Select two aspects of imported bearings mechanical seal structure

Bearing structure type mechanical seal selection is an important step in the design cycle , you must first be investigated : ① operating parameters of the medium pressure , temperature, shaft diameter and speed . ② the concentration of dielectric properties , viscosity, corrosion , with or without solid particles and fibrous impurities are easily vaporized or crystallization . ③ host work characteristics and environmental conditions continuous or intermittent operation ; mainframe installed in the indoor or outdoor ; atmosphere surrounding the nature and temperature changes. ④ host allowable leakage seal leakage direction ( internal leakage or leakage ) requirements ; life and reliability requirements. ⑤ host sealing structure or size. ⑥ operation and production process stability .
1, according to the operating parameters p, v, t Selection
Where p is the pressure of the medium at the sealed chamber , according to the size of the p-value can initially determine whether to select balanced structure and the degree of balance . NSK Bearings for medium viscosity, good lubricity , p0.8MPa, or low viscosity, poor lubricating medium , p0.5MPa when the structure is usually used unbalanced . p-value exceeds the above range , you should consider using balanced structure. When p> 15MPa , generally single face -balanced structure is difficult to achieve sealing requirements , then you can use multiple tandem seal .
Refers to the average diameter of the circumferential sealing surface velocity , depending on the value of the size of the elastic member to determine whether the rotation with the shaft , which uses a rotary spring or spring static structure , generally <20 ~ 30m / s in a rotary spring can be higher speed conditions, the rotating parts can lead to strong vibration unbalance mass , preferably spring stationary structure. If p and values ​​are high, considering the selection of hydrodynamic structure.
t is the seal cavity medium temperature , FAG bearings based on t determine the size of secondary seal material, the sealing surface of the cooling method and its auxiliary systems. Temperature t in the range of 0 ~ 80 ℃ , secondary seal is usually chosen nitrile rubber O-ring ; -50 ℃ t <150 ℃, according to the strength of corrosive media , the choice of fluorine rubber, silicone rubber or Teflon molding packing ring: temperature < -50 or t150 ℃ , the rubber and PTFE will produce low or high temperature aging embrittlement , metal bellows structure can be used at this time . Medium turbidity higher than 80 ℃, in a sealed area is usually necessary to be considered at high temperatures , the cooling time must take appropriate measures .
Second, according to media characteristics selection less corrosive media
Usually use the built -in mechanical security seals , SKF bearing its face the stress state and the direction of media leaks than the external and reasonable. For strongly corrosive media , the more difficult the selection of the spring , the choice of external or PTFE bellows type mechanical seal , but generally only applicable p0.2 ~ 0.3MPa range.
Easy to crystallize , easy coagulation and high viscosity medium , large springs should be used rotating structure. Because small spring easily be blocked solids , high viscosity media make small spring axial compensation movement blocked.
Flammable, explosive, toxic media , in order to ensure that the media does not leak , you should use a sealing liquid ( liquid separation ) of the double-end structure .
Press the dielectric properties of the selected operating parameters and the structure is often only a preliminary program , INA Bearing ultimately determine the host must also consider the characteristics and the sealing of some special requirements. For example, the rocket engine seal life just a few minutes , but requires a short time absolutely does not leak .nylon cable ties Sometimes hosts on the ship in order to obtain a more efficient space , the size of the seal and mounting position are often made ​​very demanding , and if the drain pump on submarines , submarine ups and downs in the process, the pressure varies widely and so on. In these cases , it is not the conventional structure of the selection criteria , and must be specially designed for the specific conditions , while taking the necessary complementary measures.