LEATHER BELTING Manufacture of Leather Belting.—The raw material for this article is the product of the heavy-leather tanning industry known as a Strap Butt. The best and most serviceable leather is derived from butts cut from steer hides. The Strap Butt repre sents approximately So% of the total weight of leather produced from a hide, and in area is about 41 by 44ft. Rough leather, which is hard, brittle and non-elastic, must be curried to bring it to the pliable condition essential to procure durability, good adhesion to the pulleys and the elasticity required for good power trans mission.
In currying, the rough leather is first soaked in a weak tan liquor until the fibres become fairly soft and pliable. At this stage the grain (hair side) and flesh (inside) are thoroughly cleansed from all foreign matter deposited on them during the process of tanning. Subsequently, whilst the leather is in a moist condition, a mixture of best quality cod-liver oil and tallow is well rubbed in on one surface, a dressing of cod oil to the other side, and the butts are hung up to dry. During the drying process the lighter constituents of the grease are absorbed by the fibres. Just before the leather is quite dry the butts are taken down and damped. Another application of grease is given on the opposite side to the first one. At a later stage the butts are "set out," i.e., friction and pressure is applied to the hair side by oscillating or rotary machinery, which extends the leather, works out the grain, and makes the butt as flat as possible. The butt is generally stretched because the elongation of the leather within its elastic limit is of vital importance to its efficient transmission of power.
It is stretched either as a whole or in three sections, the important factor being to leave the leather in the stretching apparatus until it is dry. After stretching and drying, the "belting butt" is put through a finishing process termed "jacking," which smoothes out the leather and gives it a glazed surface: This lends an attractive appearance to the leather but adds nothing to its transmission ability. When the currying is completed the butts are brushed over lightly with warm tallow and laid down in pile to mature. This is of great importance in producing good wearing leather, the time occupied in the whole process of currying and maturing being approximately four months. Before being cut into strips, the curried Strap Butt is finished, i.e., all surplus grease is scraped away and the surfaces are rubbed over to give them a finish.
Hides, and consequently Strap Butt, have both natural and artificial faults. The natural ones are uneven growth, poor tex ture, and at certain seasons warble holes caused by the "gad" fly. The artificial ones are butchers' cuts, fleshers' galls on the flesh, horn marks and scratches on the grain, all of which must be elim inated from the leather used in the making up of a good, service able and reliable belt. The growth of the Strap Butt is very similar to the shape of the steer, that is to say, the thickest parts are over and along the ribs. That portion which covers the spinal region is thinner but sound material, the general thickness tapering from the hind quarters to the commencement of the neck. The best hides for belting are those taken from three-year-old steers and are known as "Green Packer" steer hides. Green hides are best for belting if they are removed from the animals in the fall and winter months. During this period of the year, the hair is shorter and the hide cleaner.
Eliminating Weakness.—The tanner cuts the butts 44 to 4ift. long according to growth, but the difference in thickness between the butt end (hind quarters) and the shoulder end is too great to allow the last 8 to i o inches at the shoulder end to be used in making a high quality belt. To eliminate this weak spot, therefore, a strip 8 to i o inches wide is cut away the full width of the butt, which represents a loss of 12% in weight and quite a big loss in value. The shortened butt is now cut into two slightly unequal portions for ease in handling when being cut into strips, which is done on a circular knife running at a high speed.
The cutter carefully examines each portion of the butt for flaws and to ascertain its growth and thickness ; the centre portion of the butt, being thinner, produces narrower belting than that portion which covered the centre of the ribs of the steer. From the region two or three inches past the centre line of the ribs to within to 2 inches of the tip of the butt end flank, the growth falls away and narrower belting is cut ; ultimately a piece 3 to 4 inches wide on each portion is left, which is too poor in quality for belting requirements. This represents about 7% of the starting weight of the butt.
The cut lengths are passed forward to the squarer, who ex amines each one carefully for flaws and thin ends, and decides just where to cut away the leather which is not up to the standard required; in doing so he cuts the ends square, to facili tate the operation of splicing.
Matching the Strips.—In making up a complete roll of belt ing the strips are carefully matched and graded to ensure that they are of similar texture and as near as possible similar thickness, so that the made-up belt will be well-balanced. When satisfactory in this respect the lengths are spliced, i.e., the ends of each strip are bevelled on alternate surfaces. The bevelled surfaces are roughed up to produce a suitable surface for the cement.
The joints are now fitted, i.e., the bevelled surfaces are carefully measured and marked off to a fixed length which varies according to the width of the strips. The lips are thinned to a feathered edge, great attention being given to ensure that the spliced ends lie and fit properly on each other.
In cementing, a good adhesive gelatine in a warm liquid state is applied and well rubbed into the prepared splices. The covered areas, one spliced from the grain side, the other from the flesh side, are laid on each other, in a hydraulic box-press and pressed down every few minutes till the box is full. Pressure is now left on for several hours to enable the cement to set and also partly dry.
When the boxes are emptied each joint is carefully examined to see that the cement is well set and the lips have a good hold, the whole roll being laid down until the joints are quite dry before they are sewn. In sewing, a white or a horny lace is generally used. The holes are pierced with an awl, and the lace is threaded in and pulled up tight, the whole being a hand operation. Joints are also hemp sewn, both by machine and hand labour. Occasionally cop per-wire sewn joints are specified, but copper rivets are not essen tial, as waterproof joints can be supplied for use in damp situations.
In making "cemented only" belting, a splice about one inch longer than for sewn work is generally made and a higher grade of cement is employed.
In making double belts, two plies are first prepared as single belts with "cemented only" joints, then these two plies are ce mented together flesh side to flesh side, and as required are sup plied "cemented only," sewn with laces, hemp or copper wire. After the sewing operation the edges of the leather are finished flat or round and the roll which measures generally 300-3 5of t. long is ready for use.
A high breaking strain does not mean that the leather will wear well; in fact, the opposite is the case. The hardest wearing leather comes from the centre of the butt, and it is well known that, owing to its close texture, this region of the butt has a comparatively low breaking strain, whereas the outer edges of the butt, which are more open in texture and stretch more, always give a high breaking strain.
Initial Stretch.—The initial stretch in leather belting can be, and is, eliminated by the up-to-date manufacturer, who only leaves just sufficient stretch to provide the elasticity required for good power transmission. The process is, however, expensive and adds to the prime cost of the belting, but in these days of high-speed production the extra outlay for "stretchless" belting is a paying proposition.
Mineral Retanning of Leather.—Leather belting of first quality at its best is sometimes not highly flexible. A certain stiffness, peculiar to the leather, has been overcome by the intro duction of the mineral retanning process. This process results in a leather of extreme flexibility, increased tensile strength and in creased frictional qualities ; it enables it to stand the action of water and steam and, to a certain extent, the effect of corrosive acids.
Leather belts withstand much overloading, but they require some care and attention during their effective life. An occasional appli cation of curriers' dubbin furnishes fresh lubricants to the fibres when they become dry. Belt dressings as sold by the dealer are generally more harmful than useful, while giving temporary re lease from slipping they make the leather harsh and dry in the long run, and thus shorten its life. Leather belts are long lived and are often repaired again and again. Cases are on record of leather belts which have performed their duty efficiently for 25 to 3o and even 4o years. The best makes of leather belting are sold on a measurement basis, the per foot price-list being graded according to width and thickness.