Rubber seals are widely used in all walks of life. Once the seal fails, the equipment cannot work normally and the economic loss caused is small, and the life of the operator in the accident crisis is large. Therefore, when we operate the equipment, we must develop good inspection habits and operate in strict accordance with the equipment's safe operation regulations. If problems are found, they will be dealt with in time. More careful analysis of the problem will help us to find out the problem, and it will be convenient for us to take corresponding preventive measures in future operations and reduce the occurrence of accidents.

The reasons for the failure of the seals may be caused by many aspects, such as poor quality and aging of materials. Today, I will mainly analyze the common failure causes in the daily operation of the equipment.

1. Failure caused by improper material selection

First of all, we believe that the selection of materials is a very important part of equipment production, and the selection of the correct and high-quality materials is the basic condition to ensure the long-term effectiveness of the seal.

Commonly used rubber sealing materials are ethylene propylene diene rubber (EPDM), nitrile rubber (NBR), silicone rubber (VMQ), fluorine rubber (FKM or FPM) and chloroprene rubber (CR). The properties of these rubbers are different and their applications are also different. The selection of materials should be considered from many aspects, such as the temperature of use, whether the material can withstand the medium, the hardness of the material, compression set and wear resistance and other factors.

The material selection error is simple, but it is more complicated. It is not simple to select materials according to the purpose, but also to learn to combine the environment of use. For example, there is a customer who does not like the O-ring that is being used because the O-ring is easy to break. We checked the replaced sample and found that the surface of the sample was cracked, and the texture resembled ozone aging. We also inquired about the use environment of the O-ring and found that there are many mechanical equipment and electric motors around. The answer is now: the sparks of the electric motor can produce ozone, resulting in a high concentration of ozone in the local small environment; and the material selected by the customer is nitrile rubber, which is not resistant to ozone. In order to verify the conclusion, we conducted a test in the laboratory ozone aging box. As a result, similar cracks appeared on the surface of the new O-ring provided by the customer. Since the seal is only in long-term contact with air and has no other substances such as mineral oil, we finally recommended EPDM rubber to replace the customer's existing products.

Sometimes the use environment is more complicated, or it is a brand-new design, it is not very easy to choose the material. In addition to carefully identifying various influencing factors, functional testing is also required.

2. The quality of the seal causes the seal to fail

The production quality of the seal is closely related to the reliability of the final product. Common problems include: unstable quality of raw materials, wrong raw materials during rubber mixing, improper storage of raw materials or rubber compounds (cross-contamination), uneven mixing of rubber materials, improper vulcanization conditions (temperature, time, pressure, etc.), Improper storage of seal products, improper use of molds, etc. These problems often involve quality control in the production process. The ordering party should go through many inspections, investigations and product tests when choosing a seal manufacturer. In the process of supply, the manufacturer of the seal can also be required to provide a true and accurate inspection report.

3. Design errors

Design errors are usually caused by designers' insufficient knowledge of the product. For example, the pressure on the seal is underestimated, the understanding of the contact stress distribution on the sealing surface is incorrect, and the groove design for the seal is unreasonable.

Finite element analysis (FEA) is often used to assist seal design and failure analysis. We once made a seal for an American customer. The seal was mainly made of plastic and partially covered with rubber. In the process of inspecting the parts, the customer found that the plastic part was easily broken during the test, and concluded that the plastic part was damaged during the secondary molding (that is, the rubber was coated on the plastic part). After our analysis, we found that the plastic parts were broken in one place. Through finite element analysis, we found that the damaged part of the plastic part is actually the place where the seal is subjected to the greatest stress, where the stress has far exceeded what the plastic can withstand.

If the customer used the finite element method to analyze the product at the time of design, not only could similar errors be avoided, but also time and money could be saved. Of course, if you want to successfully analyze and predict the performance of rubber seals, you need not only suitable finite element analysis software, but also rich material experience, modeling experience and long-term data accumulation.

4. Seal failure caused by improper use of seals

A good seal, if used improperly, will also cause the entire product to fail, such as incorrect use of lubricant.

One of our customers reported that the size and requirements of O-ring parts are very different. When we analyzed the samples, we discovered that the customer had used the wrong lubricant. The O-ring is made of EPDM rubber, and the material itself is not resistant to mineral oil lubricants. Customers applying this kind of lubricant will cause the product to swell in volume. Later, it was no problem to let customers switch to silicone oil.

Another common type of problem is installation errors. For example, distortion occurred during the assembly of the O-ring; uneven pressure on the seal due to improper installation; and errors such as insufficient lubrication of the seal. If these errors are caused by the manufacturer of the seal, then this is within the scope of production quality control. If it is caused by the ordering party or a third party, it is improper use.

Reasonable design is one of the important factors to ensure the effective use of seals.

Today's science and technology are changing with each passing day, and many new seal materials and engineering designs have appeared in the market to meet various demanding requirements. At the same time, most seal manufacturers have also adopted a scientific quality management system. Unfortunately, none of these efforts can prevent seal failure. Therefore, failure analysis is particularly important.