CE290E Composites Lab

Lab #1: Composite Manufacturing

Vacuum Bagging

Lab Instructor: John F. Halterman and Dr. Ever Barbero

Feb. 25, 1999 - 10:45am to 12:30 - Room 123 ERB

Purpose: To introduce to students via hands-on experience how composites are fabricated using the vacuum bagging process.

 

Safety: Safety glasses (everyone), and latex gloves for those handling epoxy or fiberglass.

 

Summary: As a team, the class will construct an 8"x16" composite sheet. It will be made from 3 layers of fiberglass: The top and bottom layer will be straight, unidirectional fibers oriented parallel to the 16" side (16 oz/yd2), and will have a single layer of CSM (Continuous Strand Mat, 1.5 oz/ft2) sandwiched in the middle. Epoxy will be used as the matrix.

 

Pre-lab Comments: Most of the items needed to perform the lab have been pre-cut or pre-measured. This has been done to save time. During the step-by-step instruction, comments will be made to inform the reader about the purpose of what is being done.

 

Brief Concept of Vacuum Bagging: A composite under manufacture is placed in a bag that is sealed from the surround air. The air is removed from the bag, and this creates a vacuum inside the bag. This causes the bag to collapse because of the surrounding atmospheric pressure. This compresses the composite, which squeezes out excess epoxy, minimizes voids, and forms a flat, smooth, uniform composite. Essentially, this is a press in three dimensions, which can be applied to complex geometries. It is one of the simpler manufacturing methods.

 

List of Required Supplies:

    1. Plastic Sheeting
    2. Perforated Sheeting
    3. Breather Cloth
    4. Blue, Heavy Duty Scotch Tape (Flash Tape)
    5. Double Sided Sealant Tape (Old and New Tape)
    6. Straight Stitched and CSM Fiberglass Cloth
    7. Epoxy Resin and Hardener
    8. Grooved Roller
    9. Vacuum Bagging Air Pump Connection Post and Base
    10. Vacuum Bagging Air Pump
    11. Scraper
    12. Acetone
    13. Measuring Cup (in fl oz. graduations)
    14. Paper Mixing Bowl
    15. Electro-Mechanical Stirring Device
    16. Scissors
    17. Paper Towels, Latex Gloves, Safety Glasses

 

Procedure:

  1. Lay down pre-cut plastic sheeting on the base (heavy aluminum plate). Tape the sheet to the base. This covers the aluminum to prevent contamination from epoxy for future use. Make sure that the entire top surface is covered either with plastic or scotch tape.
  2. Two 8"x16" sheets of straight-fiber and one 8"x16" sheet of CSM fiberglass has been pre-cut. Place one straight-fiber sheet on the center of the covered base. Using old sealant tape (since it is not being used as a seal), place it around the fiber sheet to create a dam. This will prevent epoxy from spreading, and reinforce from movement during the vacuum.
  3. Leaving the one straight-fiber piece in the dam, mix the epoxy. For this lab, mix 6 fl oz. of epoxy resin with 2 fl oz. or epoxy hardener (3 to 1 ratio by volume). Measure using the plastic measuring cups, and mix thoroughly using the electro-mechanical stirring device (about one minute). The epoxy may be stirred in one of the paper bowls provided.
  4. Using approximately 1/3 of the epoxy mix, dump it in the dam, spreading it around during pouring. Using the grooved roller, spread the epoxy around, ensuring that all surfaces are saturated with epoxy.
  5. Place the layer of CSM on top of the straight-fiber sheet currently in the dam. Place the next 1/3 of epoxy on the laminate under construction, and spread around as before.
  6. Apply the last straight-fiber sheet down and dump the rest of the epoxy. Spread the epoxy around and ensure that the laminate is thoroughly saturated; however, any excess must be scraped off using the scraper. Excess epoxy can be sucked into the vacuum pump and cause damage.
  7. Take the pink-colored perforated sheeting and place it so that it is centered over the dam; the edges of the sheet should extend just beyond the edge of the dam. Trim if necessary. This provides a separation between the breather cloth and the laminate so the two will separate after curing.
  8. Place two layers of breather cloth on top of the perforated sheeting. At one end, add some breather cloth to create a "tongue" which will have the base of the connection post placed. This keeps the vacuum point away from the laminate to prevent epoxy from being sucked into the pump.
  9. Place new double-sided sealant tape around the edges of the aluminum plate. Do it as one continuous piece to prevent gaps.
  10. Take a sheet of plastic and cover the entire area, connecting it at the sealant tape areas. Press the plastic firmly so that it comes in contact with the plastic, forming a good seal. At places where the plastic gathers, take a little extra tape and place it in the pleat and close the gap. NOTE: DO NOT LET THE PLASTIC COME IN CONTACT WITH THE TAPE UNTIL IT IS READY TO BE SEALED. THE TAPE DOES NOT LET GO OF PLASTIC EASILY.
  11. At the location of the connecting base, cut a slit in the center with the scissors, and attach the top part of the connection post. Attach the pump to the connection post.
  12. Turn on the vacuum pump. Apply a vacuum of roughly 10 in Hg by controlling the pressure valve. Listen for areas where air is leaking in and seal using sealant tape.
  13. Once all leaks have been sealed, apply the full vacuum (roughly 23-25 in Hg), and let set overnight.
  14. Clean up. Items that came in contact with epoxy may be cleaned with acetone.

The composite plate will be tested on Lab-2.

Click Here to see how it is done!

March 4, 1999