Processing contact moulding

London, Stationery Office, 2003, pp.4, 30 cm, 2/9/04. Plastics Processing Sheet No. 14 ASSESSING AND CONTROLLING STYRENE LEVELS DURING CONTACT MOULDING OF FIBRE-REINFORCED PLASTIC (FRP) PRODUCTS. HSE INFORMATION SHEET. 

This information sheet from the Health and Safety Executive summaries the health hazards that can arise from exposure to styrene. It provides practical advance to FRP manufacturers on how to assess and control styrene levels in the workplace and how these control measures should be monitored and maintained in accordance with the Control of Substances Hazardous to Health Regulations 2002. The document applies mainly to contact moulding processes, and aims to define what level of control is currently recognised as being reasonably practicable. EUROPEAN COMMUNITY EUROPEAN UNION UK WESTERN EUROPE... 

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. 

In a number of processes, air pressure is applied to a bubble of polymer melt to change its shape. We will examine one continuous process—blown film production—and two cyclic processes—blow moulding and thermoforming. All of them involve some melt extensional flow with a resultant thinning of the bubble, and at least one side of the polymer solidifies without the constraint of contact with a mould. 

A widely used method of laminate construction is by the contact moulding process or hand lay-up . In this, a layer of catalysed unreinforced resin, known as the gelcoat , is brushed or sprayed onto the mould and allowed to cure and then layers of reinforcing-fibre impregnated with resin are built up behind (Fig. 6.3). Variations of this include resin injection and vacuum-assisted resin injection in closed moulds. After removal of the cured moulding from the mould, the gelcoat forms the outer skin and as such performs the two functions of decoration and protection ... 

Several processes are employed for the manufacture of structural foams. In the high-pressure process, the first step is to fill a mould solidly with the resin under pressure. While it is still soft, the mould is expanded or a core retracted, which provides an interior space to be foam-filled by expansion and foaming inward of the still-soft resin or by injecting foam into the Interior space. In either case, the result is a dense skin surrounding a cellular core. In the low-pressure process, a mould is partially filled and the molten resin expands to fill the mould, forming a skin upon contact with the walls of the mould. 

Contact moulding is a simple and well known method for fabrication of fibre-reinforced thermoset composites. Thermoset resins which cure at room temperature such as unsaturated polyester, vinyl ester, and epoxy are used to make glass, jute or carbon fibre-reinforced composites using contact moulding. A wide variety of structures can be fabricated using this technique without limitation with respect to the size and complexity of the shape of the structure. However, the process is very labour-intensive and time-consuming, so is used only for a short run or one-off production. 

Contact moulding Low tooling cost, simple process, no shape restriction Labor-intensive, high volatile emission, slow production rate Epoxy, polyester, vinyl ester... 

Only contact moulding by hand lay-up does not require dedicated equipment and it is for this reason that this process is so popular. 

This process is almost as versatile as contact moulding as regards selection of resin and reinforcement, and therefore the possible range of properties. Its primary advantage is that of reproducibility and reduced labour, though this is offset by increased tooling cost as it is a closed mould technique. 

Various techniques have been developed for speeding up the contact moulding process. Of most importance is the spray-up technique (Fig. 2). The cutting of random mats... 

For this section, the mould is inspected by using contact-irrstrament called Touch Probe on CNC milhng machine . By inline process, the mould is not necessary to brought out off the machine, thus there is no wasting... 

The copolymers have been used in the manufacture of extruded pipe, moulded fittings and for other items of chemical plant. They are, however, rarely used in Europe for this purpose because of cost and the low maximum service temperature. Processing conditions are adjusted to give a high amount of crystallinity, for example by the use of moulds at about 90°C. Heated parts of injection cylinders and extruder barrels which come into contact with the molten polymer should be made of special materials which do not cause decomposition of the polymer. Iron, steel and copper must be avoided. The danger of thermal decomposition may be reduced by streamlining the interior of the cylinder or barrel to avoid dead-spots and by careful temperature control. Steam heating is frequently employed. 

The hydrophilic/hydrophobic SIN composition of PDMS with poly(HEMA) and poly(AAC) were proposed as a potential apphcation for high-permeability soft contact lenses. Other sUicone-containing IPNs for contact lenses include polymerization of MMA in the presence of polymerized methacryloxypropyl trimethoxysilane, the cross-linking of a polymeric hydrogel of a copolymer of NVP during the final compression or injection-moulding process. 

Additives are needed not only to make resins processable and to improve the properties of the moulded product during use. As the scope of plastics has increased, so has the range of additives for better mechanical properties, resistance to heat, light and weathering, flame retardancy, electrical conductivity, etc. The demands of packaging have produced additive systems to aid the efficient production of film, and have developed the general need for additives which are safe for use in packaging and other applications where there is direct contact with food or drink. 

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