Belts and Belting. Flexible belts for the transmission of motion in machinery are made of leather, india-rubber, cotton, woven hair, gutta-percha and canvas, and other materials. In so limited a time, indeed, as the three years ending with 1886, patents have been taken out for making belting of most of the well-known textile fibres, including flax, cotton, coir, rhea, and some kinds of wool or hair. Sometimes two or more of these are combined along with wire.
The valuable qualities in a belt are: (1) Proper grip of the surface of the pulley. (2) Strength or capacity to resist strain. (3) Non-liability to stretch. (4) Durability. Those tanned with oak bark are the most lasting of leather belts, but much excellent belting is made from leather tanned with other substances, such as the bark of the American hemlock spruce. In order to secure uniformity of stretch, so that a belt will run straight, the strips from the tanned hide require to be cut out and combined with much judgment. These strips are prepared by being stretched by powerful machinery to the utmost tension they will stand without injuring the fibre. They are afterwards joined by riveting, lacing, or cementing and lacing, in such a way as to present an even surface to the pulley. One of the largest leather belts yet constructed was made for a paper-mill at Wilmington, Delaware. It was 186 feet long, 5 feet wide, and weighed 2212 lb. A portion of an English belt almost as large as this was exhibited at Manchester in 1887. Belts 4 feet wide are now not uncommon in America. Experiments made in America show that a belt will transmit about 30 per cent. more power with a given tension when the grain or smooth side of the leather is in contact with the pulley than when the flesh side is turned inward. Carefully made leather belts have been known to last in daily use more than thirty years.
What is called leather chain belting, or leather link belting, is formed of short pieces or links of leather joined together by metal rivets. It is employed for driving dynamos for electric lighting, and for other purposes. Solid woven hair belting is similarly used.
India-rubber belting is formed of several plies of cotton duck or canvas, each overspread with rubber composition, and then subjected to a vulcanising heat. This kind of belting is used to a larger extent in the United States than in Great Britain. It is less easily repaired than leather belting, but rubber bands can be made with only one joint, or even without any joint, which is the weak part of a belt. Rubber belting is easily injured by contact with almost any kind of oil.
Cotton belting, of which there are several varieties, some being waterproof, is now a good deal used both in England and in America.
The following are the breaking strains per square inch of section of several kinds of belts:
| Best Leather Belting..... | 3,360 lb. |
| Stout Stitched Cotton Belting..... | 6,800 " |
| Solid Woven Cotton Belting..... | 10,420 " |
| Superior India-rubber Belting..... | 4,000 " |
Rubber belting varies very much in strength, according to the quality of the canvas or duck used in its manufacture.
The safe working tension of leather belting does not exceed 330 lb. per square inch of section, or about 41 lb. per inch in width of belting th of an inch in thickness. The other kinds also require a large factor of safety.
The extensive use of belting in place of toothed gear-wheels has long been a feature in American engineering, but a preference for driving belts on account of the reduction of jar and noise, facility of adaptation, immunity from accident, and other advantages, has for some time been extending in other countries. It should be added that ropes are now frequently used where belting was formerly employed. See TRANSMISSION OF POWER.