Three-plate molds

Slider mold Stack mold Three plate mold H... 

Keyword Microcellular, Injection Molding, Three-Plate-Mold, PBT, Glass Fiber, Miner Fiber. 

The principal types are two-plate, three-plate, and stack molds. Others include the family mold that has multiple cavities of different shapes in one mold.3, 324 A further distinction concerns the feed system that can be either the cold or hot type. These classifications overlap. Three-plate molds will usually have a cold runner feed system, and a stack mold will have a hot runner system. Two-plate molds can have either feed system. 

When compared with compression molding, transfer molding provides better product consistency, shorter cycle times, and better bonding of rubber to metal [55]. However, considerable amount of material is lost as scrap in the transfer pad, sprues, and flash. The basic three-plate multiple cavity mold is more complex and expensive than a comparable compression mold but is suited better for intricate parts or securing inserts [56]. 

Most molds for injection molding are unique in design, which depends on application, fluoroelastomer compound, and feed system (hot or cold runners). Standard systems are distinguished as two plate, three plate, or stack molds [58],... 

A three-plate mold design (Figure 2.10) features a third, movable, plate which contains the cavities, thereby permitting center or offset gating into each cavity for multicavity operation. When the mold is opened, it provides two openings, one for ejection of the molded part and the other for removal of the runner and sprue. 

FIGURE 2.10 A diagram of a three-plate injection mold. 

The channels through which the plasticized material enters the gate areas of the mold cavities are called runners. Normally, runners are either hill round or trapezoidal in cross section. Round cross section offers the least resistance to the flow of material but requires a duplicate machining operation in the mold, since both plates must be cut at the parting line. In three-plate mold designs, however, trapezoidal runners are preferred, since sliding movements are required across the parting-Hne ruimer face. 

One can see from Figure 2.10 that a three-plate mold operation necessitates removal of the ruimer and sprue system, which must be reground, and the material reused. It is possible, however, to eliminate the runner system completely by keeping the material in a fluid state. This mold is called a hot-ruimer mold. The material is kept fluid by the hot-runner manifold, which is heated with electric cartridges. 

Typically, the selection of gate location and the decision between cold runner molds (two-plate or three-plate molds) or hot runner molds are important to the product design when considering the mold cost and the plastic flow within the mold. Today, about 90% of all molds built are still two-plate molds, which are considerably cheaper than three-plate or hot runner molds. For many reasons, in most cases, hot runner molds are better, but these questions must always be asked ... 

Three-plate mold n. An injection mold with an intermediate movable plate that permits center or offset gating of each cavity. 

Figure 5.67 Molds (a) two plate, (b) three plate, (c) stack, (d) insulated runner, and (e) hot runner,...

Figure 6.1. Effect of temperature on the nucleus den- Figure 6.2. Effect of nucleus density on the haze of 2 sity of iPP containing 200 ppm poly(vinylcyclo- mm injection molded iPP plates containing the three...

A film (or flash) gate permits uniform filling of flat parts. The melt fills a runner and then crosses a wide, but thin, land to enter the cavity. Pin gates are very fine-diameter (typically 0.25-1.6 mm) entrances to the cavity. They are used in three-plate molds or hot ruimer molds to facilitate degating. 

A stripper plate mold is a two-plate mold in which the core and ejector plates are combined into a stripper plate. It is used for thin wall parts and parts with symmetry and no undercuts. A three-plate mold has two parting Unes, thereby providing automatic separation of the parts and runner system. This does not work with all materials brittle materials tend to fracture on ejection. It also limits the selection of gate locations and does not eliminate scrap. A stack mold is used to mold two layers of parts without increasing clamp force. Because stack molds are not as precise as two-plate molds, they are used for low-tolerance parts such as polystyrene drinking cups. 

Movable cores Visible surface Three-plate mold Assembling... 

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