Vehicle Body Materials.pdf 4h354w

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Sheet steel  Light alloys  Plastics  Textiles  Glass  Rubbers  Wood  Insulating materials 

VEHICLE BODY MATERIALS

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Sheet steel Thickness from 0.8 mm to 1.5 mm  Obtainable in sheets or rolls  Specific gravity of 7.8  Low carbon steel with an average carbon content of 0.8 per cent and it is therefore, a good welding material  Phosphorus and sulphur contaminations are, respectively 0.04 and 0.045 per cent

In recent years copper or nickel and chrome are often added to improve the anti-corrosive properties of sheet metal.  All sheets after hot rolling go through a pickling process which removes the iron oxides or scale from the surface since this scale is a poor electric conductor which would prevent spot welding.

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Light Alloys After pickling, the sheets are cold rolled.  The number of es determines an important quality of the sheets- the smoothness of the surface. 

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Aluminium alloys find wide application in the construction of vehicle bodies, both as castings and for steel metal application.  The additions to aluminium in the alloy are copper, magnesium, nickel and silicon.  The mechanical properties of aluminium alloys depend on heat treatment and ageing. 

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Plastics 

The sp.gravity of aluminium alloy is 2.7

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Those used for castings and sheet metal workings can be welded using a special flux.

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Welding lowers the strength of the material and this type of t is therefore confined to lightly loaded parts while rivets are used for ing s which are heavily loaded BV

Plastics can be divided into those obtained from  Large organic molecules  Condensation and addition polymerisation process 

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Its disadvantage is its high inflammability. Other materials based on cellulose are cellulose acetate and cellulose butyrate.  These are more expensive than cellulose nitrate but are non-inflammable, they are used for the same applications as celluloid.

Large organic molecules are used for obtaining cellulose ( commonly known as celluloid) which is used for decorative linings, anti glare glazing, various knobs and steering wheel facings.  Celluloid with addition of pigmentations has a very attractive finish. It also possesses good mechanical properties, such as high tensile and impact strength.

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TEXTILES The most important group of plastics obtained from condensation polymerization is the pheno-plasts, often known as Bakelite.  Depending on the polymerisation process, a material suitable for casting or moulding can be obtained.  Cast phenolic resins have the advantage of being insensitive to temperature and humidity changes, with good dimensional stabilitty and surface finish. 

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In older days, cotton-based fabrics have been the traditional materials used for the internal trim of a vehicle.  The life of material is quite short and it also absorbs dust and other impurities.  It has now been almost wholly replaced by plastics, of which the most popular are imitation leathers.  These consists of soft polyvinylchloride attached to a cotton fabric base. 

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GLASS    

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Toughened glass Laminated glass The glass used for window in vehicle bodies has a specific gravity of 3.5. Safety glass must be used in vehicle body structures so that injury will not be caused to engers in the event of breakage. This characteristic can be obtained by toughening the glass so that it disintegrates into small pieces with blunt edges. BV

Toughened glass cannot be cut or drilled.  This disadvantage dose not apply to laminated glass where layers of ordinary glass are glued together with a transparent foil which prevents splintering when breakage occurs. 

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Rubbers Synthetic rubber rather than natural rubber is used in vehicle body structure  Synthetic rubber has the advantage of being resistant to fuel oil and can, therefore, be used near fuel tank and in the engine compartment.  Foam rubber are also used in bodywork and are divided into the closed and open cell type. 

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The closed cell type does not absorb water and is therefore used for outside sealing. Open cell rubber is used for seat cushions and other soft furnishings inside the body. The hardness of rubber is measure in international rubber hardness degrees. 30 degree IRHD indicates a very soft rubber 100 degree IRHD indicates a harrdest rubber in use. BV

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wood

Insulating materials

Soft woods such as pine, spruce were used for floor boards and the load containing bodywork of lorries.  Semi-hard woods such as ash and beech were used for body framework.  Hard- woods like oak, chestnut for structural elements having a complicated shape.  Special species of timber, such as walnut, acacia, mahogany are still used today for dashboard finishes in luxury vehicles. 

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A low coefficient of thermo-conductivity and a high coefficient of vibration damping are required for insulating material  These coefficients are difficult to obtain simultaneously in any one material.  Good thermal insulating properties can be obtained in materials which have included air bubbles but these make the material nonelastic and elasticity is a necessary condition for vibration damping 

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In this situation there are two possibilities First the use of two materials, one of which has the appropriate damping qualities and second of which gives thermal insulation.  The use of material with compromise properties.  

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