A hot runner system is an assembly of heated components used in hot runner injection molding pdf injection molds that inject molten plastic into the cavities of the mold. The cavities are the part of the mold shaped like the parts to be produced. By contrast, a cold runner is simply a channel formed between the two halves of the mold, for the purpose of carrying plastic from the injection molding machine nozzle to the cavities.
Each time the mold opens to eject the newly formed plastic parts, the material in the runner is ejected as well, resulting in waste. A hot runner system usually includes a heated manifold and a number of heated nozzles. The main task of the manifold is to distribute the plastic entering the mold to the various nozzles which then meter it precisely to the injection points in the cavities. Balanced melt flow: Separate melt channels are in externally heated manifolds that are insulated from mold plates surrounding them.
Hot runner systems were first developed and came into sporadic use in the early 60s with generally negative results. They gained popularity in the 80s and 90s as technological advancements allowed improved reliability and the escalation of plastic materials prices made hot runner systems more desirable and cost effective. Hot runners are fairly complicated systems, they have to maintain the plastic material within them heated uniformly, while the rest of the injection mold is being cooled in order to solidify the product quickly. For this reason they are usually assembled from components pre manufactured by specialized companies.
A hot runner controller is a temperature controller used to control the temperature in the hot runner. Hot runners usually make the mold more expensive to manufacture and run, but allow savings by reducing plastic waste and by reducing the cycle time. This page was last edited on 5 April 2017, at 15:16.
Injection molding machine molds can be fastened in either a horizontal or vertical position. The majority of machines are horizontally oriented, but vertical machines are used in some niche applications such as insert molding, allowing the machine to take advantage of gravity. Some vertical machines also don’t require the mold to be fastened. The magnetic and hydraulic clamps are used where fast tool changes are required.
The person designing the mold chooses whether the mold uses a cold runner system or a hot runner system to carry the plastic from the injection unit to the cavities. A cold runner is a simple channel carved into the mold. The plastic that fills the cold runner cools as the part cools and is then ejected with the part as a sprue. A hot runner system is more complicated, often using cartridge heaters to keep the plastic in the runners hot as the part cools.
After the part is ejected, the plastic remaining in a hot runner is injected into the next part. Machines are classified primarily by the type of driving systems they use: hydraulic, mechanical, electrical, or hybrid. Hydraulic presses have historically been the only option available to molders until Nissei Plastic Industrial Co. LTD introduced the first all-electric injection molding machine in 1983.
Hydraulic machines, although not nearly as precise, are the predominant type in most of the world, with the exception of Japan. Mechanical type machines use the toggle system for building up tonnage on the clamp side of the machine. If the tool half opens up it will create flash in the plastic product.