VULCANIZING.
The riding public as a rule knows very little about the process of vulcanization, and very often have objected to the time taken and the charges made by repairers for vulcanizing, and perhaps after reading what is here stated as to the necessary operations in vulcanization of a tire the riding public will be more gracious as regards the time allowed and be more willing to pay the charges asked for vulcanization.
The first principle to be employed to vulcanize a tire is cleanliness. A successful result cannot be expected if the hands of the operator are oily or greasy. Four ingredients are used in the vulcanization process, viz., naphtha, vulcanizing cement, friction or coated fabric and pure gum. Naphtha is used to clean the surfaces to be united. Vulcanizing cement is used to cement the surfaces to be united firmly. Friction or coated fabric is employed as a strain resisting agent, and the pure gum is used to make the hole airtight, and also to make the rubber cover as it was originally. The vulcanizing cement is nothing but dissolved pure gum of the same consistency as the pure gum.
The first operation in vulcanizing a tire is to cut a round hole in the tire where the puncture is, making the hole as small as possible; then the rubber cover which is around the hole is peeled off, so that the canvas of the tire for about three-quarters of an inch around the hole is exposed. Then the inside, as well as the outside of the tire is cleaned thoroughly with a clean rag saturated with naphtha; the naphtha is allowed to evaporate, and then the vulcanizing cement is used in the same way. The cement is allowed to dry, and when dry the cementing operation is repeated, so as to give the surfaces two coats of cement. It is important that both coats of cement are thoroughly dry before inserting the rubber patch, and before doing so soapstone is rubbed on the underside of the patch. Care should be taken not to have any soapstone on the part of the patch which is to be united to the tire. The best way to insert the patch is to roll it around a stiff wire about one-eighth inch thick, holding it closed with the fingers, and when in this position it should be dipped into the naphtha and slipped into the hole quickly; as soon as it enters the hole the patch will open. The patch remains in the tire, and the hole in the tire is sewed up. After this the upper side of the tire is pressed firmly against the patch (which lies on the inside of the tire) with the fingers, or better still, as is done in rubber factories, with a stitcher. This tool resembles a pinker without teeth, and is about one-sixteenth of an inch on its periphery. Then the surface to be vulcanized is covered with uncured gum, flush with the tire and no more. Naphtha should always be used to clean the uncured gum, as well as the part of the tire to which it is to be applied, but before this is done it is cemented as before and the cement allowed to dry. Soapstone is then rubbed over the patched part and then “baked.” The utmost care should be taken to have the proper degree of heat and the time required. A thermometer which registers the heat correctly should be employed, and not a pressure gauge, as with the latter there may be fifty pounds pressure, but not the required heat. If a thermometer is used, the heat can always be ascertained as a rule. Three hundred and ten degrees of heat for twenty minutes will vulcanize a tire. The patch to be inserted in a tire is made up as follows: (1) a layer of uncured gum; (2) one or two layers of frictioner or coated duck; (3) another layer of uncured gum. The surfaces to be united should always be wiped with naphtha, and care should be taken that no air is enclosed in the patch when preparing it. Many repairers do not sew the puncture to be vulcanized, and in such a case at least two layers of canvas should be used, or three is still better. It is not always desirable to vulcanize a valve stem. The better way to repair a defective valve stem is as follows: A new hole is cut, a brass or shoe valve is inserted, and the old hole is plugged up the same as a puncture is repaired.
CHAPTER IX.
BEARINGS AND POINTS OF CONTACT.
Friction gives us a grip on the earth, and is indispensable for propulsion, but it is not in the least wanted in cycle bearings or in any other bearings, and one of the problems of mechanics is how to reduce it as much as possible in places where it consumes power as well as produces wear.
No material thing, however polished, is quite smooth; every surface may therefore be considered as covered with irregular hooks or teeth, however flat and smooth it appears to the unassisted eye, and these catch and hold one another, producing the hang or drag called friction. Oil, being a fluid, fills up the spaces between these invisible teeth and levels off the surface; the office of lubrication is, therefore, to get between the contact surfaces and keep the hooks or teeth thereon from touching. When surfaces are desired to slip and slide on each other easily, oil is helpful; when the hooks or teeth are to catch into each other, as between locomotive driving wheels and the rail, grease is out of place, whether it is oil or grasshoppers, for it spoils the “adhesion.”
The earliest mode of reducing friction is doubtless as old as the Tower of Babel, for the idea must have occurred to the primitive man. It is simply to put a roller underneath and convert sliding into rolling motion. This is in principle equivalent to mounting the weight on wheels, and it is the solitary and final way of dealing with the problem of friction. The common grindstone bearing is a familiar example; the axle of the stone rests on the rims of a pair of small wheels which stand so as to lap past each other. Here the axle rolls the wheels as it turns, and their motion at their centres is so slight that friction is nearly eliminated.