Mold cavity split

Shear controlled orientation technology was developed to optimize plastic properties by orientation of filler particles. In this patented technology, the single feed is split into a plurality of feeds which can supply pressure to the mold cavity independent of the feed channel. Figure 7.3 shows feed arrangements. The shear is applied by a controlled movement of pistons which imposes microscopic shear. A perfect alignment of fibers can be obtained. 

Chase (shoe) n. An enclosure of any shape used to (1) Shrink-fit parts of a mold cavity in place. (2) Prevent spreading or distortion in bobbing, (3) Enclose an assembly of two or more parts of a split-cavity block and (4) A rectangular metal frame in which type and plates are locked up for letterpress printing. 

External undercut Any recess or projection on the outer surface of a molded part that prevents its direct removal from its mold cavity. Parts with such undercuts may be molded by splitting the mold vertically and opening the split to withdraw the part or by providing side draws, i.e., mold parts that are withdrawn to the sides to relieve the undercuts. 

On the wall opposite the one with the side hole in Fig. 8.9a, there is an indentation on the core side of the wall that does not protrude all the way through the wall of the part. That indent, known as an undercut, would also interfere with ejection of the part from the core. However, when the undercut is shallow, its edges are adequately radiused and the material is sufficiently flexible, an undercut can be stripped from the mold once the cavity has been removed. If the undercut is too deep to be stripped, removable core inserts or a collapsing core will be required. Undercuts can be placed in the cavity as well however, a split cavity, slides, or removable core inserts will be required if the undercut is too deep to be stripped. Cavity undercuts can be deeper than core undercuts by the amoimt of the shrinkage since the part shrinks away from the cavity wall. Removable core inserts add a considerable amount of time to the molding cycle split cavities or slides add substantial cost to the mold and collapsing cores are, generally, expensive to tool when they are feasible at all. 

To achieve needed comfort, dentures must be custom-made. To form the customized denture, in which the artificial teeth are embedded, a wax pattern is used. The wax pattern is inserted in a plaster or dental stone in a split mold flask. After removal of the wax, the surface of the resulting mold cavity is painted with a separating medium, usually an aqueous alginate solution, followed by the addition of the acrylic resin. The separating medium aids in removal of the cured acrylic from the mold. 

The first stage is where the melted plastic is injected into a split steel mold cavity. The mold produces a preform parison which resembles a test tube with a screw finish on the top. 

Weld line With moldings that include openings (holes), problems can develop. In the process of filling a cavity the flowing melt is obstructed by the core, splits its stream, and surrounds the core. The split stream then... 

Undercut Whether external or internal, undercuts should be avoided if possible to reduce mold cost (by about 25 to 30%) and simplify melt flow during molding. However many molds use external and/or internal undercuts. In cases where it is essential to incorporate them in a design, appropriate mold design is required. The mold will include action such as sliding components on tapered surfaces, split cavity cam actions to produce the needed undercut, etc. (Chapter 8, TOOLING)... 

Draft on the cavity wall such as 1° is recommended to facilitate product removal. Lower-shrinkage plastics like PC and PMMA requires l1 to 2°. Undercuts are possible, but they should be kept to a minimum. Making provisions for undercuts or no drafts usually requires higher mold costs because the mold will require action such as core pulls or splitting a mold to allow separation parallel to the undercut groove. This type of mold action usually requires additional cycle time thus increasing cost. 

Water steam is used as the energy carrier in the molding process. The steam heats up and melts the foam particles inside the forming mold. Mold walls permeable to steam and air are necessary to expose the beads inside the cavity to the steam at all. The mold is located inside a steam chamber, split into two halves like the mold to facilitate ejection by an opening stroke. 

When the parison exits the die and reaches a preset length, a split cavity mold closes around it and pinches one end of it. Usually a blow pin is located opposite the pinched end of the tube. Compressed air inflates the parison against the female cavity of the mold surfaces. Upon contact with the relatively cool mold surface, the blown parison cools and solidifies to the part shape. Next the mold opens, ejects the part, and then repeats the cycle by again closing around the parison, shaping it, and so on. 

A mold in which a split cavity block is assembled in a chase to permit the forming of undercuts in a molded piece. These parts are ejected from the mold and then separated from the molded piece. 

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