Spray-up moulding

The effect of glass size and tex on spray-up moulding is shown in Figures 4.2 and 4.3. 

The Manual processes cover methods such as hand lay-up, spray-up, pressure bag and autoclave moulding. 

In the spray-up process, a mould is made, just as in the hand-lay-up process. Continuous roving is fed into a chopper gun, which as its name suggests chops the fibres and sprays them onto the mould resin is also sprayed at the same time. The fibre and resin streams meet each other on the mould surface. The laminate is then rolled to remove as much air as possible. The fibre content achieved with this process is typically between 25-35 wt%. This method is rarely used by itself for corrosion-resistant vessels but is used in combination with filament winding for larger vessels. 

Spray-up—Fabrication technique where a mixture of chopped fibres and resin can be simultaneously deposited on a mould. 

The spray-up machine consists of a gun for spraying catalysed/accelerated resin and a unit which chops continuous glass fibre. They are simultaneously sprayed on to an open mould coated with a releasing agent. The laminate is rolled and then allowed to cure, after which the moulding is released and trimmed to size. The properties and applications are similar to hand lay-up but the use of the spray machine produces a much faster lamination time. 

There are two systems of spray-up in common use twin-pot and catalyst injection. The twin-pot machine uses one pressure pot for catalysed resin and another for accelerated resin. They are simultaneously fed to the spray gun and individually sprayed each through its own nozzle. The two streams are adjusted to meet at about 300 mm in front of the mould surface where they mbc. As the two streams only meet outside the spray head premature gelation cannot occur. The twin pot machine is relatively simple to operate but has the disadvantage that the pressure pots require frequent replenishment which is time consuming and particularly inconvenient for large mouldings. 

General polyesters are usually orthophthalic acid based resins, which are used in applications based on open moulds and hand and spray lay-up moulding. Resins with a low level of styrene emission are ideal for these applications. 

To increase the production rate, spray-up technique is used instead of a hand lay-up technique. This technique employs a multiple-headed spray gun. The resin mixture and chopped fibres are discharged simultaneously by using the spay gun on the surface of the mould where they are deposited to a uniform thickness. Sheets, storage vessels, auto body parts, boat hulls, truck bodies and building components are made using this process. 

This process has been described in a previous chapter as a means to process unreinforced resins. Fibre-reinforced composites can be fabricated in a similar way. The resin and fibre can be combined by usual hand lay-up or spray-up techniques. Glass fibre content up to 70 wt% or 50 vol% can be achieved for fibre composites processed by this technique. Press moulding offers obvious advantages like fast cycle time, good finish, structural integrity and high reinforcement content. 

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... 

Bag moulding processes use pressure applied to uncured resins on the mould in order to compact the laminates and to drive out volatiles. It can be in two different forms vacuum bag or pressure bag moulding. Either of these can be used to supplement curing in the lay-up or spray-up processes. 

Pultrusiun Filament winding Hand lay-up Hand spray-up Compression moulding... 

Random roving composites are produced by the spray-up method (section 11.2) in which an intimate mixture of roving and resin is sprayed into, or onto, a mould. Properties of aligned rovings are considered in the next chapter. 

A clear distinction needs to be made between the process of hand layup and that of spray-up as these give rise to different levels of properties (Table 11.4). The differences arise out of the processes themselves -spray-up being semi-automated in that pre-impregnated resin is sprayed onto a mould whereas hand lay-up requires individual layers to be laid up by hand and impregnated with resin. 

Hand lay-up Spray-up Filament winding Dough moulding Mat, Preform Pre-preg. Cold press... 

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... 

HAND/SPRAY LAY-UP MOULDING PROCESS CAPABILITY CHART FOR COMPOSITE MATERIALS... 

The spray-up process is based on the direct application of a GRC mix onto the surface of a mould, by using a special spray head, shown schematically in Figure 8.10. 

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