Gums, Resins, 



294 



[Oct. 1906. 



different, their properties both physical and chemical are quite distinct, and 

 moreover though the change from raw rubber to the sulphur compound of rubber- 

 that is, vulcanised rubber— can be easily effected by simple mixing and heating 

 to 300° F„ the reverse process of removing the sulphur and reforming raw rubber 

 has never yet been done. 



27. The vulcanised rubber goods which the manufacturer turns but may be 

 divided into three main classes— I, stamped and moulded goods ; II, goods built up 

 of rubber dough and other material ; and III, sheeted and spread rubber goods. 



STAMPED GOODS. 



28. All solid rubber articles— such as heel pads, soles for shoes, vulcanite 

 stoppers, rubber rings, washers, mats, buffer and rubber pads, billiard cushions 

 rubber tube, etc.,— are prepared direct from the dough by stamping them out by 

 hand or by machines, coating them with French chalk to prevent adhesion, and 

 then vulcanising simply by heating on trays or in iron moulds. The variety of 

 goods of this kind is enormous and without limit, and doughs of most diverse 

 composition from pure rubber and sulphur to mixtures where rubber is present 

 in very small proportion, are used for this kind of work. This branch of the 

 manufacture of rubber goods is as simple to understand as the art of the pastry 

 cook, who stamps out fancifully shaped little cakes, or twists up curly bread, 

 dredges with flour and bakes in an oven. The secrets are in the recipes for the 

 dough, and the art in the manner of making the shapes and regulating the baking. 

 There are many ingenious and complicated machines used to save labour, but some 

 of the simplest articles no machine can yet produce, and hand labour has to be 

 employed. Rubber rings of circular cross section, commonly called " umbrella 

 rings," have all to be made up by hand. If stamped or moulded the strength is not 

 to be relied upon. The mode of making is ingenious. A long strip is cut from a 

 thin sheet of dough, and this is cut into lengths of a few inches, not by simple cross 

 diversions but by oblique cuts. These lozenge-shaped strips are then wrapped round 

 a smooth circular rod and the sloping ends pressed together, A band is thus formed 

 round the rod and the line of junction of the two original ends of the strip passes 

 obliquely across the band. The workman, or rather workwoman, then rolls up into a 

 ring with her fingers this flat band, still upon the rod, and by rolling it backwards 

 and forwards upon the rod makes a smooth ring of it. The object of cutting 

 the strip with oblique ends— or " on the cross " — is now evident, because the line of 

 original junction which naturally would be the weakest place in the ring, is spread 

 out over a considerable length of the ring, and it is everywhere wrapped round and 

 supported by whole and unjointed layers of rubber, becoming thus nowhere more 

 than a small portion of any part of the cross section of the ring. Screw stoppers for 

 bottles are mechanically stamped out of a dough which contains a high proportion 

 of sulphur, and which gives a hard product on vulcanisation, the dough is stamped in 

 two stages, first a simple cylindrical rod is made and cut lengths of this are then 

 fed into a powerful press which produces the final shape. For large and awkwardly 

 shaped goods, such as the outer covers for pneumatic tyres, specially devised iron 

 moulds to completely encase the tyre and exert pressure upon it during vulcani- 

 sation are prepared. These moulds are in several portions and have to be fitted round 

 each tyre separately and the portions keyed into contact. Flexible rubber tubing 

 where the rubber is solid and not, as in piping associated with canvas, is squirted 

 out of a machine provided with compound nozzles, the apertures in which are ring- 

 shaped. The rubber doughls ejected through this annular orifice as a hollow tube 

 which only requires heat vulcanisation for completion. 



A^detailed account of the mechanical difficulties encountered in this part of 

 the work, and the way they are surmounted, would be of little use and certainly 



