Molding with rotation

The injection molding with rotation (MWR) is an example of processing at lower temperatures, pressure, etc. It is also called injection spin molding or injection stretched molding. This BM process combines injection molding and IBM, as performed in IBM reviewed, except it has the additional step of with melt orientation (Dow patent). The equipment used is what is commercially available for IM except the mold is modified so that either the core pin or outside cavity rotates. The rotated melt on its preform pin is transferred to a blow mold. The end product can come directly from the I MM mold or be a result of two-stage fabrication malting a parison and BM the parison.164... 

MRPMA Malaysian Rubber Products Manufec-turers Association MWR molding with rotation... 

MSW municipal solid waste MVD molding volume diagram MVT moisture vapor transmission MM billion MW molecular weight MWD molecular weight distribution MWR molding with rotation... 

Rgure 1.67 Two-shot molding with rotating mold. ... 

RM is a simple, basic, four-step process that uses a thin-walled mold with good heat-transfer characteristics. Its closed mold requires an entrance for insertion of plastic and, most important, the capability to be opened so that solidified products can be removed. These requirements are no problem. Liquid or dry-powder plastic equal to the weight of the final product is put into the mold cavity(s), which rotates simultaneously about two axes located perpendicular to each other (Fig. 8-68). These two rotation speeds can be varied to permit more... 

The next step involves heating the mold while it is rotating. Molds can be heated by a heated oven, a direct flame, a heat-transfer liquid (either in a jacket around the mold or sprayed over the mold), or electric-resistance heaters placed around the mold. With uniform heat transfer through the mold, the plastic melts to build up a layer of molten plastic on the molds inside surface. 

After the required heat-time cycle is completed, the mold is ready for cooling, which is accomplished with the mold rotating continually. Cooling is usually done by air from a high-velocity fan and/or by a fine water spray over the mold. After cooling, the final step is to remove the solid hallow product and reload the mold with plastic. 

Rotational Molding with Capron Nylon Resins... 

Gravimetric hoppers feed a mold with a prescribed weight of polymer. The feed stock is either a finely divided powder or a liquid plastisol. A plastisol is a suspension of a resin powder, typically polyvinyl chloride, in a plasticizer, used to manufacture. Rotational molders use liquids and powders in their process since both flow freely. This property permits the easy addition of the materials to the mold. More importantly, they flow smoothly around the interior of the mold as it rotates. In doing so, they coat the entire surface. 

A measured amount of powder or liquid thermoplastic (TP) is placed in the cavity that is mounted on a turret arm capable of rotating the mold. The mold in the oven spins biaxially with rotational speeds being infinitely variable, usually ranging up to 50 rpm on the minor axes and 12 rpm on the major axes. A 4 1 rotation ratio generally is used for symmetrically shaped parts. A wide variety of ratios are necessary for molding unusual and complex shapes. 

Co-injection molding involves injecting two or more different materials into a mold, generally in sequence. To accomplish this, molding machines are fitted with multiple injection units (Figure 14-53). Two-shot molding, the most common version, often utilizes an indexing mold. In this process, the mold is rotated 180° after the first shot fills a portion of the cavity, then the second shot finishes the part... 

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