Considerations in Selecting a Sprue Bushing

The plastics industry is enormous and employs nearly one million Americans. Therefore, getting the manufacturing process right is important to staying ahead of the competition. But injection molding machines are complex systems. From temperature to timing to the materials used to make the machine parts, there can be hundreds of factors that can contribute to either a perfectly formed part or a gummy mess of molten plastic. In plastic injection molding machines, the need will arise to replace sprue bushings is inevitable. Here are some considerations in choosing replacement sprue bushings:

What is a Sprue Bushing?

Before discussing a few considerations in choosing sprue bushings, a little bit of background is needed. A sprue bushing provides a pathway between molding machine nozzles and the mold. Specifically, a sprue bushing includes an opening that mates with a nozzle. To ensure a proper fit between the sprue bushing opening and the nozzle, the opening and nozzle must have the same diameter opening and the same spherical radii.

Hot or Cold?

In choosing a sprue bushing, there are two types available: hot sprue bushings and cold sprue bushings. Cold sprue bushings are simply solid metal pieces with a channel that carries molten plastic from the nozzle to the mold cavity. In other words, the molten plastic is not heated as it travels into the mold. Stated differently, the molten plastic will cool off as it passes from the nozzle to the mold.

A hot sprue bushing, on the other hand, includes a heating element in the sprue bushing that heats up the sprue bushing. Because the sprue bushing is heated, the molten plastic will not cool off as it passes from the nozzle to the mold.

A cold sprue bushing will allow the sprue to harden more than hot sprue bushings will. This means that manufacturing processes in which the ejected part is subsequently handled using the sprue may benefit from using a cold sprue bushing because the molten plastic passing through the sprue bushing begins cooling as it is injected into the mold.

A hot sprue bushing on the other hand, usually has some benefits in the efficiency of the overall manufacturing process overall because less grinding and trimming is required after part ejection. Moreover, hot sprue bushings eliminate sink which might occur in a cold sprue bushings device.

When you’re struggling to pick out the best sprue bushings replacement, rely on the help of Melt Design today.