Processing molding methods

Processing PC resins by extmsion or injection-molding methods requires melt temperatures of 290—320°C. High melt viscosity at low shear rates prevents mold flash and drool. At injection shear rates, apparent viscosities decrease, and easy melt flow allows manufacture of large, complex parts. 

Spray molding is the modification of the hand-lay process where the resin and glass fiber are deposited simultaneously on the molding tool. The fibers are mixed with the resin at the spray head before being deposited on the mold surface. Subsequent consolidation of the laminate is achieved by rolling in a similar manner to the hand-lay process. This method is suitable for large components. Here the capital cost is higher and the process is very operator sensitive. 

For several basic reasons, the extrusion process does not have the large number of possible process product interactions that the preceding molding methods presented. Due to this situation it can not fabricate the complex shapes and tighter tolerances obtained from molding. The process is a steady-state continuous production operation that can be brought to a condition of control. However it has its share of potential problems (Chapter 8, EXTRUSION). 

There are several techniques for producing polymer mixtures for further processing into articles by the reactive (chemical) molding methods simultaneous formation of two polymeric systems with mutual entanglement of their chains and the appearance of so-called interpenetrating networks synthesis of the second polymer within an expanded network of the initial polymer incorporation of oligomers into a polymer matrix as a temporary plasticizer followed by polymerization. 

Polymeric chips have been fabricated with various methods, as developed from the plastics industry. These processes include casting, injection molding, laser ablation, imprinting, and compression molding. The physiochemical properties of various polymeric materials and their molding methods have been summarized in a recent review article [7],... 

The general process of hand molding can be subdivided into specific molding methods such as those that follow. The terms of some of these methods as well as others reviewed here overlap the same technology the different terms are derived from different sections of the RP and other industries. 

Huntsman Also called the Crucible process. A method for purifying blister steel, made by cementation, by melting it in a closed clay or graphite crucible and pouring the melt into a cast iron mold. Developed by B. Huntsman, a clockmaker, around 1740, initially in Doncaster and later in Sheffield, UK. The process was not patented but was operated in secrecy for some years. It was subsequently widely operated in the UK, Europe (where the combination of this with the cemen-... 

Metal casting with the new cavityless mold process.This method is faster,cheaper,and far easier than traditional patternmaking/ moldmaking processes. 

Injection molding is the most important molding method for thermoplastics [7—9]. It is based on the ability of thermoplastic materials to be softened by heat and to harden when cooled. The process thus consists essentially of softening the material in a heated cylinder and injecting it under pressure into the mold cavity, where it hardens by cooling. Each step is carried out in a separate zone of the same apparatus in the cyclic operation. 

Binder resins for the injection molding method are poly(amide)s and ethylene vinyl acetate copolymers, and more recently poly(ether ether ketone) (PEEK) and PPS, because of their superior properties. Crystalline resins such as PPS or PEEK require a high temperature for fusion molding of 350°C or higher, so that there is a disadvantage in that the magnetic powder of the rare earth is likely to be oxidized by the molding process. 

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