Insulated Runner Molds

In use are diflbrent runner systems to meet different processing requirements. The more popular are the cold and hot runners. With a TP cold runner, the melt from the sprue to the gate solidifies by the cooling action of the mold as the melt in the cavity soHdifies. A hot runner for TP has the sprue to the gate insulated from the chilled cavity and remains hot so that the melt never cools its next shot starts from the gate rather than the nozzle as in... 

Fig. 2-7b. Types of injection molds illustrated here are insulated runner, hot manifold, and stacked (1).

A hot-runner mold that is both heated and insulated an insulated mold is a hot-runner mold that does not contain heaters. 

The use of a heated tool to cause surface melting of a part at the joint area. It is then removed before the joint surfaces being pressed together to form a fusion bond. A thermoplastic injection mold in which the runners are insulated from the chilled cavities and remain hot so that the center of the ruimer never cools in normal cycle operation. Runners are not usually ejected with the molded pieces. 

A thermoplastic injection mold in which the mold that contains the runner system has its own heating elements to keep the molding material in a plastic state ready for injection into the cavities, from which the manifold is insulated. 

Many molds, particularly those used for engineering thermoplastics, run at relatively high temperatures, for example, 80 C (176° F). If the mold is not insulated then, heat losses to the atmosphere, and to the machine, can easily equal those lost by the injection cylinder. So, insulate the mold from the platens and, if possible, insulate the outside surfaces of the mold. If a hot runner mold is being considered then, try and reduce heat exchanges between the hot runner parts and the cold, component-forming parts. 

These materials have been successfully molded in all types of mold, for example, 2-plate, 3-plate, insulated runner, stack and hot runner, en using the hot manifold type of runnerless mold, the runner channel must be streamlined so that there are no dead spots (nil flow areas) which are likely to cause degradation accurate temperature control of the manifold is essential. To maintain the sparkling clarity of this material, use vacuum smelted steel as this can take a very high polish and is non-porous. 

Hot-runner mold (insulated-runner mold) n. An injection mold for thermoplastics in which the runners and sometimes the secondary sprues are insulated from the chilled cavity plate so that they remain hot during the entire cycle. The plastic in the runners remains molten and is not ejected with the molded part, thus avoiding the normal handling, grinding, and reprocessing of sprues and runners. 

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

Molds are also classified by their runner systems. In a cold-runner mold, the sprue and runner solidify and are ejected with the part. Insulated runners have much larger diameters than standard runners. As a result, the outer part of the runner solidifies while the center remains fluid. This reduces the scrap generated during molding and facilitates the changing of materials or colors. Insulated-runner molds are more difficult to operate because the gate tends to freeze off. With hot-runner molds, the runner is always in the melt state. 

Figure 1 Basic variants of injection molds (a) two-plate mold (one cavity) (b) three-plate mold (multi-cavity). Designations a, coupling link b, ejector nxi cl + 2, center rings dl -f- 2, clamping plates e, ejector plate t, ejector pins g, distance plate h, cavity plate i, cavity j, transition plate k, sprue with cone gate 1, runner with 4 sprues m, center bolt n, runner plate o, nozzle rl + 2, insulation plates s, high performance nozzle.

Runners can be classified into two types, namely the cold runner and the hot runner. The mold temperature for the cold mnner is similar to the mold temperature for the cavity. The material in the cold runner will eventually solidify, and be ejected with each cycle. The hot mnner maintains the polymer at a melt temperature, either by insulation or by heating. This keeps the material fluid. Hot mnners are not ejected with each cycle. 

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