870 THE BKhh SYSTEM TECHNICAL JOURXAL, JULY 195-1: 



for controlling known variables must be made, however, to assure the 

 reliability demanded of heavy duty mass production machines. 



Part II — Automatic Molding of Wire Spring 

 Relay Block Assemblies 



Parallel with the effort directed toward development of wire straight- 

 ening facilities, an investigation w'as undertaken by Western to develop 

 automatic facilities for molding an array of straightened wires into small 

 plastic blocks spaced at specified intervals. These blocks were designed 

 not only to hold the ^^ires securely and to locate them accurately but 

 also to insulate them from each other electrically. The design engineers 

 at Bell Telephone Laboratories had decided, after evaluation of the 

 physical properties of available plastic molding materials, that a thermo- 

 setting phenolic type resin would best provide the characteristics needed 

 for wire spring relay block assemblies. Proceeding on this information. 

 Western Electric development engineers reviewed the merits of molding 

 methods adaptable to embedding a multiplicity of inserts, wires in this 

 instance, into phenolic resin. Such economic factors as molding time 

 and material cost were balanced against molding problems like shrink- 

 age and flow characteristics. It appeared from this review that transfer 

 molding offered the most favorable possibilities. It appeared also that 

 the shortest practicable molding cycle might be achieved by preforming 

 the phenolic resin material, preheating these preforms elect ronicalh^ 

 and automatically feeding them into the molding die. Further study of 

 the molding problems indicated that molding presses for this purpose 

 would have to be specially designed, particularly if multica\'ity dies 

 were to be used. The special design features, such as wider spacing be- 

 tween the tie rods, pro\asion of an electronic preform heater, and micro- 

 timing devices, are discussed later as they become pertinent to the 

 description of the machines finally adopted. 



automatic molding machine 



Hydraulic molding presses appeared to offer the most ad\antages for 

 this job. Essentialh% these consist of two opposed hj'draulic rams 

 mounted \'ertically; the lower and more powerful ram providing the 

 force required to close and hold closed the split die employed and the 

 upper ram providing the force needed to transfer the phenolic resin in a 

 softened or plastic state into the die cavities. 



X'nusually wide spacing between the tie rods of the press had to be 

 pro\ided to accommodate the complex progressive die required to make 



