Heat Shringing tape

General Composites Discussions Composites Talk
#1

Ok . … i made some thoughts and i would like your aid + positive criticism . Until now in some bicycle repairs repairs i did i used
easy composites shrinking tape with good results . Problem is that
i dont know how much pressure it gives to the pipe of the bike it is
being repaired so i looked to this supplier which has proper data sheets.

http://www.shrinktape.com/products/hi-shrink-tapes/Hi-Shrink-Tape-300-Series?p=312R

The principals of my choice are the above :
The cure of the prepreg material for the repair will occure at 180 F .
At 180 F the tape (see man. table ) will give pressure of about 6.4 lbs/ (1.20 cm X 2.54 cm )- (see man. claim of lbs/inch of width which i believe goes for the standard model of 12mm ) which is (6.5lbs*0.435) 2.94 kg/ 2.84 cm2 = 1.04 kg / cm2 which is close to the 0.94 kg/cm2 of the - 0.94 bar vacuum force .

So in other worlds if i put this tape around the pipe of the bike it will apply force at 80 celcius about 10 % more of the force applied by vacuum .
There are 2 things i would like to ask :

  1. Is my theory right ? - apologies for the randomness of thinking

  2. This force is applied if i wrap around one time the tape ? And if wrap it twice what happens ? it doubles the amount of pressure and 3 triple ? Until i reach the limit of the material ? And how do i know it ?

#2

I think the pressure is always the same, either you wrap only one lay or even more.
We can wait for somebody else with a different opinion

#3

Had always thought the tape pressures were much higher than vacuum pressure?

I also imagine that the pressure will reduce as the tubes get bigger.

When I use it I will do a two layer/half overlap shrink tape if there is just 1-3 layers of carbon but if there is more then I do 3 layer shrink tape which 2/3 overlapped.

I repair quite a few bikes but never use pre preg since the oven heat will likely affect the paint and plastic parts etc. Seems too risky to cook a customers bike for me.

#4

I also imagine that tape tension during application is one of the biggest contributors to compaction force. ie…tight tape = enhanced compression, loose tape = minimal compression

#5

I raise the temp up to 80 C with an appropriate cure schedule. If you leave the bike and it is black at the sun on a summer day it could could get up to 70 c . So i dont think it cant handle 80 for a couple of hours . Prepreg is the only way for me. I need to be sure and confident about the result of what i do and the material i use . With wet lay up i do not have that .

#6

The force that the tape generates is a tension. This is the force that Dunstone talks about on their website. This tension force will give you zero compaction pressure on a flat surface. The greater the curvature of the part surface, the more compaction pressure you will get (smaller diameter tube = more pressure). I wrote a SAMPE paper on shrink wrap processing, which I know that some people at Dunstone have.
Accurately calculating the compaction pressure is almost impossible because there are so many factors involved. This is why you cannot find a simple equation to use.