Multi-cavity mold

The process is used for high volume BM of very small containers such as pharmaceutical vials and whiskey bottles. A multi-cavity mold is used with an extruded parison whose circumference approaches twice the total width of the closely spaced cavities. Before the mold closes, the parison is stretched and semi-flattened laterally so that it extends across the full width of the cavities. The process is usually combined with blow/fill/seal techniques. 

Besides the two main types of clamping units (mechanical and hydraulic), there are also combinations of both systems. All systems have advantages and disadvantages. In other words, there is no universal optimum design of clamping unit. The choice of system employed in the injection molding of plastics articles is ultimately determined by the the most cost-effective production method, e.g. single- or multi cavity mold and machine suitabdity. 

The first phase consists of determining the mold principle. It is also often called qualitative design. This phase includes the decision on whether to use a single-cavity or multi-cavity mold, for example, or which type of mold (standard- or spUts-mold, article ejection or other form of removal, heating/cooling arrangement) is to be employed. 

The runner system is used to convey the plastic melt from the sprue to the gate. It is important in producing identical quality of plastic parts. Cost reduction can be carried out by using multi-cavity mold with a balanced runner system and the mold fills in the cavity at the same time. The runners deliver the plastic into the part cavities (usually multiple). 

The gate channel in the injection mold serves to convey the melt coming from the nozzle of the injection molding machine to the cavity with the lowest possible pressure and heat loss, in shortest possible time and without thermal degradation. In multi-cavity molds, the melt must be supplied to all gates uniformly [1, 2, 7, 12, 19, and 20]. 

Multi-Cavity Mold with a Common Loading Chamber... 

Multi-Cavity Mold with Individual Loading Chambers... 

FIGURE 1.87 Multi-cavity mold with individual loading chambers (1) individual loading chamber... 

FIGURE 1.160 Injection blow molding machine with injection, blow and ejection station (Upper left) work table, turning horizontally in the parting plane (Upper right) injection mold with parted multi-cavity mold (Lower left) blow unit... 

The mold (so-called form segment ) on which the part is supposed to be molded. In the case of high order size, it can be a multi-cavity mold if the forming surface and the forming machine will allow it. 

The design of a rotational mold can be very diverse due to the general simplicity of these molds. Besides the single cavity mold (in which one product is manufactured in one mold), there are also double or multi-cavity molds (in which two or more products are manufactured in one mold and are mechanically separated) and combination molds (in which different products can be manufactured in a convertible rotational mold). Figure 1.174 shows such a combination mold. 

The disadvantages of the TM technique mostly relate to the costs. The mold structure for flash-free products is very complex and expensive to manufacture. Therefore, TM processes are mainly profitable for multi-cavity molds (usually over 20 cavities). 

The use of the hot runner technology allows only certain component geometries and mold concepts. With hot runner systems, gating positions are achieved that cannot be reached conventionally the active movement or complete avoidance of fill lines can be implemented by sequential injection multi-component injection molding can be performed with up to five materials in a mold high-speed stack molds can be built film and fabric can be back injected gas and water injection technology can be implemented multi-cavity molds can be realized clean room production can be optimized and the co-injection technique can be enabled. 

In the case of multi-cavity molds or family molds, intelligent electronics recognize when the first cavity and the last cavity have been filled. Depending on the application, switch over to holding pressure can be done fully automatically in either case. 

Identical filling times eventually cause the individual molded parts to be compressed under the same conditions, which is a prerequisite for a homogeneous distribution of weight. This principle can be used in classical multi-cavity molds as well as in multi-component molds, where each component is controlled separately, as well as in processes with inserts. In any case, the process variations and the resulting reject parts are reduced to a minimum. 

FIGURE 5.25 Cascade-controlled multi-cavity mold (door sills/auto)... 

It is also possible to regulate the melt flow of the sequential-controlled multi-cavity mold so that all cavities are filled simultaneously. Figure 5.25 shows the previously... 

Unbalanced cavity in multi-cavity mold Adjust runner or gate size... 

Flow restriction in one or more cavities of multi-cavity mold Identify and remove... 

Runner layouts should be designed to deliver the plastic melt at the same time and at the same temperature, pressure, and velocity to each cavity of a multicavity mold. Such a layout is known as a balanced runner (Fig. 7.15). A balanced runner will usually consume more material than an unbalanced type, but this disadvantage is outweighed by the improvement in the uniformity and quality of the moldings. Balance in a multi-cavity mold with dissimilar cavities (known as a family mold) can be achieved by careful variation of runner diameter in order to produce equal pressure drops in each flow path. Such balancing can only be achieved efficiently by the use of computer flow simu-... 

A multi-cavity mold with ASTM tensile, impact, and flexural sample was used in this study. 

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