Copper Grease in Fractional HP Gearbox

I'm thinking nano boron

Our profit margin on these requires the solution be effective but more importantly...cost effective (cheap). I am concerned that the copper grease will work beautifully but cost too much to be implemented :-/

Drew K

I'm thinking mechanical misalignment and not lubricant could be the problem.

It could be, but the alignment is within the tolerances we can achieve. We don't make space shuttle parts here, I am just trying to get consistent gearbox survival to the 250k life cycle tests. I have frequent spring failures and gearbox seizures and get severe resistance from the overlords when I suggest drastic changes (like improving the design of the spring).

Drew K

I would use a lighter oil, not grease at all....and perhaps a different bearing structure or material...

What caused the oil to leak out of the gearboxes and and saturate the shipping boxes?

Was there less component damage when using this oil?

If so, can you revisit this arrangement with a focus on seal and gasket improvement / modification?

Pre swelling prior to tightening may close the gaps?

Quote from my benevolent overlords: "Gasket!?!? What do we want to spend money on gaskets for? They have worked for 30 years without gaskets!"

The head Engineer is a very good designer and manufacturer and likes many of my solutions but we get significant push back at any drastic changes. I think we are fighting some large egos and a presence of mind that if we change anything we will loose customer loyalty...which is backed up by the fact that there are some customers who insist on the same product we have discontinued marketing because of improved versions being released.

I submitted a great redesign for the spring failure problem only to have it shot down because such a radical change would admit that we (they) had designed it wrong 30 years ago and our customers should go to the competitor.

Why is it so hard to find a job where I can be creative and inventive and appreciated?

Drew K (is frustrated...sry for venting)

I think the historical success with it was partly due to inconsistent or a lack of analytic lab analysis. The lead engineer was a one man show and acting re-actively to developing and manufacturing problems. It feels like whenever we point out a problem we get "well it has worked for 30 years just fine".

From our modern observations going back to before my management of the lab they could not have been working so well for the last 30 years. Some of the records I have reviewed show that the greased gearboxes last significantly longer than the old oiled ones and without the mess.

We know what the best design improvement is and really want to develop a planetary gear system like what some more advanced competitors use but good engineering doesn't always beat excessive ego.

Drew K

Aha, we get to the crux of the problem....You're being restricted by aging infrastructure...You need more leverage than lubrication....haha

Well something in this great, 30 year old design has changed. It now fails during shipping. Identifying the root cause of the failure (manufacturing alignment, raw material QA, etc.) would be my approach to solving this. Then and only then can a cost effective solution (if one exists) be found.

See my above reply to Solar.

Drew K

Just put one of the gearing assemblies on the desk of the defiant one. Maybe he will get the point.

Or: talk to his boss.

I was thinking of something like a nylon gear myself, but even this may be too much change for Drew to overcome?

If torque requirements are low enough, and it appears that it may be, why not try having the gears cut out of teflon. May be slippery enough that you no longer need any lube.

That is the idea with trying to develop a planetary gear system. The reduced forces on the gears allow for more efficient (and cheaper) materials. We just need to defeat or retire the egos and convince the overlords...might as well wish for raises too :-/

Drew K

correct me if I'm wrong the sintered gears have been leaking and saturating the shipping boxes for years. Someone want to correct this. They changed the gears and changed to grease. Now your trying to select a grease that is light enough to let the gears work properly but will not leak out and stain the shipping box.

The overlords upstairs are reluctain to make any changes. Like sealing the gear box with a gasket. But they must have approved the change in the gears.

Seems to me you got a product that works. Must sell okay. Therefore the overlords reluctance for change. And all you had to do with the old gear box with the sintered gears was bag it before placing it in the shipping box.

Note RTV sealant to seal the gear box.

I'd look at Delrin^® or even Nylon^® gears.

They can be had off the shelf for pennies.

Teflon^® may be too soft.

A marine grade grease based on aluminum complex thickeners and not lithium can be better for such a case (better adhesion and waterproofing) But keeping grease quantity low can be very problematic in a box of so much empty space. S.M.

If it was me I would gasket and seal the damn thing so that it can hold a normal lower viscosity synthetic grease or oil and rebadge it as a million cycle gearbox instead of a 250K cycle gearbox and bump the price up by a factor of 3!

Maybe a worm drive and a delrin gear

That might seem good for the ratio involved, but not easy to back-drive with a spring.

Cycloidal design might be interesting, but perhaps too expensive.

In Drew's picture, I wonder if a larger shaft and bushing would help on gear 3. In the drive train shown, each successive reduction entails slower speed, greater torque, and greater shaft radial loads.

Too much back drive resistance on a worm gear system.

Drew K

Original comment removed, too costly and too effective for such a company!!!

what is the application for this box??

It operates a 2 or 3 inch plastic drain valve.

Drew K

Where did the leak happen, at the shafts or at the joint between the body and the lid? I assume between the body and the lid; therefore, something must have changed with either of these two surfaces. Sealing with no gasket depends on these mating surfaces being flat; did something change that altered this? Fewer fasteners? The wall of the body looks pretty thin for this type of seal; did "they" reduce it to save metal?

There never was any kind of seal. They just let it leak with the thought that the leaking oil was excess and acceptable.

Drew k

Yet somehow the competition has a better product.. Oh my

Careful application of some type of form-a-gasket and oil inspection after X cycles or time? Or when the form-a-gasket starts leaking?

Is the box a standard one or a proprietary design?

If a new tool for the injection cast box is not needed and if you can bring a quantified proof that the new design will be less costly and bring a better margin as well as reducing the troubles and if the original designer is not the company owner then you can have a chance.

I read all the posts.

Where does the leak occur? At the shaft seal(s) or case? A simple low tech press cut gasket is unbelievably cheap. Thank you China. They are so cheap we sometimes order them rather than make them, even for prototype work. A thirty year run seems to imply that you could buy a few at a time.

If it is a shaft seal, there are about 1000 solutions off the shelf., unless your bearing lives in an unusual seat. Why would that be the case? How long is 250K cycles in days?

I love it when you can make something and sell it for a good profit, and every person around wants to improve it. Classic war of ego over enthusiasm. Maybe you could make it cheaper, so that it made more profit. I suspect that was the original reason you were hired. Making it last longer so they can sell fewer may be defensible in the mind of the engineer, but ludicris in the mind of the owner.

No, I was hired to quantify the durability of the product. As the world moves on, customers want a product that is more durable. The problem is we have to optimize a product that has already been optimized for cost; so we need to make it better without making it more expensive.

The leak is no longer the problem, the current problem is premature failure.

Drew K

If you keep doing what you always did, you'll keep getting what you always got.

Identify whatever is failing prematurely and fix it.

I'm still in the plastic gear camp. Cures any stray current problems, and fretting.

Doesn't it fail because of the leak, resulting in insufficient lubrication, caused by changing lubricants, driven by a desire to get it to last longer, which it would do if you could use lighter lubrication oil that did not leak?

Which type of failure ?

Fretting occurs when the sliding amplitude is greater than the elastic surface deformation under friction forces.

Fretting can be avoided there where you cannot use an optimal material pair by introducing a lubricant which cannot be expelled and even as traces can offer a low friction force. Such lubricants are of solid nature as graphite or MoS2.

If failure is at the bearing level then my suggestion (plastic bushing) could be for a very low price the solution, if the failure is at the gear teeth level the solid lubricant can be the solution if you are not allowed to change the tribological condition.

What you should do is first define the problem and its origin which seams not to be yet clear.

If he had only one problem this would be trivial. It seems to me that at least two problems exist. The easy problem is the mechanics. The hard problem is the corporate politics. While both realms may have multiple roots to their problems, navigating safely through corporate politics can be much more difficult.

I agree with Nickname, and with redfred. It is one thing to change the lubrication, quite another to change administrators minds.

I suspect as in the photo he provided, Drew K has fretting on the gear mounting pins (which also serve as bearing surface, and is wearing the gear).

If the testing conditions in plant, do not match the use of the gearbox (opening and closing a valve) in the field, then they need to change how they are cycling the gearbox during testing. Are they doing testing at a range of temperatures? It might be that fretting will occur at some cold temperature if the lube cannot be brought back into contact, and that at warmer temperature there would be no failure.

If the expected temperature service range matches the test conditions, then surely failures as these will show something statistically that could be a great clue how to proceed with the changes in lubrication.

I am testing on the valves that we make the motors for. They are used in commercial laundry mats worldwide. The motor / valves are generally in warm to hot conditions, my lab setup is not quite like how they are used in the wild. I place the valves on shelves and cycle them rapidly only allowing them to fully open and fully close before cycling again. I know the rapid cycling is abusive to the gearboxes and would expect to see fewer failures in the field.

The problem with management is greater than I am willing to fight. They have moved me from Engineering to Quality Management...now I am looking for a new job. The Senior Engineer I was working for is an excellent Engineer, and a superb leader; the Quality guy is not an engineer at all and a deplorable manager with zero leadership skills.

Anyone hiring?

Drew K

You have my sympathy.!

A little advice: "Don't jump horses in mid-stream, or you could end up all wet!" This came from my dad who was a boiler man/fireman on a Navy cruiser. He was a tough old sea dog for true.

Maybe you should actually consider turning up the heat and humidity in the test lab, especially when that loser orifice boss of yours comes around. His last name isn't Trump is it?-Just kidding, Donald, but you had that one coming after all the recent name calling.

I do not share your opinion since if lubricant is cold his higher viscosity makes expulsion more difficult and adherence to walls is bigger so that spurs stay and friction does not go as high. If temperature is high the situation is exactly the opposite and risk for wear goes up.

May be the test frequency is too high and this can destroy the lubricant film also due to local temperature peaks. As long as we do not have a detailed description ( with as many pictures as possible) it will be difficult to pinpoint a cause and a solution.

Could it be possible to have more details so that the specific loads can be at least estimated? Unfortunately tribology requires more than only a qualitative analysis.

This looks more like simple corrosion from lack of a good coverage of an oil of high enough viscosity, and one that has some suitable anti-corrosive properties.

Here you do indeed have two dissimilar metals in contact (and in motion) in a moist environment. One is going to lose (and be the anode). Put a voltmeter on it, and see which one. The one with the positive lead when the DVM shows a + reading is the cathode. example: copper/saltwater/magnesium Copper is always the + electrode in that system, although the anode is magnesium, and the magnesium definitely is corroding away.

I agree. This looks like galvanic corrosion problem to me, but I'm just an EE.

If it was my job to solve this problem I would just search for a replacement COTS Delrin or other plastic gear. Then I'd run the cycle test that produced this corrosion on a gearbox with only one plastic gear and the other metal gears. Then I'd examine for corrosion after the cycle test. Depending on the mechanical load the plastic gear will see the external loads (valve & motor) may have to be altered just for this proof of cause test.

If instead my job was to perform only the quality control test of the old design, I would document a vast quantity of mechanical measurements of the unassembled pieces prior to testing, after assembly, and after this cycle test. I would then perform an analysis for a correlation between any of the before and after measurements. You may have to also perform an alloy analysis of the gear and spindle metals to look for counterfeit materials.

All the pictures above are of the same shaft, before and after cleaning with a soft cloth. There is no moisture present in this gearbox. There was a build-up of the fretting debris when I took the lid off the gearbox that only fell away when I forced the gear off the pin.

The picture with the blue lines are from notebook paper (to give you a little reference). I was using usb magnifying camera.

The pin is hard steel with no chrome I think they are .09 inch.

This gearbox sat on a shelf in the warehouse and cycled until failure. This is from a test last summer and I don't see how even the most humid summer could condense moisture inside a hot gearbox that is cycling 2 seconds on and 2 seconds off for about a week.

My suspicion is that in fearing too much grease causing back drive problems we have not used enough grease and are using the wrong grease which is why I thought of using an anti-seize.

I have been told that we might use a dry moly grease, but never got the email with the details.

Drew K

I would not waste any further time on it then. Get the dry moly lube going!

Part of fretting is the corrosive loss of metal, in this case, apparently iron which when finely divided will oxidize to red iron oxide in air. The corrosion product appearance gives rise to more wear, more corrosion due to the fretting.

Put something in there that gets in the way of fretting, and/or isolates the metals that are at different galvanic potential. Corrosion also happens in humid "non-wet" air.

About the only place it will not happen is (1) no motion, or (2) no air !

http://machinerylubrication.com/Read/693/fretting-wear

See figure 4 in the above link. frequency matters!

http://www.hindawi.com/journals/tswj/2014/919518/

Another link you might find interesting.

The loads are maxed out at the outputshaft at 10 to 14 inch pounds.

Drew K

Thanks for the pictures it will help, some more data: shaft diameter since specific load is the required parameter and if possible the rpm of the concerned gear.

Where is located the massive wear with respect to gears center lines (its angular position)?

The first feeling is that the gear is not only loaded by forces but also by a moment and this load is the most nocive. The concerned gear is too narrow and the gearing forces lead to a moment which leads to too high peak pressures at the rim.

Is the shaft chrome plated? This is what I fear looking at the worn area (picture 11).

Where is taken picture 13 ?

If I would have a sketch with the gears diameters, the real relative position of their centers and also the distances between front and back gears it would be possible to estimate the radial and friction forces on the shaft.

Does the wear always appear at same locations along the shaft?

How do you run the test ? How many turns for the concerned gear pair in one direction per cycle?

It is a very interesting problem you have and it deserves a serious treatment

In specific reference to fretting, high viscosity lubricants are the most likely to be pushed out of the way by vibrating, jittery motion. This is the diametric opposite behavior of lubricants operating with smooth continuous motion, where the lubricant is continuously drawn into the loading bearing surface zone.

Look it up, I didn't make this up.

Has anyone bothered to measure the electrical potential between the middle pin and that gear. You seem to be having a galvanic corrosion issue there. Perhaps the real issue to be solved is how to prevent so-called fretting corrosion.

If oxides of the harder metal are being removed by friction, this allows further oxides production on the microscopic scale, does it not? Perhaps an oil soluble calcium soap type grease would solve this. Don't ask me how.

The corrosion you see is something new to me. It is called fretting and can be very destructive in this situation.

Drew K

I think fretting can be seen on large pump shafts where there may be leakage current from the motor (3 PH induction motor, typically). It can also simply be the result of improper relationship between the hardness of the two surfaces in frictional contact.

Has the gear pin or the gear changed in composition? Maybe the sintered metal gears did not experience this problem as they were softer relative to the pin? I don't know.

Obviously, if you do anything to the new parts, you increase complexity, and cost.

Found this....

http://www.machinerylubrication.com/Read/693/fretting-wear

http://www.vanderbiltchemicals.com/product_categories/category/petroleum

I am going to try to get them to let me use this dry moly film lubricant.

Drew K

You will notice the PDS says not to use this in a chlorine atmosphere. What pray tell, will be found in a commercial laundry? Bleach. Bleach will always produce some chlorine vapor (fugitive emission) in air with hot water, so good luck with that.

Just test your gearbox with this lube first, with known levels of chlorine exposure. You can actually buy chlorine gas standards (they are meant for calibration of chlorine gas sensors used in industry). OR you could just overtreat some really hot water with bleach and sours.

That is good to know, because we also make pumps that are used in the pool industry and if this lube had worked we would have used it in all our gearboxes...back to the drawing board :-/

Drew K

How about Krytox grease then. It's not cheap but if they insist on not changing gears then this should work.

Red: you have the right idea here. I think Drew might want to opt for this over the Moly lube. Since a tiny bit goes a long way on Krytox, I think they can suffer the price.

As long as we're blue skying things, how about a Teflon spray like MS-122.

MS-122 Dry Lube | Contenti

Long time ago, they'd send a free sample can for evaluation.

Of course, that will turn out the be the best idea of all, since it is a known, and has worked for about a Century by now.

It is disassembled to clear the doubt about an oil soaked felt pad attached to the top of the gear.

Got to this thread late... busy looking for a new job :-/ but what about an aluminum-bronze gear (Ampco 18'ish)? Could experiment with additional lubrication... a dry moly, silicone, or even paraffin -based lubricant at assembly if you need a little more life than the non-lubricated Ampco would give you.

And sorry if this has already been mentioned, I skimmed thorough all the responses kind of expediciusly and didn't see it.

"You say I started out with practically nothing, but that isn't correct. We all start with all there is. It's how we use it that makes things possible." -- Henry Ford