belting



belting defined in 1909 year

belting - belting;
belting - See also leather, cements.

A very useful set of instructions relating to belting was compiled by the chief general mechanical engineer of the New York Central Railway, from which the following details have been taken.

It is always best to locate the machinery (or the shafting) so that the belts shall run off from each shaft in opposite directions, as this plan affords relief to the bearings from the extra friction that must result if the belts all pull the same way. When two shafts are to be connected by one belt, it is best not to put one directly over the other, for in such a case the belt must be kept tighter than otherwise to do the work, and this means extra friction. It is desirable that the angle of the belt with the floor should not exceed 45°. Whenever possible the machines should be so placed that the direction of the belt-motion shall be from the top of the driving pulley to the top of the driven pulley. The faces of pulleys should be about one-fourth wider than their belts. When possible, the tightening of belts should be effected by moving one pulley away from the other.

The transmission of power by a belt depends upon the tension under which it is run, the degree of friction between the belt and the pulley, the complete contact of the belt with the pulley, the speed of the belt, and the arc of the pulley in contact with the belt. The tensile strength of single, ordinary tanned leather belting is about 4000 lb. per sq. in. The working strain should not exceed 10 per cent, of its tensile strength. The average leather belt will not transmit a force equal to its strength, for the reason that it will slip on its pulley before it will break. As the friction of leather on leather is five times as great as that of leather on iron, the adhesion between the belt and the pulley can be greatly increased by covering the pulley with leather. The belt is thus capable of doing more work for a given width the belt tension can be lessened to get the necessary friction, thus adding to the life of the belt and unnecessary wear of the belt and a wasteful loss of power due to its slipping on the pulley are prevented. The strain to be allowed for all widths of belting - single, light double, and heavy double - is in direct proportion to the thickness of the belt, firmness of the leather being the same in all cases. Avoid running belts too tight, as great tension shortens the life of the belt, occasions a waste of power, and causes great inconvenience from hot boxes, broken pulleys, and "sprung" shafting. Belts, like gears, have a pitchline, or a circumference of uniform motion. This circumference is within the thickness of the belt, and must be considered if pulleys vary greatly in diameter and a required speed be necessary.

Belts are more satisfactory made narrow and thick, rather than wide and thin. Thin belts should not be run at a high speed, nor wide belts be made thin. Such almost invariably run in waves on the slack side, or travel from side to side of the pulley, especially if the load changes suddenly. This waving and snapping wears the belts very fast. It is greatly obviated by the use of a suitable thickness in the belts. For new belts, those that have already been filled with some good waterproof dressing are preferable o "dry" belts, for if not so filled they soon will be with lubricating oil and water, a combination that will ruin any belt. Rubber belts should be used in places exposed to the weather, as they do not absorb moisture, nor so readily stretch or decay as leather belts under like circumstances. A new belt should be made straight, and if so made will run absolutely straight if the pulleys are in line. Slots punched in the centre of a belt will allow a chance for the air to escape between the belt and the pulley, and prevent "air cushion." This is of particular advantage in all belts running at high speed.

It is safe and advisable to use a double belt on a pulley 12 in. in diameter, or larger. Light double belting runs steadily, with a minimum of "snap" or vibration, and does not twist out of place like single belting. It is successfully used for counter-belts where shifters are used, and where the work is not sufficiently hard to demand a heavy double belt; it is especially adapted for use on cone or flange pulleys, as it will keep its place and is less liable to turn over, and at the same time is pliable enough to hug the pulleys like a single belt. Double belting, light or heavy, is not recommended for twist-belts at high speed, nor for woodwork where belts are exposed to a large amount of chips or shavings, nor for places where much oil or water is liable to get on it.

As a means of making necessary alterations in the length of a belt, the laced joint is recommended. To lace a belt, cut the ends perfectly true with the aid of a try-square. Punch the holes exactly opposite each other in the two ends. The grain (hair) side of belt should be run next to the pulley, and the belt should be run off, not on to the laps. For belts 1 in. to 2¼ in. wide use ¼ in. lacing; 2½ in. to 4½ in. wide, use 5/16 in. lacing; 5 in. to 12 in. wide, use 3/8 in. lacing. For wider belts use wider lacing. Avoid thick lacing. In punching a belt for the lacing, it is desirable to use an oval punch, the longer diameter of the punch being parallel with the belt, so as to cut off as little of the leather as possible. There should be in each end of the belt two rows of holes staggered. Holes should be as small as possible. Recommended number of holes in the belt end for various widths is as follows:

Width in inches2345681023
Number of holes3457911151923


The edge of any hole should not come nearer to the side of the belt than 5/8. in., nor nearer the end than 7/8 in. The second row should be at least If in. from the end of the belt. On wide belts these distances should be even a little greater. Begin to lace in the centre of belt, and take much care to keep the ends exactly in line, and to lace both the sides with equal tightness. The lacing should not be crossed on the side of the belt that runs next to the pulley.

Belts and pulleys should be kept clean and free from accumulations of dust and grease - and particularly lubricating oils, some of which permanently injure the leather. They should be well protected against water, and even moisture, unless especially waterproofed. Resin should not be used to prevent belts from slipping. If a belt slips, see first that the pulley is not dirty. Clean all the dirt from it and from the belt; rub the pulley surface of the belt with a dressing composed of 2 parts of tallow to 1 part of fish oil, rendered and allowed to cool before using. This will soften a belt and also preserve it, and it will not build up on the pulley and cause the belt to run on one side. If the belt then slips it is overloaded, and the remedy lies in a leather-covered pulley, a wider belt, or a larger pulley.

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