It has been shown that employing an additional heat treatment step (EBNER pre-heater) immediately after quenching from solution annealing temperature (EBNER floater furnace) can lead to the formation of significantly larger and more stable zones, or nuclei, in the microstructure. The condition that is achieved is designated T4*.

This provides an optimal start to the hardening process, and can be quickly ended during reheating in a later process step.

In practice, this approach is employed in automotive applications where formed sheet parts undergo cathodic dip coating, followed by curing. As relatively short times and low temperatures are used during curing, the material quickly hardens to the desired fi nal hardness (T6). This effect is also referred to as the paint bake response. This eliminates the need for a separate and additional heat treatment step, as would otherwise be necessary.

As EBNER has been successfully manufacturing floater furnaces for solution annealing for decades, the need for improved temperature uniformity at the pre-heater when strip speeds were changed was recognized.

As the pre-aging furnace is linked “in line” with the strip handling gear of the fl oater furnace facility, different strip speeds necessarily result. Matching the pre-heat furnace to the mechanical equipment of the strip handling system is unavoidable.

The pre-heat furnace design that had been previously bought-in rapidly reached its technical limits, so EBNER – as the most innovative and competitive full solution provider in thermal processing – revised and improved the furnace and added it to its product range.