Press moulding fabrication 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. 

Fibres can also be prepared in the form of a mat consisting of randomly oriented short fibres held loosely together hy a chemical hinder, sometimes in a carrier fabric, as a continuous thin flat sheet. Mats are commercially available as blankets of various weights, thickness, and widths, which can he cut and shaped for use as preforms in some closed-mould processes and in hand lay-up, press moulding, bag moulding, autoclave moulding, and in various continuous impregnating processes. 

Ever increasing demand for faster composite manufacturing has pressed the composite industry to replace hand lay-up technique with alternative fabrication processes such as liquid composite moulding techniques. 

Disc/flat-sheet-shaped membranes are mostly applied in dense ceramic membrane reactors due to the ease of the fabrication process the ceramic material powder is pressed into discs in a stainless steel mould under an isostatic or hydraulic pressure, followed by sintering at a high temperature. Such disc-shaped membranes usually have a thickness of about 1 mm so as... 

Due to their more rigid, paper-like structure, nonwovens buckle into a complex of sharp, uniaxial bends rather than smooth 3D folds. Attempts have long been made to press-form nonwoven sheets, which have been bonded with a partially cured resin, into a required shape (Hearle, 1960). An ashtray is typically used in experiments. However, rupture or wrinkling seemed an unsolvable problem. More recently, a successful process for making deep moulded shapes has been developed at North Carolina State University (Grissett and Pourdeyhimi, 2009). The nonwoven fabric is placed between the two surfaces of a mould, Figure 1.13(a), and then pressed. 

Several engineering plastics have been used as the matrix in both of these GMT systems however the versatile and modestly priced polypropylene is by far the most popular. Both types of GMT are fabricated by a process known as hot flow stamping . This is similar to sheet moulding, but uses preheated blanks pressed in cold moulds, with a cycle time of less than one minute, comparable with injection moulding. (SMC uses heated press tools to mould cold blanks, with rather longer cycle times.)... 

Unsaturated polyester (Butanox M-60) mixed with 1.5% of Methyl Ethyl Ketone Peroxide (MEKP) as catalyst was selected as a resin for the current work. Treatedbetelnut fiber reinforced polyester (T-BFRP) composite was fabricated using hand lay-up technique. In composite preparation, a metal mould (100 x 100 x 12 mm) was fabricated. The inner walls of the mould were coated with a thin layer of wax as release agent. The first layer of the composite was built by pouring a thin layer of polyester. A prepared mat was placed carefully on the polyester layer. Steel roller was used to arrange the mat and eliminate trapped bubbles. This process was repeated until the composite block was built containing 13 layers of fiber mats and 14 layers of polyester. The prepared blocks were pressed at approximate pressure of 50 kPa in order to compress the fiber mats and to force out the air bubbles. The blocks were cured for 24 hr and then machined into specimens in the size of 10 x 10 x 20 mm. 

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