October 1, 1920.] 



THE INDIA RUBBER WORLD 



23 



canizer with cold water at the end of the cure. A source of 

 trouble encountered with return pipes is the eating avva3' of 

 the pipe, fittings and valves, due to the action of a weak solu- 

 tion of sulphurous acid formed after vulcanization from the 



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Mechanical Air Circul.\tion 



sulphur dioxide, the effect of which is worse than a strong 

 solution. 



Lead-lined pipes and fittings have been used but even they are 

 attacked by the acid especially at the joints. Extra heavy cast- 

 iron flanged or wrought-iron welded flanged pipe with extra 

 heavy cast-iron flanged fittings will give best and longest serv- 

 ice. Steel pipe should never be used. When monel metal 

 diaphragm disks become pitted they may be replaced at con- 

 siderably less expense with an alio}' of 90 per cent aluminum 

 and 10 per cent copper which gives equally good service. 



A tremendous amount of steam goes to waste, owing to the 

 fact that a steady circulation is required, and because an un- 

 obstructed exhaust is required. The only possible re-use may 

 be obtained by the installation of a specially constructed water 

 heater built of very heavy copper coils or tubes and cast iron 

 shell, allowing free passage of the e.xhaust steam. Even this 





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Circulation Without Mechanical Means 



cannot be guaranteed to withstand the acid fumes more than 

 several years. 



AUTOMATIC CONTROL AND THERMOMETER RECORDERS 

 The importance of automatic control of the steam supply and 

 exhaust to maint.iin even temperature can hardly be overesti- 



mated and a liberal installation of thermometer recorders in 

 different sections of the vulcanizer will be well repaid in the 

 perfection of the product, if the steam supply and exhaust are 

 regulated to make them record alike. This can best be accom- 

 plished by having a central control room with all recorders 

 mounted on a panel in front of an operator who can control the 

 diaphragm valves with aid of compressed-air needle valves. 

 One operator can take care of two or more vulcanizers. The 

 thermometer bulbs become pitted by the action of sulphurous 

 acid and can be renewed by an alloy consisting of 75 per cent 

 lead, 15 per cent antimony and 10 per cent tin. 

 CLOSED-CURE METHOD 

 In the closed-cure method the product is cured through the 

 medium of air heated from the radiation of steam coils, and is 

 accomplished in a box-type heater where no pressure occurs. 

 They are usually built of the following materials: (1) wood, 

 sheet iron, asbesto-cel and magnesia; (2) tile, sil-o-cel or burnt 

 cork and magnesia; (3) structural sheet iron, asbcsto-cel and 

 magnesia. All depending on cost, insulating qualities, and fire 

 hazard. No. 2 and 3 being the preferred class. Broken up air 

 space gives the best insulating qualities and can be obtained 

 with asbesto-cel. 



The Use of Mechanically Operated Shutters 



Fig. 3 shows a typical heater absolutely square for better 

 distribution of its piping arrangement. With good insulation 

 a ratio of one square foot of pipe surface to five cubic feet of 

 contents will produce temperatures up to 300 degrees F. with 

 steam at 100 pounds pressure. The number of supplies is de- 

 termined by size of the heater. A heater about 20 feot square 

 should have at least four supplies, each of which should be con- 

 trolled automatically by temperature control equipment. 



Ideal vulcanizing conditions are obtained in absolutely still 

 air with even temperatures but the latter cannot be accomplished 

 in still air and therefore a minimum of circulation should be 

 striven for in order to obtain even temperature throughout the 

 heater. The following methods may be used for accomplishing 

 this purpose: (1) use of a slow-moving paddle directly over the 

 steam coils; (2) use of a blower with perforated galvanized 

 iroa pipes, drawing the hot air over the coils and discharging 

 it at the top of the heater, as shown in Fig. 4. The capacity in 

 cubic feet per minute of blower should be 25 per cent of the 

 volume of the heater; (31 use of galvanized iron air ducts 

 without mechanical means of circulation, as shown in Fig. S; 

 (4) use of shutters in combination with any one of the above 

 methods as shown in Fig. 6. Automatic controls and tempera- 

 ture recorders should be provided liberally as mentioned under 

 the open-cure method. 



