The failure of the function of the silicone rubber seal is the most worrying situation for many electrical equipment and household appliances. Because the performance of the seals one by one is likely to cause greater losses, the main cause of the failure of the performance of the silicone rubber seals In addition to materials and processes, the reason also has a certain impact on the use of the product. In the process of use, silicone rubber seals often return to failure due to the force and some objective reasons, and the force distribution during the force is also distributed. For example, instantaneous, lateral pressure, back pressure, etc., we will explain the situation that silicone products are prone to damage.
1. Clearance bites
The gap bite phenomenon and cause of the Y-shaped sealing ring are similar to those of the O-ring, and occur at the root. Similarly, the solution is to limit the sealing gap according to the working pressure and correctly select the Y-ring material. For Y-shaped seals with a working pressure greater than 16 MPa, a retaining ring or a special seal ring with a retaining ring in the root should be used. Retaining rings are usually made of plastic materials with high rigidity, such as polytetrafluoroethylene and polyamide.
2.Back pressure damage
When the silicone seal is used as a piston seal for a double-acting piston cylinder, it must be used in pairs to seal high-pressure fluid in both directions. In this way, between the two back-to-back lip rings on the piston, or between the piston rod of the hydraulic cylinder and the two lip rings in the middle of the guide sleeve, fluid will gradually infiltrate to form a pressure accumulation. When the working pressure is removed or the accumulating pressure is higher than the working pressure during the complex movement, the special-shaped seal will be reversely squeezed from the root in the installation groove, and its lip tip will be squeezed into the gap between the cylinder and the piston. The inside was pinched, causing backpressure damage.
Preventive measures against back pressure damage are:
Make small holes in the piston to release the pressure. When the working pressure is removed, the trapped fluid can be drawn out through the small hole, and the pressure accumulation is released.
Set the support ring. The support ring acts between the two lips of the special-shaped silicone ring for the piston and bears against the seal ring so that it cannot move axially and is not squeezed out in the opposite direction. In addition, several grooves are evenly distributed along the circumference of the groove to facilitate the pressure medium to act on the recess of the Y-shaped seal through the small holes to open the lips of the Y-shaped seal; at the same time to avoid causing back pressure, Make the trapped oil drain smoothly and keep the Y-ring sealed posture. This measure is more effective to prevent the silicone seal from being damaged by back pressure.
3. Turn over. If the external torque generated by friction during movement is greater than the torsional capacity of the seal ring itself, the seal ring will be turned over or partially turned around, losing the sealing ability. To prevent the seal from flipping, you can increase the hardness of the compound or use a support ring. The setting of the support ring has a good effect on preventing various misalignment of the Y-shaped seal ring in the rotary groove. The Y-shaped seal ring can also be reversed after being inserted into the retaining ring.
4, root wear
Leakage at the seal root can cause leakage. The main reason for root wear is that the interference is too large, resulting in large friction and dry friction. Therefore, we must pay attention to the relationship between the inner diameter of the seal ring and the size of the hole shaft and groove.
For shaft Y-shaped seals, its inner diameter d1 should be larger than shaft diameter d2; its outer diameter D1 should be greater than the groove bottom diameter D2; for holes with Y-shaped seals, its inner diameter d3 should be smaller than the groove inner diameter d4; its outer diameter D3 should be smaller than the bore D4. That is, the Y-shaped sealing ring must be pressed tightly with the bottom of the groove, and there is a certain gap with the sealed sliding surface; the sealing contact stress of the sliding surface is obtained by the working pressure of the sealed medium acting on the lip of the Y-ring.
The wear of the seal ring is also related to the roughness of the sliding surface, and the rough surface accelerates the wear of the seal ring; it is also related to the processing method. For example, a polished shaft of the same level of roughness will wear the seal much less than a polished shaft.
5, abnormal sound
When the hydraulic cylinder is operated under high pressure and low speed, the sound of "Barry, Berry" sometimes occurs. The reason is that when the Y-shaped sealing ring slides along the shaft or the inner wall of the cylinder, the rubber-metal contact surface is temporarily attached-detached-adhered-detached, which will reduce the life of the sealing device. The solution is: reduce the friction coefficient of the rubber, so that the sealing contact surface always maintains the lubricating oil film; also pay attention to the viscosity of the working medium or lubricant should not be too low.
Muddy water, dust, and sand and stone intruding into the hydraulic cylinder often cause abnormal wear of the silicone rubber seal ring. A dust ring should be provided at the extended end of the piston rod to ensure the dustproof effect to prevent harmful impurities from entering the hydraulic cylinder.
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