Classification of the use of seals
Seals can be divided into two categories: static seal and dynamic seal. Static seals are mainly gasket seal, sealant sealing and direct contact sealing three categories. According to the work pressure, static seal can be divided into medium and low pressure static seal and high pressure static seal. Low and medium pressure static seals are usually made of soft and wide width gasket. High pressure and static seals are made of hard material and metal gaskets with narrow width. Dynamic seals can be divided into rotary seal and reciprocating seal two basic types. According to the seal of the relative movement of the parts is divided into sealing contact, contact and non-contact seal; according to the seal and the contact position can be divided into circumferential seal and the seal, the seal is also called mechanical seal. The centrifugal seal and spiral seal in the dynamic seal are sealed by the power of the medium when the machine is running, so it is sometimes called the power seal.
1. according to the function classification: divided into shaft seal, hole seal, dust seal, guide ring, fixed seal, rotary seal;2., according to material classification: divided into nitrile rubber, three yuan ethylene propylene rubber, fluorine rubber, silica gel, fluorine silicone rubber, nylon, polyurethane, engineering plastics, etc..
The seal according to the shape and material type, sealing structure, sealing mechanism, classification of seal for packing into the packing cavity after the gland axial compression on it (see figure 29.5-9), when the filler and relative motion, because the plastic filler to produce a radial force, and close contact with the axis. At the same time, the lubricant impregnated in the packing is extruded and an oil film is formed between the contact surfaces. Because the contact state is not uniform, the contact parts will appear the boundary lubrication condition, known as the "bearing effect"; the concave without contact to form a small oil tank, oil film thickness, contact and non-contact parts of an irregular maze, preventing the liquid leakage flow this effect, called "labyrinth effect". This is the mechanism of packing seal. Obviously, the good seal is to maintain the "bearing effect" and "labyrinth effect"". That is to say, to maintain good lubrication and proper compression. If the lubrication is bad or pressed too tight, the oil film will be interrupted, resulting in dry friction between the packing and shaft, and finally lead to burning shaft and serious wear and tear. To this end, often on the packing pressing degree of adjustment, so as to fill in the lubricant after running for a period of time loss, and then squeezed out some lubricant, pressing force relaxation while compensating for volume changes caused by filling.
