I am faced with the task of welding a ductile cast iron gear to a mild steel shaft. The shaft is approximately 2 inches in diameter and the gear is about 3 inches long and 3 inches outer diameter with bore to suit shaft. We have available GTAW, SMAW, GMAW and FCAW if suitable wire is available. This is not a repair, but new material and we have about 80 units to do. Can anyone suggest a process and procedure that will produce sound welds and minimum distortion?
Thanks Dave
Dave,
The weld you're willing to do it's impossible. Cast iron, whether ductile or gray, doesn't accept structural welds (and this is one), but only repair welds.
Generally, gears are fixed to their shafts by means of a key. Have you thought of this possibility?
Giovanni S. Crisi
Sao Paulo - Brazil
This might be useful to you: we recently had a project requiring A36 rings to be welded to ductile iron pipe. The electrode was Inco Alloys NI-ROD 44. This is available for GTAW or GMAW but no longer for SMAW. We used GMAW with 75% Ar / 25% CO2 and it ran OK for us. The welds were not the smoothest and there was quite a bit of spatter so that might be a concern for you. I don't know how well it will hold up under conditions normal for a gear but.............
The Technical Support number is 800-624-3411 and you might want to contact them. I did and found them to be helpful.
Hope this helps
CHGuilford
By -
Date 11-09-2001 21:09
You might stand a chance of making a decent weld if you use very high pre-heats. (Around 500 - 600°C)
When using these high pre-heats you can use a standard E7018 electrode, although I would still use an electrode dedicated to welding cast irons. (e.g. ENi-CI or simmilar)
Cooling down following welding should also be done very slowly. Best in an oven, but might possibly work if it cools down in an insulation blanket.
As your gear is small, the high pre-heats should be workeable. The obvious problem would be slight dimensional changes on the gear and shaft following cooling, due to the high pre-heat temperature. Only you would know how tight the dimensional tolerances are.
Regards
Niekie Jooste
Ok. I have some exp. in Cast iron. Since its the ductile kind..you are in better shape. First and formost, when welding cast iron...you must have it CLEAN CLEAN CLEAN. A good rod to use is Versaloy Plus. You can weld all farous metals with this. The tensile strenth of this rod is low around 50-60psi. So its similar to cast. In my mind and what i have been tought Versaloy is the best thing to use when welding cast. As well as NI rods.
Clean your pieces first with a SS wire brush the best you can...set the pieces up to be welded and tack them lightly.
Next start preheating. as you are preheating. stop and clean it again with the wire brush when its warm 150-250 degrees...Heat it a little more and do the same thing...heat it again..and do the same thing do this a few more times. Each time bring it up like 50-100 degrees more and clean again...all the way up till you reach the right preheat level. about 550-650 degrees. Then do it one more time.
The reason for this kind of prep work is that Cast is very porous and traps a lot of contaminates. By preheating and cleaning you are opening up the pores and releaseing contaminates to be cleaned off with a SS wire brush.
Once at the preheat level you can begin welding. When you are welding you have to maintain the constant temp of 550-650 range, this is critical...because cast is very prone to cracking. So be sure to maintain that temp range all through the welding process.
once you are done welding you have to post heat cast, you can do this with a torch or an oven if you are lucky to have on big enough for your pieces.
The post heat ....a rule of thumb is to bring the cast down to room temp or under 200 degrees... 1 inch of thickness per 1 hour. If you have a piece that is 2 inches thick..it will be 2 hours, and so on.
Bring you piece down slowly...this will take time...but it will make the weld as sound as possible...
To me welding cast is pretty easy ...Versaloy Plus is a awesome rod and the beads come out looking flawless...Practice a few rods on some mild steel to get the hang of it....In the flat position its kinda like 7018 maybe a little bit different...not much
The actual process of welding cast is only about 10% of the situation. The prep work and post heat are the other 90% To weld cast the right way, you have to follow these steps.
Dear Dave
INCO ALLOYS CO. suggest its NI-ROD 44 (A5.15: ERNiFeMn-C1) electrode for this case.
This electrode has the advantage of having a thermal expansion coefficient closely matching that of cast iron. Because of it, high solidification stresses are not placed on the partially melted HAZ of cast iron during solidification, and subsequent solidification stresses are reduced.Consequently the need for preheat is diminished.
However this electrode can experience weld-metal cracking (transverse to the direction of welding) or as centerline cracking only under condition of high restraint and when dilution exceeds 30% (i.e., the weld deposit obtained more than 30% of its volume from the cast iron).
Best Regards
By -
Date 11-13-2001 17:50
Just a thought here, on the welding of cast iron without (or low) pre-heats.
Essentially there are two overall tactics to welding cast iron:
1)Try to minimize the HAZ brittleness.
2)Try to minimize the size of the HAZ, so that even hard, brittle microstructures do not lead to such a big problem.
The first tactic requires very high pre-heats, and subsequent slow cooling, and has the "potential" to result in a weld that matches the properties of the base metal. I place potential in "" because you really have to experiment a bit to get it right.
The second tactic requires low or no pre-heats. Here the HAZ of the cast iron is very brittle, but due to the narrow HAZ, its effects are minimized.
As the weld that is proposed is to be a "structural" weld, the second tactic will in all probability not be very successfull, irrespective of the filler used. This is because the cast iron HAZ does not know what filler was used. It only knows what temperature, heating and cooling rates it sees. The filler used will only have a substantial effect on the weld metal itself.
If the purpose of the weld is merely to locate the part, or to seal it, then the second tactic would be adequate.
The other big issue with welding cast irons is that of impurities. One of the other respondents made a mention to this with the suggestion of grinding the first run off. Usually this tactic is good, but is only really feasible under repair situations. What I suggest under these circumstances (repair) is to weld on your first bead. Then try to "chipp" it off with a chipping hammer. If it stays on, then you do not have any substantial contamination problems. If it comes off, repeat the procedure till it no longer comes off. This situation is usually only helpfull where the contamination was from external sources. If you have a "dirty" casting, you can do just about anything and you will not get a satisfactory weld. The worst contaminants being P and S.
All the best
Niekie Jooste
Dave, one thing our weld instructor does when welding cast iron (if possible)...after thoroughly cleaning the surface to be welded, he runs a bead on the cast. Next he grinds all the weld out and cleans it up again. He says it pulls impurities out of the casting, improving your chances of a successful weld. Charles Hall
By -
Date 11-13-2001 17:53
Have you considered brazing? I think that it will give a much better result. As long as the clearance between the shaft and gear is not too large, the strength of this joint should be just as good as the base metal properties.
Regards
Niekie Jooste
