Polyester

Polyester Parts Production

Fiberglass preforming is a well-known technology used in large volume production runs, mainly in the automotive industry. We developed a more affordable preform technology.

Glass-fibre roving on roll

Preforms address several problems in classic polyester part production.

Polyester resin contains a huge percentage of styrene of up to 45%. Styrene has two disadvantages:

1. Workers in contact with styrene are in risk of damage to the central nervous system.

2. Styrene is a green house gas. Air treatment systems will need to be installed to combat both effects. EU regulations however are increasingly intolerant towards styrene emissions. As of 2010 these will be cut in half. The costs for the air treatment will go through the roof.

The most cost effective way of reducing styrene emissions is to use a closed mould process. But a closed mould has its own difficulties.

As opposed to a spray on technique laying up of glass fibre in a mould is labour intensive and error prone. It takes a skilled worker to correctly lay up glass fibre in a mould. In the case of a complex product the glass fibre – usually in the form of a mat – needs to be cut and positioned with necessary overlaps. These can lead to local disruption of resin flow. The product will end up with resin poor area’s that need to be repaired or the product is a write off.

The solution to this problem is to use a glass fibre preform in the final shape of the product.

Binders

Since a preform is made from chopped strands, a binder is needed that will keep the the strands together. A successful binder will need to meet the following requirements:

• The binder need not  negatively impact the properties of the final product.
• It should only be a small amount as not to have a to great an impact on the final costs of the product.
• Furthermore the binder should bind the chopped glass fibre successfully into a shape that is structurally sound enough to be handled.
• The preform should retain its shape over time.

CMPreform has developed a thermoplastic binder, which comes in fibre form. In this way a simple production process could be established. Central point of this process is the specially developed fibre cutter. The cutter is electrically driven thus being accurately controllable. Both the glass fibre roving and the thermoplastic binder are fed into the cutter so as to be sprayed on the preform mould.

Finished preforms

This process is fully automated and computer controlled. The spray gun can be mounted on a robot to produce a custom-made preform with repeatable accuracy and precision of production in spite of the complexity of the product.

The preform mould is made out of a perforated material. Air suction is applied to the mould both to keep the glass fibre binder mixture in place as to prevent the cutter to blow earlier applied glass fibre away.

The binder is then melted though heating the glass fibre binder mixture as it is held in place by the air suction on the mould. When the heat is removed the air suction cools the preform quickly so that it can be removed from the mould immediately.

The fibreglass preform can be placed into an RTM mould without any extra handling. The mould can immediately be closed and the resin injected.

For the production of preforms out of glass fabric a UV curing binder was developed. This type of binder can also be used in the production of preforms out of roving. This process is environmentally less friendly than the fibre binder, and needs a little extra equipment.

The UV curing binder is applied through a spraynozzle directly into the stream of chopped glassfibre. We use 5% (weight) of binder to produce a firm preform.

The glassfibre is held in place through air suction, and when the application is finished the fibres are compressed by placing a PE film on top of the preform. Through the clear film the UV light is passed thus starting the curingprocess.

After 3 seconds of exposure to the UV light the resin cures. The air suction can be removed and the PE film as well.