Dear All,

We are developing a Quad Construction Cable and facing the problem of very high CUPP values within the quad. The conductor dia is 0.9mm and PE Insulation dia is 1.8mm. We are using the Single Twist Bema Twinner for making the quad. Please suggest the necessary corrective actions for improving the CUPP values.

Thanks

Sheks

Hello Sheks,

For all the rest of our readers, CUPP is a fairly uncommon acronym for Capacitance Unbalance Pair to Pair.

I assume Sheks that you know that Bema makes an excellent twinner which can certainly be used as a quadder.

I also assume that you are closing all four wires together and not closing two pairs, please confirm.


There are a few things that you must do or consider to make a high quality communications quad:

(1) You must start with high quality wire. It must be accurately insulated (Very round and centered.) and if it is foam, the coaxial capacitance to ground must be stable. Likewise with foams, be very careful to ensure you have no flat surfaces on the insulation.

(2) You must have a very stable, round quad and some actually place a small nylon filler in the center to ensure that very thing. You should consider this but the filler is not a "must do" item.

(3) You must have constant and even pay-off (no jerking) tension in each of the four wires making up the quad.

(4) Most importantly, you must have planetary pay-offs so that you can select 100% to 75% back twist in each of the wires. This is absolutely necessary to eliminate the capacitance unbalances created by the minute dimensional variances in the insulation. You cannot get this perfect at extrusion and the planetary action of course averages those variances. Maillefer used to build and sell a small high speed drum twister with rotating, planetary pay-offs precisely for the manufacture of high quality quads.

Best regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

Thanks for the valuable inputs. I would request you to please elaborate on the `Backtwist Theory' i.e. what is actually happening in this phenomenon. I presume, our BEMA twinner payoffs are not equipped with this facility. The insulation in our case is solid PE.

Thanks

Sheks

Hello again Sheks,

Unfortunately I don't have the time to give you a course in the theory of stranding and cabling but your senior process engineers should well understand this and they should be able to give you all the information you are looking for.

In fact, you can actually see a small slide of the very quad planetary vs rigid phenomenon you are facing on our web page; www.stewart-hay.com/process3ie.htm

Think of it this way: "A rigid stranding device imparts a same length and direction of twist, often referred to as "foretwist", to the cabled elements. (Individual wires in your case.)" The cancellation of the "foretwist" is known in the industry as the introduction of "backtwist".

Your Bema single twist twinner is a rigid stranding device and thereby introduces "foretwist" unless it is negated by twist compensation or ("backtwist") at the pay-offs and thus for the single wires as per my previous comments.

This is why a planetary machine is defined as having "backtwist" and a rigid machine as having "no backtwist".

This should be all the information you require.

Talk with Bema or any other strander manufacturer to acquire a four reel, individually-inside-bows, double twist (Turning at half the speed as the single twist take-up bow.) gang pay-off unit with the bows mechanically or electronically locked to your twinner bow rotational speed. Likewise make sure to specify that the rotation direction of the gang pay-off should be selectable. Be sure to tell them what your application is and that good pay-off tension control is also essential. If you are planning to use foam PE at some later date, let them know that as well.

Best regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

Thanks a lot.

Sheks

Dear Sir,

I recommend to read the following two technical papers:

"Twist and Tension" Author: Andy Blackmore
"Efficient process linking and flexible production with single twist stranding" Author: Juan Carlos González Villar

Ask "Wire Journal International" for this technical papers.

Best regards

Juan

www.kabelconsulting.de
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