NEW Zealand Steel has undergone an upgrade for its skin pass steel mill, boosting the surface finish of its galvanised steel sheets.
Skin pass milling is a post-processing technique used within the galvanising process. It improves the surface finish of cold-rolled or coated steel. The NZ Steel unit uses a single roll process, and usually applies forces up to 2.5MN per side for a 1.5m wide sheet.
Moog Australia provided a new electro-hydraulic servo control system for the refurbishment, while Global Hydraulics and Controls (GHC) implemented the upgrade.
GHC built a dummy mill stand to test and confirm the functionality of the Moog control system and its interface with the NZ Steel CITECT host control system, allowing a quick switch-over to the new production system.
According to Moog, the process control required the pressure-applying roll to be lifted onto the sheet metal before applying a controlled load.
However, this simple concept needed to be precisely aligned so both sides of the roll reach the sheet at the same time. An error could cause up to 500m of product to be lost, and as much as two days of downtime to reset the line.
The solution was to synchronously lift each side of the roll onto the sheet under position control with a low level force over-ride. The over-ride limits the roll until both sides make contact.
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