Dosing of concrete mixture components. Dosing of the constituent components of the concrete mixture. Mixture composition and its adjustment

Concrete mixtures of given compositions are obtained by accurately dosing (measuring) the components (cement, aggregates, water and additives) before entering the concrete mixer.

Bulk raw materials for a concrete mixture are dosed by weight (except for porous aggregates, measured by volume with correction by weight).

Liquid components are dosed by weight or volume. The error in dosing cement, water, bulk and liquid additives should not exceed ±2%, aggregates ±2.5% by weight The industry produces three series of weighing dispensers starting materials

concrete mixture and mortar:

first series of VDB: DC-100; J-Y0; DI-500 for mixers with a finished batch volume of 165 l; DC-200, J-200; DI-1200 for mixers with a finished batch volume of 330...500 l;

second series of AVD: AVDI-425M; AVDTs-425M; AVJ-425/ 1200M for ready-mix mixers 330...500 l; AVDI-1200M;

AVDTs-1200M for mixers with a finished batch volume of 800... 1000 l; AVDI-2400M; AVDTs-2400M; AVJ-2400M for mixers with a finished batch volume of 1600...2000 l;

third series DB: AD-500 BP; AD-500-2BP; AD-500-BSCH; AD-800-2БШЧ;

AD-800-2BK; AD-200-2BZh; AD-400-2BC for mixers with a finished batch volume of 500 l; AD-800-BP; AD-1600-2BP; AD-800-BSCH; AD-1600-2БШЧ; AD-1600-2BK; AD-400-2BZh; AD-1600-2BC for mixers with a finished batch volume of 800... 1000 l; AD-2000-BP; AD-2500-BSCH; AD-500-2BZH for mixers with a finished batch volume of 1600...2000 l, where A is automatic, B is concrete. V - weight, D - dispenser, F - liquid, I - inert, K - expanded clay, M - modernized, P - sand, C - cement, Sh - crushed stone, 2 - two-fraction.

There are cyclic and continuous dispensers.

For parterre installations, two sets of dispensers are produced: VDB-250 for mixers with a loading capacity of 250 liters and VDB-500/750 for mixers with a capacity of 500 and 750 liters with automatic control equipment.

The VDB-250 set includes dispensers for DI-500 aggregates, DC-100 cement and DZh-Yu0 liquids; The VDB-500/750 set includes dispensers for DI-1200 aggregates, DC-200 cement and DZh-200 liquid dispensers.

Aggregate dispensers DI-500 and DI-1200 are designed for sequential dosing of four fractions of aggregates and are designed as a weighing device on which the bucket of a concrete mixing plant skip lift rests. The aggregates are weighed directly into the skip hoist bucket.

All cyclic dispensers consist of a load-receiving bucket or hopper, a weighing system indicating the mass for visual control dosing and a feeder that supplies material from the supply bins of the concrete mixing plant into the load-receiving bucket.

The liquid dispenser DZh-Yu0 (68) consists of a multi-shouldered double lever i, supported by prisms on frame 2. One end of lever 1 is connected by a rod to a spring dial mass indicator 3, and a load-receiving device is suspended to the other end on two prism supports ladle 5. The ladle is equipped

inlet and outlet 4 valve-type gates with a diaphragm pneumatic actuator 6 and a gate position control converter.

The cement dispenser DC-100 is completely unified with the liquid dispenser and differs only in the design of the inlet and outlet valves.

Butterfly type butterfly valves are used for cement.

The liquid dispenser J-200 differs from the dispenser DL^-100 in the size of the load-receiving bucket.

The cement dispenser DC-200 differs from the cement dispenser DC-100 in the dimensions of the load-receiving bucket and the ratio of the arms of the double lever.

For concrete plants and tower-type installations, two sets of automatic weighing batchers of the DB type are produced: for mixers with a loading capacity of 1500 (1200) l and 750 (500) l. The kits consist of batchers and control stations for the batching and mixing department of a concrete plant.

The set for mixers with a capacity of 750 (500) l includes cement dispensers AD-400-2BC, liquid dispensers AD-200-2BZH, two-fraction for sand AD-500-2BP, two-fraction for crushed stone AD-800-2BShch, single-fraction for sand AD-500 -BP, single-fraction for crushed stone AD-500-BSCH.

Dispensers can be equipped with dial indicators various types, which can weigh up to three or six grades of concrete without readjustment.

The dispensers are controlled in automatic, remote and local modes. Before starting work, the preliminary and exact mass values for each dose are set on the dial indicators of the dispensers. On the remote control station, select the recipe, operating mode and turn on the dispensers.

When working in remote mode, commands for loading and unloading dispensers, loading feed bins, loading and unloading mixers are given by the operator from the control station console.

The local mode is used when setting up dispensers.

Dispensers are loaded with feeding devices in two modes - coarse and fine supply of material with automatic mode switching using non-contact dial indicator converters. The dispensers are unloaded under the action of the piston cylinder of the load receiving device, after which the cycle is repeated.

The cement dispenser AD-600-2BTs (69) consists of a frame 3, two screw feeders 14, 16, a lever mechanism, a load receiving device, a dial indicator 11 and a stand 10, in which the local control panel and drinking water equipment are located. Inlet funnels 1, 15 are equipped with sector gates that are closed when switching to the filling mode. The outlet funnels of the feeders are equipped with dampers controlled by pneumatic cylinders.

The load receiving device is made in the form of a cylindrical hopper 7 with a volume of 0.98 m3, suspended on four rods 6, 12 to a lever mechanism, and equipped with an outlet valve 9 controlled by a pneumatic cylinder 8.

To reduce dust, the cement path is covered with soft sleeves 13.

The AD-400-2BC cement dispenser has a cylindrical hopper volume of 0.75 m3.

The AD-200-2BZH liquid dispenser has a load-receiving device volume of 0.3 m3.

Dispensers for sand and crushed stone (gravel) are single-fraction (AD-800-BP, AD-800-BShch, AD-500-BP, AD-500-BShch), the frame of which is equipped with one feeder, and two-fraction (AD-1600- 2BP, AD-1600-2BSCH, AD-500-2BP, AD-800-2BSCH) with two feeders.

The feeder is a funnel covered with a sector shutter driven by a pieum cylinder. The load receiving device is made in the form of a cylindrical hopper with a volume of 0.78 m3 for AD-800-BP and AD-800-BShch dispensers; 0.58 m3 for dispensers AD-500-BP and AD-500-БШЧ (ДБШЧ-500); 1.27 m3 for dispensers AD-1600-2BP and AD-1600-2БШch; 0.81 m3 for dispensers AD-500-2BP and AD-800-2BSCH.

In the AD-1600-2BK and AD-800-2BK dispensers, designed for dosing expanded clay and sand according to the volume-weight principle, expanded clay is first dosed, the volume of which is set by the rotation speed of the paddle feeder, then sand, taking into account the total mass of expanded clay and sand.

In addition to the considered sets of dispensers, DVK-40 dispensers are used for dosing water, which are equipped with concrete mixers with a loading capacity of 250 and 500 liters. The DVK-40 dispenser is a water meter installed on the pipeline supplying water to the mixer. The dispenser can operate in cyclic or continuous mode. In cyclic mode, water is dosed by observing the movement of the needle on the dial scale. Having measured the required dose, turn off the water with a plug valve.

Continuous weighing batchers are designed for continuous batching of aggregates and cement in automated concrete mixing plants and continuous plants, which are designed to dispense from 30 to 240 m3/h of concrete mixture. Each continuous weigher includes a feeder that supplies material from the supply hopper of the concrete mixing plant; a measuring device that determines the mass of material in a flow of a certain length,

system for automatic control of the magnitude and speed of flow, i.e., the performance of the dispenser. Weighing batchers for aggregates include batchers SB-26A, SB-110.

The SB-26A (70) dispenser is designed for continuous dosing of concrete mix aggregates (sand, crushed stone and gravel) on SB-75 concrete mixing plants. The maximum grain size of the dosed material should be no more than 40 mm. The dispenser consists of a feeder funnel 1, a weight conveyor with a drive and a lever system. The hangers of 2 prism supports are attached to the funnel, on which the conveyor is suspended.

The weighing conveyor consists of two cheeks 13, a tension drum 8 and a drive drum 10, an intermediate gear, a belt 9 650 mm wide and connecting parts that form the frame. The tape is tightened with screws 7.

The conveyor drive includes a variator 14 with a gearbox attachment and an electric motor and a chain transmission 12. The lever system consists of a linkage, a lever /5, a prism support 3, a movable damper 5 and movable loads 6.

The material from the supply hopper is supplied through a feeder to the weighing conveyor belt. The height of the material layer on the belt is set by movable and fixed shutters.

The conveyor with the material on the belt is balanced by counterweights with loads. The variator sets the required belt speed, and therefore the dispenser performance. When the mass of material passing on the belt deviates from the specified value, the conveyor leaves the balanced state and the levers associated with it open or close the outlet opening of the loading funnel with a damper. The height of the material layer on the belt changes until the mass of the material becomes equal to the specified one. When the conveyor is lowered (as the mass of material increases), the layer height decreases, and when it rises (as the mass of material decreases), the layer height increases.

The dosing capacity can vary from 8 to 40 t/h depending on the belt speed.

The SB-110 (71) dispenser is designed for dispensing fillers with maximum size grains up to 70 mm in concrete mixing plants with a capacity of up to 60 m3/h. On the feeder funnel 1 of the dispenser, brackets 2 of the hinged support 10 are fixed, on which the conveyor is suspended.

The second support of the conveyor is force converter 4. The width of the conveyor belt is 800 mm.

In addition to the automatic operating mode, the circuit provides for remote setting of performance using buttons, as well as the ability to install an automatic potentiometer for recording performance. The dosing capacity can be changed from 5 to 50 t/h. Weighing cement dispensers include the SB-71A dispenser.

The SB-71A dispenser (72) consists of a two-drum feeder U, a weighing conveyor 12 and an automatic capacity control system.

Cement is supplied by feeder 1 to belt 7 of weighing conveyor 12, which is connected to the feeder body by a hinged support P. Second

The support of the conveyor is the force transducer 3, pivotally connected to the bracket 2, fixed to the funnel, and the bracket 4, fixed to the cheeks of the weighing conveyor.

The drive of the double-drum feeder and the conveyor belt is common and consists of an electric motor, a chain plate variator with remote control and chain gears.

The weighing conveyor includes a tension (driven) and drive drums, an intermediate gear S, a belt 7 and connecting parts that form the frame. The bearings of the driven drum 10 are moved, and the tape is tensioned with 1L screws

To prevent dust, the weighing conveyor is equipped with a sealed guard 5.

Schematic diagram The dispenser is designed in such a way that its constant productivity is maintained automatically by a system of regulation of a value proportional to the product of the speed of movement of the conveyor belt and the mass of the material located on it.

The dispenser productivity is regulated in the range from 4 to 25 t/h by pre-setting the task on the indicator scale.

Volumetric dispensers provide a constant volume of bulk material on sections of the conveyor of equal length with a constant cross-sectional area and the speed of the material flow.

To ensure that the dosing error is not affected by changes in humidity, density, or grain composition of the material, volumetric dispensers are equipped with a special control system.

Continuous volumetric dispensers - belt for aggregates and screw for cement - are used in continuous concrete and mortar mixing plants with a capacity of 5 m3/h.

At these same installations, as well as at concrete mixing plants with a capacity of 120 and 240 m3/h, a tank is used for dosing water, in which a constant water level is maintained. From the tank, water flows through a dosing valve with a graduated flow area into the concrete mixer.

By changing the size of the flow area of the dosing valve, the water flow is adjusted in accordance with the given composition of the concrete mixture.

For dosing water in continuous concrete mixing plants with a capacity of 30 and 60 m3/h, metering pumps SB-32 and SB-34 with remote control with a capacity of 6 and 12 m3/h, respectively, are designed.

Concrete is a man-made stone material made from a mixture of binders, water and aggregates after it has been molded and hardened. Construction mortars do not contain large aggregates. Before forming, these carefully mixed components are called concrete mix and mortar, respectively.

The preparation of concrete mixtures and mortars consists of dosing components and mixing them. Dispensers are used for dosing, and mixing machines or mixers are used for mixing.

Fig.5

Dispensers come in volume and weight. The first dispensers dose materials by volume, and the second dispensers dispense materials by weight. Volumetric dispensers are simpler, but less accurate due to the variability of the density and humidity of the bulk materials being dosed and the conditions for filling the measuring containers. They are usually used for dosing water. For dosing bulk materials, they are used only in construction sites for mixers with a finished batch volume of up to 250 liters.

Rice. 6

Depending on the mode of operation, dispensers are divided into cyclic (portion) and continuous. In batch dispensers, the material is dosed in a measuring or weighing hopper, and in continuous dispensers, the material is fed into mixers in a continuous flow with a given capacity. The dispensers are controlled automatically or semi-automatically from the control panel.

Rice. 7

car construction road concrete

In the process of preparing a concrete mixture, the leading operation is the dosing of the material per batch of the concrete mixer. Concrete plants mainly use weighing batchers, which ensure dosing of components by mass with an accuracy of ±1-2%. The accuracy of the concrete composition depends on the dosing accuracy. Thus, cement is dosed with an accuracy of up to 5 kg, water - up to 2 liters, sand and stone wool - up to 10 kg.

Under construction site conditions for the preparation of heavy concrete mixtures, aggregates are sometimes dosed by volume, but it is necessary to take into account their moisture content, since moisture (especially sand) dramatically changes the volume of materials. Volume-weight dosing is also used: coarse aggregate is dosed by volume, and sand by mass.

To determine the consumption of materials per batch, you need to know the composition of the concrete, as well as the yield coefficient of the concrete mixture from the concrete mixer after mixing it. The yield coefficient is determined as the ratio of the volume of the resulting concrete mixture to the sum of the volumes of dry components and is usually 0.65...0.68. This is explained by the fact that when mixed, smaller components are distributed in the voids between the coarse aggregate. Depending on the capacity of the concrete mixer and the yield coefficient of the concrete mixture, material consumption rates are set for one batch.

When dosing by volume, volumetric dispensers are used. They are simple in design and allow you to easily and widely regulate the amount of material being dosed, but their dosage accuracy is not high enough, which reduces the quality of the concrete mixture.

Various measuring containers are used as volumetric dispensers. The dispenser for aggregates (sand, gravel, crushed stone) is a rectangular measuring vessel consisting of two sections. The upper section is attached to the hopper under the gate, and the lower section is attached to the upper one. The design solution is such that it can be raised and lowered, thereby changing the volume of the portion of material. To dispense the dosed material, the lower section is equipped with a release valve.

Weighing feeders provide more high accuracy measuring the material. They are performed cyclically and continuously. Cyclic dispensers weigh out specified portions of mixture components for one batch and repeat the cycle after a new load; Continuous dispensers supply ingredients in a continuous stream.

Cyclic dosers can be single- or multi-fractional. Single-fraction dispensers are located directly under the supply container of the dosed material. The work cycle consists of loading, cutting off a given amount of material and moving it into a concrete mixer. Multi-fraction dispensers sequentially weigh two or more fractions of aggregate. For such dispensers, the dosing cycle is longer. All dispensers are predominantly automatic, which ensures improved working conditions for the operator, since the work area is in very dusty conditions.

Automatic dispensers ensure that the flow of material into the dispenser container stops upon completion of the set amount. There are several types of automatic weighing dispensers; they are distinguished by the design of the actuators of the loading and unloading working bodies, and the control data transmission system.

The principle of operation of weighing dispensers is similar to conventional scales. Lever scales are used in weighing devices. A more advanced weighing device is the quadrant type. The most progressive and reliable is the system of strain gauge and strain gauge mass sensors. The strain gauge device can be easily automated and switched to weighing different doses of materials.

The dispensers are produced as a set; they are used to equip mobile (mobile), sectional (collapsible) and stationary concrete mixing plants of types SB-134, SB-140, SB-135 and others with mixers with a capacity of 250, 500, 750 and 1500 liters.

For installations of this type, sets of weighing batchers VDB-250D, VDB-500/750D, VDB-1500 are used. The kits are supplied in the following composition: VDB-250D - liquid dispensers DZh-100D, cement - DC-100D, inert (aggregates) DI-500D, control equipment unit BAU-9 or BAU-5; VDB-500/750D - dispensers DZh-200D, DC-200D, DI-1200D with control unit BAU-5; VDB-1500 - dispensers J-200D, J-100D, DC-500D, DI-2000D with a BAU-9 control unit.

Let's consider the device of a cement weighing dispenser DC-100D (Fig. 12). It consists of a hopper 1 with a shutter, a frame 2, a weight lever 3, a dial spring indicator 7. The hopper 1 is cylindrical in shape, at its base there is an outlet valve 8. A valve 9 is fixed in the neck of the shutter, rotating on an axis through a lever 14 under the action of a pneumatic chamber 12. The valve 8 is opened by a compressed air pressure of 0.4...0.6 MPa and closed by the force of springs located on the pneumatic chamber rod.

Rice. 12. Design diagram of the cement dispenser DC-100D:
1 - hopper, 2 - frame, 3, 14 - weight levers, 4 - set screw, 5, 15 - prism, 6 - rod, 7 - spring indicator, 8 - shutter, 9 - damper, 10 - sleeve, 11 - converter , 12 - pneumatic chamber, 13 - flange, 16 - pillow, 17 - hole

The closed position of the shutter is controlled by the insertion of the flange 13 into the groove of the converter 11. To prevent the material from being sprayed, the upper part of the hopper and the shutter have necks for connecting transport hoses 10. Near the neck in the upper part of the hopper there is a hole 17, closed with a lid and designed to allow air to escape when loading cement.

The lever system is an unequal-armed double weight lever 3. With the help of two prisms 5, 15 and pillows 16, the lever rests on the support legs of the frame 2. A hopper is suspended on one arm of the lever by means of prisms and pillows, and the opposite end is connected by a prism 5 and a rod 6 with dial indicator 7.

When the dispensers are turned on, the inlet valves open and the dosed material enters the containers. The force from the mass of the incoming material is transmitted through the lever system 3 to the dial indicator 7, where it is balanced by the force of the elastic spring. The deformation of the spring is converted into a rotation of the dial pointer. Upon reaching the specified mass value, the dial indicator needle moves into the groove of the corresponding sensor. A signal is sent to the control system and a command is given to stop the supply of material. The gate closes or the feeder stops.

When a command to unload the material is received from the control panel, the outlet valves 8 of the dispenser open. The material spills out and the dial indicator hands return to the zero position. The flanges of the 13 indicator arrows fit into the groove of the zero sensor. The outlet valve 8 of the dispenser closes and the cycle repeats.

The filler dispenser DI-500D (Fig. 13) consists of a load receptor, a weight lever mechanism, a dial spring indicator 1. The load receptor includes a frame 2, two load-receiver arms 3 and a platform 15. The load-receiver arms are supported by prisms on the cushions of the support posts 17, installed along corners of the frame. The levers are connected to each other and the lever mechanism using an earring 5 and a rod 4. Each lever has two setscrews 11, designed to bring the dispenser into the transport and working positions.

Rice. 13. Design diagram of the filler dispenser DI-500D:
1 - spring indicator, 2 - frame, 3 - load-receiving lever, 4, 18 - rods, 5 - connecting earring, 6 - stand, 7 - lever, 8 - container load, 9 - body, 10 - movable stop, 11 - installation screw, 12 - pin, 13 - earring, 14 - vibration damper, 15 - platform, 16 - nut, 17 - stand

The platform 15, with the help of four earrings 13 with cushions, is suspended on the prisms of the load-receiving arms 3 and has free swing in the horizontal plane. To limit the swing of the platform and dampen possible shocks, pins 12 are provided. The measured mass by the dispenser is 100...500 kg.

The dispenser works as follows. The material from the supply bins is supplied to the load receiving device. The force from the mass of the incoming material is transmitted through the lever system to the dial pointer. Upon reaching the specified mass value, the arrow of the dial indicator enters the groove of the corresponding sensor. The control system receives a signal to stop the supply of material and close the gate. A weighed portion of material enters the mixer. Then the cycle repeats.

The liquid dispenser DZh-200D (DZh-YuOD) is structurally similar to the cement dispenser DC-100D (DC-200D) and differs only in the design of the valves.

The design of the AVD series dispensers (cement - AVDTs-425M, AVDTs-1200M, AVDTs-2400M; aggregates - AVDI-425M, AVDI-1200M, AVDI-2400M; liquids - AVDZh 425/1200M, AVDZh-2400M) is based on the use of a quadrant weighing device . These dispensers differ little from the VDV series and are gradually being replaced by more progressive designs based on a strain gauge system for weighing material.

Modern dosing equipment is the KD-1500 set with a control system designed to equip concrete mixing plants of the SV-145 type. The set includes: cement dispenser DTC-500, liquid dispensers DTZh-200 and DTZh-YuO, weighing device for inert dispenser DTI-2500, level control device PKU-1, control panel BMU-1.

The BMU-1 control panel together with dispensers and actuators of the process equipment form control system, which allows you to prepare concrete mixtures in automatic mode with high degree accuracy (dispenser accuracy class 2). The permissible error of the loaded weighing device is: for cement ±1.5, liquid ±0.6, additives ±0.3, inert ±10 kg.

The required masses of mixture components and mixing time are encoded on punched templates.

The design of the cement dispenser DTC-500 (Fig. 14) consists of a cylindrical filling hopper 8. At the base of the conical part there is an exhaust valve 9. A weight lever system of two levers is used: the upper unequal arm 3 and the lower 17 with a gear ratio of 1:2. The upper lever 3 is supported by prisms 2, 6 on the cushions of the frame support posts. A hopper 8 is suspended from one arm of the lever, and the opposite end of the lever is connected by a prism 6 and a rod 7 to the lower lever. The lower lever is mounted on a stand fixed to the base of the frame, and the second end is connected by rod 7 to strain-gauge force transducer 5 (PST).

Rice. 14. Design of the cement dispenser DTC-500:
1, 15 - covers, 2, 6 - prism, 3, 17 - lever, 4 - bolt, 5 - strain gauge force transducer, 7 - rod, 8 - hopper, 9 - shutter, 10 - damper, 11, 19 - casing, 12 - sensor, 13 - flag, 14 - piston, 16 - rod, 18 - fork

The force from the lever system through the rod, lever 3 and pressure bolt 4 is transmitted to the strain gauge 12, which is placed in a sealed casing 11 on the base of the damper 10.

A valve 10 is fixed in the neck of the valve 9, which rotates on an axis through a lever 17 under the action of the pneumatic cylinder rod 16 and the fork 18. A tight fit of the valve to the neck is ensured by the piston 14 of the pneumatic cylinder until it stops at the cover 15.

The closed position of the shutter is controlled by sensor 12, into the groove of which a flag 13 fits. For safety, the moving parts of the shutter are protected by a casing 19.

The dispenser works as follows. Cement is supplied to the storage bin 8 from the supply bin. When a given mass is reached, the signal from the strain gauge force transducer 5 is supplied to the strain gauge 12, and from there to the control unit. The control unit gives a command to the pneumatic cylinder to open damper 10. The weighed dose enters the mixer. The flap closes the neck of the bolt 9, and the cycle repeats.

Liquid dispensers DTZh-100 and DTZh-200 are similar in design and differ only in the size and number of inlet valves. Liquid dispensers (Fig. 15) consist of a frame 15, on the racks of which inlet valves 9 are installed - one for the DTZh-200 dispenser and two for the DTZh-YuO dispenser, a cylindrical storage hopper 13, a weighing system with a strain gauge force transducer 16. An 8-valve type outlet valve is located on the hopper lid. Valve 11, which closes the outlet, is mounted on a rod 12, which is connected to the rod of the pneumatic cylinder of the shutter 8. The opening and closing of the valve occurs when compressed air is supplied to the pneumatic cylinder.

Rice. 15. Liquid dispenser DTZh-100:
1 - rod, 2, 14 - prisms, 3 - lever, 4 - bolt, 5 - pillow, 6 - flag, 7 - sensor, 8 - outlet valve, 9 - inlet valve, 10 - cover, 11 - valve, 12 - rod, 13 - hopper, 15 - frame, 16 - strain gauge force transducer, 17 - hook

The closed position of the inlet and outlet valves of the dispenser is controlled by discrete sensors 7, into the grooves of which flags 6 enter when the valves are closed.

The lever system is an unequal-armed double lever 3. With the help of two prisms 14 and cushions 5, the lever rests on the frame support posts. A hopper is suspended from one arm of the lever from a group of prisms and cushions, and the opposite end is connected through prism 2 and rod 1 to a strain gauge force transducer (PST). To prevent splashing of water when draining it into the concrete mixer, the outlet neck is closed with a rubber cover 10.

The weighing system is fixed with bolts 4 and a hook 17 during its transportation. The operating principle of a liquid dispenser is similar to a cement dispenser. When the required mass of liquid arrives, the PST is triggered and gives a signal to the sensor. Then a command is given to open the valve. The liquid flows through the hose into the concrete mixer, the valve closes and the cycle ends.

Of particular importance is the preparation and dosing of chemical additives. The equipment must ensure the homogeneity of the additive solution, the necessary accuracy of dosing and uniform supply into the concrete mixture.

Additive solutions are prepared by dissolving chemicals. To improve the dissolution process, the liquid is heated to 40...60 ° C and the components are intensively mixed. The finished solution is pumped using a pump into a supply tank, from where it enters the dispenser.

The dosing cycle includes drawing up a dose and dispensing it. In addition to DTZh-type dispensers, automatic volumetric dispensers SB-147, DOP6-12U4, DOP25-12U4 are used, providing dose set with an error of ±2%. A dose of the working solution enters the water dispenser of the concrete mixing plant, where it is thoroughly mixed and, together with water, is introduced into the mixer.

The DTI-2500 aggregate dispenser (Fig. 16) consists of a load receptor, a lever mechanism and a PST. The load receiving device includes a welded frame U, two load receiving arms 2U on which the platform 13 is suspended. A storage hopper is attached to the platform (not shown in Fig. 16). The load-receiving arms are supported by prisms on the pads of the support posts 3, installed at the corners of the frame. The levers are connected to each other and the lever mechanism using an earring 7 and a rod 6.

Rice. 16. Filler dispenser DTI-2500:
1 - frame, 2 - load-receiving lever, 3 - stand, 4, 7 - shackle, 5 - strain gauge force transducer, 6 - rod, 8 - support stand, 9 - lever, 10 - load, 11 - set screw, 12 - stop , 13 - platform

Each lever has two set screws 11, with the help of which the weighing system is fixed when transporting the dispenser. The platform 13 is suspended through the earrings 4 with cushions on the prisms of the load-receiving levers 2. To limit the swing of the platform, screw stops 12 are used.

The lever mechanism consists of a housing in which a support post 8 is located. A lever 9 rests on the pads of the post, connected by earrings to levers 2 and PST.

To take into account the tare weight, there is a weight 10 moved along the lever 9.

For continuous mixers, weighing dispensers of the SB series are used, which provide continuous weighing of the material. They are used in automated concrete mixing plants in continuous production plants.

The industry produces continuous weight batchers SB-71 A, SB-90 for cement with a capacity of 4...25 and 25...100 t/h; aggregate dispensers - SB-26A, SB-110, SB-111 with a capacity of 8...40, 5...50, 10...100 and 2...200 t/h, respectively.

A continuous weighing feeder consists of a feeder that supplies material from a supply hopper, a measuring device that records the mass of material in a stream of a certain length, and a system for automatically regulating the size and speed of the material flow.

The SB-26A dispenser (Fig. 17) is used for continuous dosing of coarse aggregate (sand, crushed stone and gravel) with fraction sizes up to 40 mm in SB-75 concrete mixing plants.

Rice. 17. Filler dispenser SB-26A:
1 - variator, 2 - lever, 3 - funnel-feeder, 4 - suspension, 5 - prismatic support, 6.7 - fixed and movable dampers, 8 - counterweight; 9, 10, 12 - tension and drive drums, 11 - belt, 13 - sprocket, 14 - chain drive, 15 - conveyor frame cheek

The dispenser works as follows. The material from the supply hopper flows through the feeder funnel 3 onto the conveyor belt. The height of the material layer is adjusted using a movable damper 7. The conveyor with the material is balanced by counterweights. If the mass of material on the belt deviates from the set one, the balance of the conveyor is disturbed and the levers open or close the outlet of the funnel with a damper, thereby restoring the required level of material on the belt. When the conveyor is lowered, the height of the material layer decreases, and the feed speed decreases accordingly. As the layer height increases, the material supply increases. The performance of the dispenser is controlled by the speed of the belt by changing the rotation speed of the conveyor drive shaft.

One of the most important operations in the process of preparing concrete mixtures and mortars is the dosing of components: binders, aggregates and water. There are two methods of dosing materials: by volume and by weight. With volumetric dosing, portions of material are measured in vessels of a calibrated capacity (volumetric dispensers), consisting of two telescopic prisms with two shutters; the upper one, covering the outlet hatch of the hopper, to which the dispenser is suspended, and the lower one, which serves to empty the dispenser. By sliding the lower prism into the upper one or extending it using the graduated bolts on which it is suspended, it is possible to change the portion of the material within certain limits. Volumetric ones are simple in design, but do not provide sufficient dosing accuracy, since the volumetric weight of the starting materials (for example, cement and aggregates) is not a constant value, but depends on a number of them physical properties: degree of compaction, humidity, grain size, etc. Thus, the volumetric weight of cement, depending on the degree of its compaction, can vary by up to 50%; volumetric weight of sand depending on the degree of humidity - up to 35%; gravel and crushed stone depending on the grain composition - up to 30%. Therefore, official instructions recommend only weight dosing for cement with a permissible error of 1 - 2%. Aggregates, for which the dosing accuracy is set within ± 3 - 5%, are also preferable to dose by weight, especially when the volume of concrete work exceeds 100,000 m3. Dosing water by volume is more widespread, in particular with mobile machines.

The simplest volumetric water dispenser is a tank with a float that cuts off the flow of water when it reaches a certain, predetermined level. Typical design of a water dispenser for batch concrete mixers with drums with a capacity of 250 to 1,200 liters and drums with a capacity of 150 to 750 liters. is as follows: the water meter tank is connected to the water supply network using a three-way tap. An air valve with a fill indicator is installed in the top cover of the tank. When the inlet water valve of the three-way tap is opened (the outlet valve closes), water from the network enters the tank through the feed-drain pipe, displacing air through the valve. Having reached the valve, the water lifts it and disconnects the water meter tank from the atmosphere, as a result of which further flow of water into the tank stops. When the water outlet valve is opened, the water from the tank is poured through a pipe (siphon effect) into the mixing drum, and the air valve is lowered. The flow of water from the tank continues until its level reaches the hole at the end of the dosing tube. In this case, the atmospheric air sucked in by the tube enters the siphon elbow, the water stream breaks, and the water drainage stops. By placing the end of the dosing tube at different levels, it is possible to drain different doses marked on the scale from the water meter tank; The tube is rotated using an arrow. Dispensers of this design are available in capacities from 40 to 200 liters. Although water can be dosed by volume with a sufficient degree of accuracy, however, where weighing dispensers for cement and aggregates are installed, in order to unify the equipment, it is advisable to dose water by weight. Depending on the type of concrete mixers being serviced - periodic or continuous action -

Preparation of concrete mixture comes down mainly to dosing and mixing the constituent materials. In modern concrete plants, components are dispensed by weight using automatic or semi-automatic dispensers.

Concrete mixtures of given compositions are obtained by accurately dosing (measuring) the components (cement, aggregates, water and additives) before entering the concrete mixer. The dosing error of the constituent materials of the concrete mixture is allowed for cement, water and additives ±2%, for aggregates ±2.5% by weight (SNiP IM5-76).

Cyclic or continuous dosing is carried out using batchers for aggregates, cement, water and additives.

Cyclic dispensers measure the dose of material loaded into the measuring container and, after unloading, repeat the cycle.

Continuous feeders produce a uniform flow of material that is measured continuously.

According to the principle of operation, dispensers are divided into volumetric, weight and volume-weight (mixed).

Volumetric dispensers are simple in design, but it is difficult to ensure the necessary accuracy in dosing the bulk components of the concrete mixture. This is explained by the influence of the physical and mechanical properties of bulk materials (humidity, size, volumetric mass), as well as the method of filling the measuring container (intensity and height of flow, degree of compaction). The dosing error increases with increasing material size, intensity and height of its outflow. Volumetric liquid dispensers are equivalent in dosing accuracy to weight dispensers, which is why they are widely used in the preparation of concrete mixtures.

Volumetric dosing of bulk components is used on free-standing concrete mixers and low-capacity continuous concrete mixing plants.

Weighing dispensers for bulk components of concrete mixtures provide higher dosing accuracy. Therefore, weight dosing of bulk components is used everywhere in concrete mixing plants of medium and high productivity.

Volume-weight dispensers are designed for dosing concrete components on lightweight aggregates - expanded clay concrete. Expanded clay is dosed by volume, since its dose by mass is not a characteristic value due to fluctuations in the volumetric mass over a wide range.

The total specified mass of expanded clay and sand is ensured by adding the required amount of sand by mass.

According to the control method, dispensers are available with manual, remote and automatic control.

In manually controlled cyclic dispensers, the inlet and outlet valves are opened and closed manually. When controlling continuous dispensers, they manually change productivity by adjusting the height of the material layer or the speed of its movement.

With remote control, loading, dosing and unloading of materials is carried out from the control panel. The dispenser, observing the arrows of the dial indicators, presses the corresponding buttons (keys, toggle switches) to control the actuators for loading and unloading the dispenser measuring container.

In continuous dispensers, remote control of their productivity is carried out from the remote control.

At automatic control Loading, dosing and unloading of materials on cyclic dispensers and changing the productivity of continuous dispensers occurs automatically.

In cyclic dispensers, manual and remote control used on both volumetric and gravimetric dispensers, automatic - only on gravimetric dispensers. In continuous dosers, manual control is used only for volumetric dosing, remote control for volumetric and weight dosing, and automatic control for weight dosing.

Related information:

III. Selection of a given mixture mobility, determination of actual material consumption
Analytical judgments (A.J.) - judgments, the truth of which is established without reference to reality through logical-semantic analysis of their components;