WIRE STRAIGHTENING AND MOLDING FOR RELAYS 869 



Fig. 7 — Photograph showing the affect of residual twist in the upper set of 

 wires as compared to freedom from residual twist in the lower wires. 



twist has been established which has been successful generally in main- 

 taining acceptable limits on residual twist. 



There are three variables which largely control the (luality of straight- 

 ened wire. The first is the physical properties of the wire itself. Although 

 a shipment of wire may, on the basis of the sampling method employed, 

 meet specification requirements limiting physical and chemical char- 

 acteristics, an occasional spool or part spool of \\ire can be expected 

 which will be enough outside limits to cause unsatisfactory straightness 

 and unmanageable residual twist. 



The second variable affecting straightness and twist in wire processed 

 on multiple head machines lies in small differences between the rotating 

 head assemblies. While all critical dimensions of the die blades, spindles, 

 and spindle housings are held to close tolerances, it is possible to obtain 

 an accumulation of dimensional deviations in some spindle assemV)lies 

 of such magnitude as to cause appreciable difference in ^^ire t^\ist and 

 sometimes in wire straightness. It has been necessary, therefore, to 

 provide means for balancing such dimensional variations. 



The third variable is wear on working surfaces of the die blades. Con- 

 tinued sliding of wire over die blade surfaces eventually produces grooves 

 which decrease offset and increase clearance in the wire path. It has been 

 found in general that, as the die blades wear, t\dst decreases until it 

 eventually reverses direction. Simultaneously, straightness may improve 

 to a critical point from which it rapidly deteriorates. Accordingly, re- 

 placement of die blades must be made before wear has rendered them 

 ineffective. 



CONCLUSIONS 



Satisfactory performance of the multi-head wire straightening ma- 

 chines described has been demonstrated dining the pilot plant period 

 of wire spring relay manufacture. Further refinements in the means 



