Bending 3/4" 304 stainless plate

[RacinNdrummin]

Hey guys,

So I have a line on a job with some stainless work, and one or two parts on the job require a 30" square, arc'd piece of 3/4" stainless plate with a 36" radius.

Ive had thoughts recently about building a heavy duty Shop press/press brake for my shop and this could be a way for it to pay for itself. Problem is, When I do the math, its looking like it would require somewhere in the neighborhood of 150+ tons to bend the piece.

Anybody have any good experience with bending stainless plate of this caliber??

Im thinking the shop press would have to be severely heavy duty...

[wierdscience]

Ya,it's gonna take some serious tonnage to bend that,but also some serious control,big press brake would be one answer.

Better answer is to see if you have a good sized steel service center nearby that offers plate rolling.

[x39]

If you don't already have the equipment, I'd farm out the bend and do whatever other operations are required inhouse. Unless of course you would be making a whole heck of a lot of the of the parts in question

[Evan]

3/4 by 30 inch SS plate? I would guess that 150 tons may not be enough. That is some seriously tough metal, especially if it is a high strain hardening grade. It also must be over bent by quite a lot to deal with the high degree of spring back of SS. Sounds like a job to farm out.

[squirrel]

I don't think the press brake will do a very good job if you need a radius. Very large bending rolls would do it, if you want to segment the radius that will take a minimum 500 ton capacity brake press.

[JoeCB]

How true does the radius have to be? If you start out with 30" square blanks it will be very difficult ( impossable??) to carry the curvature all the way out to the edges.
Joe B

[Ries]

Send it out.
Up here in the Skagit, I use Superior Systems, who can roll 1 1/2" x 12' mild steel.
But I am sure there are places in Auburn or Kent who can do this for you.

As mentioned above, unless they have a very expensive initial pinch roll, which has hydraulic up/down on the two pinching rolls, as well as the back roll, the part will have two straight sections at either end of a rolled section.

at 80,000lbs tensile, its somewhere around 70 to 80 tons per linear foot to bend on a press brake- you have two and a half feet, thats 175 tons or so- but multiply that out by the actual width of the press brake, and its probably gonna take a 300 ton 8 foot brake.

3/4" stainless is serious stuff.

[RacinNdrummin]

Thanks Guys, The sheet metal shop I work at has a large cincinatti press brake, but I dont know the tonnage off hand. Either way it would need dies built.

Ill get some more info and update...

[Forrest Addy]

You gotta bend a 36" R circular arc in a 3/4" stainless plate 30" square? Cold?

You might need up to a 1200 ton press brake to bend 3/4 stainless 30" long in a 2" opening V bending die. Bigger really is better here. Working to near capacity in a press brake results in less than consistant bending. The job might pencil in for a 300 ton press brake but trust me the extra tonnage of a larger press will pay off in quicker, more consistant results. Stainless is far tougher than A 36 plate. The beefier punch and die, the greater stiffness, the greater control of an exces capacity press brake will result in a better arc.

Stainless takes a bit less than double the tonnage of A36 plate to work cold. This is far beyond a home brew bending rig and for the record you can't roll an arc like this on a big pyramid roll. Yu need excess length for the arc to come out a true radius. The length bridging between the upper roll and the lower exit roll will remain straight. You'll need about 18" of tangent on each end; the excess to be cut off later.

If the plate is already cut to size, your best bet is a honkin' big press brake that can reliably bend 3/4 stainless plate in short pitch increments in a V bending die.

This is heavy dury metalwork you're proposing. I'd farm it out to a large scale fab shop, one that's used to working plate in thicknesses and has the equipment to do it.

Does the plate have to be machined after bending? A plate rolled in an arc and machined on the OD and ID will relax a fair degree because the inner and outer skin wll be plasticly deformed by bending while the inner materal may contain considerable strain energy. Machining will cause the plate to uncurl. The piece should be restrained with tack welded bracing and furnace stress relieved before machining.

I suggest if you need several parts you make them up as a rolled ring and plasma cut them into segments after tress relief. You will get 6 pieces plus tangents at some fabrication savings. If the job is to be machined, make a full welded ring (a healthy tack is all that's needed at the joint), brace the ring into circularity, stress relieve it, machine the ring, and plasma cut/mill the ring into 7 segments (a complete ring will be incremerally flanged in a pre brake to form the initial curl then the end-curled plate transferred to the pyramid roll to make the full circle.

[Circlip]

Thicker piece of plate, FB lathe and bore the internal rad.

Regards Ian.

[Ian B]

It would be nice if you could find a 30" length of 6' diameter 3/4" wall thickness 304 pipe in your local scrapyard...

Ian

[lazlo]

It would be nice if you could find a 30" length of 6' diameter 3/4" wall thickness 304 pipe in your local scrapyard...

A weldment is probably a better approach. Even bent hot, that's a massive bender.

[Forrest Addy]

I dunno. When I was an apprentice and my employer had a real boiler shop I watched the boilermaker flange (bend in a press brake) steam drums 4 ft dia 16 ft long out of 1 1/4" boler plate. This was the shell plate. The tube sheet, I undertand was forged hot but I didn't see that part. The tube sheet was 3 1/4" thick and had hundreds of steam tube holes driilled and reamed in a dense array.

A 1200 PSI Navy propulsion boiler is complex as hell. It's made up of several drums fabricated from flat steel plate. This is one of 4 boilers for a 120,000 HP Naval ship propulsion plant. Base load coal plant boilers are 100 times this size and operate at 4 times the working pressure.

Flangeing up a 30" square of 3/4 stainless plate is small change technically on the scale of such things but it has to be done right with suitable equipment if it is to be done economically with minimum waste..

[RacinNdrummin]

Thanks for the help guys, At least for this portion of the job, Ill be passing...