Design considerations of rubber seals

When designing rubber seals, you should first understand their use. The details include:

1. Working conditions, such as fluid type, working pressure, working temperature, pH, etc.

2. Size, tolerance and roughness of the contact surface between the seal and the rotating shaft, and whether the rotating shaft is coated, coated, etc.

3. Linear speed of the axis of rotation.

4. Required service life.

First, choose the right type of seal

There are many kinds of commonly used rubber seals, which can be selected according to the use situation. For example, O-ring, Y-ring, U-ring, square ring, rotary shaft seals, etc.

Second, choose the right material

Nitrile butadiene rubber (NBR) and polyurethane rubber (PU) can be selected according to the requirements of the working conditions, such as the ordinary hydraulic prop's requirements for sealing materials are not high; Downhole hydraulic support requires sealing materials with oil resistance, water resistance, impact resistance, usually butyl rubber (IIR), polyurethane rubber (PU).

Nitrile butadiene rubber (NBR) and polyurethane rubber (PU) can be selected according to the requirements of the working  conditions, such as the ordinary hydraulic prop's requirements for sealing materials are not high;  Downhole hydraulic support requires sealing materials with oil resistance, water resistance, impact resistance,  usually butyl rubber (IIR), polyurethane rubber (PU).

1. Size and tolerance The size, tolerance and roughness of the contact surface of the seal and the rotating shaft should be appropriate, too small or too large tolerances and too small roughness will cause premature damage to the seal. Usually the roughness of the contact surface should be in Ra0.8~1.6, the tolerance of the rotating shaft should be h8 or h9, and the tolerance of the seal should be f7 or g8.

2. Hardness Hardness is one of the important performance indicators of rubber seals, if the hardness is not suitable, it is easy to be worn or scratched in a short time. Usually the hardness range of O-ring is Shore A 60~90, Y-ring is Shore A 70~94.

3. After the encapsulation Angle and lip height seals are loaded into the groove, the gap between the side and the side wall of the cavity should be as small as possible to facilitate the sealing of oil. For seals with a cross-section width of W, the envelope Angle should not be less than 120°, and the lip height should not be reduced by the hydraulic force. The values of envelope Angle and lip height can be calculated according to the formula H=2.6W-0.9d, β=120°-90°+H/W, where W is the width of the seal section (mm), d is the height of the seal section (mm).

4. The suitable compression rate can make the seal better adapt to the contour size of the groove, reduce friction heat generation, and reduce the wear between the seal and the rotating shaft. Usually the compression rate of O-ring is 10% to 20%, Y, U, square ring is 12% to 25%.

4. Problems that should be paid attention to during processing

Processing quality and some factors affecting performance should be controlled, such as turning, milling, drilling and other processing errors should be controlled within 0.1mm; When mixing rubber, it should be noted that the impurities such as carbon black and vulcanizing agent in rubber should be completely mixed evenly; When molding, attention should be paid to controlling pressure, time and other parameters to avoid deformation, bubbles and other defects; When applying glue, pay attention to the uniform glue layer and no bubbles. In addition, the following points should be noted:

1. In the design, the seal should be adjusted as much as possible during assembly to avoid machining errors resulting in too tight sealing.

2. For some seals that need to be glued, attention should be paid to the cleaning of the bonding surface, and too much or too little glue should be avoided.

3. For some seals with higher precision requirements, finishing should be carried out after roughing to avoid cutting deformation of seals during roughing.

4. For some seals that need to be paired with other parts, attention should be paid to the matching accuracy and matching relationship between the matching parts.

5. For some seals that need to be used under high temperature or high pressure conditions, attention should be paid to high temperature or high pressure tests to ensure that they can achieve the expected performance indicators under the conditions of use.