Manufacturers of hydraulic cylinders are generally proficient in all aspects of the cylinder technology, but they do not necessarily have a good understanding of sealing technology. General manufacturers only know the use, not necessarily know the sealing principle, may not understand the dynamics of hydraulic cylinder seals, do not understand how hydraulic cylinder seals work in the cylinder. This is certainly not going to work. Manufacturers of hydraulic cylinders must understand the sealing technology and understand the hydraulic cylinder seals, in order to select different hydraulic cylinder seals according to different technical requirements. The hydraulic cylinder seal manufacturers must also understand the working principle of the hydraulic cylinder, using different designs to meet the technical requirements of the hydraulic cylinder, so the hydraulic cylinder manufacturer and the hydraulic cylinder seal manufacturer need to work closely together to reduce the probability of hydraulic cylinder failure.
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First, several states of hydraulic cylinder seals (lip seals)
(1) When the hydraulic cylinder seal is not installed, there are four sizes, which can be seen by everyone and measured with measuring tools. These four dimensions are: the inner diameter of the root of the seal, the outer diameter of the root, the inner diameter of the lip, and the outer diameter of the lip.
(2) When the hydraulic cylinder seal is installed in the groove and has not yet worked, the groove size remains unchanged, and the size of the seal has all changed, four dimensions: the outer diameter of the root of the seal, and the outer lip diameter changes to the groove outer diameter at the same time; The inner lip diameter is the piston rod diameter, and the root inner diameter is the amount of clearance between the seal and the piston rod plus the piston rod diameter.
(3) When the hydraulic cylinder begins to work and the pressure starts, the working state of the hydraulic cylinder seal seal is: the inner and outer lips are close to the inside, and the outer wall is slightly moved backwards. The root of the seal is squeezed backwards, and as the pressure increases, the force of the hydraulic oil on the seal also increases, and the overall deformation of the seal increases. When the duty cycle is complete and the cylinder is under no pressure, the seal returns to its original shape. Repeated deformation, repeated recovery, until the seal double lip effective amount is completely lost, the seal is damaged.
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Second, the hydraulic cylinder groove size tolerance and the hydraulic cylinder seal cooperation
(1) There are many forms of reciprocating motion seals, common ones are L-type, U-type, V-type, and Y-type, and its shape is mostly lip-shaped seal.
(2) Reciprocating motion lip seal is widely used in the reciprocating motion cylinder of the hydraulic system. The pressure surface of this hydraulic cylinder seal is lip-shaped, and there is a very small amount of interference during installation, so that the lip edge is in full contact with the sealing surface, resulting in a sealing effect. When the cylinder is working, with the increase of pressure, its contact force and contact area increase, and the sealing performance improves with the increase of pressure. When the cylinder returns, the pressure decreases, the contact area and contact force decrease, and the sealing performance is reduced, which is similar to the human breathing process. This process also acts as a lubrication of the lip.
(3) Seal manufacturers in various countries in the world have strict requirements for the tolerance and roughness of the groove size. Therefore, cylinder manufacturers must strictly produce cylinders according to tolerances and roughness requirements. If the cylinder is not produced as required, three situations can occur:
In case one, the groove is too deep, and two situations will occur:
A. The gap between the root of the hydraulic cylinder seal and the groove becomes larger, which will make the root of the seal unstable.
B. The amount of interference in the sealing lip and sealing surface of the hydraulic cylinder seal becomes smaller, and the rebound force of the seal becomes smaller, so the failure rate of the piston rod at low pressure oil leakage will increase when it runs out.
In case two, if the groove is too shallow, two situations will also occur:
A, resulting in the sealing lip and sealing surface interference increased, the contact area increased, resulting in friction become larger, in the cylinder return time seal lip can not get effective lubrication, heat increased, it will accelerate the damage to the seal lip.
B. The amount of gap between the root of the seal becomes smaller, and the probability of the root of the seal being extruded at the high pressure of the cylinder increases.
Situation three, the roughness of the cylinder
If the roughness of the hydraulic cylinder exceeds the requirements, it can also lead to two situations:
A. It will cause the friction of the inner and outer lips of the seal to increase, and the damage speed of the lip will be accelerated.
B. The amount of oil in the contact surface area of the seal and the cylinder increases, and the possibility of oil seepage increases.
The above content is excerpted from the Internet, such as invasion and deletion! For more cylinder sealing information, please visit OTHELLO official website: Industrial Sealing Import Brand - Othello Sealing Materials (China) Co., Ltd
Further reading:
What are the specific seals for hydraulic cylinder seals?
What is the cause of slow hydraulic cylinder movement and what should I do?
How to judge whether the hydraulic cylinder seal is of high quality?
A few signs of leak failure in hydraulic cylinder seals