Galling/Seizure of Ductile Iron Shaft
Galling/Seizure of Ductile Iron Shaft
(OP)
I am investigating a rash of failures that involves a rotating, ductile iron shaft seizing in an aluminum housing.
The belt-driven shaft rotates on several cast aluminum journals. Seizure is occurring at the journal closest to the drive belt.
Examination shows a galling pattern ~3 or 4 mm wide and located 1 or 2 mm away from the edge of the contact surface that extends all around the cast iron journal. The mating cast aluminum journal contains a corresponding pattern with a build-up of ferrous debris, presumably from the iron shaft.
The shaft is composed of pearlitic ductile iron (~90 HRB); the aluminum is an aluminum-silicon alloy similar to A319. The system is lubricated with motor oil.
There is no indication that any contaminants entered through the oil feed hole of the affected journal.
Any suggestions for what to look at next?
Thanks,
BergiusMaximus
The belt-driven shaft rotates on several cast aluminum journals. Seizure is occurring at the journal closest to the drive belt.
Examination shows a galling pattern ~3 or 4 mm wide and located 1 or 2 mm away from the edge of the contact surface that extends all around the cast iron journal. The mating cast aluminum journal contains a corresponding pattern with a build-up of ferrous debris, presumably from the iron shaft.
The shaft is composed of pearlitic ductile iron (~90 HRB); the aluminum is an aluminum-silicon alloy similar to A319. The system is lubricated with motor oil.
There is no indication that any contaminants entered through the oil feed hole of the affected journal.
Any suggestions for what to look at next?
Thanks,
BergiusMaximus





RE: Galling/Seizure of Ductile Iron Shaft
The excentric load on the bearing generates a non uniform pressure distribution with a peak on the side where the load acts. If the shaft diameter is bigger there are several positive aspects:
- shaft is more rigid so that the pressure peak can decrease
- the contact area is bigger and the pressure decreases but
- the sliding speed encreases in the same ration
- a bigger area with the environment will reduce the thermal resistance and allows a lower temperature
It could be possible to reduce the effects by use of a higher vicosity lubricant or with high pressure additives.
RE: Galling/Seizure of Ductile Iron Shaft
Another curisotiy, in this case you believe the shaft is softer material than the shell?
For sleeve bearings, there are conditions necessary to establish minimum film thickness. Stribeck's number S = mu * N / P needs to be kept above a minimum value , where mu is viscosity at operating etemperature, N = speed, P = load.
There are plenty of design charts available that address these factors. Maybe you can find some on google. If you post the shaft diameter, oil viscosity grade, estimated operating temperautre, speed in RPM, bearing length, and load we can get a rough idea fromt those charts.
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RE: Galling/Seizure of Ductile Iron Shaft
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RE: Galling/Seizure of Ductile Iron Shaft
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RE: Galling/Seizure of Ductile Iron Shaft
Jim Treglio
RE: Galling/Seizure of Ductile Iron Shaft
I do not know how much will cost the sputtering of WC but the best solution is to use the right combination of materials and give the right harness differences between the 2 surfaces.
The iron used is soft and the Al2O3 layer is hard so combined the higher temterature due to the too high load, the reduction in film portance due to the lower viscosity and the presence of hard particles lead to the galling.
As usual a wrong start leeds to expensive repairs.
The normal relationship is : hard shaft and soft journal ib this case it is inverted.
RE: Galling/Seizure of Ductile Iron Shaft
But I agree that usually we see a hard shaft and a soft bearing shell. As far as I know, I think the main reason is that it is usually much easier to replace or machine a removable bearing shell than replace or machine or buildup the shaft.
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RE: Galling/Seizure of Ductile Iron Shaft
to work the cutting edge has to be harder than the piece which turns.
It is exactly what happens in the analysed case.
In an assembly shaft + bearing it is expected to have the contrary: i.e. the not rotating piece should wear first.
RE: Galling/Seizure of Ductile Iron Shaft
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RE: Galling/Seizure of Ductile Iron Shaft
RE: Galling/Seizure of Ductile Iron Shaft
RE: Galling/Seizure of Ductile Iron Shaft
RE: Galling/Seizure of Ductile Iron Shaft
In determining which surfaces to coat, consider the following: For a 'hard-soft' bearing system, coating the softer of the two surfaces will extend the life of the system. However, the harder a substrate material, the more effectively the lubrication will perform.
Generally speaking, the coefficient of friction will be slightly higher if both mated surfaces are coated than if only one surface is coated. However, wear life will increase if both surfaces are coated.
So, you will have to determine which is more important: longer wear or greater efficacy in lubrication.
Let me know if you need help with coatings. Because, that's what I do.
William
IndustrialCoatingsWorld
RE: Galling/Seizure of Ductile Iron Shaft
I'd forgotten to include this link:
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Good luck!
William
IndustrialCoatingsWorld
Hi.
In determining which surfaces to coat, consider the following: For a 'hard-soft' bearing system, coating the softer of the two surfaces will extend the life of the system. However, the harder a substrate material, the more effectively the lubrication will perform.
Generally speaking, the coefficient of friction will be slightly higher if both mated surfaces are coated than if only one surface is coated. However, wear life will increase if both surfaces are coated.
So, you will have to determine which is more important: longer wear or greater efficacy in lubrication.
William
IndustrialCoatingsWorld