Fiberglass Pool Manufacturing Process
The part fabrication process is similar to the steps followed in making the mold. When working with a female mold, start by applying the appropriate surface coat to the mold surface. This step isn't absolutely necessary when fabricating parts, but a much better cosmetic appearance for the finished part will be achieved if it is used. Applying the first layer of resin and fabric directly to the mold surface can result in surface irregularities, pinholes, and print-through of the fabric weave pattern if a heavier fabric is used. These blemishes can be corrected once the part is removed from the mold, but it will require tedious sanding and filling. Use of a lightweight fabric, such as two-ounce or four-ounce, as the first layer can minimize these problems if a gel coat or surface coat isn't used. As an alternative to gel coat, Duratec Surfacing Primer can be sprayed into the mold, providing a durable surface finish.
Polyester gel coats come in either white or clear form, which is pigmented to a variety of colors. Clear gel coats reproduce colors very accurately, while white gel coats yield pastel colors. Epoxy surface coat is white in color, and can also be pigmented.
When applying gel coat to the mold, the best results will be achieved by spraying unthinned gel coat with a cup gun, in much the same manner as tooling gel coat is applied in mold construction. Slowly build up the gel coat in three passes, to a thickness of 15-20 mils. A gel coat thickness gauge is the best tool to use for determining the thickness. Check in several locations on the part to make certain an even coat is being applied. Too much of too little in some areas can cause wrinkling or distortion when the gel coat cures. When using an epoxy surface coat, it should be brushed into the mold.
Adhering to the guidelines in the mold construction section of the white paper, follow the gel coat with an initial stabilizing layer of reinforcement. If you've pigmented the gel coat and want the same color throughout the part, the resin can also be pigmented to match.
When laying up the reinforcement, try to utilize a single, uncut piece of fabric for each layer. Unfortunately, this is not always possible. Sometimes a part is too large to be covered by as single piece of fabric, so two or more pieces must be used. When two separate pieces must be joined together in a mold, it is best to overlap the pieces by one-half to one inch, as opposed to butting the pieces tougher. Butt two pieces together to form a seam only when maintaining constant thickness is necessary.
The contours and shapes of a part may also make it difficult to get good adhesion using a single piece of fabric. Indentations and sharp angles, in particular, present this kind of problem. Composites can be formed into many shapes, but it is very difficult to achieve sharp angles (90 degrees or sharper) with continuous pieces of fabric. The fabric will tend to lift in these areas, resulting in air bubbles and weak spots in the laminate. If a sharp angle is required in a part, the best way to approach it is by butting two cut pieces of fabric together at the turn. For added strength at these butt joints, mix a small amount of resin with milled glass fibers to form structural putty filler. Apply this to the joint before lying in the fabric. With indentations, it's better to cut a smaller piece of fabric to fit the indentation rather than trying to force a larger piece of fabric down into it.
As with mold construction, use rollers and squeegees to thoroughly saturate the fabric, work air pockets out of the laminate and compacts the layers as much as possible. This will help avoid weak spots and delamination problems into the finished part. As the layers of reinforcement fit into the mold, pay attention to the orientation of the fibers if using woven cloth, alternating the orientation by layer to increase part strength.
If a sandwich core construction is going to be utilized, determine which type of core material best suits the application. Polyurethane foam is very rigid and doesn't conform well to contours, whereas vinyl foam can be heated and formed to a variety of shapes. Balsa, which generally consists of small end grain blocks held together by a scrim of fabric, can conform to mild curves. Honeycomb core materials are very flexible and will bend to a variety of shapes.
Several steps must be taken to prep core material, in order to get a strong piece. After cutting and shaping the core material to the contours of the part, bevel the edges of the core's perimeter to a 45-degree angle to smooth fabric transition. Mix a portion of resin with glass microspheres to a slurry consistency, and use this to fill any gaps, as well as splice multiple pieces or core material together. Pretreat open-celled foams and honeycomb cores with this slurry mix, in order to fill the open cells with something lighter than pure resin. Once these steps are completed, the core can be bonded in place.
When dealing with multiple-piece molds, almost always assemble the pieces of the mold before laying up a part. Laying up a part and then assembling the mold pieces will make it difficult to get a good bond between the pieces and a smooth cosmetic finish. The exception to this rule would be an enclosed item, such as a fuel tank, which would be impossible to lay up if the mold was assembled in advance.
If a compression mold is being used, the other half of the mold can be clamped to the first half once all of the reinforcing layers are in place. If a compression mold is not being used, but a smooth surface is desired on both sides of the part, a surface coat can be applied over the final layer of reinforcement. When the laminate reaches the "leathery" semi-cured stage, trim the edges with a sharp utility knife. Doing this now will significantly reduce finishing time and dust generation down the road.
Once the part has cured, remove it from the mold in much the same manner as the mold was removed from the plug. Any residue from the release agent can be rinsed off the part, and it can be finished in whatever manner is necessary. Finishing usually involves sanding down any seams and sanding the edges of the part. Inspect the mold for any damage or dulling of the mold surface. If everything is fine, reapply the release agent when you're ready to build the next part. If repairs or buffing are necessary, carry out those operations as previously described.