I understand, and have made a few small tubes for bicycle head tubes.
Custom turned and polished PTFE mandrel, cured part slides right off.
Question is, I wrap the wet layup as tightly as possible with high shrink tape, overlapping 75%, get some squeeze out. Heat and get plenty of squeeze out. Finished tube has 60% + fiber (CF) o 40%- resin, so it is OK.
The question, how much pressure does heat shrink tape generate?
Not a real exact process. You could test if you really needed numbers…wrap tape around a load cell and then vary your process to bound your variables (wrap technique, wrap tension, heat application, etc).
Otherwise use good process control methods and then make some sample parts and cut them up to look for voids, dry areas, etc.
I think from reading somewhere that it is about 90 psi which is equivalent to an autoclave. Plenty of pressure (if I am right) but it probably varies and depends on the tube diameter??
There is an equation that a heat shrink tape manufacturer gives on their website.
http://www.shrinktape.com/engineers-corner/important-formulas.aspx
it seems to me that the formula you refere to is only related to winding a tape not heatshrink tape (IMHO)
I have talked to the manufacturer of the heat shrink tape and if i recall correctly the tape they give you you has a force rating too, say at 5 pounds. So you add that number to how ever much you are pulling the tape in tension. If that makes sense. I would contact wherever you got the tape and see if they can send you a data sheet your way.
Dunstone Hi Shrink polyester .002" with 1" width.
Need some way to measure initial wrapping tension as a start. I have a basic jig that holds the tape, with a spring pressing on the spool, and a jig that holds the mandrel.
Thanks all for some good ideas.
I am not unhappy with results I am getting, but I’d like to do better. Always curious about how others do the same thing.
I have seen a wrapping machine where the tape pressure is set with the friction in the pivot that it spins on so there is simply a nut and you can adjust to your liking with a spanner.
It does not need to be very tight but you want it to be firm and tidy rather than loose. The heat will take care of the rest.
[ame=“http://www.youtube.com/watch?v=eED2WeiyN0Q&list=PL-kD4H36kETe5gznvtPB1l-kshGwZL57C&feature=share&index=8”]How It’s Made - Carbon Fibre Masts - YouTube[/ame]
These guys use cellophane tape which wont contract much. They are getting the compaction from tension in the tape instead. They also autoclave it too. You could probably oven cure it and get a similar result too.