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EPDM or Ethylene Propylene Diene Monomer is a family of synthetic elastomers with lower cost, steam and chemical resistance, particularly for applications involving sealant, solvents, acids and other mild chemicals. It is a complex yet inexpensive rubber that has a wide range of uses. It is commonly used in roofs for waterproofing, as EPDM seals very nicely. It is also a common material for freezer room seals, as it is an insulator and has excellent low temperature tolerance. It is most commonly used in Plumbing, Electrical, Automotive and Construction Industries.

Types Of EPDM Rubber O Rings

During the manufacture of EPDM Rubber, the compound can be cured with either sulphur or peroxide. The choice of curing method is determined by the end-use and application.

• Sulphur Cured EPDM O-Rings – Sulphur curing of EPDM is more common, more readily available, and generally more commercially attractive. Sulphur cured ORings have higher tensile strength & tear strength. Sulphur cured EPDM Rubber O Rings can resist temperatures up to 120°C (250°F).
• Peroxide Cured EPDM O-Rings possess a superior chemical & thermal resistance compared to sulfur cured. Peroxide curing also improves the compression set and aging resistance of the Components. Peroxide cured ORings are used in hot water, steam, alcohols, ketones, engine coolants, organic and inorganic acids and bases. Peroxide cured EPDM ORings can withstand temperatures up to 150°C (300°F).
• PTFE Coated EPDM O Rings are dry to touch, providing excellent adhesion and friction properties compared to traditional ORings. PTFE Coated O Rings do not rub off easily, comes in a wide array of colors & does not leave behind visible residue. PTFE Coated ORings are helpful in the lubrication, corrosion protection, extended component life, cleanliness, color identification & easy installation.

Mechanical Properties

• Good Compression Set
• Good Heat Stability
• Fair Shorter Term Resilience
• Good Wear Resistance
• Good Permeation Resistance
• Excellent Electrical Insulation

Temperature & Hardness Range

• Temperature Range : -60°F to +300°F (-51° to +150°C)
• Hardness Range : 40 to 90 Shore A

Applications Of EPDM ORings

• Automotive Brake systems
• Automobile Cooling Systems
• Door, Window & Trunk Seals
• Water & Flow Pumps
• Plumbing Pipes & Fittings
• Door Window Profiles
• Thermostats
• EGR Valves
• EGR Coolers
• Heaters, Oil Coolers & Radiators
• Medical Devices
• Electronic Appliances
• Solar Panels

O Rings are the most commonly used seals and are unlike most of the materials that engineers and designers encounter. As the name implies, Rubber O Rings are shaped like a doughnut & are installed in cavities known as glands and then compressed. The resulting zero clearance within the gland provides the seal that blocks the flow of liquids and gases. The success of this O Ring requires careful design, selection, and installation procedures.

The combination of stresses on the O Rings can be complex and difficult to evaluate. Therefore, it is crucial that both the ORing compound and the Sizes should be tested in the real environment of its service. Below you’ll find the most common reasons that cause O Ring failure:

• Improper Gland Design
• Incorrect ORing Size
• Incompatibility Of ORing Material
• Improper ORing Installation
• Inadequate ORing Lubrication

Also Read: Causes of Rubber Parts Deterioration

10 Most Common Types Of ORing Failure

1. Abrasion Of Rubber ORings – This is very common in dynamic applications. Abrasion occurs due to repetitive contact between the O Ring surface and the housing resulting in excessive friction between the two. Improper lubrication or surface finish of the metalwork increases this risk.
2. Chemical Attack On Rubber ORings – Sometimes chemicals will react with certain elastomers. This results in an increase in cross-link density, resulting in a hard and brittle material and reduces the ability to provide a reaction force. Occasionally cross-link density may reduce, resulting in a softer tacky material, which leads to a loss of its original shape and integrity.
3. Swelling Of Rubber ORings – Swelling is caused by the ingress of media into the elastomer, as the result of a chemical similarity between the compound and the media. The increased seal volume can lead to gland fill, extrusion and loss of sealing. Chemical swell can also result in a loss of physical properties such as tensile strength.
4. Poor Compression Set Of ORings – Physical and chemical changes can occur to an elastomer at elevated temperatures that result in set. Cross-link density can increase, this results in the ORing losing its elasticity and ability to return back to the original shape, this is a permanent chemical change. The reduction in cross section results in a lower contact sealing force, which increases the risk of leakage in systems where thermal and pressure cycling occurs. Other causes include improper gland design, volume swell due to system fluid and incomplete curing of the seal during production.
5. Extrusion and Nibbling On O Rings – High stresses, usually as a result of high pressures, forces the material into the clearance gap, this process is typically called extrusion. Pulses of high pressure can cause the clearance gap between the mating edges to open and close. This can lead to the ORing becoming trapped between the sharp edges of the mating surfaces, resulting in physical damage to the seal surface often referred to as nibbling.

   Also Read: A Guide To Know The Difference Between Silicone Rubber & EPDM !!

6. Explosive Decompression On O-Rings– When elastomer seals are exposed to high-pressure gas at elevated temperatures for a prolonged period of time the gas absorbs into the polymer compound. When the external pressure is reduced, the gas dissolved within the material comes out of solution to form micro bubbles. As the gas expands, it will permeate out of the material. Failure occurs if the rate of decompression and expansion is high, and the trapped gas within the seal expands beyond the materials ability to contain the gas bubbles.
7. Damage Of ORings During Installation – Installation damage can take a wide range of forms, from ‘skiving’ of the seal with metal components through to damage caused by careless installation of dirty, twisted or improperly lubricated seals. Incorrect sizing of the seal for the application is also a significant factor in installation damage.
8. Out-Gassing In O Rings – Ingredients within the elastomer formulation can be released (volatilized) under vacuum conditions. These ingredients can be either a part of the elastomer formulation or the decomposition products of the ingredients or other gasses which are trapped in the polymer matrix during the molding process. In semiconductor applications, out-gassed molecules can cause contamination during wafer processing. In industrial applications it can affect vacuum performance.
9. Thermal Degradation Of O Rings– This happens when the temperature of the application has exceeded the maximum temperature ceiling of the selected seal material or excessive temperature cycling has occurred. High temperatures can increase the cross-link density in elastomers resulting in an increase in hardness and modulus, making them less elastic.
10. UV Degradation Of ORings – Ultraviolet light exposure on an elastomer material can have a destructive effect. UV light has short wavelength, therefore it has high energy, which can interact with the molecular structure of the exposed side of the elastomer. This generally results in cleavage of the polymer chains and causes cracking on the surface, which will lead to leaking and premature failure.

Rubber is a polymer which has the ability to stretch and shrink. Rubber has very good properties like strength, long lasting, water resistance & heat resistance. Other benefits like being non-slip, soft, durable & resilient which makes this Rubber Seals the first choice for various Domestic, Industrial & Automotive Applications.

Before knowing the Rubber production process, it would be helpful to know about different types of rubbers and processing of raw rubber which are sent to manufacturing units for product processing.

Basically, there are two types of rubber namely:

• Natural Rubber (NR)
• Synthetic Rubbers –
  • Styrene Butadiene Rubber (SBR) 
  • Nitrile Rubber (NBR, Buna-N) 
  • Chloroprene (CR) 
  • Ethylene Propylene Diene Monomer (EPDM)
  • Hydrogenated Nitrile Rubber (HNBR) 
  • Polyacrylic Rubber (ACM) 
  • Chlorosulfonated Polyethylene (CSM) 
  • Silicone (VMQ) 
  • Fluoro-Elastomer (FKM)

Overview of Rubber Products Processing

Rubber is used as a name in 3 categories, which may also be called the main processing stages:

• Raw Rubber – This is the prime raw material for any rubber product which determines the main characteristics of the final product.
• Semi-Manufactured Product – The addition to raw rubber with chemicals and fillers, to impart desirable properties, is termed compounding. The material is however still malleable and plastic.
• Final product – As a result of the vulcanisation process, the rubber compound gets its elastic properties and gives shape to the final product.

There are many types of rubber products such as tyres, mats, moulded products, extruded products, etc. These rubber products have their unique process of manufacturing. However, most of the rubber products are processed with four major steps and are listed below.  

• Compounding –It is through compounding that the specific rubber is designed to satisfy a given application in terms of properties, cost, and processability. Rubber is always compounded with additives. Additives include fillers which act either to enhance the rubber’s mechanical properties (reinforcing fillers) or to extend the rubber to reduce cost (non-reinforcing fillers). Chemicals such as Sulphur are added for vulcanization.
• Mixing – The additives must be thoroughly mixed with the base rubber to achieve uniform dispersion of ingredients. If vulcanizing agents were present from the start of mixing, premature vulcanization would result in spoiling the product. To avoid premature vulcanization, a two-stage mixing process is usually deployed by the processing units:
  1. First Stage Mixing – Carbon Black and other non-vulcanizing additives are combined with the raw rubber. The term Master Batch is used for this first-stage mixture.
  2. Second Stage Mixing – After Stage 1 Mixing is completed, and time for cooling has been allowed, Vulcanizing Agents are added.
• Shaping –This process helps in providing the shape to the product in the required form. Shaping and related processes for rubber products can be divided into four basic categories:
  1. Extrusion – The extruder is used to give shape to the rubber compound through the die fixed. The rubber is fed from one end it comes out with the preformed shaped as per the die used. Some of the end product from this process includes hoses, rubber beadings, cables, etc.
  2. Calendering – Rubber is passed through a series of gaps of decreasing size made by a stand of rotating rolls. Rubber sheet thickness determined by final roll gap. Some of the end products include conveyor belts, bonding gum, etc. 
  3. Coating – This process is used when a Fabric is coated with rubber. The equipment is similar to calendering equipment. Some of the products made by this process are automobile tires, conveyor belts, inflatable rafts, and waterproof cloth tents and rain coats.
  4. Moulding and casting – Moulded rubber products include rubber mats, gaskets and seals, bush, chappal soles, straps and bottle stops. Also, many foamed rubber parts are produced by moulding. In addition, moulding is an important process in tyre Production as well. There are different types of moulding processes followed. The major types are as follows:  
     • Compression Moulding  
     • Transfer Moulding  
     • Injection Moulding
• Vulcanizing –Vulcanisation is generally a heating process that accomplishes cross-linking of elastomer molecules, so that the rubber becomes stiffer and stronger but retains extensibility. During the vulcanization process, the number of cross-links increases, the polymer becomes stiffer and behaves more and more like a thermosetting plastic (hard rubber).