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Fully composite layups are similar to overwrap, except the tube (called a mandrel, because it is used to form layups) comes out to leave a fully composite tube.Our current procedure needs to be improved (see suggestions below), but the current process is outlined below. This process could also be used for coupler tubes.

Materials:

  • 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 layers (called plies)
  • Double stick tape
  • 2mm Mylar
  • Epoxy resin system
  • PPE: gloves, lab coat, safety glasses
  • Rubber scrapers for spreading epoxy

Procedure:

  1. Generously coat the mandrel with mold release
  2. 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
    1. 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
  3. 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.
  4. Place the mandrel on the layup jig, to allow it to rotate without being touched
  5. Mix the resin system according to the directions
  6. Wear the appropriate PPE (safety glasses, gloves, and probably a lab coat - composite dust and epoxy are skin irritants)
  7. Begin the layup as if it were an overwrap - place one end of the fabric along the tube axis and tack on with epoxy
  8. Using rubber scrapers, spread epoxy over fabric to fully coat it without adding too much excess
  9. 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