I'm going to jump in to try to highlight an important fact about peel ply.
The product that is linked above is a teflon-coated nylon fabric. It allows epoxy to bleed out of it, leaving a finish which is nice to finish for paint, and ensuring even wet-out of the fiberglass/CF/whatever underneath.
However, coated nylon or coated polyester peel plies leave behind their coating on the surface of the composite part, which prevents glue from sticking to it.
A different type of peel ply, uncoated dacron, does not have a coating to leave behind; the finely textured surface left behind by dacron peel plies is ideal for bonding fins or more fabric down. However, it is not a release wrap; it requires considerable effort to remove it from the surface of the composite part. It is, however, cheaper. https://www.aircraftspruce.com/catalog/cmpages/peelply3.php
I found this information through a TRF thread in the archive I believe; it was in an old paper from Northrop Grumman that looked at micrograph images of the surfaces of composite wing panels that failed, and it was because of a teflon-coated peel ply that was substituted on the factory floor for the dacron peel ply the engineer called for.
I'm going to jump in to try to highlight an important fact about peel ply.
The product that is linked above is a teflon-coated nylon fabric. It allows epoxy to bleed out of it, leaving a finish which is nice to finish for paint, and ensuring even wet-out of the fiberglass/CF/whatever underneath. However, coated nylon or coated polyester peel plies leave behind their coating on the surface of the composite part, which prevents glue from sticking to it.
A different type of peel ply, uncoated dacron, does not have a coating to leave behind; the finely textured surface left behind by dacron peel plies is ideal for bonding fins or more fabric down. However, it is not a release wrap; it requires considerable effort to remove it from the surface of the composite part. It is, however, cheaper. https://www.aircraftspruce.com/catalog/cmpages/peelply3.php
I found this information through a TRF thread in the archive I believe; it was in an old paper from Northrop Grumman that looked at micrograph images of the surfaces of composite wing panels that failed, and it was because of a teflon-coated peel ply that was substituted on the factory floor for the dacron peel ply the engineer called for.
I'm going to side with tfish on this one. The only thing I can add is the tests that I've done have shown no bonding issues at all. I'm thinking tfish's tests of Mach 2.4 is good enough to me.
I do a lot of fiberglass work and usually use Mylar when I want a smooth surface. The typical peel ply is used to leave a slightly rough finish so that subsequent layers of epoxy will bond to it. It's also used together with breather fabric in order to soak out excess epoxy. I do a lot of vac-bagging and use it for that purpose.
I'm curious if anyone using this for HP airframes has tried something like Mylar which leaves a very smooth surface, or aren't you using for that purpose?
When I first started making tubes, I tried to get a smooth surface with mylar. The problem I could not solve was to avoid air bubbles at the overlap. Those took too much remediation to fix. I also didn't find any practical (and actually effective) means of providing compression. So, I just went with the peel ply and it works fine.
There is a write-up on the compositerockets site by Mick Kelly that explains the mylar method in detail.
Jim
There is a release material designed specifically for the application of making tubes. It is something like a roll of heat-shrink. One wraps it around the tube in a spiral with overlap, then when it is heated it shrinks tighter. It leaves a glassy surface with a spiral line at the edge of the overlap, but the line is fairly thin. Due to the shrinkage, and since one wraps it on a little snugly to start, it provides some fiber compaction which is a good thing. The fiber ratio will be closer to optimal - meaning the strength to weight ratio of the tube will be higher. BTW, in my experience it does not leave any residue behind. It also releases easily.
https://www.cstsales.com/shrink_flash.html - top of the page. That is one example of this type of product.
It helps to make a jig to rotate the tube while the operator spools the shrink tape on smoothly and uniformly. Key to best results is to use uniform tension when wrapping. A drill can be used at its slowest speed setting to rotate a tube. A rod of some sort, two bulkheads, and two pieces of wood with holes, plus one drill...
If you pre-wet fabric and put it on wet, then you can weigh it to check the fiber ratio. Manufacturers of fabric have suggested optimum ratios of fiber to epoxy. One can wet out fabric, put on some wax paper (it won't be even close to drippy if the ratio is right) and weigh it. Subtract off the weight of the wax paper of course! It would be good to do that experiment to get a feel for the optimum ratio before doing a part layup. It may prevent making a tube with excessive epoxy content.
I just thought I'd throw this out there to provide some info for an alternative method.
Gerald
I've used the heat shrink tubing with mixed results. I was using it for 40mm tubes and the seam in the heat shrink tubing was pretty thick and always left a bump on my finished airframe. I was using very thin fiberglass and determined that the heat shrink tubing just didn't work for that material. However, I imagine it would work better as the airframe diameter gets larger. I haven't bought some in awhile but imagine that it's still not too cheap.
I've also used the perforated tape that simply gets wrapped around the airframe. I like that much better because it allowed the excess epoxy to get squished out as it was being wrapped around the layup on the mandrel. The rubber heat shrink tubing would sometimes capture the epoxy and not let it escape. I know that they suggest that you first start in the middle of the layup and apply the heat as you work it towards both ends. But as my buddy used to say, "it looks good on paper, but not in practice".
I've used it on tubes as small as about half an inch diameter. One has to cut the strip to half width when working that small! But, I didn't have excess epoxy to squeeze out as the weight of epoxy was matched to the quantity of fabric. YMMV. I'm not sure we are talking about the same thing. This isn't a tube which is put over the layup and shrunk. This isn't normal heat shrink material like that used for electrical work. This is a ribbon which is wrapped around the tube under some tension. It is stretchable and flexible and not all that thick. FWIW, I've never run across directions suggesting heating as one applies it! Or for that matter, starting in the middle! I have no idea how one could do that successfully.
One can make a tube overlength leaving no fabric at the very ends. Tape the strip down and start wrapping off the fabric, progress over the fabric, and continue wrapping to the other end where it gets taped off. An overlap of 1/3 up to 1/2 would be normal IMHO.
I've done the wrapping as a two person operation. The other person rotated the tube while I stretched on the ribbon. Others have used a drill at slow speeds for small tubes and it is then a one person operation. Any sort of a rotisserie arrangement with sufficient torque and slow RPM should work. Uniform tension is key to getting good consistent results. That is easier to achieve when it is not a person applying the power but it can certainly be done by a person! For our two person arrangement, we just made a crank handle from a metal rod.
One can often re-use this ribbon, with a little cleanup. I'm not sure its worth the effort as the cost is not all that high.
I've seen this ribbon in widths up to 2", which may be more suitable for large diameter tubes.
Gerald
PS - One can also get perforated versions of much the same thing. That may be what you want if you don't have the epoxy content sufficiently controlled so there would be notable excess to remove.
For multiple-wrap tubes, I've had the best luck hanging weight off of the end of the fabric. I just rolled a 3", 7-wrap tube that was 44 inches long. I hung an AMW 98- motor case on the end of the fabric to hold tension while I rolled the tube. It was exciting, but there's probably room to increase the weight even further.
Jim: how do you keep the tension on at the end of the wrap? Does applying tension during the inner wraps prevent wrinkles and squeeze "outward" on the outer layer enough to make it not necessary? Are there ever voids in the outer layer?
For Disappearing Act, which has my first (and so far only) truly successful scratch tube (which is 38mm), I rolled it in three steps, with the second one vacuum bagged. First, I applied two uncompressed inner wraps of thin woven glass to make a good core and allowed it to cure. Then, I vacuum bagged on 4 or 5 layers of thick unidirectional s-glass. That naturally wrinkled up a storm, but once it cured I sanded it down to uniformity (not a problem because it's unidirectional) and applied another three wraps of thin weave on the outside, uncompressed, and then sanded off the outer layer. By using the bare minimum of woven glass needed for workability and hoop strength, about 60% of the tube thickness was vacuum bagged for max fiber content.
I don't know any way to get truly good compaction on tubes rolled from woven cloth, except perhaps shrink tape which I haven't tried personally. On the aforementioned tube I could get closer to optimal, because much of the tube volume was vacuum baggable uni, but if I had wanted a thinner wall (had I needed less strength) I couldn't well have done anything but used fewer uni layers, thus increasing the proportion of resin.
Jim: how do you keep the tension on at the end of the wrap? Does applying tension during the inner wraps prevent wrinkles and squeeze "outward" on the outer layer enough to make it not necessary? Are there ever voids in the outer layer?
I thought I had some better pics, but the one below is the general approach. The cloth is just taped (securely!) to the tube. With longer pieces of cloth, I just put a pivot a few feet away so the weight still hangs. I have to apply about 1/2 of the first wrap before taking up weight, and I cut the weight off when it gets to within a few inches of the layup. Each time I move the tube (usually 1/8 of a turn at a time), the epoxy oozes out from below. One other thing I noticed is that multi-wrap tubes are very firm and not mushy. I realize that the amount of tension being put on any given strand isn't that much, but I do think the technique results in a much better tube. When the layup is done, I put peel ply over the top.
Jim
When I was making tubes they were fairly small diameter. The fabric was wet out on the bench on top of wax paper or mylar or something of the sort - I think wax paper. The paper was weighed first, on top of a sheet of foam which went on the scale. Then fabric was put on dry and weighed. The fabric weight was used to compute the additional weight of laminating epoxy (MGS) needed per manufacturer's recommendations. Epoxy was added in excess of this weight to assure good wet-out of the carbon. Next the fabric went into a vacuum bag with paper towels on top, and vacuum was drawn for a short period. The paper towels were discarded, and the fabric weighed. If there wasn't enough epoxy, a little bit was rolled in. If there was too much, it went back into the bag for a bit more. Once the fabric had the proper epoxy content, the mandrel was rolled over the fabric to pick it up. To facilitate this operation, a narrow strip, about 1/2", was left dry. This was misted with 3M77 so it would stick to the mandrel enough to start to roll the fabric in place. Once the fabric was rolled into place, the fabric was wrapped with the release tape and put into a hot box at perhaps 120 degrees for initial cure.
The mandrel was fairly heavily coated with spray low temp mold release wax. To remove the tube, the mandrel and tube were immersed in hot water. This melted the wax and allowed the tube to be slid off the mandrel. The wax was then cleaned out of the inside of the tube.
For my purpose at the time, except for trimming the ends, no other cleanup was required.
To obtain a layup with biased fabric on the inside and outside of the tube, and uni in between, one layer of biased fabric was used whose dimension was somewhat over twice the circumference of the tube. Layers of uni were laid on this, starting a half inch from one edge, and in a staggered fashion, extending to about half way across the bias fabric. That half inch initially left dry of epoxy is the part that is tacked onto the mandrel with a very light coat of 3M77 spray contact adhesive. The fabric stack is rolled onto the tube with the woven fabric towards the tube. So the first full wrap around the tube obviously has the woven fabric against the mandrel. But then the woven fabric climbs the progressive layers of uni until it ends up on top, where it completes the last wrap. Properly done, one ends up with a nice tube. Improperly done, one ends up with varying wall thickness. One just needs to compute the required widths of uni and stagger the layers slightly, and of course cut them to width accurately!
I hope this gives some idea of what I was doing, and answers the questions. This method would require a work area of some size if the tubes were large. I probably left off some details here and there to keep the post from being too long.
Gerald
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