How to gain better control over the molding process and solve common part defects.
Having proper control over the molding process is critical to achieving excellent part cosmetics, and new advances in hot runner technology are providing a level of control not previously available. This additional control allows molders to solve cosmetics problems, even for the most challenging applications.
Hot runner systems fall into two main categories that pertain to gate function: thermal gate systems and valve gate systems. Thermal gates have no moving parts. After the cavity is filled and the polymer begins to freeze in it, plastic freezes inside of the hot runner gate as well. When the mold opens and the part pulls off the A side of the tool, the solidified plastic in the gate breaks; some of this frozen plastic stays with the part and some stays behind in the hot runner gate. What remains in the gate acts as a dam, preventing molten plastic from flowing out while the tool is open. Then, when plastic is injected into the hot runner on the next cycle, the pressure behind this plastic dam forces it to shoot out, opening the gate again so plastic can fill the part (see Figure 1).