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tends to shrink. If the fiber is not sufficiently hard as manufactured, 

 it will also flow under pressure. 



In telephone relays of a commonly used type, illustrated by Fig. 5, 

 the contact springs are insulated from each other by thin sheets of 

 phenol fiber, and any material change in dimensions of these insulators, 

 due to moisture absorption or cold flow, will alter the spacing of the 

 contacts, thus throwing the relay out of adjustment. To measure 

 these tendencies on materials used in spring pile-ups, we use the method 

 illustrated by Fig. 6. It will be seen that a Brinell machine, usually 



Fig. 6 — Modified Brinell machine for flow-test of insulator laminations. 



employed for metals testing, has been modified to use a flat-ended 

 plunger resting on a pile of insulating material. The test material 

 is first cut into pieces 'jA" square and then subjected to atmospheric 

 conditions which would cause it to take up an amount of moisture 

 comparable to that expected under manufacturing conditions. The 

 pieces are then stacked and a pressure of 2,000 pounds per square inch 

 applied. The testing apparatus is installed in a heat insulated box 



