Pressure bag

If more pressure is required than what is available with the bag system, a second envelope can be placed around the whole assemblage and air pres- 

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

Variations on this basic process are (i) vacuum bag moulding and (ii) pressure bag moulding. In the former process a flexible bag (frequently rubber) is clamped over the lay-up in the mould and a vacuum is applied between the moulding and the bag. This sucks the bag on to the moulding to consolidate the layers of reinforcement and resin. It also squeezes out trapped air and excess resin. The latter process is similar in principle except that pressure is applied above the bag instead of a vacuum below it. The techniques are illustrated in Fig. 4.67(b) and (c). 

Pressure bag molding This is a take-of to vacuum bag molding where the bag and mold is placed in a closed system and is subjected to pressure during the curing cycle. 

Compression molding Filament winding Hand lay-up Mat molding Pressure bag molding Continuous pultrusion Injection molding Spray-up... 

Contact Molding. Spray-up Pressure Bag Filament Winding Continuous Pultrusion Premix/ Molding Compound Matched Die Molding with Preform or Mat... 

Prepreg draping and consolidation by vacuum or pressure bag moulding, autoclave... 

Figure 5.25. Principle of pressure bag moulding after draping...

Pressure-Bag Molding. This is similar to vacuum-bag molding, but 345 kPa (50 psi) air... 

Autoclave Molding. This is similar to pressure-bag molding, but it is carried out in an autoclave to apply the pressure to the outside of the cover film. 

Compression Molding Flexible Plunger Flexible Bag Molding Laminate Hand Lay-Up Vacuum Bag Molding Vacuum Bag Molding and Pressure Pressure Bag Molding Autoclave Molding Autoclave Press Clave Wet Lay-Up... 

Depending on the resin preparation, the material in or around a mold can be cured with or without heat, and commonly without pressure. Curing needs include room temperature conditions, heat sources, vacuum bags, pressure bags, autoclaves, etc. An alternative is to use preimpregnated, B-stage TS polyester or sheet molding compound (SMC), but in this case heat is applied with low pressure via a impermeable sheet over the material. This process can produce compact... 

This process is used when more pressure is required than those processes just reviewed. A second envelope (or structure) is placed around the whole assemblage and air pressure admitted between the inner bag and outer envelope, or between the inner bag and structure. Application of pressure (air, steam, or water) forces the bag against the product to apply pressure while the product cures. Using this combination of vacuum and pressure bags results in ease of air or gas removal and higher pressures resulting in more densification. 

This method is a take off between RTM and hand lay-up. The reinforcement and a room temperature curing TS polyester resin are put into a mold. In turn, the mold is put into an air pressure bag where the resin is slowly forced through the reinforcement in the mold cavity at low pressures of about 200 to 500 kPa (30 to 75 psi). The RP is cured at room temperature in unheated molds. It is a slow process so one or a few products per day are usually molded. 

In pressure-bag molding the reinforcement and the resin mixed with catalyst are placed in a mold, and a flexible bag is placed over the wet lay-up after a separating sheet (such as cellophane) is laid down. The bag is then inflated with an air pressure of 20-50 psi (1.4—3.5 kg/cm ). The resin and reinforcement follow the contours of the mold (Figure 2.47). After the part is hardened, the bag is deflated and the part is removed. The technique has been used to make radomes, small cases, and helmets. 

SPRAY UP 1 PULTRUSION 1 CONTACT 1 VACUUM BAG 1 1 PRESSURE BAG 1 AUTOCLAVE... 

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