Hot runner system

This is only true for a hot runner system. However, in many injection molding processes the runner system is directly inside the cooled mold, and the flow is not isothermal. 

With backpressure the process is performed in conventional injection molding machines (IMMs) (Chapter 4). The cover stock is inserted and located in an open mold. A shear edge mold permits draw-in of the cover stock during the closing cycle to avoid wrinkles and damage by stretching of the fabric. Molds require special attention. They generally use a hot runner system with its shut-off nozzle(s). All mold elements such as ejector, core pulls, and slides have to be on the injection side mold half. 

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. 

The feed system is an unwanted by-product of the molding process, so a further requirement is to keep the mass of the feed system at a minimum to reduce the amount of plastic used. This last consideration is a major point of difference between cold and hot runner systems. The cold runner feed system is maintained at the same temperature as the rest of the mold. In other words, it is cold with respect to the melt temperature. The cold runner solidifies along with the molding and is ejected with it as a waste product in every cycle. The hot runner system is maintained at melt temperature as a separate thermal system within the cool mold. Plastic material within the hot runner system remains as a melt throughout the cycle, and is eventually used on the next cycle. Consequently, there is little or no feed system waste with a hot runner system. Effectively, a hot runner system moves the melt between the machine plasticizing system and the mold to a point at or near the cavity(s).3 32> 326-332,490... 

The color formulator must learn as much as possible about the processing conditions the colorant system will encounter. Important conditions to determine are cycle times and process temperatures. Hot runner systems commonly used in today s injection molding processes may add temperature to the polymer melt and add to the time the polymer is under heat. Remember that the heat stability of any colorant and additive system is a function of both time and temperature. An excellent color match may be produced, but if the formulation cannot withstand the stress of processing without breaking down or changing shade, then effort and time have been wasted. 

Attempts have been madei 1 to devise sprueless systems for injection molding of fluoropolymers. A hot runner system is necessary for sprueless molding that meets a number of criteria ... 

These conditions were met by a hot-runner system with the nozzle design in Fig. 6.34 which shows the key part of the system in which the copper-beryllium (Cu-Be) nozzle is heated by a strong spiral heater. Cu-Be is an outstanding thermal conductor which, in combination with a lowering of the heater in the center area, can help produce a uniform temperature... 

Hot runner systems are therefore used in the processing of thermoplastics. However, the processing of elastomers involves the use of cold runner systems, which prevent the elastomer compound from cross-linking prematurely in that system (see Figure 4-5). 

With cold-runner systems for TPs (or hot-runner systems for TSs), the projected areas include runners and sprues. For hot-runner TPs (cold-runner TSs), runners and sprue are not included. As an example, if the projected area is 132 sq. in., and a pressure of 4,000 psi is required, the clamp force is ... 

Once the interlocks are satisfied, the mold closes. Then the injection unit occasionally moves slightly forward to coimter a motion called sprue breakaway. With cold runner systems, the injection rmit is moved slightly away from the sprue bushing to facilitate sprue removal and/or prevent nozzle freeze-off. Thus, injection unit must be moved forward to provide intimate contact between the nozzle and sprue bushing during injection. Sprue breakaway is not used with hot runner systems. 

Dura Centi-Shot, Hot runner system, Mold-Masters... 

Master Hole Saw, Fiber-reinforced plastics carbide hole saw. International Carbide Corp. Master-Probe, Hot runner system, Mold-Masters... 

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