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Can nylon gall aluminum

Can nylon gall aluminum

Can nylon gall aluminum

(OP)
I am working an a design that involves a linear sliding interface.  One of the surfaces is 6061-T6 and the other is MDS filled nylon.

I chose MDS filled nylon because I heard it was good for bearing surfaces.  It turns out that the aluminum surface, which initially was smooth (~32), now looks like what can best be described as a galled surface.

Is it possible for nylon to gall aluminum?  What materials would be better than MDS filled nylon?  I can not use any lubrication nor can I use Teflon.

Thanks,

Kevin

RE: Can nylon gall aluminum

Is the aluminum anodized or anything?  If not I wonder if oxidation could be a contributing factor?

UHMWPE or maybe Delrin or some other acetyls like Pomalux might be worth a look depending on application.
 

KENAT,

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RE: Can nylon gall aluminum

Is your MDS filled Nylon perhaps graphite filled Nylon by mistake?

RE: Can nylon gall aluminum

(OP)
Sorry....the aluminum is not plated or coated.

I was going to try both Delrin and UHMW.  I think we have some laying around here.  I'm not familiar with Pomalux.



 

RE: Can nylon gall aluminum

(OP)
MintJulep,

I suppose it's possible.  I bought it from Mcmaster.  They have made mistakes before.

 

RE: Can nylon gall aluminum

need to look at your loading density, ie too little surface area

RE: Can nylon gall aluminum

Delrin would tear itself up, you'd be better off with a HDPE, UHMW or Nylon for wear.

Look at what Igus is doing, they've got great information on their bearing materials and wear characteristics with different shafting materials.

James Spisich
Design Engineer, CSWP

RE: Can nylon gall aluminum

Nylon should not gall aluminum.  However if it were graphite instead of MDS then you would very likely have anodic corrosion of the aluminum, which might look like galling.

RE: Can nylon gall aluminum

(OP)
MintJulep - How long do you think the anodic corrosion would take to cause an issue?  The damage occurs in less than two hours of operation.

Kenet - We have not ruled out contamination. After the first test there were aluminum particles as well as a few very small machining type chips laying around.  The orientation is such that any particles shed fall away from the test surface.  I know this may be hard to imagine without a picture. The test surface is near the upper most portion of the machine.

Thanks for the ideas so far.

 

RE: Can nylon gall aluminum

(OP)
The actual numbers are 11300" at 70"/min. This works out to 161 min ( A bit longer than my initial guess).  It runs along a path that is about 27" and then returns over and over.

RE: Can nylon gall aluminum

I have never actually seen MoS2 filled nylon. It has always been a mixture of MoS2 and graphite. as MoS2 does not work as a lubricant when embedded in nylon but graphite works very well in that regard. The MoS2 actually helps by acting as a very effective nucleating agent and creates a much higher level of crystallization and a much finer crystal structure in the nylon. This crystal structure (however it is achieved) gives a harder smoother bearing surface.

The best plastic to use as a bearing is very dependent on a number of factors, including the nature of the opposite surface, lubrication, cooling, speed, pressure and cycle rate.

Hard anodizing the aluminium would help a lot. Even a bit of water as a lube can help. unmodified nylon might do better. Are you sure your nylon is not glass fibre reinforced. The presence of glass fibres certainly gauls aluminuim. I have never seen molly and graphite filled nylon gaul aluminium in the past, but I have only ever used it in contact with aluminium in piston buttons to hold gudgeon pins in place where the circlips are prone to fail. This is hot, bathed in oil and has little motion against the aluminium surface. I suspect glass fibre is present in the nylon.

 

Regards
Pat
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RE: Can nylon gall aluminum

Ohhh..

MoS2+ graphite + aluminum = battery.

The MoS2 acts as an electrolyte and the aluminum corrodes.

 

RE: Can nylon gall aluminum

Neat nylon has been under-rated as a structural, wear resistant material. Two experiences with major projects were solved with neat nylon.

RE: Can nylon gall aluminum

I agree with plasgears and note that a highly nucleated grade makes a better bearing for the same reasons as MoS2 filled.

Bar stock is unlikely to be nucleated. Fast cycle injection moulding grades are nucleated, but may be difficult to get in the size and numbers you require but it's no big deal if you can't get it unless the nylon part fails.

Nylon 4.6 or Stanyl is a better bearing than type 6 or 6.6 and is inherently crystalline enough to not need extra neucleation, but is a lot more expensive and not justified unless you have a failure with the others.

Regards
Pat
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RE: Can nylon gall aluminum

Just a gentle thought, why are we concentrating on the nylon, rather than wondering why a sliding joint uses aluminium anyway? I know if you anodize it you can get some hardness and wear resistance into it, but, frankly, like the Cornish villager said to the tourist when asked for directions, If Oi wanted to get there Oi wouldn't be starting from here.
 

Cheers

Greg Locock

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RE: Can nylon gall aluminum

As has been suggested I would look at commercial solution from someone like IGUS or trstar.

Is there any reason you don't want a bearing grade of teflon?

UHMW as many have said is a good solution. It can be found in tape form for a quick test. It could also test the galvanic corrosion theory.

Hard anodized AL parts can also be treated to reduce friction.
 

RE: Can nylon gall aluminum

There are some companies that can apply Teflon to your aluminum surfaces.  We used this for potting tooling, where a plug was need to create a recess in potting.  It was a nice coat and it was pretty flexible too.

RE: Can nylon gall aluminum

(OP)
Wow...thanks for all of the feedback.

Some quick replies.

Teflon is ruled out because it is considered a contaminate in one of the environments we will operate.

That IGUS tool is awesome.

It is quite possible our loading PV is too high.  I will follow up with that.

We must use aluminum because of weight.  Hard anodizing while not optimal for us is not out of the question.

I'm not sure if the material I used contains graphite.  The only description given was 'MDS filled cast nylon 6'.

MinyJulep - You mentioned corrosion caused by the combination of materials.  Would this be a factor in just a couple of hours?

 

RE: Can nylon gall aluminum

I don't know.

You've got all the parts - do a test.

RE: Can nylon gall aluminum

one of the drawbacks of Mcmaster is that you don't know what you are getting. Try to get an MSDS for the material from them. That would list some of the ingredients. For production go to a regular supplier that will give you the details of what you are buying and you can complain if they switch grades or brands.  

RE: Can nylon gall aluminum

UHMW should be your first choice as a liner way bearing material on Anodized aluminum.

MDS filled Nylon would never even be on my list, neither would 6061 in a T6 only condition.

Use UHMW and anodize....  

Charlie
www.facsco.com

RE: Can nylon gall aluminum

cobra46,

"Teflon is ruled out because it is considered a contaminate in one of the environments we will operate."

Wow!  That's a weird operating environment.  One of the most desirable properties of PTFE is that it is the single most chemically inert and stable substance known to mankind.

As for filled nylon galling aluminum, that's what you would expect if debris is present in the contact area.  The bits of debris embed themselves into the softer nylon surface and then abrade away the relatively harder aluminum mating surface.  The aluminum surface exhibits the wear patterns since that is the joint component that is sliding relative to the debris particles.  The nylon does not exhibit wear patterns since the debris particles are easily embedded into its soft surface.

You need to find the source of the debris.  Nylon is corrosion resistant and chemically stable, so I doubt it's the source.  Aluminum on the other hand, oxidizes very readily, and aluminum oxide is a very hard and abrasive compound.

Good luck.
Terry

RE: Can nylon gall aluminum

If you want to get fancy, coat the aluminum with diamond like carbon.  We've done this before.  www.entegris.com  If it is just a corrosion issue coat the aluminum with Whitford's Xylan 1010 (Don't bake over 325F).   Of course, Xylan is a fluoropolymer based coating which you can not tolerate.  If you want to look at other polymers I would suggest a PPS.  Try Techtron HPV.  I've had good luck with it in high PV loading applications.

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