Hardness Selection of O-ring Seals

The choice of O-ring hardness is more important. For example, the sealing ring of a water pump turbine in a power station with a hardness of 70 (Shore) often peeled off or even cut off laterally. Then a sealing ring with a hardness of 85 to 90 (Shore) was used, and the effect was ideal.

It has low hardness and is easy to install, but it is prone to peeling, installation damage, extrusion and even pressure explosion. The hardness is too high and installation is inconvenient.

Usually the hardness of O-rings is 40 to 90 IRHD, but in use, 70 IRHD is generally more suitable. The exception is silicone rubber, which generally uses 60 IRHD.

O-ring trimming

Unvulcanized O-ring rubber is a viscous fluid under high temperature and pressure. However, in the molding vulcanization stage, the rubber quickly fills the mold cavity, and the excess part (in order to prevent lack of glue, the rubber filled in the mold cavity must be Maintain a certain excess) overflow vulcanization, resulting in glue overflow (also called waste edge, flash edge). Once the overflow is formed, it must be removed in order to make the appearance neat and beautiful. This process is commonly called edge trimming. The requirements for trimming are accurate size and neat appearance. in actual production. The trimming of products is often time-consuming and labor-intensive. For products with strict requirements, a slight carelessness during trimming may cause defects, so we must treat it with caution. Generally speaking, the smaller the product size and the more complex the configuration, the more difficult it is to trim the edges and the more waste there will be.

O-ring trimming is divided into three categories: manual, mechanical and frozen:

1. Manual trimming. The operator holds the tool and gradually removes the overflow along the outer edge of the product. This is the most primitive method. The efficiency is low and the quality is difficult to ensure. Especially for O-rings that are small in size and require high precision, it is difficult to clean thoroughly and cleanly, and it is easy to damage the connection between the product body and the overflow edge. Teeth marks and gaps are often left, leaving oil leakage, air leakage and other residual problems that affect the seal. in addition. The dependence of hand trimming on operator proficiency is also prominent.

2. Mechanical trimming. In order to improve efficiency and quality, mechanical trimming appeared. Common ones are special electric trimmers with rotating blades. The blade used must closely match the size of the product. If the product has overflow on both the inner and outer edges. It can be designed as double-edged or multi-edged. To achieve one-time completion. The processing accuracy of mechanical trimming exceeds that of manual trimming, and the efficiency is doubled. Especially for products with multiple cavities in one mold, matching tools can be designed according to the arrangement and distribution of the products. After the product is released from the mold. It can be put on the whole page and punched out in one go. With the cooperation of heating, dozens of pieces can be repaired at a time. The key is that the punching temperature must be well controlled to prevent adhesion after being too high.

3. Freeze trimming. The vulcanized finished product together with the waste edges are removed under freezing conditions. This technology was jointly invented and improved by Japan's Showa Carbonate and China's Zhaoling Precision. Over the past few decades, with the selection and replacement of freezing media and improvements in mechanical movements, frozen trimming has also gone through several generations of improvements, becoming increasingly mature and perfect. , work efficiency and processing quality have been significantly improved.