How do I Unbending/flatten steel plate?

[Macrosloth]

I've got a piece of 1/2 inch steel plate that is curved. I want to flatten it out as well as possible with clamps and weld it to a frame. Which method is best, or is there any difference.

Clamp the ends and pull it into place, or flip it and clamp the middle to pull it into place?

I can Weld additional box in place to hold it required. I don't have access to a torch and surface grinding will cost too much.

Cheers.

 

[NASTYZEN]

Flatten it first by putting two blocks of wood on the floor. Place a block underneath each end of the plate and lay the plate with high part of the arc upwards and strike with a large hammer. Could be done in a press also.

 

[ishiboo]

Trying to flatten steel plate with clamps is some sort of joke, right?

You could try to use a press but remember you have to go BEYOND flat to get it back to flat.

Since you obviously have a welder, I would use some weld beads to pull it back flat.

 

[Macrosloth]

Clamping the plate to the box allowed me to pull it almost perfectly flat. Once the box was welded in place I'd imaging that it would hold the plate fairly flat, I guess there would always be tension on the plate/weld though..

I could try to block up either side and jump on it first.. Its 5.5 feet long so I might be able to straighten it a little prior to pulling it flat.

Its too wide for my press. Im starting to think about my hydraulic jacks though..

 

[ishiboo]

You said "box", I thought it was an open frame so it would still bow in the middle when you released the clamp.

Use the welder to flatten it.

 

[Bondo]

Clamping the plate to the box allowed me to pull it almost perfectly flat. Once the box was welded in place I'd imaging that it would hold the plate fairly flat, I guess there would always be tension on the plate/weld though..

I could try to block up either side and jump on it first.. Its 5.5 feet long so I might be able to straighten it a little prior to pulling it flat.

Its too wide for my press. Im starting to think about my hydraulic jacks though..

Ayuh,... At that size, block it up on the floor, 'n Drive yer truck over it,....

 

[BBC71Nova]

How much bend does it have in it?

 

[PugetDude]

In order to flatten the plate you need to bend it past the yield point to get it to take a set , and overbend it just enough to compensate for springback.

You don't say how wide the plate is, but chances are that jumping up and down on it isn't going to do much, if anything for a 1/2" plate.

An old school trick is to jack up a heavy vehicle, set the plate and 2x4s under a wheel, then slowly lower the vehicle onto the plate between the wood blocks. You can start with 2x4's fairly close together, slowly move them apart, add a second layer, etc... just go slow and check your progress with a straightedge, moving the plate back and forth under the wheel as you go. The idea is to use the vehicle weight to bump the plate much like you would do with a press, applying just enough of a bend to get the plate flat.

Good luck.

 

[kerrynzl]

If you hammer it between 2 hard surfaces [ a Hammer and Steel ]it will get thinner and stretch

But if you hammer it between 1 hard surface and 1 soft surface [ a wooden Hammer or a wooden buck] it will thicken and shrink.

If you press it straight you need to allow for spring back. So if you clamp it to a straight piece [ face down, as in the lower of your diagram ] then use a wooden/plastic mallet you should be able to shrink the outside of the curve straight again.



I've done this successfully on 3mm steel

 

[A_Pmech]

A few weld beads parallel to the axis of the bend on the convex side will pull it flat.

Alternatively, use a strongback and jack to push it straight.

 

[ishiboo]

A few weld beads parallel to the axis of the bend on the convex side will pull it flat.

Alternatively, use a strongback and jack to push it straight.

I figured you'd be on the same page

 

[A_Pmech]

I figured you'd be on the same page

One can use welding distortion to their advantage or fight it.

 

[Zeke]

You could easily make this worse and end up with a large potato chip. I think I'd put a few cross members going both ways under it and tack it in the center bay. Then weld an X across the under side with the convex at the bottom as Pmech says. If that flattens out satisfactory, move to the next bay and repeat. Start your X small and lengthen as necessary.

If this was my project I'd take the piece to the scrap yard and sell it and then buy a better one.

 

[BFBOB]

Second (or third) using the weight of a vehicle. I've done this several times in different ways, and it works. Pick the size of the blocks so that it will go about the right distance overbent, redo with thicker blocks if necessary. Something around half the amount of the bend is a good starting point.

Good luck!

 

[readhead]

I'm with Zeke. Go trade it in for a flat piece.

 

[motobilt]

Trying to understand exactly what you have. You have 1/2" Thick plate that is roughly 65 inch long... correct? How wide is the plate?

 

[Macrosloth]

Thanks for the responses.

The plate is 66x24.

The 24 inch section has a bend about 1/8th of an inch from the straight edge in the centre.

The 66 inch section has bend about 3/16.

I like the idea of slowly lowering a vehicle onto it to have a more controlled bend. Just driving on it makes me think I could warp it more.

I bought it new, so am a little upset that its bent. Does anyone know what the flatness spec for 44w steel plate is? As its a custom cut, I dont know that I can return it.

I am hoping the frame that I weld it to will be strong enough to keep it pulled flat. Having the frame warp the plate would **** even more

 

[Professur]

Call whoever you bought it from. If they had to tools to cut it, they have the tools to straighten it.

 

[Zeke]

Cupped like that is really going to give you fits. At least call the supplier and ask about this. I don't see so much of a problem lengthwise but an eighth in 24 on 1/2" plate is going to take way more than the weight of one corner of a car or truck and some fancy blocking. You have more chances of messing this up or getting nothing done than you have for success.

Prove me wrong and I'll bow down.

 

[mechan]

I could be wrong but I think you will find that is well within the flatness / camber tolerance for general A36 steel plate.

I am not 100% on what the intended purpose is for the plate from skimming the thread, but if the frame work is rugged enough you can probably some if it out when you weld it to the frame by using dogs.

 

[A_Pmech]

The flatness tolerance for commerical plate under 120" in length and 60" in width is 7/16 in width and 5/8" in length per ASTM A6. There are some multipliers to take into account for a plate your size, but it's should still fall within flatness.

Nothing about commercial steel plate is flat.

 

[Macrosloth]

In future if I want flat plate, what are my options. Is there a different grade I should ask for, or is the only option guaranteeing flatness buying blanchard ground plate?

 

[PugetDude]

I am hoping the frame that I weld it to will be strong enough to keep it pulled flat.

HOPE is not a course of action....

 

[readhead]

You need to find a different supplier. We buy plate every day and I have not seen anything that far out. Especially on the 24" side.
Mills will offer end runs that are not very flat but cost less.
We can also specify dead flat plate. It just takes a little longer to get.

 

[A_Pmech]

In future if I want flat plate, what are my options. Is there a different grade I should ask for, or is the only option guaranteeing flatness buying blanchard ground plate?

I've never seen plate out as much as yours is, but it is still within commercial mill specification so far as I'm aware. My guess is the warp in the plate is from shearing to size. It's really not a big deal, fabricators deal with it every day. Even if you did get a dead flat sheet, by the time you welded it to the frame it would no longer be flat. Dealing with distortion is a BIG part of fabricating.

"Stretched" or "leveled" plate is available which is basically as flat as can be achieved without machining.

Blanchard grinding alone isn't sufficient. The steel must be stress relieved before grinding, otherwise no grinding shop will guarantee flatness, only thickness.

 

[kazlx]

You have to remember even with blanchard grinding, the plate is going to be sucked flat by a huge electromagnet while grinding, so without prior work, you wouldn't be any better off than you are. When I had my top done for my fab table, the guy was nice enough to put it in their press and get it close. After they ground it, it was only out about a 1/16" over the length. I just just drilled and tapped my frame and adjusted the bolts until it was to my liking.

I Just recessed the cross members in my table about 1/4" below the perimeter frame and then had room to work on the adjustments.