PLASTIC MATERIALS IN TELEPHONE USE 



489 



hold them in their true position. Hence more delicate inserts are 

 possible by this method of manufacture. Since the material is en- 

 closed in an auxiliary pressure chamber and is not exposed to the 

 atmosphere, greater freedom from room dust is possible, rendering 

 this method ideal for colored plastics. A terminal block used to 

 terminate the subscribers telephone cord is made from thermoplastic 

 molded cellulose acetate compounds as shown in Fig. 3. 



Finishing and trimming methods are largely determined by the 

 design and the class of service required of a molded part. In the case 

 of the injected cellulose acetate terminal block mentioned above the 

 gates are trimmed off by a simple trimming punch and the scrap is 



Fig. 3 — Terminal block. 



reused. This part is covered in service and the appearance of the 

 block is therefore not a major factor. 



The telephone handset, since it is in the hands of the public, must 

 be carefully finned for two reasons: (t) to avoid surface roughness 

 and (2) to provide good appearance. The handset handle was orig- 

 inally ground along the fin left by the semi-positive mold and then 

 buffed. The operation was not only expensive but tended to grind 

 off a large portion of the surface of the handle. This removed the 

 resin-rich surface and tended to expose the filler of the phenol plastic 

 molding compound, thus reducing the appearance life of the handle. 

 The more recent product of the Bell System is being grooved along 

 the die parting line. This removes the fin, a minimum of the resin- 



