Glass reinforced plastic is molded plastic reinforced with lengths of glass fibre. Injected molded GRP has very short fibre length up to 3 mm whereas composite laminating and DMC and SMC molding have long or continuous lengths of glass fibre reinforcement.
Gross Rating Points
Group. An abbreviation.
Glass-reinforced plastic is a material or fiber-reinforced plastic made of a plastic reinforced by fine fibers made of glass. Like carbon fiber reinforced plastic, the composited material is commonly referred to by the name of its reinforcing fibers (fiberglass). The plastic is thermosetting, most often polyester or vinylester, but other plastics, like epoxy , are also used.
The manufacturing process for GRP fiber glass uses large furnaces to gradually melt the sand/chemical mix to liquid form, then extrude it through bundles of very small orifices (typically 17-25 micrometres in diameter for E-Glass, 9 micrometres for S-Glass). These filaments are then 'sized' with a chemical solution. The individual filaments are then bundled together in large numbers to provide a 'roving'. The diameter of the filaments, as well as the number of filaments in the roving determine its 'weight'. This is typically expressed in yield-yards per pound (how many yards of fiber in one pound of material, thus a smaller number means a heavier roving, example of standard yields are 225yield, 450yield, 675yield) or in tex-grams per km (how many grams 1 km of roving weighs, this is inverted from yield, thus a smaller number means a lighter roving, examples of standard tex are 750tex, 1100tex, 2200tex).
These rovings are then either used directly in a composite application such as pultrusion, filament wounding (pipe), gun roving (automated gun chops the glass into small lengths and drops it into a jet of resin, projected onto the surface of a mold), or used in an intermediary step, to manufacture fabrics such as chopped strand mat (CSM) (made of randomly oriented small cut lengths of fiber all bonded together), woven fabrics, knit fabrics or uni-directional fabrics.
An individual structural glass fiber is both stiff and strong in tension and compression—that is, along its axis. (Although it might be imagined that the fiber is weak in compression, it is actually only the long aspect ratio of the fiber which makes it seem so; i.e., because a typical fiber is long and narrow, it buckles easily.) On the other hand, the glass fiber is unstiff and unstrong in shear—that is, across its axis. Therefore if a collection of fibers can be arranged permanently in a preferred direction within a material, and if the fibers can be prevented from buckling in compression, then that material will become preferentially strong in that direction.
Furthermore, by laying multiple layers of fiber on top of one another, with each layer oriented in various preferred directions, the stiffness and strength properties of the overall material can be controlled in an efficient manner. In the case of glass-reinforced plastic, it is the plastic matrix which permanently constrains the structural glass fibers to directions chosen by the designer. With chopped strand mat, this directionality is essentially an entire two dimensional plane; with woven fabrics or unidirectional layers, directionality of stiffness and strength can be more precisely controlled within the plane. A glass-reinforced plastic component is typically of a thin "shell" construction, sometimes filled on the inside with structural foam, as in the case of surfboards. The component may be of nearly arbitrary shape, limited only by the complexity and tolerances of the mold used for manufacturing the shell.
GRP is an immensely versatile material which combines lightweight with inherent strength to provide a weather resistant finish, with a variety of surface texture and an unlimited colour range available.
GRP was developed in the UK during the Second World War as a replacement for the molded plywood used in aircraft radomes (GRP being transparent to microwaves). Its first main civilian application was for building of boats, where it gained acceptance in the 1950s. Its use has broadened to the automotive and sport equipment sectors, although its use there is being taken over by carbon fiber which weighs less per given volume and is stronger both by volume and by weight. GRP uses also include hot tubs, pipes for drinking water and sewers, office plant display containers and flat roof systems.
Advanced manufacturing techniques such as pre-pregs and fiber rovings extend the applications and the tensile strength possible with fiber-reinforced plastics.
GRP is also used in the telecommunications industry for shrouding the visual appearance of antennas, due to its RF permeability and low signal attenuation properties. It may also be used to shroud the visual appearance of other equipment where no signal permeability is required, such as equipment cabinets and steel support structures, due to the ease with which it can be molded, manufactured and painted to custom designs, to blend in with existing structures or brickwork. Other uses include sheet form made electrical insulators and other structural components commonly found in the power industries.
Storage tanks can be made of GRP with capacities up to about 300 tonnes. The smaller tanks can be made with chopped strand mat cast over a thermoplastic inner tank which acts as a preform during construction. Much more reliable tanks are made using woven mat or filament wound fibre with the fibre orientation at right angles to the hoop stress imposed in the side wall by the contents. They tend to be used for chemical storage because the plastic liner (often polypropylene) is resistant to a wide range of strong chemicals. GRP tanks are also used for septic tanks.
Glass reinforced plastics are also used in the house building market for the production of roofing laminate, door surrounds, over-door canopies, window canopies and dormers, chimneys, coping systems, heads with keystones and sills. The use of GRP for these applications provides for a much faster installation and due to the reduced weight manual handling issues are reduced. With the advent of high volume manufacturing processes it is possible to construct GRP brick effect panels which can be used in the construction of composite housing. These panels can be constructed with the appropriate insulation which reduces heat loss.
GRP and GRE pipe systems can be used for a variety of applications, above and under the ground.
Cooling water systems
Drinking water systems
Waste water systems/Sewage systems