Selection of abrasives and surface roughness

　　1、 Definition of abrasive

　　Under the propulsion of compressed air, water flow, or a throwing head, granular materials that can clean, cut, erode, wash, or change the surface state of the workpiece at a certain speed are called abrasives. Abrasives can be natural, artificial, or made from industrial by-products.

　　2、 Abrasive type

　　Before selecting abrasives, a comprehensive understanding of the object to be cleaned should be obtained, such as the original state of the steel surface, the corrosive environment in which the steel components are located, the coating matching scheme and requirements for roughness, and the sandblasting equipment and conditions of the coating subcontractor.

　　Abrasives suitable for outdoor open sandblasting include quartz sand, copper slag, etc. In the portable weld sandblasting machine, brown corundum and recyclable materials are used.

　　Quartz sand is a commonly used non-metallic abrasive, disposable. It has hard edges and strong scraping effect when sprayed onto the surface of the workpiece. Although the surface is bright, the free silicon generated during the process of spraying quartz sand not only pollutes the environment, but also easily causes occupational diseases such as silicosis among operators.

　　Quartz sand and copper slag are both disposable abrasives that cannot be recycled, resulting in higher costs. Another type of abrasive is metal abrasive, which is used in steel plate (or section steel) pretreatment lines and recycling sandblasting rooms in shipyards, container factories, and steel structure factories. The main metal abrasives in China are steel grit, steel shot, and steel wire cutting.

　　3、 Shape of abrasive particles

　　If the surface of the workpiece is vertically cut open after sandblasting and rust removal, and a continuous curve is observed under a magnifying glass, it is composed of countless connected valleys and peaks, which is called the roughness profile curve.

　　4、 Particle size of abrasive

　　The sandblasting process is actually a process in which abrasive particles continuously strike the cleaned surface. From the kinetic energy formula:E=½mv2

　　As can be seen from the formula, the size of abrasive particles determines the efficiency and roughness of sandblasting. The larger the abrasive particles, the greater the kinetic energy, which can produce a larger surface roughness. However, the particle number/mass ratio is small, which means that under the same mass conditions, the number of particles is small, the cleaning coverage is low, and the cleaning efficiency is not high. On the contrary, small abrasive particles have low kinetic energy, resulting in low roughness values, high particle number/mass ratio, high coverage, and high cleaning efficiency.

　　5、 Hardness of abrasives

　　The hardness of abrasives is a major factor affecting surface roughness. The higher the hardness of the abrasive, the rougher it becomes. The cleaning effect is also fast, but the lifespan is short and the consumption is high. For steel abrasives, the appropriate hardness is HRC 40-50. In addition, the harder the abrasive, the greater the wear on sandblasting or shot blasting equipment.