The concrete mixing station is a combined device used to centrally mix concrete, also known as a concrete prefabrication yard. Widely used in the concrete industry. This article mainly introduces the composition system and main types of concrete mixing plants.
1. Composition system of concrete mixing plant
The concrete mixing station is mainly composed of 5 major systems: material storage system, material weighing system, material conveying system, mixing system, powder storage system, powder conveying system, powder measuring system, water and admixture measuring system and control system. And other ancillary facilities.
1. Mixing host
The mixing host is divided into forced stirring and free-fall stirring according to its stirring method. The forced mixer is the mainstream used in domestic and foreign mixing stations. It can mix a variety of concrete such as fluidity, semi-dryness and dryness. The self-falling main mixing machine mainly mixes liquid concrete, and it is rarely used in mixing stations.
According to the structure, the forced mixer is divided into a spindle planetary mixer, a single horizontal shaft mixer and a double horizontal shaft mixer. Among them, the comprehensive performance of the double horizontal shaft forced mixer is the best.
2. Weighing system
Material weighing system is a key component that affects the quality of concrete and the production cost of concrete. It is mainly divided into three parts: aggregate weighing, powder weighing and liquid weighing. Under normal circumstances, the mixing station below 20 cubic meters per hour uses the superimposed weighing method, that is, the aggregate (sand, stone) is weighed with a scale, cement and fly ash are weighed with a scale, water and liquid admixture are weighed separately , And then put the liquid admixture into the water weighing hopper to pre-mix. In the mixing station of more than 50 cubic meters per hour, the method of weighing each material independently is mostly used, and all weighings are controlled by electronic scales and microcomputers. Aggregate weighing accuracy is ±2%, and cement, powder, water and additives are all weighed to within ±1%.
3. Conveying system
Material transportation consists of three parts:
Aggregate transportation: There are two methods of hopper transportation and belt transportation in the mixing station. The advantages of hopper lifting are small footprint and simple structure. The advantages of belt conveying are large conveying distance, high efficiency and low failure rate. The belt conveyor is mainly suitable for the mixing station with temporary storage of aggregates, so as to improve the productivity of the mixing station.
Powder conveying: The powders available for concrete are mainly cement, fly ash and mineral powder. The commonly used powder conveying method is screw conveyor conveying, and large-scale mixing plants are pneumatically conveyed and scraped. The advantages of screw conveying are simple structure, low cost and reliable use.
Liquid delivery: mainly refers to water and liquid additives, which are delivered by water pumps.
4. Storage system
The available materials for concrete storage are basically the same. Aggregates are stacked in the open air (there are also closed silos for large urban commodities); powder materials are stored in fully enclosed steel structure silos; and admixtures are stored in steel structure containers.
5. Control system
The control system of the mixing station is the central nervous system of the whole equipment. The control system has different functions and configurations according to the different requirements of the user and the size of the mixing plant. Generally, the control system of the small mixing plant available on the construction site is simpler, while the system of the large mixing plant is relatively complicated.
2. The main types of concrete mixing plants
Continuous
Most of the batch mixing stations are on the market. The technological process is as follows: the raw materials that are not greater than the mixing capacity of the mixer are first prepared during production, and then thrown into the mixer for mixing. After mixing, unload it into the truck.
1. Process
1) After starting production, each raw material starts the uniform batching process according to its distance from the mixer inlet, and reaches the mixing tank mouth synchronously;
2) All materials enter the mixer inlet uniformly in proportion;
3) While the mixer is rotating and stirring, the material is pushed forward, and the material starts to be stirred/advanced from the inlet to the outlet and becomes the finished product.
4) After the production reaches the preset volume, each material will be stopped in sequence according to the distance from the mixer inlet.
5) From the start of production to the end of production, batching, stirring/pushing, and discharging are carried out continuously.
2. Features
1) The host machine works smoothly: the raw materials enter the mixer evenly over a relatively long period of time. No intermittent burst feeding process.
2) The entry of the finished product is stable: the concrete enters the vehicle evenly over a long period of time without intermittent burst discharge.
3) Less space occupation: the large finished product bucket and the aggregate storage bucket are reduced, the height is low, and the floor space is small.
4) Low abrasion of wear-resistant parts: no impact and smooth mixing, while the mixing amount is small.
5) Low energy consumption: the installed power is small, the mixing amount is small at the same time, and a small amount of raw materials enters the mixer evenly and is easy to mix evenly.
6) Low use and maintenance costs: fewer structural links, short belts, and stable work.
3. Composition of five major systems
Sand and gravel system: including three feeding sand and gravel buckets (two or four according to different requirements), which are respectively used for metering and feeding of sand and gravel. Each gravel hopper is composed of collecting hopper, weighing sensor, reducer, feeding belt and auxiliary equipment.
Powder system: composed of storage silo, storage silo butterfly valve, lifting screw, metering silo, disc feeder, etc. The powder storage silo includes a main silo and an auxiliary silo with a single volume of 100T-300T. Both the main warehouse and the auxiliary warehouse are equipped with automatic arch-breaking device and material level signal indicating device. The powder storage bin also has a dust removal system.
Water and admixture system: It is composed of admixture tank, pool (or water tank), pumping station, water and admixture weighing hopper and pipeline.
Transmission-mixing-storage system: composed of belt conveyor, mixer and mixing rack. The gravel is loaded onto the belt by the batching machine and enters the mixer. Fly ash and cement are directly fed into the mixer through the disc feeder and aggregate screw on the metering bin.
Low-voltage electrical appliances and automatic control systems: including power cabinet, sensors and control center.
4. Advantages
1). Large output and high efficiency: continuous and stable operation, and the single output of continuous mixing station is high.
2) Mixing evenly: the mixture entering the mixer is a homogeneous material, and the mixing process in the mixer is mixing and hydration process, so the mixing time can be shortened.
3). No slurry leakage and little wear: the feeding end of the continuous mixer is dry material mixing and the reverse spiral is added on both shaft ends. Therefore, there is no slurry leakage problem. The requirements of the mixer on wear-resistant materials are not high.
4) Low failure: The number of start and stop times of all equipments in the continuous mixing plant is only 1/7-1/3 of the gap type mixing plant, so the equipment has a long service life and a low probability of failure.
Intermittent
5. Composition of intermittent mixing plant system:
1). Mixing system is a double horizontal shaft mixer with multi-dimensional assembly of foreign key components. Users can also specify other foreign mixers.
2). Aggregate measurement of the measuring system: the standard type adopts the incremental method for measurement, and the improved type uses the electronic decrement method for measurement; powder measurement: the cement measurement and fly ash measurement hopper are placed above the mixer, and the standard type mixing station uses AC contact The controller controls the lifting screw without a precise matching device; the improved mixing station uses a frequency converter to achieve coarse and precise ingredients. Water measurement: A three-point hanging weighing mechanism is used, equipped with coarse and fine matching circuits and other devices to ensure measurement accuracy. Admixture metering: the direct load of the sensor is used, and the coarse and fine matching circuits and the metering box and pipeline are arranged separately to ensure accurate measurement.
3). Dust removal system The mixing station is equipped with an independent centralized dust collector for centralized processing, which has a good dust removal effect and avoids the formation of negative pressure in the mixer cavity to affect the powder measurement accuracy. Aggregate feeding system The aggregate is lifted into the middle storage hopper at one time by the feeding belt conveyor. It has the characteristics of compact structure, high reliability and easy maintenance.
4) The automatic control system uses a distributed computer system to achieve centralized management and reliability.
Technical advantages of improved concrete mixing plant: five high two practical
Five high
The system configuration is high. The host can choose 名媛直播 of internationally renowned brands according to user requirements, and can also choose domestically assembled mixers with imported key parts.
High batching precision The use of frequency conversion technology to achieve coarse and precise distribution of various materials. Coarse blending reaches 90-95% of the required dosage, and fine blending achieves a batching accuracy better than 0.5%.
High reliability The operation frequency of the cylinder and other moving parts is low, and the reducer is also controlled by the inverter to avoid the impact of hard start, the failure rate is low, and the reliability is high.
High productivity guarantee
High cost performance With the performance of a mixing plant, the price is only 1/3 ~ 1/2.
Two practical
Practical data management system saves the production data of the mixing plant in real time. It has a strong combination query and various report output functions, and automatically prints the delivery note.
Practical slump monitoring system The practical slump monitoring system can intuitively judge the slump of concrete based on the displayed mixer current curve.
Structural characteristics of intermittent cement concrete mixing plant
The lower discharge port of the storage bin is large, and the material in the bin will not arch (the vibrator does not need a vibrator). The feeding speed is fast, and the feeding time is small. One time of feeding can produce one truck of concrete, the cylinder has a small operating frequency and a long service life.
The amount of material added by the storage bin to the weighing hopper does not affect the proportioning accuracy.
The batching time and lifting time are combined into one, the storage warehouse feeding time to the weighing hopper is short, and the batching time and lifting time are longer. Therefore, the sensor has sufficient stable response time, the overshoot of the ingredients is small, and the lifting load is small.
The speed of the strong-pull belt is controlled by a computer and a frequency converter to achieve soft start and stop, with little impact and less belt sticky material. All kinds of aggregates are discharged, mixed and lifted evenly within a basically fixed time.
Using frequency converter for speed regulation, high-precision batching can be achieved in a short time.
