Talk Composites - The Forum for Advanced Composites

Material choice for stepped mandrels and shrink tape questions

http://www.talkcomposites.com/Topic16907.aspx

By gsport - 5/7/2015 12:05:27 PM

Apologies if this is the wrong forum or has been discussed many times before, couldn't find anything definitive using search.



I am planning on making some CF bearing housings by hand layup over turned stepped mandrels which I will make. 

I can make these mandrels out of Aluminium or a range of plastics (Acetal, Nylon, PP, HDPE, etc) is there a significant difference in how easily they will release from the epoxy (They will have zero draft in places due to being bearing seats and I was going to use PVA as a release but open to suggestions)? Any materials that I should specifically avoid due to reaction with epoxy?

I was going to consolidate by wrapping in heat shrink tape and/or then over vacuum bagging, but there seems to be some horror stories about the heat shrink tape with people over heating and boiling the epoxy?!?

How hard is it to shrink the tape well? (using a hot air gun with temperature control) Is it better to keep the temperature down and go slow, or give it a quick blast of high temp air to try to keep the epoxy cool more like a baked alaska?

Any hard won advice much appreciated.

George
By Fasta - 5/20/2015 4:01:26 AM

I have moulded pre preg carbon parts off acetyl moulds and it works great without any release system applied. Although being pre preg the oven heat expands the acetyl a small amount and this helps with the carbon part self releasing when it cools and it falls off, literally.




For a wet laid part it may not release as easy without the heat/expansion.




Hot air guns work well with the shrink tape but I worry about your stepped mould shape as these tapes are not so good with tapered parts or shapes as the tapes tries to slip off as it is wrapped and can slip further when heated/shrunk. It needs a min heat to shrink so going slow may not heat it enough. You will see it shrink as you go, so you know then to move on.