The conically wound spool of stitching wire is designed to be dewound “overhead”, the cone shape winding eliminates the possibility of “dropping laps” which causes wire tangles. The bobbin remains stationary and a “torsion” effect builds up in the wire.
The parallel wound spool of stitching wire is designed to be revolved off usually into inline stitching on Presses.
Because the wire is dewound by revolving there is no “twist” in the wire.
Basically there are two types of galvanised/zinc coatings.
a) Electrogalvanised
b) Hot Dipped Galvanised
Both wires are acceptable providing that the wire is perfectly clean prior to zinc coating. After galvanising the wire is drawn through a series of wire drawing dies which work hardens the wire and at the same time promotes a smooth, bright and adherent coating.
We always apply a lubricant on top of the galvanised coating to help the wire slide through the guides of the finishing machines.
Usually when the zinc comes from the surface of stitching wire it is being mechanically removed by scrapping over machine parts or insufficient tolerance on wire guides.
Remember is it always good practise to regularly maintain machine parts, ensure good wire alignment through guides and apply a light machine or synthetic oil to help the wire through your equipment.
A simple test to detect defective zinc coating is a “wrap” test by wrapping the suspect material around it own diameter. Close examination reveals an “orange peel” effect or “sparkles” if the zinc lifts from the surface of the wire.
We always ensure that the wire is properly heat treated to give consistent ductile properties, and the carbon content and work hardening process in the steel gives the strength to penetrate the work piece.
Brittle wire can be as a result of bad steel making practise,poor heat treatment,or metallurgical defects.
It is easy to identify a “brittle” wire by doing a simple snarl test ie. bend the wire tightly through 360 degrees then bend is back on its self. If the wire breaks it is brittle.
We usually find that breaking stitches are as a result of badly set equipment which causes a “notch fracture” on the corner of the crown of the stitch. When clenched the corner fractures.
The "cast" in the wire is the natural curvature in the wire wound onto the reel.What ever the size of spool is being employed on your finishing equipment, the wire should be adequately cast to a diameter which is slightly bigger than the flange diameter with no helix.
Sometimes the natural diameter of the wrap of wire can be considerably smaller than the flange diameter,or there can be a “wild helix”,both of these defects can be detrimental to satisfactorily dewinding and stitch formation.
page last updated: 24/08/2018
