With the shortage of natural sand and gravel, artificial sand is gradually used in major engineering projects, especially the increase in infrastructure projects in recent years has made it more and more widely used. In the sand and gravel production system, choosing the correct sand making process and reasonable equipment configuration becomes the guarantee of the quality of artificial sand and the basis for ensuring the safe, stable and efficient operation of the entire production process.
1. Process design
1.1 Crushing process
(1) Selection of the number of broken sections
Generally, three-stage or two-stage broken artificial sand and gravel will be selected, and the specific selection should be judged according to the grindability of the artificial sand and gravel.
Some sand and gravel materials are hard and difficult to crush. You can choose a three-stage crushing process, such as: basalt, granite, etc., which are commonly used in cone crushers or gyratory crushers; some rocks have poor compression resistance and are easier to crush. You can choose large One-stage or two-stage crushing processes, such as limestone, etc., are commonly used in impact crushers or gyratory crushers.
Different types of rocks have very different crushability. We have to choose different numbers of crushing sections according to different characteristics.
(2) Crushing production process
In the three-stage crushing process, the first two stages will be open circuit production, and the last stage will use closed circuit production.
In the two-stage crushing process, the first stage is open-circuit production, and the latter stage is closed-circuit production. The closed-circuit production can evenly deploy various grades of stones.
1.2 Sand making process
According to the separation method of stone powder, the sand making process can be divided into "wet sand making", "dry sand making" and "semi-dry sand making"; according to the process, it can be divided into "single sand making" and "combined sand making"; according to the structure The form can be divided into "flat sand making" and "floor sand making".
Wet sand making is mainly aimed at making sand from raw materials with large mud content such as river pebbles, which can effectively reduce the mud content, but the loss of fine sand is serious and sufficient water is required. Dry sand production is mainly aimed at sand production using mountain quarrying gravel as raw materials. There is no loss of fine sand, the content of stone powder is controllable, and the sand gradation is more reasonable, but the mud content of the raw materials is strictly required.
1.3 Screening process
Usually we see more wet screening, which is equipped with a sand washing machine or a stone washing machine under the machine, which can quickly dewater. For example, limestone will produce a large amount of mud and sand in the production process. This is because the amount of mud and sand is large, so it needs to be equipped with a stone washing machine to wash the materials.
In addition to wet screening, there is also a dry screening. However, the dry screening process may pollute the environment and form a large amount of dust, so the screen surface must be closed, and dust extraction equipment can be installed to protect the environment more effectively.
1.4 Process selection
First of all, to meet the demand for finished aggregates, and on this basis to reduce the cycle compliance of each process, it is necessary to ensure that the equipment configuration and load distribution are balanced.
When processing large-scale sand and gravel, we can choose the wet process, but also to recycle the produced stone powder. You can choose to use the segmented closed-circuit process to produce coarse aggregates, and for small and medium-sized sands, you can choose all Closed-circuit process to produce.
If you want to produce fine aggregate, you need to choose an ultra-fine crusher in the process of processing, or you can adopt a semi-dry process for small artificial sand. If the needle-flaky content of the finished coarse aggregate exceeds the standard, then the process needs to be adjusted and transformed into a shaping process.
In addition to different material properties, different crushing and sand making processes should be selected. Different weather conditions will also affect the effect of this process, so site surveys must be done well.
2. Equipment configuration selection
2.1 General principles
According to the production volume of the system and the quality requirements, choose different equipment types and equipment quantities. Under the premise of ensuring quality, it is more effective to improve economic benefits. Choose different equipment for each process, ensure that the conformity of different processes is roughly the same, and unify the types and specifications of the entire operating equipment. Because of the different types of artificial sandstones, some of them are strong and harder, which may wear the machine, so the spare condition of the whole machine should be considered.
2.2 Crushing equipment
(1) Equipment selection for coarse crushing workshop
In the process of selecting equipment for the coarse crushing workshop, the production intensity and the source of raw materials should be considered.
Generally speaking, if the artificial sandstone is limestone with low hardness, the jaw crusher is widely used when choosing coarse crushing equipment, because it has simple structure, high work efficiency, and can produce products with uniform particles. Operating costs are also relatively low, and generally can meet the requirements of limestone material production. If a large-scale artificial sand production line can also choose a large-capacity gyratory crusher.
In recent years, the supply of sand and gravel has been continuously updated, and mobile crushing plants have also begun to be used in various projects, especially those with tight schedules and small-scale projects.
(2) Equipment selection in the crushing workshop
When selecting equipment in the crushing workshop, it should be selected according to the main tasks of the equipment. The equipment is mainly used to crush super-diameter materials, and the production capacity should be adjusted reasonably according to the demand of coarse aggregate. Under normal circumstances, cone crushers and impact crushers are widely used. The former has a higher cost and the latter has a better grain size, which can meet the requirements of material shaping.
2.3 Equipment selection in sand making workshop
Rod mill machine-made sand is a traditional sand making process, but in the production process it will generate a lot of energy consumption, low efficiency, high cost, and the workload is small, generally not in line with the amount of civil engineering. At present, most domestic projects use vertical shaft impact crusher as the main production equipment for sand making. It has the advantages of high production efficiency, good sand grain shape, low operating cost, small amount of civil engineering and installation works, and the ability to reshape small and medium stones. . However, the finished sand grading of vertical shaft impact crushing is not very ideal. It is an intermittent gradation of "more at both ends and less in the middle". Therefore, the combined sand making process of rod mill and impact crushing is sometimes used.