With the development of social economy and market demand, concrete machinery is also used more and more frequently in the concrete industry, and the situation continues to pick up. For some novices, it is necessary to understand and master the operation specifications and maintenance of concrete mixing plants.
1. Operation specification of concrete mixing plant
1. The knowledge that the operator should possess
a. Master the basic knowledge related to concrete;
b. Familiar with the purpose and performance of each part of the concrete mixing plant and the function of each control component of the mixing plant;
c. Familiar with the concrete mixing process and the operation process of the mixing station.
d. Summary of concrete knowledge that operators should master
1) Introduction to concrete
Concrete is a kind of artificial building material made of cement as a cementing material and solidified by sandstone and other materials. After hardening, it has the nature of stone. It is referred to as concrete for short.
The types and properties of concrete required for different construction projects are very different. When producing, if you have an understanding of the properties and uses of the concrete produced, you can adjust the equipment accordingly to improve the quality of concrete mixing, and Not easy to make mistakes.
One of the main signs of the performance of concrete is its strength, which is measured by a compression test after a 28-day standard curing with a cube test block with a side length of 150mm. The commonly used strength range is 10-60Mpa, and the general strength level is C20 —C60 said.
The workability of freshly mixed concrete, or workability, refers to whether the concrete mixture is easy to construct and operate, and obtains uniform quality and compact performance. It is a general term for the performance of concrete technology. Including the three aspects of fluidity, cohesion and water retention. Mobility means easy to flow and easy to fill corners of pouring formwork. Cohesiveness means that the structural properties of concrete are uniform and stable, and are not prone to delamination and segregation. Water retention refers to the difficulty of bleeding.
Among the workability, the greatest impact on concrete construction is fluidity. The fluidity of plastic concrete is expressed by slump, and its range is generally 10-200mm. The larger the value, the stronger the flowability. The dry hard concrete is expressed by the Weibo consistency, and its range is generally 5 to 35 seconds. The larger the value, the higher the dry hardness of the concrete.
The workability of the designed concrete depends on the engineering structure and construction method. Most of the current construction sites use fluid or highly fluid concrete, and only precast concrete components use dry hard concrete.
2. The nature and types of sand, cement and other raw materials
Understanding the characteristics and properties of various raw materials is of great help to correct operation.
Sand and gravel is generally called aggregate (also called aggregate), which means that it acts as a skeleton in concrete. Coarse aggregate refers to stones with a particle size greater than 5mm. In a mixing station, a handful of pebbles should have a particle size not greater than 80mm, and a crushed stone with a particle size not greater than 60mm. Fine aggregate refers to sand and gravel with a particle size of not more than 5mm, mainly referring to sand. It is generally divided into coarse sand, medium sand, fine sand and extra fine sand. According to its particle size specification, it is expressed by fineness, from 0.7 to 3.7.
Sand and gravel aggregates generally require good gradation of particle size, that is, they are large and small, and can fill gaps with each other. In this way, the formed concrete is dense and easy to work, and it is not easy to segregate during transportation.
Cement is a hydraulic cementitious material, which mainly acts as a binder in concrete. Common cement is commonly used in civil engineering. In addition to the selection of cement according to the characteristics of various cements, the amount of cement in the concrete mix ratio is mainly determined according to the strength index. The strength of cement is reflected in the strength grade of cement (formerly called the label). The strength grade of cement is formed by the strength obtained through the compression test of the 28d mortar test block. For example, the strength of cement with strength grade 425 is about 42.5Mpa at 28d. If the storage of cement exceeds 3 months from the date of leaving the factory, its strength shall be re-examined.
The strength of cement in concrete should be slightly higher than or equal to the strength of concrete. When the strength of concrete is very low, admixtures can be used to save cement. The maximum amount of cement in each concrete should not exceed 550 kg.
Domestic drinking water that meets national standards can be used for concrete production. Other water sources can only be used after passing inspection.
Admixtures and admixtures are two additional materials used to improve the production process and performance of concrete to meet special needs. Additive materials play an increasingly important role in the production and application of concrete. The amount of admixture is usually greater than 5% of the amount of cement, and its fineness is the same or finer than cement. The amount of admixture is usually not more than 5% of the amount of cement.
3. The nature of the material has the following effects on the workability of the fresh concrete:
Aggregate gradation is good, its workability is good; coarse sand is fine, workability is not good;
The workability of pebbles is good, there are more needle-like stones, and their workability is poor;
Sand ratio refers to the percentage of the weight of sand and gravel aggregate in concrete. If the sand rate is too small, the concrete will bleed and segregate. When the sand rate is too large and the amount of cement is small, the workability will deteriorate.
The finer the cement, the smaller the bleeding, and the better the workability; when the amount is too much, its dry shrinkage increases.
Water-cement ratio refers to the weight ratio of water to cement in concrete. If the ratio is large, the workability is good, but too much water will cause segregation and bleeding, and the strength will be greatly reduced, so the water consumption of concrete must be strictly controlled. Under the condition that the water-cement ratio is unchanged, the appropriate increase in the amount of cement slurry can improve workability.
4. Operational factors that affect the quality of concrete.
The effect of operation on the quality of concrete is mainly in the measurement and mixing process.
During production, pay attention to observe the measurement error, adjust the overshoot, and grasp the residual amount in the feeding process to ensure that the accuracy of the measurement meets the requirements. The following aspects need special attention:
The added materials have a great influence on the concrete, and some of them are used in small amounts. In this respect, special attention should be paid to the accuracy of the measurement.
The slump of concrete has a direct impact on the performance and quality of concrete, but the moisture content of sand and gravel cannot be guaranteed to be stable. In this way, if the equipment cannot automatically adjust the moisture content of the gravel, it is necessary to constantly observe and grasp the dry and wet degree of the gravel and the slump of the concrete at the discharge port, and if necessary, the ratio of sand to water Make adjustments to ensure that there is no large deviation in slump.
The mixing process is mainly based on the characteristics of the concrete produced to adjust the timing of feeding and the time of mixing and releasing to ensure that the concrete is mixed and mixed evenly to meet the design requirements and performance.
When admixtures are used in the produced concrete, the mixing time should be properly extended. When dry admixed, the mixing time of the fly ash concrete is 10-30 seconds longer than that of ordinary concrete, and the concrete of other admixtures is extended 30-60 seconds.
2. The principle and composition of concrete mixing equipment
Concrete mixing equipment is a device that mixes various raw materials that make up concrete according to a certain ratio, and then mixes and stirs according to a certain process, and finally produces concrete with certain performance.
Although the concrete forms of concrete mixing plants produced by various manufacturers are varied, their basic forms and composition structures are similar. Nowadays, the popular mixing station is basically based on the computer as the core of control, controlling the automatic batching, automatic lifting, mixing and discharging of various materials, and some auxiliary functions such as data statistics and report printing.
Functionally, various concrete mixing plants are generally composed of the following parts:
1) Storage silo: store sand, stone, cement, water and other materials and feed the batching mechanism;
2) Proportioning mechanism: measure materials such as sand and gravel according to a certain proportion, mainly composed of various scales, and also use flow metering equipment that measures by volume;
3) Lifting mechanism: mainly used to lift gravel aggregate;
4) Mixer: Mix various raw materials to form concrete;
5) Control system: control the coordination of various parts to complete a certain production process.
3. Familiar with the function and performance of each component of the mixing station to be operated
Only when the working performance and operation of the mixing station to be operated are fully understood can it be correctly operated and used. When problems occur, it can be discovered and eliminated in time.
Understand the operation principle of each component of the equipment, grasp the maintenance status and degree of maintenance of the equipment, and the use status of the equipment. For example, the working pressure range of the air compressor, the intact condition of the batching machine, and the deviation of the belt. Only by knowing the condition of the equipment can production be safe and stable.
Specific knowledge will be described in the operating instructions.
4. Master the function and operation of each control component
The concept of the function of each control component of the mixing station must be clear, and the correct operation sequence and operation regulations must be mastered. Only in this way can it be handled correctly in an emergency situation, to avoid operating errors that cause equipment damage and material loss.
5. Familiar with the mixing process and production process of concrete
The main points of operation of the basic mixing process are as follows:
1) The venue is kept clean, the drainage is smooth, and the relevant signal communication is smooth;
2) The feeding system should prevent the aggregate from entering the running mechanism; generally, the gravel and cement cannot be fed in the same tube slot; the materials in the hopper, tube slot and other parts should be unloaded every time, and should not be reserved for the next feeding.
3) One-time feeding and multiple-time feeding can be used. One-time feeding is to put the materials into the mixer according to a certain process sequence, but it is not allowed to put cement first, so as to avoid the cement sticking to the shaft; in order to avoid the cement being wrapped by water to form cement balls It should be mixed with cement and gravel first, so that the cement is dispersed, and then sprayed with water; multiple times of mixing and mixing concrete, also called shell concrete, its feeding operation is more complicated, and it needs a program in the mixing station and mixing building. Special processing can be achieved.
4) During the operation, the first is to control the measurement accuracy and mixing time to ensure that the process requirements are met; the second is to check for abnormalities and faults, such as whether there is water leakage or slurry leakage at the discharge port. If there are any abnormalities and faults, they must be repaired in time.
5) Before the machine is shut down, clean concrete must be produced; before the machine is shut down after the work is completed, a small amount of stones should be used and the mixer should be washed with water; at the same time, the mixing site should be cleaned. When there is a sudden power failure or fault shutdown, care should be taken to remove the concrete in the host in time.
6. Safety Any personnel must observe the operating procedures and safety precautions to ensure safe production.
The operator should follow the following production process:
1) Before production, you must receive a production task notice and strictly follow the content of the task order; when there are multiple task orders at the same time, you must be clear-headed, and the mixed concrete must correspond to the invoice;
2) Before mixing, check whether the types of various materials correspond to the control parts and whether the quality of the materials can meet the requirements; check whether the equipment is in a normal state and ready.
3) Whether it is necessary to adjust the proportion of sandstone according to the water content; whether the overshoot, the timing of feeding and the stirring time need to be adjusted.
4) Because the first tank has mortar adhesion in the mixer, consider whether to compensate for sand addition, cement and stone reduction.
Other considerations:
The setting of the stirring time needs to be according to the requirements of the test personnel, generally ranging from 30 seconds to 3 minutes, when the admixture or admixture is added, the stirring time should be appropriately increased according to the mixing method and process requirements to ensure The quality of concrete meets the requirements.
2. Maintenance of concrete mixing plant
Because the specific structure of the mixing plant is different, only a general description is made here, and special parts need to be maintained in accordance with the instructions.
It should be particularly pointed out that the dustproofness of the mixing station is particularly important. The accumulation of dust brings great inconvenience to the maintenance and repair of the mixing station, which reduces the performance of all equipment, shortens the life, and damages the lubrication. Therefore, the structure should be very principled The above minimizes the generation of dust and is regularly cleaned and maintained.
1. Maintenance of mechanical parts
1. Main points of maintenance and maintenance of mixer and batching system:
a. Transmission system
All transmission gears, reduction gearboxes, chains, etc. should be filled with lubricating oil (grease) as required; the sound of the transmission part is normal, and the reduction gearboxes and bearings do not heat or leak oil;
The triangle conveyor belt is suitable for tightness (10-15mm can be pressed in the middle), and the center of the transmission chain should not sink more than 20mm;
The steel wire rope has no major wear, the chuck and the connection are firm, and the surface has grease (graphite calcium base);
The brake and clutch performance is good, and the brake pad must be replaced when it wears to a certain extent.
b. Other lubrication parts
The shaft seal of the mixer is refueled at the start of the host or at regular intervals according to the regulations to ensure the long-term normal operation of the oil seal structure;
Other refueling points such as each rotation, rotating wheel and track should be refueled regularly.
c. Mixing system
The mixing drum runs smoothly, and the lining board and blades are not loose. If damaged, replace them in time; when the lining boards, blades, scrapers, and mixing arms are worn to a certain degree or cannot be adjusted, they should be replaced in time.
Clean the sticky concrete in the mixer in time or regularly. When the concrete on the inner wall of the mixer becomes thicker and thicker, not only the volume of the mixer should be reduced, but also the speed of sticking concrete will be accelerated; Bonding makes the opening of the bucket door of the discharge port obstructed. The cement discharge port will become smaller and smaller due to the adhesion of water vapor, which will cause difficulty in feeding, so it should be cleaned regularly. The feed line of the admixture may slow down the feed rate or cause blockage due to precipitation and solidification, and it should be cleaned regularly.
d. Installation, fastening and cleaning
The installation and connection of the main body and support, loading support and other facilities should be firm, and all fasteners should be complete, complete and firm; the main body, site and operation room should be clean and free of cluttered items; no water can accumulate around the foundation, Water storage during freezing season; fastening of vibration parts and connecting parts.
2. Main points of gas circuit maintenance and maintenance:
a. Maintenance of air compressor
The oil level in the crankshaft oil tank of the air compressor should be above the minimum oil level marking line. Check the oil level and the quality of the lubricating oil every half a month or periodically, and add or replace if necessary; use No. 19 compressor oil in summer, Use No. 13 compressor oil in winter.
The air compressor should be placed in a flat and clean place, and should not be allowed to work in damp, dirty and dusty places. Put the oil and water in the gas cylinder once every two shifts, check the sensitivity of the safety valve once every 3 months, clean the muffler once after working for 250 hours, and change the lubricating oil after working for 500 hours.
b. Gas channels and triplets
The vent tube and the connection head should be kept smooth and firm, to avoid discounts, friction with other prismatic objects during action, and repairs should be made immediately when air leaks.
The gas passing sequence of the triplet is filter-reducing valve-oil mist device. When the filtrate in the filter is full, it should be discharged in time, and the lubricating oil in the oil mist device should be added in time.
When adding oil, it should be carried out without pressure. Before the operation, clean the surrounding dust and other debris to avoid entering the lubricator. You can use lubricating oil with a viscosity of 2.5-7 degrees or industrial #40 engine oil.
c. Solenoid valve and cylinder
Solenoid valve should be installed firmly. There should be protective devices around it to prevent foreign objects from damaging the housing and wiring. Muffler plugs must be installed at the exhaust port to prevent dust from entering the valve body and blocking the valve core; when the solenoid valve and cylinder are connected together Or when the electromagnetic valve is shocked during operation, the fasteners on the valve body and the cylinder must be shock-proofed.
On the one hand, the cylinder needs to work outside the specified air pressure, and its installation position must be proper. The screws tightened and connected so far must be checked regularly for looseness.
3. Maintenance and maintenance of cement storage and transportation equipment
The biggest threat to cement storage and transportation is rain and moisture, especially in the south with more rain. Therefore, at the time of initial installation, carefully check the tightness of the entire passage, and deal with moisture and rain from the principle and structure. This is necessary to prevent future troubles.
If the design is not very strict, the lower valve of the cement silo, the interface with the screw machine and the central interface of the screw machine and the connection with the cement weighing hopper may be invaded by rain and moisture, resulting in agglomeration and reduced performance of the cement The phenomenon. In this case, on the one hand, the seal should be strengthened as much as possible, and on the other hand, the screw conveyor and the weighing bucket should be free of cement.
The firmness of the screw conveyor's fixing and connection should be checked frequently. The lubrication of the screw machine, the middle support and the seal of the tail should be filled with oil for every 1000 square meters produced; refer to the instruction manual for the maintenance of the gear motor.
The connection between the inlet of the upper part of the cement weighing hopper and the screw machine should not be too tight or too loose, too tight will affect the accuracy of the scale, and too loose will affect the smoothness of the feed; the cement weighing hopper and the main machine will be fed When the connection of the port is not handled well, the hard block formed by the accumulation and solidification of the material will support the scale bucket, and the measurement of the scale may be inaccurate; the cement feed channel of the host is affected by the moisture in the host. The wall is easily sticky with cement, which makes the cement feed channel thinner and thinner, which affects the feeding speed, and the cement is not easy to feed clean. Therefore, the upper and lower channels of the cement weighing hopper should be regularly checked and cleaned to ensure accurate measurement of cement.
4. Maintenance and maintenance of waterways and admixture channels
Water with more impurities will cause damage to the seal of the pump. For mixing equipment that uses flow or time relay metering, unclean water sources may cause blockage of the water circuit and even the water metering is inaccurate or out of control, so the water used in the mixing station must be Strict control must be achieved to meet the prescribed standards.
When measuring water with a time relay, the installation position and sealing of the centrifugal water pump have a great influence on the safety of water metering and should be closely controlled.
During normal operation, the leakage of the water pump seal is less than 3-5 drops/minute, and it should be repaired in time when an abnormality occurs. After the production in the freezing season, the waterway and all the water in the storage tanks should be put in clean water.
In addition to the antifreeze in winter, the main problem of the admixture channel is the adhesion and sedimentation. If the pipeline design is not reasonable, the pipeline is likely to become thin and blocked. Therefore, it should be cleaned regularly; another aspect to be noted is that the external The admixture is best mixed with water for feeding, so that the admixture can be evenly distributed in the concrete.
5. Main points of maintenance and maintenance of electrical control system:
a. Lightning protection and grounding
The lightning protection of the mixing station is very important in areas with heavy thunderstorms. Regularly check the connection and corrosion of the lightning protection device. If necessary, measure the resistance of the lightning protection grounding; regularly check the safety grounding of the fuselage and the anti-interference grounding of the system , The damaged should be repaired immediately.
b. Electrical connection
Regularly check the hidden dangers of obstructing electrical facilities and lines, and tighten the electrical connections; check the contacts and fixing conditions of electrical components to make them contact and conduct well; outdoor connection parts should have dust, moisture, and safety protection measures;
c. Maintenance of weighing system
The weighing system includes sensors, connectors (or connecting parts), amplifiers, etc. It is a vital part of the mixing station, and its protection points are as follows:
①, anti-lightning strike, electric welding current burning;
②, do a good job of dust, moisture and prevent all kinds of external damage;
③, handle the connection part well, make it firm and safe contact;
④ Prevent abnormal material overload and damage.
d. Electrical safety
All electrical installations should comply with safety regulations from design to installation; all electrical equipment has safety protection measures and safety signs, and all electrical equipment is protected by specially set switches or insurance;
e. Protection and inspection of outdoor electrical equipment
All electrical equipment in the open air, such as the terminal of the motor, the wiring and contacts of the limit switch, etc., regularly check their electrical conditions to detect the sensitivity and reliability of their actions.
