The concrete mixing station mainly consists of five major systems: material storage system, material weighing system, material conveying system, mixing system, powder storage system, powder conveying system, powder metering system, water and admixture metering system and control system. And other ancillary facilities.
The mixing machine is divided into forced stirring and self-dropping stirring according to the stirring mode. The forced mixer is the mainstream used in mixing stations at home and abroad. It can mix a variety of concretes such as fluidity, semi-dryness and dryness. The self-propelled mixing machine mainly mixes the fluid concrete and is rarely used in the mixing station.
The forced mixer is divided into a spindle planetary mixer, a single-shaft mixer and a twin-shaft mixer according to the structure. Among them, the twin-shaft forced mixer has the best comprehensive performance.
The 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 adopts the superposition weighing method, that is, the aggregate (sand, stone) is weighed with a scale, cement and fly ash with a scale, water and liquid admixture. Then, the liquid admixture is placed in the water scale to be premixed. In the mixing station of more than 50 cubic meters per hour, the weighing method of each material is used independently, and all weighing is controlled by electronic scale and microcomputer. Aggregate weighing accuracy is ±2%, and the weighing accuracy of cement, powder, water and admixtures is ±1%.
Material handling consists of three parts:
1. Aggregate conveying: There are two ways of conveying the hopper and conveying the belt. The advantages of the hopper lifting are small footprint and simple structure. Belt conveyor has the advantages of large conveying distance, high efficiency and low failure rate. Belt conveyor is mainly suitable for mixing stations with aggregate storage bins, which increases the productivity of the mixing plant.
2. 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 the large mixing building is transported by pneumatic conveying and scraping. The advantages of spiral conveying are simple structure, low cost and reliable use.
3. Liquid transport: mainly refers to water and liquid admixtures, which are transported by pumps respectively.
The materials available for storage in concrete are basically the same. The aggregate is stacked in the open air (the closed silo for large-scale commercial concrete mixing stations in the city); the powder is stored in a fully enclosed steel structure silo; the admixture is stored in a steel structural container.
The control system of the mixing station is the central nerve of the complete set of equipment. The control system has different functions and preparations according to different requirements of the user and the size of the mixing station. Under normal circumstances, the control system of the small mixing station available on the construction site is simple, and the system of the large mixing station is relatively complicated.