Plastic forming

Turning on a pouer s wheel is the oldest forming process 

Extrusion molding used to make differently shaped slugs and tubes, so-called preforms 

Plastic forming is based on the plasticity of water-containing clay ceramic pastes and, in the form of the potter s wheel, is the oldest known sort of forming. This turning of ceramic products can be automated on a large scale using the roller process. 

In extrusion molding so-called slugs are produced from the paste as preforms. These are subsequently formed into their final shape. In the manufacture of insulators the piston is dried to a leathery hardness , which does not undergo any further shrinkage. These preforms are further processed with profiling tools. 

A new plastic forming process has been developed, injection casting, in which clay ceramic pastes are injected into the mold and further compressed by closing the slightly opened tool. This process can also be used for manufacturing nonrotationally symmetric articles. 

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Injection-molded articles can be decorated by in-mold labeling or by post-mold decoration. In the former method, printed film is inserted into the mold cavity before injection. The plastic forms an intimate contact with the graphic material. Post-mold decoration includes hot stamping, dry offset printing, and decal printing. 

Forming additives or processing aids (2,33—37) are commonly used to render ceramic powders more processible. Binders and plasticizers (qv) are typically added to improve or aid dry powder and plastic forming, whereas deflocculants, surfactants (qv), and antifoams are commonly used in slurry processing. 

Liquids. Liquids (33) are common forming additives in plastic, paste, and slurry processing. In plastic forming operations, the Hquid aids forming and serves as the binder/plasticizer for the system. In pastes and slurries, other additives are also dissolved or dispersed in the Hquid/solvent. Water is a good, inexpensive solvent that can be recycled. Organic Hquids such as alcohols are used to process water-sensitive materials and to dissolve water-insoluble forming additives, however, at considerably more expense. 

Plastic Forming. A plastic ceramic body deforms iaelastically without mpture under a compressive load that produces a shear stress ia excess of the shear strength of the body. Plastic forming processes (38,40—42,54—57) iavolve elastic—plastic behavior, whereby measurable elastic respoase occurs before and after plastic yielding. At pressures above the shear strength, the body deforms plastically by shear flow. 

Both pistoa and auger type extmders are used ia plastic forming. The former provide maximum coatrol of the extmsioa pressure and rate and are good for forming large parts. The latter provide a maximum extmsion rate without excess power requirements and are desirable ia the coatiauous productioa of simple clay ware. 

The limited tractability of the polymer makes processing in conventional plastics form very difficult. Nevertheless the materials have been used in the manufacture of seals, gaskets and piston rings (Vespel-Du Pont) and also as the binder resin for diamond grinding wheels. 

Plastic Forming and Fracture of Metals and Alloys and of Composites 358... 

PLASTIC FORMING AND FRACTURE OF METALS AND ALLOYS AND OF COMPOSITES... 

Group of plastics formed by polymerization of ethylene or by the copolymerization of ethylene with various unsaturated compounds. 

Polyelectrolytes such as the ion exchange plastics form an interesting group of materials because of their ability to interact with water solutions. They have been used in medical applications involving the removal of heavy metal ions from the human body. They can be used to interact with external electric fields and change their physical properties drastically as is illustrated by the fact that some electrically active liquid crystals are polyelectrolytes of low molecular weight. 

These qualities are considered in most applications for transparent plastics, forming a basis for directly comparing the transparency of various grades and types of plastic. The data are of value when a material is considered for optical purposes. Many transparent plastics do not have water clarity, and, for this reason, the data should indicate whether... 

The usual form of sulfur is known as the rhombic form, which is stable at temperatures up to about 105 °C. Above that temperature, the monoclinic structure is stable. A plastic form of sulfur can be obtained by pouring liquid sulfur into water to cool it quickly, but on standing it is converted to the rhombic form. On a molecular level, the element exists as S8 rings that have the structure... 

Bisphenol A, a compound highly used in the production of epoxy resins and polycarbonate plastics, forms monochloro-, dichloro, trichloro-, and tetrachloro derivatives when chlorinated [127], Its reaction with ozone produces as major transformation products, catechol, orthoquinone, muconic acid derivatives of bisphenol A, benzoquinone, and 2-(4-hydroxyphenyl)-propan-2-ol [128],... 

Process Steps. Casting powder manufacture is basically a plastics-forming operation, utilizing a volatile solvent to impart mobility to the polymeric binder. The process is shown schematically in Figure 2 in terms of the major equipment used. For discussion, the process may be divided conveniently into the following operations ... 

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