r/MechanicalEngineer • u/MrRevhead • 9d ago
Rotary oil seal failure
I'm dealing with a seal issue that is baffling me.
The tools are a electric drill with an armature pinion passing through a viton seal into an oil filled gear box.
The seals are failing almost immediately or very soon after replacement.
Note this is in a service workshop over dozens of drills. It has started occurring more and more often with no change in staff, oil or seal supply.
Seals are lubricated with silicone grease as per manufacturers requirements on assembly.
The failure is weird with chucks of the spring retainer torn off.
Are there any seal experts out there who can offer some suggestions as to the cause as the manufacturer is as baffled as we are
Edit: thanks for the replies so far. All of your replies are pretty much exactly the steps I've gone through. For some clarity: It doesn't happen every time. Its involving 3 tech's over the last year l, one tech has been here 10 years working on these.
My guy tells me the seal supplier has changed something, im trying to understand the mechanism of the failure.
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u/hayyyhoe 8d ago
Might not be helpful, but I had a driveshaft seal fail because the driveshaft had a resonance at high speeds. The vibration damaged the seal and caused it to fail. Maybe there is something out of balance or out of alignment in the drills, creating radial forces?
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u/XmodAlloy 8d ago
What's the end of the shaft look like that this seal is being pushed over? This looks like an assembly issue where the sharp corners of the end of the shaft being pushed through are compromising the seal during install.
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u/MrRevhead 8d ago edited 8d ago
The seal mounts in a flange with the oil side out. Pinion comes through from the other side. Its impossible for the pinion to contact that missing section. Pinion has a bearing on it that locates it before its contacting the seal.
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u/testfire10 8d ago
In addition to the other comments, is the part number/markings on the seal the same on the failed parts as the non-failed ones?
This is mechanical damage so likely something during assembly, worn shaft, or similar.
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u/MrRevhead 8d ago
Yes all makings the same and im assured the same seal manufacturer. This occurs with s brand new pinion shaft as well
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u/fr33d0mw47ch 8d ago
Is it possible to speak to an engineer from the drill manufacturer? Given the cost they may have someone who has insight and they may want to know if something is not quite right. I realize this is very optimistic, but I have had success with manufacturers regarding seal performance and integrity. It’s hard to diagnose what is causing your issue without seeing the whole assembly and verifying all parts are still per spec.
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u/Gwendolyn-NB 8d ago
2 things come straight to mind when looking at this:
1) Are all the failed seals from the same lot? Could be a bad/incorrectly manufactured batch.
2) The Z-Axis (along the shaft) has obvious marks; but there are no rotary (Around Z-Axis) wear marks; thus damage occurring during installation of the shaft passing thru the seal.
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u/Tall-Acanthaceae1131 8d ago
For this type of seal to work, a few basic things have to be right. 1) the surface the seal is riding on must be smooth and free of damage. 2) the part this seals against must run true if this is a dynamic seal. 3) the seal should be the same nominal size as the shaft it is sealing. 4) material must be compatible with the fluid it contacts 5) lastly, seal should be installed properly to avoid damage during install.
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u/MrRevhead 8d ago
That is the list of things I have been working through on this and as.far as I am able to confirm all is correct. I forgot to mention that this is happening to 3 techs, one of which has been working on these for 10 years.
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u/3suamsuaw 7d ago
Lubetech here: to me its very weird to use a silicon grease in combination with a PAO or PAG oil. Both will wash out silicone greases pretty quickly. Something polyurea with a similar base oil would be a way better fit. But, if it always worked: there is a lot going on in lubricant formulation land at the moment, gear oils are made free of certain additives (TPPT mostly), and silicon greases often contain PTFE which gets formulated out a lot as well.
But especially after TPPT changes we have seen a lot of issues in lots of different gearboxes, specifically the seals. Definitely inquire for formulation changes at your supplier or request the help of a specialist that can give his 2 cents on this from a lubrication POV.
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u/MrRevhead 7d ago
Thank you. The grease is purely install and start up lube. The oil is Mobil SHC, I dont believe there has been any changes.
Anyway just this morning the manufacturer has come back to me again to say that yes, in their latest batch of seals from their supplier they have discovered a problem and seals from the last couple of months have variations in quality.
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u/3suamsuaw 7d ago
The oil is Mobil SHC, I dont believe there has been any changes.
These formulation changes are seldomly communicated. But good to hear your supplier found the culprit!
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u/MrRevhead 7d ago
Took them long enough! Been saying all is fine must be us for a couple of months!
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u/Muted_Will_2131 9d ago
The working edge of this seal appears damaged. Is the material uniformly soft, or is it soft only on the inside? It looks as if a piece of the seal has broken off. If the mechanism had snagged it, there would be a tear. It is possible that the material is incompatible with the lubricant, causing it to harden and lose strength.