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How Can Repair the Sealing Surface of A Valve and Improve Air Tightness?

How Can Repair the Sealing Surface of A Valve and Improve Air Tightness

Valve after long-term use, the valve, and the valve seat sealing surface will be worn, and the tightness will be reduced. Repair of the sealing surface is a large and very important work, the main method of repair is grinding, the sealing surface of the serious wear, is the first surfacing by turning process and then grinding.

Valve grinding including cleaning and inspection processes, grinding processes and inspection processes1. Cleaning and inspection process.

1. Cleaning and inspection process

Cleaning the sealing surface in the oil pan, use professional cleaning agents while washing and checking the damage to the sealing surface. With the naked eye is difficult to determine the fine cracks that can be used for the color flaw detection method.

After cleaning, the valve flap or gate valve and the valve seat sealing surface should be checked for tightness, check with a red pencil. With the red Dan test red, check the sealing surface imprinting, to determine the sealing surface of the sealing surface; or with a pencil in the valve flap and seat sealing surface of a few concentric circles, and then the valve flap and the seat of the sealing rotate, check the pencil circle erased, to determine the sealing surface of the sealing surface of the sealing surface.

If the fit is not good, the standard plate can be used to test the valve or gate sealing surface and the valve body sealing surface, to determine the grinding part.

Valve cleaner

2. Grinding process

The grinding process is essentially a cutting process without the lathe, valve head, or valve seat on the pitting or small holes in the depth of 0.5mm or less, you can use the grinding method for overhaul. The grinding process is divided into coarse, medium and fine grinding..

Rough grinding is to eliminate the abrasion, indentation, etching, and other defects on the sealing surface, so that the sealing surface gets a high degree of flatness and a certain degree of finish, for the sealing surface of the middle grinding to lay the foundation.

Rough grinding using grinding head or grinding seat tools, using coarse-grained sandpaper or coarse-grained abrasive paste, its particle size 80 # – 280 #, coarse particle size, cutting volume, high efficiency, but the cutting grain is deeper and the sealing surface is rougher. Therefore, coarse grinding as long as the valve head or valve seat is leveled to remove the numbness.

Medium grinding is used to eliminate coarse grains on the sealing surface and further improve the flatness and finish of the sealing surface. The use of fine-grained sandpaper or fine-grained abrasive paste, a particle size of 280 # – W5, fine particle size, small amount of cutting, is conducive to reducing the roughness; at the same time should be replaced with the corresponding research tools, research tools should be clean and clean.

After grinding, the contact surface of the valve will be shiny. If you use a pencil to scratch a few lines on the valve head or seat, the valve head or seat against a light turn, the pencil line should be erased.

Fine grinding is the valve grinding after a process, mainly to improve the finish of the sealing surface. Fine grinding can be used W5 or finer microparticles with oil, kerosene, and other diluted, with the valve head to the valve seat for grinding, without acting, which is more conducive to the sealing surface of the close.

Grinding is generally clockwise turn 60-100 ° or so, and then turn the opposite direction of about 40-90 °, gently grinding for a while, must check once, to be ground to shiny and luminous, and in the valve head and seat can be seen in a circle of very thin line, the color to black bright, and then gently grind a few times with motor oil, with a clean gauze can be wiped clean.

After grinding, and then eliminating other defects, that is, should be assembled as soon as possible, so as not to destroy a good grinding valve head.

Hand grinding regardless of coarse or fine grinding, is always through the lift, put down; rotate, reciprocate; tap, change direction, and other operations combined with the grinding process. Its purpose is to avoid the repetition of abrasive particle trajectory so that the grinding tool and sealing surface are uniform grinding, improving the flatness and finish of the sealing surface.

3. Inspection stage

The grinding process is always throughout the inspection stage, its purpose is to grasp the grinding situation at any time and to do a good job so that the grinding quality meets the technical requirements. It should be noted that different valve grinding should be used to adapt to a variety of sealing surface forms of grinding tools to improve grinding efficiency and ensure grinding quality.

Valve grinding is a very detailed work, that needs to be experienced in practice, felt, and improved, sometimes grinding is very good, but after mounting or leakage of steam leakage, this is because in the grinding process, there is grinding bias imagination, the hand holding the grinding rod is not perpendicular, skewed, or the angle of the size of the research tool is caused by deviation.

As the abrasive is a mixture of abrasive and abrasive fluid, and the abrasive fluid is only general kerosene and motor oil. Therefore, the key to the correct choice of abrasive is the correct choice of abrasives.

Aluminum oxide (AL2O3) Aluminum oxide, also known as corundum, its a high hardness, and its use is very common. Generally used to grind cast iron, copper, steel stainless steel, and other materials.

Silicon Carbide (SiC) Silicon Carbide is available in green and black, and its hardness is higher than that of Aluminum Oxide. 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, brass, and so on.

Boron carbide (B4C) is second only to diamond powder in hardness and harder than silicon carbide. It is mainly used to replace diamond powder for grinding cemented carbide and hard chrome-plated surfaces.

Chromium oxide (Cr2O3) Chromium oxide is a kind of high hardness and very fine abrasive, hardened steel fine grinding often uses chromium oxide, generally also used to polish.

Iron Oxide (Fe2O3) Iron oxide is also a very fine valve abrasive, but is less hard and abrasive than chromium oxide, and is used for the same purposes as chromium oxide.

Diamond powder that is crystallized 磮C, is a hard abrasive, and cutting performance is better, especially for grinding carbide.

In addition, the abrasive particle size (the size of the particle size of the abrasive) of the coarse and fine on the grinding efficiency and the surface roughness after the research has a significant impact. In rough research, the valve workpiece surface roughness requirements are not high, enough to improve the grinding efficiency of the choice of coarse grain size of the abrasive; fine research grinding margin is small, the workpiece surface roughness requirements are high, can be used fine grain size of the abrasive.

Seal surface coarse research abrasive particle size is generally 120 # ~ 240 #; fine research for W40 ~ 14.

 Valve modulation abrasive, usually to the abrasive directly into the kerosene and motor oil. With 1/3 kerosene plus 2/3 oil and abrasive modulation synthesis of the abrasive is suitable for coarse grinding; 2/3 kerosene plus 1/3 oil and abrasive modulation synthesis of the abrasive can be used for fine grinding.

When grinding higher hardness workpieces, the effect of using the above abrasives is not satisfactory. In this case, three abrasives can be used plus a heated lard blending up, after cooling to form a paste, and then add some kerosene or gasoline to mix it properly when using.

5. Selection of grinding tools

Valve and seat sealing surface due to different degrees of damage, can not be directly on the research, but first with a certain number of pre-specialized specifications of the fake valve valve (i.e., grinding head), fake valve seat (i.e., grinding seat), respectively, on the seat, the valve valve for grinding.

The grinding head and grinding seat made of ordinary carbon steel or cast iron, size and angle should be placed on the valve with the valve, and valve seat equal.

Grinding is manual, need to configure a variety of grinding rods. The grinding rod and grinding tool should be properly assembled, not skewed. To reduce human labor intensity, accelerate the speed of grinding, often using an electric grinder or vibration grinder grinding.

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