Leather: From the Raw Material to the Finished Product

by K. J. Adcock

Machine Belting, Harness, and Saddlery Leathers

These leathers are rarely made by one firm; usually, strap butts and most kinds of belting leathers are dressed by curriers, whose trade is quite distinct from that of currying shoe leather. The tanning and currying of harness and saddlery leathers is another special branch. Besides these three important trades, there is the dressing of hydraulic, mechanical, and other industrial leathers, which likewise form special sections of the heavy leather industry.

Belting leather is an important item in the trade, and, as a good proportion is made from the finest hides, this class of leather is among the most expensive made. At present, there is much controversy in the trade as to whether the vegetable-tanned or the chrome-tanned article is the more economical in use. Briefly, chrome belting is superior in works where there is much steam or mineral acids, as it is not affected by these conditions to the same extent as bark-tanned belting. Its tensile strength is also greater, but against these advantages must be set its higher cost and tendency to stretch unduly in comparison with the vegetable-tanned product. It can be safely said, however, that the use of chrome belting is on the increase, although its production is not nearly on such a big scale as that of the old type of belting.

The tannage of belting leather is similar to that of sole leather, except that there is no necessity to continue the process, after the tannin has struck through, with the object of increasing its firmness and weight. Attention must also be paid to the class of tanning materials used, especially for belting of the best quality, as it must have great tensile strength and stand a severe strain in the dynamometric test. Tannins that rapidly oxidise in contact with light and air have, therefore, to be avoided. The oak bark tannage, with a little chestnut and oakwood extracts to finish the process, is a good method of imparting to the hide the right degree of firmness and flexibility.

As in the case of sole leather, belting may be artificially weighted during the tannage, although it is usually done in the currying process, if at all. There can be no doubt that a quantity of adulterated belting leather is made, and will continue to be made while the practice of selling by weight is in vogue. As a rule, sophisticated belting leather has a much weaker tensile strength than the pure product and is of relatively poor value, since the reduction of price is usually a matter of only a few pence. If users of belting bought on the principle of value instead of price, they would never buy adulterated leather.

Fig. 35

LEATHER-STUFFING DRUM

In tanning hides for belting, the shoulders and bellies are cut off and usually dressed for sole or harness leather, leaving the butt, the prime part of the hide, 4-1/2 ft. in length (Fig. [23]). The tanned butt is first shaved to level the substance, then washed in a solution of borax, and sumached in the drum. After smoothing the leather in the striking-out machine, it is partially dried ("sammed") and then rubbed on both sides with a dubbin of cod oil and tallow. In this condition the butts are left piled up for a few days, so that the dubbin penetrates the leather, which is then extended with the sleeker (Fig. [32]) to make it smooth and to remove surplus grease, which is sold to soap-makers under the currier's name of "moisings." The leather is finally dried, rolled (optional), stretched by machine, and cut up in the width of belting required. Instead of "hand-stuffing" the leather with cod oil and tallow, which is still the best method, a large quantity of butts are now "drum-stuffed," the object being to make use of stearines, which are harder and heavier greases than tallow. The type of drum shown in Figure 35, in which the grease is incorporated with the leather by means of live steam, gives satisfactory results, although hot air apparatus is now replacing the steam injector.

A patent has lately been granted to an American inventor for the production of a strong and cheap belting. Flesh splits of hides are simply stuck together with a collodion or nitrocellulose solution. Any number of layers may be used, according to the substance required, the only essential quality being that the leather should be free from grease. The adhesive property of nitrocellulose solutions is probably stronger than that of any other material, but, unfortunately, the tough film they form on drying does not grip a greasy surface. Before the solution used to join the pieces of leather together is dry, the leather is rolled under heavy pressure, and, when thoroughly dried, can be cut up for belting.

The dressing of harness leather is similar to the manual process of making belting, with the exception that the butts or bends (half butts) are stained either black or a pale straw colour, the latter being known to the trade as the "London colour." Annatto is often used to get this colour. The bright, greasy finish on harness leather is obtained by rubbing buck tallow over the grain and polishing with a glass sleeker or a piece of flannel. The operation is sometimes done by machine, in which the working cylinder is covered with pieces of cotton rag.

Saddlery leathers are dressed on similar lines, but the finish is not so greasy as harness. Pig skins make the best and toughest leather for this purpose. They are dressed in a similar manner to harness hides, but special attention has to be given to pig skins to get rid of the large quantity of natural grease they contain.