Coil of tapered wire

Abstract

A coil of tapered wire for forming coil springs, formed by winding substantially in concentric loops a quench-hardened and tempered tapered wire having a successive arrangement of tapered wire segments each consisting of a thick section, two thin sections and two tapered sections connecting the thin sections to the opposite ends of the thick section, respectively. The tapered wire is subjected to a preforming action immediately before being wound in loops on a winding drum, to form plastic bends in the thick sections and plastic bends of a radius of curvature greater than that of the plastic bends in the thick sections so that the tapered wire is wound in substantially uniform, concentric circular loops on a winding drum. When the tapered wire is unwound from the coil and is subjected to a straightening process of a fixed straightening arrangement of a series of straightener rollers before being coiled in tapered wire coil springs on a coil spring forming mill, the thick sections undergo a straightening action greater than that acts on the thin sections, so that which the tapered wire unwound from the coil of tapered wire is straightened in a substantially straight tapered wire and thereby the tapered wire is coiled in tapered wire coil springs having a correct size and a uniform shape.