154 HAND LAMINATING AND THE AUTOCLAVE PROCESSING OF COMPOSITES ⊙②x ①Teflon Film Teflon Film (holes every 50 mm) ②Peel Ply ⑧Vent Cloth ③Laminate ⑨Cork/Rubber Dam ④Peel Ply ⑩Aluminum Plate ⑤Teflon Coated ④Release Agent Glass Fabric 12 Vacuum Bag 6 Glass Bleeder(1 per 3.5 plies) FIGURE 4.8 The lay-up assembly of different layers. Usually several coats of the release agent are applied,each coat being al- lowed to dry before the next one is put on.Release films are usually made of low surface tension polymer such as Teflon.Sometimes the release film is applied on top of the liquid release agent.After the release film,a peel ply may be applied to add to the release action,and also to provide a texture for the surface of the part. In order to prevent resins to flow out of the prepregs in the plane of the stack of prepregs,dams made of ceramic or metal blocks are placed along the periphery of the stack. 2.5.2.2.Laying Up the Stack of Prepregs After the release agents and peel ply have been placed on the surface of the mold,stacks of the prepregs are positioned.This has been done by hand,thus the term hand lay-up(HLU).One may ask why such high tech parts as composite components for airplanes are made by such a rudi- mentary technique as HLU instead of by machines,which perform with greater consistency.The reason is the low volume production for aircraft components:airplanes are more or less custom-made for different cus- tomers,so aircraft companies do not mass produce them.Because partsUsually several coats of the release agent are applied, each coat being al￾lowed to dry before the next one is put on. Release films are usually made of low surface tension polymer such as Teflon. Sometimes the release film is applied on top of the liquid release agent. After the release film, a peel ply may be applied to add to the release action, and also to provide a texture for the surface of the part. In order to prevent resins to flow out of the prepregs in the plane of the stack of prepregs, dams made of ceramic or metal blocks are placed along the periphery of the stack. 2.5.2.2. Laying Up the Stack of Prepregs After the release agents and peel ply have been placed on the surface of the mold, stacks of the prepregs are positioned. This has been done by hand, thus the term hand lay-up (HLU). One may ask why such high tech parts as composite components for airplanes are made by such a rudi￾mentary technique as HLU instead of by machines, which perform with greater consistency. The reason is the low volume production for aircraft components: airplanes are more or less custom-made for different cus￾tomers, so aircraft companies do not mass produce them. Because parts 154 HAND LAMINATING AND THE AUTOCLAVE PROCESSING OF COMPOSITES FIGURE 4.8 The lay-up assembly of different layers