Failure Analysis of Rubber Seals

Rubber seals, a key component widely used in various industries, can have serious consequences if they fail. Minor failures may lead to the malfunction of sealed equipment, resulting in economic losses; severe failures may cause personal injury or death, with incalculable consequences. Therefore, failure analysis of rubber seals is particularly important. Through this process, we can not only deeply analyze the root cause of the problem and provide strong support for subsequent preventive measures, but also help customers and seal manufacturers jointly improve existing technologies, achieving a win-win situation for both parties.

1. Design Error Analysis

Design errors often stem from designers' insufficient understanding of product characteristics. This may involve underestimating the pressure that seals are subjected to, misunderstanding the stress distribution on the sealing surface, and flaws in the design of the seal installation groove, among others. Finite Element Analysis (FEA) is an effective auxiliary tool that is frequently used in the design and failure analysis of seals. For instance, we once designed a seal for an American client, which was mainly made of plastic with rubber covering certain parts. During testing, the client found that the plastic part was prone to cracking, leading them to suspect that the rubber had damaged the plastic during the secondary molding process. Through in-depth analysis, we discovered that the location of the plastic part's damage was highly consistent with the maximum stress point, and this stress far exceeded the plastic material's tolerance limit. If FEA had been used for prediction during the design stage, such errors could have been avoided, along with significant time and cost savings. Of course, successful performance prediction not only relies on appropriate FEA software but also requires extensive material knowledge, modeling experience, and long-term data accumulation.

2. The Impact of Improper Material Selection

When it comes to the selection of rubber sealing materials, common options include ethylene propylene diene monomer (EPDM), nitrile butadiene rubber (NBR), silicone rubber (VMQ), fluorine rubber (FKM or FPM), and chloroprene rubber (CR), among others. Due to their distinct properties, these materials are suitable for different applications. Designers must take into account multiple factors such as operating temperature, resistance to media, material hardness, compression set, and wear resistance when making a selection. However, due to a lack of familiarity with material properties, incorrect material choices are often inevitable. An experienced rubber sealing component supplier can quickly identify and point out material selection issues during the design phase.

A customer reported that the O-rings they were using were prone to damage. Upon inspection, it was found that the surface of the samples had cracks similar to those caused by ozone aging. Further investigation revealed that the O-rings were used in an environment surrounded by mechanical equipment and electric motors. It was speculated that the sparks from the electric motors might have increased the local ozone concentration, and the nitrile rubber chosen by the customer was not resistant to ozone. To verify this assumption, we conducted tests in an ozone aging chamber in the laboratory, and the results showed that the new O-rings provided also developed similar cracks on their surfaces. Given that the seal was only in long-term contact with air and no other substances such as mineral oil, we ultimately recommended that the customer switch to EPDM to replace the existing product. In complex usage environments or new designs, material selection can indeed be challenging. Besides carefully analyzing various potential factors, functional testing is also of great importance.

3. Seal Quality Control

The production quality of seals is crucial to the reliability of the final product. During the production process, various problems may arise, including unstable quality of raw materials, incorrect raw material input during rubber compounding, cross-contamination due to improper storage of raw materials or compounded rubber, uneven mixing of rubber compounds, inappropriate vulcanization conditions (such as temperature, time, and pressure), as well as improper storage of seal products and incorrect use of molds. All these potential issues need to be effectively controlled in the production process. Therefore, when selecting a seal manufacturer, the ordering party should conduct in-depth investigations and research, and implement strict product testing. Additionally, during the supply process, the ordering party can request the manufacturer to provide genuine and accurate inspection reports to ensure that the quality of the seals meets the requirements. 

4. Improper Use Scenarios

Improper use of seals can also lead to product failure, such as incorrect selection of lubricating oil. A customer once reported that the O-ring parts they used had significant dimensional differences from the requirements. After a detailed analysis, we found that the customer had mistakenly used lubricating oil. This O-ring was made of ethylene propylene diene monomer (EPDM) rubber, which is not resistant to mineral oil-based lubricants, and thus caused the product to swell in volume after use. Subsequently, we suggested that the customer switch to silicone oil, and the problem was resolved.

In addition, incorrect installation is also a common issue. For instance, during the assembly of O-rings, they may be distorted, resulting in uneven pressure on the seal; or due to insufficient lubrication, the sealing effect is affected. The causes of these mistakes can be diverse. If they are caused by the seal manufacturer, they fall within the scope of production quality control; but if they are due to improper operation by the ordering party or a third party, they are considered improper use.

In the context of rapid technological development today, the market has seen the emergence of numerous new seal materials and engineering designs to meet various harsh usage conditions. At the same time, most seal manufacturers have established scientific quality management systems. However, these measures still cannot completely prevent seal failure. Therefore, failure analysis becomes increasingly important as it helps identify the problem and take corresponding improvement measures.