Ejector half

The function of the clamping unit is to move the one mold-half called clamp , movable or ejector half towards the stationary, fixed half and the application of clamping force to seal against the separating force of the cavity pressure. 

At the end of the cooling phase, the clamping force of the machine is released and the mold opens which means that the ejector half moves back. A reliable removal of the injection molded part can be assured by an adequate break time or mold open time . Automated removal devices which are used increasingly, activate a release signal for the next closing process. 

PW Position of the moving mold half (ejector half) FS Clamping force ... 

Basic injection molds are made of two halves Fixed half (often abbreviated as A) and Ejector half (often abbreviated as B), which are consisting of several plates (Figure 1.10). Due to an easier machinability and interchangeability, the cavity is formed by inserts which are tailored to the surrounding frame plates. 

After opening the mold, the molded part usually remains on the ejector half. Undercuts (lateral breakthroughs), bosses, offset or internal threads require additional moving mold parts. 

FIGURE 1.14 Ejector half of a mold for vacuum cleaner housing... 

Arrangement of the inclined bolt and the locking wedge on the fixed half, whereas the slider guidance is on the ejector half of the mold. 

If the molded part provides convenient side walls in the ejector half of the mold the tunnel hole can be positioned in the ejector half (Figure 1.37). In this case the separation of the gate occurs during the ejection of part and runner. 

FIGURE 1.56 Sealing of the cavity for applying vacuum before injecting On the left Ejector half with peripheral sealing ring On the right Fixed half with vacuum connection above the cavity [15]... 

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. 

With backpressure the process is performed in conventional injection molding machines (IMMs) (Chapter 4). The cover stock is inserted and located in an open mold. A shear edge mold permits draw-in of the cover stock during the closing cycle to avoid wrinkles and damage by stretching of the fabric. Molds require special attention. They generally use a hot runner system with its shut-off nozzle(s). All mold elements such as ejector, core pulls, and slides have to be on the injection side mold half. 

To remove the cylinder and ejector of the pocket pistols, opsn the pistol urdil the piston protrudes half way, raise the barrel catch and turn the cylinder tiuo tuna to the left. 

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. 

A top plate B core pin C male half D guide pin E push-back rods (to return ejection system) F guide bush G bottom plate H risers or parallels J ejector pin... 

K ejector or knock-out bar L female half M pressure pads... 

If imdercuts are not practical, the fixed mold half may be provided with spring-loaded or mechanically actuated hold-down pins, which are ejector pins that assist the molded part in leaving the fixed mold half and in following the moving mold half during breakaway and initial travel, perhaps 6 mm or more. 

The draft specification controls the way the mold is built as the direction of draft normally indicates the direction of draw (removal of the part from the tool) since reverse draft would be an undercut condition. For injection molding, the mold designer will attempt to locate the core on the back, or movable, half of the mold. That is the side where the molding machine s ejector bars are located, and locating the core on that half makes the ejector mechanism available to push the part off the core. Part designs with cores from both sides of the part may require slight undercuts to keep them on the side of the mold which has the ejector mechanism. The draft specification will also control the location of the parting line, which should be indicated. 

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