A sprue is a circular passageway through which molten plastic pours into the mold-tapered hole that transports plastic material from the nozzle of the injection molding machine's heating cylinder to the mold's distributing runners.

To prevent the sprue disassociation brought on by high injection pressure, a fastener sprue bush, which is a sprue fastened with two bolts, is used. Sprues, runners, and gates move molten plastic from the injection unit's hose to the designated cavities.

Direct sprue gating has been demonstrated to exist in specific molds when the sprue is related to the molded item. The capacity of a particular injection mold is typically assessed using the cooling time of this sprue.

Types of Sprue in Injection Molding

Hot Sprue in Injection Molding

Hot sprue bushings are placed inside the old to generate a hot route between the nozzles of the molding apparatus and the mold chamber. The resin melt is kept hot inside the brushing using a heat exchanger that is located inside the brushing.

Cold Sprue in Injection Molding

To provide a passage between the mold cavity and the injector of the molding machine, cold sprue bushings are integrated into the mold. They are unheated if aesthetics are a concern, which results in a sprue that must be excluded, frequently through a further operation. There are two crucial measurements on the hose end of the bushing, i.e., the circular radius and the "O" dimension hole entrance.

Sprue Bush Design

Sprue bushings typically have a nozzle radius of half or three-quarters of an inch, but flat-type brushings with a flat surface are also offered. Customers must also select a number of additional dimensions.

Sprue bushes can be created using your calculations or bought from another supplier. Small molds are utilized with two-bolted sprue, which can be used with injection machines weighing less than 350 tons. Large molds often employ sprues with four bolts, and injection machines weighing more than 200 tons can use them.

The ball radius of the sprue must be bigger than the radius of the nozzle when designing or choosing a sprue bush. If it is smaller, there will be a space between the sprue and the nozzle, the resin will overflow, and the injection machine's tension will be lost. If it is greater, tension will be maintained.

Which Sprue Should You Use?

The design of your sprues, runners, and gates should be decided by the product being created, as is the case with most decisions. Larger runners are needed for products made of ABS (Acrylonitrile Butadiene Styrene), a popular injection molding material, than for products made of nylon or other materials.

The design of your runners is significantly influenced by several additional parameters, including the product's size and thickness. As a result, larger cavities will call for larger and more exact gates, which serve as the last conduit for plastic to enter the mold.

Recycling of spruces

After the finished components are removed from the sprue, you can have a lot of plastic waste on your hands. There are several applications for this sprue that were left over. It is possible to gather, melt, and turn it into useful plastic prepared to undergo injection molding.

Bottom Line

A sprue and runner system connects the equipment tip and chambers link. Molten material moves to the cavities through the sprue and runner during the injection phase of the molding cycle. To acquire the greatest products and services on the market, it is advised to engage a plastic injection molding OEM (original equipment manufacturer).

It's key to work with a skilled tool manufacturer you can rely on. Get in touch with SCTools if you want to start a project; we have the knowledge and expertise to handle your injection molding project successfully.

If you have any questions about carbide cutting tools, end mills, drills, etc. be sure to reach out to us @ sctools.co/Home or call us at (877)737-0987. We help you machine better!