The grinding process is essentially a cutting process without a lathe. The depth of pits or small holes on the valve head or valve seat is generally within 0.5mm, and can be repaired by grinding. The grinding process is divided into coarse grinding, medium grinding and fine grinding.

Rough grinding uses a grinding head or grinding seat tool, and uses coarse-grained sandpaper or coarse-grained abrasive paste. The particle size is 80#-280#. The particle size is coarse, the cutting volume is large, and the efficiency is high. However, the cutting lines are deep and the sealing surface surface is rough. Therefore, rough grinding only requires smooth removal of pits on the valve head or valve seat.
Medium grinding is to eliminate rough lines on the sealing surface and further improve the flatness and smoothness of the sealing surface. Use fine-grained sandpaper or fine-grained abrasive paste with a particle size of 280#-W5. The particle size is fine and the cutting amount is small, which is beneficial to reducing roughness; at the same time, the corresponding grinding tools should be replaced and the grinding tools should be clean.

Fine grinding is the last process of valve grinding, mainly to improve the smoothness of the sealing surface. When finely grinding, W5 or finer parts can be diluted with engine oil, kerosene, etc., and then the valve head is used to grind the valve seat against the valve seat without drama, which is more conducive to the tightness of the sealing surface.

When grinding, generally turn it clockwise about 60-100 degree , then turn it in the opposite direction about 40-90 degree , grind it gently for a while, and check it once. It will shine brightly and can be seen on the valve head and valve seat. When you have a very thin line and the color reaches a bright black color, rub it gently with machine oil a few times and then wipe it clean with a clean gauze.

Alumina (AL2O3) Alumina, also known as corundum, has high hardness and is widely used. Generally used to grind workpieces made of cast iron, copper, steel, stainless steel and other materials.

The hardness of boron carbide (B4C) is second only to diamond powder and harder than silicon carbide. It is mainly used to replace diamond powder for grinding cemented carbide and grinding hard chromium plated surfaces.

Chromium oxide (Cr2O3) Chromium oxide is a high-hardness and extremely fine abrasive. Chromium oxide is often used when grinding hardened steel and is generally used for polishing.

Iron oxide (Fe2O3) Iron oxide is also a very fine valve abrasive, but its hardness and grinding effect are worse than chromium oxide. It has the same purpose as chromium oxide.

In addition, the thickness of the abrasive grain size (the particle size of the abrasive) has a significant impact on the grinding efficiency and surface roughness after grinding. During rough grinding, the surface roughness of the valve workpiece is not required, and coarse-grained abrasives should be used to improve grinding efficiency; during fine grinding, the grinding allowance is small and the surface roughness of the workpiece is required, so fine-grained abrasives can be used.
The grain size of the abrasive for rough grinding of the sealing surface is generally 120#~240#; for fine grinding, it is W40~14.
The valve modifies the abrasive, usually adding kerosene and engine oil directly to the abrasive. An abrasive compound made of 1/3 kerosene plus 2/3 engine oil and abrasives is suitable for coarse grinding; an abrasive compound made of 2/3 kerosene plus 1/3 engine oil and abrasives can be used for fine grinding.

When grinding workpieces with higher hardness, the effect of using the above-mentioned abrasives is not ideal. At this time, you can use three parts of abrasive and one part of heated lard to mix it up. After cooling, it will form a paste. When using, add some kerosene or gasoline and mix thoroughly.