Does the area where the weld separated from the sprocket appear to have fractured (1) "Under" the weld, At the EXACT junction of the weld metal to sprocket, or in the weld metal only? IN addition to the questions by Lawrence
What is the thickness of the sprocket and tube?
Had you change any parameters, materials, techniques, or people prior to this occuring.
Here are some thinks that you could consider however since there are few details these may be all wrong.
1) 1045 Steel could show underbead cracking depending upon preheat, process, and thickness. The lower the carbon the greater the weldability . If you have an option to use a lower carbon steel and there is not a reson to use 1045, CHANGE .
2) It the tubes are thin compared to the sprocket and the welding parameters have been set too low, lack of fusion on the thicker piece could occur. Directing the arc at the thicker piece with higher parameters could improve fusion with the thicker piece.
3) Surface contamination including mill scale could be a problem if not removed.
4) If this is performed manually and the travel speeds are high, slight variations by the welder could cause areas of non fusion.
Well let us know . More info will follow by others .
Have a nice day
Gerald Austin
Again, thanks for the info so far. I have listed a few things that I know so far, more to come today. Thanks again!
In addition the suggestions already provided, you should check the actual chemical composition of the new sprockets and the old ones (if you have one). Chemical analysis can be done fairly inexpensively by most local materials testing labs. The problem you described sounds like you may have a material mixup or substitution from the supplier, which is not uncommon for commercial grade materials. Also, check the sulfur content of the steel when you have chemical analysis performed. Sulfurized steels (free-machining) are commonly used for high volume machined parts because they can be machined faster, but the sulfur content is usually too high for welding. This could also cause the problem you described. You want the sulfur content to be around 0.030 wt.% or less for welding.
We have the opportunity to change to 1035 steel, which we can still induction harden the teeth to Rc40. The 1045 had inductioned hardened teeth to Rc 45-52. We know the 1035 will weld better, now there is a concern about the teeth at Rc40 being the same hardness as the roller chain. We have heard that as a general rule you want your sprocket teeth to be harder or softer than the chain rollers. Any thoughts? I don't know this to be absolutely true, but it makes some sense.
I've heard it for bearings, that one part (usually the journal) should be harder than the other for best wear. It is said that this is more wear resistant than both hard. This is hearsay and should be treated as such.
Bill
I can see some logic behind having the journal harder then the bearings. This allows for foreign objects to embed into the bearing and not scratch both surfaces and bearings are usually cheaper and easier to replace then a worn journal. An example is in car engines with the use of soft babbit bearings. On a sprocket, what ever part is cheaper and easier to replace, should be softer.
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