Plastic solidification

In RPs, insufficient compaction and consolidation before plastic solidification or cure will result in air pockets, incomplete wet-out and encapsulation of the fibers, and/or insufficient fiber or uniform fiber content. These deficiencies lead to loss of strength and stiffness and susceptibility to deterioration by water and aggressive agents. 

In the case of semi-crystalline plastics, the temperature window within which a plastic is liquid is strictly limited by sudden crystallisation and setting of the plastic, and thus the AT window more precisely defines the thermal window for HR gate patency (the temperature range at which a melt can flow through a gate) for these plastics - solidification takes place immediately the temperature T is exceeded. 

Traditionally, production of metallic glasses requites rapid heat removal from the material (Fig. 2) which normally involves a combination of a cooling process that has a high heat-transfer coefficient at the interface of the Hquid and quenching medium, and a thin cross section in at least one-dimension. Besides rapid cooling, a variety of techniques are available to produce metallic glasses. Processes not dependent on rapid solidification include plastic deformation (38), mechanical alloying (7,8), and diffusional transformations (10). 

Two approaches have been taken to produce metal-matrix composites (qv) incorporation of fibers into a matrix by mechanical means and in situ preparation of a two-phase fibrous or lamellar material by controlled solidification or heat treatment. The principles of strengthening for alloys prepared by the former technique are well estabUshed (24), primarily because yielding and even fracture of these materials occurs while the reinforcing phase is elastically deformed. Under these conditions both strength and modulus increase linearly with volume fraction of reinforcement. However, the deformation of in situ, ie, eutectic, eutectoid, peritectic, or peritectoid, composites usually involves some plastic deformation of the reinforcing phase, and this presents many complexities in analysis and prediction of properties. 

Powder Techniques. Highly alloyed materials made by the processes described are particularly susceptible to segregation of alloying elements during solidification both on a macro- and a microscale. Much plastic working was necessary to minimise this susceptibiUty before service appHcations. 

Technology Descriptions The use of thermoplastic solidification systems in radioactive waste disposal has led to the development of waste containment systems that can be adapted to industrial waste. In processing radioactive waste with bitumen or other thermoplastic material (such as paraffin or polyethylene), the waste is dried, heated and dispersed through a heated, plastic matrix. The mixture is then cooled to solidify the mass. 

During cooling, a point D is reached where the internal air temperature decreases less quickly for a period. This represents the solidification of the plastic and because this process is exothermic, the inner air cannot cool so quickly. Once solidification is complete, the inner air cools more rapidly again. Another kink (point E) may appear in this cooling curve and, if so, it represents the point where the moulding has separated from the mould wall. In practice this is an important point to keep consistent because it affects shrinkage, warpage. 

Residual stress There is a condition that develops, particularly in products with thin walls. This is a frozen-in stress, a condition that results from the filling process. The TP flowing along the walls of the mold is chilled by heat transferring to the cold mold walls and the material is essentially set (approaching solidification). The material between the two chilled skins formed continues to flow and, as a result, it will stretch the chilled skins of plastics and subject them to tensile stresses. When the flow ceases, the skins of the product are in tension and the core material is in compression that results in a frozen-in stress condition. This stress level is added to any externally applied load so that a product with the frozen-in stress condition is subject to failure at reduced load levels. 

Fig. 6-4 Viscosity changes during the processing of TS. The B-stage represents the start of the heating cycle followed by a chemical reaction (cross-linking) and solidification of the plastic.

Some TPs and TSs begin as liquids that can be cast and polymerized into solids. In the process various ornamental or utilitarian objects can be embedded in the plastic. By definition, casting applies to the formation of an object by pouring a fluid plastic solution into an open mold where it completes its solidification. Casting can also lead to the... 

The contact with the hot mould plasticizes the material, which, by the pressure applied, takes the form of the cavity. The cooling of the mould leads to part solidification and lows demoulding. 

Blow-molding processes consists of five main operations plastication of the resin, formation of the parison, inflation of the parison, solidification of the part, and removal of the part from the tooling. The best process economics will occur with a part optimized for weight and a minimum cycle time. In order to have a minimum cycle time, the cooling operation must be the rate-limiting step. For the case study... 

Conversely, in most observed cases where solidification occurs as a result of continued depletion of solvent (as described in Case B), the highly concentrated polymer layer solidifies as a relatively dense, amorphous, plasticized film. Water diffusion into this highly plasticized layer becomes prevalent (Case A) at a stage where the contraction has gone "too far" to yield even a microporous membrane structure. 

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