Parting plane

The two main parameters for machine size are, the maximum shot size that can be injected in a single forward movement of the screw, and the maximum mould clamping force / damp- The shot size is usually quoted in terms of the mass of polystyrene that can be injected. The clamping force, typically in the range from 100 kN to 100 MN, restricts the maximum projected area A of a moulding onto the mould parting plane (Fig. 5.24). A typical average melt pressure p in the mould is 20 MPa, and the condition... 

Cutting laminations are mainly caused by fixtures in the die. Such fixtures are always unavoidable if a die with cores is employed in order to produce a perforated column, as with pipes, hollow profiles, common bricks, honeycombs, etc. The core bows, which are fitted crosswise to the flow direction, separate the body. If the distance between the core bow and column exit is too narrow or if the flow pressure is too low, the parting planes cannot sufficiently weld together. (5)... 

The processing of thermoplastics usually involves the use of horizontal injection molding machines (see Figure 2-2). Because the parting plane between the mold halves is arranged vertically, the completed articles can drop into a container, once they are released from the mold. 

In the vertical machine, the parting plane between the mold halves nms horizontally. As a result, this machine is especially well suited to the production of insert moldings (e.g., electrical plugs) (see Figure 2-3). Most moldings made of elastomers are produced on vertical machines. 

Once the molding has solidified within the cavity at the end of the cycle, it is important to ensure, that the finished article can be removed from the mold. For that purpose, the mold consists of two halves, so that it can be opened at the parting plane. Figure 4-10 shows an open mold. In this diagram, the molding is being removed by the ejector. 

As soon as the mold has been opened, the article can be removed at the parting plane. In the simplest cases, this can be performed manually. However, the injection molding process is designed specifically for mass-producing articles at a fast rate and should ideally operate in fully automatic mode. It is therefore obvious, that manual removal takes too much time. Furthermore, the cycle time fluctuates as a result of the operator s intervention in the machine cycle. This can cause variations in the molding s quality. With thermoplastics, manual removal is used only in exceptional cases, where articles are dehcate or of complex shape. 

Removal is generally performed by automatic ejectors, which are operated by the machine when the mold opens in the parting plane at the end of the injection molding cycle. These ejectors ensure, that the article is separated from the surrounding cavity in spite of imdercuts, adhesive forces, and internal stresses which tend to retain the part within the cavity. 

But there are even more tasks for the mold. It must close tightly during the injection phase so that the melt flows only into the cavity and not into the parting plane. At the same time, however, it must be possible to open the mold so that the molded part can be removed from the cavity at the end of the injection molding cycle. 

As soon as the set cooling time in the injection molding cycle has expired-in other words, once the injection-molded article has solidifed within the mold-the mold opens in the parting plane. The mold halves separate far enough to allow the article to be ejected. 

During the ejection operation the controls coordinate the sequence of movements performed by the clamping unit and ejector. The ejectors cannot be allowed to move too quickly because this might cause them to pierce the molding. The movement opening the mold in the parting plane should also start slowly to avoid damaging the molded article. 

One layout step is the consideration and dimensioning in the clamping direction. The criterion for this aspect of the layout is that platen deflection must not give rise to any prohibitively large gaps in the parting plane, which... 

Flash Develops, when plastics melt penetrates the mold s parting plane (mold parting force too high)... 

Projected area n. In molding, the area of a cavity, or all the cavities, or cavities and rurmers, perpendicular to the direction of mold closing force and parallel to the parting plane. In injection molding and blow molding, this area must be safely less than the quotient of the force apphed to hold the mold closed divided by the maximum melt pressure or blowing pressure within the mold. In transfer molding, it must also be about 15% less than the cross-sectional area of the pot. 

FIGURE 1.127 Mold with auxiliary parting plane and drag plate (a) Mold closed (b) mold open, position for the part removal and application of the mold release... 

FIGURE 1.128 Venting at the parting plane (a) Section (b) Top view... 

Molds for flexible, PUR integral skin foams are required in the production of motor cycle seats, sun visors, and simple seat upholstery. These large molds usually consist of two parts. For suitable venting, molds for annular headrests require auxiliary parting planes that can be mounted with hinges on one of the mold halves. 

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