Seals are indispensable sealing devices used in automobiles, airplanes and other vehicles, construction machines, equipment at petrochemical plants, home appliances, and various other machines. MKC offers a wide variety of seal products of very high reliability, including oil seals, based on its constant and focused research on materials, workings, and design.
Rubber materials
Rubber materials are common materials of seals. It is necessary to select an appropriate material for each seal after careful consideration of its purposes and use environment.
A variety of rubber and resin materials used for seals are described below.
NBR Nitrile rubber (NBR)
Nitrile rubber is widely used as a sealing material for various products including automobiles, and has the best balance of performance, workability and price. This is the result of its polymer structure that allows the heat resistance and oil resistance to be improved when the acrylonitrile group is increased, and the cold resistance to be improved when the butadiene group is increased. Thus, the heat resistance, cold resistance and oil resistance can be varied widely by changing this copolymerization ratio.
In terms of material properties, it has excellent mechanical strength and compression set resistance, but it is slightly less resistant to ozone and heat than other materials.
Operating temperature range |
-20°C to +110°C (high nitrile), -40°C to +100°C (low nitrile) |
Applications |
Areas of application include oil seals, O rings, heat-resistant hoses, and belts. |
Hydrogenated nitrile rubber (HNBR)
Hydrogenated nitrile rubber (HNBR) is a material in which the double bond of butadiene, which had been a drawback of NBR, is highly hydrogenated in response to the recent demands for use under higher temperatures and a longer service life. It is superior to NBR in terms of heat resistance, oil resistance, mechanical strength, and compression set resistance; however, it has the disadvantages of lower cold resistance and higher cost.
More applications are expected in the future, and recently, an HNBR copolymerized with a third component, giving improved low temperature performance, has been developed.
Operating temperature range |
-35°C to +140°C |
Applications |
Areas of application include oil seals, O rings, heat-resistant hoses, and belts (special applications include lip seals and O rings for car air-conditioning systems). |
Acrylic rubber (ACM)
Since the main component is composed of acrylic acid esters and has a side chain of highly polar ester groups on the main chain of ethylene, ACM has superior oil resistance, heat resistance and ozone resistance compared to general-purpose diene rubber. It is widely used as a sealing material for lubricants.
On the other hand, water and ester-based synthetic oils cause softening with significant swelling. In addition, its mechanical strength is inferior to that of NBR and HNBR. Improvement in the molecular structure of the polymer has improved its cold resistance, and enabled the material to be applied to -40 ° C, and its applications are expected to expand. In addition, the resistance to compression set has been improved by the development of a new vulcanization system, and the possibility of applying it to O rings and gaskets has emerged.
Operating temperature range |
-30°C to +160°C |
Applications |
Areas of application include seals for transmissions, differential pinions and other driveline equipment, and bearing seals for railroad vehicles. |
Silicone rubber (VMQ)
A general-purpose silicone rubber with a methyl group bonded to a polysiloxane structure, VMQ has excellent heat and cold resistance as well as lubricant and water (LLC) resistance. In addition, it is easy to color because it is possible to design materials with low hardness.
On the other hand, the disadvantages are that the mechanical strength of the material is low and that the polymer structure is susceptible to hydrolysis by acids and alkalis that are added, for example, to lubricating oil, which can cause unexpected deterioration even within the applicable temperature range. Conventionally, VMQ has been widely used as a sealing material for engines, but because of this hydrolytic degradation, the material is increasingly being replaced by FKM.
Operating temperature range |
-70°C to +200°C |
Applications |
Areas of application include cylinder liner gaskets, electrical connector gaskets, and various waterproof gaskets. |
Fluororubber (FKM/VITON)
Fluororubber (FKM) has the highest heat, oil, and fuel oil resistance of all rubber materials, but it has disadvantages in terms of low temperature performance and cost. The material includes binary polymers consisting of vinylidene fluoride (VDF) and hexafluoropropylene (HFP), and ternary polymers consisting of VDF and HFP with tetrafluoroethylene (TFE) as an oil/fuel oil resistance improver. The fluorine content is approximately 66 to 70 weight percent. In general, the higher the fluorine content, the better the heat and oil resistance, but the worse the cold resistance.
Operating temperature range |
-30°C to +230°C |
Applications |
Areas of application include various engine related seals, fuel-related seals for injectors and other fuel-related items. |
Ethylene propylene rubber (EPDM)
Ethylene propylene rubber (EPDM) has a structure in which a small amount of unsaturated group having a double bond of the third component is introduced as a cross-linking site into a copolymer of ethylene and propylene, and since the material does not have a double bond in the polymer molecular chain, it has excellent ozone and heat resistance. In addition, it shows excellent resistance to water vapor, cold, and polar solutions including LLC.
The disadvantage is that because of its polymer structure, EPDM is not resistant to ordinary mineral oil-based lubricants.
Operating temperature range |
-50°C to +150°C |
Applications |
Areas of application includes gaskets for radiators, seals for brake fluids, and seals for water-based liquids.
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