TRANSMISSION' OF POWER 95 



PARAGRAPH XVI. 



TRANSMISSION OF POWER. 



(A) BELTS. Belts in woodworking establishments are always dry and dusty and are kept at a high 

 and often irregular rate of speed. Dust materially decreases the transmitting power of belts. 



The heavier the belt, the more powerful is it; use light belt on small pulleys, however, for high speeds. 



I. Pointers about belts: - 



(a) Belt tighteners are required where a belt itself is not heavy and not long enough to cause a 

 sufficient sag; 



(b) The sag should always be on top and not on the bottom of the belt ; 



(c) The angle of belt against the horizon should not exceed 45 degrees, to prevent loss of power; 



(d) Placing the driven pulley above the driving pulley requires a tight belt. Heating in the bearings 

 and destruction to the belt are thus invited; 



(e) Belts should run off a shaft in opposite directions to relieve one-sided friction of shaft in bearings; 



(f) The pulley must be wider than the belt; 



(g) The larger the pulley the greater the tractive power of the belt; 

 (h) Belts should not rub against any beam or other solid object; 



(i) Long belts have greater adhesion than short belts, because they have more weight; 



(i) Belt dressing, to prevent slipping-off of belt, is objectionable, because it gathers dust and dirt, 



except perhaps linseed oil used on rubber belts; 

 (k) Belts will slip if:- 



1. The pulleys do not run in one and the same plane. 



2. The shaftings are not parallel. 



3. The pulley is not as wide as or wider than the belt. 



4. The belt ends are improperly joined. 



5. The speed is too high for the weight of the belt. 



II. Kinds of belts: - 



(a) Le.ather belts. Leather belts are either single or double. They come in rolls of from 200 feet 

 to 300 feet, are run with the grain side in and are preferably joined with studs -not by leather laces 

 requiring holes ; belt cement is now largely used, laps being reduced to a fine edge. 



Leather belts must be well protected from moisture, grease, lubricating oil, <Sc. 



Transmitting power of a single belt is only 70 per cent of that of a double belt. 



The price of a 7-inch single belt per running foot is --"M ; for double belt -y2, approximately. 



(b) Rubber belts. Rubber belts withstand moisture better than leather belts. They are cut from 

 Vs inch to ' 4 inch shorter per foot than the circuit on which they run and are run with seam side out. 



They are sold as 2, 4, 6 or 8- ply rubber belt, the 4 -ply being equivalent to single leather belting 

 and the 6-ply to double leather belting. 



The price of 4-ply 7-inch rubber belting is 70c per running foot; of 6-ply, -v-l, approximately. 



The ends are joined either by belt cement or by lace leather. The laps are strengthened by a strip 

 of leather on the outside. 



Metal studs should never be used in rubber belts. 



(B) PULLEYS. Pulleys are made either of iron or of wood; quite recently also of steel. 

 The adhesion of leather to wood is much greater than to iron; hence greater transmitting power of 

 wooden pulleys. 



