Perforated Metal Warping 3

[steris]

I am working on a design where we are looking to replace wire rack shelving with perforated metal. The shelves will hold liquid containers and need to be fairly flat. However, all the prototypes we have constructed suffer from an oil can type warping. The rack will bow up in the center and then as you put weight on it, it will suddenly pop down. We installed a support in the center however now we have two sections that bow - one on each side of the support that bow about half as much. Adding more supports creates more sections that bow however each section bows less.

I understand that the perforating process stretches the material, however I am at a loss of how to address this. Adding lots of supports solves the problem but yields a fairly ugly and time consuming product. Anyone have any ideas on how to reduce the warping?

 

[BrianPetersen]

Form ridges or grooves into the shelves at periodic intervals. The ridges/grooves can point down to avoid causing trouble with whatever is on the shelf.

 

[rstupplebeen]

Try stamping a channel in it similar to gas cans.

http://www.okoffroad.com/gifs/stuff/gascan-1.jpg

A picture would be more helpful. How are the perforations made? I hope this helps.

Rob Stupplebeen

Rob Stupplebeen

 

[steris]

We are purchasing the material from a perforated metal supplier. The material is fabricated out of 16 gage 316L stainless sheet stock. It is punched 1/2" holes on 11/16" centers on a staggered 60deg pitch.

http://www.accurateperforating.com/images/patterns/large/RS096.jpg

Thanks for the suggestions! I am unable to place a channel or grooves into the shelf because the surface must be flat. Also, I am worried about tearing the material along the perforations with any sharp bends. Is there some way to mildly stretch the other side too? Would annealing or bead blasting help reduce the residual stresses from the stamping?

-Steris

 

[SnTMan]

steris, there is just about no way to prevent punched perf metal from warping, however some suppliers can have the sheets levelled after perforation. Not cheap though.

You may find something else is more practical to use.

http://www.iperf.org/perfhandbook.html

Regards,

Mike

 

[MTPipeliner]

This is way outside my area of expertise so maybe this won't even work, but is it possible to punch half the holes, then flip it over to punch the other half?

 

[mcgyvr]

The bottom surface of the shelf has to be flat also? Your putting supports on the bottom surface of the shelf aren't you? Those supports obviously aren't flat. I think you missed the fact of having beads formed on the bottom side of the shelf. So the bottom will have the bumps and the top is still flat with grooves indented down.

 

[dvd]

I think your corners are overly constrained. Try fully constraining one corner and let the other corners float. You may need to use slots and shoulder screws to accomplish this.

 

[berkshire]

Have the sheets stretch leveled after punching and before continuing with the rest of the fabrication.
Per SnTMans suggesion.
The punching stretches the metal around the holes and will cause the oil canning you describe.
B.E.

 

[steris]

Thanks for all the suggestions. I am looking into the stretch leveling to see if that is cost feasible. That solution seems like it should be easily doable.

As far as the bottom being flat - I meant that the top surface (where the containers rest) must be flat. Stamping a channel similar to gas cans, while an excellent idea, would not work for our situation. The supports I've already tried are attached to the bottom surface of the shelf and do not disturb the surface where the containers rest.

Thanks again for all the help!!

 

[SnTMan]

steris, you may find 16 ga. oilcanning anyway without some means of stffening it.

Good luck,

Mike

 

[ginsoakedboy]

Have a diagonal brace tack-welded to the bottom after the perforation process. Then you will not need the levelling process.

 

[MikeHalloran]

16 gage is too thin for even a solid flat shelf, much less a perforated one with minimal support.

Another option: Use much thicker sheet, and have it perforated by laser or waterjet. No warping, no limits on 'punch' shape, no limits on spacing.

The only limit on complexity is that the cutters price their work by length of cut or machine time (same thing, really).



Mike Halloran
Pembroke Pines, FL, USA

 

[StoneCold]

What about making the shelf out of wedge wire?
I like that stuff.

 

[CorBlimeyLimey]

What size is the shelf?
How is it supported?
What shape, size and weight are the liquid containers?
Does it absolutely have to be stainless steel?
Without little details like those, the best answers you get will be pure guesswork.

Instead of trying to fix the problem, eliminate it.
If the material is creating the problem, then use something else.

A thinner material with suitable edge forms and stiffening ribs can be surprisingly rigid.

Have you considered laminating a thin sheet of material onto a honeycomb/lattice structure?

Ore even the same perf sheet you have, but suitably reinforced with stiffening ribs, and with a very thin sheet of material bonded on top to give the flat surface?

 

[rb1957]

weld angle of tee extrusions onto the lower face. how heavy are the liquid containers ? how wide and long are the shelves ?

 

[steris]

Thanks for all the help. I looked into the stretch leveling but the perf manufacturers are fairly confident that it won't solve much of the problem.

I will look into the diagonal braces as well as the water jet cutting. It turns out the laser cutting is really expensive but with the waterjet they may be able to stack multiple sheets on top of each other. Also, I am examining the possibility of bumping to 14 gage.

The laminate or solid sheet over honeycomb is an interesting idea. That could work but I also need drainage in case the containers leak. These shelves are 22" wide by 30"-55" long and will hold no more than 100 lbs UDL.

 

[MikeHalloran]

You might have mentioned the need for a drip tray earlier.
Obvious question: Does it have to contain _all_ of the possible leakage, i.e., is it secondary containment or just for nuisances?

Another question that has a bearing on what's appropriate: How many shelves will you be making or buying?

And: What's the environment? By which I mean, oilcanning and deflection of sheet shelving is largely a cosmetic consideration. Is the shelving in a retail or other environment where appearance is important?



Mike Halloran
Pembroke Pines, FL, USA

 

[berkshire]

Steris
It should be possible to make a shelf out of 16 Ga perf SS that size that does not, oilcan.
Are you bending flanges on the outside of the shelf, if so how deep?
If they are 1.5" to 2" deep, you should be able to run the edges through a 3 roll bending roller clamped tight,( not a pyramid roller) to pre-stretch the material before you form the flanges. There is a fine line to this, not enough and the part will oilcan, too much and the part will flip flop diagonally across the corners. The shelf will still deflect under load but should not oilcan. If possible put a 1/2" return under the bottom of the flange, and tack weld there, try to avoid welding the vertical corners.
B.E.

 

[macthenife]

Cut the shelf into wide strips.
Bend and reverse the long sides to form a "shelf slat."

A typical slat could be say 30 inches long by 6 inches wide
by 1/2 deep.

These will not oil can but rivet,screw or bond in position to avoid twist.