Plastic Part Injection Mold
Hot Runner Molds: Speed at a Price
Hot runners exist for one reason: once the plastic has filled the mold cavity and cooled, it has also filled the runners. If left alone, it will cool as well and be ejected along with the part (depending on the mold type, they either remain attached to the part or are separated before ejection). Heated runners make use of a heated manifold that keeps the plastic in the runners molten, which has some significant advantages and disadvantages.
Hot Runner Advantages
Eliminates waste plastic because the runner plastic doesn’t need to be ejected with the part. Have plastic ready to go in the runners leads to faster cycle times and higher part volume. Without the resistance of the cooling plastic in the runners, less pressure is needed. Without having to worry about plastic cooling in the runners, molds can make larger parts.