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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
- 2mm Mylar
- Epoxy resin system
- PPE: gloves, lab coat, safety glasses
- Rubber scrapers for spreading epoxy
- Peel ply
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- Generously coat the mandrel with mold release
- 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, and probably a lab coat - composite dust and epoxy are skin irritants)
- 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 and remove all air bubbles, but be careful to touch the fabric as little as possible and spread epoxy in the fiber direction to avoid distorting the fabric
- If there are seams, 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 tube
- After all of the fabric has been placed, do one final check to make sure the fabric has been covered with epoxy and has no air bubbles or pulls in the fabric
- Wrap another layer of peel ply 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
- Wrap a layer of breather fabric around the tube
- Wrap a layer of vacuum bag around the tube, and attach to the bottom vacuum bag with vacuum tape.
- Pull vacuum to 0.7 barr
- Cure in oven based on epoxy system guidelinesAllow to dry for 10-15 hours for slow cure epoxy
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.