Cold runner systems are used in injection molding machines to convey material from the nozzles to the mold cavity. The material is cooled in the channel between the nozzle and the cavity (the runner) and ejected with the part. Cold runner systems provide a simpler and less expensive alternative to hot runner systems, specialized temperature controllers that keep injection-mold components at the design temperature in order to keep the mold material flowing. In addition to their ease-of-use and lower costs, cold runner systems offer advantages such as reduced maintenance requirements and rapid color changes.
The cold runner molds that cold runner systems produce use either two or three plates. Two-plate molds have one parting plane along which the mold is split into two halves. By contrast, three-plate cold runner molds have two parting planes. When a part is ejected, the mold splits into three sections. Three-plate cold runner molding provides for greater design flexibility and allows gates to be installed according to application requirements. Because the cold runner mold has not one but two parting planes, these cold runner systems are located on one plane and the part on the other. This facilitates plate separation.
Cold runner systems differ in terms of product specifications and features. The number of nozzles is especially important to consider. Some valve pins require rotational alignment, and there may be an electronic control option for stroke-limiter control. Other factors to consider include part weight, part material, and total shot weight; locating ring diameter; whether the alignment uses two or four pins; and whether the assembly screw orientation for cold runner systems is from the parting line or from the back side.
With cold runner systems, there are two methods of retaining the cold deck to the platen: mold clamps and bolt-to-platen. Mold clamps require the clamp ledge requirements. Bolt-to-platen involves specifying the bolt size, the direction of the bolts, and any other applicable platen data. Additional specifications for cold runner systems include the interface dimension between the cold deck and the machine barrel tip assembly. Typically, dimensions are specified in inches or fractions of inches (in), or in metric units such as centimeters (cm) or millimeters (mm).