In recent years, the depletion of natural sand resources has led to the emergence of manufactured sand in response to market demand, with its applications becoming increasingly widespread. Although the processing of artificial sand and gravel has a history spanning several decades, selecting the appropriate production process to ensure reliable operation, advanced technology, and costeffectiveness remains a critical challenge in the design of artificial sand and gravel processing systems. This article introduces four widely used sandmaking processes currently in practice.

1. Vertical Shaft Impact Crusher Sand Production Process

　Currently, most domestic projects primarily use vertical shaft impact crushers as the main sandmaking equipment. Regardless of whether the crushing chamber employs a "rockonrock" or "rockoniron" configuration, the production process follows the sequence of "feedingcrushingscreeningreturning (or storage)." A simplified flow diagram is provided below (for illustrative purposes, examples such as 2.5mm and 5mm screening sizes are used; actual production specifications may vary).

Using vertical shaft impact crushers for sand production offers advantages such as high efficiency, excellent particle shape, low operating costs, minimal civil and installation work, and the ability to reshape small and medium-sized stones. However, it also presents the following issues:

1) The process flow is simple with low unit energy consumption;  

2) For aggregates sized between 5~2.5mm, repeated cyclic crushing is required, resulting in poor crushing efficiency and slightly higher energy loss;

3) The gradation of the finished sand is suboptimal, exhibiting a discontinuous gradation pattern of "more at both ends and less in the middle";  

4) Controlling the fineness modulus of the finished sand is challenging (subject to human factors);  

5) The yield rate of finished sand is relatively low;  

6) For conventional concrete, the stone powder content may exceed the standard limit.

2. Sand-making Process with Rod Mill

　　Rod mill sandmaking is a traditional sand production process where the rotation of the rod mill drives the movement of steel rods inside, including tumbling and falling. These actions crush, grind, and impact the parent rock fed into the mill to produce sand. This method offers the following characteristics:

　　1) The fineness modulus of sand is easily adjustable and can be manually controlled (in actual production, it can be adjusted within the range of FM=2.4-3.0);

2) The sand has good gradation and stable particle size distribution;

3) The production efficiency is low;

4) The operating costs are high, with substantial civil and installation engineering requirements.

3. Combined Sand-Making Process with Vertical Shaft Impact Crusher and Rod Mill  

To address issues such as insufficient content of mediumsized sand and low production capacity in the sandmaking process using vertical shaft impact crushers, a combined process involving both vertical shaft impact crushers and rod mills was adopted. The process flow is as follows:

After being crushed by the vertical shaft impact crusher, the stone material is graded by the screening machine. The material larger than 5mm is entirely returned to the transfer bin, while the 52.5mm fraction enters the rod mill for further crushing. After passing through the spiral classifier, it is mixed with the material smaller than 2.5mm and conveyed to the finished product bin.

This process has the following characteristics:

1) It combines the advantages of vertical shaft impact crushers and rod mill sand-making while overcoming their drawbacks, effectively addressing issues such as insufficient intermediate particle content and excessive loss of stone powder;

2) The finished sand exhibits stable quality and excellent particle shape;

3) High water and electricity consumption with significant steel rod wear;

4) Substantial construction and installation workload;

5) Complex process flow and diverse equipment types.

4. Combined Sand-Making Process with Standard-Speed and High-Speed Vertical Shaft Impact Crushers

The sand-making process flow of the vertical shaft impact crusher with two-speed combinations is shown in the figure below:

After being crushed by the vertical shaft impact crusher, the stone material is graded by the screening machine. The material larger than 5mm is entirely returned to the transfer bin, while the 5~2.5mm material enters the rod mill for further crushing. After processing by the spiral classifier, it is mixed with the material smaller than 2.5mm and conveyed to the finished product bin.

This process has the following characteristics:

1) It combines the advantages of vertical shaft impact crushers and rod mill sand-making while overcoming their drawbacks, effectively addressing issues such as insufficient medium-sized sand content and excessive loss of stone powder;

2) The finished sand exhibits stable quality and excellent particle shape;

3) High water and electricity consumption, with significant steel rod wear;

4) Substantial construction and installation workload;

5) Complex process flow and diverse equipment requirements.

4. Combined Sand-Making Process with Conventional and High-Speed Vertical Shaft Impact Crushers   The sand production flow chart using two-speed vertical shaft impact crushers is shown below:

The stone material is transported from the transfer bin via a feeder and belt conveyor to a vertical shaft impact crusher for crushing. After crushing, it enters a screening machine for classification. The material larger than 5mm is returned to the transfer bin, while the 52.5mm material is sent to a highspeed vertical shaft impact crusher for further crushing. The recrushed material is then mixed with the material smaller than 2.5mm before being conveyed to the finished product bin.

This production process is suitable for dry and semi-dry methods, while further research is required for wet production.

　　This joint sandmaking process enhances the yield and quality of finished sand, achieving the "crushing instead of grinding" technique, making it feasible to completely abandon rod mill sand production.

　　1) The crushing chamber of a standard-speed vertical shaft impact crusher can operate in either "rock-on-iron" or "rock-onrock" mode.

These two modes differ only in quantitative aspects rather than qualitative ones. The former yields higher sand output but with slightly inferior particle shape, higher stone powder content, and greater anvil wear.For details on the differences between "rockonrock" and "rockoniron," please refer to "The Two Crushing Modes and Two Feeding Methods of Sand Making Machines: Wrong Choices Will Significantly Affect Your Production Efficiency!"

2) For high-speed vertical shaft crushers, the "rock-on-iron" crushing chamber is preferable with reduced feed volume. This is because the 5-2.5mm stone particles are smaller and lighter, requiring more effective collision energy to achieve proper fragmentation.

3) When using dual-speed vertical shaft impact crushers for sand production, appropriately increasing the particle size of feed material for the high-speed crusher can further enhance the stone powder content in the finished sand while reducing its fineness modulus.

　　In summary, each of the four sandmaking processes mentioned above has its own advantages and disadvantages. Vertical shaft impact crusher sandmaking, as well as combined sandmaking with a rod mill, are currently the more widely adopted processes in China. For projects with high requirements for finished sand quality, the latter approach is often employed, where the rod mill primarily serves an adjustment role by producing medium and fine sand. The sand produced by both types of equipment is blended together, resulting in a more reasonable gradation composition of the finished sand and thereby improving its overall quality.