Design considerations for rubber parts

Designing rubber seals is a skill and process that is required in many industries, such as for medical, transportation, industrial and commercial applications. During the design process, these are some of the most important considerations:

  • The finish of the surface area
  • Flatness
  • How parallel the design is
  • How much it can tolerate
  • Extreme temperature capability
  • Friction resistance
  • Compression resistance
  • Chemical compatibility
  • Stress relaxation

Surface Finish – The type of surface is important as problems here can lead to potential for damage or leakage. The smoother the surface, the easier it will bind to other surfaces and the longer it will last. The surface finish is the result of factors such as the mold surface quality, flash removal process and type of rubber used. The Association for Rubber Products Manufactures has four levels of surface finish categories:

F1 – A perfectly smooth surface free from dents, nicks and scratches

F2 – Very smooth but without small tool marks polished out

F3 – Also known as a commercial finish and no special finish will be specified

F4 – A satin-like finish

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Flatness – This quality also helps to prevent leakage. Flatness is a measure of any deviation between the point of two lines on a plane. For advice on Rubber Moulding UK, contact a site like

Tolerance – The amount that a material can tolerate is essential to know for reliability and suitability for a particular application. Tolerance includes factors such as shrinkage, precision, use of and location of inserts, distortion, storage and environmental resistance.

Temperature – Having a low temperature capacity is important because when rubber becomes cold it is more susceptible to breaking or cracking. Even if the rubber doesn’t break, its strength and performance is greatly reduced.

Friction – Friction controls the amount of movement that can occur between two materials. Friction slows down movement so if a rubber component needs smooth and fast movement, an elastomer with a lower coefficient of friction will be chosen for the application.

Compression – To avoid the risk of leaks and to provide long-life sealing capabilities, a material must be able to withstand compressive force. This is a measurement of the damage caused once a compressive force is released. Once a material reaches its compression set, it won’t be able to bounce back to its original form and this can lead to leakage.

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Chemical compatibility – Different elastomers have different thresholds of resistance in terms of chemical exposure. The same material can also react differently to the same chemical when under different heat conditions. Volume swell relates to how much the material deteriorates when exposed to different volumes of chemicals.

Stress relaxation – over time the amount of force that pushes against a valve, for example, will cause it to become deformed. If a design doesn’t factor this in, then it will not have the kind of service life that you would hope for.

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