Runner demolding

The additionally needed opening width used for runner demolding can be disadvantageous. The combination with a heated sprue channel decreases in the bulkiness of the runner is therefore not rare. Three- plate mold- gates are used for applications with very small gate distances not achievable by hotrunner nozzles because of their space requirements. A typical example is day light of 7 mm for the individual gating of narrow chambers which are positioned next to each other in molded parts for medical use. 

Injection molds are often classified by the basic design of the mold. A standard two-plate mold opens in one direction, and the part is demolded by gravity, ejector pins, or ejector sleeves. The sprue, runner, and parts are connected after ejection with the sprue and runners forming part scrap. Two-plate molds are used for all kinds of moldings that do not contain undercuts and provide the best overall part properties. 

A runner layout of pieces to be demolded by simple ejection should be achieved so that the sprue picker takes the runner easily. A row layout of the mold cavities is more favorable for sprue picking than round or star layout versions. It is often practical to form the upp>er end of the runner with an extra cone which guarantees an easy take-off. 

Keywords cavity, demolding, design aspects, EUROMAP, gas assisted injection molding, hot runner, mold construction, mold design, part ejection, robot, runner, sprue, three-plate mold, two-plate mold. 

If the injection molding compound solidifies in the feed channel, the sprue has to be demolded, either in combination with the molded part or already separated from the molded part, which can be done using a mechanism inside the mold. All of the solidified runners need a correspondingly higher injection volume on the machine side. 

For demolding the multi-gate runner, an additional parting surface is needed. The mold now consists not only of "fixed plate and ejector plate but has an additional middle plate which is moved by latches and stopped by anchor bolts. The parting surface of the gate opens first. 

Using restraining undercuts helps keeping the runner on the fixed half which leads to tearing off the pinpoint gate. Similar to the tunnel, the runner has to be demolded out of its undercuts using elastic deformation. 

Injection technique Cold rod Q Cold mnner CH Cold runner with demolding using an Q... 

An injection molding machine (Fig. 7.1) can be divided into six components plastification/injection section, clamping unit, mold including the runner system, control system, and tempering devices for the mold. The most important part of the process is the mold, which is made of at least two parts to allow ejection (demolding) of the molded part. The injection molding process can be divided into six steps. Table 7.1 presents the main function of each step. 

Cold Runners Cold runners are machined into the mold plates therefore, the temperature corresponds with the overall mold temperature. The material in the mnner freezes after injection, and needs to be demolded with the part after each injection molding cycle [8]. The optimum runner cross-sectional shape for SPS is the full-round mnner profile shown in Rgure 14.11. The trapezoidal and modified trapezoidal profiles are common alternatives. 

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