Reasons for locking of fasteners, fillers and gaskets of valve fittings and ways to prevent locking

Reasons for locking of fasteners, fillers and gaskets of valve fittings and ways to prevent locking

Gasket can be divided into two kinds of soft plastic and hard, soft plastic is generally non-metallic material, such as thick cardboard, plastic, asbestos rubber board, PTFE and so on. Hard is generally metal composite materials or metal materials covered with stone wool, alloy and stone wool coiled. Gaskets come in many shapes, including flat, round, oval, toothed, lens, and other unique shapes. The production and manufacture of gate valve parts of many raw materials, including a variety of different types of light metal and precious metal and aluminum alloy, a variety of non-metallic materials.
1. Raw materials for fasteners
Fasteners mainly include anchor bolts, multi-head bolts and nuts. Fasteners directly bear forces in gate valves, which are of great significance to avoid the loss of media. Therefore, the raw materials selected must ensure sufficient strength and fracture toughness at the application temperature. Select fastener data according to medium pressure and temperature.

Heat treatment process is required when carbon steel materials are used. When the tightening parts have special corrosion resistance standards, Cr17Ni2, 2Cr13, 1Cr18Ni9 and other stainless acid resistant steel can be selected.
Two, filler raw materials
On the valve body, the packing is used to fill the indoor space of the single flow valve packing chamber to avoid media leakage through the valve seat and the single flow valve packing chamber indoor space.
1. The demand for fillers
1) Good corrosion resistance, packing and medium contact, must be able to resist the corrosion of the medium.
2) Compact structure, packing does not leak under the influence of medium and working temperature.
3) Low friction resistance to reduce the friction torque between seat and packing.
2, the type of packing
Packing can be divided into soft plastic packing and hard packing two kinds:
1) Soft plastic filler: it is made of green planting material, namely,  linen, cotton, linen, etc., or by mineral, namely glass fiber cotton, or by glass fiber cotton with iron wire and outside coated flake graphite rope woven, and ground into the forming filler, and the new opportunities of flexible graphite filler raw materials in recent years. Green plant material packing is more cost-effective, mainly used for low pressure valves within 100℃; Mineral packing is suitable for 450-500℃ gate valve. In recent years, the construction of plastic O-ring as filler is gradually popularized, but the medium temperature is generally controlled within 60℃. The packing in the high temperature and high pressure valve is also made of pure asbestos and flake graphite powder.
2) Hard packing: packing made of metal materials or metal mixed with asbestos, high purity graphite and polytetrafluoroethylene pressing calcination and forming packing, metal packing application is less.
3, the selection of stuffing
The selection of filler should be based on the medium, temperature and pressure to select, common raw materials have the following points:
1) Oil to asbestos cloth, can be selected according to Table 5-2.
2) Plastic asbestos cloth: can be selected according to Table 5-3.
3) High purity graphite asbestos cloth: asbestos cloth coated into flake graphite, the temperature can be used above 450℃, the working pressure can reach 16Mpa, generally suitable for high pressure steam. Recently and gradually the use of pressure adult font filler, lap speed placement, compact structure.
4) polytetrafluoroethylene: This is a more widely used filler at this stage. Especially available on the corrosive medium, but the temperature can not be more than 200℃. Generally, it is made of suppressor or round rod, as shown in Figure 5-1 below.
Note: Appearance number F indicates square, through-core or one to double braid; Y indicates that it is round, with a twisted mandrel in the middle and one to two layers of braid outside; N means twisted.
Three, gasket material
The gasket is used to fill 2 joint surfaces (such as the surface between the oil circuit plate and the single flow valve) between all the uneven, in order to avoid media leakage from the joint surface.
1. The demand for sealing gaskets
Gasket material has certain elasticity and plasticity and sufficient compressive strength at operating temperature to ensure tightness. At the same time, it should have better corrosion resistance.
2, gasket material type and judgment
Gasket can be divided into two kinds of soft plastic and hard, soft plastic is generally non-metallic material, such as thick cardboard, plastic, asbestos rubber board, PTFE and so on. Hard is generally metal composite materials or metal materials covered with stone wool, alloy and stone wool coiled. Gaskets come in many shapes, including flat, round, oval, toothed, lens, and other unique shapes.
The raw material of sealing gasket is generally 08, 10, 20 quality carbon steel and 1Cr13, 1Cr18Ni9 stainless steel plate, dimensional accuracy and surface smoothness requirements are very high, suitable for high temperature and high pressure valves. Non-metallic material gasket material general plasticity is good, with relatively small working pressure can achieve sealing. Suitable for ultra-low temperature and low pressure valve. Gasket materials can be selected according to Table 5-4.
Table 5-4
The production and manufacture of gate valve parts of many raw materials, including a variety of different types of light metal and precious metal and aluminum alloy, a variety of non-metallic materials.
Raw materials for the production and manufacture of gate valve parts should be selected according to the following factors:
1, working medium pressure, temperature and characteristics.
2, the bearing capacity of the parts and often play a role in the valve structure.
3. Good process performance.
4. Under the premise of meeting the above conditions, relatively low cost is required.
The metal fasteners in fasteners will always rust for various reasons. When rust occurs, some fasteners will lock completely, resulting in the loss of efficiency in the actual operation of fasteners themselves. In fact, it is impossible to disassemble or lock fasteners continuously. The complete locking of fasteners may only occur within a few seconds, so it is necessary to have a clearer understanding and use of fasteners to prevent locking. Fastener locking is generally in stainless steel plate or aluminum alloy material made of goods…
Metal fasteners will always rust for various reasons. When rust occurs, some fasteners will lock completely, resulting in loss of efficiency in the actual operation of fasteners themselves. In fact, it is impossible to disassemble or lock fasteners continuously. The complete locking of fasteners may only occur within a few seconds, so it is necessary to have a clearer understanding and use of fasteners to prevent locking.
1. Main reasons for fastener locking
The locking of fasteners generally appears on the commodities made of stainless steel plate or aluminum alloy material, mainly because the metal composite material itself has anti-rust ability, once the metal surface of fasteners is damaged, it is easy to appear oxide layer to provide maintenance and prevent the aggravation of rust, but when the fasteners are tightened, The pressure heat generated by the reaction force will damage the oxide layer and promote the plugging or cutting between the metal materials, resulting in adhesion, which is actually locking.
2, fastener to prevent locking method:
★ The locking of fasteners cannot be completely avoided, but we can reduce the probability of locking by paying attention to each element, such as ensuring the load strength of fasteners, selecting nuts and bolts with more compressive strength, etc.
★ Fastener screw cleaning is not cleaning also has a certain impact on whether locking, when the screw is not smooth or not cleaning, locking more often, so before use to ensure the fastener cleaning work, iron pin or waste.
★ After proper and moderate wetting processing of fasteners, the heat generated by the metal material position can be effectively reduced due to the bearing force, which will naturally reduce the probability of fastener locking.
★ Fasteners should be sealed and installed in the correct way, less and less locking occurs.