Two catterpillers for extrusion lines

What are the advantage for having a pay off caterpillar for an extrusion line? I worked with extrusion lines having a caterpillar before take ups.

But I saw extrusion lines with a caterpillar after pay off (Before extruder) as well as caterpillar before take up (After extruder). What are the advantages with such set up?

Hello Kishor,

The reason you had only one caterpillar at the take up is that the cable/ wire on the pay off reel was comparatively light. Thus there was no need to isolate the pay off section of the machine. In your case, the take up caterpillar was the line speed speed control and I imagine it was a thermoplastic extrusion line.

Heavy pay off reels (Power cable for example.) are driven, often controlled with a dancer/ accumulator and following that, a pay off caterpillar which isolates the payoff section of the extrusion line and thus tension variations. This pay off caterpillar is the extrusion line speed controller and it is very close to the extruder(s) thereby giving very accurate plastic thickness control. CCV lines often employ a belt capstan as the pay off isolator and line speed controller in lieu of a caterpillar.

The take up caterpillar then operates on tension control to keep the cable taunt between the two caterpillars. (In a CCV line, the haul off caterpillar is speed regulated by a dancer or position sensor/ controller in or adjacent to the CV tube. In fact these lines may have a third caterpillar after take up accumulator/ dancer but before the take up. This third caterpillar would be speed controlled by the take up dancer/ accumulator or by digital speed control below.)

In the digital age, the two/ three caterpillars can all be in speed control if the drives and caterpillars are sufficiently accurate, properly sized and under proper process control.

This is about as straightforward as I can make it and now I am sure you can now see the advantages.

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

Another application for the 2 capstan setup is in fiber optic loose tube manufacture. In this case the 1st capstan (typically single drum) is after the extruder and after the tube has gone through a hot water cooling section. The 2nd capstan (caterpuller or belt wrap) maintains tension (usually with dancer) on the product during the final cooldown in order to control the shrinkage of the tube and thus the ratio of the length of the tube versus the length of the optical fibers inside the tube.


Erik Macs
VP North American Machinery Sales
Fine International Corporation
148 Oak Street
Natick, MA 01760 USA
508-315-8200 fax: 508-315-3621
This email address is being protected from spambots. You need JavaScript enabled to view it.

Thanks Eric,

I always forget about optical fiber buffer tubes I guess because I haven't worked with them since about 1978.

As I recall, I think that this was originally the patented Pirelli (Prysmain) method of manufacture but of course that patent expired long ago.

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

Thanks a lot for information on two catterpiller set up. Information provided is very clear & useful for me & I can see advantages of such system. Once again thanks to Mr.Peter & Mr.Eric.