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Rustybolt
11-22-2006, 09:42 PM
I was always taught that ,in stressed parts, that you weld along the axis not across it. My employer today has caused me to question my instincts.
He welded a table out of 2x2x.125 tubing that is going to hold a 600 lb vibrating bowl. All the welds are butt welds with no ground grooves. Most of the welds run accross the long axis. Welded mounting plates are welded all the way around. The mounting plates are square. This guy loves to weld and is very proud of the fact that he never has any 'training'
While the bowl is only 18 inches off the ground I still don't want anyone to get hurt. Somebody tell me I'm an old worry wort.

Dawai
11-22-2006, 09:55 PM
Hey, I got one of them air vibrators they put on bulk train cars to unload them.. I was plannin on using it on a magnaflux table... but??? It'd make a vibratory cleaner from heck.. lil hard on the compressor thou..

Is that how this one works?

I could mount it on a chair, imagine I was riding a harley?

I could put it on the bottom of the sandblast pot and keep it shook down..

I could make a earthquake machine by timing it to the resonant harmonics of the bedrock under my place?

Yeah, I'd worry when it breaks.. I got crappy welds done by sound everywhere here.. Some look good.. some are beautiful right there next to the seam.. It don't take a whole lot of 10,000psi rod to hold something forever..

barts
11-23-2006, 01:09 AM
Well, if this is an inertial shaker on the bowl, there's not a lot of
load on the table as long as the rubber mounts let the bowl move
freely. If the motor is mounted to the table and drives the bowl
w/ an arm, look out; I've seen that kind of ag machinery try to
tear itself apart.

I'd worry far more about the frame geometry than the welds.
With a correct geometry for the loads involved, weld strength
will be a minor concern.

Rustybolt
11-23-2006, 09:11 AM
Well, if this is an inertial shaker on the bowl, there's not a lot of
load on the table as long as the rubber mounts let the bowl move
freely. If the motor is mounted to the table and drives the bowl
w/ an arm, look out; I've seen that kind of ag machinery try to
tear itself apart.

I'd worry far more about the frame geometry than the welds.
With a correct geometry for the loads involved, weld strength
will be a minor concern.


Yeah they are inertial shakers with variable controlls. It's just a frame with legs. No bracing. Dispite the rubber mounts we lost a small one(200 lbs) when a bad weld in a leg let go. We got the table back to the shop and all the leg welds were cracked. We could knock them off with a hammer, and we did. I think were gonna systematically get all of the tables he welded back to the shop and stiffen them up. Ya need a liscience to buy a gun, but anybody can buy a mig welder;-)

It's a major concern to me because some of these bowls have feeders attached that are six feet tall and hold a tub of parts. Some of the tubs can weigh a ton. Almost all of the machines have somebody close by.

dicks42000
11-23-2006, 09:49 AM
Rusty;

It sounds to me like your employer is setting himself up for failure here. Several factors come together. As said the "geometry" of the joints is probably suspect for the application. I'd prefer to call it the design or lack there of. As you say, the welding ability & lack of joint prep. are suspect too.

While I don't like seeing large amounts of time wasted doing stress analysis on a workbench or stand, common sense & caution would dictate some understanding/ calulation of the joint loading, appropriate bracing and good weld proceedure in cases where the public/ employees could be injured.

In weldment design, welds are assumed to be capable of resisting loads of "X" lbs. per inch of weld for a given fillet size. This is assuming a sound weld using the appropriate rod, weld prep. (gouging, grinding....) pre/post heat etc. as dictated by the material. If your boss (the "weldor" ???) is ignoring some/ all of these aspects, then he's setting himself & the job up for failure, as you have already mentioned; let alone not allowing the welding process achive what strength it can. Why would someone be proud of a lack of training ? Given all the info. available about welding, you can see it's a vast field with lots to learn. Geez, some of it is even interesting and can make you a better ( and more profitable...) weldor. Take a little course or read a book.

If the legs of the stand are subjected to any torsional movement or racking forces, bracing is needed. Heavy loading of the tub may also require diagonal bracing of the "table to legs" variety. Adequate vibration isolation might also be a factor here, but that's another field of mechanical engineering.

Sounds to me like you already know the welding is suspect. Can you weld stick or mig ? Check out the Lincoln handbook for the relavent rod/wire/prep/proceedure or ask Torker or one of the other pro's on here. Weld it yourself & put the boss to shame, if necessary. Maybe get a raise. :)

HTH

wierdscience
11-23-2006, 10:29 AM
It's called contraction stress and that table if the parts were butted up solid and welded is full of it.

When the weld contracts while it's cooling there must be somewhere for that stress to go.Otherwise it will
A: pull out of the base metal(crack)
B: crack the weld itself
C: warp the weaker part
or D: all of the above.

Gap welding is the prefered method,the parts would be fitted up with a gap equal to the rod diameter if stick welding ,wire you would take 1/3 the material thickness in gap and bevel down to that either side or from the one side depending on access.

If the material is thick enough to require multiple passes ALL passes should be run in the same direction.If you ran one pass left to right,then the next pass right to left there is a good chance that the second pass would fracture internally due to the opposing contraction stress.

That table would best be gap welded after a local pre-heat to 450-500f.That would give you the best chance of it being a sucess without stress relieving it.

tattoomike68
11-23-2006, 10:45 AM
The problem I see is the .125 wall tube , thats ornamental iron in my book. It may be fine if you are building a swingset for kids or a hand rail.

Rustybolt
11-23-2006, 02:17 PM
Rusty;

It sounds to me like your employer is setting himself up for failure here. Several factors come together. As said the "geometry" of the joints is probably suspect for the application. I'd prefer to call it the design or lack there of. As you say, the welding ability & lack of joint prep. are suspect too.

While I don't like seeing large amounts of time wasted doing stress analysis on a workbench or stand, common sense & caution would dictate some understanding/ calulation of the joint loading, appropriate bracing and good weld proceedure in cases where the public/ employees could be injured.

In weldment design, welds are assumed to be capable of resisting loads of "X" lbs. per inch of weld for a given fillet size. This is assuming a sound weld using the appropriate rod, weld prep. (gouging, grinding....) pre/post heat etc. as dictated by the material. If your boss (the "weldor" ???) is ignoring some/ all of these aspects, then he's setting himself & the job up for failure, as you have already mentioned; let alone not allowing the welding process achive what strength it can. Why would someone be proud of a lack of training ? Given all the info. available about welding, you can see it's a vast field with lots to learn. Geez, some of it is even interesting and can make you a better ( and more profitable...) weldor. Take a little course or read a book.

If the legs of the stand are subjected to any torsional movement or racking forces, bracing is needed. Heavy loading of the tub may also require diagonal bracing of the "table to legs" variety. Adequate vibration isolation might also be a factor here, but that's another field of mechanical engineering.

Sounds to me like you already know the welding is suspect. Can you weld stick or mig ? Check out the Lincoln handbook for the relavent rod/wire/prep/proceedure or ask Torker or one of the other pro's on here. Weld it yourself & put the boss to shame, if necessary. Maybe get a raise. :)

HTH



I'm pretty good with a Mig welder. I at least know how to prep a joint for welding and recognize what a good weld joint is supposed to look like. The other guy in the shop is pretty handy as well. When left to ourselves we usually weld a coupon out of the material we're going to use and then try to break it. Only after that will we go ahead. We both have been blamed for making weldups "too complicated" and wasting material.
The boss is too young and full of himself to ever take anyone elses advice about this.He's not ignoring anything. He never knwew it to beguin with. What he ignores is any advice on how to do it right.I'm too old to worry about someones feelings when safety is an issue.
Well. Screw it for this long weekend. I'll worry about it on monday. Thank you guys for the input. I learn something here just about everytime I log on.Something else to be grateful for. have a good turkey day.