Vulcanizing.—When in this condition and properly mixed with sulphur, it may be vulcanized, which destroys the stickiness, and makes it firm and elastic. Vulcanizing is a kind of baking process, the maximum heat being about 275 degrees, but generally less. The time required is from 12 to 15 minutes, dependent on the thickness of the mass to be vulcanized.
Fig. 15. Vulcanizer.
When the torn or cut portion of the tube or tire is carefully cleaned, it is filled with the plastic rubber, and the heater is applied. The heater, one form of which is shown in Fig. 15, is merely a shell with a heater connection, and this being partly filled with water, generates steam, the temperature of the shell being, of course, dependent on the pressure of the steam developed.
To repair the inner tube, it should be first rubbed with sand paper, and liquid rubber cement applied. When this becomes tacky apply the patch and dry. It is then ready to be vulcanized.
Oil as an Enemy of Tires.—All literature on the subject of tires give warnings as to the insidious character of oil, which deteriorates the rubber. Most manufacturers now make an oil proof quality, but the cheaper grades are not to be depended on.
The action of oil shows itself in several ways, but principally because it dissolves the rubber.
Non-Skidding Tires.—Various means are provided in the shape of tire treads to prevent skidding, the most important being vacuum cups, the herring-bone formation, and various ribbed or ridged surfaces. Nevertheless, for smooth asphalt pavements, chains or similar substitutes are found most satisfactory.
Sudden application of the brakes, or the sliding of wheels on hillsides or the skidding of the car in making short turns at too great speeds, are the most destructive things for tires, however good they may be.
Tires For City Use.—A tire which may be of good service for country roads, might not be available for city work. The tendency of many drivers is to hug the curb too closely, and the result is a wear on the side, which is its weakest point. It is like the side of a shoe, the upper of which can be readily worn through, whereas the sole will stand hard usage.