From time to time, serious accidents have taken place, and the progress of work stopped, by the sudden snapping of driving belts in machinery, and, as a general rule, it is found that the collapse is attributable either to faulty leather or insecure joining. A great improvement of the leather intended for belts has been brought about during the last few years, by the introduction of improved processes for currying and the subsequent treatment. Paterson has worked successfully a patent for rendering belt leather more pliable, and lessening the tendency to stretch. Under this treatment the leather is either curried or rough dried, and then soaked in a solution of wood, resin, and gum thus, or frankincense, first melted together, and then dissolved, by the application of heat, in boiled or linseed oil. The leather, after this process, is soaked in petroleum or carbon bisulphide containing a little India-rubber solution, and is finally washed with petroleum benzoline. Should the mixture be found to be too thick, it is thinned down with benzoline spirit until it is about the consistency of molasses at the ordinary temperature. The leather so prepared is not liable to stretch, and can be joined in the usual way by copper riveting, or the ends can be sewn.
A good material for smaller belts, and for strings and bands for connecting larger ones, is that recently patented by Vornberger, in which the gut of cattle is the basis. After careful cleansing, the gut is split up into strands, and treated with a bath of pearlash water for several days. The strands are then twisted together, and after being dipped in a solution of Condy's fluid, are dried. They are then sulphured in a wooden box for twenty-four hours, after which the twisting can be completed. They are by this process rendered pliable, and can be used in this state for stitching the leather ends of larger belts, or can be stiffened by plunging them into a bath of isinglass and white wine vinegar. After drying they are susceptible of a fine polish, emery cloth being usually employed, and the final "finish" is given to the material with gum arabic and oil.
Canvas and woven fabrics, coated with India-rubber, are also now being used for driving belts and for covering machine rollers. As this material can be made in one piece, without the necessity of a joint, it is uniform in strength, and is recommended as a substitute for leather belts requiring joints. A patented material of this description is due to Zingler, who boils the canvas or similar woven fabric under pressure in a solution of tungstate of soda for three hours. It is then transferred to a bath of acetate of lead solution, and drained, dried, and stretched. When in this condition it is coated, by means of a spreading machine, with repeated layers of a composition consisting of India-rubber, antimony sulphide, peroxide of iron, sulphur, lime, asbestos, chalk, sulphate of zinc, and carbonate of magnesia. When a sufficient thickness of this composition has been applied, it is vulcanized under pressure at a temperature of 250° F., or a little higher. The material produced in this manner is said to have the strength and durability of the best leather belts.
Attempts have recently been made to obtain a glue suitable for joining the ends of driving belts, without the use of metal fastenings or sewing, and Messrs. David Kirkaldy & Son have reported favorably on such a belt glue, which is being introduced by Mr. W.V. Van Wyk, of 30 and 31 Newgate street, E.C. In the test applied by them, a joint of this "Hercules glue," as it is called, in a 4 in. single belt was stronger than the solid leather. When a tensile stress of 2,174 lb., equivalent to 2,860 lb. per square inch of section, was applied, the leather gave way, leaving the joint intact. Belts fastened by a scarf joint with this glue are said to be of absolutely the same thickness and pliability at the joint as in the main portion of the belt, and thus insure freedom from noise and perfect steadiness. The instructions for use are simple, and it requires only fifteen minutes for the joint to set before being ready for use. From a rough chemical analysis of the sample submitted to us, we find that it consists of gelatine, with small amounts of mineral ingredients. Josef Horadam, some few years ago, patented in Germany a process for preserving glues from decomposition, by the addition of from 8 to 10 per cent. of magnesium or calcium chlorides.
The addition of these salts does not impair in any way the strength of the glue, but prevents it from decomposing, and it may be that the "Hercules glue" is preserved in a similar manner.
A cement of this nature, if thoroughly to be relied on, must be of great value, although the great variation in the quality of leather, apart from the difficulty hitherto experienced of securely connecting the ends together, opens a wide field for a material of uniform composition, and capable of being made in one piece in suitable lengths for driving belts and other machine gear. - Industries.