Open mould processes

Quality-control tests and important process variables 

The process is very labour intensive, but survives because it is adaptable to many mould designs and is useful for making relatively large mouldings (since there is no size limitation), which would be cost-prohibitive with other processes (such as injection moulding). Advances in processing include 

Typical systems include room-tempemture-curable polyester resins, epoxy resins and vinyl ester resins, and glass-fibre and mat reinforcement. 

Open-mould processes have traditionally developed through trial-and-error processing and have not been modelled formally, unlike the similar case of process modelling in the metal industry, as reviewed by Thomas (2002). 

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Open-mould processes are thermoset moulding processes with open moulds in the male or female form. In this process the mould is made from a pattern and the reinforced thermoset is applied to the mould to reproduce the shape and finish of the mould. Typical examples would be boat hulls made from fibreglass-reinforced gel coats. Figure 6.10 shows the basic contact-moulding process. 

These thermosetting resins contain a urethane prepolymer in methyl methacrylate monomer. Although they are cured in a similar fashion to polyesters, their initial viscosity is much lower and the cure reaction is more rapid. The speed of cure along with the odour of the monomer preclude the use of open mould processes, but these resins are especially suitable for fast processing by methods including pultrusion and resin... 

Open mould processes are operated manually, with one exception (filament winding) while closed mould processes are either semi-automatic or completely automatic (Figure 9.4). 

Depending on the differences nsed in the application methods of layers and curing details, there are different open mould processes (such as hand lay-np, spray-np, automated laying... 

An orthophthalic designed to provide good wet-out and long trim times in open mould processes, c. 550 e. 22.5/25... 

The application of instrumentation to the automatic control of a sequence of operations, e.g., injection moulding processes. Once the mould has been loaded with inserts (assuming a rubber to metal bonded part) into the press, the operation of a push-button starts the controller which closes the press, injects the rubber, controls the cure cycle, recharges the injection unit, opens the press, operates the ejectors and presents the mould for cleaning and loading of inserts. 

Figure 6.5 Flow scheme of polydicyclopentadiene production via ring-opening metathesis polymerisation in the reaction injection moulding process...

A series of five nanocomposite elastomer systems were prepared for this study incorporating 0, 1, 2, 4 and 8% (on total resin mass) of the organically modified montmorillonite clay Cloisite 6A. The appropriate level of Cloisite was dispersed in a starting resin blend of OH terminated PDMS (M -77,000 and Mn -550 g mol in a 3 1 ratio) by a combination of mechanical mixing and ultrasonic processing to give a nano-dispersion of clay platelets. The blend was subsequently crosslinked with a stoichiometric level of tetrapropoxysilane (TPOS) in the presence of 5% diphenylmethylsilanol (DPMS) chain terminator and 5% tin(II) 2-ethylhexanoate catalyst, cured in an open mould at 65°C for twenty minutes, then removed from the mould and post cured for a further fifteen hours at 65°C to give an elastomeric mat. 

A development of the matched-die moulding process is to vacuum assist the resin into the tool. Dry reinforcements are placed in an open tool. The layup is sealed by a flexible vacuum bag and vacuum is applied. The resin is forced under pressure into the... 

P(4) The moulding area shall be properly sealed in order to prevent material escape during the moulding process. The locations to be sealed are typically the outer edges of the mould and the open ends of the sections to be joined. 

The process uses an open mould which is generally itself FRP previously produced from a timber pattern. 

Hand lay-up is a wet process and it is the simplest yet most labour-intensive and the most commonly used technique, since the 1940s. It is most suited for the production of similar components in limited numbers, (i.e., fibre-reinforced plastic (FRP) infill panels). In this method, successive layers of resin and reinforcement, (i.e., rovings, fabric, mat or randomly arranged chopped fibres of glass), are manually applied to an open mould, with the following basic procedure of five steps ... 

Spray-up is a less labour intensive process than hand lay-up, and it is an another way to mechanise the application of resin-fibre layers and to reduce the time needed for the process. In this technique, liquid resin and chopped GF are simultaneously sprayed and deposited onto the open mould. Continuous rovings are chopped in the spray gun (to fibres of 25-75 mm length) and are added to the resin stream as it exits the nozzle. Spray guns are either internal mix with air, airless internal mix, external mix with air, or airless external mix. The technique requires considerable operator skill if operated manually (for control of the thickness of the composite and to maintain a consistent polymer/glass ratio), however, the tooling costs are not too high. Spraying can also be... 

The LCM operator usually has very little scope for influencing or controlling the process once initiated. While this may produce a more repeatable process than traditional open-mould techniques, it also puts more emphasis on the process design. Owing to the cost of materials used in LCM, process... 

Blow-moulded products are associated with certain inherent limitations concerning shapes and wall thickness. While the blow-moulding process normally yields one-piece, closed, hollow products, pairs of open, hollow products have been made by splitting closed mouldings. 

Thermoplastic injection moulding is by far the most common moulding process in use, as well as being amongst the most complex. Normally, injection moulded parts have features which are formed parallel to mould opening (two-dimensional features). Features perpendicular to mould opening are possible... 

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