questions about my arc welding

[Paul.]

Belting welds with a big hammer is of very limited, if any use for weld testing, as Richard has said controlled testing methods,using properly prepared specimens such as bend tests, nick break and macro etching, or for sheet butt welds cupping tests, these can all be easily be carried out at home and in the small workshop, and if you learn what to look for will tell far more about weld quality than any amount of hammering.
Keep the sledge hammer for knocking in fence posts, and use a bit of thought for the weld testing

http://www.mig-welding.co.uk/wiki/Weld_Testing

 

[Kent]

Hey, you have the science way and the farmer test. As most know science tells us a bumble bee cant fly and most farmers will tell you they blooming well can when you mow over their hive

To be fair breaking in a big tool room press has been a test on many jobs over the years, its just a big hammer is so much more useful for other tasks. Its called destructive testing IMO its better than some guy spouting waffle about what is best

BTW fence posts are knocked in with a big Rubber sledge which it no good for testing welds or a fence post ram connected on a tractor (now there is an idea)

 

[rich r]

Bumblebee flight was fully modelled and understood in the late 1980s. It's a bit of an urban myth that physicists didn't understand it. It's all about vortex shedding off the trailing edge

 

[PTvor]

IIRC, the statement was made in the 1920s and was along the lines that according to aerodynamics as understood then, mostly applying to planes, a bumblebee shouldn't be able to fly because its wings were too short. It was something of a lament about the poor state of knowledge at the time.

 

[Jan]

There are currently 3 different theories on how & why anything can fly - as long as it can fly. None of them agree with each other in many fundamental details and yet all 3 appear to explain the physics of flight. Engineers and physicists have chosen to agree to disagree for a couple of decades as neither can explain or prove which, if any, explains the real truth.

In barn workshop practice most forms of sophisticated testing are impractical. Does any one here have home access to a metallurgical X-ray machine? an ultrasound machine? a 10+ton press? I sure as hell don't. You might just have the time to cut a section, grind, polish and etch it to examine the microstructure of the grain. But isn't it quicker and just as effective to simply bray seven bells out of it (preferably to a precisely guesstimated degree in excess of its in-use stresses) and see if it holds up? And if it doesn't then closer examination with a hand magnifying glass it can be enough to help explain why it failed.

 

[Richard.]

I don't recall any of the last posts suggesting x ray, UT, as you say not practical. Ten tonne press again not a suggestion and not practical. Bend testing along the face and the root is a practical and effective way to determine how the joint holds out under strain and permanent deformation. Hitting it with a hammer is not an indication to tell how well your welded joint holds out under strain . It's a completely different type of force. Last time I was down at TWI I did not see the guys in the test house wacking joints with hammers.

 

[Kent]

Whacking something with a blooming big hammer is entirely realistic, The only steel structure I know of that failed was hit multiple times with a fork lift. To be honest no its not scientific but it is realistic. Actually I showed a client a bad weld someone had done in the past on a job just a few days ago and told him were it would fail and how quick, it had to come off anyhow and three good smacks and it did I was proved correct, the other previous work on the job was total top notch and I told him I had a gob on my hands just removing those with grinders and cold chisel.
The first thing that was impressed on me was "welds should not fail only the material directly adjacent to them" , it might be un scientific in the eyes of others but has stood me in good stead and I shall continue to bray hard on anything I wish to test to destruction.

 

[Richard.]

Ok I'm interested now so just a few questions.
At what point would you decide the weld is no good?
Do you measure in number of bats to break or size of hammer it takes to break it?
Where do you wack it to carry out the test?
Do you carry out this form of testing on all joints or certain ones?
For a weld that is designed to be put under a consistant load of say 2 tonnes, would you test this in the same way?
Cheers.

 

[Jan]

There is hell of a difference between static stresses and dynamic ones! Put a lot of torque on the 'other' end of a welded bar and the metal may bend before the weld lets go, but if it sees a lot of shock stresses in normal use the weld could be the part to give way first.

Example: A cast iron manhole cover can take the weight of a 40 odd tonne trucks driving over it for years, but hit it with a sledgehammer a couple of times and it will shatter into multiple pieces. Yes, I know that's all down to the microstructure of the material, but it's just one way that different stresses can cause unexpected consequences. In automotive applications static stresses are only a fraction of the problem. In the aerospace industry dynamic stresses cause more headaches than beer has been since man started drinking the stuff! Just ask DeHavilland!

 

[Richard.]

Yes, this is spot on different applications are put under different stresses so any testing carried out should represent as close as possible what stresses the joint is going to go through. Bend tests, sharpys, nick break even hardness testing are all application or joint dependant. They are not all practical but in my opinion the ones that are will give me better results than more brutal methods used. Just my opinion though if it works for some people great.

 

[Kent]

Ok I'm interested now so just a few questions.
At what point would you decide the weld is no good?
Do you measure in number of bats to break or size of hammer it takes to break it?
Where do you wack it to carry out the test?
Do you carry out this form of testing on all joints or certain ones?
For a weld that is designed to be put under a consistant load of say 2 tonnes, would you test this in the same way?
Cheers.

When it busts, especially if it broke with inclusions evident in the break (generally one expects a near weld break not a weld break at all)
No just belt it till it beaks or you give up trying
Depends, normally were I feel I might do it most harm
No just when I want to test an aspect, I doubt client should except twisted, bent and narled up work
No it should be done as lifting gear with a measured overload if it such as I think you mean, other than that test joints and blooming big hammer

I don't recon this will become an officially excepted testing procedure, though people have been doing it for a long while before we had specialised gear in industry. Its also very good for those learning and practicing new stuff. Its not even something I do monthly, just something I do if there is any doubt about anything I am about to try. I have had one weld fail on an actual job a long,long time ago, it was a fault in the metal - this highly scientific big hammer test should have picked it up as it was no harm was done and the only embarrassed person was my old boss who was penny pinching on unknown materials. Low Hy rods and preheat sorted the job, you just couldn't MIG this pipe as he intended, so the penny pinching cost more in time in the end.

Nearly all small Fab shops do not have proper test gear but they all have big hammers or similar things that can break stuff and lads that are rather good at and seem to enjoy busting stuff especially if somebody else welded it

 

[Kent]

Yes, this is spot on different applications are put under different stresses so any testing carried out should represent as close as possible what stresses the joint is going to go through. Bend tests, sharpys, nick break even hardness testing are all application or joint dependant. They are not all practical but in my opinion the ones that are will give me better results than more brutal methods used. Just my opinion though if it works for some people great.

All very good if you have that stuff on hand but some test is often better than no test

 

[dannyp]

a 10+ ton press is easy aquired they arnt that special.

if you hve a good vice weld a short bit of flat to a piece of angel thats held in the vice, to the bit of flat weld a large leaver and pull it round by hand.

tho cutting a weld giveing it a quick sane a a drop of weack nitric acid will soon show how your doing