Balata

A product analogous to rubber, but resembling gutta percha in its chemical and physical properties. Largely used in the un-vulcanised condition for the manufacture of golf ball covers and for transmission belting.

Blooming

A whitish, opaque appearance occasionally seen on rubber goods, due to the formation of a layer of minute sulphur crystals on the surface.

Calendering

The manufacturing process used to prepare smooth sheets of uniform thickness from compounded but unvulcanised rubber, or to apply thin coatings of rubber to textile fabrics. The calender, the machine used for the purpose, consists of three or four adjustable heavy steel rolls in a strong vertical frame.

Caoutchouc-See Rubber.

Coagulation

The process by which the rubber is separated from the water constituents of the latex, usually by the addition of a small proportion of acetic acid.

Cold Cure

A process in which vulcanisation is effected by dipping the raw rubber in a dilute solution of sulphur chloi ide, usually in carbon disulphide. 1 his process is suitable only for thin films of rubber. A variant of the process is the 4i vapour cure," in which the vulcanisation is effected in a large chamber into which a small quantity of sulphur chloride is vapour-ised.

Compounding

Also known as 41 mixing." The process in which i the vulcanising ingredients and the substances added to impart toughness, colour, or any other desired modification in physical properties, are admixed with the masticated rubber.

Compounding Ingrcdienls

The ingredients added to rubber for promoting vulcanisation, colouring, or modifying the physical properties of the final product. They may be roughly classified as pigments, reinforcing ingredients, fillers, softeners, and accelerators.

Crepe,- See Rubber.

Curing

See Vulcanisat ion.

Dough - See Spreading.

Dry Heal Cure

A process in which vulcanisation i< effected by heating the compounded rubber in a hot-air chamber. The presence of litharge or a powerful organic accelerator in the mixing is essential, and the process is confined mainly to the production of boots, shoes, and black calendered garments (see Vulcanisation).

Ebonite

See Vulcanite.

Extruding

See Tubing.

Faclice

See Substitute.

Filler

- A compounding ingredient added for the purpose of cheapening the product rather than modifying its physical proper ties.

Forcing

See Tubing.

Freezing

A temporary change which takes place in raw and vulcanised rubber when stored for considerable periods at low temperatures, the product becoming relatively hard and inelastic. The effect is shown only to a slight degree by vulcanised articles, and disappears after warming for a short lime.

Gas Cure (Peacheit Process)

In this process rubber is vulcanised by successive treatments wit h hydrogen sulphide and sulphur dioxide, the sulphur liberated by the inter-action of the two gases effecting the vulcanisation.

Gutta Percha

A product analogous to rubber in its chemical nature, but tougher and hornier in character. Largely employed in the unvulcanised condition for electrical work and for utensils used for chemical purposes.

Hard Rubber

See Vulcanite.

Inlia Rubber

See Rubber.

Latex

A milky juice obtained from the bark of certain trees and other plants, the most important being hevea braziliensis, which furnishes the bulk of the world's supply of raw rubber. Latex consists of a suspension of microscopic rubber particles in a watery liquid.

Mastication Or Milling

A process employed to render raw rubber plastic, so as to facilitate compounding and the subsequent mechanical operations, such as moulding, tubing, and calendering.

Mixing

See "Compounding.

Open Steam Cure

The method of vulcanisation in which the compounded rubber is heated by being placed in an autoclave, which is then filled with steam (see Vulcanisation).

Para

See Rubber.

Pear.hetj Process.-See Gas Cure.

Perishing

The last stage in the process of ageing in vulcanised rubber, the rubber becoming oxidised with the formation of resinous substances and losing its characteristic elastic properties. The term is generally used to denote the premature failure of rubber goods due to over-vulcanisation, contact with copper, exposure to sunlight and high temperatures, or a combination of such influences.

Pigment

This term, in addition to its usual meaning, is sometimes used as a name for inorganic compounding ingredients in general.

Press Cure

The methods of vulcanisation in which the compounded rubber, usually contained in a mould, is placed between the steam-heated platens of a press.

Reclaimed Rubber Or Reclaim

A product obtained from waste vulcanised rubber by thorough cleansing and softening by heat and the addition of softeners. It is insoluble in the solvents which dissolve raw rubber, and is much inferior to the latter in physical properties, but forms a useful ingredient for the manufacture of certain goods not required to resist distortion.

Reinforcing Ingredients- -Finely divided substances, such as zinc oxide and gas black (a form of carbon), which are incorporated in rubber to render it tougher and increase its capacity for storing energy when subjected to mechanical deformation.

Resins

Natural constituents of raw rubber, usually representing some three per cent, of the total.

They facilitate the vulcanisation of the rubber and retard the perishing of the vulcanised material.

Rubber

Also known as india rubber, caoutchouc (France), and kautschuk, or gummi (Germany). The name indicates its first technical application, namely, the removal of pencil marks. Rubber is a hydrocarbon possessing unique properties, obtained by the coagulation or evaporation of latex, and contains small proportions of resins, proteins, sugars, and mineral substances, varying according to the botanic origin of the latex and the method of preparation. The bulk of the world's supply is derived from plantations in the East, and is mainly marketed in the forms known as smoked sheet, crepe, and amber blanket. The native-prepared product, known as para, from indigenous trees in Brazil, is still employed to a considerable extent for special purposes. Smoked Sheet.-See Rubber.

Softeners

Substances added to rubber mixings during the compounding process to render the product more plastic and thereby to facilitate the incorporation of compounding ingredients and the subsequent manufacturing operations.