Industry finds frequent need for identifying markers employed in tagging components of complicated assemblies. This is particularly so in the case of complex electrical assemblies such as, e.g., wiring systems employed in aircraft and the like. In such cases, the practice heretofore has been to impress identifying characters into the insulation of electrical conductors, an expedient which risks impairment of insulative integrity. More recently, it has become common to impress or print identifying information onto plastic tubes which are then slipped over the opposite ends of electrical conductors, permitting their tracing when combined with other such conductors in a cable bundle. That process, proceeding as it does on a substantially piecemeal basis, has proved undesirably laborious and, in addition, the dimensional tolerance required for facile addition of the tubular markers to electrical conductors has permitted their free movement on the conductor, so as to require a sharp bend in the wire end to prevent loss of the marker during handling of the free conductor.
Conceivably, the problems of piecemeal printing on wire markers and the like could be alleviated to a degree by a "ticker tape" approach in which a tube was flattened and fed through a typewriter. However, such a system would require extensive typewriter feed system modifications. Moreover, the type, ribbon and platen of a conventional typewriter are designed to make clean impressions on relatively hard, smooth surfaces. In the case of a merely flattened tube, the keys would strike a double layer of soft plastic separated by a small air gap, likely resulting in fuzzy, multiple impressions with standard type mechanisms. Again, by the ticker tape route, the markers are attached in order end to end, so that only the markers at the ends of any given group would be available for installation. Moreover, care would be required to prevent a twist in the tube during the typing since any twist would cause the type to spiral about the tube. With the "ticker tape" tube designed to be heat-shrinkable for minimum bulk installation on a wire or cable, it would not be susceptible to radiant heating to render indelible printed characters thereon, because that heating would prematurely effect heat recovery. Finally, such a tubular marker, unless made heat recoverable would continue to pose the retention problem previously alluded to, i.e., the necessity that wire ends be bent to prevent loss during handling after marker application.
Until the present invention, a need existed for a marker system free of the foregoing problems.