Mold-cavity ejector

The plate, usually drilled for steam or water, on which demontable pieces, such as mold cavities, ejector pins, guide pins, and bushings, are mounted. 

Ejector pins help to separate the finished molding from the mold cavity. These are driven mechanically during the mold-opening stage of the cycle. 

The injection mold is a series of steel plates, which when assembled produces the cavity that deflnes the shape of the molded part. Conventional molds consist of the mold frame, components, runners, cooling channels, and ejector system. The mold frame is a collection of steel plates that contain mold components and runners, cooling and ejection systems. Components are parts inserted into either bored holes or cutout pockets in the mold frame. The polymer melt enters into the mold cavity or cavities through the runners, which are passages cut into the mold frame. The hot polymer material in the mold... 

The clamping unit is open. There is no molded part in the cavity of the mold. The ejectors are in the retracted position. The mold has been adjusted to the prescribed temperature. 

Ejection is usually carried out by guided metal pins - ejectors - that are part of the mold. These ejectors push the molding off the cavity surfaces. Here it is important to ensure, that the article is not damaged by the ejector pins. 

The uniformity of injection molding process of different compounds was characterized by melt pressure measurement inside the mold cavity. A piezo-electric sensor (9221 AA0.6, Kistler, Switzerland) incorporated inside the tensile mold cavity and located behind and in contact to the ejector pin to measure the force exerted to the pin by melt pressure during the cyclic molding process against the time. The influence of nano-CaC03 inclusion in the PP... 

A large part with a complicated shape may not be demolded readily even when mold release agent is sprayed or brushed on the mold cavity in this case, mechanical ejectors should be mounted on the mold to ease the demolding as shown in Fig. 9.14. However, the tip of the ejectors and the impact force should be designed so that the surface of the matrix of the composite is not damaged while demolding. 

A diagram of the injection molding process is shown in Figure 6.22. The extruder is similar to other fabrication techniques where the granular resin enters a hopper, where the material is transferred to a heated barrel and a reciprocating screw moves the molten plastic to the molding cavity. The molding cavity is unique to this process. The molten polyethylene is forced xmder pressure into a closed mold that is continually cooled. After the molded part cools, the mold opens and the fabricated part is ejected from the mold. An injection molded article can usually be identified by the ejector pin marks that are usually present on the molded part. 

These improvement possibilities are not restricted to injection molds. Thus, in addition to the mold cavities for thermoplastic, thermoset, and elastomer processing, also extrusion molds, slides and jaws, ejector systems, melt control systems and return valves are treated with success. Also for the treatable types of mold materials, the frontiers have been pushed back in recent years. In addition to typical mold steels, nonferrous metals like aluminum or copper alloys can be optimized through different surface and coating technologies. 

Thin-gauge products are often flexible enough to be pulled from minor undercuts, such as detents. If necessary, ejector pins or rings are used. Moveable mold elements are used with undercuts of thick products or for plastics that are stiff at product removal time. Simple moving elements are hinged to swing away as the product is withdrawn. For severe undercuts, pneumatic cylinders are activated to move elements away as the product is pulled from the mold cavity. Orphan mold elements exit with the product are removed and are reassembled in the mold for the next cycle. 

When the mold is opened, the part should be easily removable. Cavities are made with a slight taper to reduce frictional drag of the part on the mold. The half of the mold attached to the movable platen is equipped with ejector pins, which push the part out of the cavity while the mold is being opened. When the mold is closed, the pins are flush with the cavity surface. Release agents or lubricants facilitate ejection and shorten the mol ding cycle. Some complex parts require that the mold open in several directions in addition to the direction of the platen movement. For a threaded part, eg, a bottle cap, part of the mold must be rotated to remove the article from the mold. 

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