Hollow objects fabrication

Fluoropolymers can be fabricated into hollow objects by rotomolding. They are, however, hard to mold due to their relatively high melting point andmelt viscosity. The most frequently rotomolded fluoropolymers are PFA, FEP, PVDF, ETFE, and ECTFE. Fluoropolymers constitute about 1% of all rotomolded parts. 

A molding process used to produce hollow objects in which a hollow tube (parison) is forced into a shape of the mold cavity using internal air pressure. The two primary types are injection blow molding and extrusion blow molding. Blow molding is a method of fabrication in which a warm plastic parison is placed between the two halves of a mold and forced to assume the shape of that mold cavity by use of air pressure introduced through the inside of the parison that forces the melt against the surface of the mold. 

The range of processes that may be used for fabricating a plastics product is determined by the scale of production, the cost of the machine and the mold, and the capabilities and limitations of the individual processes. For example, complex and precise shapes can be achieved by injection molding, hollow objects via blow molding and rotational molding, and continuous lengths by extrusion. 

Blow Molding. Blow molding is a multistep fabrication process for manufacturing hollow symmetrical objects. The granules are melted and a parison is obtained by extmsion or by injection molding. The parison is then enclosed by the mold, and pressure or vacuum is applied to force the material to assume the contour of the mold. After sufficient cooling, the object is ejected. 

One of the most influential innovations in the history of LbL technology so far must be LbL assembly on a colloidal particle with subsequent hoUow capsule preparation [220-223]. In the first decade of LbL technology, researchers regularly assembled films on a flat solid support of visible dimensions. However, the mechanism of the LbL assembly does not exert any limitations on the size of supports or their shape. Therefore, LbL assembly on microscopic solid surfaces dispersed in solution is reasonable, opening the way to fabrication of both three-dimensional structures and nano/micro-sized objects through the LbL process. As shown in Fig. 8, the concept of the assembly is simple. LbL films are assembled sequentially on a colloidal core in a similar way to conventional LbL assembly on a flat plate. Dissolution of the central particle core upon exposure of the particles to appropriate solvents then results in hollow capsules. 

This is the primaiy processing technique used to fabricate hollow plastic objects, particularly bottles, which do not need a very uniform distribution of wall thickness. It is a secondary shaping technique that inflates the preprocessed plastic (usually extruded) against the inside walls of the mold with a blow pin. In addition to extrusion blow molding, injection blow molding and stretch blow molding are commonly employed. With most polymers, especially when the product size is... 

Blow molding is a versatile conversion process used to produce a wide variety of objects by inflating a molten tube of polymer inside a hollow mold. Two major variations of the method exist extrusion blow molding and injection blow molding. The former is predominant in polyethylene molding. Common items fabricated by blow molding include bottles, drums, chemical storage tanks, and toys. 

The most common tools in plastics processing are molds. A mold is a premade object, which is used to guide the final form or shape of another object. Molds can be open, like a baking pan, allowing for soft or molten material to be poured or draped over the mold surface. After the material cools or solidifies into its final shape, it is then removed from the mold, and the mold is used again. Molds can also be closed, with internal hollow spaces, allowing soft or molten material to fill these spaces. Closed molds are usually made of several parts, and fabricated in such a way that the mold can be opened, allowing for part removal after the plastic material has solidified. 

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