302 Spring Wire - Kinks and Pay-Off Tension Control
302 stainless steel spring wire
,kink-resistant spring wire
,pay-off tension control wire
302 Spring Wire - Kinks and Pay-Off Tension Control
Of all the defects that stop a coiler, the kink is the least visible on a certificate and the most expensive in lost time. A kink is a short permanent bend where the wire was folded tighter than its own elastic limit, and it cannot be straightened by tension. It arrives at the feed rolls as a hard spot, jams the tooling, and if it reaches the spring it leaves a notch that fails in fatigue. This page explains where kinks come from, why the pack form and the pay-off arrangement matter more than the wire itself, and how to set up a coil so that the wire comes off straight every time.
Product Specifications
| Item | Specification |
|---|---|
| Product Name | 302 Soap Coated Stainless Steel Spring Wire |
| Material | AISI 302 / SUS302 / UNS S30200 |
| Diameter Range | 0.15-12 mm |
| Diameter Tolerance | ±0.01 mm (fine wire), ±0.02 mm (0.5-3 mm), ±0.03 mm (above 3 mm) |
| Tensile Strength | 1400-1800 MPa, spring temper (size dependent) |
| Cast Diameter | 300-600 mm typical, agreed per pack form |
| Pack Form | Free coil, level wound spool or drum, chosen to suit the pay-off arrangement |
| Coil Weight | 1-100 kg |
| Surface | Bright drawn, soap coated |
| Applicable Standards | ASTM A313, EN 10270-3, GB/T 24588 |
What a Kink Is and Why It Cannot Be Fixed
A Fold Beyond the Elastic Limit
Wire can be bent and will spring back as long as the surface strain stays below the elastic limit. A kink is what happens when the bend goes far enough that part of the section yields permanently: the wire now has a short segment with a different curvature and, at the transition, a local reduction in section. Pulling the wire afterwards does not remove it, and the spring-back that follows only redistributes the deformation. The kink stays, and the section at the fold is thinner than everywhere else.
What It Does to the Part
There are three consequences, and any one of them justifies rejecting the coil. The feed rolls lose grip at the fold and the cut length becomes wrong. The coiler tooling takes a shock load and the pitch scatters. And if the wire is used, the fold becomes a stress concentration on the inside of a coil, which is where bending stress is already highest, so the spring fails there rather than anywhere else. At 0.2 mm the fold is small enough to pass a visual check and still ends the life of the spring.
Where Kinks Come From
Pay-Off Geometry
Most kinks are made at the machine, not at the mill. An over-end pay-off pulls the wire off the coil along its axis, so every turn adds a twist and the wire can loop back on itself when tension drops. A tangential pay-off takes the wire off the outside of the coil without twisting it. Where a free coil is used on a machine set up for a spool, kinks appear within the first few metres and then intermittently for the rest of the coil.
Cast That Is Too Tight
A tight cast means the wire wants to form a small circle, and the loops press against each other in the pack. When the wire is pulled, the loop that comes free has to open against the tension, and at low pay-off tension it snaps over and folds. A slightly looser cast pays off smoothly at low tension, which is why the cast value should be matched to the machine rather than set as tight as possible.
Manual Handling and Storage
Coils dropped, stacked on their side, or opened by hand to find the end develop kinks before they ever reach the machine. A coil that has been stored on a pallet with weight on top takes a permanent set that shows up as a wavy pay-off. Storage on a proper stillage and opening the pack correctly are free measures that prevent most of these.
Setting Up So the Wire Comes Off Straight
Match the Pack to the Pay-Off
A level wound spool with a controlled traverse pays off tangentially and needs only a light brake. A free coil needs a turntable or a de-reeler with a dancer arm to keep tension constant as the coil diameter changes. A drum needs a flyer or a capstan take-off. Choosing the pack form to match the machine removes the kink mechanism entirely, which is more reliable than trying to correct it downstream.
Keep a Minimum Tension
Kinks form when tension drops near zero, because that is when a loop can cross over itself. A dancer arm or a spring-loaded brake that maintains a minimum tension through the whole pay-off cycle, including when the machine stops and starts, prevents the condition. Setting the brake only high enough to stop backlash is a common mistake; the requirement is a stable minimum, not a high average.
Check on Arrival, Not on the Machine
Drawing two or three metres off the outside of the coil and letting it hang shows both the cast and any kink. Running a gloved hand along the length feels a fold immediately, even at fine diameters where the eye will not catch it. Doing this before the coil is loaded costs a minute and prevents a stopped line.
Applications
High Speed CNC Coilers
Machines running several hundred parts a minute cannot tolerate a kink anywhere in the coil. These lines are normally fed from level wound spools with a dancer controlled pay-off, and the cast is specified to suit the machine rather than to a general value.
Fine Wire for Instruments and Mesh
Below 0.5 mm the wire is light enough that a loop can lift off the coil on its own, so the pay-off path is usually enclosed and the tension is controlled at a low but constant value. Fine wire for weaving is normally supplied on spools for the same reason.
Wire Forms and Bending Machines
Bending machines index by length, so a kink that changes the effective length produces a part out of tolerance before anything jams. These machines benefit from a straightener between the pack and the feed rolls, but the straightener only removes cast and helix, not a kink that has already formed.
Product Advantages
- Cast and helix controlled and stated, so the pay-off behaviour can be matched to the machine before the coil is loaded.
- Pack form available as free coil, level wound spool or drum, suiting tangential, dancer or flyer take-off.
- Coil winding tension controlled during packing, avoiding the tight cast that causes tangling at low pay-off tension.
- Diameter tolerance of ±0.01 mm on fine sizes, keeping the feed grip and the cut length stable at small diameters.
- Surface free of seams and laps, so a snag in the feed path is not confused with a wire defect.
Quality Control
Cast and helix are checked on samples from each packing lot using the agreed method. Diameter, tensile strength and elongation are tested per lot, and the surface is inspected over the full coil length. Where a kink is found in a delivered coil, the position along the coil and the pack form are recorded, because a pattern usually points to the packing or the transport rather than to the drawing.
Selection and Ordering Notes
- State the pay-off arrangement on the machine: over-end, tangential, dancer controlled or flyer. The pack form follows from it.
- Give the cast range the machine needs rather than a general figure, since too tight is as damaging as too loose.
- Specify the pack form explicitly: free coil, level wound spool or drum, together with the coil weight.
- Mention any straightener in the line, as it changes how much cast the pay-off has to tolerate.
- Agree a minimum pay-off tension with the machine builder, because kinks form when tension approaches zero, not when the average is low.
A kink is a joint failure of the pack, the pay-off and the handling, and it is prevented by matching all three rather than by tightening the wire specification. Send the machine type, the pay-off arrangement and the wire diameter, and the pack and the cast can be specified together with the temper.
