Sharing knowledge about sealing with everyone

Thread Content

Basic Knowledge of Sealing 1.1 Leakage Leakage is one of the common faults that occur in mechanical equipment. There are mainly two reasons for such leaks: First, as a result of mechanical processing, the surfaces of mechanical products inevitably have various defects as well as deviations in shape and size; therefore, gaps inevitably form at the joints between mechanical parts ； Second, a pressure difference exists on both sides of the seal, causing the working medium to leak through the gap. Reducing or eliminating gaps is the main way to prevent leakage. The function of a seal is to close the gap between the mating surfaces, isolate or block the leakage path, increase the resistance in that path, or incorporate small elements that generate pressure on the leaking fluid, thereby offsetting or completely balancing the pressure difference that causes the leakage and preventing it from occurring. Regarding the sealing of vacuum systems, in addition to leakage through the sealing surfaces caused by the aforementioned sealing materials, two other forms of leakage must also be taken into account: Seepage: This refers to the leakage of the medium being sealed through the capillaries in the sealing material material, under the effect of a pressure difference. {TodayHot} ； Diffusion: That is, under the influence of a concentration difference, the transfer of substances through seal gaps or the capillarity of sealing materials by a sealed medium is known as diffusion. 1.2 Classification of seals Seals can be divided into two main categories: static seals, which are used between surfaces that remain relatively stationary, and dynamic seals, which are used between surfaces that move relative to each other. Static seals mainly fall into three categories: point seals, adhesive seals, and contact seals. Based on operating pressure, static seals can be divided into medium and low pressure static seals and high pressure static seals. For medium and low-pressure static seals, softer materials and gaskets with a wider width are commonly used, while for high-pressure static seals, harder materials and metal gaskets with a very narrow contact width are employed. Dynamic seals can be divided into two basic types: rotary seals and reciprocating seals. Seals can be classified into contact seals and non-contact seals, depending on whether the seal comes into contact with the components that move relative to it. Generally speaking, contact seals offer good sealing performance, but are limited by frictional wear and are suitable for applications where the linear speed of the sealing surfaces is low. Contactless seals have poor sealing performance and are suitable for applications at higher speeds. 1.3 Selection of Seals The basic requirements for seals are good sealing performance, safety and reliability, long service life. Additionally, it is desirable that they have a compact structure, a simple system, be easy to manufacture and maintain, and have low costs. Most seals are wear-prone components; interchangeability should be ensured, and standardization and serialization should be achieved.