MATS324C5 HLUspray.ppt

Contact moulding: spray and hand lamination techniques,John Summerscales,Outline of lecture,Spray techniquesHand laminationVacuum bagging,Spray techniques,Spray techniques,hand-held ‘gun’ feeds a stream of chopped fibres into a spray of catalysed liquid resin. stream projected onto the mould tool. deposited materials left to cure under standard atmospheric conditions. fibres normally settle onto the tool in a random (quasi-planar) orientation composite mechanical properties limited by discontinuous fibres (ηl 1), random fibre orientation (ηo =3/8), and no significant consolidation pressure (low Vf).,Spray techniques: equipment,pump generally air-operated positive displacement type catalyst pumps may be piston or peristaltic chopper cott wheel moves the fibres through the chopper against the cutter wheel with embedded blades spray head assembly (gun) integrates the chopper and resin mixing.,Spray techniques: mixing,common forms of mixing are: external mixing: typically 4 air-driven nozzles in a square pattern around the chopper with two nozzles dispensing resin and two nozzles dispensing catalyst. airless external mixing: catalyst and resin fed from pressure pots with mixing by stream impingement. air-driven internal mixing: air, catalyst and resin are mixed within the head before ejection. airless internal mixing: high pressure mixed in head two-pot system: high pressure resin and catalyst streams arranged to impinge around 150 mm ahead of the gun,Spray techniques: health & safety,traditionally a stream of fine droplets so significant vapourisation of styrene CFA “Controlled Spraying” to reduce vapour spray gun pressure calibration overspray containment flanges operator training potential for automation by robots,Spray techniques: advantages,low equipment and tooling costs. inexpensive materials cheapest form of fibre is continuous roving fast deposition rates. low labour costs (re. hand-lamination). versatile part shape/laminate configuration, including thickness v