The materials that can stretch at least doubles of original dimensions at room temperature, and when the strength released, return to its approximate original dimensions and shape are defined as elastomer. Elastomers are obtained the result of a chemical change of the rubber materials (cross linking or vulcanization). The rubber is the polymer having the property that can make the cross-link, but not cross-linked normally. The materials show both the fluidity and the flexibility property by their nature under temperature and pressure at the particular time.
The cross-linking can be clarified with the vulcanization, which are the process fetching to the state having elastic properties irreversibly by changing the rubber chemical structure.
1.1. Acrilo Nitrile Butadiene Rubber (NBR)
NBR is the rubber material having widespread use and proposed for a big part of sealing products in the industrial application. NBR is the polymer including Acrylo Nitrile (ACN)-Butadiene.
In the industry, this polymer type gives well-resistance against the aliphatic hydrocarbons (Propane, Butane, Petroleum), the mineral oil (lubricants, Group H, HL, HLP type oils), the non-flammable hydraulic oils and grease (HFA, HFB, HFC), the vegetable and animal grease oils and diesel. Acrylo Nitrile (ACN) rate is to change between 18 and 50. With increasing of ACN rate;
- The swelling resistance increases against the mineral oil, grease and the fuel,
- Flexibility property increases,
- Gas permeability decreases,
- Rebound resilience increases,
Yet, the low temperature property improves with decreasing of ACN rate. Kauflex® have skill to make NBR compound that changing to different applications and specification. Acrylo Nitrile (ACN) rate used in NBR compound is to change between 18 and 50.
Standard NBR compound is proposed to use between -30 °C and +105 °C. It can be used for short range operations up to +130°C.
1.2. Polyacrylic Rubber (ACM)
ACM is a polymer including ethyl acrylate or butyl acrylate. ACM rubber gives better temperature resistance according to NBR rubber. ACM is preferred against the oils containing an additive and in the insufficient situation at high temperature ranges for seal application based on NBR. Air aging and ozone resistance is very good. The swelling resistance is efficient for mineral oils and additive materials (.motor, reductor, gearbox oils).
Its resistance is not proper against the aromatic and chlorinated hydrocarbons, the alcohol, the brake oils, oils with low flash point, hot water, the steam, acid, alkaline and amines. ACM performance on shaft is worse than NBR (Slothful Material). It is proposed to use between -25 °C and +150°C.
1.3. Ethylene Acrylic Rubber (AEM)
AEM is polymer including ethylene, methyl acrylate and carboxyl. AEM have better heat resistance than ACM and is between FKM and ACM. It presents well-swelling resistance against mineral oils with additive, paraffin, water and cooler. Despite that, it is bad the resistance to the gear box oils, aromatics, brake oils, acids.
It is proposed to use between-40 °C and +160°C.
1.4. Fluorocarbon Rubber (FKM)
FKM, can occur from vinylidene fluoride and one or more monomers such as hexafluoropropylene (HFP), tetrafluoroethylene (TFE), 1-hydropentaflourpropylene (HFPE), perfluouro methyl vinyl ether (FMVE). For instance,VDF/HFP co-polymer or VDF/HFP/TPE ter-polymer. Viton® or Flourel® is known as trade name. FKM is material having high temperature and chemical resistance and low gas permeability. In the vacuum systems it gives good result. Having good resistance to the ozone, the weather, the light, the flame.
Amines, ether, keton, concentred alcalin and freon affects significantly the FKM. Its resistance against every type grease, aromatic and the aliphatic hydrocarbons, the aircraft engine oil, mineral oils, the corrosive oils, fuels is well enough.
It is suggested to use between -30 °C and +225°C.
1.5. Silicone Rubber (VMQ)
VMQ, is rubber type including groups of materials in which vinyl-methyl. Silicones are to maintain characteristics a wide temperature range. Its high and low temperature resistance is good and it has good insulating (low dielectric coefficient). They also have good ozone and weather resistance. At the room temperature, its gas permeability is better than other elastomer. This condition is especially demanded in the thin-walled diaphragms.
It can serve up to +100°C in hot water, but at higher temperatures its structure is disturbed. Also, salt water and alcohol resistance is good. Esters, aromatic and the aliphatic hydrocarbons, acid and alkaline resistance are bad.
While used between-60° C and +200°C, it has the specified type VMQ that can withstand up to +300°C.
1.6. Styrene Butadiene Rubber (SBR)
SBR is polymer including styrene and butadiene monomers. If styrene rate increases the hardness, If the butadiene rate increases, the flexibility increases. Elasticity and abrasion resistance is good. It is preferred for hydraulic brake application.
In the places, where Inorganic and organic acids, bases, ketone, aldehyde, alcohol, water, brake oils, glycol esters, can be used.
It is proposed to use between-50 °C and +100°C.
1.7. Hydrogenated Acrilo Nitrile Butadiene Rubber (HNBR)
HNBR is a polymer type obtained with adding the hydrogen to nondouble-bonded butadiene of NBR rubber. Chemical resistance is similar to NBR. HNBR vulcanized with peroxide, reaches to high operation temperature. Especially, it is preferred in automotive sector and hydraulic application and in the places where the tidal movement.
It is proposed to use between-30 °C and +150°C.
1.8. Polychloroprene (CR)
CR is characterized to very good chemical, aging, weather, ozone and flame resistance.
its resistance is good against the mineral oil with high aniline, greases, a lot of the cooler and water, the mineral oils, aliphatic hydrocarbons. Proper for the places requiring resistance both oils and weather and ozone. In the applications such as the tie rod end protection bellows are choose.
It is proposed to use between-45 °C and +100°C.
1.9. Natural Rubber (NR)
NR, the polymer of polyisoprene, after the vulcanization it present the high strength, flexibility and low temperature resistance. Due to the good mechanical properties, NB is asked in the places such as vibration wedges, diaphragms, the mould pieces. As is evident from it’s name, it is natural and produced from the rubber tree milk. Having resistance to dilute acid and base, also the dilute alcohol and water at low temperature. But, the mineral oils, greases, hydrocarbons and the fuel have a negative effect upon it.
It is proposed to use between-60 °C and +90°C.
1.10. Ethylene Propylene Diene Rubber (EPDM)
EPDM is a polymer including ethylene, propylene and a small amount diene. The oil seals made from EPDM, are preferred for the washing machines, dishwashers and plumbing fixtures. Also, it’s used in the hydraulic systems HFC, HFD group non-flammable hydraulic oils and hydraulic brake oils. Exhibiting excellent resistance to hot water and steam and ozone. Not having the resistance against the mineral oils, greases, fuel oil and hydrocarbons.
It is proposed to use between-50 °C and +150°C
2. Thermoplastic Elastomers (TPE)
TPE having elastomeric structure, is polymeric materials with complex structure but can be shaped and handled like the plastic. The structure occurs from minimum two type polymer and tripleblock of these polymers. Two of these blocks located in the edge is shorter, blocks where located in the middle are longer and elastomeric. For example, In an thermoplastic elastomer such as styrene-butadiene-styrene type, butadiene is elastomeric and styrene is plastic. At the high temperature, the polystyrene melts, the material takes fluent a state and it gets shape of the mold, when flowed into the mold. When cooled, the styrene hardens again and the shape happens the permanent. As a result, after the curing time, any chemical change is not to be, only the physical change is to be. With the recycle it can again be used. Polyester elastomers are used support ring and as the rear adapter to seals in the hydraulic and the pneumatic systems the nature of it. The most important property of the materials excellent resistance to the hydraulic oils and high viscosity strength. These materials having;
- High tensile strength,
- High tensile module,
- Good elasticity,
- Resistance to solvents,
- Resistance to the acid, aliphatic hydrocarbons, and alkaline solution and various grease and oils.
TPE-E is prefered to use in the hydraulic and the pneumatic systems due to elastomeric property.
It is proposed to use between-40 °C and +120°C.
This polymer type is named as thermoplastics or engineering plastics. Today, Thermoplastic materials are used in many different areas for a lot of different application including the seals materials.
The thermoplastics that the mechanic properties is strong, (e.i; polyamide, acetal resin etc), while used together with the metal materials, the soft thermoplastics (polyethylene, PTFE etc.) is to compete with the elastomers in various application. It’s not concerned a structure that has the cross linking as the elastomers. Therefore, its the compression set presents low performance according to the elastomers. Generally, the plastomers used in the seals materials are the polyacetal, polyamide and PTFE (Teflon®) materials.
3.1. Poliüretan (PU)
PU, is formed by reacting a di- or poly isocyanate with an polyol and a polymer having the high molecule weight expressed with size of urethane group. PU exhibits some characteristic features at particular temperature limits. That is;
- High elongation at break, tear strength an abrasion resistance,
- Very well airand ozone resistance,
- Mineral oils, greases, water and water-oil mixtures, the aliphatic hydrocarbons resistance,
It is suggested to use between -30 °C and +100°C.
3.2. Polytetrafluoroethylene (PTFE)
PTFE is a polytetrafluoroethylene polymer. This the nonelastic material attract the attention the following properties;
- The surface tension is lower than all the solid material and it not adhere to the any material. Static and dynamic friction coefficient is almost same. The friction coefficient of it is like the ice. The PTFE can be used as the unoxidized up to +200 oC
- The chemical resistance of it is better than the elastomer and the thermoplastics. Excellent the swelling resistance in any environment.
- Virgin PTFE is very good insulator due to low dielectric coefficient.
- The operation temperature is between -200oC ile +260oC. Because it still can hold the elastic property in the -200oC operation temperature, PTFE can be utilized in the application that the sealing is requested, and in the production and the processes made in very low temperatures. For example, for the storage and the transport of liquid gas.
- PTFE is low the abrasion resistance and the thermal conductivity.
- The elasticity is worse than the elastomeric materials. When designing the seals, PTFE is to be used as with the graphite, glass fiber, bronze, and carbon. In this way, the properties requested according to the the application condition can optimally be obtained.
3.3 Polyacetal (POM)
POM is a thermoplastic that well mechanical load resistance. Hence, it’s used as the bearing material in the hydraulic and the pneumatic systems or the support ring. According to usage, there are types such as the virgin or with the glass fiber. in the mineral oils, HFA, HFB, it can confidently be applied. With the glass fiber type, High pressure resistance can be obtained.
Having the operation temperature between-40 °C and +100 °C and in the intermittent operation can be used up to +140°C.
3.4. Poliamide (PA)
PA is a material with high strength. It has the properties such as the abrasion resistance, damping capacity, a hard material structure and ability to work the dry. Therefore, it is especially used in various machines. For instance, the gear, the flat bearing elements, the guide strips, wedges, etc. it’s used as the bearing material and the support ring in the hydraulic and the pneumatic systems like the Polyacetal. Depending on the places used, the mechanical properties and the operation temperature range can be changed. There are the virgin and the glass fiber reinforced types.
- Good mechanical strength,
- Good the acid and the bases resistance in the particular situations,
- Good X-Ray-Gamma and UV resistance.
It is suggested to use between -40 °C and +85 °C.