NEW RECORDING MEDIUM 



533 



and forming the compound into bands by conventional rul)ber molding 

 and curing techniques. The i-esulting bands show a tensile strength of 

 about 2500 pounds per scjuarc inch, and the elongation before breaking 

 is about 700 per cent. No particularly difficult mainifacturing problems 

 are encountered, and present evidence indicates that satisfactory overall 

 quality control can be achieved by carefully controlling the compounding 

 constituents, the milling and the molding. 



Several bands which are used in telephone services are shown in Fig. 1 . 

 These bands are utilized in recorder-reproducer mechanisms by stretch- 

 ing them over a cylinder, on which pivoted magnetic pole-pieces trace a 

 cylindrical or a helical track as it rotates. 



When the bands are first taken from the mold they exhibit a high 

 coefficient of friction. After a few hours enough paraffin migrates to the 

 surface to form a thin, slippery film. If the bands are then put into 

 service the pole-pieces form a polished track and the continuing migra- 

 tion of paraffin maintains the lubricating film between the band and the 

 pole-pieces. 



If tliis recording medium is used intermittently, the self-lubrication 

 may cause difficulty. The migration of lubricant to the recording surface 

 is continuous, and the lubricant may accumulate on the surface in suffi- 

 cient thickness to impair the contact with the magnetic head if the 

 recording equipment is not operated for several weeks. It may then be 



Fig. 1 — Typical magnetic rubber bands used in telephone applications. 



