CHAPTER XXXVI.

BELT GEARING.

THE belts employed for driving wood-working machinery should by preference be made of leather, except when used out of doors or where likely to be wetted, when the use of valcanised indiarubber or indiarubber cloth is advantageous. They are sometimes. made of other materials, such as cotton; and recently, at the International Exhibition held in Paris (1878), a belt made entirely of paper supplied motive power to some twenty wood-working machines. This belt was manufactured by an American firm, and was known as Crane's patent Japanese paper belt, and after twelve months' wear it appeared in capital order. It is claimed. for these belts that they are less in first cost and wear longer than leather. This, however, we are not in a position to verify.

In 1853 Mr. W. Paxton, of Johnstone, introduced driving bands composed of a series of cylindrical cotton bands or cords attached together, side by side and rolled flat, giving to the finished band a transverse section similar to that of leather. This form of band should possess a large amount of driving power and be suitable for moderate speeds.

Leather, from its strength, pliability, and durability,

is up to the present the best known material to employ for all ordinary machine bands, but for extra-wide main driving belts vulcanised indiarubber is used and preferred by many. It has the advantage over leather of lower first cost and greater driving power; but it is a moot question, considering the difficulty of repairing by unskilled labour and other points, which in the long run is most economical to use. For narrow belts, or belts that are obliged to be run at short centres or high velocities, engendering a considerable amount of heat, our opinion is there is nothing like leather.'

We have seen in use some of Gandy's patent driving belts, made of American cotton, which was folded and sewn together longitudinally, and saturated with some. oily composition, which renders them proof against water or change of temperature. In joining them transversely the ordinary jump-joint, sewn with laces, was used. They appeared to run true and grip the pulleys well; but as to their wearing capabilities we are not in a position the speak. From tests made by Kirkaldy, of London, their breaking strain, as compared with leather, is very high. Experiments were made on belts of 6 inches in width, with the following results-Best ordinary leather, breaking strain 6,299 lbs.; Helvetia leather, 7,522 lbs. ; eight-ply American cotton, 11,763 lbs. As these cotton belts are produced at a considerably lower first cost than leather, we purpose taking an early opportunity of testing their suitability for driving high-speeded machinery.

In calculating the transmission of speed by means of belts allowance must always be made for the 'slip' and deviation of the belt, but more especially in connection with wood-working machinery; running, as it

does, at high speeds, oftentimes at short centres and over small pulleys, in the midst of dust, which renders the leather less pliable, the grip' or driving power of the belt is considerably lessened.

The strength of the best ox-hide belts used for belting has been calculated at about 3,086 lbs. per square inch of section. This is reduced at a riveted joint to 1,747 lbs., and to 960 lbs. at a laced point. One-third of these figures may be given as a safe-working tension. As belts, however, vary much in thickness, the following table in lbs. per inch width of safe-working tensions may be of use:—

For transmitting power in high-speeded machinery belts should be made about one-third wider than is found necessary in machines running at a slow speed, and the smooth side of the belt should run next the face of the pulley. All belts should be made even in thickness. and neatly joined, and the driving pulleys accurately turned and rounded on face, or some difficulty will be found in making the belts run true. Twisted belts should be avoided as much as possible; but if it is found necessary to connect by belts shafts that are not parallel, care should be taken that the belt should always be in the plane of rotation of the pulley to which it is approaching, without regard to the retiring

side, which may be deviated from that plane without affecting the belt. If this rule is borne in mind, little trouble by belts running off the pulleys will be experienced.

When belts are required of a greater width than 9 inches, a double belt is preferable to a single one and is found to run truer.

As regards joining belts, hooks, malleable toothed plates, and numerous other plans have been introduced. Many users, however, still prefer the ordinary plan of lacing. We have found the double I belt-fasteners, known as Green's patent, to be both expeditious and economical, especially for narrow belts, where the tensile strain is not great.

We have recently seen some endless driving bands formed of crucible steel wire woven into a network or chain. The wires are arranged to run parallel to the width of the belt, and possess great flexibility and driving power, and will run with ease round the smallest pulley. As regards their economy in wear, we cannot speak from experience. These bands are also constructed with a leather or elastic lining, to prevent stretching, which plan we should think would be an advantage, at any rate for high-speeded machinery, as the friction engendered by the steel wire on the castiron pulley would be considerable, and the consequent breakage of the wire from expansion and contraction must be looked for. The use of metals for driving bands is not, hovever, new, as in 1856 the Earl of Caithness took out a patent for constructing driving bands out of sheet metal, such as iron, steel, brass, or composition metals.

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The following 'hints,' taken from the Textile

Manufacturer,' may be found useful to users of machine bands :

'Belts stuffed with tanner's dubbin on the flesh side will become as smooth all over as the hair side, and will outlast six belts which are run on the hair side exclusively.

'Three times the adhesiveness is gained by softness and pliableness of belting leathers over those which are dry.

'Long belts are preferred to short ones, but care must be taken that the length be not too great.

'Horizontal, inclined, and long belts give a much better effect than vertical and short ones, and those that have the driving side below than otherwise.

'Belts of coarse loose leather will do better service in dry, warm places. For wet or moist situations the finest and firmest leather should be used.

Experience says, the hair side of a belt put next to the pulley will drive 34 per cent. more than the flesh side.

The strongest part of belt leather is near the flesh side, about one-third the way through from that side. 'Leather belts must be well protected against water, and even moisture.

'Short belts require to be tighter than long ones. A long belt, working horizontally, increases the tension by its own weight, acting in the curve formed between the pulleys.

'Sufficient care is seldom taken to let belts run free and easy, and it has been one of the greatest errors, more or less prevalent in all large factories, to run the belts so tense as greatly to injure them and rapidly increase the wear of the bearings.