Mold types Single cavity

FIGURE 2.1 Three basic types of molds, (a) single-cavity (b) dedicated multiple-cavity (c) family multiple-cavity. 

An alternative approach for injection molding is the use of a rotary table injection machine. This type of machine uses the multistation concept, each station having a single cavity mold generally using a point gating/ injection point as previously mentioned. Consider a rotary table machine with eight stations, station one would be the injection station and station seven would be the unload and load metal insert station. This type of process has been successfully used for different types of lip type rotary shaft seals where more expensive elastomers are used and waste needs to be kept to a minimum. 

The use of multinozzle injection machines. In general, this type of machine has a horizontal reciprocating screw that feeds four injection nozzles each connected to a single cavity mold thus minimizing waste. However, one concern with this approach is the need to have the mold accurately lined up (the top and bottom surfaces of the mold will be in the vertical plane) to eliminate compound leakage at the nozzle/mold interface. 

The basic types of mold, regardless of whether they are compression, injection, transfer, or even blow molds, are usually classified by the type and number of cavities they have. For example, Figure 2.1 illustrates three mold types (a) single-cavity, (b) dedicated multiple-cavity, and (c) family multiple-cavity. 

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. 

Recent studies have contributed robustly to the realization that shear induced melt variations developed in runner sections will affect the manner in which a mold and part forming cavity will fill. These effects occur in, but are not limited to, multicavity molds. The filling patterns of single cavity molds are also affected by flow variation caused by shearing differences. These effects not only influence the way a single cavity mold will fill but how the polymers are oriented and consequently how the part will shrink and warp (1). The varying manner in which neat materials and filled materials shrink and how shear imbalances affect these two different types of materials is the focus of this study and subsequent write up. 

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. 

LIM employs two or more pumps to move the components of the liquid system (such as catalyst and resin) to a mixing head before they are forced into a heated mold cavity. In some systems, screws or static mixers are used. Only a single pump is required for a one-part resin, but usually two (or more)-part systems are used. Equipment is available to process all types of resin systems, with unsophisticated or sophisticated control systems. A very critical control involves precision mixing. If voids or gaseous by-products develop, vacuum is used in the mold. 

A gate connects the runner to each mold cavity. With a sprue gate, the gate connects directly to the cavity. This type is commonly used on larger parts in single... 

A different type of inspection is needed for the re-installation of a mold that has been in storage for some time. Even though the mold assembly— the mold, its vacuum box, plug plate, plugs, air and coolant line quick disconnects, and its pressure box—may have been stored as a single unit, often bits and pieces are scavenged for other molds. Installation may be delayed until the missing pieces are found or replaced. The same is true with trim dies, trim fixtures, and elements of stackers. It is vital that the mold and press set-up protocols are stored with the mold. If these are stored electronically on a disk or chip, a paper printout of the access codes to the protocols is required to ensure that the appropriate software is available. An example of the product should also be placed in the mold cavity. 

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