22 



THE INDIA RUBBER WORLD 



[OCTODER 1, 1920. 



STEAM REQUIREMENTS FOR VULCANIZING 

 By IVallcr J. Biltcrlich 

 'T'liE most important requirements in vulcanizing rubber prod- 

 •*• nets are even temperatures. Different products require 

 varying time durations of cure and some require a steady rise 

 in temperature, whereas others require a quick rise and then a 

 constant tempcratnrc. The steam distribution should be de- 

 signed to meet the different requirements. 



Engineers who are not familiar with vulcanizing processes 

 believe that rubber plants are great wasters of steam ; how- 

 ever, until there is a perfect trap on the market that will 

 allow a steady instead of a fluctuating circulation, steam-traps 

 will be by-passed that a continuous flow of steam may be ob- 

 tained to insure even temperatures. 



OPEN-CURE METHOD 



In this method the steam comes in direct contact with the 

 product and the cure is accomplished in a shell vulcanizer where 

 pressures between 20 and 70 pounds are used, depending on 

 goods to be vulcanized. The essentials for this method are 

 dry steam, ample supply, and quick discharge. The former may 

 be obtained by supplying boiler pressure up to ISO pounds, super- 

 heated at the boiler, directly to vulcanizer and reducing the 



^ ^imc^ £b^/-^ Til 



SO » /e'O ~H>^tr^/xa/r 



dSooD^ ,arf<j^n /fvfrr -^tkA^ ^^b tX ff. 



yve /V&/ 



Piping for 5 by 16-Foot Jacketed He.mer 



pressure by means of a diaphragm valve close to vulcanizer. 

 This has a superheating effect on the reduced pressure entering 

 the vulcanizer, due to the high temperature of the higher pressure 

 in the main supply. 



A superheating effect of from 3 to 4 degrees F. is sufficient and 

 if superheated steam of higher temperature is in the main supply 

 pipe, its temperature cannot be controlled evenly by automatic 

 vulcanizer control. To overcome this efifectivcly it is necessary 

 to install a saturator which is a commercial temperature control 

 that automatically sprays water into the main steam supply, 

 thereby lowering the steam temperature to within 3 to 4 degrees 

 F. of its saturated value. 



Should the steam be wet or condense as it enters the vul- 

 canizer, the goods will l)e stained, causing a defective product. 

 To avoid this the vulcanizer is warmed up first. This may be 

 accomplished in several ways, namely: (1) by jacketing the shell 

 vulcanizer and supplying it with steam at higher pressure. The 

 jacket, however, is expensive in first cost but some goods can- 

 not be cured otherwise with good results. The temperature of 

 the steam should be about 10 degrees F. higher than the steam 

 entering the vulcanizer; (2) by installing coils in the interior of 

 the vulcanizer at bottom and sides and supplying steam at higher 

 pressure; (3) by using compressed air, superheated to high tem- 



peratures; (4) by using a combination of two or all three of the 

 above methods, depending on the quality of goods to be cured 

 and quality of steam available. 

 Fig. 1 shows a typical piping system for a S by 16-foot jacketed 



*'>»J»*..w ^ t ) %r ^ 



/ys A/o2. 



Superheating Coils and Heated Compressed Air System 



vulcanizer. Fig. 2 shows the warming-up' feature with super- 

 heating coils and the heated compressed air system. 



Referring to Fig. 1, the steam supplied through perforated 

 pipes inside the heater near the bottom is to insure hot steam 

 at the bottom. If the supply entered near the top the hot steam 

 would remain near the top and the bottom would be lower in 

 temperature. The total area of all the perforations should be 

 at least 10 per cent less than the area of the pipe to create an 

 equal velocity through each perforation. 



The several bottom outlets serve two purposes, one of which 

 is to drive out all the air which is heavier than steam and which 

 if mixed with steam during vulcanization has a powerful oxidiz- 

 ing effect on the product. Particular care should be taken to 

 locate the outlets as close to each end of the vulcanizer as pos- 

 sible as this is where the air is most likely to pocket. The other 

 purpose is for quickly discharging the steam at the end of 



T^f^ -^foh ^irmr ^<T 0*4«- 



-Si«^2- 



tvtji .5VVW-T Sm^^ 



• *" J 



armiffiriiiimiiiiaiiiii 





/yca/VaS 



Typical Square Heater 



the cure to prevent overcuring and to allow immediate removal 

 of the goods. 



In this respect the main return pipe should be amply large 

 with no back-pressure valve on the exhaust riser. In pit vul- 

 canizers for tires, overcuring is prevented by flooding the vul- 



