Electrical news and engineering . nclosures is passing away. As men-tioned before, frequent inspection is necessary for motorsused in cement mills, and this inspection trip can serve aswell for the cleaning of the dust from the air ducts, by com-pressed air, and blowing the rings clear. The use of the compeb mill, which requires as high as500 horse-power, has had a marked effect on the type ofmotor used in the cement industry. This mill is a con-stant speed load and the synchronous motor with its unity i W^ 9 i Ki 19 Induction Motors, each 1V5 , 660 Volt, belted to tube Cement
Electrical news and engineering . nclosures is passing away. As men-tioned before, frequent inspection is necessary for motorsused in cement mills, and this inspection trip can serve aswell for the cleaning of the dust from the air ducts, by com-pressed air, and blowing the rings clear. The use of the compeb mill, which requires as high as500 horse-power, has had a marked effect on the type ofmotor used in the cement industry. This mill is a con-stant speed load and the synchronous motor with its unity i W^ 9 i Ki 19 Induction Motors, each 1V5 , 660 Volt, belted to tube Cement Co., Limited, Longne Pointe, Montreal. power-factor has been found to give a very satisfactorydrive; since 1918 it has been gradually displacing the slipring motors previously used for the purposes. The high starting torque requirement of the tube millhas been one of the difficulties in the way of a general adop-tion of synchronous motors, which cannot deliver 120 to 130per cent, of normal torque during the starting period. This. Motor Driving Crusher—Canada Cement Company has been overcome by the use of magnetic clutches whichallow the bringing of the mill lines up to speed after themotor is started light; this type of clutch has been developedsince 1913, when it was first used in rubber mills. The clutch rating adopted should be that of the maxi-mum developable power of the motor, thus a motor of nor-mal 250, capable of developing 500 or over, shouldUc cfiuipped with a clutch of that rating. .\s this type of clutch is operated by direct current, some source of this is required, and it is often supplied from generator for the synchronous motor. The general appearance of the clutch is that of twoannular plates, mounted in close proximity on the shaft con-necting the mill and motor. One is an electro magnet car-rying an annular coil, and it draws tlie other plate when the
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