WIRE STKAir.IlTKXlNfi AND MOLDING FOK RELAYS 873 



for this purpose. To obtain uniformly low water content in these pre- 

 forms, it is necessary to store them in an air conditioned chamber for a 

 three week period to assure attaining eciuilibrium conditions. 



PREFORM HEATING 



An electronic preform heater is a means of increasing molding ma- 

 chine production by shortening the time the phenolic resin must be re- 

 tained in the molding die during each cycle. This is done by adding to 

 the preform, just before it enters the die, much of the heat required to 

 plasticize the resin. Thus, as one charge of compound is being molded 

 in the die cavity, another is being preheated as part of the molding 

 cycle. The amount of preheat that can be permitted is limited by the 

 extent to which heat induced chemical reaction can be tolerated outside 

 the molding cavity and varies with the size and contour of the die cavity. 

 The rate at which the preform is heated influences its consistency at a 

 given temperature. 



A feed mechanism has been provided to convey the preform from a 

 magazine to the electronic heater and thence to the die. This mechanism 

 consists of a horizontal guide plate extending between the two grids in 

 the upper part of the press. The preform is pushed along this guide plate 

 by a metal bar mounted on endless roller chains at each side of the guide 

 plate. In operation, a preform from the magazine is pushed to a position 

 between the electrodes of the dielectric heater. The push bar is then 

 backed away a small distance so that it will not interfere in the inductive 

 field. Upon completion of the preheating operation, the push bar shoves 

 the heated phenolic preform to and beyond a drop off position above the 

 open end of the transfer cylinder of the molding die. The conveyor 

 continues to operate until the push bar has removed a new preform from 

 the magazine and loaded the heater in preparation for the next cycle. 



PRESS CONTROLS 



The electrical controls or "brain" of the production unit are housed 

 in a cabinet adjacent to the molding machine. The operation of the 

 press, the electronic heater, the feed mechanism and the pneumatic 

 device on the die are all coordinated into precise sequences by micro- 

 adjustment of these controls. Fig. 10. Any operational sequence or 

 length of cycle desired can be established for repetitive manufacture. 

 On the other hand, the press and the electronic heater can be placed 

 on manual control at any time. 



