Overlap molding

When thick-walled hollow molded artieles and molded articles with a shape having thick-walled sections and thin-walled sections are produced, the molded article is produced in two parts. These parts are eventually eon-nected by welding. Alternatively, the two parts are placed in another mold so that they face each other at the parting lines. Then, molten resin is injected about the periphery of the opposed faces to connect the parts. This technique is addressed as insert molding, or overlap molding. Other welding methods include ... 

This paper reviews the results of investigations into low-frequency mechanical and high-frequency (ultrasonic) vibration effects upon flowable polymeric systems, primarily, on molten commercial thermoplastics. We tried to systematize possible techniques to realize vibration in molding of polymers. Theoretical and experimental corroboration is provided for major effects obtained at cyclic (shear and bulk) strains of molten polymers and compositions based thereon. It is demonstrated that combined stress of polymeric media is attained under overlapping vibrations and this results in a decreased effective viscosity of the melts, a drop i the pressure required to extrude them through molding tools, increased critical velocities of unstable flow occurrence and a reduced load on the thrust elements of extruder screws. 

The paper gives an overview of effects occurring or acoustic treatment of dissolved and molten polymers. Emphasis is made on acoustic cavitation discovered recently not only in low-viscous fluids but also in molten polymers. Major guidelines have been specified for practical utilization of acoustic treatment of flowable polymers in molding intensification of extrusion processes, reduction in thickness of produced films, directed mechanical destruction, chemical activation of melts, etc. Efficiency of overlapping high-frequency vibrations in molding of molten thermoplastics is discussed in terms of power consumption. 

Different casting processes are used. They tend to overlap and could be identified by other processing methods. An example is liquid injection molding that can be identified as injection molding (Chapter 4) or reaction injection molding (Chapter 12). Many decades ago the reaction injection molding process was initially called liquid injection molding. 

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. 

The principal types are two-plate, three-plate, and stack molds. Others include the family mold that has multiple cavities of different shapes in one mold.3, 324 A further distinction concerns the feed system that can be either the cold or hot type. These classifications overlap. Three-plate molds will usually have a cold runner feed system, and a stack mold will have a hot runner system. Two-plate molds can have either feed system. 

There appear to be two major groups of stimuli which can produce asthmatic manifestations discrete antigens and nonspecific stimuli. Numerous specific antigens are known. These may be inhaled or ingested, and their specificity in the individual patient can be demonstrated by an increase of airways obstruction after exposure to such agents. Ragweed, dust, molds, aspirin, and fish are a few examples. The other type of stimulus is relatively non-specific and can adversely affect CB patients as well. These stimuli include cold air, exercise, dusty environments, etc. The mechanisms by which these two types of stimuli lead to airways obstruction are different, although there is some overlap in their ultimate physical effect. 

Laminated tubes are made from multilayer materials that usually contain paper as well as plastic, and often also include aluminum foil as a barrier layer. The preprinted tube bodies are sealed into a cylinder, with the edges of the sleeve overlapped and compressed, squeezing some of the plastic out around the raw edges of the foil and paper to make a good seal. Next the tube is cut to length, and finally the head is molded and assembled to the body. To improve the barrier in the head, a premolded insert of polybutylene terephthalate or urea can be incorporated in the injection mold when the head is formed. 

Further classification of polymers in the groups of additional polymers and condensation polymers has been on monomer composition, because this provides an orderly approach, whereas classification based on polymer uses, such as plastics, elastomers, fibers, coatings, etc. would result in too much overlap. For example, polyamides are used not only as synthetic fibers but also as thermoplastics molding compounds and polypropylene, which is used as a thermoplastic molding compound has also found uses as a fiber-forming material. 

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