Manufacture of Rubber.

Kaipara and Waitemata Echo, 2 October 1914, Page 2

Manufacture of Rubber.

Through the introduction of rubber for the tyres of motor-cars and cycles the demand for this product has increased so rapidly that, had it not been for the further cultivation of trees from which rubber is produced, tyres would now cost at least four times the present price.

Three or four years ago the price of the raw material was 12s. per lb.; to-day it is 2s. lOd. for the same quality. "Millions of these trees have been planted in various parts of the world having a hot, humid climate, and as the trees do not produce sap until they are from five to seven years old, the supply will keep up with the demand. .On well-managed estates, the rubber, can now be prepared for Is. 3d. per lb. No doubt many people who enjoy the luxury of riding in a car fitted with rubber tyres will be interested to know how the raw material is obtained, and the way the tyres are made. Rubber is the sap of a tree which grows in a wild state in countries having hot, humid climates. The best qualities are produced from trees growing in the upper reaches of the Amazon river in South America, and are known as Para. These trees also grow wild in many other hot countries, but in no other country can they grow rubber equal to Para, which always commands the best price and leads the market. DRYING THE SAP. The trees have a smooth bark, with large, long leaves, and grow to about thirty-five feet high. To obtain the sap incisions are made in the bark, and cups are hung underneath to catch the sap which flows from the tree, and looks very much like milk. The sap is placed iv vessels holding large quantities. A piece of wood formed in the shape of a paddle is now dipped into the sap to cover the flat end, and is held in the smoke from a fire made from a special kind of wood. Tlii's dries or cures the sap, and tlv process is repeated until a large mass of rubber is formed on the end of the paddle. A cut is then made, and the paddle withdrawn, the mass being now known as a ham of Para. In cultivated rubber, the trees are treated in a similar manner to procure the sap, but instead of dipping and smoking, the sap is mixed with an acid, which causes it to curd ; the curds are pressed and run through rollers, which form it into long, thin sheets. When the rubber is received by the manufacturer, it is placed in hot water for a. few hours to soften, and is then run between strong iron rollers placed close together, upon which water is running continually. After bei':ig put through these rollers several times, all dirt and foreign matter being washed away, the rubber, now in long, thin sheets, is hung in a warm room to dry thoroughly, and is now known as masticated. The rubber is now put between large iron rollers, heated by steam, and is mixed with a number of ingredients, according to the. purpose for which it is required, and the price at which it is to be sold. Sulphur is the most important, for without this the rubber would not vulcanise ; litharge Lr-ing added to conduct the heat in a regular manner through the mixing during vulcanising : lime to absorb any mixture and prevent the tyre being porous ; whiting and byrates to add weight ; lime to win ten it : lamp black for dark and red antimony for red tyres. In the cheaper qualities recovered rubber is used. This is made from old tyres, inner tubes, etc. The waste is put between large; rollers., having the back roller running three times as quickly as the front, which reduces the waste to a powder. This powder, after being passed through magnets, which take out any metal it may contain, is put into a strong boiler or vulcanising j pan, into which steam is forced under pressure for from twelve to twenty hours. Tho powder is now desulphurised, and will mix with the new rubber and make tyres.

OONSTHIJ CITING A TYRE

When the rubber and ingredients have been thoroughly mixed together, it is run through large calenders into sheets about fifty feet long, three wide, and a sixteenth thick, cotton sheeting being placed | between to prevent the rubber from sticking together. A skilled workman th,en ( cuts from this sheet strips with which he builds up, upon prepared canvas, the tyro he requires. This is then placed into an iron mould, having the shape and markings of the complete tyre, bolted up tightly, heated for about one hour, and vilcanised. When taken out the tyre is ready to be put on the car. There have been many attempts to make artificial or synthetic rubber, several companies having been formed to exploit this article ; but so far they have not met with any great success, and as the natural product becomes cheaper as cultivation extends the incentive for producing synthetic rubber will no longer exist. Rubber substitutes have been made for years, and are used for mixing with the rubber to! cheapen it :>: . y are made from rape or linse, d oil. Eight ounces of chloride of sulphur are put into half a gallon of naptha : this is ,'oured into one gallon of oil, and in a few minutes the oil will have I changed into a spongy mass of j soft, flry, elastic material. —"Weekly Telegraph."