PLASTIC MATERIALS IN TELEPHONE USE 



491 



of making all of these tests have been worked out and are supplemented 

 by apparatus tests made on the manufactured product. 



There is no known test that will measure completely the quality 

 of a phenol plastic part and it is necessary to resort to the expedient 

 of testing standard bars molded under specified conditions. Five bars 

 are molded in a positive type die as shown in Fig. 5. The step arrange- 



Fig. 5 — Specimen mold and bars. 



ment provides for flow within the die similar in many respects to the 

 molding of actual parts. The test bars provide transverse or flexural 

 strength, impact insulation and cold flow test specimens. The methods 

 used, whenever possible, are those of the American Society for Testing 

 Materials. 



