Round Rubber Gasket
Sanshi Rubber is a supplier of round rubber gaskets. No matter the environment or application, Sanshi Rubber has the experience to solve your sealing problems.
Due to the critical nature of performance, our design team can consult on configurations and materials. We offer thoughtful design assistance that can also enhance the appearance of the final product.
Designing a custom molded round rubber gasket or seal involves three steps.
1. Understand the need for a molded rubber gasket.
2. Determine the proper compression force.
3. Understand the environment in order to select the correct material.
Custom molded round rubber gaskets offer many advantages over other types of gaskets and seals, but they are typically more expensive than extruded gaskets or die-cut gaskets. In general, if the application can be sealed with either of the other two options, that is the direction to take.
If the profile or cross-section of the gasket does not vary along its entire length, then an extruded gasket can be used. Keep in mind that one of the disadvantages of extruded gaskets is the presence of splices. Spliced joints are usually not as strong as the material itself and can provide leak paths if not handled properly.
Die-cut gaskets may work where the gasket is of uniform thickness and not contoured. Keep in mind that sometimes it may not be possible to use die-cut washers if the part is too thick or if the contour size is too small compared to the thickness.
Another limitation of die-cut washers is thickness tolerance - we've seen situations where die-cut washers with tighter thickness tolerances are required given the stack height and the components in the mating part.
Finally, die-cut gaskets thicker than 0.125" may develop a disc shape along the edges, and the thicker the material, the more pronounced the disc shape. "As shown below, the 'disc' effect is a depression in the die-cut edge (due to the compression of the material by the die-cut pressure). The width "W" (or length) of the top and bottom surfaces is slightly greater than the width "WX" in the center."
All round rubber seals and round rubber gaskets work because they are compressed between two mating parts. The compression force required to seal depends on the pressure and particle size (air, water, or oil) being sealed. The higher the pressure and/or the smaller the particle size, the higher the compression force on the gasket must be.
Three related material properties also affect the designed compression force.
Compression Deflection - A measure of the tendency of rubber to lose its ability to "bounce back" after a period of compression.
The most common test is ASTM D395, which involves a test sample approximately 0.500 inches thick that is compressed to a thickness of 0.375 inches and held in that condition for 22 or 70 hours in a 158F - 300F oven. After baking, the sample was removed from the oven and cooled for 30 minutes before measuring the compression fixture and thickness. C B, the compression permanent deformation B is given by C B = [(t o - t i ) / (t o - t n )] * 100, where to is the original specimen thickness, t i is the specimen thickness after testing, and ton_ is the shim thickness or specimen thickness during the test.
Materials with low or poor compression permanent deformation values usually do not make good seals or gaskets because after a period of time they will fit into mating parts that could lead to leak paths.
Stress relaxation - the loss of pressure over time as the rubber "adjusts" to its compressed state. In the description of compression deformation above, if one were to measure the force required to compress a sample from 0.500 inches thick to 0.375 inches thick, the pressure required to do so would decrease over time. Examples such as these are considered stress relaxation.
Creep - Simply put, creep is a combination of the two terms listed above. More technical explanations of creep (and other terms) are available in materials science textbooks.
Materials can be formulated to minimize compressive deformation, stress relaxation and creep. As with all physical properties, when improving one or two properties, other properties must usually be compromised.
Choosing the right material for a molded round gasket or molded round seal is important, and Sanshi Rubber can help you select the most cost-effective material for your application.
