■November 1, 1920 



THE INDIA RUBBER WORLD 



91 



There are numerous types of mechanical ckitches which have 

 been apphcd to mill drives, most of them without brake. Among 

 these, the spiral coil clutch and a disk clutch operated by com- 

 pressed air are used probably more than other types. No doubt 

 a mechanical clutch can be designed for quickly cutting off the 

 power, but a great many of these clutches now in use do not 

 release readily. In no event should a mechanical clutch be in- 

 stalled without a powerful brake in connection therewith. 



The foregoing methods have been applied principally to groups 

 of mills driven by one motor, but the method is equally ap- 

 plicable to an individual mill with its motor drive. An indi- 

 vidual clutch for each mill on a line of mills is not so advisable 

 as one clutch controlling a number of mills, because the greater 

 the number of mills, the greater is the resistance and the quicker 

 is the stop. 



It is possible that the best throw-out mechanism that might 

 be devised may not operate when most needed, and therefore it 

 is veo' necessary that daily inspection and tests be made to 

 determine the condition of these safety devices, and a record kept 

 of the surface travel of the rolls. No day should begin without 

 this test, and no mill should be operated until its safety throw- 

 out is in perfect operating condition. Frequent tests with the 

 mills loaded should be made to ascertain the surface travel of 

 the rolls. 



The location of the mill pan has much to do with the safety 

 of the operator, particularly as to the distance which the operator 



may he increased to as much as 4 feet 6 inches without making 

 it difficult to feed stock into the mill. 



The speed of the mill rolls should not exceed twenty-live revo- 

 lutions per minute. Higher speeds cause ditTiculty and danger 

 in cutting and rolling of stock. 



The roll-adjusting screw which projects through the front of 

 the housing should have threads of large lead, so that the mill 

 rolls may be separated in the shortest possible time, thereby 

 releasing an operator caught between the rolls before he can 

 be burned seriously. With threads of large lead, the adjusting 

 screw will tend to back off, because of vibration, but this can be 

 overcome by placing a quick operating clamp back of the head 

 of the screw. • ''I'TT '. ( 



Between the roll-adjusting screw and front-roll bearing is 

 usually placed a safety breaking cup. This cup often breaks into 

 many small pieces which frequently strike the operator. A band 

 or screen ought to be placed around the cup to confine these 

 pieces. 



Gears ought to be guarded most thoroughly if it is probable 

 that a workman may be compelled to be adjacent to them. It 

 is advisable in any case to enclose the outside perimeter or face 

 of gears with a sheet steel band to prevent oil or grease from 

 depositing on the floor of the pit. For most thorough guarding, 

 a solid enclosure of steel plate should be provided over faces of 

 gears and down the sides beyond the depth of the teeth, and the 

 point of contact between gears covered completely. Projecting 



Fig. 1. DoiHLE Throuiu't Tvfe 



OF S.\FETV Stop Device 



FOR Mills 



I'lG. 2. Ei.ECTRic.\L Wiring From Mill 



Switches Should be Carried 



IN Conduits 



Fig. 3. The Brake on the Mag.m tic- 

 Clutch Should be Operated by 

 A Counterweight 



is kept from the face of the rolls. One of the principal precau- 

 tions for safety in mill operations is to prevent the operator 

 from placing his hands beyond the top of the nearest roll. It 

 has been found excellent practice to have the least distance from 

 the bite of the rolls to the edge of the pan 3 feet 8 inches on 84- 

 inch mills, and 3 feet 1 inch on 60-inch mills. If, for any reason, 

 it is not practical to locate the edge of the pan so far from the 

 rolls, then a bar or pipe guard should be placed at the equiva- 

 lent location. The front and rear edges of the pan should be 

 smooth, preferably turned down or beaded, to prevent injury to 

 the workmen's legs. 



The height of the top of the mill rolls above the floor upon 

 which the operator stands should not be less than 4 feet 2 

 inches. A height less than this gives the operator too great an 

 opportunity to place his hands too far into the mill. This height 



keys, and other projecting revolving parts, as well as spokes, 

 ought to be covered with removable wire mesh, which will not 

 prevent visual inspection of the gear parts. Proper door open- 

 ings must be provided in various parts of the guards, to facilitate 

 inspection of the gears, and the guard designed so that it may 

 be quickly removed when necessary to repair the mill. Guards 

 should be attached neatly and rigidly to a machine to prevent 

 rattling or sagging, or being knocked out of shape, for other- 

 wise the guard may suddenly be removed by a self-appointed 

 specialist, because of its being an aggravation and eyesore. 



If there is no passageway between the ends of mills set in 

 a group, then there is no necessity to guard the gears so 

 thoroughly. Instead, a pipe railing, at least 3 feet 6 inches high 

 may be placed between the mills and be fastened to the mill 

 housings. Pipe railing, with gate, should be set around motor 



