The Particle Size of Abrasives and Techniques for Selection
Release Date：2023-05-24 11:06
In the process of selecting and applying abrasives, particle size, known as granularity, plays a crucial role as a key parameter. It describes the particle size and surface roughness of the abrasive. Understanding the meaning of granularity and selecting the appropriate granularity is essential for achieving the desired machining precision, surface roughness, and grinding efficiency. Below, we will introduce the meaning of granularity, the selection method, and the corresponding standards.
Meaning of Granularity:
Abrasives can be classified into four categories: grains, powders, micro powders, and ultrafine powders. The granularity number for grains and powders is represented by the number of mesh openings per inch of the sieve screen, indicated by adding the "#" symbol to the upper right corner of the granularity number. For example, 240# indicates that there are 240 openings per inch of the sieve screen, and a larger granularity number indicates finer grains. On the other hand, the granularity number for micro powders and ultrafine powders represents the actual particle size and is denoted by adding the letter "W" before the size number. For instance, W20 indicates that the actual particle size of the abrasive is between 20μm and 14μm.
Selection of Granularity:
The selection of the appropriate granularity should be based on the requirements for machining precision, surface roughness, and grinding efficiency. Generally, if a higher roughness is desired for the workpiece, a coarser granularity abrasive should be chosen. Conversely, if lower surface roughness is required, a finer granularity abrasive should be selected. When the workpiece has high geometric precision requirements, the contact area between the grinding wheel and the workpiece is also a factor to consider. For smaller contact areas, finer granularity should be chosen, while for larger contact areas, coarser granularity is preferred. When both high geometric precision and low surface roughness are required, a mixed granularity abrasive is recommended. Additionally, the hardness, toughness, and thermal conductivity of the workpiece material are crucial factors to consider. For harder and more brittle materials, finer granularity abrasives are suitable, while for softer and more ductile materials, coarser granularity is preferred. If the workpiece has poor thermal conductivity and is prone to thermal deformation or burns, a coarser granularity abrasive should be selected.
In China, the commonly used granularity standards are based on the sieving method. For example, 80/100 represents a granularity number indicating the superhard abrasive particles that fall between sieve sizes of 180μm and 150μm. Among them, the particles retained on the upper limit sieve are the coarsest, often referred to as large particles and strict control is necessary due to the potential surface scratching defects. The particles retained on the upper inspection sieve are coarse, on the lower inspection sieve are medium, on the lower limit sieve are fine, and below the lower limit sieve are the finest particles.
Considerations for International Standards:
In international communication, different countries may adopt different granularity standards. Therefore, it is important to pay attention to matching the granularity numbers with the standards of the target country.
To summarize, the selection of granularity should consider the requirements for machining precision, surface roughness, and grinding efficiency. Based on the desired roughness, choose the appropriate granularity. For higher roughness, select a coarser granularity abrasive, while for lower surface roughness, choose a finer granularity. Additionally, factors such as workpiece geometric precision, material hardness, toughness, and thermal conductivity should be taken into account to determine the most suitable granularity.
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