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ABS - An Engineering Plastic

Plastics replace metals and alloys and permit the realisation of parts which
could never have been thought of before.

Many of the engineering applications do not require heat resistance higher
than 150 C and tensile strength above 700 kg/cm2, and thus engineering plastics
are well suited for these applications.

The word ABS plastics is derived from the first letter of each of the following three different monomers-


Acrylonitrile improves -

The tensile strength,
Heat resistance,
Chemical resistance Etc.

Butadiene improves the impact strength

And Styrene improves the processability

ABS plastics possess an excellent combination of mechanical,
thermal and chemical resistance.

In short ABS plastics are termed as -
Tough - Hard - Rigid materials.

The outstanding attribute of ABS is that by adjusting the composition of various monomers, it is possible to vary the mechanical properties considerably in terms of impact strength. But the increase in impact strength always bring down the tensile and flexural strength.

The impact strength of ABS is in the range of 10 to 60 kg.cm/cm notch. This value is higher than most of the engineering thermoplastics like acetal resin, nylons etc. It also exceeds that of metals like magnessium alloys, tin bronze alloys etc. This impact strength does not fall drastically with the fall in temperature. At low temperature also, ABS has good impact strength. The impact strength of ABS is not highly directional and hence there is a minimum tendency towards orientation during processing. Furthermore, the effect of section thickness on impact strength is not so predominant with ABS and this material is not as notch sensitive as certain types of PVC. Hence mouldings from ABS exhibit better impact strength in all directions.

The ultimate tensile strength of ABS is generally in the range of 350 to 550 kg/cm2 at normal temperature. This tensile strength is retained over a wide range of temperatures. The retention of a fairly high tensile strength at forming temperature makes ABS sheet a good vacuum forming material.

The hardness of ABS is rockwell R 80 to R 114. This is a measure indicative of scratch resistance. The higher the number, the harder the material.

Thus ABS offers a good balance of impact strength, tensible strength, flexural modulus, and hardness, while creep at stress level below 150 kg/cm2 is negligible. This characteric imparts high resistance to dimensional changes under loads and enables different parts of the assembly to retain tolerances and tight fit.

It is probably the combination of these properties that makes ABS such a stand out. There are thermoplastics that are stiffer but their impact strength is lower, while there are other thermoplastics that have higher impact strength but lower stiffness.

As regards to heat resistance, the Vicat softening point of ABS plastics ranges from 90 C to 100 C. There are high heat resistance grades available having heat resistant temperature as high as 115 C. The coefficient of thermal expansion of ABS is approximately ten times higher than metal and it is 9 x 10-5 cm/cmC.

The electrical properties of ABS are unaffected by temperature and humidity.Its dielectric constant is sufficiently good to allow ABS to be used in electrical applications like coil formers, connectors etc.

Some plastic materials absorb certain quantities of moisture and change their mechanical properties with the quantity of moisture absorbed. Also the dimensions of such materials change with the quantity of moisture absorbed. However, in case of ABS, the moisture absorbed does not affect the properties of the finished item as well as the dimensional stability. Moisture absorption in case of ABS plastics is less than one percent.

As regards to flame and fire resistance, ABS plastics are slow burning and do not drip while burning. The flame retarding grades of ABS are now developed and available. These flame retarding grades comply with the international norms required by the electric, electronic and building industries. The major outlet for the flame retarding ABS grade is in the manufacture of T.V. housings and back, in electrical, electronic applications like junction and switch boxes, in housings for electronic equipments, etc.

ABS Plastics have better chemical resistance. They are resistant to Aqueous Acids, Alkalies, Salts, Concentrated Hydrochloric and Phosphoric Acids, Alcohols and Oils. ABS Plastics are swollen by Glacial Acetic Acid, Carbon Tetrachloride and Aromatic Hydrocarbons and are attacked by concentrated Sulfuric and Nitric Acids. They are soluble in Esters, Ketone aned Ethylene Dichloride.

The Introduction of proper ABS formulations has been made possible by the Electroplating of ABS - a commercial and technological success. Being an Engineering plastic it replaces many metals and alloys like Zinc die casting. ABS plastic parts can be injection moulded at a lower cost and with greater freedom in design as compared to die-cast parts. They are corrosion resistant and comparatively lower in weight. The final polishing and buffing process of die-cast metal parts are eliminated for electroplated ABS plastic parts. The Electroplated ABS parts show improvement in properties like surface hardness, tensile and flexural strength, heat resistance, chemical resistance, weather resistance etc., over non-plated ABS parts. The plated ABS parts replace die-cast metal parts in industries such as bath-room fittings and hardwares, radios and television, refrigerators, fans, measuring tapes, novelty articles, automotive, umbrella etc.

Thus the complete range of mechanical, thermal and electrical properties have made ABS a versatile engineering plastic.


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