Mold types Cold runner

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. 

Unfortunately, solidified TS runners, flash, and defective parts cannot be recycled as they are with TPs. Some operations can use this material as a filler after it has been granulated but in practically all molding plants using TS, the material is lost and has to be considered in the part cost. One should consider using cold runners with TSs. Materials must be of a type that will permit their use for example, the time cycle should permit material to remain in the fluid state. As different hardeners, accelerators, and so on, can be used, it is practical to use cold runners. They have limited use in TM but are used more widely in IM. 

When designing molds for HIPS, and GPPS, the principles are very similar but these materials do tend to flow more easily. This results in smaller runner systems, e.g. 2.5 to 5.0mm (0.098 to 0.197in) in diameter, and thinner wall sectioned components. It can also withstand being flexed without cracking. Due to the flexible nature of HIPS, submarine type gates and reverse tapered sprue pullers are widely used for cold runner molds which are intended to cycle automatically. Small undercuts can be jumped or bumped off during ejection of the component. 

Full round runners are preferred where typical diameters of 6 to 8mm (0.236 to 0.315in) (for component wall thicknesses of up to 4mm (0.157in)) and 8 to 12mm (0.315 to 0.472in) (for component wall thicknesses of greater than 4mm (0.157in)) are recommended. Z type, cold slug well pullers are preferred for cold runner molds. 

Regranulation of the feed system of a cold runner type mold may be accomplished by using a work handling device so that the feed system, when removed from the mold, is... 

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. 

Figure 11-30. Gate breaking and clipping are low-cost removal methods when the part design permits locating a recessed gate in a hidden area, as in this handle. This type of problem is eliminated by using hot runner molds for TPs and cold runner molds for TSs.

The most sophisticated type of gate is valvegating. It is used in both hot and cold runner molding. The principle of valve-gating is that the opening and closing of the gate is controlled by mechanical means such as hydraulic or pneumatic... 

---