Shaft seal, anodizing, re-surfacing

[spike7638]

Hi. In previous visits I've gotten remarkably good advice on some tricky (for me!) problems, and I've some back to the well, so to speak.

I've got an assembly in which an inner cylindrical piece (diameter 40mm, or about 1.6") of anodized aluminum revolves inside an outer collar, with a couple of bearings and two grease-seals. The anodized surface on which the seals ride got marred, and I'd like some advice on how to deal with this.


Here's the setup. I've made a rough cross-sectional drawing of the assembly:

Here are the two main parts, lying on their side:

When I separate them, you can see that the surface of the smaller piece on which the bearings and seals ride got somewhat damaged by an aggressive 'helper' who tried to remove some snap-rings with the wrong set of pliers. The surface of the collar also got damaged a bit (by me this time!), but that's less of an issue.

The picture above shows two deep grooves (in which the snap-rings fit) and one shallow groove to hold a thin plastic ring that shields one of the seals from the elements (that end of the inner piece is the one that points upwards when everything is assembled). Just to the left of the left deep groove, you can see where one of the seals 'rides', a slightly lighter color. A little bit farther to the right of the right deep groove, you can see the track of the other one. And you can see in each case that the tracks go over some damaged area. (The left one doesn't look bad...but that's because you can't see the other side.)

This isn't an ordinary shaft-sealing kind of application: the assembly spins about 20 turns, twice a day, at a speed of perhaps 300 RPM, i.e., it turns for a little more than 3 seconds, twice a day.

I'm considering various alternatives:

(a) continue smoothing things out with emery cloth until it feels pretty smooth to the touch, and hope that a combination of thick grease and the spring on the seal-lip will do the job

(b) clean the exposed areas with acetone and/or xylene, then smear the area with JB-Weld, and then remove the excess with emery cloth to get a nearer-to-smooth surface

(c) turn down the damaged area by a thousandth of an inch or two, clean well, mask everything else, and try to re-anodize the newly-exposed metal, and trust to the spring in the seal to absorb the reduction in diameter.

Any thoughts, suggestions, better alternatives?
I'm at best an amateur machinist, so if it involves welding aluminum, etc., I'll need to get a pro involved.
Thanks in advance,

--John

 

[Nutfarmer]

it depends on the end use and how critical a part it is. Most of the damage looks like it is from disassembly not wear. If it was in an easy accessible area on something like my farm equipment I would smooth it out by sanding it and see how it holds up. If on a critical application say on fire equipment I would replace the unit.

 

[spike7638]

it depends on the end use and how critical a part it is. Most of the damage looks like it is from disassembly not wear. If it was in an easy accessible area on something like my farm equipment I would smooth it out by sanding it and see how it holds up. If on a critical application say on fire equipment I would replace the unit.

Thanks...that's a good point. The damage is definitely from disassembly, not wear. It's not in a critical application, but also not all that easily accessible, so it'd be nice to 'do it right' if at all possible -- there's at least a couple of hours of work involved in extracting it to examine things.

 

[Canus]

Does this unit use grease or oil? Look up the seal and find its inner (where the seal contacts the shaft) dimensions. This will tell you how much you can remove from the OD of the internal component and still allow the seal to function. Then go with option (a). If necessary you may be able to find a new seal with a slightly smaller ID to compensate for the material removed from the internal part.

 

[Cadillac]

I’d clean it up with precision bench stones so it would only take off the high spots. It would not remove existing anodizing which is good. Reassemble and go with it.
I don’t think you can spot treat anodizing.

 

[paradox_pete]

Not knowing the application, it's hard to make a recommendation; however based on your explanation, I'd probably try to find a sealed version of the specified bearing and not worry about the lip seals. Based on their orientation in the drawing their purpose is to keep oil or grease in rather than contaminants out....

 

[spike7638]

Does this unit use grease or oil? Look up the seal and find its inner (where the seal contacts the shaft) dimensions. This will tell you how much you can remove from the OD of the internal component and still allow the seal to function. Then go with option (a). If necessary you may be able to find a new seal with a slightly smaller ID to compensate for the material removed from the internal part.

It uses grease. But it's aluminum, and with exposure to sunlight it presumably grows and shrinks a bit, so without a decent seal it might tend to squeeze some out (and/or suck some rainwater in, which is what worries me).

 

[spike7638]

Cadillac: using stones makes some sense
paradox pete: sealed bearings would give me an extra layer of defense, which would be nice. I'd been pretty carefully trying to replicate the original, but perhaps technology has improved in the 25 years since this was installed (and in the more-than-30 years since it was designed!)

Much obliged to all of you for these ideas.

 

[Mill Lee farm]

Separately, if you’re worried about corrosion of the aluminum where the anodizing was scratched off you can use an Alodine pen (Chromate conversion coating) they’re quite expensive, so it really depends on your thoughts on weather exposure etc.

Henkel Aerospace 592939 Gold Bonderite 1132 Touch-N-Prep Pen, 4 oz Tube https://a.co/d/7yPyG0s


I second the idea of precision ground stones. They are perfect for just this kind of thing. Just taking off the high spots. How big are the scratches? Can you fill them with superglue maybe?

Apologies if you already know, but make sure you get a dual lip seal and fill the seal groove with some good grease before assembling everything. Grease inside the dual lip can help on longevity

Of course there’s always a speedy sleave… then you have a fresh seal mating surface. I’m not sure you need to go that far though…
Also, they’re steel so they’ll be prone to corrosion as well

REPLACEMENTKITS.COM Brand Shaft Wear Sleeve Repair Kit Fits .873 - .877 shafts Replaces 99087 https://a.co/d/8myyWWp

 

[tq60]

Assuming the only chemical inside is the Grease for bearings so the damage inside may not matter.

Speed is slow, with no pressure other than from expansion, so as others stated, use a stone to take off high spots.

Now, find a good razor blade.

Hold the edge of the blade against the surface, parallel to the shaft at the places where damaged.

Hold it over a lamp to see light through the low spots.

A couple options.

BURNISH the area around small imperfections, more light will pass but the seal may still work.

EPOXY can be used, but not the box store kind, there are good ones, not cheap.

We have some made for repairing HVAC condenser and evaporator coils, aluminum and high pressure, just what you need.

Clean with acetone.

Mix tiny amount and work into the scratches.

It takes a day or 2 to fully cure.

The razor blade can be used to plane off excess before fully cured, then you need to get it smooth.


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