Fibreglass/ Glass Reinforced Plastic

This podcast and set of revision cards explains everything you will need to know about the material fibreglass for the exam. You must remember you cannot refer to it as fibreglass, only glass reinforced plastic.

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What is Fibreglass?

-Fiberglass, is a material made from extremely fine fibres of glass.

-It is used as a reinforcing agent for many polymer products.

-A simple way of describing a polymer is that it is a plastic.

-The resulting material, is known as glass reinforced plastic(GRP) although it is commonly called "fiberglass”.

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How is mass production possible?

Glassmakers throughout history have experimented with glass fibres, but mass manufacture was only made possible with the invention of specialist 'finer' machine tooling which is used to create the fine strands and the sunsequent matting.

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What are the Benifits of Fibreglass?

It is light weight. It has a high strength to weight ratio, meaning it could have a light weight but remain very stong. It is corrosion resistant which means it does not rust. It is weather resistant which means it would be left outside and would not rust or rot. It has low thermal conductivity which means it does not conduct heat well. It is non-magnetic, this benefit is fairly self explanatory. It has high impact strength, this means if it was bumped or dropped it would not break and would remain strong. It is a good insulator which mean it does not lose heat. It requires low maintenance which makes it a cheap material to use. It remains durable for a long time. It can take on any surface finish.

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How does it's shell like construction affect it's

A GRP component is typically of a thin "shell like" construction, (although some components are sometimes skinned on the top / bottom and filled on the inside with a different ‘Core’ material e.g. structural foam , as in the case of surfboards for additional buoyancy…or with a honeycomb matting). These effectively provide a laminate (layering of materials) and can dramatically increase strength and resist bending . The component made using GRP can be an arbitrary shape (virtually any shape the designer wishes), limited only by the complexity of the mould used for manufacturing the shell.

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What are the properties of an individual glass fib

An individual structural glass fiber is both stiff and strong in tension and reasonably strong in compression. This is mainly due to the length of the fiber for example because a typical fiber is long and narrow, it buckles easily). On the other hand, the glass fiber is unstiff and unstrong in when not under tension or compressi. Therefore is it is being cut or broken it is unstiff and unstrong.

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How are weaknesses removed from the material?

When adding the resin to the fibres during molding it is always better to ensure that they are arranged in an appropriate direction so there is no weaknesses in the mold. Furthermore, by laying multiple layers of fiber or resin on top of one another, with each layer oriented in different directions, the stiffness and strength properties of the overall material can be increase and controlled in an efficient manner. This is the best way of ensuring the strength of the piece you are molding. In the case of glass-reinforced plastic, it is the resin with hardener or plastic matrix which permanently fixes the structural glass fibers into directions chosen by the designer.

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In what form do we use the glass fibres?

The fibres or filaments can be bundled together in large numbers to provide a roving. These rovings are then either used directly in a composite application such as; gun roving, gun roving is when an automated gun chops the glass into small lengths and drops it into a jet of resin, it is then projected onto the surface of a mold, and is mainly used for larger moldings. They can be used to manufacture fabrics such as chopped strand mat. This is made of randomly oriented small cut lengths of fibre all bonded together which will then be used to mold something. Woven fabrics, knit fabrics or uni-directional fabrics are also made using these filaments. Both the Woven Fabrics and the CSM can be used in the ‘Hand Layup’ process.

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General information about fibreglass.

Glass-reinforced plastic (GRP) is a composite material made of a plastic reinforced by glass fibers. The composite material is commonly referred to as fiberglass) Thermosetting plastics are normally used for GRP production— Epoxy is commonly used as is polyester resin . A catalyst is added to create the reaction. A typical example of a catalyst is MEK peroxide

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What are Epoxy & Polysester Resin?

Epoxy and polyester resin are both polymers. They are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties. They are thermosetting plastics and, as with other resins, cure exothermically (give off heat) . The use of excessive catalyst can, therefore, cause charring or even ignition (catch fire)during the curing process. As with many other composite materials, the two materials act together, each overcoming the deficits of the other. Whereas the plastic resins are strong in squashing forces and relatively weak in pulling forces, the glass fibers are very strong in tension but have minimal strength against compression. By combining the two materials, GRP becomes a material that resists both compressive and tensile forces well. The two materials may be used uniformly molded or the glass may be specifically placed in layers in different directions & thicknesses. This is often done in those portions of the structure that will experience increased tensile loads.

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Layer one of modelling.

When creating a product in GRP you will first have to make a PLUG from a given material (for example it could be made from wood). This is quite a skilled task and can be quite expensive if professionally made by a pattern maker. Once the Plug has been made you can then use this to make the actual mould you will use to make your part from. The side that will be in contact with the GRP must be very smooth, it is often painted and covered with a releasing agent e.g. a wax (in order for the part to released from the mould more easily).

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Layer two of modelling.

The next layer that goes on top of the wax is the Gelcoat. A Gelcoat is a liquid material (usually painted / sprayed on) that is used to provide a high-quality finish on the visible surface of a fibre-reinforced composite material. The most common gelcoats are based on epoxy or unsaturated polyester resin chemistry. Gelcoats are modified resins which are applied to molds in the liquid state. They are set to form crosslinked polymers.

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Layer three of modelling.

Layer three is a mixtures of polyester resin and fiberglass. There are three main kinds of fibre. Carbon being the strongest..then Kevlar and then glass. The glass is layered inside the mold. This is called ‘laying up’ and then the resin (with hardener added) is stippled (brushed) into the matting causing it to WET OUT and loosening the weave between the filaments and allowing the operator to manipulate the fibres into the desired shape.This happens when the resin and catalyst give an Exothermic reaction. An exothermic reaction is when heat is generated, and the glass strands or rovings are fixed into the desired shape. Before the resin has cured it is important that the operator uses a small metal roller to squash the matting thus removing any air… which can cause weaknesses in the final shell. This method is not used for mass production as it is too time consuming.

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The Mass Production Process

This is very different to the hand lay-up process. The difference comes is the application of the fibre and resin material to the mold. Spray-up is an open-molding composites fabrication process where resin and reinforcements are sprayed onto a reusable mold. 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 and eradicate air . Wood, foam, or other core material may then be added, and a secondary spray-up layer embeds them between the laminates. Laminates is the name given to the layers of GRP. The part is then cured, cooled, and removed from the mold.In both techniques the surface that was next to the mold will be coloured and smooth. Gelcoat is commonly pigmented to provide a coloured, glossy surface which improves the aesthetic appearance of the article. It can also be clear or sprayed over again to give a better quality finish if required. Gelcoats are designed to be durable, providing resistance to the sun and water, this is useful for pedalos.

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