PLASTICS AND THEIR MANUFACTURE
it possible to manufacture building elements that are highly transparent. Woven
4.41 Different forms of glass fibre products.
staple-fibre glass textile represents an especially soft and absorbent variant, another type is the spacer fabric. The latter consists of two textile finishing layers 4.43
of E-glass with a silane coating, which are bound together and held apart by vertical spacer fibres. Once impregnated with polyester resin or epoxy resin, the textile automatically assumes its design thickness. This makes it very easy to fabricate sandwiched laminates. Spacer fabrics are most commonly used for manual laminating methods. The waviness of a textile generally has a negative effect on its orthotropic stiffness. in particular in the direction of the warp a certain degree of structural extension is unavoidable. roving
MANUAL TECHNIQUES Hand lay-up lamination is a comparatively straightfor-
ward process and is suitable for the fabrication of small quantities of freeform 4.44
prototypes and sheet-like building elements. Various materials can be used for the formwork. Simple forms can be made of sheet metal or timber formwork. rigid polyurethane foam with a density of 400 kg/m3 is easier to use for making freeform or biaxially curved concave forms. Forms that are applied from outside the building element and describe its outer surface are known as negative or female moulds. Forms that describe the inner surface of the element are known as positive or male moulds. An important criteria for the choice of material for the mould is resistance against the solvent used in the resin. A suitably durable material should be chosen for moulds or forms that are to be used repeatedly. Large moulds are made of several individual parts that are assembled and glued together. The sur-
Textile glass mat
Fabric: plain weave
Fabric: braided weave
face of the mould defines the surface quality of the resulting formed element. The surface not facing the mould is always rough and may need additional finishing if it needs to be of a certain quality. A constraint for the development of moulds is the fact that not all geometric forms can be removed from the form. For this reason, forms that are undercut or significantly twisted should be avoided. The process of lamination begins with a thin (0.3â€“0.6 mm) non-reinforced â€œgelcoatâ€?. This stops the structure of the fibres from showing through and serves as a weather protection layer. it can also be used to lend it a certain colour. The matrix material and fibre matting are then applied wet on wet in alternate layers. A certain degree of skill is required to create evenly dense layers of material with as few trapped air bubbles as possible. Hand lay-up lamination is a rather laborious but low-cost method. The manufacture of high-performance building elements using manual lamination is difficult as it is hard to precisely control the material properties. The fibre proportion is generally less than 45 % by volume. The quality of the laminate can be improved by applying different pressure techniques. With a vacuum forming technique, the still wet laminate is covered with a porous adhesion-preventing film and an absorbent textile. After covering with a vacuum bag and sealing the edges, a vacuum is created. All excess resin and trapped air bubbles are sucked out and the laminate then hardens under normal atmospheric pressure. This results in very dense laminates with a high fibre content. Using this technique it is also possible to impregnate dry lay-up laminates with resin afterwards. This so-called resin infusion
Published on Oct 1, 2010
Published on Oct 1, 2010
This book seeks to fill that gap by providing an introduction to the structural and design possibilities of plastic. It introduces the mater...