Davenport Iowa plate stress relief by hydraulic jacking

Alcoa's Davenport, Iowa rolling mill — "the world's largest" — rolls aluminum plate up to four inches thick for 747 wings, then mechanically stress-relieves it by 1–3% stretch in a large hydraulic machine. Used to introduce the T651 / T63 temper designations as mechanical-stress-relief codes.

They don't do that just with sheet, they do that when they roll the four-inch-thick plate to make the wings of the aircraft. Aluminum, because of its high thermal conductivity and the fact that it has to be heat treated and then quenched in order to get the best strength in the quench-tempered alloys, can develop significant residual stresses in plate or big bar. Remember that little washer I showed you that was supposed to be stress relieved? Out at Davenport, Iowa, Alcoa has the world's largest rolling mill. The rolls are probably as wide as this room and they're about eight feet tall. It's bigger than any steel rolling mill, because they're rolling the sheets for the wings of the aircraft. For a 747, they're going to roll some great big sheet. It might be four inches thick, could be a little thicker. You can use some really big ingots to roll aluminum. Aluminum's so light — if you try to do that in a steel mill you have a problem with the crane capacity, but in an aluminum mill you can start with really big ingots.

Referenced as the production-scale analog to the washer's -51 treatment. World's largest rolling mill — for aluminum, not steel — produces aircraft wing plates for Boeing and the former McDonnell Douglas. Hydraulic expanders pull 30-foot, 4-inch plates 1–3% in plastic strain to relieve quench stresses.

Tensile relief of residual stresses by mechanical means is common in a lot of aluminum alloys. They take whole plates at the Davenport, Iowa world's largest rolling mill — which is not for steel, it's for aluminum. In Davenport they have these about twelve-foot-wide rolls with four-foot-diameter steel rolls to roll the world's largest aluminum plates. What do we use the world's largest aluminum plates for? The world's largest aircraft wings. All the aircraft wings for Boeing — not necessarily for Airbus, they may get theirs from somewhere else — and when McDonnell Douglas was in business, all came out of the Alcoa Davenport works.

Cross-reference for the mechanical (T-51) stress relief mechanism. Tom invokes the Davenport six-inch-thick plate stretching as the canonical example of the operation Sikorsky's washer process destroyed.

Now, I've mentioned to you the government contractor defense — that military hardware has been determined by the Supreme Court to be cutting edge technology, or some people call it bleeding edge technology. You can relieve the stresses by stretching. We talked about the great big Alcoa plates, where they pull on the whole six-inch-thick plate to stress relieve it. That's mechanical stress relief in tension — a T-51 heat treatment. You can also stress relieve in compression. In this case it should have been a T-62 heat treatment.

Mechanical stress relief example. Six-inch plate, ten feet wide, pulled 3% in hydraulic jacks the size of half a football field. Used as the canonical case of mechanical (not thermal) stress relief in heavy aluminum plate.

I'll talk about this more when we get to aluminum alloys. The Davenport, Iowa plant of Alcoa where they roll heavy plate — they stress relieve mechanically. Six-inch-thick plate, ten feet wide. They have huge hydraulic jacks in a room about half the size of a football field. They grab the plate and pull it three percent. Figure out the force: 70 ksi yield, ten feet wide, five or six inches thick — millions and millions of pounds. A lot of force to pull these things apart. But getting rid of residual stresses is something you need to do.

Alcoa's Davenport Works rolls aluminum aircraft-wing plate up to six inches thick on the world's largest rolling mill, then relieves residual stresses by hydraulically stretching the plate one to three percent (the "T51" temper designation). Tom has visited the facility. Used to teach that aluminum residual stresses cannot be relieved by heat treatment for metallurgical reasons, so a mechanical solution is required.

This is aluminum alloy 7050 plate and sheet manufactured by Alcoa. It's an alloy they developed, and of course they're supplying the world's best — I don't know if they mean best products or best companies that they're selling to, they're trying to pander to their customers anyway. They have a bunch of different heat treatments here. You can get 7050 up to six inches thick. That's what I want you to see here. Here's another one up to six-inch-thick plate.