The World' s Leading Tire Factories.—No. 5.
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A Visit to the Polack Company's Works at Waltershausen.
Prominent among the companies that are connected with the manufacture of solid rubber tires is the Polack Tyre Company, Limited, of 31-34, Basinghall Street, London, E.C., which company has its works at Waltershausen, in Germany. This concern was recendy incorporated as a limited liability cornpany (see our issue of the gth January), the object of the Change being the raising of additional capital, for the purpose of carrying out extensive additions to the works and machinery in order to meet the over-growing demand for its excellent tires.
The most distinctive feature of the Polack tire is the manner in which it is secured to the steel rim which surrounds the wooden felloe, In " TnE COMMERcrAL MoTotz " for the 4th April last, we illustrated the three component parts of this tire separately, in order to show how the bayonet slot-ring engages with the teeth on the steel rim, and how, by reason of the inclined faces of the teeth on that rim, the rubber tire is firmly gripped between the sol:d flange and the loose slot ring. After tightening up the latter, it is prevented from slackening back by means of a coupk of set screws. The tire is prevented from creeping round the steel rim by means of a key, which is left solid on the rim, and which engages with a keyway that is cut in the inner circumference of the steel band. The drawing reproduced on page 548 shows a sectional view of this maker's tire, and throughout this article we shall adhere to the notation of the parts as given thereon.
Our representative who recently visited this company's works at Waltershausen—where all the photographs for this article were specially taken for
THE COMMERCIAL MOTOR "—had an opportunity of observing all the varied processes through which a tire passes in its evolution from the raw rubber to the finished article. As received from South America, Africa, and other rub
ber-producing countries, the rubber contains a large amount of foreign matter. The first operation to which it is subjected is, therefore, that of cleansing. The irregularly-shaped balls of raw material are first cut into halves, and these are then boiled, in order that the material may be partly disintegrated before it is passed through the washing mill. The latter machine conskis of a pair of heavy, polished steel rollers, through which the boiled material is passed, and from which all foreign matter, such as ash, sand, small pieces of bark, and small stones, is washed out by the action of the jets of water which are directed on to the-material while it is passing through the rollers. After it is washed, the sheets of rubber are placed in the drying rooms, where they are kept at a tern perature of about too degrees Fahrenheit by means of currents of hot, dry air. The better qualities only of the rubber leave the washing machines in the form of sheets (the surfaces of which are very rough and closely resemble the hide of a croco dile), whilst the inferior qualities, which will not hold together in sheets, after leaving the rollers, have the appearance of shredded sponge; this loose material is spread on shallow trays for the purpose of drying. After it is dry, the rubber is ground between steam-heated rollers—a pair of which are shown at the bottom of page 548—so as to destroy its fibre, and to bring the rubber into a fit condition to receive the various compounds that are added. These vary within very wide limits : for pure rubber, sul
phur only is added, in order that the material may be vulcanised; but, in order that the rubber may have certain qualities imparted to it, according to the purpose for which it is required, other ingredients, such as zinc oxide, Paris white, chalk, litharge, lamp black, and antimony are added, and, in some special cases, where high tensile strength is desired, a material known as " Murac " is incorporated with the rubber. Although, in many cases, the principal reason for compounding, is the production of the finished articles at a lower price, this is by no means the only reason, and the fact that cheap organic or inorganic matter is added to the rubber cannot, therefore, be considered as adulteration; such added substances may be absolutely necessary, especially in the rubber for motor tires, in order that the material shall have the necessary resiliency, the tensile strength, and the quality of endurance,. which are demanded by the automobile engineer and the motor user. The mixture is again subjected to the rolling action of powerful mills, and, when thoroughly mixed, and in a perfectly homogeneous condition, the material leaves the machine in the form of sheets of varying thicknesses. These_ sheets of unvulcanised rubber are now ready to be cut up into strips, and with these the tire is roughly built up to resemble its finished section.
The way in which a solid rubber tire is built up is as follows :—The steel hand is first thoroughly coated with rubber solution, and thin layers of a quality Of rubber which, when vulcanised, becomes very hard, are wrap
ped round it. Around these bands, laver upon layer of softer rubber is rolled on by hand : in order to carry out this operation, the steel band is mounted, by means of a spider, on a spindle which is fixed at the end of the workman's bench, as may be seen in the left-hand view at the bottom of the previous page.. These layers are of gradually-decreasing widths, in order to give to the tire the approximate shape
of the finished article. The tire is shown in this condition in the illus tration above, where the separate layers of soft unvulcanised rubber may be easily distinguished. The tire is now placed in a cast-iron mould, consisting of three pieces—a central portion, or mandrel, and two pieces which are hol lowed in order to give the correct size and shape to the tire when finished. After placing the tire in this mould, the two hollow portions are clamped firmly together, as may be seen in the illus tration of the tire vulcanising room, in the foreground of which view, three sets of tire moulds are seen standing. Several of these moulds are then put into one of the large vulcanising boilers, into which steam is admitted at pressures varying according to the thickness of the mass of rubber within the moulds. The effect of the heat treatment upon the material within the moulds is to bring about the chemical combination of the sulphur with the rubber. When this process has been completed, the material is no longer so extremely sensitive to small changes of temperature. After leaving the vulcanising room, the tires are ready for the user.
Different tire makers have their own ideas as to how a tire should be made, but the above description is, put briefly, the method of manufacture in vogue at the Polack works. The Polack Company makes a variety of sizes and strengths of tire, to suit the numerous types of vehicles on which they are to be employed, but all its tires are guaranteed to run I0,000 miles on good public roads, provided that they are not called upon to carry greater loads than those for which they were supplied.
In addition to the making of highclass solid and pneumatic tires, this company also makes large quantities of " mechanicals," as they are known in the rubber trade, and under which name an articles, such as jointing material, gland packing, gauge glass rings, jointing rings for steam and water piping, suction hose, and rubber belting, are included. For working up the rubber for all these articles, the same machinery used for the washing and compounding of the tire rubber is employed, but, on account of the varied nature of the goods, specially-shaped pans or boilers are, used for the vulcanising process. The manufacture of armoured, suction hose is particularly interesting, but the limited space at our disposal precludes us from entering into the details of its construction.
As far as the tire department is concerned, the Polack Company has always aimed at producing a tire of the best quality, and one that is free from those defects which so often lead to early failure on the road.