The Milling Process: Forging the Future

Carrie Stambaugh, Managing Editor


Braidy’s state-of-the-art 1.8-million-square-foot (about 40 acres) aluminum mill will “walk” before it “runs” when it opens in 2020, said Mill General Manager Gregg Whigham. “We will start with some easier aluminum products. They are not all the same. Some of them are easy to make and they go into easy applications,” he explained.

“Then, progressively we will get into more challenging aluminum products, and in pretty short order, we will get to the automotive products. Automotive products have very high performance requirements and very high surface quality requirements… We won’t get there right away, but we have a plan to get there,” he said.

“It all starts in our cast house,” said Whigham. “All types of aluminum” will come into the mill, including both ingots of prime aluminum direct from a supplier as well as scrap aluminum from Braidy’s own customers. “We give them a sheet of aluminum and they stamp a door out of it, there are all kinds of bits and pieces left over and that will be coming back. We put that right back in the furnace and melt it,” he explained. Some scrap aluminum will also be purchased on the open market but it will all be clean. “We won’t be melting cans or painted or oily scrap,” he added.

“All that comes into the cast house and we will put it in a (natural-gas fired) furnace to begin the recycling process,” he said. “Then, there is a whole lot of metallurgy and chemistry control that goes into the process,” said Whigham.

“We are trying to hit a very specific recipe based on what the customers’ needs are. The great thing about aluminum is that it can be made very soft and formable like an aluminum can, or you can make it armor-plated and it is stronger than steel. It all starts in the cast house. The molten aluminum, which has a temperature of about 1,500 degrees Fahrenheit, will then be cast into large slabs of aluminum. After the slabs cool, a series of thermal processes “to change the microstructure of the metal” will be undertaken, said Whigham, explaining the process “gives us some formability and strength benefits.”

Next, the rolling process begins. The slabs, approximately 24 inches thick, will be hot rolled into giant coils that will be approximately one-fourth-inch thick and up to 100+ inches wide.

“Then, we will cool the coil and cold roll it,” said Whigham. The cold rolling process brings the aluminum down to “final customer gauge,” which for automotive aluminum is approximately .085 inches thick, according to Whigham.

But it isn’t done yet. “After cold rolling, we will heat treat it again with another thermal operation and then put a surface treatment on the metal,” he said, explaining the last process is a chemical treatment that prepares the surface of the aluminum to have a super-adhesive applied to it. Many modern cars aren’t solely welded, they are glued together, he said, adding, 

“The finished coil is carefully packaged because it has to arrive in pristine condition to our customers.”

 


Aluminum 101:

„    Primary Aluminum: Aluminum produced directly from mined ore, which is refined and reduced to elemental aluminum.  Aluminum makes up approximately 8 percent of the earth’s crust.

„    Bauxite Ore: The world’s primary source of aluminum. A rock, bauxite is primarily comprised of aluminum oxide compounds (alumina), silica, iron oxides and titanium dioxide.  It must be refined through a process into alumina. Then alumina is refined through the Hall–Héroult electrolytic process into pure aluminum metal.

„    Hall-Heroult Process: The major industrial process for smelting aluminum. It involves dissolving alumina in molten cryolite (an aluminum compound with a lower melting point) and electrolyzing the molten salt bath.

„    Recycled Aluminum: Aluminum is highly durable and infinitely recyclable.  Nearly 75 percent of aluminum ever produced is still in use today.

„    Casthouse: Molten aluminum is poured into mixing furnaces, where various metals are added to bring its chemical composition up to customer specifications and cast into ingots.

„    Ingot: A mass of metal that has been cast into a specific size and shape.

„    Hot Rolling: The aluminum is rolled at a high temperature – above its recrystallization temperature - to reduce thickness and make thickness uniform.

„    Cold Rolling: Aluminum is rolled a temperature below its recrystallization temperature, increasing its strength and improving its surface finish.

„    Alloys:

  •  3,000-series alloys are alloyed with manganese and can be work hardened – used for building
  • 5,000-series alloys are alloyed with magnesium to offer superb corrosion resistance often used in marine applications and aerospace
  • 6,000-series alloys  - automotive body sheet
  • 7,000-series alloys are alloyed with zinc, magnesium and cooper, and can produce highest strengths of aluminum for aerospace.