High temperature gear pump due to corrosion caused by mechanical seal failure:
a) Sealing surface pitting, or even penetrated.
b) Due to the tungsten carbide ring and stainless steel seat and other welding, the use of stainless steel seat easy to produce intergranular corrosion;
c) Welded metal bellows, springs, etc., are prone to rupture under the combined effect of stress and medium corrosion.
Mechanical seal failure due to high temperature effect:
a) Hot cracking is the most common failure phenomenon of high temperature gear oil pump, such as residue pump, refueling oil pump, atmospheric vacuum tower bottom pump, etc. Because of the dry friction in the sealing surface, the cooling water suddenly breaks down, the impurities enter the sealing surface, Case, will lead to radial cracks appear on the torus;
b) Carbonization of graphite is one of the main reasons for the failure of sealing when using carbon-graphite rings.If the graphite ring exceeds the allowable temperature (generally -105 ~ 250 ℃) in use, the surface of the graphite ring will precipitate resin, friction Near the surface of the resin will occur carbonization, when there is a binder, it will foam softening, so that the sealing surface leakage increases, the seal failure;
c) Auxiliary seal (such as fluorine rubber, ethylene propylene rubber, all rubber) will exceed the permissible temperature, it will quickly age, crack, harden the missiles. Now use flexible graphite high temperature resistance, corrosion resistance than Good, but its resilience is poor. And easy to brittle, easy to damage during installation.
Seal failure due to wear of seal face:
a) The materials used for the friction pair have poor wear resistance, large friction coefficient, excessive pressure on the end face (including spring pressure), etc., which will shorten the service life of the mechanical seal. For the commonly used materials, the order of wear resistance is: Carbide - Carbon Graphite, Carbide - Carbon Graphite, Ceramic - Carbon Graphite, Sprayed Ceramic - Carbon Graphite, Silicon Nitride Ceramics - Carbon Graphite, HSS - Carbon Graphite, Surfacing Carbide - Carbon Graphite .
b) For solid particles containing medium, the sealing surface into the solid particles is the main reason leading to failure of the seal. Solid particles into the friction side of the abrasive surface effect, so that the seal wear and tear failure. Reasonable sealing surface clearance, and mechanical seal The balance of the degree, as well as the sealing end liquid film flashing are all the main reasons for opening the open end of the solid particles.
c) The degree of mechanical seal balance β also affects the sealing wear.Generally, the balance of β = about 75% of the most suitable.β <75%, although the wear loss decreases, but the leakage increases, the possibility of opening the sealing surface increase Large. For high load (high PV) mechanical seal, due to the larger end friction heat, β generally take 65% to 70% is appropriate for low boiling point hydrocarbon media, due to the temperature of the gasification of the media is more sensitive, To reduce the impact of friction heat, β take 80% to 85% as well.
Mechanical seal leaks due to errors in installation, operation, or equipment:
1, due to poor installation, resulting in mechanical seal leakage mainly in the following areas:
1) moving, static contact surface uneven, bump when installed, damaged;
2) moving, static ring seal size is wrong, damaged or not compressed;
3) moving, stationary ring surface foreign body;
4) moving, static ring V-ring installed in the opposite direction, or install the anti-edge;
5) Leakage at the sleeve, seals are not installed or pressing force is not enough;
6) uneven spring force, single spring is not vertical, multiple springs vary in length;
7) sealed chamber end face and shaft perpendicularity is not enough;
8) There is a corrosion point on the shaft seal ring.
2, equipment in operation, the main reasons for mechanical seal leakage:
1) the axial displacement of the gear pump impeller exceeds the standard, the shaft vibration occurs periodically and the process operation is not stable, the pressure in the sealed chamber often changes will lead to periodic leakage seal;
2) friction pair damage or deformation can not run together to cause leakage;
3) improper choice of sealing material, swelling bullet;
4) big spring steering wrong;
5) Vibration is too great when the equipment is running;
6) moving, static ring and the shaft between the formation of scale so that spring shells can not compensate for the sealing surface wear;
7) Crack ring and so on.
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