What is a hot runner?
A hot runner is a set of heated nozzle and pipe installed on an injection device. This assembly allows the plastic cartridge material to remain in the feed mechanism to keep the fluid after the injection, while the part itself cools and solidifies. Injection forms equipped with hot runners are more economical and have faster cycle times and less waste. These savings are possible due to the fact that the pipes and nozzles keep the plastic fluid between the injection cycles, eliminating the unnecessary time and material associated with stiff "runners" in conventional cold forms. The installation of the heated assembly contributes significantly to the cost of any form, which limits the viable use of devices to processes with high production. When the injection process is complete, the forms and parts are allowed to cool and solidify, allowing the product to be fired from the mold cavity. The path inside the mold followed by molten plastic before reaching the real cavity is known as a pipe or runner. They usually composefrom one or more narrow channels. Each ends in the nozzles that form the entrance to the cavity. In the conventional cold mold processes, plastic in these channels and nozzles cools down and solidifies together with the formed part.
These stiff wizards or "runners" are then discarded before the next injection cycle. This not only represents material waste, especially when runners cannot be recycled, but also adds a production step to the process. This increases cycle times, limits productivity and increases unit costs for the parts produced. The use of a hot runner system almost eliminates these problems in the distribution channels and a jet fluid between the injection cycles. This is achieved by including electric heating elements in pipes and nozzles, which keeps these parts at a constant temperature of approximately 550 to 590 ° F (290 to 310 ° C).
hot runner heating elements fall into two categories:Internal and external types. The outer hot running heaters are located with the pipe body directly adjacent to the channels and around the outer side of the nozzles. The inner elements of the heater are located inside the channels and nozzles. Although the internal heating method is used in some specialized applications and older machines, the more efficient method of external heating has replaced it to a large extent. While the use of Hot Runner systems represents significant savings, the cost of high -related installation limits their use.