Often underappreciated but vital to thousands of machines and household appliances, rubber gaskets help make our everyday life possible. They seal our refrigerator doors to keep food fresh; they keep ammunition protected from moisture; they help build bridges. What is a rubber gasket and how is it used in all of these applications? Well, it is a mechanical seal that is used primarily to prevent leaks of gas or liquid, but can be used as a barrier between two objects, such as two metals or chemicals. They are often utilized as protection from outside elements as well. In a camera lens, they combat moisture and dust to ensure that the lens stays focused and speck free. Used in almost every industry, this fabricated rubber product is versatile and necessary for thousands of applications. There are rarely two applications that use the same shape or size gasket. Gaskets are made specific to each use and this makes this industry very unique!
To best suit the needs of different uses, a rubber gasket must be cut or shaped into required sizes using varying sheets of rubber. (In this article we are discussing gaskets that are flat! Products like O-Rings, 3-dimiensional parts, and profiles are not covered here.) Engineers design equipment that having moving parts and need rubber parts to protect them. The designer or engineer choses a sheet rubber product that will suit the needs of the application and that will withstand the conditions the rubber is exposed to. Criteria like media temperature, rubber hardness, tensile strength, and percentage of compound are some of the concerns when choosing rubber gasket materials. The drawing and the material specs are then sent to gasket cutting. Engineer who designs a part must understand the needs of the equipment and the capabilities of the elastomers and them match the two together.
When deciding upon rubber gasket material it is important to remember that each rubber compound has different physical characteristics like durometer and tensile strength. Durometer refers to the hardness of a material or the resistance to permanent indentation. The lower the durometer the more impression you can make on the sheet. Lower durometer rubber products are generally less dense and more supple. Higher durometer rubber sheets are less flexible, more dense, and a little heavier. Tensile strength is the maximum stress that material can undergo while being stretched or pulled. This means whether or not a material is brittle or more tear and crack resistant. What happens if you apply more force than the tensile strength of the rubber? Failure. How it fails is a function of lots of other factor. Each rubber sheeting will have differing durometer and tensile strength profiles. A good analogy is that cars can have variations in horsepower, and rubbers can have differing flexibility measures. It is important to also note their abilities to withstand temperature and chemicals, as well as their color and aesthetics. These are just a few considerations when choosing amongst rubber sheet products. The most common rubber gasket materials are listed below:
Neoprene – An all-purpose polymer, neoprene gaskets are moderately resistant to petroleum products, but offer good resistance to the ozone and weathering. They are easily compressed and excellent for sealing refrigeration fluids due to their temperature range of -65 to 250 degrees Fahrenheit. Neoprene offers three gasket forms: homogenous, sponge, and diaphragm. Homogenous Neoprene offers moderate resistance to oil and ozone damage and is generally used for bumpers and pads. Sponge Neoprene contains tiny individual sealed cells to resist moisture, dirt, and air even at cut edges. This makes this material a great sound and vibration insulator as well as shock absorber. Diaphragm Neoprene reinforced with cotton duck, enhancing the interior structure of the material. Neoprene is generally black in color with a smooth finish.
EPDM - Ethylene Propylene Diene Monomer (EPDM) offers excellent resistance to weathering, ozone, UV rays, grease and oils. Able to withstand a large range of temperatures from -40 to 212 degrees Fahrenheit, EPDM gaskets are generally used in outside applications. EPDM Gaskets are also available in two durometers. The medium durometer of 45-55 is moderately flexible, while the harder version of 55-65 is better resistant to physical abrasive environments. EPDM gaskets have a black plate finish.
Nitrile – One of the most widely used materials, a nitrile gasket is very resistant to petroleum products and animal fats with superior abrasion and tear resistance. Unlike EPDM gaskets, a nitrile gasket is not as well-suited for ozone and weathering applications. But this material reins supreme in automotive applications, since the presence of oils make it a necessity. A nitrile gasket or pad is sometimes present in food processing equipment, since animal by-products do have greases and oils.
Silicone – Often used in the automotive industry, Silicone is very resistant to oxygen, ozone, and ultraviolet light. With a working temperature of over to 450 degrees Fahrenheit, Silicone is perfect for extreme temperature applications, such as in automobiles. This product is also good for electrical insulation and is often used for electrical applications. Silicone is also able to withstand large amounts of pressure, so it can be used in areas with more physical stress. However, Silicone has poor tear strength and does not work effectively against oils.
Santoprenes – A high performance thermoplastic elastomer, Santoprene combines great flexibility with low compression. With both a smooth and a block surface design, this product is extremely versatile and perfect for automotive applications.
When sheet rubber products are made, the factory can vary the content of any of the above compounds when mixing. For example EPDM’s can be produced with 10% EPDM content or up to 100%. If the mixture is 10% EPDM and 90% SBR, this makes the end-result far less effective as an EPDM gasket! Now that we have chosen amongst some of the options in rubber gasket materials, we can discuss fabrication.
The four most used rubber gasket cutting methods are listed below:
Hand cutting – The most traditional method, hand cutting a rubber gasket usually involves an assembly line to speed up the process. Hand cutting is reserved for less critical applications and prototyping. It also usually includes a skilled craftsman that has years of experience and lots of friendly tools.
Die cutting – Customized to the item created, a die cutting machine is made to punch a unique shape out of the sheet material. The die is made based on the drawings or simple dimensions of the requisition. Once the desired shape is determined, the machine will do the gasket cutting. This method has limits in terms of the thickness of materials used, and generally sheet goods 3/8” or less are die-cut.
Water jet cutting – In response to demand for precision cutting for gaskets, water jet cutting is able to create a cleaner cut on thick rubber materials without the edge concavity from die cutting.
Molded – Gaskets can also be created from molds. Custom fit molds are best for unique jobs with the need for high volume production.
For gaskets larger than 48”, it is best to use rubber rolls to accommodate larger format gaskets. It may be difficult to find material to suit this as most companies offer up to 48 inch widths. Rubber-Cal does offer up to 72” rolls so that it is possible for you to create a larger format gasket than with the typical rubber roll.
The options in rubber gasket materials and gasket cutting methods allow you to choose based on your project’s demands on what to use and how to cut it. A nitrile gasket is completely different from EPDM gaskets; from durometer and tensile strength to just aesthetics alone, the material of each gasket is extremely important to ensure your gasket works properly. Never wonder what is a rubber gasket again! Just know that it can be literally in any size or made from any one of many rubber compounds. Just evaluate your needs and pick a rubber gasket with this list of chemical, temperature, and chemical resistant criteria that suits your needs.