After a valve is used for a long time, the sealing surface of the valve disc and valve seat will be worn and the sealing will be weakened. Repairing the sealing surface is a very important task with a lot of workloads. The main method of repair is grinding. For the severely worn sealing surface, the surfacing is firstly conducted and then grounding after turning.
The grinding of the valve includes the cleaning and inspection process, grinding process, and inspection process.
Cleaning and inspection processes
Clean the sealing surface in the oil pan. Use a professional cleaning agent, and check the damage to the sealing surface while washing. Fine cracks that are difficult to identify with the naked eye can be tested by the liquid penetrant test.
After cleaning, check the tightness of the sealing surface of the valve disc or plate and valve seat. Use red colors and pencils when checking. Use red lead to check the sealing surface, and determine the tightness of the sealing surface, or use a pencil to draw several concentric circles on the sealing surface of the valve disc and valve seat, and then rotate the valve disc and valve seat. Check the pencil circle to confirm the sealing of the sealing surface.
If the sealing is not good, a standard flat plate can be used to test the sealing surface of the valve disc or plate and the valve body respectively to determine the grinding position.
Grinding processes
The grinding process is essentially a cutting process without a lathe. The depth of the pits or small holes on the valve head or valve seat is generally within 0.5 mm, and the grinding method can be used for maintenance. The grinding processes are divided into rough grinding, average grinding and fine grinding.
Rough grinding is to eliminate defects such as scratches, indentations, and corrosion dots on the sealing surface so that the sealing surface can obtain a high level of flatness and a certain degree of smoothness, and lay a foundation for the average grinding of the sealing surface.
Rough grinding adopts grinding heads or grinding seat tools, sandpaper or grinding paste with coarse grains, with a particle size of 80# to 280#, which has features of coarse particle sizes, great cutting amount and high efficiency, deeper cutting lines and rough sealing surfaces. Therefore, rough grinding only needs to smoothly remove the pitting of the valve head or valve seat.
Average grinding is to eliminate rough lines on the sealing surface and further improve the flatness and smoothness of the sealing surface. Use sandpaper or abrasive paste with small grains. The particle size is 280# to W5. The particle size is fine; the cutting amount is small, which is beneficial to reduce the roughness. At the same time, the corresponding grinding tool should be replaced, and the grinding tool should be clean.
After the average grinding, the contact surface of the valve should be smooth. If you draw a few strokes on the valve head or valve seat with a pencil, turn the valve head or valve seat lightly around, and the pencil line should be erased.
Fine grinding is the last process of grinding valves, which is mainly used to improve the smoothness of the sealing surface. When fine grinding is performed, a particle size of W5 can be diluted with engine oil and kerosene.
When grinding is performed, generally, turn clockwise about 60° to 100°, and then turn 40° to 90° in the opposite direction. Gently grind for a while. The valve must be checked once until it is polished and a very thin line can be seen on the valve head and valve seat. When the color of the line is black and bright, lightly rub it with engine oil several times, and wipe it with clean gauze.
After grinding, eliminate other defects. Assemble as soon as possible so as not to damage a ground valve head.
For manual grinding, whether it is rough grinding or fine grinding, always involves grinding processes of lifting, lowering, rotating, reciprocating, tapping, and reversing. The purpose is to avoid the repetition of the abrasive grain track so that the grinding tool and sealing surface can be uniformly ground, and the flatness and smoothness of the sealing surface can be improved.
Inspection
In the grinding process, inspection is always required to grasp the grinding situation at any time so that the grinding quality can meet the technical requirements. It should be noted that when grinding different valves, grinding tools suitable for various sealing surfaces should be used to improve grinding efficiency and ensure grinding quality.
Valve grinding is very meticulous work, which requires constant experience, exploration, and improvement in practice. Sometimes the grinding is very good, but after installing the valve, it still leaks. This is because there is an imagination of grinding deviation in the grinding process. The grinding rod is not vertical, or the angle of the grinding tool is not correct.
Because the abrasive material is a mixture of abrasive and grinding fluid, and the grinding fluid is only general kerosene and engine oil. Therefore, the most critical part of the correct selection of abrasives is the correct selection of abrasives.
The grinding of the valve includes the cleaning and inspection process, grinding process, and inspection process.
Cleaning and inspection processes
Clean the sealing surface in the oil pan. Use a professional cleaning agent, and check the damage to the sealing surface while washing. Fine cracks that are difficult to identify with the naked eye can be tested by the liquid penetrant test.
After cleaning, check the tightness of the sealing surface of the valve disc or plate and valve seat. Use red colors and pencils when checking. Use red lead to check the sealing surface, and determine the tightness of the sealing surface, or use a pencil to draw several concentric circles on the sealing surface of the valve disc and valve seat, and then rotate the valve disc and valve seat. Check the pencil circle to confirm the sealing of the sealing surface.
If the sealing is not good, a standard flat plate can be used to test the sealing surface of the valve disc or plate and the valve body respectively to determine the grinding position.
Grinding processes
The grinding process is essentially a cutting process without a lathe. The depth of the pits or small holes on the valve head or valve seat is generally within 0.5 mm, and the grinding method can be used for maintenance. The grinding processes are divided into rough grinding, average grinding and fine grinding.
Rough grinding is to eliminate defects such as scratches, indentations, and corrosion dots on the sealing surface so that the sealing surface can obtain a high level of flatness and a certain degree of smoothness, and lay a foundation for the average grinding of the sealing surface.
Rough grinding adopts grinding heads or grinding seat tools, sandpaper or grinding paste with coarse grains, with a particle size of 80# to 280#, which has features of coarse particle sizes, great cutting amount and high efficiency, deeper cutting lines and rough sealing surfaces. Therefore, rough grinding only needs to smoothly remove the pitting of the valve head or valve seat.
Average grinding is to eliminate rough lines on the sealing surface and further improve the flatness and smoothness of the sealing surface. Use sandpaper or abrasive paste with small grains. The particle size is 280# to W5. The particle size is fine; the cutting amount is small, which is beneficial to reduce the roughness. At the same time, the corresponding grinding tool should be replaced, and the grinding tool should be clean.
After the average grinding, the contact surface of the valve should be smooth. If you draw a few strokes on the valve head or valve seat with a pencil, turn the valve head or valve seat lightly around, and the pencil line should be erased.
Fine grinding is the last process of grinding valves, which is mainly used to improve the smoothness of the sealing surface. When fine grinding is performed, a particle size of W5 can be diluted with engine oil and kerosene.
When grinding is performed, generally, turn clockwise about 60° to 100°, and then turn 40° to 90° in the opposite direction. Gently grind for a while. The valve must be checked once until it is polished and a very thin line can be seen on the valve head and valve seat. When the color of the line is black and bright, lightly rub it with engine oil several times, and wipe it with clean gauze.
After grinding, eliminate other defects. Assemble as soon as possible so as not to damage a ground valve head.
For manual grinding, whether it is rough grinding or fine grinding, always involves grinding processes of lifting, lowering, rotating, reciprocating, tapping, and reversing. The purpose is to avoid the repetition of the abrasive grain track so that the grinding tool and sealing surface can be uniformly ground, and the flatness and smoothness of the sealing surface can be improved.
Inspection
In the grinding process, inspection is always required to grasp the grinding situation at any time so that the grinding quality can meet the technical requirements. It should be noted that when grinding different valves, grinding tools suitable for various sealing surfaces should be used to improve grinding efficiency and ensure grinding quality.
Valve grinding is very meticulous work, which requires constant experience, exploration, and improvement in practice. Sometimes the grinding is very good, but after installing the valve, it still leaks. This is because there is an imagination of grinding deviation in the grinding process. The grinding rod is not vertical, or the angle of the grinding tool is not correct.
Because the abrasive material is a mixture of abrasive and grinding fluid, and the grinding fluid is only general kerosene and engine oil. Therefore, the most critical part of the correct selection of abrasives is the correct selection of abrasives.
Next: The Selection of Abrasive Materials and Tools of Valves