A poorly durable silicone rubber seal can seriously damage your brand reputation. Compression set is a key factor affecting the service life of silicone rubber products. This guide shows you how to control compression set through testing standards, key factors affecting performance, and specific applications.
Importance of Compression Set in Silicone Rubber
What Is Compression Set?
Compression set occurs when you place the silicone rubber in a specific temperature environment and subject it to a prescribed compressive strain for a certain period of time.
Under such conditions, the silicone rubber may lose part of its elastic recovery capability, leading to permanent deformation and it will no longer fully return to its original shape.
You can calculate the percentage of the stress release that cannot be restored to the original thickness. This directly defines the elastic recovery ability of the silicone rubber you have chosen. The lower this value is, the better the elastic recovery of the silicone rubber is and the stronger its anti-deformation ability is.
Impact on Sealing Performance of Silicone Rubber
When used in a sealed application, the elastic property of the silicone rubber enables it to return to its original shape and closely adhere to the two surfaces that hinder the flow of liquids and gases, thereby forming a seal.
When you are purchasing silicone rubber for sealing applications, the compression set is the key factor that determines whether the product can meet the standards and can operate stably for a long time.
If the value of the selected silicone rubber is too high, leakage problems may occur after a period of use. This not only will cause mechanical failures in your products, damaging their reputation, but also lead to customer complaints, after-sales repairs and other issues. It might even require batch recalls, thereby directly causing economic losses.
Impact on Service Life of Silicone Rubber
No matter which field you are in, the compression set is directly linked to the competitiveness of your silicone rubber products.
Low compression set silicone rubber can maintain stable elasticity and sealing performance under long-term high-temperature, high-pressure or repeated compression working conditions, thereby extending the service life of end products and reducing your maintenance costs.
On the contrary, if you choose inferior silicone rubber, even if the initial product can meet basic requirements, it will shorten the product’s service life due to deformation after long-term use.
Mainstream Test Standards for Compression Set of Silicone Rubber
Understanding the testing methods for the compression set of silicone rubber can help you precisely control the quality of imported materials, thereby avoiding procurement risks caused by using materials that do not meet the standards. Next, we will mainly introduce two international testing standards to you.
ASTM D395 Method B
ASTM D395 Method B is the most widely used and mainstream international standard for measuring compression sets. If you need to serve customers from the Americas or have products for the American market, this testing standard is more suitable.
The samples for this testing method are mostly cylindrical in shape. The compression amount is strictly controlled at 25% of the original thickness, and then they are placed in an oven. It should be maintained at the specified temperature for either 22 hours or 70 hours.
The temperature will be matched according to the working temperature of your product. After removal and release, it needs to be left at 23±2℃ for 30 minutes before measuring the final thickness. Then, you can calculate the compression set using the general formula.
ISO 815-1
ISO 815-1 follows the same principle as the former and is also compressed to 25% of the original thickness. It is widely used in numerous industries and has a broad scope. If your customers come from multiple regions, such as Asia and Europe, then this testing standard will be more applicable.
However, the ISO 815-1 standard can be used for testing O-ring sealing gaskets. These small test samples may be more difficult to restore to their original state compared to cylindrical objects. Therefore, even though the two testing standards are generally similar in principle, providing the same sample will still result in different test results.
Differences of the Two Test Standards
The ASTM D395 Method B places greater emphasis on practicality. Its steps are clear and concise, making it suitable for material development and batch testing; while ISO 815-1 is more versatile and has a higher global recognition rate, especially being suitable for quality certification when you engage in cross-border trade or product exports.
Key Factors Affecting Compression Set of Silicone Rubber
The ability of silicone rubber components to resist permanent deformation depends on various factors. By understanding these factors, you will be able to assess the professional capabilities and reliability of the suppliers, thereby ensuring the quality of the products you purchase.
Selection of Curing System
The choice between peroxide-cured silicone rubber and platinum-catalyzed addition-cure silicone rubber is of crucial importance. The notable difference between them lies in:
If you are using it for medical and food-grade applications, we recommend choosing the platinum catalytic system. Because such silicone rubbers typically exhibit better compression set performance, higher purity, and a more stable crosslinking network.
Although the peroxide system offers cost advantages, in some cases, the peroxide-cured silicone rubber performs poorly in terms of compression deformation.
If you need to frequently replace the sealing silicone rubber gaskets, then the compression set of the special formula peroxide-cured silicone rubber can be close to the performance of the platinum catalytic system and is also cheaper.
Post-Curing Process
Post-curing involves placing the finished silicone rubber components into a secondary oven for heating. This can remove volatile by-products and residual catalysts, ensure that the cross-linking reaction is fully completed, and significantly improve the compression permanent deformation.
If you require critical mission seals, then it is usually necessary to perform a post-curing process for 2 to 4 hours at a temperature much higher than the operating temperature.
We would like to remind you that some suppliers offer silicone rubber with no post-cure (NPC) and innovative formulations that do not require a second vulcanization process. However, the compression set performance of such rubber is usually not as good as that of the post-cured type.
Filler Content and Types
To enhance the mechanical strength of the silicone rubber, the supplier may add fumed silica to the silicone rubber products you ordered for reinforcement.
You should be aware that an increase in the content of the filler can enhance the hardness of the material. However, if the addition exceeds the optimal level, the filler will affect the elasticity of the silicone rubber and have a negative effect on the compression set performance.
Furthermore, if you notice that the purchased silicone rubber contains heat stabilizers (such as iron oxide), this can help you avoid the risk of substandard performance. Because heat stabilizers prevent silicone rubber from oxidation and thermal degradation at high temperatures, while maintaining its compression recovery performance.
Compression Set of Silicone Rubber in Different Applications
Automotive Engine Sealing and Pipe Gaskets
If you are involved in the manufacturing of automotive components, especially those related to the engine area, silicone rubber would be a great choice for you.
Inside the car engine compartment, the silicone rubber gasket is constantly exposed to high temperatures (up to 200℃) and vibrations/shocks during the engine’s operation. By using a silicone rubber gasket with low compression and permanent deformation, it can maintain an effective seal even after thousands of thermal cycles.
Fluorosilicone rubber combines the higher compression set value of standard silicone rubber with enhanced oil and solvent resistance. You can use this type of silicone rubber to solve the most challenging problems in the automotive industry.
Waterproof Sealing for Electronic Devices
When you manufacture electronic devices, the sealing components of their casings are usually designed to remain in a compressed state for an extended period.
If the sealing component loses its elastic rebound ability gradually after being compressed for a long time, resulting in an increase in the gap between the sealing surfaces, this will allow moisture and dust to enter, eventually causing damage to the internal electronic components.
And your consumers usually think that it’s the poor performance of your electronic components that has damaged your brand reputation. Therefore, using a good waterproof silicone rubber seal is very important. Compared to improving the electronic components, this approach can bring you lower costs and higher returns.
Valves and Diaphragms for Medical Devices
If you are going to apply silicone rubber in medical pumps, valves and long-term implant devices, you need to know that in peristaltic pumps, the catheter must withstand millions of compression cycles. High compression set can cause the catheter to flatten, thereby reducing the flow accuracy and ultimately leading to pump failure.
And platinum-cured silicone rubber is safe, with high fatigue resistance and low permanent deformation. It can meet the strict requirements of such life-saving devices and is your preferred material.
Long-term Compression Components for Home Appliances
Silicone rubber is also widely used in your home appliance industry, covering two major categories: white goods (refrigerators, dishwashers, washing machines, ovens) and small home appliances (coffee makers, steam irons, microwave ovens, rice cookers).
Silicone rubber can withstand repeated impacts from dry heating or high-pressure steam, and also meets the safety and hygiene requirements for food contact as stipulated by the market.
If you manufacture coffee machines, you will understand the high requirements for the long-term compression components of such devices. The low compression set ensures that these components maintain their elasticity and do not leak water even after thousands of usage cycles.
FAQ
What is the Typical Value of Compression Set for Silicone Rubber?
High-quality silicone rubber is tested for 22 hours at a temperature of 125℃. The final measured compression set value is usually between 10% and 30%. The specific value may vary depending on the hardness and grade of your silicone rubber.
At What Compression Set Will Seal Failure Occur?
According to industry experience, when the compression set value of the silicone sealing ring exceeds 40%, its resilience has significantly decreased, which can lead to leakage. If you continue to raise the working temperature, the compression set value of this silicone rubber seal will also increase significantly.
What Causes Compression Set Failure of Silicone Rubber?
If you choose the wrong type of silicone rubber, such as using a silicone rubber with poor performance or one that is not fully cured, it will result in the failure of the compression set.
Also, if the operating temperature you use exceeds the tolerance range of the selected silicone rubber material, it will cause the material to harden or accelerate aging, and may also lead to failure.
How to Evaluate Compression Set When Procuring Silicone Rubber?
Firstly, the supplier is required to provide test reports and compliance certifications. Secondly, compare the data of different silicone rubber products, preferably under the same product specifications and testing conditions. Finally, if you are certain about large-scale procurement, you can request the supplier to provide samples for physical testing.
How to Prevent Silicone Rubber Seal Failure Caused by Compression Set?
You can choose high-quality and low compression set silicone rubber seals, and pay attention to matching the correct operating temperature. During purchase, conduct random inspections of the silicone rubber seals and perform regular maintenance and replacement after use to avoid unnecessary losses.
Final Thoughts
Legensilico is a professional silicone manufacturer in China, capable of providing you with silicone rubber products with excellent compression set performance. If you are interested in our products or want to learn more about silicone rubber, please feel free to contact us at any time.
