There are four main reasons for the failure of rubber seals: design errors, incorrect material selection, seal quality problems and improper use.

1. Design errors

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

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 the plastic can withstand.

If the customer used the finite element method to analyze the product when designing it, 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.

2. Wrong material selection

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 characteristics of these rubbers are different and their applications are also different. The selection of materials should be considered from many aspects, such as the use temperature, whether the material can withstand the medium, the hardness of the material, compression set and wear resistance. The wrong material selection is often because the designer is not familiar with the properties of various materials. An experienced supplier of rubber seals can point out the problem of material selection at the beginning.

We have a domestic customer who doesn't like the O-ring being used because it 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 operating environment of the O-ring, and found that there are many mechanical equipment and electric motors around. The answer is now: the spark of the electric motor can produce ozone, which causes a high concentration of ozone in the local small environment; and the material selected by the customer is nitrile rubber, which is not ozone resistant. In order to verify the conclusion, we conducted a test in the laboratory ozone aging box, and the result of the new O-ring provided by the customer also appeared similar cracks on the surface. 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 our customers' existing products.

Sometimes the use environment is more complicated, or if it is a brand new design, choosing materials is not very easy. In addition to carefully identifying various influencing factors, functional tests are also required.

3. Seal quality

The production quality of the seal is closely related to the reliability of the final product. Common problems are: unstable quality of raw materials, wrong raw materials during rubber mixing, improper storage of raw materials or rubber compounds (cross-contamination), uneven rubber mixing, 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. During the supply process, the seal manufacturer may also be required to provide a true and accurate inspection report.

4. Improper use of seals

A good seal, if used improperly, can 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 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, there is no problem if 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, it is within the scope of production quality control. If it is caused by the ordering party or a third party, it is improper use.

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 even more important.

5. Failure analysis of rubber seals

Failure analysis of rubber seals not only requires technical personnel to have comprehensive material knowledge, but also must have rich engineering experience, and must be good at using some analytical instruments and equipment, so complex failure analysis often requires a team to complete.

When a customer's product has a sealing failure, the first reason they think of is often the rubber seal. The question they most often ask is: Has the supplier changed the material? In fact, it can be seen from the above that material replacement is only one of the possible influencing factors. Therefore, when encountering a sealing failure, we should start from the following four aspects, fully grasp the information, and draw conclusions based on data rather than guesses.