Filament curling method

Claim 1

In the method for producing curled plastic filament in which said plastic filaments are helically wound around a mandrel to curl the filaments and are thereafter moved along the mandrel through a heat-treating chamber to permanently set the curl, the improvement comprising heat-treating said plastic filaments while wound around the mandrel in the heating chamber with a combination of steam and heat derived from an electric heating coil, said heating coil being maintained at a temperature above the melting point of said plastic filaments whereby if said heating coil were used alone, the heat from said heating coil would cause the surface of said mandrel to reach a temperature above the melting point of said plastic filaments during extended residence time in said heating chamber, said steam being introduced into said chamber at a temperature below the melting point of said plastic filaments, so that the combination of the heat generated by said coil and said steam result in an atmospheric temperature in said heating chamber above the plastic deformation temperature of said filaments and below the melting point of said filaments which is sufficient to permanently set the curled filaments moving through the heating chamber but is insufficient to melt said filament, and in a surface temperature on said mandrel below the melting point of said filaments whereby extended residence time in said heating chamber will not cause said plastic filaments to become melted on to said mandrel thereby avoiding the necessity for clean-up if said method is interrupted.