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THE INDIA RUBBER WORLD 



November 1, 1920 



Safety and Sanitation for Rubber Mills and Calenders ; 



By C. B. Mitchella' 



SAFETY AND SANITATION fof rubber mills and calenders covers 

 so many opportunities that if discussed fully it would fill a 

 large volume. Many schemes have been tried with varying 

 success for accomplishing the same purpose, and it is the inten- 

 tion that this paper shall present only the most important pre- 

 cautions and the most successful installations. 

 EDUCATION OF OPERATOR 

 Although the education of the operator is the most important 

 of all precautions in preventing injuries on mills and calenders, 

 this part of the subject will not be presented in detail; instead, 

 the discussion will be confined to mechanical safeguards. How- 

 ever, a few pointed suggestions, or rules, to develop mental 

 alertness of the operators are submitted as follows: 



GEinSRAL RULES 



1. Follow instructions of your foreman and your inspectors 



only. 



2. Wear no clothing which can be caught in the machines, 

 such as long sleeves, loose neckties, aprons or unbuttoned jackets. 



3. Keep your eye on the job all the time, and give your work 

 your entire attention. 



4. Keep your hands off moving rolls. 



5. Never force the rubber into the bite of the rolls with your 

 hands. 



6. Never oil, clean or repair your machine while it is in 



motion. 



7. When cutting stock oflf roll, always cut below the center. 



8. If you feel ill, or in such condition as to interfere with 

 your work, report at once to your foreman. 



9. Stop machine at once in case of emergency. Do not wait 

 for instructions. 



BT7LES FOB UILLS 



1. Never allow your hand to go past the top of the roll, and 

 never reach over one roll to work on the other. 



2. Watch your hands when the rubber folds over. Don't let 

 them get caught in the folds. Be careful in doubling the ends 

 of batches when "batching out." 



3. Never cross arms when cutting or rolling stock from the 

 mill. Learn to cut and roll with both hands. When cutting 

 from left to right, cut with right hand and roll with left. When 

 cutting from right to left, cut with left hand and roll with right. 



4. Never take anything out of the rolls while the mill is in 

 motion. Stop the machinery. 



5. Never stand on the mill pan, compound boxes, platforms 

 or makeshifts. 



6. Never work with one hand under the rolls while the other 

 is above them. 



7. Take care not to catch your fingers between the guide and 



roll. 



8. The back roll of the mill runs faster than the front. Be 



careful. 



aULES EOS CALEKDEBS 



1. Never pick stock out of the bite of the rolls. 



2. In starting end of liner in building up plies, keep your 

 hands at least six inches from the rolls. 



3. Never start calender unless properly signaled. 



SAFETY IN OPERATION OF MILLS 



SAFEGUARDS ON MILL PARTS 

 A safety throw-out to stop the mill in case of accident con- 

 sists of a horizontal throw-out bar heavy enough to resist the 

 struggling of an injured operator, placed over each mill roll. 



These bars should be located six feet above the floor upon which 

 the operator stands, and in plan be located 18 to 21 inches to 

 the front and rear of the bite of the rolls. Fig. 1 illustrates this 

 double type of throw-out. The cross bars are made of one-inch 

 steel rods rigidly attached to the double levers. 



There are three predominating methods of cutting off the 

 power from the mills: (1) magnetic clutch brake mounted on 

 motor shaft; (2) mechanical clutch on either the drive gear 

 of the mill, or on the motor shaft; (3) dynamic braking of the 

 motor. From the experience the writer has had on all the above 

 types, recommendation is made to use either the magnetic clutch 

 brake, or the dynamic brake, preferably the former, and the dis- 

 cussion is confined to those types of apparatus. If the magnetic 

 clutch brake is used, it is best to place over one housing of each 

 mill an electric cut-out switch. Many installations of mill lines 

 have been made with only one switch for the whole line, the 

 switch being operated by a cable running from one end of the 

 line to the other, or operated by an equivalent rod. This method 

 is not perfectly reliable because of the lost motion due to the 

 variable tension in the cable, or the torsional deflection and 

 binding of the rod, any of which will slow down responsiveness 

 of the switch. In order that the cut-out switch may be opened 

 with the least travel of the safety throw-out bar, the switch spindle 

 should be geared up to the throw-out lever shaft in a ratio of 

 about five to one. Consequently, it is not necessarj- to move the 

 safety bar a distance of more than three and one-half inches 

 either up or down. The travel of the safety bar and lever is 

 limited by an adjustable stop, which prevents damage to the 

 electric switch by being thrown too far, and which makes the 

 safety bar more rigid to resist the struggling of an injured 

 operator. It should not require more than a five-pound force 

 on the safety bar to throw the switch. 



Tlie electric switch should be. entirely enclosed so that dirt 

 cannot gather on contacts. The wiring from the mill switches 

 should be carried in conduits down the housing, and through 

 the mill pits to the panel board and magnetic clutch as shown 

 in Fig. 2. The brake on the magnetic clutch should be operated 

 by a counterweight and be capable of bringing the mills to a 

 complete stop in no greater time than one second. While the 

 mills are running, this counterweight is held inoperative by a 

 solenoid electrified by a circuit which connects the mill safety 

 switches and the clutch. This circuit is fed through circuit 

 breakers which are held closed by a solenoid operated latch. 

 .After the clutch circuit is broken these circuit breakers cannot 

 be closed except by the operator's going to the panel board and 

 resetting by hand. Therefore the clutch cannot be engaged if 

 the operator should first close the safety switch. It is probably 

 useless to describe the well-known construction of the magnetic 

 clutch, but it may be mentioned briefly that this clutch is of 

 the disk type, the two disks being drawn together by electro- 

 magnets. 



Dynamic braking is accomplished by cutting off the current 

 which feeds the motor and at the same time placing a low re- 

 sistance short circuit across the brushes of the motor armature. 

 The motor then acts as a generator requiring considerable driv- 

 ing power. Obviously this power comes from the rotating parts 

 of the mills, decreasing their momentum. As the speed decreases, 

 the power generated by the motor decreases and brings the motor 

 and mills to a smooth yet rapid stop. 



iPaper read before the Rubber Division of the National Safety Council 

 at Milwaukee. Wisconsin, September 30, 1920. 



'Engineering Department, The B. F. Goodrich Co., Akron, Ohio. 



