News & Articles

Why is Core Pull Preload Important for Injection Molds?

Why is Core Pull Preload Important for Injection Molds?

Although many plastic component designers may not think about it, core preload is an essential part of any successful injection molding project requiring precision and uniformity. As the creators of KOR-LOK® Side Action Systems, PFA has a unique understanding of preload and the critical importance of choosing a hydraulic locking cylinder (HLC) that will maintain proper preload even if hydraulics drop out during injection. PFA staff is trained and ready to help explain the advantages of preload and assist in sizing preload for your specific needs.

What exactly is core preload, and what role does it play in the successful completion of an injection molding process cycle?

During the injection molding process, cores undergo intense forces that will often cause the core lengths to decrease, and core face positions change from the initial set position. Evidence of force effects can often be seen on the molded part, as if the entire core has “backed up” as much as .020”, depending on the geometry.

Using a Holding Force Design

With proper core preload, undesireable movements and flex can be eliminated, with the product retaining the desired shape, with no backup variation seen on the completed part. Maintaining part shape is due to preserving core preload even when no hydraulic pressure is applied to the cylinder.

Using a Preload Force Design

Achieving proper core preload and “locking it in” mechanically means producing parts more easily with perfect match lines, tighter tolerances, and cleaner textures.

The unique characteristics of PFA KOR-LOK Side-Action Hydraulic Locking Cylinders make creating complex parts easier by making cores easier to design, install, time, and maintain.


How Can KOR-LOK® Improve Injection Molds?

What makes the KOR-LOK® Side Action System different from other hydraulic core pull cylinders and various clamping and rod lock cylinders available to manufacturers is its ability to preload cores at incredibly high forces. Unlike spring-locking, hydraulic-activated locking cylinders and other piston-locking cylinders, KOR-LOK® can achieve preload to the rated load and can continue to maintain that preload even at zero psi. While PFA makes other locking cylinders for general industrial use, such as the Spring loaded self-locking version, the recommended KOR-LOK® achieves high force preload and cylinder locking to full rated load in a simple–to–install system.

Once set using only a minimum of 1,500 psi hydraulics, KOR-LOK® Side-Action Systems provide 100% preload to rated load – 10 times more force than a standard cylinder. KOR-LOK® does not just lock, it “super locks” by preloading and locking in the force so hydraulics are no longer needed. The result is 100% preload to rated load at zero pressure. This is a feat that is often not achievable with mechanical systems or other cylinders. If you are interested in learning how KOR-LOK® can improve your injection molding processes, we would love to talk!



Plastic & Injection Molding