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View Full Version : So, how strong is a weld?



alan waters
05-28-2006, 09:15 PM
Here's the test. Lets suppose we have 5 pieces of 1 inch thick x 4ft.x 8ft. steel plate stacked on top of each other and we want to move them with our overhead bridgecrane. At 40.8 lbs per square ft. thats 1,305 lbs. each. We have a piece of 3/8 thick x 2in wide x 2.5 inch tall plate which has a one inch hole in the top. This will be welded to the center of the 1 inch plate and used to attach the chain from the crane.The question is, what is the SMALLEST amount of weld we can get by with? Remember, we need to be able to knock the 3/8 plate off with a hammer to use on the next piece of 1 inch.

gnm109
05-28-2006, 09:39 PM
Here's the test. Lets suppose we have 5 pieces of 1 inch thick x 4ft.x 8ft. steel plate stacked on top of each other and we want to move them with our overhead bridgecrane. At 40.8 lbs per square ft. thats 1,305 lbs. each. We have a piece of 3/8 thick x 2in wide x 2.5 inch tall plate which has a one inch hole in the top. This will be welded to the center of the 1 inch plate and used to attach the chain from the crane.The question is, what is the SMALLEST amount of weld we can get by with? Remember, we need to be able to knock the 3/8 plate off with a hammer to use on the next piece of 1 inch.


First off, I'm not a structural or mechanical engineer. That said, IMHO, 3/8" is not thick enough for more than a half ton.

As to welding it, if it's strong enough to lift the plate without breaking, you certainly won't be able to knock it off with a hammer.

If I were doing such a thing in a commercial/industrial setting with employees in the area, I would want nothing less than a proper sized tab, a full penetration fillet weld around the plate where it attaches and, I would want it done in accordance with an applicable welding specification. I would also want an engineer to approve the configuration in writing.

Reason is, if it falls, the results will be unpleasant.

My 2 cents.

elvergon
05-29-2006, 12:23 AM
let me make a guess....

if you use 7018 rod which has a tensile strenght of 70,000 Lbs per square inch and if you need to hold 2202 lbs which means that you would neeed to deposit .04 square inch of rod. This.......NAH i dont think that .04 square inchs of 7018 rod would hold a 1 ton plate. Better ask someone else lol. SRY

chopper5
05-29-2006, 05:56 AM
in short don't try you'll get some one hurt or kill trying to cut corners
if it's welded so you can SAFELY lift it you can't knock it off with a hammer
i would use a magnet made to lift plate that size

wello
05-29-2006, 06:49 AM
the weld you need to lift that safely wouldn't be knocked off with a hammer

I work by a rule I was told a long time ago as to weldstrenght (as well as tried and tested ones )if you wouldn't trust your life with it don't do it
after all if the welder is worried about the weld what hope is there for everyone else

I would use a bigger piece than 3/8 thick x 2in wide x 2.5in to lift it

bigger the better nothing wrong with overkill 2x3/8 lifting 8x4x1" could =messy

Thom2
05-29-2006, 09:30 AM
I'm going to throw an idea in the pot, and you may want to do your own research before attempting this.

Vacuum, I use vacuum quite a bit for making jigs in woodworking and have to calculate the force that a particular sized jig will have on the workpiece (I work with mostly small stuff), but I do know that 2" of vacuum is roughly equivalent to 1 psi. So with that known, a 12"x12" plate is 144 square inches, at 20" of vacuum it would theoretically be capable of lifting 1440 lbs. A 2' square plate would be capable of lifting 5760 lbs.

Harbor Freight sells an automotive vaccum pump for air conditioning for $10 on sale, this is what I used to make my rig.

While I can't say I've ever tried this for you application, if I did have to move something that big and heavy in my own shop, this would be the technique that I'd try first. (admittedly very cautiously initially).

Just a thought.


Thom

Big B
05-29-2006, 09:43 AM
Everyone here has made valid points. I would listen to gnm109 he is a structural engineer and gave you a professional and industrial opinion. I don't mean to minumize everyone elses opinion, all have good points. And I also want to make a point.

If I understand correctly, you are going to lift this plate from the center with the piece of 3/8" metal. My first SWAG (Scientific Wild *** Guess) is that you are not going to be able to perfectly balance the sheet of plate . Regardless of how you measure and find the center.

When it shifts, when lifted, what's it going to do. Who knows? When the shift takes place you will go from a tensil load to a tortional load. Even if you had a perfect 100% 7018 weld. That 70,000 lb. tensile yeild is out the window when the tortional stress takes place.

If I were doing it I would lift from all four corners angled toward the center. Get Three more pieces of metal or even step up to larger pieces as suggested. Go ahead and weld them good. Forget the hammer. Get a cutting torch and an angle grinder to remove your pieces. You can remove them and grind down the weld and have practically no sign of the welds. You will have a heat affected zone on the corners. I don't know how that will figure into the use of your plate. You would need a welding engineer to answer that question for you.

As pretty much everyone else has said don't do it the way you are thinking.

gnm109
05-29-2006, 10:27 AM
Everyone here has made valid points. I would listen to gnm109 he is a structural engineer and gave you a professional and industrial opinion. I don't mean to minumize everyone elses opinion, all have good points. And I also want to make a point.

If I understand correctly, you are going to lift this plate from the center with the piece of 3/8" metal. My first SWAG (Scientific Wild *** Guess) is that you are not going to be able to perfectly balance the sheet of plate . Regardless of how you measure and find the center.

When it shifts, when lifted, what's it going to do. Who knows? When the shift takes place you will go from a tensil load to a tortional load. Even if you had a perfect 100% 7018 weld. That 70,000 lb. tensile yeild is out the window when the tortional stress takes place.

If I were doing it I would lift from all four corners angled toward the center. Get Three more pieces of metal or even step up to larger pieces as suggested. Go ahead and weld them good. Forget the hammer. Get a cutting torch and an angle grinder to remove your pieces. You can remove them and grind down the weld and have practically no sign of the welds. You will have a heat affected zone on the corners. I don't know how that will figure into the use of your plate. You would need a welding engineer to answer that question for you.

As pretty much everyone else has said don't do it the way you are thinking.


I'm blushing now. Please re-read my post. As I said, I'm NOT a structural or mechanical engineer. I have worked in manufacturing, however and I was a safety consultant for an insurance company for a number of years and I've seen and heard about large pieces of metal hitting the ground on several occasions when not properly secured.

I see that the other posters don't think this situation a good idea, either. Actually, it's not so much a welding issue as it is a design issue.

Pieces of metal such as this are routinely lifted in shipbuilding using electromagnets and other types of proper-sized rigging. Anything less when employees are in the area is not wise.


Good luck to all involved!

Big B
05-29-2006, 11:09 AM
gnm109 I'm sorry I missed the not, but what you said sounded like it came from an engineer. Just the voice of experience as a consultant, I guess. Sorry about the promotion or demotion ever how you look at it. Maybe you should have been an engineer.

welderjim
05-29-2006, 11:14 AM
its what i would call over engineering? a plate 4x8 normally use plate clamps and if you have to weld a lifting lug use a piece of similar thickness about 3 to 4 inch sqare with a hole in it weld one side with a 3.2 /4mm rod above 6mm fillet weld and it should lift ok and it can be removed with a hammer. now whats all the fuss about :cool2:

gnm109
05-29-2006, 11:49 AM
its what i would call over engineering? a plate 4x8 normally use plate clamps and if you have to weld a lifting lug use a piece of similar thickness about 3 to 4 inch sqare with a hole in it weld one side with a 3.2 /4mm rod above 6mm fillet weld and it should lift ok and it can be removed with a hammer. now whats all the fuss about :cool2:


I agree with all you say....except for being able to remove that with a hammer.......what size hammer? :) LOL


.

alan waters
05-29-2006, 12:06 PM
Gentlemen.............. I believe you have misunderstood my question. I'm not asking how to do it. I'm asking how much weld does it take to lift 1300 lbs? Safty is not an issue since we are not actually lifting.

TxRedneck
05-29-2006, 12:08 PM
Well I do dissagree with the hammer comment. If you put a weld on one side, you can pick some might big stuff up, and then knock the eye off with a hammer by beating it from the opposite side of the weld. Of course this poses the complication in rigging and handling, must be aware this same can occur by lifting it wrong. Always put the weld to the same side as the load force will be going. As far as whether as specific weights, wont even go there. If I have engineered drawings, no guess work. If not, I use my judgement and nobody gets underneath, but if someone must I put the eyes on right. I generally go overkill on the eyes if I think someones gona be under them.

welderjim
05-29-2006, 12:16 PM
Well I do dissagree with the hammer comment. If you put a weld on one side, you can pick some might big stuff up, and then knock the eye off with a hammer by beating it from the opposite side of the weld. Of course this poses the complication in rigging and handling, must be aware this same can occur by lifting it wrong. Always put the weld to the same side as the load force will be going. As far as whether as specific weights, wont even go there. If I have engineered drawings, no guess work. If not, I use my judgement and nobody gets underneath, but if someone must I put the eyes on right. I generally go overkill on the eyes if I think someones gona be under them.
I fully agree with all you say, just put it a bit shorter. lol ;)

TxRedneck
05-29-2006, 05:16 PM
I fully agree with all you say, just put it a bit shorter. lol ;)
lol no pun taken, lol

lotechman
05-29-2006, 09:27 PM
A quarter inch fillet can easily take a thousand pounds per inch on a straight pull.
I would run a one inch bead at each end of your lifting lug and take it around the edge at both ends. Make dead sure your lug is centered on the plate.... or dead might mean something else!
That is twice the weld you need but it does not take into account any twisting action. That is why you should return the bead around the end.
The 2 inch wide lifting lug is a poor choice of material. I would have used a 4 X4 inch or even 6 X 6 inch piece of 3/8th material to separate your two one inch beads at each end of the lug. ( don't forget the return)
A two pound hammer will easily knock off a 4 X 4 but it will be difficult because you selected a 2 X 2.5
Each time you knock the piece off and tack it to the next piece you will be putting in a worse quality weld unless you dress the end of the plate with a grinder.
A couple of months ago we were lifting 20 foot by 8 foot plates with a 6 by 6 lifting lug welded on one side with returns at both ends. As a fabricator I do not have time to make full size welds that I will have to gouge off later. Making small welds that can be snapped off is pretty standard.
Now comes the caveat! We were moving these plates into position and they rarely were more than a foot off the ground and no one was standing nearby. These minimal welds can be done but do not lift higher than you want the plate to drop and if you are clumsy with the crane and tend to swing your loads don't even consider such a tactic.
If you are lifting to transport or to place over people there are lifting lug specifications in most rigging textbooks. They have a PROPER safety margin.

alan waters
06-02-2006, 12:18 AM
Before I started welding tonight I looked at some parts a first shift guy had welded. After looking at the print I had to laugh out loud. The print called for .250 [1/4] inch all the way around. This guy had .530 [1/2 inch plus] all the way around. Now why is that? The engineer who designed the part most likely threw in a 25% safety factor. This is why I ask the question, how strong is a weld? I do believe most welders do not have a clue how stong a weld is. I have done a fair amount of destructive testing through the years. This is due to the "Just gotta know thing" Must have been born with it. The answer to the orginal question how strong is it? I really don't know. This I can tell you. I have lifted 1500lbs 3 inches off the floor with the 2 x 2 and 1/2 inch tab welded only on each end. Thats 3/8 inch wide x 3/8 high on two sides. How much smaller could I go? That is unknown. I don't intend to find out because I do not want to be anywhere close when to that much energy when it finally lets go. I encourage you to find out for yourself. Weld some scrap together and beat it apart with a hammer. You may be surprised.

alan waters
06-02-2006, 12:22 AM
Lotechman may want to share some of his experience in these matters.

ss42768
06-02-2006, 12:33 AM
I'm not an expert on AWS code specs, but I believe they call for a filet weld size of 75% of the base metal thickness. A lot of people will look at a 3/16" filet weld done on 1/4" and say "the weld's too small" When in reality that 3/16" weld if done correctly (travel speed, gun angle, stickout, etc; all correct) will hold a heck of a lot more than a weld that is way too large.

76GMC1500
06-02-2006, 02:13 AM
I would start with a plate a little thicker than 3/8ths, maybe 1" or so to give you weld some legs to give the eye strength. Weld up 3 sides of a rectangle and stop a little short of the end of the stock you are using to create notches. Notches are the breeding grounds for cracks, so when you strike it with the hammer it will hopefully crack the weld, making it easier to knock the eye off.

In engineering speak, tensile stresses are usually insigificant. Bending moments can contribute hundreds or thousands of times the stress generated by the tensile loading alone.

alan waters
06-02-2006, 11:04 AM
Like I said, No clue.

halbritt
06-02-2006, 03:59 PM
I'm not sure if it's been mentioned yet, but if one is welding mild steel and achieves proper penetration and bead profile, then the weld bead should always be stronger than the parent material. A36 is spec'd at 60KSI tensile and 36KSI yield (I think, that's from memory). Most filler metals used for mild steel generally run about 80KSI tensile and 70KSI yield with satistfactory elongation.

Ascertaining the weld strength of other materials such as stainless, alloys such as 4130, or aluminum takes a bit more engineering expertise. 4130, for example is usually welded with a filler metal that has lower tensile and yield strength but greater elongation that along with the dilution of the parent metal minimizes the potential for cracks and the need for pre-heating or post-weld heat treatment. Joint designs have to be adjusted accordingly.

zapster
06-02-2006, 06:16 PM
i'd just do what was needed 7018 5/32 @ 180-200 amps 'till it looked good to me..
maybe about 1/2 inch around on the corners only

but i would grind the weld area before hand..:angry:

and its not coming off with a hammer.....saftey first


is there any merit to this?

...zap!

zapster
06-02-2006, 06:45 PM
after going thru this again..

it would never happen over and over

lets see .."we'll just break this off (if you could) with a hammer and use it over and over..."


yeah right...

you CANNOT keep welding over and over on the same weld and expect to have it continue "sticking" to where anyone would be anywhere near this thing...

sorry

it aint happenin' without grinding the old weld off each and every time...

not if your working near me anyhoo...:realmad:


...zap!:D

lotechman
06-03-2006, 09:45 PM
Weld strength: First off: There is a much higher authority at your finger tips. If you ever want to learn about welding design go no further than the menu at the top of the web site and click on “columns”. Read all of Blodgett’s writings then move over to the Lincoln site and read his stuff there. If not satisfied then purchase his texts on welding design. They are straightforward, as is all their writings. The father has passed the torch on to the son.
Weld strength can be calculated a variety of ways. One way recounted to me was to apply a rule that a one inch fillet weld one inch long would be able to take a straight pull of 9600 pounds. A quarter inch fillet four inches long would take the same load. A thousand pound load would only need a quarter inch weld 0.41 inches long. From my experience, it is not far off the mark.
I have lifted a 20-foot by eight-foot plate one inch thick with a lifting lug in the middle. I would run a bead for the six inches along the side of the lifting lug. It took too long to remove after positioning so at the insistence of my foreman I was down to an inch at each end with returns. Using so little weld allowed us to simply take a sledge and knock it off with one or two blows. This lift was about a foot off the floor and simply set the plate onto a grid work of ribs.
I was sure we were going to see the plate drop the foot as it flexed over the length drooping like a piece of paper. The lugs never let go and we did over twenty of these panels over the months.

scsmith42
06-05-2006, 09:35 PM
Alan, interesting theoretical question. It seems to me that if you calculated the amount of square inches of weld surface area (where it attaches to your base metal), times the material strength of the weld metal (or the base metal - whichever is weaker), you'd have your number.

For instance, if you had a 1/4" wide contact patch on your weld, 4" long, then you would have the equivalent of 1 square inch of filler rod. If it's a 70Ksi rod, then you'd have 70ksi of theoretical gross weld capacity. However, if the base metal is 36ksi, then your max theoretical gross would be 36ksi for that same 4" weld, since the base metal's strength is the lowest common denominator. Therefore, a 1" long, 1/4" weld would have a max capacity of 9K, and your 3/8" weld would be somewhere around 4K.

Clearly there are other factors such as torsional loads, etc, and thus the in an actual application the welds should have a much greater safety margin, but I think that this comes close to answering your original "theoretical" question.

Make sense? Regards, Scott

halbritt
06-06-2006, 12:36 AM
For instance, if you had a 1/4" wide contact patch on your weld, 4" long, then you would have the equivalent of 1 square inch of filler rod. If it's a 70Ksi rod, then you'd have 70ksi of theoretical gross weld capacity. However, if the base metal is 36ksi, then your max theoretical gross would be 36ksi for that same 4" weld, since the base metal's strength is the lowest common denominator. Therefore, a 1" long, 1/4" weld would have a max capacity of 9K, and your 3/8" weld would be somewhere around 4K.


There wouldn't be a clearly delineated point where the filler metal stopped and the parent material began. The parent material is diluted with the filler metal which can have and additive or subtractive effect on the tensile, yield, and elongation of the parent material.