The Shop > Composites & Plastics
Vacuum pump
Brass_Machine:
I am considering building a vacuum pump system to do some vacuum bagging for some composite work. I have been thinking about this Guys plans. I already have most of the stuff in his plans including a decent vacuum pump. Just need to get off my @ss and do it. He has some decent plans... check them out.
Eric
PTsideshow:
They are very clean in design and build. ;D
Rog02:
--- Quote from: Brass_Machine on May 26, 2008, 12:39:48 AM ---I am considering building a vacuum pump system to do some vacuum bagging for some composite work. I have been thinking about this Guys plans. I already have most of the stuff in his plans including a decent vacuum pump. Just need to get off my @ss and do it. He has some decent plans... check them out.
Eric
--- End quote ---
Hi Eric:
Those are some pretty nice looking vacuum set-ups for laminating veneers. There really is no need for a reservoir for bagging composites however. I have bagged my fair share of pre-preg at the helicopter company and never needed a vacuum reservoir for anything except the vacuum forming table. A properly constructed reservoir will increase the volume of air that can be displaced in a hurry which may be nice when vacuum clamping furniture pieces, but may be too quick for composite work. It is usually desirable to evacuate the bag slowly as it allows for last minute adjustments and prevents wrinkling which can in turn leave uneven resin dispersion in the matrix. A properly constructed bag will have little volume to evacuate.
Should you decide to build the reservoir, remember vacuum can create some high crushing pressures. We used to crush five gallon thinner cans by hooking them up to the shop vacuum supply. I have however constructed resin traps from heavy pvc fittings and they have performed well.
A word of caution on vacuum pumps is in order as well. Many people are using old AC service vacuum pumps for small projects. Be advised that most of those pumps are "oil pumps" and can introduce oil into the bag once the seal has been established and the atmosphere has equalized.
For some basic "How-To" on getting started with composites look at the Fibre-Glast Learning Center. http://www.fibreglast.com/contentpages-main-Learning-Center-283.html
West Systems Epoxy also has some good information and articles available on their website.http://www.westsystem.com/
http://www.bertram31.com/proj/tips/vaccuum.htm Is a brief primer on the process and shows both the full sleeve bag and the surface seal bagging method.
Brass_Machine:
Thanks Rog Thats some great DVD collection from fiberglast. I do own a decent vacuum pump. It is a decent one and not an old refrigerator unit. I am just not sure how to use it in a vacuum bagging situation... like what do I need?
A vacuum gauge? A shut off valve? How do I make a resin trap?
Eric
Rog02:
Hi Eric:
Composite structure is deceptively simple. It may look simple, but requires some pre-planning and knowledge. My suggestion would be to read everything you can find on the topic, invest in some basic materials and experiment some before you begin a project.
Edit;
First let me encourage you to always wear safety glasses and an appropriately rated organic breathing mask whenever handling or in the presence of composite materials. The solvents will blind you instantly and the effects of prolonged inhalation of the fumes are catastrophic. I also strongly urge the use of nitride gloves when ever handling resins.
In addition to the vacuum source you will need the following;
HARDWARE:
Vacuum gauge Available from numerous sources. Surplus Center, Mc-Carr, etc. Over the years I have accumulated a few gauges and frequently install more than one on larger lay-ups to insure I am getting an even distribution of vacuum.
Ball Valves Plain old ball valves. Available from local sources and the usual mail order suppliers. I have had good luck with the 1/2" ball valves that Harbor Freight runs on sale.
Reinforced hose For plumbing the bag to the vacuum source. Use the kind with the reinforcing ply as it tends not to be sucked shut.
Sucker fitting This is a specialty item available from any of the resin suppliers. While there are sources on the net that advocate the use of air hose fittings for quick disconnects it is worth considering that the quick disconnect fittings for air supply are designed to specifically hold pressure. When vacuum is applied the seals may leak as the pressure differential is 180 degrees out of design parameters.
Scales Used to measure resin and catalyst for mixing.
Bagging Supplies: (Mostly expendable items and may not be re-used)
Peel Ply This is a release layer placed over the matrix before subsequent layers to eliminate the bonding of the bagging materials to the structure. Peel Ply also promotes a smoother finish in the finished structure. The type of peel Ply used will be dictated by resin type used.
Breather Cloth A polyester blanket of non woven material that allows the air to flow out of the bag evenly.
Bag Tape For sealing the bag and plugging holes and tears.
Bagging Material The actual membrane material used to construct the atmospheric barrier. Again your choice of resins will dictate the bag material type used.
Resin and Catalyst OK this is up to you and will be determined by many factors such as type of structure, temperature in the shop, ultra violet exposure, end use temperature, and many other factors. Best advice is to read the suppliers material and ask questions. Do Not! mix suppliers. Resins and catalyst are formulated to work together and less than desirable results may occur should products from different suppliers are intermingled.
Reinforcement Material E-glass, Bi weave, Roving, Mat, Kevlar, Carbon fiber? This is another choice that will be dictated by the engineering of the part.
Fillers Micro-Balloons, Cabasil, Talcs, etc. These are materials often added to the resin mix to thicken it. Useful when building up fillets, etc.
This just the short list of materials and hardware. Also to be considered, shop environment, ventilation, and Personal safety equipment. There have been text books written on this topic and I personally endured a 4 credit hour course on Non Metallic Structure while working on my Engineering degree.
The schematics shown at http://www.bertram31.com/proj/tips/vaccuum.htm will give a good overview of the basic process.
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