Fiberglass spray lay-up process

Spray-Up also known as chop method of creating fiberglass objects by spraying short strands of glass out

of a pneumatic gun. This method is used often when one side of the finished product is not seen, or when

large quantities of a product must be made cheaply and quickly without regards to strength.

It is very different from the hand lay-up process. The difference comes from the application of the fibre and

resin material to the mould. Spray-up is an open-moulding composites fabrication process where resin and

reinforcements are sprayed onto a reusable mould. The resin and glass may be applied separately or

simultaneously "chopped" in a combined stream from a chopper gun. Workers roll out the spray-up to

compact the laminate. Wood, foam, or other core material may then be added, and a secondary spray-up

layer embeds the core between the laminates. The part is then cured, cooled, and removed from the mould.

Manufacturing Process

1. The mould is waxed and polished for easy removal.

2. The gelcoat (a smooth, hard polyester resin coating) is applied to the mould surface and is

given time to cure before re-applying. Usually two coats of gelcoat are used.

3. The barrier coat is applied to avoid fibre print and a rough surface through the gel coat.

4. The barrier coat is cured in an oven and left to cool to room temperature.

5. After curing, calcium carbonate and aluminium trihydrate fillers are added using a high shear

mixing unit.

6. A wax-like additive is added into the resin to reduce styrene discharge by 20% during

lamination.

7. A fibreglass chopper is mounted on the spray gun.

8. The mixture of catalyst, resin and fibreglass is then sprayed evenly in a fan-like pattern to

assure even coverage.

9. A roller is used for compaction after each layer has been applied, this removes trapped air.

10. Where desirable, wood, foam, or honeycomb cores are embedded into the laminate to

create a sandwich structure. Corner and radius coverage is also checked.

11. The part is cured in an oven and left to cool to room temperature.

Processing Requirements

Manufacturing Process12. The mould is removed and is ready to be waxed and polished for the next manufacture

cycle.

13. Finishing is done by trimming edges of excess fibreglass and drilling holes as needed.

14. After the part is assessed by quality control personal, it is weighed, structurally checked, and

the surface finish is inspected prior to packing and shipping.

Advantages

It is a very economical process for making small to large parts.

It utilizes low-cost tooling as well as low-cost material systems.

It is suitable for small- to medium-volume parts.

Processing Requirements

The processing steps are very similar to those in hand lay-up. In this process, the release agent is first

applied to the mould and then a layer of gelcoat is applied. The gelcoat is left for two hours, until it hardens.

Once the gelcoat hardens, a spray gun is used to deposit the fibre resin mixture onto the surface of the

mould. The spray gun chops the incoming continuous rovings (one or more rovings) to a predetermined

length and impels it through the resin/catalyst mixture. Resin/catalyst mixing can take place inside the gun

(gun mixing) or just in front of the gun. Gun mixing provides thorough mixing of resin and catalyst inside

the gun and is preferred to minimize the health hazard concerns of the operator. In the other type, the

catalyst is sprayed through two side nozzles into the resin envelope. Airless spray guns are becoming

popular because they provide more controlled spray patterns and reduced emission of volatiles. In an airless

system, hydraulic pressure is used to dispense the resin through special nozzles that break up the resin

stream into small droplets which then become saturated with the reinforcements. In an air-atomized spray

gun system, pressurized air is used to dispense the resin.

Once the material is sprayed on the mould, brushes or rollers are used to remove entrapped air as well as to

ensure good fiber wetting. Fabric layers or continuous strand mats are added into the laminate, depending

on performance requirements. The curing of the resin is done at room temperature. The curing of resin can

take two to four hours, depending on the resin formulation. After curing, the part is removed from the

mould and tested for finishing and structural requirements