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WEST SYSTEM 881 Breather Fabric is a 45" wide lightweight polyester blanket that pro- vides air passage within the vacuum envelope and absorbs excess epoxy. A variety of other materials can be used such as mosquito screen, burlap, fiberglass cloth or a bubble type swimming pool cover. 2.2.4 Vacuum bag The vacuum bag, in most cases, forms half of the airtight envelope around the laminate. If you plan to use vacuum pressure of less than 5 psi (10 hg) at room temperatures, 6-mil poly- ethylene plastic can be used for the bag. Clear plastic is preferable to an opaque material to allow easy inspection of the laminate as it cures. For higher pressure and temperature appli- cations, specially manufactured vacuum bag material should be used. A wrinkled type film is available from Film Technology, Inc. Its special texture is designed to channel air and eliminate the need for breather fabric. WEST SYSTEM 882 Vacuum Bag Film is a 60" wide, heat stabilized nylon film that can be used at temperatures up to 350°F (176°C) and high vacuum pressures. The vacuum bag should always be larger than the mold and allow for the depth of the mold. When a bag wider than the standard width is needed, a larger bag can be created by splicing two or more pieces together with mastic sealant. See Appendix C for a list of vacuum bagging equipment and material suppliers. 2.2.5 Mastic sealant Mastic is used to provide a continuous airtight seal between the bag and the mold around the perimeter of the mold. The mastic may also be used to seal the point where the manifold enters the bag and to repair leaks in the bag or plumbing. WEST SYSTEM 883 Vacuum Bag Sealant is a 12" by 332" flexible adhesive strip that peels easily from the mold after use. Generally, the better the airtight seal between the mold and bag material, the smaller the pump you’ll need. Poor seals, or material which allows air leaks, will require a larger capac- ity pump to maintain satisfactory vacuum pressure. 2.2.6 The plumbing system The plumbing system provides an airtight passage from the vacuum envelope to the vac- uum pump, allowing the pump to remove air from and reduce air pressure in the envelope. A basic system consists of flexible hose or rigid pipe, a trap, and a port that connects the pipe to the envelope. A more versatile system includes a control valve and a vacuum throttle valve that allow you to control the envelope vacuum pressure at the envelope. A system is often split to provide several ports on large laminations, or may include some type of mani- fold within the envelope to help channel air to a single port. A variety of pipe or tubing can be used for plumbing as long as it is airtight and resists collapsing under vacuum. Vacuum hose is designed specifically for vacuum bagging and autoclave laminating. It is available along with fittings, pumps, and other vacuum bagging materials from manufac- turers specializing in vacuum bagging equipment. Because of its higher cost, this type of plumbing system is most appropriate for large scale or production laminating operations. Other types of wire reinforced hose may work, but they should be rated for crush resistance or tested under vacuum for the appropriate length of (cure) time. Semi-rigid plastic tubing, with adequate wall thickness, can be used for a plumbing system, but it is often awkward to handle. If the laminate is to be post-cured during vacuum bagging, the tubing must also be heat resistant. Plastic tubing that may be able to withstand vacuum at room temperature may soften and collapse if heated. Rigid 3⁄4" PVC or CPVC pipe, elbows, T’s, and valves work well. They are low cost and available at most local hardware or plumbing supply stores. The pieces do not need to be cemented together and can be rearranged to suit any configuration. This type of plumbing system, because of its low cost and versatility, is ideal for small scale or occasional laminat- ing operations. Vacuum Bagging Equipment 7 2PDF Image | Vacuum Bagging Techniques 002150
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