Hot Set

To all,

Are there any relationship between hot set, permanent set and shrinkage for crosslinked polyethylene (XLPE)? I am wondering how a good hot set result will affect the shrinkage result. Or are there any suggestions as to how shrinkage of cable happened and to overcome it? Has it got to do with my side or my compound supplier side?

Hello,

I believe it is now getting to the time when you should be buying chemistry books on polymers for your company's library such as:
- Plastics Testing and Characterization: Industrial Applications By Alberto Naranjo, Maria del Pilar Noriega, Tim Osswald, Alejandro Roldan-Alzate, Juan Diego Sierra, 2008, 375 pages
- Polymer Chemistry by Andrew Peacock, Allison Calhoun, 2006, 350 pages
- Polymer Extrusion, 4th Edition, Chris Rauwendaal, 2001, 794 pages
- Polymer Testing, Edited by Wolfgang Grellmann, Sabine Seidler, 2007, 680 pages
- Polyolefin Blends Edited by Domasius Nwabunma, Thein Kyu
- Principles of Polymer Processing, 2nd Edition, Zehev Tadmor, Costas G. Gogos, 2006, 961 pages
The above are availale from The Society of Plastics Engineers at www.4spe.org/ You can review those books and many others on that web site.

There is also the following book at the WAI Store:

- SPE Guide on Extrusion Technology and Trobleshooting, Technical editors John Wagner and John Vlachopoulos, 2001, 413 pages. www.wirenet.org/waistore/productdetail.cfm?productid=5

You should also be having regular discussions with the technical people from your XLPE resin supplier/ manufacturer. These folks are a very valuable and economical resource for you, as a customer, to use.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

HST, Permanent Set or Cold Elongation Set and Shrinkage are three different tests. HST and PS can be combined as two parts of a single test, but shrinkage is a totally different test. The test temperature, the test duration and the testing method are all different.

The material definitely plays an important role in success of shrinkage test but processing techniques play just as much of an important role in the success of shrinkage test.

If you use pressure or hybrid tooling during extrusion of XLPE rather than tubing there are more chances that the test will pass.

If you are bound to use the tubing technique due to sector shaped conductor or due to taped conductor, use vacuum behind the cross head and hot water in first trough.

During testing put the test samples in talcum powder rather than putting them on frame.

Hi there Sahota and thank you very much for the information. One small point:

Your statement "If you are bound to use the tubing technique due to sector shaped conductor or due to taped conductor, use vacuum behind the cross head and hot water in first trough." refers to a moisture cure XLPE compound instead of the standard CV type, peroxide bearing XLPE compound where pressure extrusion is the norm.

Regards
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com