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Wire crossovers on double twist bunnching
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TOPIC: Wire crossovers on double twist bunnching

Wire crossovers on double twist bunnching 2 years, 3 months ago #467

hi gents,

I have a double twist buncher where I face a wire crossover problem with a particular size esp 2.5mm². This creates a problem of wire break at my insulation process. I am unable to increase my core diameter further due to the restriction imposed on my eccentricity. For stranding, I use a die size which is 2% more than the diameter of the strand I obtain. The die is observed to be free of defects.

Re: Wire crossovers on double twist bunnching 2 years, 3 months ago #468

Hello anishj2002,

First we are going to assume that you are discussing a 7 wire conductor and that you have the strand tension control all properly done. This means that the 6 strands all have the exact same pay off tension and that the center strand has a slightly higher tension to account for the excess length created by the second twist. (The center wire must slip back slightly to remove the excess length which occurs when the six wires make their second twist about the center wire.)

If indeed this is the case, then you must investigate what is happening when the machine is stopped (But not turned off.) for whatever the reason during the run. Sometimes when the machine comes to a stop, the strands before the closing die will relax slightly or the pay-offs may pull the stranded wire back slightly from the closing die. Then, when the machine is re-started, one of the strands may be crossed at the closing die.

Your careful investigation will chart the course for the rectification of this problem. (IE) Using time delay relays and a rubber lined clamp to gently hold the stranded wire just after the closing die so that it cannot be pulled back by the pay offs when the machine is stopped (But not turned off.).

Please let us know what your investigation turns up.

I hope this helps you.

Kindest regards,
Peter J. Stewart-Hay
Stewart-Hay Associates

Re: Wire crossovers on double twist bunnching 2 years, 3 months ago #469

Greetings from Toronto,

Crossovers in a double twist process do not occur prior to the closing die, meaning the size of the closing die will not have an impact on the consistent geometrical formation of the strand.

Assuming you are utilizing a machine suitable for the application the reasons for the crossovers could be at various points:

Tension control:
If we assume you are running a 0.67 mm wire for the 7 wire 2.5 mm2 construction on a 630 mm high speed double twist (which should be able to run at 5,500 TPM) I would suggest you tension the core wire at 1,700 gr. and the 6 outer wires at around 1,500 gr. Always keep the core wire tension 10% higher than the 6 outer wires.
If your pay-offs do not allow for accurate tensioning you always can use a tension equalizer.

It is imperative that all wires in the outer layer are of equal tension.

Obstructions in the Wire Path:
Check that all deviation pulleys are running freely and their bearings are in top shape. Also ensure that the wear-strip inside the bow is not worn – if it shows grooving substitute it.
Check the wire path with a strobe light to see if the strand is touching at any of the transitions from the deviation pulley to the wear-strip.

Wire Quality:
Make sure the wire is free of oxidation or other contamination since that would create undue friction in the bow which could lead to single wires separation from the formation. This is easily seen when you check the strand during production with a strobe light. The best place to look is under the bow clamp.
Let me know how you are making out.

Best Regards,

Willy Hauer

Re: Wire crossovers on double twist bunnching 2 years, 3 months ago #470

We already have a tension equaliser installed on the machine. The tension we apply on the outer 6 wires is around 1450g and 2000g on the inner wire.
I feel it is necessary to say that this cross wire phenomenon doesnot occur on all the drums we make from the particular machine. Its just one or two drums in a row of 10 drums that we get this defect.
One thing i doubt is the quality of the wire from the intermediate wire drawing machines. I feel that when wire breaks on the drawing line there are chances that some portion of the wire on a bobbin is a hard wire which can give rise to crossovers. I dont know how far i am right, but i would rather be pleased if could someone give some insight into this.

Re: Wire crossovers on double twist bunnching 2 years, 3 months ago #471

Good day..

We seem to be having a similiar problem, not with crossover but with 1 or 2 ends popping out during the twist. We are running in a unilay construction. Would tension be a factor. I also noticed that they are putting wires into the center as if it was a core but all going in same direction, is it possible that these wires are popping out??

thank you

Re: Wire crossovers on double twist bunnching 2 years, 3 months ago #472

Greetings from Toronto,

In order to provide you with a usable response please let us know following:

• Strand construction (Matl., no. wires, wire diameter, lay-length)
• Production machinery (single twist, double twist)
• Size of take-up reel

Best Regards,

Willy Hauer
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