140 



PARA RUBBER. 



other methods it takes days to dry, or which cannot be dried at 

 all, when placed in these chambers are usually dry after a few- 

 hours, without the substances being in the least impaired 

 through being overheated. 



" The charging of the chamber is simple and easy, the work- 

 ing very clean and reliable. The temperature can be regulated 

 by valves in the steam pipes. The drying is absolutely certain 

 and is quite independent of climatic conditions. 



" By using hot water for heating, and by means of an air 

 pump giving a high vacuum, the evaporation of the water con- 

 tained in the materials that are to be dried takes place at as 

 low a temperature as 63 Fahr. (17 Cent.). 



" The rubber sheets, biscuits, or crepe are spread evenly three 

 or four layers deep on trays, which are then placed between the 

 heating shelves of the dryer. By means of a small air pump a 

 vacuum of about 28 to 28^ inches is produced within a few 

 minutes of the closing of the swing hinged door. This pump 

 requires from ii to 2 H.P. at first, but in a few minutes | or 

 i H.P. suffices to maintain the vacuum. 



" The steam that has been used to drive the pump is passed 

 to the heating shelves of the chamber and is sufficient to dry 

 the rubber. 



" When the temperature of the wet rubber reaches about 90 

 Fahr., evaporation most rapidly takes place. The vapour passes 

 to a small surface condenser, the pump being a dry one. 



" The temperature of the drying rubber remains constant, 

 slowly rising towards the completion of the drying. A charge 

 is dried in from ij to 2 hours, and four to five charges can be 

 dried within 10 to 12 hours. 



" Vacuum dried rubber remains much more elastic and softer 

 to the touch than air dried ; this is owing to the absence of the 

 air with its oxygen, its surfaces have not become hardened or 

 oxidised. The only heat required is the steam to drive the 

 air pump ; its steam cylinder is 4^ in. diameter by 6~^ in. stroke, 

 or say steam equivalent to about I H.P. 



" The drying is quite independent of climatic conditions, and 

 the space occupied is very small. 



" The chamber, pump, and condenser are erected and tested 

 in the works for air and steam tightness. The pump and con- 

 denser are packed and sent complete ready for placing in 



