wrapped spirally with a bandage of sheeting or light duck about three inches wide. Next the air bag is inflated to 40 or 50 pounds pressure, and the tire is placed in the heater and cured, the period of curing depending upon the size of the repair, varying from 30 minutes to one hour and at pressures of steam varying from 40 to Fig. 446.-Corner of Typical Repair Shop, Showing Practical Application of Vulcanizer on Both Tube and Casing Work. Notice Insertion of Air Bag in Casing Before Putting Same in Sectional Mold. 50 pounds. In curing special care must be taken and in this process many inexperienced operators make error. If a casing is cured too long the rubber will be too hard and will lose resiliency or life: while if the curing process is hastened and the tire is not properly heated, the rubber will be soft and repair unsatisfactory. After removing the tires from the heater they are allowed to cool about 30 minutes, then unwrapped and hung up for a day or two to set. Steam at a pressure of 40 pounds has a temperature of about 250 degrees Fahrenheit and is the heat commonly used in curing rubber. Dry Cure Methods.-There are two systems of vulcanizing when making sectional repairs or retreading, that best adapted for general use being the dry cure system in which the desired pressure for vulcanization is secured with pads instead of with an air bag and where the tire is cured by the application of heated elements rather than wrapping it and placing it in a steam oven. A number of molds used in the dry cure system and sold for use with the Haywood vulcanizer have been previously described and illustrated in connection with that outfit at Fig. 430. Additional appliances are shown at Fig. 448. That at A is known as an inside patch or relining mold and may be used in relining, patching or for drying out the interior of a casing before a reenforcement is started. On blowout work, especially of the larger and more difficult class, it is often necessary to apply two or three layers on the inside of a tire, and although considerable heat is conducted from the outside mold it is well to give the repair a twenty minute cure on the inside which is best accomplished with the form of mold shown at A. Solid pads and clamps are used in connection with the various types of Haywood molds for obtaining pressure on the curing stock. These pads conform to the curvature of the mold on which they are used. There are a number of advantages given for the pad and clamp system, over the air bag system. It is said that the properly built pads last indefinitely, whereas the air bags have a definite life and are subject to the uncertainty incidental to the use of pneumatic appliances. With a solid pad on one side of a repair and a substantial accurately machined mold on the other and with three to five heavy iron clamps drawing the two together it is possible to exert more pressure on the curing stock than by any other system and pressure is considered an essential to good work. The pad and clamp system is simple and easy to operate and there is nothing in its operation that calls for skilled labor. It not only produces considerable pressure on a repair but also localizes the heat to the portion being repaired. The method of using the pressure pad in making a repair on a defective tire bead is shown at Fig. 448, B. The side wall and bead mold is shown at C, while the appearance of a repaired portion of a casing having a long rim cut and blown side wall is shown at D. Retreading may be also easily accomplished by the dry cure method. The appearance of a tire needing retreading is clearly shown at Fig. 449, A. This is only practical if the layers of fabric are in good condition. The old tread is stripped off as previously de Fig. 448.-Molds for Use with Dry Cure Process of Vulcanizing. |