November 1, 1920 



THE INDIA RUBBER WORLD 



9.' 



preferred type of mill hood. The preferred type is the ordinary 

 box style of hood with the air duct connected to the middle of 

 the top through a flared connection. This style uf hood insures 

 that the air currents carrying dust and heat from workmen will 

 go directly to the middle of the top of the hood, where the duct 

 connection is made. An alternate type of hood is also illustrated 

 in Fig. 4-A. This type of hood has a so-called false ceiling 

 which makes a small space through which the air passes near the 

 outside edges of the hood. This small space creates a higher 

 velocity near the edges of the hood. There is also an opening in 

 the top of this ceiling directly into the air duct. This alternate 

 type does not carry all the dust-laden air directly from operator to 

 the middle of the hood. It has the objection of carrying a great 

 portion of the dust to the front or rear edge, where there is a 

 possibility of its rolling out from underneath the hoods, and it 

 is necessary in order to overcome this last objection to main- 

 tain a very high velocity of air which will actually carry away 

 all of the dust. 



In the preferred type a slower air velocity may be maintained, 

 and it is found that near the center of the hood a considerable 

 amount of the dust actually drops back onto the rolls and is 

 mixed in with the rubber. This is one of the best features of 

 this type of hood, for it does away with the necessity of an air 

 washer, and the small amount of dust which is carried away 

 through the ducts is easily collected. The hood should be con- 

 nected to the air ducts by a flexible connection so that the vibra- 

 tion created on the mill will not be carried to the ducts and 

 cause leaky joints. The ducts are carried to a centrifugal multi- 

 vane exhaust fan which discharges into, preferably, a vertical 

 flue carried to the top of the building. In the case of a one- 

 story building it is preferable to carry this exhaust flue at least 

 forty feet above the ground level. At the base of this flue is a 

 collecting chamber located below the entrance of the fan duct, 

 into which nearly all the dust descends by gravity and may be 

 removed through a cleaning door. For an 84-inch mill the volume 

 of air for the preferred type of hood is 3,800 cubic feet per min- 

 ute, at a velocity of 1,300 feet per minute. The static pressure 

 necessary to be maintained in the ducts varies according to the 

 design of the ducts and the length of runs. Such pressure will 

 rarely exceed one and one-half inches of water. 



In order to offset the large volume of air removed from the 

 mill room through the hoods, it is necessary to feed in fresh 

 air. In suttmier time this is easily accomplished by opening the 

 windows, but in winter it is necessary to force heated air into 



A ir Current carrying 

 I ^ f ♦ + I Dust and Heai away 

 jJJ\ \!;\^rom Workman. 



Alternate Type of 

 Mill Hood 



FIG.4A 



Air J 

 Ducf \ 



\ -Flexible 

 \\v Connection 



^ I 



i-Canvas Curtain on 'xX 



Spring Roller both n 



front and rear if desired 



Przfe,rrzdi Type of Mill 

 Hood 



Fig. 4-A. The Preferred and the Alternate Type of Hood 



the room by fans. This air ought to be heated to about 90 de- 

 grees F. and distributed equally over the entire room. It is also 

 possible, in order to save expense of heating the entire volume 

 of air, to recirculate a portion fed into the flue by exhaust fans, 

 and also to draw air from other portions of the building, pre- 

 ferably from stair and elevator towers. 



With the best type of ventilating system, as described, there is 



still an opportunity- for dust to collect in various parts of the 

 mill room. Perhaps the most frequent cause is from dusting 

 batches of stock with bags of soapstone. This dust will ac- 

 cunnilate on the floor and stock racks. To keep these parts of the 

 building and floor in the cleanest condition a vacuum cleaner is 

 advisable. With this system of cleaning there is no dust stirred 

 up, as is the case with brooms or brushes, and the cleaning is 

 more easily facilitated. With the vacuum cleaner system one man 

 under ordinary circumstances, ought to clean 3,500 square feet 

 of floor per hour. This system is also very desirable to clean 

 walls, ceilings, pipes, machinery and equipment, and motors. 

 Another aid to cleanliness is the running of curbs around all 

 pits, so that rubbish, etc., may not be kicked into them. 



SAFETY IN OPERATION OF CALENDERS 



SAFEGUARDS ON CALENDER PARTS 



The various methods of quickly stopping mills, previously de- 

 scribed, arc equally adaptable to calenders. The dynamic braking 

 of the motor is perhaps most simply applied and operated and re- 

 quires no extra floor space. A throw-out bar is necessary in 

 both front and rear of the calender, and this bar should be a 

 steel rod or pipe, and be placed full width between the calender 

 housings. 



Signal bells,"or their equal, should give warning each time the 

 calender is to start or stop ; one bell to be so connected that any 

 workman may signal when he desires the calender started or 

 stopped, and another bell directly connected with the motor con- 

 troller or other starting and stopping device. The latter bell 

 will automatically give warning to all workmen. If calenders 

 are operated in trains, the safety appliances should be so ar- 

 ranged that operation of any one of the safety switches on the 

 various calenders will instantly stop the entire train. The opera- 

 tion of a train of calenders should be as a unit, and under the 

 control of one operator, the only person who can start the 

 machines. 



All switches and control boards should be of the enclosed type, 

 making it impossible for the operator to be in contact with live 

 parts. Control panels are best situated in a separate room open 

 only to authorized electricians. Rubber floor mats are necessary 

 in front and rear of all control boards. 



Feeding stock into calenders has caused more accidents on 

 these machines than any other operation. Nearly all of them 

 resulted from feeding fabric or sheet rubber into the calender 

 rolls, and into the wind-up. Statistics show that comparatively 

 few accidents have occurred from feeding batched gum, and there 

 is no good reason why any should occur. A sheet metal table 

 about twelve inches wide and the same length as the rolls, lo- 

 cated about six inches below the bite of the rolls, will hold the 

 gum while feeding. If it is necessary to feed small pieces of 

 gum this may be done with the aid of a wooden paddle or 

 pusher. 



Feeding fabric or sheet gum is not so easily accomplished, and it 

 is necessary for the operator to place his hands close to the rolls, 

 unless it is possible to use a guard which will also assist in 

 starting the fabric into the rolls. Although numerous efforts 

 have been made, it seems that no really efficient guards of this 

 type have been devised, and experimental ones have generally met 

 antagonism from the workmen as being a hindrance to rapid 

 and successful work. Such a safeguard is most needed to feed 

 sheet stock between closed rolls, but the space available is not 

 sufficient to provide safety without impeding production by mak- 

 ing it impossible for workmen to place the sheet within a rea- 

 sonable distance from the rolls. 



If a calender does not require the two bottom rolls to be in 

 contact with each other, and if the bottom roll is used only 

 as an idler roll to return the stock to other side of calender, then 

 the bottom roll should be lowered about three inches so that 



