The principle of 1 packing seal
In the machinery industry, packing seals are mainly used as dynamic seals, often used as centrifugal pumps, compressors, vacuum pumps, and rotating shaft seals of agitator. Packing into the packing cavity after the gland screws on it when the axial compression, and the filler has the relative motion, because the plastic filler to produce a radial force, and close contact with the shaft. At the same time, the lubricant impregnated in the filler is squeezed out and the 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. Good seal is to maintain "bearing effect" and "labyrinth effect". That is to say, it is necessary to maintain good lubrication and appropriate pressure. If the lubrication is bad, or the pressure is too tight, the oil film will be interrupted, causing dry friction between the packing and the shaft, and finally causing the burning shaft and serious wear. Therefore, we need to adjust the packing degree of the packing regularly, so that the lubricant in the filler will run away for a period of time, and then squeeze out some lubricants, and compensate for the tightening force caused by the volume change of the filler. Of course, the packing is often squeezed, and the impregnating agent will be exhausted at the end, so it is necessary to replace the packing regularly. In addition, in order to maintain the liquid film and take away the friction heat, it is also necessary to have a small amount of leakage at the packing.
Problems in the use of 2.2 packing seal in the use of industrial pumps
The industrial pump generally adopts abrasion resistance, heat resistance, good flexibility, high strength, we found that the packing in the packing, has the following disadvantages: the filler surface roughness, friction coefficient, leakage, and long time immersed in the lubricant used to drain. The new fixed equipment running in good condition when the shaft seal, but before long, the leakage will increase, the adjustment and replacement of packing gland work gradually frequently, running to a cycle, Bush had been worn into the vase shape, there will be serious wear sleeve off, and the back seal ring is not changed the packing is rotten, can not play a role in sealing. (3) the direct contact between the packing and the shaft, and the relative rotation, causes the wear of the shaft and the shaft sleeve, so it is necessary to replace the shafts regularly or unregularly. (4) in order to make the friction heat produced by the disc root and the shaft or shaft in time dissipate, the seal must keep a certain amount of leakage, and it is not easy to control. The friction between the disc root and the shaft or shaft sleeve causes the effective power of the motor to be reduced and the electric energy is consumed.
2.3 principle of mechanical seal
The mechanical seal is also called the seal, it is the seal device of a rotating machine, which consists of a pair of end faces perpendicular to the axis of rotation in the liquid pressure and the elasticity of compensation organizations (or magnetic) device and the role of the coordination of auxiliary seals to keep up with the relative sliding to prevent fluid leakage. Its main function changes the leakage of the axial seal to the face seal which is difficult to leak. It is widely used in the seal of the rotating shaft of the pump, the kettle, the compressor and the similar equipment. Mechanical seals are usually made up of a moving ring, a static ring, a compacting element and a sealing element. The movable ring is rotated with the pump shaft, and the dynamic ring and the static ring close tightly together to make up the sealing surface to prevent the leakage of the medium. The moving ring depends on the pressure of the liquid in the sealing chamber to compress the end surface on the static ring end surface, and generate an appropriate pressure on the two ring face and maintain a thin liquid film to achieve the purpose of sealing. The pressure is generated by the pressing element, so that the pump can also keep the end face fit under the condition of no operation, ensuring that the sealing medium is not leaking, and prevents impurities from entering the sealing face. The sealing element plays the role of sealing the gap between the ring and the shaft, the gap between the static ring and the cap, and the elastic element cushioning the vibration and impact of the pump. Mechanical seals are combined with other components of the pump in actual operation. The normal operation of mechanical seals is closely related to their own performance and external conditions. But we must first guarantee the performance of its own parts, the auxiliary sealing device and the technical requirements of the installation, so that the mechanical seal should play its due role.
2。4 problems in the use of mechanical seals in the use of industrial pumps
Mechanical seal parts failure rotating equipment in operation, often face wear, hot cracking, deformation, damage and other conditions。 Spring for a long time will also relax, fracture and corrosion。 The auxiliary sealing ring also appears crack, distortion and deformation, rupture and so on。