V 



200 THE RUBBER TREE BOOK 



out again wetting them, but a good deal of heat is evolved in 

 the operation and the rubber is apt to be affected thereby. 



It is very important to have at least one extra mill available 

 in the case of breakdowns. Where and when the macerating, 

 creping and finishing-mills cannot be all duplicated, at least the 

 crper should be. The next in importance to duplicate is the 

 macerator. 



A spare pair of rollers ought always to be kept in stock in 

 the storehouse for each type of mill. If there are two or more 

 mills of a type such as the creper in a large factory one spare 

 pair will suffice for stock. 



These spares should be kept thoroughly well greased and 

 from time to time inspected to see that they are in a good state 

 and not turning rusty. Having a spare pair may be the means 

 of preventing very serious inconveniences in the case of acci- 

 dents or from rollers wearing out and not doing their work 

 properly. 



Misunderstandings arise as to the output capacity of the 

 mills from the fact that when an engineering firm states that 

 a mill can turn out 300 Ibs. of rubber daily, the fact is over- 

 looked by some inexperienced people that the same 300 Ibs. 

 of rubber have to pass successively through the macerator, 

 the creper and the finisher. A battery of three mills to 

 which always should be added at least one extra to lighten 

 work and as a stand-by in breakdowns is capable of under- 

 taking a yearly output of 250,000 Ibs., working ten hours daily. 

 This is really as much as such a plant is able to handle satis- 

 factorily if the rubber is to be thoroughly washed and thoroughly 

 rolled. In actual practice it is found that eighteen mills are 

 quite severely enough taxed to get through an output of 

 i,35o,ooo Ibs. per annum with one of the mills occasionally off 

 for repairs. This is the experience of working year in year out 

 of the best-equipped factories and may be taken as a safe 

 guide. 



It is no doubt the case that crpe-rubber can be overworked 

 in the washing-mills at the expense of much of its nerve and 

 tensile strength. It is a well-known fact that molecular changes 

 set in in a steel spring when it is " fatigued " by being too often 

 bent, and the tearing and stretching to which crpe is subjected 

 in the washing-mills in all probability effects molecular changes 



