After the valve has been used for a long time, the sealing surface of the disc and valve seat will wear out and the tightness will be reduced. The repair of the sealing surface is a large and important work. The main method of repairing is grinding. For the serious wear surface, it is first surfacing and regrinding after turning.
The grinding of the valve includes:
The process of cleaning and checking;
1 cleaning and checking process
Clean the sealing surface in the oil pan, use professional cleaning agent, and wash the edge to check the damage of the sealing surface. Fine cracks that are difficult to determine with the naked eye can be carried out by coloring flaw detection.
After cleaning, check valve or gate valve and valve seat sealing surface tightness, check with red and pencil. Use red red to test red, check seal face seal, determine seal face density, or draw several concentric circles on the valve and seat seal with pencil, then rotate the valve and seat close together, check the pencil circle to erase the situation and confirm the sealing surface.
If the seal is not good, check the disc or gate sealing surface and the valve sealing surface with standard flat plates, and determine the grinding parts.
2 grinding process
The grinding process is essentially a cutting process without a lathe. The point or hole depth on the head or seat of the valve is generally within 0.5mm, and the grinding method can be used for maintenance. The grinding process is divided into coarse grinding, medium grinding and fine grinding.
The coarse grinding is to eliminate the defects on the sealing surface, such as scratch, indentation, and corrosion point, so that the cover is better than Gaoping and a certain degree of finish.
Rough grinding head or grinding seat tool is used for coarse grinder. The coarse grit paper or coarse grind paste is used. The grain size is 80#-280#, the grain size is coarse, the cutting quantity is large and the efficiency is high, but the cutting path is deeper and the surface of the seal face is rough. Therefore, rough grinding can only remove the pitting of the valve head or valve seat smoothly.
Medium grinding is to eliminate rough lines on the sealing surface, and further improve the smoothness and smoothness of the sealing surface. With fine grit paper or fine grind paste, its size is 280#-W5, the grain size is fine, the cutting quantity is small, it is beneficial to reduce the roughness; at the same time, the corresponding research tools should be replaced, and the research tool should be clean and clean.
After grinding, the contact surface of valve should be bright. If pencil is used to draw a few lines on the valve head or valve seat, turn the valve head or the valve seat to a light circle, and the pencil line should be erased.
Fine grinding is the last process of valve grinding, mainly to improve the smoothness of the sealing surface. The fine grinding can be diluted with W5 or finer micro and oil, kerosene and so on. The valve head is used to grind the valve seat with the valve head, instead of acting, which is more beneficial to the sealing surface.
When grinding, it usually turns 60-100 degrees clockwise and about 40-90 degrees in the opposite direction and gently grinding for a moment. It must be checked once, to be polished and glowing, and a very thin line can be seen on the valve head and seat. When the color reaches black and bright, the oil is gently worn several times, and clean gauze is used. It's clean.
After grinding, remove any other defects, that is, assemble them as quickly as possible so as not to destroy a well worn valve head.
Manual grinding, whether rough or fine grind, is always through the lifting and lowering; rotating, reciprocating; tapping, reversing and other operations combined with the grinding process. The purpose is to avoid repeated grinding path, so that the grinding tool and the sealing surface can be evenly grinded to improve the smoothness and smoothness of the sealing surface.
3 test stage
During the grinding process, the inspection stage is always worn. The aim is to grasp the grinding situation at any time, so that the quality of the grinding can meet the technical requirements. It should be noted that different valves should be used for grinding tools that are suitable for various sealing surfaces in order to improve the grinding efficiency and ensure the grinding quality.
Valve grinding is a very careful work. It needs to be experienced, groped and improved in practice. Sometimes it is very good grinding, but it is still leaking after loading. This is because in the process of grinding, there is a grindy imagination, the hand is not vertical, skew, or the size angle is deviated.
Since abrasive is a mixture of abrasives and grinding fluids, the grinding fluid is only a common kerosene and engine oil. Therefore, the most important part of the correct selection of abrasives is the correct selection of abrasives.
4 how to choose the valve grinding agent correctly?
Alumina (AL2O3) alumina, also known as corundum, has high hardness and is widely used. Generally used for grinding cast iron, copper, steel and stainless steel and other materials.
Silicon carbide (SiC) silicon carbide has two kinds of green and black, and its hardness is higher than alumina. Green silicon carbide is suitable for grinding hard alloys; black silicon carbide is used for grinding brittle materials and soft materials such as cast iron and brass.
The hardness of boron carbide (B4C) is second only to the diamond powder and is harder than the silicon carbide. It is mainly used instead of diamond powder to grind hard alloy and lapping the surface of hard chromium plating.
Chromium oxide (Cr2O3) chrome oxide is a high hardness and very fine abrasive. Hardened steel is often oxidized with chromium oxide and is usually polished.
Iron oxide (Fe2O3) iron oxide is also a very fine valve abrasive, but its hardness and grinding effect are both worse than chromium oxide, and its usage is the same as chromium oxide.
Diamond powder, crystal C, is the hardest abrasive and has better cutting performance. It is especially suitable for grinding cemented carbide.
In addition, the particle size of the abrasive (the size of the abrasive particles is large)