After years of experience, we summarize the reasons for mechanical seal failure of gear oil pump:
1) The verticality of the seal cavity end face and shaft is not enough;
2) the spring force is not uniform, the single spring is not vertical, and the length of many springs is different;
3) the shaft sleeve leakage, sealing ring is not installed or the compression force is not enough;
4) The direction of the dynamic and static v-type sealing ring is reversed, or the side is reversed when it is installed;
5) There are foreign bodies on the surface of dynamic and static rings;
6) The size of dynamic and static ring seals is wrong, damaged or not pressed;
7) Uneven contact surface of dynamic and static rings, collision and damage during installation;
1, due to poor installation, resulting in mechanical seal leakage. Mainly in the following aspects:
Leakage of mechanical seals due to errors in installation, operation or equipment itself:
A) The balance degree of mechanical seal β also affects the wear of seal.
B) scale is formed between the moving and static rings and the shaft sleeve so that the spring loses its elasticity and the wear of the sealing surface cannot be compensated;
C) The vibration of the equipment is too large during operation;
D) Wrong steering of large spring;
E) Improper selection of sealing ring materials, swelling and loss of ammunition;
F) Leakage caused by friction pair damage or deformation;
G) The axial momentum of the blade wheel of the gear oil pump exceeds the standard, the rotating shaft has periodic vibration and the process operation is unstable, and the pressure in the sealing cavity changes frequently, which will lead to periodic leakage of the seal;
2. In operation of the equipment, the main reasons for leakage of mechanical seal are:
1) There are corrosion points at the movable part of the sealing ring on the shaft sleeve. For commonly used materials, according to the order of wear resistance: silicon carbide - carbon graphite, carbide - carbon graphite, ceramic - carbon graphite, spraying ceramic - carbon graphite, silicon nitride ceramic - carbon graphite, high speed steel - carbon graphite, hardfacing carbide - carbon graphite. Because in use, if the graphite ring once exceeds the allowable temperature (generally at -105 ~ 250℃), the surface will precipitate resin, resin near the friction surface will occur carbonization, when there is a binder, will foam and soften, increase the sealing surface leakage, sealing failure;
2) Hot crack is the most common failure phenomenon of high temperature gear oil pump, such as slag oil pump, oil refining pump, gas and vacuum tower bottom pump. In the sealing surface due to dry friction, cooling oil suddenly interrupted, impurities into the sealing surface, evacuated, will lead to radial cracks in the torus;
Mechanical seal failure due to high temperature effect:
3) Welded metal bellows and springs are prone to rupture under the combined action of stress and medium corrosion. Reasonable clearance of sealing surface, balance degree of mechanical seal, and flash of liquid film of sealing end face are the main reasons for opening the end face and allowing solid particles to enter.
4) Due to the tungsten carbide ring and stainless steel base welding, the use of stainless steel base is easy to produce intergranular corrosion;
A) Pitting corrosion or even penetration of the sealing surface.
5) Cracking of sealing ring, etc.
6) The abrasion resistance of the material used by the friction pair is poor, the friction coefficient is large, and the specific pressure of the end face (including the specific pressure of the spring) is too large, which will shorten the service life of the mechanical seal. β<75%, although the amount of wear is reduced, but the leakage is increased, the possibility of sealing surface opening is increased. For high load (high PV value) mechanical seal, due to the end friction heat is larger, β generally 65% ~ 70% is appropriate, for low boiling point hydrocarbon medium, due to temperature is more sensitive to medium gasification, in order to reduce the impact of friction heat, β 80% ~ 85% is good.
Seal failure caused by abrasion of seal face:
A) Auxiliary seals (such as fluorine rubber, ethylene propylene rubber, whole rubber) will rapidly age, crack, harden and lose ammunition after exceeding the allowable temperature. Now the use of flexible graphite high temperature resistance, corrosion resistance is good, but its resilience is poor. And easy to crack, easy to damage when installing. In general, the optimal balance degree β=75% or so.
B) Graphite carbonization is one of the main causes of seal failure when using carbon-graphite ring.
C) For media containing solid particles, the sealing surface entering solid particles is the main cause of sealing failure. Solid particles into the end face of friction pair as abrasive, make the seal wear and failure.
