Hot-runner plastic mold 

injection plastic mold in which the runners are kept hot and insulated from the chilled cavities. Plastic freezeoff occurs at gate of cavity; runners are in a separate plate so they are not, as is the case usually, ejected with the piece.Hot runner molds are two plate molds with a heated runner system inside one half of the mold.A hot runner system is divided into two parts: the manifold and the drops. The manifold has channels that convey the plastic on a single plane, parallel to the parting line, to a point above the cavity. The drops, situated perpendicular to the manifold, convey the plastic from the manifold to the part.

Disadvantages

Hot-runner plastic mold is much more expensive than a cold runner, it requires costly maintenance, and requires more skill to operate. Color changes with hot runner molds can be difficult, since it is virtually impossible to remove all of the plastic from an internal runner system.

Advantages

They can completely eliminate runner scrap, so there are no runners to sort from the parts, and no runners to throw away or regrind and remix into the original material. Hot runners are popular in high production parts, especially with a lot of cavities.

Advantages Hot Runner System Over a Cold Runner System include:

• no runners to disconnect from the molded parts
• no runners to remove or regrind, thus no need for process/ robotics to remove them
• having no runners reduces the possibility of contamination
• lower injection pressures
• lower clamping pressure
• consistent heat at processing temperature within the cavity
• cooling time is actually shorter (as there is no need for thicker, longer-cycle runners)
• shot size is reduced by runner weight
• cleaner molding process (no regrinding necessary)
• nozzle freeze and sprue sticking issues eliminated

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