What is GRP?

The chief process for manufacturing large structures is the hand lay-up method, of which important attributes are:

-Large structures can be made without complicated moulds

-Heat resistance is superior compared with mosts thermoplastics sheet materials

-Strength and rigidity are good (2-10 times superior to most thermoplastics) at densities less than that of most metals (1,6-1,8 g/dm³)

The cauldron of potentiality op GRP industry bubbled for more than a century.

But the best is yet to come because new methods of reinforcing polyesters and further improvements continue to be fostered and arrive on the scene with amazing regularity

The main customer of GRP:

Several interesting ways of recording reinforced polyesters consumption are used in various phase of the industry. There are nine markets which singly reflect in action in the reinforced polyester industry

- Aircraft an Aerospace

• appliances and equipment
• construction
• consumer goods
• corrosion equipment
• electrical industry
• marine industry
• transportation :
  
  

One of the most valid methods of evaluating this market is by observing the number of pounds of plastics used in individual cars. Any listing should include parts, equipment and seating for automobiles, trucks, buses, truck-trailers, tank trucks, railroad and subway cars, and smaller speciality vehicles such as dune-buggies, mail delivery carts and moter scooters.

Hand lay-up Usage
The hand lay-up method of production reinforced plastics generally comeprises impregnating dry fiber glass reinforcement with a liquid, thermosettable resin in in open mold and inducing cure at room temperature with little or no external pressure. Fabrication of RP/C parts by hand lay-up procedures is indicated when the size of the piece is obviously too large or when the form of the piece is too complex for matched-metal tooling or for similar types of press molding. Examples: Boats and ships, “unitised” bathroom fixtures and assemblies, swimming pools, … These and many similar kinds of unconventional components may be designed and prepared for fabrication by the hand lay-up process. History Hand lay-up reinforced plastics were truly born during World War II in answer to the need for materials which could replace scarce materials. Method Hand lay-up molding typically uses a single mold, either plug or cavity type. The mold may be prepared by use of a gel coat and/or standard release agents. Procedures include both wet lay-up and prepreg molding. The steps normally required in the hand lay-up procedure include mold preparation, application of release agents, selection of proper resin and reinforcement, insertion of reinforcement and introduction of resin (for wet lay-up), roll out and distribution of the resin, gelation of resin, preliminary finishing, allowance for full cure, removal from mold, and final finishing. Materials Mold release and sealers : because the resins used in reinforced plastics have been designed for their good adhesive and cohesive properties, it is immediately apparent that a method must be provided to prevent the molded product from adhering to and becoming a permanent part of the mold on which it is made. To provide this seperability, agents known as mold releases are used. By definition, a mold-release agent is any material or substance which, when applied to a substrate, creates a high surface-contact angle, thereby resisting or preventing wetting of the substrate by any material applied over the release agent. In hand lay-up molding, most releases are applied to the mold and are not of the “internal-release” type. The latter are agents included in the resin mix which are to be expelled during cure to provide separation. When porous materials, such as wood or plaster, are used for tooling, the surfaces must be completely sealed before mold-release agents are applied. A proper sealing material should penetrate deeply into the wood or plaster surface, filling all voids without causing any degree of material build-up on the surface. Care must be taken in the selection and use of these materials however, since many are severely degraded when exposed to molding temperatures. Gel coats: a gelcoat is a resinous, mineral filled, pigmented, non-reinforced layer or coating which is applied first to the mold but which becomes the outer protective layer for hand lay-up laminate when completed. Laminating resins : are categorized as unique, low-pressure or room-temperature curing liquids that become solid materials. They permit the formation of high-strength, high performance articles or structures for many functional purposes. Curing systems . Several type of simple organic liquids added to styrene modified alkyds (polyesters) generate a process that moves through free-radical initiation, attack of and cross-linking with the unsaturated bonding, and final cure. The ultimate result is a rigid solid in which the matrix resin has joined chemically and mechanically with the reinforcing fibers to provide a synergistic composite structure, whose properties are greatly different and significantly superior to those of either material alone. Hand lay-up processes usually employ room-temperature cures based primarily on methyl-ethyl-ketone (MEK) peroxide catalyst plus cobalt-naphthenate promoter. Other catalysts are available for specific purposes. Fiber glass reinforcements Fibrous glass reinforcing materials have been developed and designed to meet a number of varied and combined requirements of in-process functionality and end-use performance. Equipment and tooling Molds: construction and use: Well-engineered molds for hand lay-up may be constructed by the exact processr for actually molding the finishing parts. The mold gel coat originally taken from the master pattern will of course be on the side or surface against which the part gel goat is subsequently to be applied. Laminate contruction over the gelcoat will naturally ensue, and the hand lay-up mold are braced, bolstered, and liberally reinforced for dimensional stability.