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Taking composite materials as a whole, there are many different material options to choose from in the areas of resins, fibres and cores, all with their own unique set of properties such as strength, stiffness, toughness, heat resistance, cost, production rate etc. However, the end properties of a compo Oakley Sunglasses Outlet site part produced from these different materials is not only a function of the individual properties of the resin matrix and fibre (and in sandwich structures, the core as well), but is also a function of the way in which the materials themselves are designed into the part and also the way in which they are processed. This section compares a few of the commonly used composite production methods and presents some of the factors to be borne in mind with each different process, including the influence of each process on materials selection Oakley Sunglasses Outlet .The high styrene contents of spray lay up resins generally means that they have the potential to be more harmful and their lower viscosity means that they have an increased tendency to penetrate clothing etc.Limiting airborne styrene concentrations to legislated levels is becoming increasingly difficult. caravan bodies, truck fairings, bathtubs, shower trays, some small dinghies.Resins are impregnated by hand into fibres which are in the form of woven, knitted, stitched or bonded fabrics. This is usually accomplished by rollers or brushes, with an increasing use of nip roller type impregnators for forcing resin into the fabrics by means of rotating rollers and a bath of resin. Laminates are left to cure under standard atmospheric conditions. epoxy, polyester, vinylester, phenolic.Fibres: Any, although heavy aramid fabrics can be hard to wet out by hand.Resin mixing, laminate resin contents, and laminate quality are very dependent on the skills of laminators. Low resin content laminates cannot usually be achieved without the incorporation of excessive quantities of voids.Health and safety considerations of resins. The lower molecular weights of hand lay up resins generally means that they have the potential to be more harmful than higher molecular weight products. The lower viscosity of the resins also means that they have an increased tendency to penetrate clothing etc.Limiting airborne styrene concentrations to legislated levels from polyesters and vinylesters is becoming increasingly hard without expensive extraction systems.Resins need to be low in viscosity to be workable by hand. This is achieved by sealing a plastic film over the wet laid up laminate and onto the tool. The air under the bag is extracted by a vacuum pump and thus up to one atmosphere of pressure can be applied to the laminate to consolidate it.Resins: Primarily epoxy and phenolic. Polyesters and vinylesters may have problems due to excessive extraction of styrene from the resin by the vacuum pump.Fibres: The consolidation pressures mean that a variety of heavy fabrics can be wet out.This process is primarily used for hollow, generally circular or oval sectioned components, such as pipes and tanks. Fibre tows are passed through a resin bath before being wound onto a mandrel in a variety of orientations, controlled by the fibre feeding mechanism, and rate of rotation of the mandrel. e Oakley Sunglasses Outlet poxy, polyester, vinylester, phenolic.Fibres: Any. The fibres are used straight from a creel and not woven or stitched into a fabric form.Cores: Any, although components are usually single skin.Fibres are pulled from a creel through a resin bath and then on through a heated die. The die completes the impregnation of the fibre, controls the resin content and cures the material into its final shape as it passes through the die. This cured profile is then automatically cut to length. Fabrics may also be introduced into the die to provide fibre direction other than at 0. Although pultrusion is a continuous process, producing a profile of constant cross section, a variant known as ‘pulforming’ allows for some variation to be introduced into the cross section. The process pulls the materials through the die for impregnation, and then clamps them in a mould for curing. This makes the process non continuou Oakley Sunglasses Outlet s, but accommodating of small changes in cross section.Resins: Generally epoxy, polyester, vinylester and phenolic.Fabrics are laid up as a dry stack of materials. These fabrics are sometimes pre pressed to the mould shape, and held together by a binder. These ‘preforms’ are then more easily laid into the mould tool. A second mould tool is then clamped over the first, and resin is injected into the cavity. Vacuum can also be applied to the mould cavity to assist resin in being drawn into the fabrics. This is known as Vacuum Assisted Resin Injection (VARI). Once all the fabric is wet out, the resin inlets are closed, and the laminate is allowed to cure. Both injection and cure can take place at either ambient or elevated temperature.Resins: Generally epoxy, polyester, vinylester and phenolic, although high temperature resins such as bismaleimides can be used at elevated process temperatures.