Why Post-Annealing Aluminum Caps Need Special Threading Parameters

From our years of tuning aluminum cap production lines for different clients, we've noticed a common overlooked issue with annealed aluminum caps.

After annealing treatment, the aluminum material becomes much softer. Its surface hardness drops by roughly 35%, while ductility increases significantly, this physical change makes finished caps easier to shape and seal better for packaging, but it also brings new challenges to threading work.

Many factories still use general standard threading parameters for these softened caps, in actual mass running, we've recorded that nearly 30% of post-annealing cap defects occur in the threading stage. Common issues include slightly expanded cap mouths, uneven thread lines, and subtle body deformation, these small errors won't show obvious flaws at a glance, yet they often cause unstable sealing and assembly problems in later packaging processes.

Based on our on-site debugging experience with cap processing equipment, we've adjusted and sorted out exclusive parameter ranges for annealed aluminum, instead of fixed standard settings, we match proper rolling pressure and feeding speed according to the soft material's actual toughness.

This tailored processing way can well avoid excessive extrusion deformation, it helps maintain complete cap appearance and keeps thread sizes within stable tolerance for most daily production runs.