WHAT ARE THE FACTORS AFFECTING THE SEALING EFFECT?

Nowadays, more and more machines need seals. There are many types of seals, such as gland packings and mechanical seals. Among them, the mechanical seal has types of spring seals, elastomer bellow seals, etc. Every type of seals has different sealing effect. So what affects the sealing effect? According to the research, the factors are the choice of sealing structure, oil film formation, pressure, temperature, material compatibility, material, hardness, geometry, surface finish, etc. of the working surface contacted by the dynamic seal.

1. Compatibility of sealing materials and hydraulic oil (liquid)

One of the sources of particle contamination of hydraulic oil is the "debris" or "abrasive debris" generated by the seal material and the hydraulic oil. The "debris" produced by the damage of the seal due to "swelling" or the unbound inorganic materials and filler reinforcement materials that are "extracted" will damage the seal and fail, and at the same time, it pollutes the oil, causing the hydraulic oil to deteriorate and cause failure.

The vane pump is widely used in the hydraulic system. When its working pressure is greater than 6.9MPa, the wear problem becomes prominent, so anti-wear agents are used in the hydraulic oil. In order to adapt to the hydraulic system near high-temperature heat sources and open flames, we use flame retardant phosphate ester, water-glycol hydraulic fluid, oil-in-water and water-in-oil emulsion, etc. And various types of hydraulic oils (liquids) for different purposes configured with various types of compound additives appeared, such as: zinc-free (ashless type) anti-wear hydraulic oil compound agent, which uses hydrocarbon sulfide, phosphate ester, phosphite, etc., and also contains sulfur, phosphorus and nitrogen.

The reason why the seals "swell" or "extract" is due to the various chemical elements and their concentrations contained in the additives in the hydraulic oil. According to the principle of "similar miscibility", they have different effects on different sealing materials. It is also the medium resistance of the sealing material. With the continuous research and development of hydraulic oil, in order to improve the performance of oil (liquid), various anti-wear, extreme pressure additives, metal deactivators, demulsifiers and anti-foam additives, etc, which affect the sealing material of the seals, should be checked.

2. Testing and evaluation of oil-resistant performance of sealing materials.

Oil resistance (liquid) performance of rubber seals. Generally, we use standard test oil, soak under the temperature conditions and test time specified in the test standard, by comparing the test values before and after soaking (such as the change in hardness of the material, the change rate in tensile strength, the change rate of breaking elongation, etc.), evaluate its performance.

3. The influence of hydraulic oil (liquid) on the performance of seals.

Seal theory believes that there is a complete lubricating film between a dynamic flexible seal and its mating surface. Under normal conditions, it is with this layer of lubricating film to achieve the purpose of sealing and extend the life of the seal.

In the hydraulic system, in addition to the compatibility of the medium or the sealing material, the viscosity of the oil, the change of the viscosity with the temperature, the reciprocating (rotation) movement speed, pressure and the shaft, material, hardness, geometry, surface finish of the cylinder and the piston rod, and the structure of the seal, which affect the formation and characteristics of the lubricating film, all affect the sealing effect. Generally speaking, forming a continuous lubricating film can obtain the ideal sealing effect.