Hazelett process vs. conventional casting processes
Below is a review of the three major process routes used to process aluminum into sheet, with a focus on the Hazelett twin-belt process.
The schematic above depicts each of the major process routes. The conventional DC casting/hot mill process route is shown first. It's easy to see the many processing steps required by this route. There is molten metal preparation and alloying, DC casting, sawing, surface milling, rolling ingot preheating, and hot rolling (both roughing and finishing). The hot-rolled strip is subsequently cold rolled to finished gauge.
By comparison, the continuous casting process routes are much shorter. There are two major continuous casting processes utilized for the production of aluminum sheet: twin-roll casting and twin-belt casting. With twin-roll casting, the steps include molten metal preparation and alloying, casting, and coiling. The strip is subsequently cold rolled to finished gauge. In the twin-belt process, casting is followed by in-line hot rolling to produce a hot-rolled strip that is thinner than twin-roll cast strip, requiring less subsequent cold rolling.
Taking a closer look at the continuous casting processes, this table above compares twin-roll caster and Hazelett® twin-belt caster mass flow and process parameters. It reveals that the scale of these two processes is quite different.
The Hazelett caster is 15 – 20 times more productive than the twin-roll caster. The Hazelett caster also has a broader alloy and product range than twin-roll casters.
Hazelett® casters currently produce 1XXX, 3XXX, 5XXX, 6XXX, and 8XXX series alloy strip. Applications include foil and fin stock, building sheet, common alloy sheet, and medium strength sheet products. Although beverage container sheet has been cast in several test series with promising results, we don’t yet have a commercial reference. In automotive, Hazelett-cast 5XXX series alloy strip is used for internal auto components; development of 6XXX series alloy strip for auto body sheet is ongoing.
Hazelett casting technology
Our twin-belt caster features a straight, parallel moving mold using belts as mold surfaces. The moving belts define the upper and lower mold surfaces. Chains of moving edge blocks form the side of the mold
Molten metal is introduced between the belts and is solidified as it travels within the moving mold. Solidification occurs as heat is transferred to water on the backside of the belts. Heat transfer can be adjusted and controlled to achieve high production rates and superior strip quality.
Behind the belts, precisely machined finned back-up rolls support the belts while allowing water to pass. Magnetic back up rolls, positioned in the first part of the mold, counteract belt instability due to thermal bending induced by high heat fluxes.
The rendering above depicts a Hazelett line, starting with the holding furnaces on the upper left and continuing through metal treatment, casting, in-line hot rolling, and coiling.