The Inner Tube of Rubber Tires
Hidden from sight, the inner tube usually does not get the recognition from the tire users its importance deserves. In the life of the tire, the inner tube must, despite its elasticity and the peculiar demands which are put upon it, be practically as strong and durable as the casing. When inflated the tube contains an air pressure representing energy sufficient to run a locomotive. The slightest weakness, an air bubble, or imperfect joint and the tube is doomed. In its manufacture only the best of rubber and workmanship should be employed. Made of up-river fine para, no foreign matter except the trace of sulphur is needed for curing, or in the case of the red tube, a little antimony is used in Firestone tubes. The advantage of the finest pure rubber tube lies in its superior toughness, its greater expansive and contracting powers, its density of texture and its ability to withstand heat. Thin sheets of rubber arc wrapped lengthwise layer on layer on pipe-like cores. Scrutinized carefully while the process of building is going on, the tube when passed is certain to be free of flaws. Not a trace of an air bubble or blemish of any kind is permitted to get by. When completed, the tube, still on the core, is swathed in canvas strips and cured, the several layers of rubber merging into one. After the cure the tube is stripped from the mold, being turned inside out in the process. The valve stem is dropped in and the ends of the tube vulcanized together, but not until it is again inspected and gauged for correct thickness and weight of the walls. The valve stem is fitted into place and the tube is inflated and tested for any leaks.