Configuration selection of bearing sealing structure

The shaft is supported by two bearings in radial and axial directions. The bearing on one side is called fixed end bearing. It bears radial and axial loads and plays the role of fixing the relative axial displacement between the shaft and the bearing housing. The other side is called the free end, which only bears the radial load and can move relatively in the axial direction.
For the medium with high viscosity and good lubricity, p0.8mpa, or the medium with low viscosity and poor lubricity, p0.5mpa, the non-equilibrium structure is usually selected. When the p value exceeds the above range, the balanced structure shall be considered. When p > 15MPa, the general single face balanced structure is difficult to meet the sealing requirements. At this time, the series multi face seal can be selected.
It refers to the circumferential speed of the average diameter of the sealing surface. Whether the elastic element rotates with the shaft is determined according to the value, that is, the spring rotating type or spring static type structure is adopted. Generally, the spring rotating type can be adopted if it is less than 20 ~ 30m / s. under the condition of higher speed, the uneven mass of the rotating part is easy to cause strong vibration, so the spring static type structure is better. If the values of P and are high, the hydrodynamic structure can be considered.
The fixed end bearing must be fixed with the shaft and bearing housing at the same time. The more suitable bearings are radial bearings that can bear composite loads, such as deep groove ball bearings, self-aligning roller bearings, double row or paired angular contact ball bearings or tapered roller bearings. Radial bearing combinations bearing simple radial load, such as cylindrical roller bearings with inner and outer rings without retaining edges, can also be used as fixed end bearings through combination with deep groove ball bearings, four point contact ball bearings or two-way thrust bearings. At this time, the second bearing provides two-way axial positioning, but it must be installed at a certain radial distance from the bearing housing. When the length of the free end bearing changes due to thermal expansion, there will be no extrusion in the bearing. Axial displacement can occur inside the bearing, as well as the bearing ring and bearing seat.
The structure selected according to the above working parameters and medium characteristics is often only a preliminary scheme. The final determination of the bearing must also consider the characteristics of the main engine and some special requirements for sealing. For example, the sealing life of a rocket engine only takes a few minutes, but it is required that there should be no leakage in a short time. Sometimes, in order to obtain more effective space, the main engine on the ship often puts forward very strict requirements for the size and installation position of the seal, such as the drainage pump on the submarine, the pressure changes greatly in the process of submarine sinking and floating, etc. In these cases, the standard structure cannot be selected according to the routine, but the specific working conditions must be specially designed and necessary auxiliary measures must be taken.