Rod breakdown: Loops around capstans

Hello,

I have been wondering about this for a while with no reasonable answer: what is the point of making loops around a rod breakdown machine's capstans? Is there a way to determine which capstans get looped once or a few times? I reckon that it has something to do with increasing pull force, is this right?

Thanks!

Hello fuhrerwire,

Your supposition is correct but this is the way to think of it:

- Any slip type drawing machine such as the one you are describing is a non-positive machine.
This means that more metal must be supplied to each die than actually can be used so the excess must slip back through the machine.This is one reason for the drawing lubricant and smooth, circular capstans.
On the other hand, there must be sufficient capstan/ wire friction to pull the wire through the preceding drawing die. There is a mathematical equation for this but the common method is to experimentally determine the number of wraps needed on each capstan to achieve the proper wire tension in the wire proceding each capstan. The dry capstan of course has no slip.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com
519 641- 3212