Vulcanising Plants for Motor Tires.
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A Few Particulars of the " H.F. " Process of Making Repairs to Solid and Pneumatic Tires.
The " H.F." process of effecting repairs to rubber tires has proved so reliable, and the many different types of appliances which have been introduced by Harvey Frost and Company, Limited, of 39, Great Eastern Street, London, have been found so practical and efficient that we think many of our readers will appreciate the few particulars which we are now able to give, as the result of a visit to the company's " school," where we examined the apparatus which is here illustrated and described. The above company has introduced many forms of vulcanisers, the shapes and capacities of which are suited to the requirements of different classes of users. Private owners of cars, and the proprietors of garages have long been using the smaller sizes of vulcanisers which are made by this company, but many a user of commercial motors would find that the installation of a plant, suitable for the tires with which his vehicles are fitted, would be a profitable investment.
The " H,F." vulcanisers are ingenious devices, and they are entirely self contained. Looked at in its simplest form, a vulcaniser is simply a generator of heat, which can maintain an exact degree of heat for any definite length of time; it carries out its object in exactly the same manner as is adopted when the original tire is manufactured, i.e., it causes the new material, in the form of a plastic compound, permanently to adhere to, or to combine with, the material of which the tire is made. The application of a uniform heat, for a given length of time, to the new compound sad the old rubber of the tire, causes the sulphur to combine chemically with the rubber, and the ultimate result is that the united faces are practically as strong as the original material. The principle on which all sizes of this apparatus depends is that of maintaining a uniform temperature by means of steam. At any given pressure, saturated steam always has the same temperature, and, therefore, the desired temperature for any particular repair is easily maintained by keeping the steam within the boiler at the pressure which corresponds to that temperature. For most repair work on tires, the required temperature is that possessed by steam when under a pressure of about 50 to 6o lb. per square inch, and, therefore, most of the sizes of the " H.F.1 vulcanisers are designed to work between those pressures, but for very thick sections of rubber it is sometimes necessary to work at a pressure of 75 lb. per square inch ; that pressure should never be exceeded. All the boilers are fitted with safety valves which are tested and adjusted to blow off at ioo lb. per square inch. The first of our illustrations shows one of the company's standard " A " models, and it is a very useful form of vulcaniser for quickly effecting local repairs to either inner tubes or outer covers. Both the sides, and the top surface of the boiler can be used at the same time ; there area couple of clamping screws at each side, and two more at the top, for the purpose of holding the work, under pressure, while it is being "cured." Standing out from one of the end walls of the boiler, there is a quite unique fitting : this consists of a steam-jacketed ring, in the circumference of which a gap is left to enable a tube to be inserted without 4' threading," and the necessary pressure is put on the tire tube, while it is being vulcanised, by means of an expanding mandrel, such as is illustrated herewith. The maker refers to this fitting as a " jointless tube joiner," and its object is to join an inner tube without the union being apparent, or the tube-section being any thicker at the joint than at any other part. The main operations are : (a) one end of the inner tube is passed through the mandrel, and is folded back over the outside ; (b) the rubber tube is folded back on itself, and the other end of the tube is drawn over the mandrel until the two ends butt together ; (c) the ends of the tube are treated to several coats of a semi-liquid compound, and the interstices filled in with a special plastic material ; and (d) the mandrel and rubber tube are placed in position within the steam-jacketed ring, and the mandrel is expanded by turning the ratchet-locked pinion which is seen in the illustration This is but one of the many special appliances which may be used in conjunction with any of the larger sizes of vulcanisers which are made by the company.
Another useful plant is the standard " B " pattern, which embodies every appliance that is necessary for executing all kinds of repairs. It is a most complete plant, and it should be found of very great use in the repair shops of motorcab garages, or by large owners of light vans. Each appliance is operated independently, but one steam generator serves to heat the whole plant. This set includes : two steam-heated, adjustable moulds; three inside steam-heated mandrels; a patent mandrel support and steam-heated pad; a valve seater ; a mould for making valve parts; a set of templates for ensuring perfect contact between the mould and the work; a bench plate for adapting the mandrel support as a convenient rest and former on which to prepare the work; and one of the " jointless tube joiners " to which we have already referred. Our second illustration shows a " B "pattern plant with some of its very useful fittings in position. Although the company considers that it is only necessary to stock moulds which are suitable for the standard sizes of outer covers for pneumatic tires, moulds to suit any make or section of solid-rubber tire can be made specially at a very low cost. The steam-heated moulds enable the heat to be applied to the actual part which is being treated, and each section of the mould may be heated independently, or both the moulds may be heated simultaneously. This is a very complete and useful plant, and one that will not only meet all present-day requirements, but one that can always be adapted at a slight cost, for future, and special work. The boiler is so constructed that all the heated parts are fully utilised for vulcanising, and no metal is heated that is not so requieed. The boiler contains only a minimum quantity
of water, and the plant is provided with an automatic water feed, but water may at any time be added if necessary, without appreciably affecting the steam pressure which may at the time exist. All the standard apparatus is designed for use with gas, but, without any loss of efficiency, the burners can be adapted to consume ordinary paraffin.
One of the 'latest introductions of Harvey Frost and Company is the No, i, re-treader, which we illustrate on this page. This plant has been designed to meet the requirements of large repair shops, where the operation of re-treading tires is undertaken. The construction of the boiler is very ingenious, and there is practically none of the heat of the burners wasted : in the first place, the pan is jacketed by the boiler, and the latter is jacketed by the outer walls of the furnace. The apparatus is self-contained, and it is, in many respects, far ahead of the vulcanising boilers which are in use in some of the large tire factories. The vulcanising pan is 42 inches in diameter, and it will take six tires of average size at one time. While the tire is being fitted with its new tread, it is mounted on a flexible mandrel of spirally-wound wire, and, after the new tread has been solutioned down, the necessary pressure is applied by "taping" the cover on to the mandrel. The covers are then placed inside the vulcanising pan, in which they are separated from one another, and, after bolting down the lid, steam is admitted through the short flexible tube, which may be seen in the illustration.