Release time：2020-01-16 18:44 Browse：
The parting line on extra-long screws is a normal result of the molding process, caused by the junction between the upper and lower dies of the mold during high-pressure forming. This line typically runs along the screw shaft or the edge of the head.
For extra-long screws (over 150mm) or with thin shafts, segmented forging or long-stroke molds are used. This leads to a more visible parting line.
Insufficient die precision or poor lubrication can make the parting line more obvious.
While the parting line does not affect mechanical performance, it can be polished, ground, or shot-blasted for applications with higher appearance requirements.
| Feature | Forging Machine (Die Forging) | Cold Heading Machine (Multi-Station) |
|---|---|---|
| Principle | Mold closes and pressure forces metal into shape | Cold forming using multiple stations and punches |
| Best for | Extra-long or complex-head screws | Standard-length, high-volume fasteners |
| Advantages | Can form complex heads and long shafts | High efficiency, high precision, good surface finish |
| Limitations | Slightly higher cost, slower output | Higher material and tooling requirements |
| Forming Precision | Lower, with visible parting lines | Higher, with smooth surfaces |
Parting lines are normal in the production of custom or ultra-long screws.
Use cold heading machines for high-volume standard screws.
Use forging machines for customized, extra-long or complex-head screws.
For customers with higher appearance expectations, secondary finishing is recommended.
