Rubber (material)

“ When ordinary vulcanized rubber is heated to 230° Centigrade, (446° F.) or until it melts, a permanently viscous product is obtained, and this substance, if mixed with emery and sulphur to a kind of paste, forms a material out of which the so-called agglomerated emery wheels or grinders may be140 formed, the mixed materials being next hardened or cured by the application of a steam heat. ”

“ The great lumps of gum are torn to pieces and washed free from gravel and dirt without going to powder, because owing to their elasticity they yield27 and as fast as torn apart the pieces tend to reunite. Again india rubber is mixed with pigments and vulcanizing reagents by a method practically one of grinding or masticating, but the material while it changes its shape, and by the admixture of the various ingredients becomes less strong or easier torn, still remains intact, as it welds together or coheres as fast as disintegrated. ”

“ This rolling of the mixed india rubber into sheets of definite thickness is done by special calendering rolls. The product is termed “mixed sheet.”
In the mixing rolls the incorporation of other material is often brought about. Zinc white, lead sulphide, antimony sulphide, chalk, clay, talc, barium sulphate, plaster of paris, zinc sulphide, lead sulphate, white lead, oxides of lead, magnesia, silica, form a list of ordinary mixing ingredients. These lower the cost of the finished material and are often serious adulterants. ”

“ By pressing the point of a knife against it the period of vulcanization can be told. Before the material is heated it is elastic and resists the pressure of the knife; as heat is applied it becomes soft like putty; as the heat increases it again stiffens and becomes quite elastic. At this point the press can be opened and the sheet and matrix can be taken out or the platen swung aside. On pulling or stripping the sheet from the matrix it will be found to reproduce the model in elastic india rubber to the minutest detail. ”

“ To carry out the process most simply the press if of metal may be placed upon a support over a gas burner or kerosene lamp, or even on a kitchen range or stove. It will in a few minutes become warm. The sheet of india rubber is now dusted off and is placed in the press upon the matrix. The platen of the press is screwed down upon it.
As the india rubber becomes hot it begins to soften and flow. By the action of the screw of the press it must be forced down from time to time as it softens. This drives the putty-like material into all the interstices of the mould. ”

“ The word elastic, in physics, is the name given to the tendency which a body exerts, when distorted, to return to its original shape. Rubber possesses more elasticity than any other material known, it being possible to stretch a piece of rubber cord to eight or nine times its original length without fracture. Rubber also possesses the added requisite of lightness and will store up more energy than any form of steel spring. ”

“ Plaster of paris or dental plaster mixed with dextrine or gum arabic water or the zinc oxychloride cement, already described, is to be recommended for the moulds. They should be made, if deep, in frames or “flasks” of tin, as plaster if unsupported is liable to split open when the rubber is forced home.
For many articles the hot press can be used. Such articles are mats and other thin flat pieces. The rubber stamp sheet is a good material for them. For thicker articles a thicker sheet can be used, and sheet of any gauge can be procured from the maker. ”

“ The quality of rubber is almost impossible of determination by brief inspection or by chemical analysis. The relative amount of pure gum and of cheaper composition may vary, or good material may be injured by defective vulcanization. ”

“ As the rubber joist sags between its ends, we observe that its upper half is compressed, and its lower half extended, the two effects though small being quite measurable. As we approach the central line, A B, this compression and tension gradually fall to zero; it is clear that only the uppermost and undermost layers [10] fully call forth the strength of the material, the inner layers doing so little that they may be removed with hardly any loss. ”

“ From some of the pans we see coolies lifting big lumps of a white substance that looks like very heavy dough. These are put into a machine which tears them into small pieces. A second machine, which has rollers covered with a diamond pattern, kneads the pieces together, and turns out a long strip of material which looks like tripe. When this has been passed two or three times through a third machine, which has smooth-faced rollers, a strip of “crêpe” rubber is ready to be taken to the drying-room or to the smoking-room. ”

“ India rubber can be so readily shaped in moulds and the latter are so readily made of plaster of paris that any one who is interested in such things will find endless amusement in working out different designs. ”

“ Air goods, such as cushions, beds, gas bags, and so forth, are made of textile fabrics which have been coated with mixed rubber either by the spreading process above described, or by means of heated rollers, the curing being then effected by steam heat. The manufacture of overshoes and fishing boots is an analogous process, only the canvas base is more thickly coated with a highly pigmented rubber of low quality. ”

“ It should be remembered, however, that no rubber can be made strong enough to be absolutely proof against tearing or puncturing by extremely sharp edges, such as stiff stubble, sharp-edged rocks, broken glass, etc. ”

“ Sheet rubber is made from the blocks of masticated gum by slicing. A machine is used for the purpose which carries a knife which works back and forth in the direction of its length at high speed, making two thousand cuts a minute. ”

“ Rubbers for large surfaces 23are usually made of soft old flannel, firmly and compactly put together somewhat in the form of a ball, and the more they possess softness and compactness, and are large and solid, the more quickly and satisfactorily will they polish extensive surfaces. Small pliable rubbers are usually employed for chairs or light frame-work. Perhaps for a beginner a rubber made of old flannel may be best, as it takes some little practice to obtain the necessary lightness of hand. ”

“ There are grounds for believing that raw rubber is superior in some respects to fully vulcanised rubber, if prepared without the addition of finely divided mineral substances which exert a toughening effect. ”

“ It will pay you to take some trouble to protect the rubber strands as far as possible. Lay them away in a can or jar in some cool, dry and dark place when they are not in use. Some boys cover the rubber with powdered chalk. When the surface of the rubber begins to granulate, its best days are over. Rubber is originally white in color, while the refining process gives it the familiar gray tone. ”

“ If the timber is too green, steam is formed as well as smoke, and the sheets of rubber may have a moist surface glaze.
Sun-Drying Sheet Rubber.—Among the first curious sights which impress the visitor or newcomer to this country is the spectacle of sheet rubber hanging in the sun on native holdings. From what one has learned of the extraordinary [148] care which must be exercised in all the processes of rubber preparation, one fails to understand how such rubber reaches the market without becoming tacky. ”

“ The manipulation of pure sheet rubber is simple, yet is liable to lead to disappointment. When two pieces are laid face to face and cut across with a sharp knife, or scissors, the edges will adhere with considerable tenacity. This may be increased by applying some thick solution of india rubber in a volatile solvent, and by manipulating the sheets so as to bring the entire surfaces of the cuts together. ”

“ And rubber makes a belt around the world in its natural as well as in its manufactured form. The rubber-bearing zone winds north and south of the equator through both hemispheres. In South America rubber is the latex of certain trees, in Africa of trees and vines. The best "wild" rubber still comes from Para in Brazil. It is gathered and prepared for shipment there today by the same methods the natives used four hundred years ago. The natives in their canoes follow the watercourses into the jungles. ”

“ In the hospital the doctors use surgical instruments that have important parts made of rubber, and many of the patients are provided with rubber necessaries, such as elastic87 stockings, made of rubber thread, for bad legs, and false teeth on a plate of vulcanite, which is chiefly rubber. Travellers take rubber baths and rubber cushions about with them. Golfers play with rubber balls. Machinery would be at a standstill without rubber belting. What an inconvenient world this must have been to live in less than a hundred years ago, when anything made of rubber was a novelty! ”

“ Out oozes a thickish white substance, some of which drops on to your fingers. Without a moment’s thought or hesitation, it comes natural to you to rub thumb against sticky fingers, whereupon the substance gradually solidifies, and at last breaks loose in the form of a tiny pellet. In a similarly simple way the mere savage discovered rubber hundreds of years ago ”

“ Block rubber is considered to possess certain advantages in securing a constant proportion of water, and in being satisfactory for transport. The best condition and form in which to export rubber cannot be regarded as settled. The probabilities are that in the end the production of a rubber as nearly as possible free from water and impurities and of constant composition will be realized as best meeting the requirements of the modern manufacturer. ”

“ It is on rubber that infants cut their teeth; after all the teeth are gone old age makes use of rubber in plates for false teeth. Ten million motorists and other millions of cyclists in the United States ride on rubber tires that are durable, noiseless and airtight. Balloons of rubber float aloft, and huge submarines plow their routes beneath the ocean's surface propelled by electricity stored in great rubber cells. Sheathed in rubber, the lightning makes a peaceful way through our homes, offices and factories, furnishing light and telephone service. ”

“ The earliest experiment in cultivating rubber was made only as far back as the seventies of last century. And it is only within the present century that cultivated rubber, or, as it is more generally called, “plantation rubber,” has become a power in the industrial world. ”

“ Rubber is a substance of so many important characteristics that its uses are countless. It is used for certain purposes because it stretches, for others because it is airtight and watertight, for others because it is a non-conductor of electricity, for others because it is shock-absorbing, and for others because it is adhesive. ”

“ The rubbers are heavier than the pacs and more protection to tender feet, but are more likely to tire the wearer, especially since rubber clings so fondly to all brush and weeds with which it comes in contact. ”

“ The sheets of rubber, after being dried, are taken to the “compound” room, where they are sprinkled with whiting, to prevent sticking, and weighed. Next they are taken into the calender room to a “mixer,” by [235] means of which the rubber is combined with other substances, which include sulphur, litharge, whiting, lampblack, tar, resin, lime, palm oil, and linseed oil. ”

“ Para rubber from Brazil generally contains about 15% of water, whilst “plantation” Para is usually nearly dry and contains 1% of water or less. It would appear, however, that the finest “wild” Para rubber as a rule possesses greater tensile strength than the “plantation” rubber. This has been ascribed by some to the presence in “wild” rubber of certain impurities derived either from the latex or introduced during the preparation of the rubber which are thought to enhance the physical properties of the caoutchouc. ”

“ No matter how much synthetic rubber may be manufactured or how many rubber trees are set out there is no danger of glutting the market, for as the price falls the uses of rubber become more numerous. One can think of a thousand ways in which rubber could be used if it were only cheap enough. ”

“ With regard to the method of collecting rubber by scraping a hole in the earth, and leaving the sap which trickled down into it to be dried by the natural heat of the earth and the air, I can only assure you that the white man found the aborigines “making” raw rubber in this way, so they must have invented the plan themselves. ”

“ Have the vulcanized rubber all ready, as made in long strips 3 inches wide and 1/8 of an inch thick, cut off the size of the intended stamp, remove the plaster cast from the type, and place both the cast and the rubber in a screw press, applying sufficient heat to thoroughly soften the rubber. ”

“ It must be recognised also that the machines are liable to considerable damage if extraneous substances are allowed to enter—for example, tapping-knives, stones, pieces of iron, spouts, etc., which are sometimes present in the loose scraps of rubber or shavings, owing to the carelessness of coolies. ”

“ Two strong spiral springs may be dropped over the bolts, the nuts being screwed on above them, or a powerful spring of flat brass or steel ribband bent into the shape of a shallow letter V may intervene between nuts and platen, the centre of the bend bearing against the centre of the platen. ”

“ In the house there are rubber washers on the taps, rubber rings on the stoppers of the ginger-beer bottles within the pantry, a teapot on the kitchen dresser has been mended with a rubber spout, and the children are playing with rubber balls, dolls, and toy balloons. ”