Application of Rubber in Automobile

Special rubber has replaced ordinary rubber products in many fields, especially in the automobile industry, with its special and excellent performance. According to the specific requirements of different rubber parts of automobiles, different special rubber materials should be selected accordingly. (69)
Various high-pressure rubber hoses for automobiles are gradually adopting special rubber to meet higher performance requirements

There are many rubber parts used in automobiles and they play different roles in automobile systems. For example, tape is used for motion transmission, seals are used to support radial or reciprocating motion parts, gaskets and O-rings are used to seal oil or fuel, rubber hoses are used to transport liquids or gases, and diaphragms are used to control fluids or gases. The requirements for the type and performance of the rubber used are different due to different uses. The material shall be selected according to its flame resistance, oil resistance, heat resistance, low temperature flexibility and sealing capacity. Sometimes, different materials may be selected for the same device, mainly depending on the application temperature, fuel and oil types and the design requirements of the vehicle.

Automobile engine

Timing belt

The timing belt is used to drive the crankshaft cam to run synchronously. Compared with the metal chain, the synchronous belt can effectively reduce the contact noise between the belt and the sprocket, does not need lubrication, and has the characteristics of lightweight. At the same time, due to its flexibility, it can also be used for multi axis drive. In Japan, more than 70% of cars use synchronous belts, while in Europe, more than 80% use synchronous belts.

Previously, the rubber synchronous belt was mainly covered with neoprene (CR). However, hydrogenated butadiene rubber (HNBR) has more superior performance, so it has been widely used in automotive synchronous belts. The comprehensive performance of HNBR is superior to that of CR, and it has stable complex modulus, good low-temperature performance, heat resistance and ozone resistance, excellent flex resistance and good oil resistance in a wide temperature range.

In the tape function test, the heat resistance level of HNBR is 40 ° C higher than that of CR covering rubber under the same operation time. At the same time, the service life of HNBR is twice that of CR, and its durability exceeds 100000 km.

Seals and gaskets

The sealing system is mainly used to prevent leakage of liquid or other materials. Sometimes metal, plastic or fabric is used to make seals, but more often rubber is used. When petroleum series lubricating oils are used for engines and transmission systems, the sealing materials are generally butadiene rubber (NBR), acrylate rubber (ACM), silicone rubber (VMQ) or fluororubber (FPM).

Engine oil requires long service life, low viscosity (oil saving), smooth lubrication under high temperature, etc. Therefore, engine oil usually contains a variety of additives. NBR will be seriously damaged in the environment of purifying agent, anti-aging agent and anti-wear agent, while HNBR, FPM and ACM can maintain good strength performance after being immersed in oil containing additives at high temperature for a long time. Although the tensile strength of ACM is low, it can maintain stable performance in all additives except alkyl phosphate and lead naphthenate. The physical properties of FPM are not high, but it has excellent heat resistance and oil resistance. The tensile strength of HNBR is the highest among these rubbers, and its resistance to various additives is also the best. Only zinc dithiophosphate has a slight impact on it.

For a long time, the automobile industry has been using NBR and cork rubber to make gaskets for engines, but now it mainly uses ACM and VMQ to meet the requirements of heat resistance, sealing capacity and compression durability. Under normal conditions, VMQ is better than ACM in low temperature flexibility and heat resistance, but VMQ will soften significantly after being soaked in engine oil for a long time. In contrast, FPM and ACM have no deterioration.

Oil radiator hose and air delivery pipe

The rubber tube of lubricating oil radiator and the rubber tube of oil radiator are mainly composed of inner rubber NBR and outer rubber CR. In order to improve the heat resistance, chlorinated ether rubber (ECO) and chlorinated polyethylene (CM) were also used, and now ACM and AEM are widely used. The air delivery pipe and intake pipe must have good flexibility, weather resistance, shock absorption, vacuum collapse resistance and oil resistance. A variety of elastomers (such as CR, NBR/PVC, EPDM, ECO, CM, ACM) and thermoplastic elastomers (such as blends of polyester, polypropylene and EPDM) are selected for this purpose, based on different design requirements for different vehicles.

Fuel system and hydraulic system

Rubber hose for fuel system

The fuel system is generally composed of fuel tank, filter, pump and connecting pipe. The fuel delivery pipe can be made of steel, thermoplastic (usually polyamine) or reinforced rubber.

1) Fuel hose

There are currently two types of fuel supply systems: carburetor and fuel injection pump. NBR or NBR/PVC (PB) has always been used as the inner glue and CR as the outer glue for the rubber hose used in the carburetor system. The situation did not change until the gasoline with high aromatic component content was put into use. Gasoline with high aromatic component content will cause cracking of inner NBR, which can be solved by using liquid NBR as a plasticizer without extraction.

As the temperature of the engine room rises, the outer glue of the fuel hose has changed from CR to chlorosulfonated polyethylene (CSM) or trimer of epichlorohydrin ethylene oxide allyl glycidyl ether (GECO), and the ozone resistance and heat resistance of GECO can be improved by increasing the content of allyl glycidyl ether (AGE) in GECO. GECO is now widely used as the outer rubber of fuel rubber tube. Compared with CR and CSM, it still has excellent dynamic ozone resistance after being extracted with test oil.

In the fuel injection system, there are mainly two types of rubber hoses: the high-pressure rubber hose between the oil pump and the injection valve, and the low-pressure rubber hose between the pressure regulator and the oil tank. The inner rubber of high-pressure rubber hose adopts FPM, because it has low gasoline permeability, good oxidation gasoline resistance and excellent heat resistance. FPM or HNBR shall be used for the inner layer of low-pressure rubber hose. Compared with FPM, HNBR has poor fuel permeability, but its price is low. Compared with NBR, HNBR has higher tensile strength and better comprehensive physical properties after soaking in oxidized gasoline.

2) Oil filler rubber tube

The filler hose connecting the filler cap and the oil tank is always made of PB. Recently, FPM trimer inner rubber and GECO outer rubber injection hose have been developed to further reduce gasoline permeability. This is critical in the context of increasingly stringent volatile regulations.

3) Volatile rubber hose

The volatile rubber tube is made of the same material as the rubber tube used for the fuel system of the carburetor, that is, NBR is generally used as the inner rubber and CR as the outer rubber.

4) Control rubber tube (connecting vacuum control valve and suction manifold)

Three kinds of rubber materials are used for the control hose, depending on the use temperature. With the increase of working temperature, the material changes from NBR/CR to GECO until ACM. A new type of ACM compound has been developed, which has good comprehensive physical properties.

Seals and diaphragms for fuel systems

The fuel pump diaphragm is a typical fuel pump structure in the carburetor system. In order to withstand the thermal impact of the engine, the diaphragm must not only have good durability in gasoline, but also have high heat resistance. The materials used to be NBR and PB have been changed to HNBR and FPM, because oxidation resistant gasoline is required. For seals, NBR, PB, HNBR and FPM can be used for shock absorbers, insulators and oil seals. The material used depends on the specific use temperature.

Rubber products for hydraulic steering system

Hydraulic steering system has two kinds of rubber hoses: high-pressure rubber hose between oil pump and gearbox; Low pressure rubber hose between gearbox and oil tank. In the past, NBR and CR were used as the inner layer and outer layer of the two rubber hoses respectively. ACM or CSM is now used for the inner layer of low-pressure rubber hose to improve its heat resistance. The new high-pressure rubber hose composed of HNBR inner layer rubber and CSM outer layer rubber has better heat resistance than the previous rubber hose.

Rubber products for air conditioning systems

When the refrigerant is CFC12, the inner rubber of the rubber tube is NBR and the outer rubber is CR. Now the refrigerant and lubricating oil have changed, requiring the use of better materials, and the rubber hose has changed from two layers to three layers. The inner layer has high heat resistance and low permeability, the middle layer has low permeability, and the outer layer has high heat resistance and weather resistance. The currently used rubber hoses are three layers of rubber hoses, namely, PA and EPDM blends, IIR and EPDM or modified PA blends, IIR and chlorinated IIR (CIIR).

Rubber materials used for air conditioning compressor seals need to have high solvent resistance, both CFC-12 and HFC-134a. No single rubber material can withstand two refrigerants at the same time, but the blend material can meet this requirement. This material is called RBR (material resistant to two refrigerants).

The automobile industry has put forward higher and higher requirements for various parts. Special rubber with heat resistance, long service life, low permeability and high wear resistance will be widely used in the automobile industry.

Post time: Nov-09-2022