Signature Products Hand Lay Up Process For Contact Moulding

To explain the process involved for hand lay up contact moulding, we have taken some information from FRP Institute Worcester, MA, US and from Crystic Composites Handbook by Scott Bader

A chopped strand fiberglass mat is most commonly used for contact moulding. The use of woven and various combination materials has increased considerably over the years. The preparation of reinforcement packs, specifically tailored to the mould being used, saves time and redHand Lay Up Contact Moulding Processuces wastage.

The amount of resin required for a laminate can be calculated by weighing the reinforcement to be used. For chopped strand mat the resin to glass ratio should be between 2.3:1 and 1.8:1 (30% to 35% glass content).Resin to glass ratios of 1:1 is normal for woven roving.(50% glass content).

Once the applied gelcoat has cured sufficiently, a liberal coat of resin is applied as evenly as possible. The first layer of glass is then pressed firmly in to place and consolidated using a brush or roller. This action will enable the resin to impregnate the glass mat and dissolve the binder which holds the fiber together. The reinforcement will then conform readily to the contours of the mould .Once the first layer of mat is fully impregnated further resin can be added, if necessary, before applying subsequent layers of reinforcement. It is important that the first layer is as free of air bubbles as possible as any air trapped immediately behind the gelcoat could lead to blistering, should the moulding be exposed to heat or water during its working life.

Impregnation of the reinforcement can be carried out using a brush, or a mohair or polyester roller. If a brush is used, it should be worked with a stippling action, as any sideways brushing motion will displace the fibers and destroy their random nature. The use of rollers is advantageous when working on large moulds and they are available with long or short pile. Long pile rollers pick up more resin than short pile ones, but care need to be taken to accurately control resin to glass ratios. Consolidation of the laminate is more effective if carried out using a roller.

Subsequent layers of resin and reinforcement are applied until the required thickness has been achieved ensuring that each layer is thoroughly impregnated and properly consolidated. It is recommended than no more than four layers of resin and reinforcement are applied at any one time, to prevent the buildup of excessive exotherm. Where thick laminates are required, each series of four layers should be allowed to exotherm and then cool before subsequent layers are applied, though lengthy delays should be avoided unless a resin with a long term stage is used.

Should a moulding need to be strengthened this can be achieved by incorporating reinforcing ribs in to the laminate. The stage at which the ribs are put in to position will depend on the shape, thickness and end use of the moulding, though as a general guide, it is best to locate them immediately the last layer of reinforcement is applied. The rib formers should be covered with the reinforcing mat and thoroughly impregnated with resin. The final layer of reinforcement can then be applied over the whole area of the moulding to give a uniform appearance to the back surface.

DSC_0312Metal inserts are sometimes necessary, as locating of fixing point, etc. and these can be put in to place during the laminating operation. If an insert is likely to be subjected to a heavy load, the thickness of the moulding to be tapered away from the insert, in order to spread the load. Inserts need to be placed as near to the middle of the laminate as possible and the contact area between the laminate and the insert should be as large as practicable.

The back surface of a moulding can be rather coarse in appearance, particularly if chopped strand mat is the reinforcement used. It can be improved in one or two ways, either by incorporating a surface tissue at the final layer of the laminate to give a smoother ,resin rich surface, or by coating the surface , once it has curved ,with a formulated flow coat such that in the Crystic range. The use of flow coat gives the added advantage that it can be pigmented if required.

If you require any additional information, please don’t hesitate to contact us info@signatureproducts.com

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