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- Aluminum mandrel with outer diameter (OD) equal to the desired inner diameter (ID) of the composite tube
- Mold release (we're currently using Frekote, but Stoner, honey wax, and teflon mold release are other options)
- Fabric (carbon fiber, E- or S-glass fiberglass) - enough for about 9 5 layers (called plies)
- Double stick tape
- High temperature vacuum bag
- Vacuum tape2mm Mylar
- Epoxy resin system
- PPE: gloves, lab coat, safety glasses
- Rubber scrapers for spreading epoxy
- Peel ply
Procedure:
Procedure:
- Assemble the mandrel. The coupler mandrel does not require assembly, but the tube needs to be slid together with the two smaller ends of the tapered mandrel in the middle. To ensure a good friction fit, put a couple of small pieces of painter's tape along the coupler to keep the mandrel from bending at the seam.
- Slide the tube mandrel onto one of the aluminum rods that store the fiberglass rolls if you're doing a tube layup; slide the mandrel endplates into the end of the coupler mandrel for a coupler layup
- Slide the aluminum rod or mandrel endplates onto the layup jig
- Generously coat the mandrel with mold release
- Cover the mandrel in a layer of high temperature vacuum bag (mandrel length x 19" wide). To do this, wrap the tube in a vacuum bag of the appropriate size. Using double stick tape, tape the vacuum bag to itself at the seam, making sure it is tight around the tube and does not allow air bubbles. Make sure it is not in any way adhered to the tube, because it will not come off
- If the width of the fabric is wider than the section of the tube, you can just roll it off the roll onto the tube. If it is too short, or if you are using +/-45 degree plies, you will need to cut the fabric to the correct size
- When cutting the fabric, make sure you aren't cutting into a table, and be careful not to stretch the fabric when you're cutting. To avoid this, you can cut slowly with a scissors, and hold down the fabric on either side of the cut to prevent it from pulling
- Cover the mandrel in a layer of 2mm thick mylar. To do this, wrap the tube in a Mylar sheet of the appropriate size. Using double stick tape, tape the mylar to itself at the seam, making sure it is tight around the tube and does not allow air bubbles. Make sure it is not in any way adhered to the tube.
- Place the mandrel on the layup jig, to allow it to rotate without being touched
- Mix the resin system according to the directions
- Wear the appropriate PPE (safety glasses, gloves, respirator, and probably a lab coat - composite dust and epoxy are skin irritants, and the epoxy is harmful to breathe)
- Begin the layup as if it were an overwrap - place one end of the fabric along the tube axis and tack on with epoxy
- Using rubber scrapers, spread epoxy over fabric to fully coat it without adding too much excess
- Turn mandrel to keep wrapping fabric around the tube, and cover with epoxy.
- Make sure to wrap the fabric tight
- Remove all air bubbles
- as they appear by spreading towards the edges of the layup or towards the dry fabric
- Be careful not to touch the
- wet fabric (even with gloves) because it will pull and compress the fabric, which will result in air bubbles
- Spread epoxy in the fiber direction to avoid distorting the fabric
- . Ideally, everyone should spread the epoxy along the circumference of the tube
- If you need to use more than one sheet of glass, make sure to offset the next layer by an inch or two from the seam
- Continue to add epoxy and fabric, spreading the epoxy so the fabric is fully wetted, but not dripping - we typically use 9 plies of fabric for a fully composite tubeno excess epoxy is added.
- Wrap enough layers of glass around the tube to withstand the flight loads. You can determine the flight loads and test samples of composite tube by following yet to be written wiki articles.
- After all of the fabric has been placed, do one final check to make sure the fabric has been wetted (covered with epoxy), has no excess epoxy, and has no air bubbles or pulls in the fabric
- Wrap another a layer of peel ply (layup length x 20") around the tube to provide even pressure and aid the surface finish. The epoxy should keep it well attached to the tube, but using some rags in order to apply even pressure, smooth out the peel ply around the tube. Make sure there are no air bubbles that could harm the surface finish
- Allow to dry for 10-15 hours for slow cure epoxy
- Wrap a layer of breather fabric (layup length x 22") around the tube
- Wrap a layer of vacuum bag around the tube (layup length x 24"), and attach to the bottom vacuum bag with vacuum tape.
- Pull vacuum to 0.7 barr
- Cure in oven based on epoxy system guidelines
To finish the tube, you will need to sand it. First cover the tube in a protective layer of epoxy - you don't want to sand off the carbon fiber, and this will help fill in any crevices. Sand starting with 60 grit sandpaper and working your way up to 500 grit. Always wear a respirator when creating a significant amount of composite dust, and wear gloves and a lab coat to protect your skin from the dust. Make sure to smooth out any lumps, and fill in any crevices left behind by with an epoxy filler.