PDA

View Full Version : Sheet metal strength and weight questions.


boytyperanma
10-12-2011, 03:08 PM
I want a 6 1/2 foot circles of metal. My options are stainless steel, steel, or aluminum.

What would the weights of these circles be for 1/8 and 1/4inch thicknesses?

If these are individually laid flat and only supported at 6 points evenly distributed around the outside edge(within an inch underneath) would they deflect under their own weight? No corrugation or other support methods could be used.

What size sheets do metal fabrication shops generally have available to them? Is 6.5 foot stock within the realm of possibility? Would it be more practical to seek out say 4 foot stock and weld it to get the needed 6.5?

beowulff
10-12-2011, 03:19 PM
That’s 33.2 square feet of metal.
1/4 thick steel weighs 10.21 lbs/sq foot, so it will weigh 340 lbs.
1/8 (if you can find it) will weigh half as much.
1/4” aluminum weighs about 3.7 lbs/sq. foot, so it will weigh 123 lbs.

You’ll have to go to a steel yard to find sheets wider than 4', but they are available.

boytyperanma
10-12-2011, 03:22 PM
That’s 33.2 square feet of metal.
1/4 thick steel weighs 10.21 lbs/sq foot, so it will weigh 340 lbs.
1/8 (if you can find it) will weigh half as much.
1/4” aluminum weighs about 3.7 lbs/sq. foot, so it will weigh 123 lbs.

You’ll have to go to a steel yard to find sheets wider than 4', but they are available.

Is 1/8th inch steel hard to find? What are the standard thicknesses?

TriPolar
10-12-2011, 04:11 PM
The standard thicknesses are just about everything. I can recommend Mid-City Steel (http://midcitysteel.com/index.html)here in New England. They can cut the circles for you. They have used steel for sale also at a lower cost, except you have to buy whole pieces. 1/8" steel is pretty strong, and heavy, and it will deform a little under it's own weight in the situation you describe, but it won't fold up or anything. You would be better off with aluminum weight-wise, but it will cost more (although aluminum prices have gone down lately, but it's almost a day by day thing).

Machine Elf
10-12-2011, 04:43 PM
If these are individually laid flat and only supported at 6 points evenly distributed around the outside edge(within an inch underneath) would they deflect under their own weight? No corrugation or other support methods could be used.

Yes, for all metals and all thicknesses, the unsupported center of your disk will sag out of plane, and the only question is how much.

The thinner your metal plate, the more it will sag; it weighs less than a thicker disk, but because it's thinner it's also less resistant to the sagging.

Aluminum is about 1/3 the density of steel, but also exhibits about 1/3 of the material rigidity of steel or stainless steel, so you would expect aluminum, steel, and stainless steel disks of the same thickness to sag about equally under the influence of gravity (they will of course respond differently to externally applied loads).

Someone running a finite-element simulation could predict fairly accurately how much sag you should expect for the various material/thickness combinations. A SWAG would be maybe 1.5-2 inches of sag (at center) for the 1/8" thickess disks, and maybe a third of that for the 1/4" thickness disks.

TriPolar
10-12-2011, 05:08 PM
Do these disks absolutely flat, and on both sides? They could easily be reinforced on one or both sides to minimize sagging.

Hyperelastic
10-12-2011, 05:26 PM
The amount of sag can be calculated from formulas such as those appearing here (http://en.wikipedia.org/wiki/Bending_of_plates#Circular_Kirchhoff-Love_plates). The 6-point support is probably close enough to continuous to be considered a simply supported edge.

boytyperanma
10-12-2011, 06:02 PM
Thanks everyone for the info so far it's certainly saved me some time.

Do these disks absolutely flat, and on both sides? They could easily be reinforced on one or both sides to minimize sagging.

My recommendation was an angle iron x on either side but that was shot down. They want it unobstructed area.

A few inches of sag in the middle is acceptable.

Due to weight my original recommendation was 1/8 inch steel or 1/4 aluminum. Being reasonably movable by two people is the ideal. beowulff's math confirmed that for me.

A person involved in the project doesn't like aluminum, as a concept not any reasonable engineering concern. I'd have preferred 1/4 Aluminum because 1/8th inch is a pretty sharp edge to deal with.

I think the material of choice is going to be stainless steel, that is until I source it and they realize how much money that is going to be, then steel might seem more reasonable.

Daylate
10-12-2011, 07:09 PM
For general weight calculations

Wt of steel = 494 lbs per cubic ft = .286 lbs per cubic inch.
Wt of aluminum = 174 lbs per cubic ft = .100 lbs per cubic inch.

FYI, concrete weighs quite a bit less than aluminum.

Wt of reinforced concrete = 150 lbs per cubic ft = .087 lbs per cubic inch.

Every time I'd mention that during my stay at Boeing I'd get funny looks.

rbroome
10-12-2011, 09:02 PM
For general weight calculations
FYI, concrete weighs quite a bit less than aluminum.
Every time I'd mention that during my stay at Boeing I'd get funny looks.

ha, no imagination!
but now that they have built an airplane out of (carbon fiber) cloth, can a concrete airplane be far behind? :)

electronbee
10-13-2011, 03:01 AM
How about a sandwiched, honey comb, aluminum sheet? I know there is a name for it but I can't recall it. The top and bottom will be a solid sheet of aluminum but within is a honeycomb structure to both reduce weight and increase rigidity. Probably have to go for 1/4" thickness though.

You could also go with 1/8" aluminum or steel, place it on the supports, and then deflect/bend it ever so slightly. Then flip it back over and see if the deflection will compensate for the sag.

nitroman88
10-13-2011, 03:29 AM
stainless steel all the way I used to operate a very large cnc plasma table. SS steel is more rigid espeically after its heated and then cooled then it gets extremelly rigid.

Moonshiner
10-13-2011, 09:07 AM
Sheet Metal Thickness Gauges (http://unc.edu/~rowlett/units/scales/sheetmetal.html)

Just to point out you have lots of options between 1/8" and 1/4".

brewha
10-13-2011, 09:28 AM
How about a sandwiched, honey comb, aluminum sheet? I know there is a name for it but I can't recall it. The top and bottom will be a solid sheet of aluminum but within is a honeycomb structure to both reduce weight and increase rigidity. Probably have to go for 1/4" thickness though.

You could also go with 1/8" aluminum or steel, place it on the supports, and then deflect/bend it ever so slightly. Then flip it back over and see if the deflection will compensate for the sag.


It's just called aluminum honeycomb. Super rigid and light weight. We used it in all the interior cabinets in the Gulfstream jets.

It would work, but it's really expensive. I think you're looking at something like $1200 for a 12'X4' sheet. I dont' know if you can get it in 6' widths either.

Rhythmdvl
10-13-2011, 09:35 AM
By the way, boytyperanma, how much do henchmen get paid these days? Are you getting bonus pay for working on a doomsday device? Oh, and please tell us you don't have to wear one of the red uniforms!

LSLGuy
10-13-2011, 09:37 AM
A possible design consideration ... If this thing is installed horizontally it will sag, at least a smidgen, and as other have said above, maybe more like a couple inches. That wll form a large shallow bowl. If this is installed outside it will be able to hold a few gallons of water.

That much rain water or snow (depending on location) probably won't weigh enough to break the supports or buckle the disk. Unless you're in Buffalo where 5' of lake effect snow would weight about a ton.

But a snow or water load may interfere with whatever function you are using the disc for. At a minimum after a good rain it may stay wet for a few days & become a mosquito breeding reactor.

JoelUpchurch
10-13-2011, 09:51 AM
Everything deflects under it's own weight. You need to quantify how much deflection you are willing to accept for your application. For some applications you can quantify the deflection and compensate for it.

zut
10-13-2011, 10:54 AM
The amount of sag can be calculated from formulas such as those appearing here (http://en.wikipedia.org/wiki/Bending_of_plates#Circular_Kirchhoff-Love_plates). The 6-point support is probably close enough to continuous to be considered a simply supported edge.

Agreed. Here's a calculator (http://efunda.com/formulae/solid_mechanics/plates/calculators/cpFS_PUniform.cfm) that will do the math for you. It requires only radius, thickness, Young's modulus, Poisson's ratio, and loading (which is really, in this case, weight per square meter).

boytyperanma
10-13-2011, 05:17 PM
By the way, boytyperanma, how much do henchmen get paid these days? Are you getting bonus pay for working on a doomsday device? Oh, and please tell us you don't have to wear one of the red uniforms!

No bonus pay what so ever, no real pay to begin with, just sorta potential for future work. I can wear whatever I want.

I think I'd just be considered a subcontractor for this dooms day device. My contact works for essentially an eccentric millionaire so it could well be a evil plot to take over the world. I'm not well informed as to what the hell they are doing.

They have open air tanks, They are sorta like small above ground pools. So the six points refer to the corner posts of the pools. The covers will actually sit on the top which is a continuous edge. The covers are to prevent animals from getting inside. I'd have thought plastic or plywood would have been fine but this seems as much an art protect as anything else.

As far as I knew the tanks are just holding tanks for irrigation. They had wood covers before that have lasted 20 years. Now if they want to buy 1500 dollar stainless steel covers, I'll just keep my mouth shut and nod my head. When they need new pumping equipment to supply the needed water I'll be happy to sell it.

The tanks seem kinda small for raising sharks with lasers on their freaking heads, maybe the lasers can't cut metal? I only put so much thought into speculating what the evil plot may be.

bluezooky
10-14-2011, 05:09 PM
A possible design consideration ... If this thing is installed horizontally it will sag, at least a smidgen, and as other have said above, maybe more like a couple inches. That wll form a large shallow bowl. If this is installed outside it will be able to hold a few gallons of water.

That much rain water or snow (depending on location) probably won't weigh enough to break the supports or buckle the disk. Unless you're in Buffalo where 5' of lake effect snow would weight about a ton.

But a snow or water load may interfere with whatever function you are using the disc for. At a minimum after a good rain it may stay wet for a few days & become a mosquito breeding reactor.

I'd be inclined to add couple of creases to the top to add some rigidity as well as drainage.

Best Topics: sandwich vinegar pink palms usps media idle conquest ozone smell electronics bomb squad outfit basil expedition letter of transit cobras in vietnam virginia pronunciation expired sudafed cadillac pimp car ether knockout alumni alumna youngest hookers trugreen cost boo etymology chicken cars michelle meyrink imdb marines soldiers lucifer's hammer movie beastiality or bestiality passive night vision pixelated eyes kamchatka risk reckless abandon definition copenhagen vs stockholm tiny cc com mexican polkas heaviest beatles songs quicksilver bread stubbly legs did portuguese come from spanish how many lumens is 1 million candlepower tower isle beef patties move cable box to another room why are motorcycles allowed to be so loud half and half vs light cream walking to lose inches does this song have swear words one hen two ducks three squawking geese novels based on the bible myopia improves with age how to catch a rat in the house why i hate doctors late period birth control pills balling the jack meaning how to clean dingy white towels just for laughs actress wells fargo change email does permanent hair dye fade what to do if ambien doesn't work growth spurt at 22 how often to seal coat asphalt what romans looked like alternatives for to whom it may concern why do words sometimes look wrong land o lakes butter boobs isn't this putting descartes before the whores? where to buy chloroform cut throat pool game rules excel solver multiple variables pecan pie with walnuts instead dont have a car non biological father quotes can you rename a cat making a pass at lg dryer keeps shutting off