Mold parts Bottom plate

In drybag pressing, the elastomeric mold is fixed into the pressure vessel. The mold is filled with powder and sealed with a cover plate. Then pressure is applied between the mold and the vessel wall. After pressure release, the cover is removed and the part removed. Then the procedure starts again. Pressure vessels with both top and bottom plate are also in use, and allow more rapid removal of the compact. 

Figure S.7 Cross section of a split cavity mold for producing a molded spool. A and B form the two halves of the cavity. Chase, C, folds the halves together. Other parts are D, core pin E bottom plate and F, the force plug or plunger. (Ref Buckleitner, E.V., ed., Basic Mold Types and Features , Plastics Mold Engineering Handbook, S " ed.. Chapman Hall, New YotIc)...

This molded spacer provides a series of flat surfaces upon which individual plates sit. In a top view, the shape of each surface is modified such that plates slip easily over the top of the spacer, but are locked into position when the spacer is rotated 90°. As long as the spacer is accurately molded, no cumulative plate spacing error results. For midfixture plate supports, a similar part of smaller diameter is used. Short screws at the top and bottom plate secure the support in place. Alternative methods use machined bars around the periphery of the fixture. Either method results in accurate fixtures, reduced parts count, and ease of assembly. 

Description of the Function of the Casting Mold. As shown in the schematic representation (Fig. 4.23), the casting mold consists of a rigid base structure, 18 movable star-shaped supports, ribs between the star-shaped supports, segmented bottom plates above the star-shaped supports and the ribs, and a segmented mold wall. The bottom plates and the wall plates are covered with a parting compound. 

Figure 14.14 Sample bottom mold half with part cavity plate and ejector pins.

Add wood furnish (384 g, moisture content 6.02%) to the bowl of a rotary blade paddle mixer (such as a Kitchen-Aid KSM90) and agitate at the lowest speed setting. Add Mondur 541 (7.39 g, 1.9% w/w, a polymeric diphenylmethane diisocyanate of 31.5% NCO, Bayer) dropwise over a 5-min period using a disposable syringe. Continue blending for an additional 10 min and then transfer the blend to an 8 x 8 x 2 -in. metal form at the bottom of which is a metal plate which fits inside. The resin-coated furnish is evenly spread inside the form and another metal plate is placed on top. All parts of the form and plates are presprayed with mold release. The completed form assembly is placed into a hydraulic press (such as a model PW-22 manufactured by Pasadena Hydraulics) with platens heated at 350°F. The furnish is then pressed between the two form plates to a thickness of j in. Press controls are used to ensure consistency of board thickness. The assembly is heated for 4 min. before demolding the cured wood panel. 

Ejection of a molded plastic article from a mold can be achieved by using ejector pins, sleeves, or stripper plates. Ejector pins are the most commonly used method because they can be easily fitted and replaced. The ejector pins must be located in position where they will eject the article efficiently without causing distortion of the part. They are worked by a common ejector plate or a bar located under the mold, and operated by a central hydraulic ejector ram. The ejector pins are fitted either to the bottom force or to the top force depending on whether it is necessary for the molding to remain in the bottom half of the female part or on the top half of the male part of the tool. The pins are usually constructed of a hardened steel to avoid wear. 

The basic parts of the mold are illustrated in Fig. 5.69. The sprue receives the polymer melt from the nozzle and delivers it to the runners. The runners are as short as possible and provide minimum pressure and temperature drop from the sprue to the cavity. There are four basic types round, half round, trapezoid, and modified trapezoid. Round runners are the most efficient type, but are the most expensive because they must be machined into both plates of the mold. Since half-round runners produce the highest pressure drops and greatest cooling of the melt, they are seldom recommended. Trapezoidal runners are a compromise between round and half round, and modified trapezoidal runners merely have rounded bottoms. These runners are machined into only one mold plate, but reduce the pressure and temperature losses observed with half-round runners. Runner sizes are determined from the part-wall thickness. The diameter of the runner connecting directly to the cavity is typically equal to the part thickness, and each upstream branch is increased in diameter as " ... 

Ejector pads are plates that, in essence, are used as knockout pins. They form part of the molding surface, which eject cold molded products from a mold, the material being too soft to withstand small area knockout pins. Such steel pads may cover the entire bottom surface of the mold or form substantial areas of the molded piece. 

Self-cleaning vents can be located in the bottom of cavities by grinding flat surfaces 0.010-0.020 in. deep on the side of knockout pins, and cavity vents 0.002 in. deep as shown in Fig. 7-19. This self-cleaning type of vent can become clogged when mold release spray is used. If parts tend to burn, the knockout plate can be moved forward and the flats wiped clean. 

Boundary conditions for structure analysis of molding feature are detennined in due consideration of designed micro mold system and the condition of injection molding machine, (figure 3) The part of spiral feature which is pressured by resin is affected by the pressure of 120MPa. Fixed part is Z-axis because the bottom face of core is propped by the support core fixed in the support plate. Besides, three axes contacted with mold plate are fixed and so the rotational direction of core is fixed. Apphed material properties are summarized in Table 1. 

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