Designing Balanced Multi Cavity Runner Systems for Polymer Injection Tooling
Balanced multi cavity runners match flow length, shear history, and pressure drop across all branches to achieve simultaneous mold cavity filling.
Sprue Puller Z Pin
Meaning
Mechanical features located opposite the sprue orifice ensure that the solidified plastic remains attached to the moving half of the mould during opening. Sprue puller z pin is a specific type of ejection component that uses a Z-shaped undercut to grip the sprue. As the mould opens, the pin pulls the sprue out of the stationary bushing so it can be subsequently ejected with the rest of the runner system.
This design is simple and robust, making it a standard choice for two-plate moulds.
The Undercut
Geometry on the pin captures a small amount of molten plastic that freezes into a rigid hook. When the ejector plate moves forward, the sprue puller z pin pushes the sprue off, allowing it to fall into the collection bin or onto a conveyor. This mechanical action must be timed perfectly with the rest of the ejection pins to avoid bending the runner.
If the pin is worn or damaged, the sprue may not release cleanly.
Frequent Inspection
Maintenance of the undercut area is necessary to prevent the buildup of degraded plastic or lubricant. A clogged sprue puller z pin fails to grip the material, leading to part hang-ups and potential damage to the mould faces. The surface finish of the pin also influences how easily the plastic releases during the ejection stroke.
Hardened Tool Steel
Construction prevents the undercut from rounding over.