RUBBER TYPES

In these few pages devoted to rubber we shall sum up some characteristics and methods of employing rubber and its derivatives, without any pretension to a thorough scientific approach. Descriptions are going to be sketchy, but they may provide useful indications to people who are not well acquainted with such details; you shall therefore find a basic outline of the materials we most frequently utilize, the treatment they undergo and the products they are turned into, together with the applications for which they are suitable

Introduction

(an excerpt from a book by Khairi Nagdi, published in Italy by Tecniche Nuove as ‘Il Manuale della Gomma’)

lavorazioneRubber is definitely a peculiar material. Its most remarkable feature is its elasticity. You can stretch a rubber band until it becomes much longer than it was, yet it will not break; as you release it, it will immediately recover its original size and shape. Similarly, you can compress it, bend it or twist it; every time, once you leave it, it will take back its shape.

There are NO OTHER MATERIALS with the same degree of elasticity. This explains why rubber and rubber-like materials are called “ELASTOMERS“.
This, and countless other reasons, led

CHARLES GOODYEAR to say that:

“THERE IS NO OTHER SUBSTANCE WHOSE PROPERTIES CAUSE SO MUCH CURIOSITY, SURPRISE AND AMAZEMENT LIKE RUBBER”…..

TastSiElastomers also have a number of other valuable properties: most of them are hardly permeable to water and air and have good abrasion and tensile strength. Special types can even withstand temperatures in excess of 200°C. and even many of the most aggressive chemicals cannot eat into them. Other types preserve their elasticity at temperatures as low as about – 100°C.

The raw matter for making elastomers may be either NATURAL (Hevea) RUBBER or SYNTHETIC RUBBER. Rubber is then mixed with several chemical additives and hot cured (or ‘vulcanized’); cold curing is much less frequent.
Only after curing does the mixture acquire its typical elastic and mechanical properties such as strength, tensile strength and extensibility.

Hevea rubber

Natural rubber is obtained from the latex of some plants, among which Hevea Brasiliensis – hence the name. A sort of tree, the latter is the most important source of the product and is currently cultivated in large plantations in Brazil and the tropical belt of East Asia.
Further details are available under the heading “Did you know that…”.

Properties

  • Heat resistance: up to a maximum temperature of 80 – 90°C. After a long exposure to high temperatures natural rubber tends to harden temporarily, but this may be followed by softening because internal links break.
  • Resistance to low temperatures: up to about -55°C.
  • Electrical properties: Properly proportioned mixtures feature a satisfactory insulating effect.
  • Gas permeability: is high, so hevea rubber is not suitable when this is an issue.
  • Resistance to ozone, ageing and weathering: rather limited. However, can be improved adding anti-ageing substances and ozone blockers such as protective wax.
  • Resistence to chemicals:
  • good to below average to:
    • Water, alcohols, glycols and some peculiar ketones (e.g. ACETONE)
      Glycol-based brake fluids
      Silicone-based oil and grease
      Diluted aqueous solutions of not very aggressive acids, bases and salts
    • Does not resist to:Mineral oil and grease
      Fuels, such as gasoline, kerosene and Diesel fuel
      Hydrocabons like propane, butane, hexane, light gasoline, heptane, pentane.
      Hydrocarbons in general.
      Oxidizing agents like nitric and chromic acids, chlorine, bromine, etc.

Applications

  • All sorts of technical articles: hose, gaskets, membranes, rubber or metal/rubber spring elements, engine suspensions.
  • Tires, belt conveyors, rubber belts.
  • Other articles such as rubber boots, soles and heels, gloves, pacifiers (dummies), sponges, rubber threads, glues, etc.



   

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