82 



THE INDIA RUBBER ^A^ORLD 



[December i, 1902. 



VARIABLE SPEED DEVICES FOR RUBBER MILLS. 



By J. U. De Wolf. 



MANY of the machines in a properly equipped rubber 

 factory are an exception to Shakespeare's saying that 

 "Still constant is a wondrous excellence," for the 

 varying conditions under which they are run have 

 rendered variable speeds necessary and have taxed the in- 

 genuity of our mechanics in this direction. 



Without attempting to refer to many of the different kinds 

 of rubber machinery that are rendered more efficient by an easy 

 and economical variation in speed, brief attention will be called 

 to a few of the devices in use. The order in which they are 

 mentioned implies nothing as to relative merit or extent of use 

 of the different types of apparatus, but follows the general 

 order in which the writer became acquainted with them. 



Numerous devices are in common use for operating and 

 varying the speed of machine tools, but although many of them 

 are found in connection with the rubber industry, they will not 



,. be described 

 now, but refer- 

 ence will first be 

 made to what is 

 unquestionably 

 the most impor- 

 tant machine for 

 which a varying 

 speed is desired 

 — that is, the cal- 

 ender. 



The form of 

 gearing shown in 

 Fig. I is repro- 

 duced by cour- 

 tesy of the Par- 

 rel Foundry and 

 Machine Co., 

 and is designed 

 to give three 

 speeds to the 

 calender. The main driving shaft, which runs at a constant 

 speed of from 50 to 75 revolutions per minute, carries three 

 friction clutches attached to gears. Each of these clutch gears 

 is in contact with a gear keyed on the calender-driving shaft. 

 These gears can be proportioned to give almost any three 

 speeds desired, and the change from one speed ttj another is 

 made by simply throwing in the proper clutch. Starting and 

 stopping is also controlled by the same clutches. It will be 

 noted that with this arrangement it is possible to use but three 

 different speeds, and another, or different, speed cannot be ob- 

 tained except by removing a pair of gears and replacing them 

 with another pair of a different size and ratio of diameters. 

 There is, however, little to get out of order ; the speeds are 

 positive, and for a calender requiring only such changes of 

 speed as the arrangement is capable of, it does its work in a 

 most satisfactory manner. The floor space required by such a 

 device, giving three speeds, is about 8 feet 6 inches in length, 

 parallel to the calender shaft, by 5' feet 6 inches wide. In case 

 only two speeds are desired, one clutch and pair of gears can be 

 omitted, and the floor space would then be shortened to about 

 5 feet 9 inches long. 

 In cases where more changes of speed are desired, use has 



FIQ. 1.— THE FARREL CALENDER DRIVE, No 7. 



been made of friction driving devices, the driving surfaces be- 

 ing either discs or cone pulleys. The first of these that will be 

 described is the Evans friction cone, and is in successful use, 

 driving a variety of different kinds of machinery, although 

 none have been applied to rubber calenders. The cut (Fig. 2) 

 shows the principle and construction of these cones, but does 

 not shpw the attachment to any machine. The two cones have 

 their axes parallel, but are separated from each other by a 

 space about the thickness of the friction belt which transmits 

 the power from one to the other. This belt can be moved 

 longitudinally along the cones by a shipper arranged for that 

 purpose, and the speed thus varied anywhere within the limit 

 for which the cones are made. There is also means for forcing 

 the cones together, so that they will press tightly against the 

 friction belt. In the overhead type of cones this tightening 

 device is operated by a handle similar to an ordinary belt or 

 clutch shipper, and is used to start and stop the machine the 

 same as a clutch. The Evans cones are made to give quite a 

 wide range of speeds and powers, although their use is confined 

 principally to work under 15 or 

 20 H. P. 



Another form of controller that 

 is in successful use is the Con- 

 solidated speed controller, shown ^ 

 in Fig. 3. driving a rubber calen- 

 der. The essential features of this ' 

 device are a pair of discs with 

 deep annular grooves in their op- 

 posed faces. One is fastened to 

 the shaft and the other to a sleeve -[|jg 

 surrounding the shaft. Between , 

 these discs are two friction rol 

 lers, supported on bearings sepa-i^^^j>.JiW, 

 rate from the discs, and so ar- 

 ranged that both can be turned 

 simultaneously and made to vary the angles made by their 

 axes with the axis of the discs. The radii of the rollers are the 

 same as the radii of curvation of the annular grooves in the 

 discs. If the friction rollers are set so that the planes of the 

 rollers are parallel to the shaft carrying the discs, and power 

 is applied to revolve one of the discs, then the other will re- 

 volve at the same speed in the opposite direction, as the fric- 

 tion rollers are in contact with both discs at the same distance 

 from their axes. Now if the friction rollers are moved so that 

 their axes are not parallel with the main shaft, then they will 

 be in contact with one of the discs nearer its center than their 

 place of contact with the other disc, and consequently the rel- 

 ative speed of the disc will be changed. Pressure between the 

 discs and friction rollers is obtained by a spring operated by a 

 clutch. 



The controller shown in the cut is a double one, having, for 

 greater power, two pair of discs and friction rollers instead 

 of one pair ; with this machine a maximum speed of five times 

 the minimum speed can be obtained and the floor space occu- 

 pied is about 7 feet ginches long by 3 feet 4 inches wide, includ- 

 ing the clutch, which is a part of the device and is used for 

 starting and stopping. 



Fig. 3, which appears on the following page, represents an 

 installation in the factory of the Hood Rubber Co. 



FIQ. 2.— EVANS FRICTION CONE. 



