDS+

MIXING EQUIPMENT FOR CHEMICAL PRODUCTIONS

General information

The process of mixing (or mixing) is understood as such a mechanical process, as a result of which the initially separately located components, after uniform distribution of each of them in the mixed volume, form a homogeneous mixture.

The reverse of the mixing process is the segregation process, which leads to the separation of the mixture into separate components.

Stirring accelerates all operations associated with the transfer of heat or mass (heating or cooling, suspension, dissolution, crystallization, adsorption and other heterophase processes). It leads to an increase in temperature and concentration gradients at the interface of interacting phases due to their reduction in the volume of the apparatus and a decrease in the thickness of the boundary layer.

In the production and processing of materials in chemical technologies, various mixing machines and apparatus are used.

According to their technological purpose, mixers

Based on the organization of the technological process, they are divided into continuous and batch mixers.

Continuous mixers are superior in performance to batch mixers, allow for complete automation of the mixing process, and have low energy consumption per unit of production and low metal consumption. Continuous mixers also allow several processes to be carried out simultaneously, for example: mixing and granulating; mixing, granulating and drying; mixing, granulating and classification; mixing and grinding, etc. However, with all its advantages compared to batch mixers, difficulties arise in dosing materials in strictly specified quantities. Therefore, batch mixers are used to prepare multicomponent mixtures and mixtures of high homogeneity.

To mix materials, pneumatic, hydraulic, gravitational mechanical, and combined methods are used.

Pneumatic mixing

consists of passing a stream of air or other gas through a layer of a stirred system (bubbling).
The hydraulic method of mixing is carried out This creates a reduced pressure, the second liquid component is sucked in and mixing occurs). The mechanical method of mixing consists of creating complex intensive movement of mixed materials using various devices that ensure the movement of the medium in different directions.
Mixing devices are made in the form of blade, frame, anchor, propeller, turbine, planetary, screw, vibration and other mixers. Gravity mixing is carried out The mixing process is often characterized by the degree of mixing, intensity and efficiency of mixing. The degree (uniformity) of mixing characterizes the distribution of the concentration of the mixed substance in different parts of the apparatus.

In any microvolume of an ideally homogeneous mixture, from a phenomenological point of view, there must be particles of all components in quantities determined by their given ratio. However, such an ideal arrangement of particles in the volume of the mixture is not actually observed. In arbitrarily selected micro-volumes of the mixture, a large number of combinations of the relative proportions of various components are possible, i.e. their distribution in the mixture is random. Therefore, most methods for assessing the homogeneity (or quality) of a mixture are based on statistical analysis methods.

To simplify calculations, all mixtures are conventionally considered two-component, consisting of a so-called key component and a conditional one, which includes all other components of the mixtures. This technique allows you to evaluate the homogeneity of a mixture by the distribution parameters of one random variable - the content of the key component in mixture samples. As a key component, a component is usually chosen that is easily subject to quantitative analysis, or its distribution in the mixture is strictly regulated by the technical requirements for the finished mixture.

The homogeneity of the mixture is assessed by analyzing samples taken at a certain moment of mixing from various parts of the apparatus volume. As a quantitative indicator of mixing homogeneity, the degree of mixing I

or
coefficient of variation k
c, which are expressed in fractions of unity or percentage.

Mixing degree I

calculated using the formula [1]:

I=(x1+x2+ … +xn)/n

.
(1) Here n
is the number of samples;
x1, ..., xn
– relative (volume or mass) concentrations of the substance in the samples, determined by the formulas:
xi
= (at) and (at), where
сi
is the concentration of the key component in
the i
-th sample of the mixture, %; — arithmetic mean value of the concentration of the key component in all samples of the mixture, %;

The closer the degree of mixing is to unity ( ), the greater the homogeneity of the distribution of the concentration of the key component in the mixture.

Coefficient of variation kc

, in relation to the process of mixing dispersed materials, is called
heterogeneity coefficient .
It is expressed by relations [2] or . (1a)

As the heterogeneity coefficient of the mixture increases, its concentration heterogeneity increases. For the same mixture, the value of the heterogeneity coefficient depends on the mass of the samples and their number. The smaller the mass of samples taken, the greater the value of k

c.
If, for example, the volume of the sample is taken equal to the volume of the apparatus, then at any time the average concentration of the key component in the sample is equal to its average concentration in the apparatus. If sample volumes are comparable to the sizes of molecules, then due to molecular fluctuations, ideal uniformity of distribution in the volume of the apparatus is generally unattainable. The number of samples n
taken from the mixture and then subjected to quantitative analysis for the content of the key component determines the reliability of assessing the quality of the mixture.

If the studied indicator of the content of the key component in the mixture obeys the normal distribution law, which is usually the case in practice, then it is possible to estimate the confidence probability that the value differs from the true value c

is by an amount less than c:

.

Usually limited to a confidence level of 0.9 or 0.95; the accuracy of the estimate is determined by the formula

,

where is the statistical standard deviation; tc

=
c
/
c
– Student’s coefficient, which depends on the sample size
n
and the specified confidence level (Table 1).

Table 1

Student coefficient values

In a number of cases, during experimental studies it is necessary to determine the minimum sample size n

(number of experiments), which with a given accuracy
c
and confidence probability will allow us to determine the desired value.
When a random variable is distributed according to the normal law, which is often encountered in practice, and with a known standard deviation c or coefficient of variation k
c , the sample size is calculated from the relation

,

where = is the relative measurement accuracy;

If c or k

c are unknown, they are determined based on the results of preliminary studies.

For bulk material, the minimum permissible sample weight G

m, expressed in grams, is determined from the formula [3]:

G

m=1.2 104 ,

where d

e—equivalent particle diameter, cm;
h—density of the particle material, g/cm3; c
0 is the concentration of the key component in the mixture, %.

For powdery materials, the sample weight is usually 1-5 g.

For mixtures of high homogeneity, the heterogeneity coefficient is k

c < 2%, good quality - 2% <
k
c < 5%, low quality - 5% <
k
c < 8%.
In industrial mixers it is not possible to obtain a mixture with values ​​of k c
< 1.5% (with a sample weight of 1 g).

During a periodic mixing process, the experimental dependences of k

c versus mixing time
t
, obtained for various designs of mixers and their operating modes, are called kinetic mixing curves. These curves have three characteristic sections (Fig. 1), each of which corresponds to a specific mixing period [4].

In period I, the mixing process prevails compared to the segregation process. Due to the reduction of aggregates of identical particles and their convective transfer throughout the internal volume of the mixer, a sharp decrease in the heterogeneity coefficient occurs.

In period II, the rate of the mixing process becomes commensurate with the rate of segregation, therefore the values ​​of kc

from moment tk

change insignificantly over The mixing process is carried out mainly by moving and

The kinetics of the periodic mixing process is most often described by an equation like:

k

c(
t
)=
ak
co at ,

where k

c(
t
) is the mixture heterogeneity coefficient at time
t
;
a
– proportionality coefficient;
k
co is the mixture heterogeneity coefficient at the initial moment of mixing (determined by the ratio of the mixture components);
Фt
is a function (or parameter) that depends on the physical and mechanical properties of the mixture, geometric dimensions and technological parameters of the mixer and has a dimension inverse to time.

Mixing time (homogenization) is the period of time required to achieve the technologically required degree of homogeneity of the system. Knowledge of it is necessary when conducting metabolic reactions and crystallization processes, preparing solutions, suspensions, and dry mixtures. It is especially important when carrying out continuous processes. In addition, the mixing time can serve as a criterion for comparing the operating intensity of different devices.

If the parameters of the periodic mixing process do not change, then taking the logarithm of equation (1), after transformations we obtain an expression for the mixing time:

,

where kcm

— the maximum value of the heterogeneity coefficient, determined by the technical specifications for the finished mixture.

With a continuous mixing process, the supply of components for mixing and the delivery of the finished mixture are carried out continuously. The quality of the prepared mixture in such mixers depends not only on the mixing process, but also on the characteristics of the feed streams and their dosing. Almost no feeder or dispenser can provide a continuous supply of material in a strictly specified quantity at each time. Consequently, an additional condition is imposed on the main task of the mixer (high-quality mixing of incoming components) to smooth out fluctuations in the supply flows.

The residence time of an elementary volume of the reaction mass in a continuous reactor (cascade of reactors) is a probabilistic characteristic.

With sufficiently intense mixing, a stable turbulent regime is achieved in almost the entire volume of the reactor. The movement of an individual element of a liquid volume (solid particle) is extremely complex. Under these conditions, any volume element in a relatively short time can end up at any point in the reactor, and it is impossible to predict in advance the trajectory of its movement. Any of the particles or molecules present in the reactor can with equal probability end up at any point in the reactor, including at the exit from it. Along with this, there are particles in the reactor that for a very long time did not manage to get to the outlet of the reactor. Thus, the residence time of a particle in the reactor is a random variable that can take values ​​from 0 to infinity. Here, the mixing process is characterized by the average statistical value of the residence time of the mass in the reactor, determined with a certain confidence probability.

The mixing intensity is assessed by the rate of change over time in the degree of mixing or the heterogeneity coefficient dk

c/
dt
.
The efficiency of mixing is determined by the amount of energy expended on it to achieve a given technological effect.
Of the two devices, the one that achieves the required technological effect with less energy and/or time will work more efficiently. There are various approaches to theoretical analysis of the operation of continuously operating mixers, from practical recommendations based on engineering experience in carrying out mixing processes on mixers of various designs, to a deterministic mathematical description.

If there is insufficient information about the physical essence of occurring phenomena or if it is not possible to create a deterministic model of them in the form of functional dependencies that reflect the physical nature of the phenomena, experimental statistical methods are used. As a result, the mathematical description of the mixing process is carried out at the level of empirical relationships connecting the main characteristics of the mixing process. Within the framework of the approach under consideration, purely formal processing of experimental data is often carried out, using relationships (such as regression models, etc.) outside of physical concepts about the mechanism of the mixing process and thereby deliberately limiting the possibility of using the calculated equation to the narrow framework of the experiment.

Apparatus for mixing liquids.

Based on the dynamics of the mixing organs, devices for mixing liquids are divided into devices of static and dynamic operating principles.

Static mixers (Fig. 2) are devices with fixed mixing elements 1 built into a cylindrical pipe 2. Mixing and dispersing liquids and suspensions is carried out by using the energy of the flow when it is repeatedly divided into elementary streams and their reorientation.

Fig. 2. Diagram of a static mixer.

The advantages of static mixers over capacitive equipment with mixing devices and dynamic (vibrating) mixers, with comparable results in the quality of the resulting mixtures, are associated with low energy and metal consumption, ease of manufacture and maintenance, compactness and low cost. Static mixers are widely used in the emulsification of liquids.

Apparatuses with stirrers . Mechanical mixing is carried out in devices of a dynamic operating principle, which are generally called devices with mixers. In particular cases, they are named based on the specific purpose of the device (reactor, extractor, repulpator, causticizer, etc.). Mixing is carried out in order to create homogeneous solutions and suspensions and intensify the processes of heat and mass transfer (physical or in combination with a chemical reaction). To achieve these goals, mixers and apparatus of various designs are used, taking into account the characteristics of each specific process.

Vessels for apparatus with agitators are cylindrical in shape and have a flat, conical or elliptical bottom. They are usually installed vertically. Currently, the chemical engineering industry produces 10 types of standardized vessels for apparatus with mixers (GOST 20680-75) with a capacity from 0.01 to 100 m3 and a diameter from 273 to 3200 mm. They can operate under vacuum and pressure up to 6.4 MPa. The housings of the devices are manufactured in 22 versions. The index of a standard apparatus is designated according to GOST 25167-82 as follows. For example, the index 1110-25-0.6U-001-U2 means that the device has an elliptical bottom and a welded elliptical lid - the first digit (1); smooth welded jacket - second number (1); frame mixer (10); capacity 25 m3; can operate under pressure of 0.6 MPa; made of carbon steel - letter U; model number - 001; the next letter U indicates the climatic version, and the last number (2) indicates the placement category.

The selection and ordering of standard devices with mixers is carried out according to catalogs.

The body of the device can be made entirely welded (Fig. 3, a) or with a removable cover (Fig. 3, b). On the cover of the device there are fittings for filling, installation of instrumentation, inspection windows and a hatch that serves for inspection of the internal surface and repair. As required by the installation conditions, the devices are manufactured with side legs and a lower fitting for emptying (Fig. 3, b) or on stands welded to the bottom and with a pipe for squeezing (Fig. 3, a) with compressed air or inert gas. Apparatuses of the latest design are usually used for batch processes.

Partitions can be mounted inside the body of the apparatus to prevent turbulence of the liquid and the formation of a funnel. The presence of reflective partitions in the apparatus causes a significant increase in the power consumed by the mixer, but has little effect on the intensity of mass transfer. Therefore, placing them in

solvents and crystallizers is considered impractical.

Depending on the conditions of the technological process, the devices are manufactured

Rice. 3. Reactors with stirrers:

A

— periodic action with a frame mixer and a pressing pipe; b-continuous action with a propeller mixer and diffuser. 1 - electric motor; 2 - gearbox; 3 — stuffing box seals; 4 — hatch; 5 - thermometer; 6 — fitting for steam supply; 7 — fitting for condensate; 8 — support paw; 9 — air vent; 10 — compression pipe; 11- fittings for supplying reagents; 12 — drain fitting; 13 — diffuser; 14 — emptying fitting.

supplied with or without a heat exchange jacket. If dilution of the solution does not play a significant role, it can be heated with live steam supplied through an ejector introduced into the solution. It is undesirable to use devices with coils in the production of crystalline substances because they quickly become fouled with sediment and make cleaning difficult.

If it is necessary to quickly mix two solutions, the inlet fittings for both solutions are placed in the upper part of the central pipe enclosing the mixer shaft. The upper part of the pipe protrudes from the solution, and the lower part approaches the propeller mixer, which pushes the solution down. This design of the apparatus allows you to quickly mix concentrated solutions without diluting them with the reacted solution, which is important when carrying out the process to obtain highly dispersed sediment (for example, in the production of barium sulfate and carbonate).

A rapid reduction in supersaturation (when obtaining a coarse-crystalline precipitate) is achieved by diluting the initial reagents with the reacted mixture. To do this, solutions are introduced into the reactor through submersible fittings to the lower end of the diffuser, in which a propeller mixer is located, pushing the solution upward (Fig. 3, b

)
.
The solid phase present in the reactor can serve as a seed for the newly crystallizing substance.

Although the design of apparatus with agitators refers to ideal mixing apparatus, in continuous processes complete mixing cannot be achieved in a single apparatus. In addition, when conducting mass transfer processes (dissolution, crystallization, etc.), it is difficult to ensure the required residence time of solid particles. Therefore, mixing apparatuses are combined into multi-stage systems in which the solution flows from one apparatus to another by gravity. Structurally, multi-stage systems are designed either in the form of a cascade of series-connected devices (Fig. 4) or in the form of a horizontal device divided into sections by partitions (Fig. 5).

Fig.4. Cascade of apparatus with mixers (battery of crystallizers).

Fig.5. Reactors for the production of extraction phosphoric acid.

A

– cylindrical sectional extractor; b – rectangular sectional extractor

In devices (sections) of large capacity, several mixers should be installed to create intensive mixing throughout the entire volume (Fig. 5, a).

In cases where equalization of the solution concentration throughout the entire volume of the apparatus is unimportant, but long-term residence of particles (slowly settling) in the apparatus is necessary, apparatuses with a large vessel height ratio H

to its diameter
D
, equipped with frame or blade mixers that create intense circumferential circulation (for example, a mixer of known milk with filter liquid in soda production or a causticizer of the first stage of causticization in the production of caustic soda using the lime method).

When absorbing gases, you can use devices whose height is several times greater than the diameter, and several turbine mixers are located on the shaft at a distance of 0.8 D

from each other.
This solution makes it possible to provide intensive mixing throughout the entire volume, to achieve a large and precisely defined contact time, which ultimately allows one to achieve a large driving force for the process. Energy consumption in this case is lower than in a larger diameter apparatus with one stirrer. When installing several mixers on one shaft, the distance between them should not be less than the diameter of the mixer d
and usually does not exceed
3d.
The liquid level above the top mixer is (1.5 2.0)
d.
The design of the stirrer, as well as the type of vessel, play the most important role in the mixing process. Thus, an apparatus with reflective partitions provides a different mixing mode than an apparatus without a partition, even if they have the same stirrer installed.

Basic inorganic technology uses propeller, turbine, paddle and frame mixers. GOST 20680-75 regulates 12 main types of mixers. The most commonly used types of mixers are shown in Fig. 6. .

Fig.6. Mixer types:

a, b

– turbines with inclined blades;
c
- three-bladed;
d, e
- turbines with straight blades;
e
- bladed;
f-u
- frame.

In the most general case, they can be divided into high-speed and low-speed. High-speed ones include propeller and turbine mixers, the operating diagram of which is shown in Fig. 7. These mixers, depending on the shape of the blades and the way they are installed, can create radial, axial and radial-axial flows of liquid.

High-speed mixers usually operate in devices with reflective partitions. The absence of partitions leads to turbulence of the liquid and the formation of a funnel (Fig. 7, c

).
In this case, the liquid does not mix well, reducing the flow turbulence and the useful volume of the apparatus. The number of partitions in the devices is usually four, and their width is 0.1D .
In the case of liquids with a viscosity close to the viscosity of water, the partitions are located near the walls of the apparatus. For liquids with high

high viscosity (> 7 Pa s), this arrangement of the partitions leads to the formation of stagnant zones around the partitions, so in this case they are located at a certain distance (0.2 0.5) V

from the wall of the apparatus. The role of partitions that prevent the formation of funnels can be played by coil struts, thermometer sleeves, immersed filling pipes, etc.

Low-speed ones include paddle and frame mixers. They create primarily a circumferential fluid flow.

Rice. 7. Scheme of operation of turbine and propeller mixers:

A

— turbine, apparatus with partitions;
b - propeller, apparatus with partitions; c
– propeller, apparatus without partitions.

For example, the mixer for soda production and the 1st stage causticizers for the production of caustic soda are equipped with frame mixers, and the collectors and pressure tanks for lime milk are equipped with paddle mixers; Propeller mixers are used in reactors and vacuum crystallizers for the production of barium compounds; phosphoric acid extractors are equipped with turbine mixers.

Vibrating mixers mix liquid media with turbulent jets that arise during the axial movement of the disk (Fig. in a stirred medium [5]. The design diagram of a vibration mixer is shown in Fig. 8. A perforated disk is placed in the vibrating mixer body, mounted on a rod and oscillating through a vibration exciter. The latter is isolated from the supporting structure with the help of an elastic suspension. To mix the pulps, the disk is installed at a short distance from the bottom of the apparatus using an oscillatory perforated movement (0.3 0.5 jet length, determined experimentally) to erode the resulting bottom of the sediment from the heaviest pulp particles. The perforation cone is directed with its large base downwards. The optimal angle of the cone is 970. The diameter of the disk usually does not exceed 700-800 mm, with large diameters design solutions are required that increase the rigidity of the disk. The diameter of the rod in modern devices is limited measuring about 70-100 mm, its length is 4.5 m. The sealing of the device cover, through which the rod passes, is ensured by diaphragms made of sheet rubber. In the chemical industry, vibrating mixers with a device volume of 0.2–3 m3 are used.

control of the amplitude of oscillations and better balance of the system

2.1. Stirrer selection [1]

At present, no universal criterion has been developed that allows choosing the optimal mixer option. When choosing a mixer, they are often guided by the results of laboratory and industrial experiments. Preliminary selection of the mixer can be made according to Fig. 9, where the corresponding curve shows the upper limit of the operation of this type of mixer.

One of the most important characteristics of a screw mixer is its pitch, which relates

specified with the blade inclination angle at radius r

addiction:

A

= 2
r
tg .
Typically these mixers are designed with a constant radial pitch. The inclination of the blades changes. The minimum slope is on the outer surface, the maximum is at the bushing. The most common mixers are with pitch a
=
d
or =180.
There are also mixers with a blade tip angle of 450. These mixers have a pitch a
=
d.
They provide better fluid circulation in the device.
Sometimes propeller mixers are equipped with a diffuser (circulation pipe), which makes it possible to ensure clearly axial circulation of the liquid in the apparatus and allows the propeller to be installed higher, which reduces the length of the shaft. Propeller mixers have from 2 to 4 blades (usually 3) and a rotation speed of 7 40 s-1. At the ratio a/d
= the propeller mixer turns into a turbine mixer with straight blades of an elliptical configuration.

Propeller mixers are most effective when it is necessary to create significant liquid circulation in the apparatus, especially in vessels with a convex bottom. They should not be used in devices with a flat bottom. The diameter of dispersed particles should not exceed 0.5 mm, and their volume fraction should not exceed 10%. When mixing in very large containers, propeller mixers are more effective than turbine mixers, but they are not suitable for dispersing gas in liquid. Due to the complexity of manufacturing screw mixers, it is recommended to use three-blade mixers instead with a blade angle to the plane of rotation of 240 and their width b

= 0.2
d
(see Fig. 6,
c
)
.
These mixers have characteristics similar to screw ones.
Turbine mixers are equipped with 4-8 blades (usually 6). d/D
ratio as for propeller ones, is 0.20 0.33.
The rotation frequency n
= 2 20 s-1, so that the peripheral speed
u = dп
of the ends of the blades fluctuates within 3 16 m/s.

Turbine mixers with straight blades (see Fig. 6 d,e

) create mainly a radial flow of liquid, and mixers with inclined blades (see Fig. 6
a, b
)
create
a radial-axial flow. The angle of inclination of the blades is usually 450.

It is recommended to use turbine mixers for processes of dissolution, heat exchange, suspension, gas absorption and chemical reactions.

In processes using suspensions, it is preferable to use turbine mixers with inclined blades to prevent sedimentation of particles.

High-speed mixers are installed in the vessel at a height of 0.3 D.

The height of the liquid in the apparatus is (1.0 1.3)
D.
Paddle mixers (see Fig. 6, f

) differ from turbine ones in the
d/D ratio,
rotation speed and number of blades.
The diameter d
and width of the blades
b
are usually taken within the limits
d
= (0.5 0.8)
D
and
b
= 0.l
d
.
The installation height from the bottom of the vessel h
= (0.1 0.3)
D
, and the height of the liquid in the vessel
H
= (0.8 1.3

)
D. The number of blades is usually 2, rarely - 4. For mixing in tall apparatuses, several height mixers can be installed on one shaft, the distance between which is chosen to be 0.3-0.8 d.
Their peripheral speed is in the range of 1.5–5 m/s. Mixer blades are usually positioned vertically or with an inclination of 450. Inclined blades mix the liquid more intensively than straight blades.

Due to their ease of manufacture, blade mixers are used in cases where there is no need for intensive radial-axial circulation of liquid in the apparatus. They create mainly circumferential fluid circulation and only a slight radial-axial one. Their disadvantage is the weak intensity of mixing.

Frame mixers ( see Fig. 6g – i

) are distinguished by low values ​​of rotation frequency (0.3 1 s-1) and peripheral speed (0.5 2.5 m/s).
The diameter of the stirrers approaches the diameter of the apparatus, and the gap between the blade and the wall of the vessel is usually within the range of (0.005 0.1) D
;
b=
0.06
d.
Frame mixers can be used for mixing liquids (suspensions) with high viscosity (up to 100 Pa s).

To enhance the turbulence of the liquid and the intensity of mixing throughout the entire volume of the apparatus, additional mixers can be installed inside the frame, preferably with inclined blades (see Fig. 6, h

).

Frame mixers are used when it is necessary to create intensive mixing due to circumferential circulation. They prevent (slow down) the fouling of the walls of the apparatus with solid particles due to high fluid velocities along the walls.

Vibrating mixers , compared to paddle mixers, are structurally simpler and more reliable, have higher productivity, lower operating costs and provide better mixing quality. For example, an emulsion of paraffin oil in water prepared in a vibrating mixer begins to separate after 360 s, while the same emulsion obtained in a rotating mechanical mixer begins to separate after 180 s.

Mixers of this type can also be successfully used when carrying out technological processes (dissolution, leaching, dispersion, etc.), which require the supply of a gaseous component. At the same time, the absorption of gas by liquid (for example, chlorine with lime milk) improves by 2 to 10 times. The direction of oscillation of perforated disks is vertical. At a frequency of 50-100 Hz the vibration amplitude is 2-4 mm, for frequencies 25-30 Hz - 3-4 mm.

Vibrating mixers are particularly suitable for suspensions with microbiological structures. For this purpose, a number of contact devices are produced with a volume from 1-6 liters (laboratory version) to 5000 liters. The devices are equipped with the necessary measuring devices (pH, pO2 sensors, etc.), a jacket with coolant to maintain the operating temperature, and devices for automatic control.

How to choose a construction mixer?

it will not be difficult to insert attachment from the mixer Further. Quite a few rotary hammers have a built-in mechanical gearbox that allows you to operate at different speeds. Then, obviously, the whole point of performing a new function for a rotary hammer is concentrated in its drive. All hand hammers, as well as mixers, are equipped with a universal commutator motor, the shaft speed of which is controlled by decreasing or increasing the supply voltage. The question then comes down to the characteristics of these engines, the main ones being the maximum engine speed, shaft power and shaft torque. Let's consider the operation of a perforator separately for two types of mixed media: low-viscosity and high-viscosity. To stir a low-viscosity solution, a small torque and different shaft speeds are required. It is known that single-speed rotary hammers are controlled by the force of pressing the trigger, which is usually located in the handle of the power tool. By applying different forces of pressing the trigger, we smoothly change the revolutions of the shaft (spindle): with a weak press - low revolutions, and with a strong press - high speeds up to the maximum.

The problem is that the speed lock, as a rule, only works when the trigger is fully pulled, that is, at maximum engine speed. This is very inconvenient when stirring. The solution, obviously, is to operate such a tool through a step-down transformer (you can use LATR), the power of which should exceed or be equal to the power consumption of the hammer drill. In this case, the work of the hammer drill as a mixer has every chance of success.

In addition, there are currently models of rotary hammers with adjustable speed control, which can also be used as mixers. You should always remember that the lower the power supply voltage of the rotary hammer motor, the lower the efficiency of such a motor.

The situation is more complicated with highly viscous media. Mixing them usually requires low speeds and high torque. If the speed can be adjusted by connecting a step-down transformer to the hammer drill (as in the above-described case of working with low-viscosity media), then this will not work with torque, since when the voltage supplied from the transformer decreases, the torque on the shaft drops along with the shaft speed (smooth characteristic) .

It follows that working through a transformer (at low voltages) is beneficial only in the case when the torque of the hammer drill exceeds the required torque for mixing the medium, and this does not happen very often. Otherwise, the hammer will require additional cooling (especially at low shaft speeds, at which the fan built into the engine does not create more or less normal air flow to the manifold of such an engine), since otherwise the overheating protection will work (the engine temperature sensor will turn off the power to the hammer) .

In addition to additional cooling, you can use some other techniques: reducing the diameter of the working part of the nozzle (This is one of the most effective ways to reduce the required torque!), reducing the diameter of the container and/or the height of the mixed layer. The ideal option is a multi-speed hammer drill. Using it, you can work with viscous solutions at the first speed at low shaft speeds and at the second speed with low-viscosity solutions at high speeds.

Let's consider the operation of a perforator in relation to high-speed mixing to produce foamy solutions or fine suspensions and/or emulsions.

The standard maximum operation of a rotary hammer is approximately 1000 - 2000 rpm, which is quite enough for most mixing in normal mode.

However, to obtain high speeds with the help of such hammer drills without the use of external

mechanical gearboxes are not possible, since engine operation is limited by the supply voltage (220 V). For rotary hammers with a built-in gearbox, the maximum shaft speed will be equal to the highest gear ratio of the gearbox and at the maximum supply voltage.

Thus, the hammer drill can be used as a mixer. For slightly viscous media, an additional step-down transformer may be required, although this is not necessary. Highly viscous fluids may require additional motor cooling or more frequent mixing pauses than normal to cool the motor. For high-speed (very fast) mixing exceeding the maximum rotary hammer shaft speed, an additional external mechanical gearbox may be required

Turbine mixer

There are two types of turbine mixers: open and closed. The impeller of a turbine mixer has the shape of a water turbine wheel with inclined, flat or specially shaped blades mounted on a shaft (Fig. 3). In containers and devices with a turbine stirrer, as a rule, a radial flow of liquid occurs. If the turbine mixer operates at high speeds, then a circular (tangential) flow of liquid in the container or apparatus is likely to occur, resulting in the formation of a funnel. In this case, reflective partitions are installed in the container or apparatus at a short distance from the walls to eliminate stagnant zones during mixing or dispersion. Closed turbine mixers produce a much more pronounced radial flow than open turbine mixers. If it is necessary to create a clearly defined radial flow, in addition to the wheel (impeller), a guide vane (stator) is installed. The stator ensures a strictly radial flow of liquid from the mixer and prevents the formation of a central funnel in devices with turbine mixers.

Figure 3. Open (left) and closed turbine mixers

Open turbine mixers are essentially an improved design of simple paddle mixers. The rotation of several blades located at an angle to the vertical plane creates, along with radial flows, axial flows of liquid, which contributes to intensive mixing in large volumes. The intensity of mixing increases when reflective partitions are installed in the vessel.

Closed turbine mixers are usually installed inside a guide vane, which is a fixed ring with blades bent at an angle of 45–90°. Closed turbine mixers create predominantly radial fluid flows with little kinetic energy consumption. The resulting radial fluid flows have a fairly high speed and spread across the entire cross-section of the apparatus, reaching its most remote points. Liquid enters the mixer through the central hole and exits tangentially to the wheel. In the wheel, the liquid smoothly changes direction from vertical (along the axis) to horizontal (along the radius) and is thrown out of the wheel at high speed. With such a directed and repeated movement of the liquid many times per unit time, rapid and effective mixing is achieved throughout the entire volume of the vessel. To improve and speed up mixing (which is especially important in continuous equipment), turbine mixers with blades or wheels located at different heights are used.

Turbine closed and open mixers operate at 100 – 350 rpm and produce intensive mixing of the entire volume of liquid located in the container or apparatus. The power consumption of turbine mixers operating in containers and apparatuses with turbulent mixing mode and reflective partitions does not depend on the viscosity of the stirred medium. This type of mixer can be used for a product whose viscosity changes during mixing. The shape of the turbine mixer blades is determined by the nature of the liquid being mixed and the purpose of mixing. For ordinary liquid mixtures, it is advisable to use mixers with smooth, straight blades. If it is necessary to increase the pumping action, inclined blades are used. Blades inclined against rotation are advantageous when mixing a mixture of viscous substances; the profile of the blades and their curvature affect the conditions for liquid drainage from the mixer, and, consequently, the transfer of energy from the mixer to the liquid.

Turbine mixers are used in a wide variety of mixing applications, such as slurry formation, dissolution, chemical reactions, gas absorption and heat transfer enhancement. Less often they are used for mixing pastes and dough-like materials. For mixing in very large containers, they are, however, less advantageous than propeller mixers and nozzles. The main areas of application of turbine mixers are:

• intensive stirring and mixing of liquids of various viscosities, which can vary within wide limits (open-type mixers up to 105 spz, closed-type mixers up to 5 • 105 spz);
• fine dispersion and rapid dissolution;
• stirring up sediments in liquids containing 60% or more solid phase (for open mixers - up to 60%); permissible solid particle sizes: up to 1.5 mm for open mixers, up to 25 mm for closed mixers.

The advantages of turbine mixers are fast mixing and dissolution, efficient mixing of viscous liquids and suitability for continuous processes. Turbine mixers can be used for wide variations in the viscosity and density of mixed mixtures. The upper limit of the viscosity of liquids that can be mixed using turbine mixers has not been precisely established. Moreover, when operating in turbulent mode, energy consumption remains almost unchanged over a very wide range of viscosities. Thus, turbine mixers can be used for mixtures whose viscosity changes during mixing. The disadvantage of turbine mixers is the relative complexity and high cost of manufacturing.

Recently, similar to portable propeller mixers, portable turbine mixers have been manufactured. They are equipped with devices for fastening to the edge of the vessel and are installed eccentrically in most cases. The shaft of a portable turbine mixer is usually positioned vertically, which most closely matches the nature of the fluid flow created by the mixer.

A hammer drill as a substitute for a mixer when mixing mortar and other compositions

If the volume of repair and construction work is generally small, then there is always a strong temptation to use other equipment that is most suitable for the mixing process. Often in this case the choice falls on a hammer drill. Let's consider the question to what extent a hammer drill can be used as a mixer when mixing mortar or other construction and repair media.

Stirring using a magnetic field

The essence of this method is as follows. A vessel with non-magnetic and electrically non-conducting walls is placed in an alternating magnetic field generator. As a generator, you can take the stator of any asynchronous machine, in which a rotating magnetic field is induced. The vessel is filled with substances that need to be mixed and ferromagnetic particles.

Under the influence of an external magnetic field, force and torque are applied to the ferromagnetic particles. In addition, eddy currents are induced in ferromagnetic particles, which form their own magnetic field, which also interacts with the external magnetic field. As a result of these interactions, the particles begin to move quickly and simultaneously rotate around their axis. Colliding with each other, they move along complex trajectories, forming local “vortices”.

As a result of this movement, the environment in which the ferromagnetic particles are located is thoroughly mixed for a short period of time.

Advantages of mixers in which mixing is carried out by a magnetic field:

1. Speed ​​of the process.
2. Greater homogeneity of the mixture.
3. Simplicity of design.
4. 4. Possibility of absolute sealing of the volume in which mixing is carried out.
5. Small dimensions.
6. High efficiency
7. The ability to carry out a continuous mixing process.

Why do we consider a hammer drill as a substitute for a mixer?

Firstly , a hammer drill is a tool whose internal structure differs little from a mixer. Indeed, both the mixer and the hammer drill are equipped with an electric motor that creates torque on a shaft with a special-purpose attachment mounted on it. Accordingly, all the main power characteristics of both the mixer and the hammer drill are tied precisely to the characteristics of the electric motor.

Secondly , a hammer drill is the most common power tool on construction sites and in premises being renovated. In addition, it is known that a hammer drill often performs several functions, among which we will be interested in the function of a drill, that is, rotation of the shaft and attachment without chiselling.

A hammer drill and a mixer as tools for mixing liquid solutions. Comparative analysis

Both the hammer drill and the mixer are easily controlled in terms of changing the number of revolutions of the electric motor shaft. If they are equipped with a universal commutator motor, then the speed can be controlled using a conventional laboratory step-down transformer, connecting it directly to the mains and changing the supply voltage. In this case, the tool shaft speed will vary depending on the incoming supply voltage to the electric motor.

Thus, we get any speed from the lowest to the maximum, which is indicated in the technical specifications for the tools themselves. However, such control is only suitable for mixing solutions with low viscosity. The fact is that when the input voltage decreases, not only the speed of the electric motor shaft drops, but at the same time the torque on the motor shaft also drops.

In other words, when mixing non-viscous media at high and low speeds, a rotary hammer based on a commutator motor is fully consistent with a mixer if the technical specifications for the rotary hammer state maximum speeds that are equal to or greater than those required for the mixing that you are going to carry out. But with viscous media everything is much more complicated. Let's consider what options are possible here.

Firstly , when mixing a viscous solution with a perforator, you can use a mixer that is more suitable for this case: the length of the blade of the mixing device should be minimal. However, as is known, during mixing processes, the diameter of the container in which the working solution is located is related to the diameter of the paddle mixer by a certain ratio.

For viscous media, this ratio is usually taken to be approximately 1 to 2, and for non-viscous media – 1 to 4. Then it turns out that having chosen a mixing device with a smaller blade diameter, we must select a container for this mixing device with a smaller diameter.

It turns out that the productivity of such mixing will drop sharply, however, as stated above, we are considering the case of private use of a hammer drill as a substitute for a mixer for one-time work, so productivity does not play a special role for us.

Secondly , the advantage of a hammer drill (especially relative to stationary mixers) is its dynamism. When carrying out mixing, you can easily move the perforator itself during mixing to the desired depth and at different distances from the center of the axis of symmetry of the working container.

The disadvantage of such mixing is the difficulty of carrying out (it is difficult to hold and control the hammer) and the unevenness of the mixing itself (it is difficult to obtain a homogeneous, well-mixed solution). However, with “rough” mixing, which is usually required in the repair and construction industry, this approach is completely justified.

Thirdly , you can try to increase the operating time of the hammer drill by further enhancing its cooling. The fact is that under heavy load (viscous media) on the drive, the electric motor will overheat, which will automatically sooner or later trigger the overheating protection system - the temperature sensor built into the body of the hammer drill and located together with the electric motor will trigger.

Inside all rotary hammers, the electric motor is air-cooled - a small fan is installed on the shaft on the opposite side of the drive, which automatically rotates along with the shaft when the shaft itself rotates. At low speeds (viscous solutions), such a fan will rotate very slowly and, accordingly, the air flow cooling the electric motor will be minimal. This will lead to increased overheating of the electric motor.

If it overheats, the temperature sensor will automatically disconnect the electric motor from the mains power. You can, of course, be content with only short-term work, and then leave the hammer drill to cool for a while. However, this is not always advisable.

Disabling the sensor does not make much sense, since this can lead to the combustion of the electric motor itself. The solution is to install an additional forced cooling system for the commutator motor.

Since mixing is usually carried out under stationary conditions, both air and water cooling systems can be used. With any implementation, the electric motor will not overheat at low speeds and, thus, the mixing performance will increase significantly.

Recently, tools (and rotary hammers in particular) are becoming very popular not on universal commutator motors, but on asynchronous electric motors . This hammer drill has its own characteristics. The number of revolutions of the electric motor shaft changes not under the influence of changes in the supply voltage, but under the influence of changes in the frequency of the current.

For this purpose, an electronic frequency converter is built into the design of the tool. Thus, the speed of an asynchronous motor changes under the influence of a change in the frequency of the current. Such tools cost significantly more than conventional ones, but if you have just such a hammer drill, then it is well suited for mixing viscous solutions.

The main advantage of such a hammer drill is maintaining the shaft rotation speed constant, regardless of the load on the shaft. Hence it turns out that mixing viscous media with such a perforator is quite possible.

The only drawback is the rather high price of the unit. Using such a “delicate” hammer drill as a mixer for mortar can lead to its failure, and repairs can cost even more than a new hammer of the same type.

Paddle mixers

A paddle mixer (Fig. 1) is a mechanism consisting of two or more blades, rectangular in shape. The impeller with blades is mounted on a rotating shaft, vertical or inclined. Special-purpose paddle mixers also include frame (anchor) and sheet mixers. Among the main advantages of paddle-type mixers are the relatively low manufacturing cost and simplicity of design, convenience and ease of maintenance. The rotation frequency of such mixers ranges from 18 to 80 rpm; When the rotation speed increases above the specified one, the mixing efficiency sharply decreases and energy consumption increases.

Figure 1. Paddle mixer

The disadvantage of paddle mixers is the weak axial flow, which does not ensure complete mixing of the entire volume of liquid in the container or apparatus. Due to the insignificant creation of axial flow, the paddle mixer mixes mainly those layers of liquid that are located close to the mixer blades. In the volume of the mixed liquid, the development of turbulence occurs slowly and the circulation of the liquid is small. Therefore, paddle mixers are recommended for mixing low-viscosity liquids up to 100 cP; they are not suitable for mixing easily separated substances.

So, the main disadvantage of paddle mixers is that when they are used, the development of turbulent motion throughout the entire volume of liquid occurs very slowly and circulation is negligible. When using paddle mixers, a significant concentration gradient is also observed in the stirred liquid. The liquid acquires vortex motion when reflective partitions in the form of vertical strips are installed in a vessel with a stirrer. When liquid flows around the partitions, a zone of low pressure is formed behind them, in which vortices arise. As the number of revolutions increases, the vortices break away from the partitions and move in the direction of rotation of the blade. In the case of a further increase in the number of revolutions, a random vortex motion of the liquid occurs, with the vortices colliding with each other throughout the entire volume of the liquid. Under these conditions, high uniformity and intensity of mixing is achieved. At the same time, in the presence of partitions that prevent the rotation of the entire mass of liquid, the depth of the funnel is sharply reduced. Usually four symmetrically installed radial baffles are sufficient to improve mixing. However, with the installation of partitions, energy consumption for mixing increases.

The position is also slightly improved by tilting the blades by 30 and even 45 ° to the shaft axis. As a result, the axial movement of the liquid increases and a decrease in the concentration gradient in it is achieved, although the concentration gradient is not completely eliminated. A mixer with inclined blades is capable of holding particles in suspension that have a low sedimentation rate and is also suitable for mixing in the case of slow chemical reactions. It has been established that in production conditions paddle mixers are always more expensive in cases where axial flow is necessary to achieve the required technological effect. A paddle mixer with a blade inclination of 45 ° when forming suspensions causes the same effect in the mixed system as a propeller of the same diameter, but requires three times more time and a 25% increase in power consumption. Main applications of paddle mixers:

• mixing liquids of low viscosity;
• dissolving and suspending solids;
• rough mixing of liquids.

As already mentioned, simple-type paddle mixers are most effective when mixing low-viscosity media (up to 100 cP). For mixing liquids with viscosities above 2500 cP, frame mixers or paddle mixers in vessels with baffles are more suitable. In these applications, paddle mixers provide good mixing with low energy consumption. Paddle mixers are not suitable for rapid dissolution, fine dispersion, or for obtaining suspensions containing a high-density solid phase. To better mix the entire volume of liquid in the vessel, several pairs of horizontal blades are installed on the shaft, i.e. multi-bladed (three, four) as well as frame mixers are used, consisting of several horizontal and vertical, and sometimes inclined flat blades (see below).

Mixers for rotary hammers: how to choose and use?

At a construction site of any scale, there is a need to mix various liquids and solutions. This can be done either with a special tool or with various auxiliary machines. In the second case, if the amount of solution being processed is small, it is useful to use a mixer for a hammer drill.

Peculiarities

There are good reasons to consider a hammer drill. Its internal structure is very close to that of a stand-alone mixer. Both mechanisms have an electric motor that creates torque and transmits it to the shaft. The shaft already serves as the base for a specialized attachment. Therefore, key operating parameters are closely related to the energy released by the electric motor.

A hammer drill can be found on construction and repair sites more often than other tools that have a rotating part. A suitable mode for mixing solutions is to simulate a drill. The system easily adjusts the number of revolutions on command. If you have to mix a highly viscous liquid, it is advisable to choose a mixer with a short blade length. But it is important to understand that the hammer drill itself is an expensive and highly sensitive device; it easily fails.

Advantages and disadvantages

The main advantage of the drill mixer is the possibility of its multifunctional use. On the one hand, the tool is classified as a drill, therefore, in addition to mixing mortars, it can be used to form holes in various types of surfaces, even the hardest and densest. On the other hand, a drill of this type belongs to the low-speed category, so it cannot replace a drill 100%, but at the same time, it is the low speeds that make it possible to mix even the densest mixtures.

Hot topic

So, according to the technical characteristics, it is quite possible to mix the solution with the hammer drill itself. But this is expensive and impractical. However, one should not abandon the idea at all; it has its own rational grain. Completing the task with the help of a hammer drill is quite possible, and even with minimal negative consequences. You just need to use the right attachment.

Selecting the right product

Mixers for rotary hammers have two main parts: a shank and a working whisk. The size of the tip varies depending on the type of substances being mixed and the target volume of work. Manufacturers always describe in the accompanying materials what mixtures can be mixed. As when choosing other products, it is useful to give preference to products from well-known companies. Even the multiple difference in comparison with unknown brands is fully justified by the high quality of the products.

Much attention should be paid to the selection of beaters according to the shank format. Traditionally they have a cylindrical or hexagonal configuration. Also in some cases, M14 and SDL-Plus connectors are used. The choice is determined by which connector is provided by the hammer drill manufacturers. Bosch Corporation, for example, equips its products with SDL-Plus connectors.

Most often, you can simply tell the sellers what device the mixer is being purchased for. They will be able to offer the optimal nozzle. The basket of a regular whisk is from 10 to 11 cm with a diameter of 8-15 cm. If the hammer drill is very powerful or you will have to mix a lot of solutions, it is better to choose a larger basket. As for the length of the mixer, the choice is not difficult - you need to focus on the height of the container where the solution will be mixed.

Whisks with a length of 50 to 60 cm allow you to easily stir the putty in a plastic bucket. Or shake the plaster in an additional box. At a speed of 600 rpm, the mixer can confidently handle even heavy and viscous media. When a repair is planned, a household-grade nozzle will do. But for building a house, it is advisable to choose something more serious.

Mixing devices based on sound and ultrasonic vibrations

To generate sound and ultrasonic vibrations of the medium, piezoelectric, magnetostrictive, aero- and hydrodynamic emitters are mainly used, differing from each other in the operating principle and spectrum of emitted frequencies. The first two types of emitters, as a rule, operate in a narrow ultrasonic frequency range and are expensive. Therefore, their use in industry is limited.

Hydrodynamic emitters have found wider application. In emitters of this type, sound vibrations are generated using rotary pulsation devices (RPD). The main parts of the RPU (Figure 12) are: a stator and a rotor rotating relative to the stator.

Figure 12 - Rotary pulsation device

Structurally, they are made in the form of a set of coaxially located cylinders, the walls of which have slots (slots). The rotor slots overlap the gaps between the stator slots. When the RPU rotates, the liquids being processed enter the rotor cavity, since a vacuum zone is formed in its central part. Then, under the influence of centrifugal force, they pass through the slots of the rotor and hit the spaces between the slots of the stator, causing a hydraulic shock. Therefore, the fluid flow in the rotor cavity and the apparatus chamber has a pulsating character. The apparatus with RPU combines the operating principles of dismembrators, disintegrators, centrifugal pumps and colloid mills. The simplicity of design, reliable operation and low cost of such devices is their undoubted advantage over others. The RPU has a wide range of generated frequencies and the ability to smoothly adjust them by changing the rotor speed. The disadvantages of the RPU include the low frequency of radiation of elastic vibrations, which is one of the reasons for the low acoustic efficiency.

How to mix the solution with a perforator longer

Once a device is selected, a problem may arise due to premature shutdowns. The reason is simple:

• electric motors of rotary hammers operate with air cooling;
• the fan rotation speed coincides with the speed of the shaft;
• if a viscous liquid is mixed, the speed is low and the force is significant;
• because the motor overheats quickly.

The electronics do not allow the hammer to be restarted until it has completely cooled down. Attempts to remove the sensor from the system, bypass it, or disable it will only lead to premature failure of the device. The radical solution to the problem is the use of external coolers. But still, if the volume of work is very large and it has to be done frequently, it is better to buy an autonomous construction mixer. Of course, we are not talking about renovating one room, but about ongoing large-scale work.

Additional recommendations

Using a hammer drill you can mix a variety of substances:

• plaster of all types;
• cement;
• putty;
• tile adhesive.

When performing such work, it is unacceptable to use the impact mode. It is also unacceptable for the mixed liquid to come into contact with equipment. After finishing work, both the hammer drill itself and the mixer must be thoroughly washed and dried at room temperature. This helps extend the life of the device.

Attention: if dusty compounds are mixed, it is better to wear a respirator when working.

If the working part of the device becomes clogged with glue, it is necessary to stop it, disconnect it from the network and wash off the contamination. If you do not do this in a timely manner, you may be afraid of failure. It is extremely important to ensure that the wires are positioned correctly. Winding them around the rim can result in serious injuries. The hammer drill must be held firmly in your hands and not be distracted by extraneous stimuli.

The number of revolutions is adjusted according to how deeply the whisk is immersed. If you mix at full speed at the very top of the bucket, splashes will inevitably occur. As soon as the kneading is completed, reduce the speed and remove the whisk. Immediately immerse it in a bucket of clean water and run it again for 2-3 seconds to completely clean it. This technique allows you to prepare the tool for work again.

To learn how to choose a mixer, watch the following video.

How to do it yourself?

If you wish, you can make a construction mixer with your own hands. For this you need to use the most ordinary drill as a drive, and any product with a hexagon-shaped shank is suitable as an attachment. Such a device is quite easily fixed in the drill chuck, the main thing is that the dimensions of this hexagon correspond to the minimum size of the chamber that can be placed in the chuck.

However, keep in mind that the motors and gearbox of a standard mixer are designed exclusively for a longitudinal surface, so using such a homemade tool you can only mix very small portions of the construction mixture.

In the next video you will find the main features of drill mixers.

From time to time, even the strongest and most independent woman who does not like to cook wants to feel like a real cook.

Inspiration for culinary feats can strike a woman at any time; the lack of a mixer should not prevent her from achieving them.

As a rule, such a desire is not limited to simple scrambled eggs; you definitely want something like that. For example, make a mind-blowing bizet, but, as luck would have it, there was no mixer at hand, without which it is simply impossible to beat the egg whites properly. A sudden creative impulse should not be suppressed simply by the lack of a mixer. Homemade mixers can be for the kitchen, children's or construction.

If you have a whisk, then a regular drill can save the situation.

Electric mixer vs concrete mixer: real use experience

The construction season is in full swing. Many self-builders are puzzled: is it possible to mix concrete using an electric mixer? From this article you will learn the answer to this question and make an informed choice of what to buy - a drill mixer or a concrete mixer.

• How to Make Concrete Mix with an Electric Mixer
• What is the difference between mixing concrete with a mixer and in a concrete mixer?
• Video showing in detail the process of mixing concrete with a mixer
• Pros and cons of mixing concrete with a drill mixer

Mixing in static mixers

Mixing in static mixers whose main elements are small metal spiral belts (“screw elements”). They are made by twisting a flat plate at a certain angle along the axis. The assembled elements are inserted into a cylindrical pipe (mixer body) so that left- and right-curved spirals alternate along the entire length, and there is no gap between the wall and the side edges of the spiral (Figure 14).

Figure 14 - Static mixer

To carry out the homogenization process, it is enough to pass the mixed components once through a pipe with screw elements. The required degree of homogenization of the mixture is regulated by the number of elements. Static mixers are successfully used in continuous lines for the production of marmalade, soft drinks, and beer.

Mixing concrete with an electric mixer: features and operating techniques

Everyone who builds a house on their own, without hired workers, wants to simplify the task for themselves. For example, use a concrete mixer to mix concrete. A high-quality concrete mixer is not a cheap pleasure. Many will say that its price will be recouped during the construction season. But I want to save money and not break my back mixing concrete with a shovel. This is where the idea comes - to use an electric mixer to mix the solution of sand, cement and crushed stone.

I saw a video on YouTube - a man, alone, using a two-spindle mixer, mixed concrete and poured a strip foundation in two days. I thought maybe this was an advertisement for a tool? The builder claims that it is more convenient to knead with a mixer than with a concrete mixer. The question is relevant for me. I mixed concrete in a concrete mixer. It's hard for one. We have to lift buckets. Load the pear. I rented a concrete mixer. There is nowhere to store yours. And with a mixer you can knead the concrete right at the pouring site. It weighs a little. Tell me, is this realistic if you knead small volumes? Maybe someone has already used a mixer? Will the tool break?

I think tools should be used strictly for their intended purpose. A mixer is needed to mix plaster and adhesive mixtures, and a concrete mixer is needed for concrete. The weak point of the mixer is the attachments. On heavy concrete with crushed stone, the rim's blades may come off or it will bend.

Compare the price of a normal mixer and a concrete mixer. The difference is small. It seems to me that health is more important! Using a concrete mixer, you can work together. One carries sand and crushed stone, the second monitors the batch. You work alone as a mixer. Oh, what strength is needed for this. You'll get tired quickly. My concrete mixer is already 10 years old, and it has long since paid for itself.

Now let’s listen to the opinion of those FORUMHOUSE participants who actually kneaded concrete with a mixer.

I poured the strip foundation for the fence using a mixer. Tape length 25 m. Section – 200x300 mm. I also concreted a 5 m lintel under the gate and wicket. From my own experience, I will say that you get more tired not from working with a mixer, but from throwing sand, cement and crushed stone, and pulling out concrete. But you also need to throw ingredients into the concrete mixer. It still needs to be washed later, but the mixer spun in the water and went home. Of course, I wouldn’t dare to pour a foundation for a house with a mixer, but for small volumes, it’s quite a suitable option.

The Bath1 mixture was prepared as follows:

1. First he mixed dry sand and cement.
2. Then he added water. The consistency of the mixture is like sour cream.
3. Then he threw in 3 buckets of crushed stone. Stirred the mixture. Then I added another 1.5 buckets of crushed stone.

I mixed concrete in a cast iron bath with a two-spindle mixer. Two spindles are better than one. The torque is damped and, in the case of a wedge, will not wrap around the tool. I threw cement, sand, crushed stone of fraction 5-20. I stirred for ten minutes and 200 liters of the mixture was ready. I won’t say it’s easy, but it’s not hard either. The crushed stone between the augers did not jam. The tool didn't break.

Briefly speaking. I listened to everyone and also decided to knead concrete with a mixer. I'm reporting. I mixed about 1.5 cubic meters of concrete for the columnar foundation. The mixture is hard. Proportions: 1 part cement, 3 parts sand, 4 parts crushed stone and 0.75 liters of water. Mixed in a 100 liter trough. I made 5-7 batches per day. I couldn't do it anymore. Your arms, especially your hands, get very tired. I’m not saying that I’m weak, but the twisting load on my joints is decent. Crushed stone of fraction 5-20 did not get stuck between the rims. The instrument also held up. Verdict: the method is suitable for small volumes for one-time work.

I wonder if it is possible to fill larger volumes using a mixer? The construction experience of FORUMHOUSE users says: “Yes.”

My assistants and I poured 4 cubes of concrete with a mixer. There were 4 people working - two men and two women. The women put cement and enriched sand and gravel mixture into buckets. One man is kneading. The second one carries the buckets, and then the two of us dump the mixture into the formwork. Mix proportions: 1 bucket of cement, 1 bucket of sand, 3 buckets of OPGS, 0.7 buckets of water. In total, we made 115 batches with smoke breaks. It was still raining. The old tub was also leaking. They repaired it. As a result: started at 10 am, finished at eleven o'clock in the evening. Then they added a little more in the morning. The back gets tired, but if you get used to holding the mixer without bending over, with your legs spread wide apart, there is no fatigue. If they started to interfere at 7 am, there were 3 men, not women, it didn’t rain, and the tub didn’t leak, then I think they would have finished it before 6 pm. The mixer kneads the mixture quickly. The main fatigue comes from dragging buckets with OPGS through the formwork and lifting the bucket to the level of the formwork to dump the concrete.

Veter753 tips for using a mixer when mixing concrete:

• First load water, cement and sand.
• Knead the mixture until it becomes sour cream.
• Add 2 buckets of OPGS.
• Stir the mixture until it is a uniform gray color.
• Add another bucket of OPGS.
• Stir evenly again.

The two of us, in 4 days, poured 17 cubic meters of concrete with a mixer. Monolithic slab. Concrete was mixed in a bathtub. They placed it on the reinforcement inside the formwork and turned it over after each batch. We were tired, of course, but we would have been tired with a concrete mixer too. I liked working as a mixer. It gets in the way quickly. He doesn’t twist his arms, his back doesn’t hurt, even though they kneaded with a single-spindle tool. You get more tired of carrying sand, cement and crushed stone.

Mixing concrete with a concrete mixer and a mixer: similarities and differences

I'm interested: the concrete mixer bulb rotates at 30 rpm, and the mixer produces up to 600 rpm. Does this somehow affect the quality of the mixture?

Despite the difference in the number of revolutions of the units, the output you will get is concrete of high quality. The main difference is that with a gravity concrete mixer the pear with the mixture rotates, but when working with a mixer, on the contrary, the container is stationary, and mixing is carried out by a rotating crown. Why are the speeds of a concrete mixer and a mixer different? If you increase the speed of the pear, then under the influence of centrifugal force, the ingredients will simply stick to the walls of the drum, and there will be no mixing process. If, on the contrary, you reduce the speed, the ingredients will slide along the lowest plane of the pear, practically without rising up. There will be no mixing process. Therefore, 25-30 rpm is optimal for a concrete mixer. If you increase the speed of the mixer, the mixture will splash out of the container. If you lower the speed, you will have to stir the mixture for a very long time.

One more thing. It is difficult to mix the so-called in a concrete mixer. hard concrete with a low water-cement ratio. Such concrete is mixed in forced mixers, which are expensive, or, alternatively, with a mixer.

I mix heavy concrete with a mixer. I work alone, so I’ve already developed the optimal technique. The tool is a mixer with a power of 1.4 kW. Two spindles. I mix concrete in an 80-liter round plastic tub. This is the optimal volume. If you take more, it’s a no-brainer. Don’t chase too much volume at once! I mix 1-2-4 10 liter buckets per batch. Compared to a concrete mixer, the laying speed has almost doubled. And one more thing: the stirrer rims, depending on the configuration, can row the solution either up or down. For concrete, buy a whisk so that it will row up and you will be pulled down. It’s more convenient to work this way than trying to push the mixer through the concrete. By the way, my back doesn’t hurt, my arms don’t twist.

Circulating mixing of liquids

Mixing liquid-phase systems with a stream of liquid flowing from the nozzle

When flowing from the nozzle, the liquid stream takes the shape of a cone, expanding as it moves away from the nozzle mouth. This is due to the following reasons:

1. The flow flowing out of the nozzle displaces the volume of liquid located in front of the nozzle.
2. The stream of flowing liquid sets in motion (parallel to the stream) nearby layers, due to the transfer of part of its energy to the environment. The transfer of momentum is determined by the tangential stress between the moving and stationary layers of liquid, as well as the turbulent penetration of liquid particles from the jet into the environment. In this case, the product of the mass and speed of the moving fluid remains constant (without taking into account losses from internal friction).

Each layer that begins to move, surrounding the stream of liquid, sets the neighboring layers in motion along its path. Therefore, as it moves away from the nozzle, the liquid jet has an increasingly larger cross-section and lower speed. In any section normal to the direction of the jet, its speed decreases as it moves away from the axis.

1. After nearby layers of liquid are captured by the jet and set in motion, a vacuum is created in the space they previously occupied. This leads to the suction of adjacent (stationary) layers of liquid, which are thereby also set in motion. This cycle repeats continuously.

Mixing liquids with gas

When circulating pneumatic mixing of liquids (Figure 9), a central guide pipe is installed in the apparatus, which limits the suction of liquid from the surrounding volume. Gas enters the liquid in the form of bubbles.

Figure 9 — Scheme of circulating pneumatic mixing

As the bubbles rise, the surrounding liquid is set in motion toward the liquid surface under the action of tangential stress. Behind the rising bubbles, a vacuum is formed, causing the suction of liquid from the surrounding space. The bubble is subject to hydrostatic pressure from the liquid column above it. As the bubble moves, the magnitude of this pressure continuously decreases and the diameter of the bubble increases accordingly. At the same time, the intensity of mixing also increases, because as the bubbles expand, energy is gradually released, which causes the liquid to flow. This is the fundamental difference between pneumatic mixing and mixing with a submerged nozzle. After the gas reaches the surface, the liquid carried by the gas flows to the walls of the apparatus and sinks to the bottom, where it is again sucked into the guide pipe.

Impeller mixer

An impeller mixer is used to ensure good gas-liquid contact while simultaneously vigorously mixing (Figure 10). The stirrer shaft is placed inside pipe 1, through which air is supplied under slight excess pressure (in some designs, air is sucked in when the stirrer rotates). The mixer has a row of blades, and at the end of the pipe there is a stator with blades 2. The presence of two rows of blades, movable 2 and fixed 3, ensures good mixing of liquid and gas.

1 - central pipe; 2 — stator blades; 3—mixer (rotor) blades. Figure 10 — Impeller mixer

Pulsation mixing

It consists of mixing the treated medium with pulsating jets.

By design, pulsating devices are simple and convenient. The reciprocating and forward movement of liquids in them is carried out using a pulsator (usually a valveless piston pump), which is connected in one of two ways:

1. To the bottom of the apparatus (Figure 11, a);
2. To the light liquid supply line (Figure 11, b).

Figure 11 - Pulsation devices
To protect the pulsator mechanism from the effects of the processed liquids, a membrane, bellows or pneumatic device is used, in which there is a buffer layer of air between the pulsator and the medium. The expansion or compression of this layer of air causes vibrations of the liquid in the apparatus.

Consequently, the intensification of the processes carried out in pulsation devices is achieved by superimposing low-frequency oscillations on the reagents with the possible addition of the oscillatory motion of the liquid with a jet one.

There are no moving parts in the working area of ​​the pulsation apparatus, and the energy source - the pulsator - is removed from the apparatus. Converters of the oscillatory motion of a liquid into its other types are stationary and are an integral part of the apparatus.

Pros and cons of mixing concrete with a drill mixer

Let's summarize. Advantages of mixing concrete with a mixer:

• A mixer with a power of 1 - 1.5 kW costs 4500 - 6000 thousand rubles. The price for a high-quality concrete mixer with a volume of 160 - 180 liters starts from 10 thousand rubles.
• Instead of a mixer, you can buy a drill mixer and get a two-in-one tool that can be used to mix mortars and concrete, as well as drill holes in metal and wood.

• Unlike a concrete mixer, the mixer is lightweight and does not take up much space. At the end of the work, you can throw it into the trunk of a car or put it away in the household.
• The mixer mixes “hard” concrete.
• High speed of concrete mixing for 1.5-2 cubic meters.

Disadvantages of preparing concrete with a mixer:

• The complexity of preparing a solution with a volume of more than 3 cubic meters. You will need assistants to carry sand and gravel.
• Double work of manually putting in and dumping out the ingredients and the finished mixture from the tub, while the mixture is dumped out of the concrete mixer by turning the steering wheel of the pear.
• It is physically easier to work with a concrete mixer. You will have to hold the mixer with your hands.

Note to DIYers! Try to modify the mixer, turn it into a mini forced-action concrete mixer, using the tool for mixing mixtures and adhesives in the photo below as a basis. For example, make a frame to hold a 200 liter metal drum. Weld an axle with a steering wheel to it, secure the mixer to a rotating support and lower the crowns of the nozzle into the container. Moreover, the axis of the mixer shaft should not run strictly in the middle of the barrel, but closer to its edge. Place the ingredients for the concrete solution into the container. After stirring the mixture, the concrete from the barrel is dumped into the formwork or into a wheelbarrow. Then the cycle repeats. Do you think this is a workable idea?

• What is more profitable: buy a forced-action concrete mixer, or make a forced-action concrete mixer yourself.
• How to make sifters for bulk building materials from a factory mixer and a cheap concrete mixer with an engine from a washing machine.
• How to make high-quality self-mixing concrete: part one - Is it profitable to make self-mixing concrete yourself and part two - Making durable concrete on a construction site with your own hands: proportions, calculation of ingredients and water-cement ratio.

Basic tools for mixing concrete by hand

Mixing concrete, like every work process, begins with the preparation of materials - water, cement, sand. You also need a container - a large vessel - to mix it all.

Let us consider in detail the most important elements in preparing manual kneading of material:

1. Capacity

If you can mix manually with a shovel directly on the ground or on a metal sheet, then you need a bowl for the mixer. The container for mixing concrete should have a trough shape. The most convenient is a metal bathtub or basin. You can also do it in a barrel if it is shallow. The dimensions of the trough depend directly on your need for the finished product. For small amounts of concrete, it is better to take small containers. If it is necessary to lift the finished solution to a height, use containers with special hooks to secure the rope. To extend the service life of such vessels, you should follow a few simple rules. The first of these, which is mandatory, is to constantly clean the inner surface of concrete residues after each use.

2. Construction mixer

Preparation of concrete in small quantities involves the use of a construction mixer. Only this unit allows you to create a uniform mixture, which can then be easily distributed over the work surface. A mixer is the key to high-quality concrete pouring. To mix concrete, you should choose a powerful device that can withstand the full force of the workload. The quality of the nozzle, its material and shape also play an important role. You choose it yourself, since there are cases when the whisk is included. For concrete, screw nozzles are most often used, which prevent air from entering the mixture. A hand-held construction mixer will quickly and easily handle a uniform mixture.