Open circuit and closed circuit of the crushing process in the production line of large factories

In production, we often hear that there are two sections and one closed circuit, three sections and one closed circuit, and three sections and one open circuit. What do they mean?

Two paragraphs and three paragraphs, as everyone may understand, refer to the number of stages in the crushing process.

The whole sand and gravel production line includes coarse crushing, medium crushing, fine crushing, and ultra-fine crushing. Each link has corresponding processing equipment. The process of processing stone into the required finished product through the operation of the equipment is called the crushing process. Usually, there are two-stage crushing, three-stage crushing, and four-stage crushing processes. The second stage and the third stage are more commonly used, and the fourth stage is rarely used. It mainly appears in large-scale sand and gravel plants, which are used for crushing with large hardness and large size. Larger quarry.
What do close and open circuits mean? What are the characteristics?
During the working process of the crusher, its crushing and screening are combined operations. Before crushing, the materials to be crushed usually contain some smaller particles, which can be screened and then crushed to improve the crushing efficiency. Among the crushed materials, due to the difference in the principle of the crusher, some materials often have a relatively large particle size, and the large-grained materials that do not meet the standard also need to be screened for multiple crushing.
If the crusher wants to achieve better performance, it is very important to cooperate closely with the screening system. Usually, the composition of the crusher and various screening systems mainly has two working modes: open circuit and closed circuit.
Open circuit crushing process and characteristics
When the material passes through the crusher at one time and the undersize does not enter the crusher, it is an open-circuit crushing process.
Feature analysis:
For open circuit production, the product particle size is controlled by the discharge port of the crusher. In addition, the discharge opening is only the width of a long “slot”, which can only control the one-dimensional size of the material. Long and flat rocks can pass through the discharge opening if their dimensions are small enough. In other words, the particle size of the product obtained from the open circuit process is not particularly well controlled.
Closed-circuit crushing process and characteristics
Unlike the open-circuit crushing process, the closed-circuit process has an inspection and screening process. It can be understood that there are basically two types of crushing systems: pre-screening and inspection screening. Those without screening or only pre-screening are open-circuit processes, and those with inspection and screening are closed-circuit processes.
Feature analysis:
There are various combinations of equipment in the closed-circuit crushing process. Usually, the screening machine is installed behind the crusher so that the material on the screen can return to the crusher. The particle size of the product is controlled by the screen holes on the screen surface (that is, the two-dimensional control). The sieve hole is not as changeable as the discharge opening. Flat and flake materials also enter the recirculation flow, so that the closed-circuit operation can improve the shape of the product, so as to obtain a more standard product.
The crusher has to accept recirculated material, which means that the circuit can accept a correspondingly lower amount of new feed. If the mesh size is reduced as much as possible, the resulting product will be finer, but the amount of recycled material will increase. The net capacity of the loop will generally be reduced. Higher breakage rates are obtained at reduced throughput. However, the product particle size does not decrease appreciably when the amount of material recirculation is increased. When the particle size of the separated material is much smaller than the narrow end of the discharge opening of the crusher, the crushing circuit will appear unstable.

In summary:
(1) To put it simply, the difference between open-circuit and closed-circuit processes lies in the screening process. There is no screening process or only a pre-screening process in the open circuit process. There is an inspection and screening process in the closed-circuit process, which can well separate large pieces of The material screened out to improve the crushing rate of the whole process.
(2) The advantage of the open circuit process is that it is relatively simple, with less equipment and fewer sand-blowing points. The disadvantage is that when the particle size of the crushed product is required to be finer, the crushing efficiency is low, and the product sometimes contains a few finished products that are larger than the qualified product.
(3) The closed-circuit process can screen out large pieces to ensure that the product size is qualified. The crushing efficiency is higher than that of the open-circuit process, but it requires more equipment and the process is more complicated.