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A vacuum port connects the exhaust tubing to the vacuum bag. It can be designed specifi- cally for the purpose or built from commonly available materials. One of the simplest ports is a hollow suction cup that sits over a small slit in the vacuum bag. Cups designed for use with car top carriers can be easily adapted by drilling through the center of the cup. A control valve should be incorporated into the vacuum line to allow you to control the vol- ume of airflow at the envelope. The control valve affects the rate of air removal, but not the vacuum pressure. A second valve, the vacuum throttle valve, can be placed between the control valve and the envelope. This valve, incorporated with a “T” fitting, acts as an ad- justable leak in the system to control the envelope pressure. For convenience, valves should be placed close to the envelope. A trap should be incorporated into the line as close as possible to the envelope. The trap collects any excess adhesive that gets sucked into the line before it reaches the valves or pump and prevents a build up of adhesive in the line. A trap can easily be built with a small section of pipe, a “T”, and an end cap. A vacuum gauge is necessary to monitor the vacuum level/clamping force during the cure time of the laminate. Most gauges read in inches of mercury from zero (one atmosphere) to 30 (inches Hg below one atmosphere). The reading of negative pressure inside the bag equals the net pressure of the atmosphere pressing on the outside of the bag. To approxi- mate this reading in pounds per square inch (psi), simply divide the reading by two. A vac- uum gauge, available at most automotive stores, is modified by threading a hollow suction cup (similar to the port) to the base. A 11⁄2" PVC pipe cap, with a hole drilled and tapped to match the gauge, will also work. The end of the cap is sealed to the vacuum bag with mastic. A manifold is used in some situations to assist in air removal from the envelope. It can be a thicker section of breather material or other material that provides a channel for air move- ment under the vacuum bag to a port. A 3⁄4" PVC pipe with holes drilled along its length was used in the applications shown later in this manual. Any hard object (such as the manifold) placed under the vacuum bag can leave an undesirable impression in the laminate. The WEST SYSTEM 885 Vacuum Bagging Kit is a starter kit for room temperature repairs and small laminating projects up to 13 sq ft The kit includes a venturi vacuum generator (re- quires an air compressor delivering at least 65 psi), three vacuum cups (ports), 10 ft of 1⁄4" tubing, a vacuum gauge, two T fittings, 15 sq ft of release fabric, 15 sq ft of breather fabric, 15 sq ft of vacuum bag film, 25' of mastic sealant, and kit instructions. Refer to the WEST SYSTEM User Manual & Product Guide for more information. 2.2.7 Mold Release Mold release is essential for preventing the epoxy from sticking to the mold when laminat- ing a part. There are generally three types of mold release used depending on the mold ma- terial and desired characteristics of the finished part. The most common type is a carnauba based paste wax. This is usually put on in up to 5 layers for new molds and at least one layer before each new part is molded. It is also a good idea to use something like PVA (polyvinyl alcohol) over the 5 coats of wax on a new mold to help prevent sticking. Fine detail and gloss level are obtained with the use of paste wax, but it can be difficult to buff anything with a textured surface. The second type of release is the semi-permanent formulation. Many different manufactur- ers provide liquid release systems that apply much easier than paste wax and last for multi- ple parts on one application of the product. Generally a sealer and a release are used to provide the best results for new molds. Fine detail and gloss level are obtained as well as texture since buffing to remove excess is not usually necessary. The final type of mold release is of the general contaminant variety. This can range from things like grease and Vaseline to toilet bowl wax, hair spray, hair gel or even clear packag- ing tape. These are generally used on rough or porous surfaces where detail, gloss, and tex- ture are not issues for the final part. While not the prettiest, these release agents quick, cheap and widely available. Vacuum Bagging Equipment 8 2PDF Image | Vacuum Bagging Techniques 002150
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