Splined Shaft Wear
Splined Shaft Wear
(OP)
Folks,
Here's a photo album of the splined shaft from my hydraulic pump. The interior splines of the mating PTO are identically worn.
I'm in the process of identifying the steel, but I believe it to be a high tensile steel (4140 or 4340). My apologies for not being able to narrow this down just yet.
Wondering if these wear patterns tell a story to the metallurgists out there?
https://pi casaweb.go ogle.com/d mb2000/PTO PumpSpline s?authkey= Gv1sRgCNSl oqW9qonCaQ
Thanks,
David
Here's a photo album of the splined shaft from my hydraulic pump. The interior splines of the mating PTO are identically worn.
I'm in the process of identifying the steel, but I believe it to be a high tensile steel (4140 or 4340). My apologies for not being able to narrow this down just yet.
Wondering if these wear patterns tell a story to the metallurgists out there?
https://pi
Thanks,
David





RE: Splined Shaft Wear
RE: Splined Shaft Wear
I notice that when looking at a spline tooth in the radial direction, the wear is curved; i.e., there's more wear in the center then the ends - the center is knife edge while the ends still have machine marks on the top edge of the tooth. Is this fretting or load imbalance or something else?
David
RE: Splined Shaft Wear
I see blue tint that is suggestive of overheating, but photographing bright metal surfaces is difficult. Brownish-red, which can be well attached to the surface, indicates fretting wear, a.k.a. fretting corrosion.
RE: Splined Shaft Wear
There is evidence that there are several other factors at play.
Have you fully investigated the possibility of misalignment as there is evidence that there is a non-uniform load distribution along the teeth flanks?
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Splined Shaft Wear
Aaron Tanzer
www.lehightesting.com
RE: Splined Shaft Wear
Let me get the PTO cleaned up and I'll post some detailed pics.
David
RE: Splined Shaft Wear
Thanks,
David
RE: Splined Shaft Wear
Based on both albums, this looks to me like adhesive wear where sliding contact is causing material transfer, in this instance on both sides. This mechanism generates friction and heat, accounting for the apparent heat tinting. In the spline pictures, the wear marks suggest relative movement was in the radial (as opposed to axial) direction. Could there be too much slack in the fit-up between the spline and the PTO?
Check out Systematic Analysis of Gear Failures by Lester E. Alban for a more detailed description of gear adhesive wear failures.
Aaron Tanzer
www.lehightesting.com
RE: Splined Shaft Wear
Fretting failures tend to be self-perpetuating. With splines, there is always a small amount of debris generated due to boundary contact conditions and relative motion. Unless this debris is flushed away from the contact interface it simply acts like an abrasive, causing further surface degradation and friction.
As brimstoner noted, there also appears to be some possible evidence of overheating. The initial fretting damage can lead to increased friction, and if the relative spline motion is significant enough it can overheat the materials, leading to loss of temper/strength.
Hope that helps.
Terry
RE: Splined Shaft Wear
When new is there any rotational play in the coupling?
If they are loose to start with then this happens faster. A very thin coat of a thick synthetic grease will slow this down, but if they don't fit well it will eventually happen.
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Plymouth Tube
RE: Splined Shaft Wear
In real life the metal also has a blue tint, so heat is definitely a factor.
It's not a VFD. The pump hangs off a PTO which is mounted to an Allison transmission with a heavy duty diesel engine as the prime mover.
In a different thread we did an analysis of compressive and shear stresses and found that the spline is undersized for the torque and expected lifetime involved.
My plan is to take the easy route and go with an upgrade from an SAE 'B' to SAE 'BB' shaft (7/8" to 1"). The problem is that the constant mesh PTO is known to have issues with motion in the output shaft. I'm looking into PTO alternatives.
If I had my way I'd go with an SAE 'C' shaft with wet lubrication, but as it stands returning lubrication fluid from an SAE 'B' or 'BB' shaft to the transmission, unfiltered, doesn't seem prudent.
I apologize for the tangent, but thought you might enjoy some background.
Thanks,
David
RE: Splined Shaft Wear
I've been selling Chelsea PTO's for about 20 years now and the shaft wear has been an issue for several years. From what Chelsea engineers are saying, the newer engines have a torsional vibration that causes the wear... I think that is certainly a portion of the problem, another being so much off shore product coming to North America in recent years, the quality of product has decreased...
We recommend pulling the Pump back from the PTO as a yearly maintenance and apply new lubricant. Chelsea Part # 379688 is what the Chelsea people recommend, sorry I don't have technical specifications on that...
I've found the best solution is to go with the DIN5462 PTO output, but depending on your location, the support for that maybe limited. Chelsea output designation "XY" and of course, I'd need to know the pump model to give the part number for it, if even possible... Sadly, Chelsea doesn't offer the SAE C shaft with the B mount on the 277/278 series as of yet...
If you can let me know your application then I can toss some recommendations, not sure if going to an electric over hydraulic shift would help or possible...
I'm not an engineer, just been around and broke enough stuff to know enough to be dangerous... I just found this thread as I was searching for information on a SAE BB shaft twisting and how much torque is required to do that...
RE: Splined Shaft Wear
I'd like to see the proof that they have to make such claims.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Splined Shaft Wear
You'd be better off to run the coupling dry.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Splined Shaft Wear
90% of all truck mounted hydraulics are not specified by engineers, but by parts guys and ordered by owner operators, they look for the cheapest solution... If it was me designing this, the pump would have the SAE BB or DIN shaft...
I'm not a fan of the wet spline, another leak point... The greasable shaft is available but most people use the wrong grease or never grease them anyway...
I will see what I can dig up on the Lubricant supplied with the PTO...
RE: Splined Shaft Wear
It can get so bad that the coupling loses the ability to handle any misalignment.
The combination of dried grease and debris can become so hard and tough that the only way it can be removed is with a chisel and hammer.
You might as well assemble the spline with a handful of lapping compound.
If you can't regularly insert new grease; then adding any grease at all is a recommendation that, IMO and experience, will only cause the joint to fail sooner.
A specification for a once per year application is just plain silly.
It's a poor attempt at a remedying the problem and is often used as an excuse (lack of lubrication) for covering up the fact that the spline joint is simply under rated.
Once again, show me the proof to the engineer's claims of torsional vibration being the cause of failure.
We design and build dry spline connections for 600Kw rock crusher shafts that are driven by diesel engines...........now there is a good example of torsional vibration in a system.
The only reason why these splines wear out is as a result of misalignment because of poor fitting practices.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Splined Shaft Wear
" bonded coatings containing MoS2, surface pressures up to the yielding point of constructional steel are possible."
Kluber Microlube GL261 survived in our 8000 rpm spindle's spline drive for the life of the spindle, making disassembly possible and even the re-use of the parts sometimes. Previous lubes did not protect against wear so the parts would be found seized solid with fretting debris.
It would not surprise me if Kluber had other products that they might recommend for your application.
BMW motorcycles maintenance includes re"grease"ing the various splines in the driveline every now and then. Some years have plated splines in an effort to fend of corrosion and allow longer re-lube schedules. For a while BMW recommended the Microlube, but a klingy product called Wurth Sig 3000 is earning respect and gaining popularity on some BMW and similarly spliney MotoGuzzi enthusiasts' boards.
RE: Splined Shaft Wear
There is no fix for a bad design.
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Plymouth Tube
RE: Splined Shaft Wear
Adhesive wear occurs on sliding surfaces when pressure between the contacting asperities is sufficient to cause local plastic deformation and adhesion. The energy absorbed from the plastic deformation takes the form of heat - hence the blue heat tint observed. The process feeds on itself because the heat softens the surface increasing amount of adhesion and increasing plastic deformation. Eventually the process results in galling, where there is relative movement between the shaft and PTO. The wear marks on both surfaces indicate galling. The wear marks also indicate a radial direction of galling wear contact between the teeth (and not axial).
The mechanism is consistent with a coupling that is inadequately designed to handle the applied load. This root cause may mean a larger shaft/coupling may be required to handle the applied load and prevent initial plastic deformation. The mechanism could also be consistent with a root cause involving inadequate lubrication in the sense that that an appropriate lubricant and maintenance cycle could have the potential to prevent local plastic deformation and frictional heating involved in formation of the adhesive wear mechanism in the first place. Finally, the issue here could be a root cause from the combination of both factors - both inadequate design and improper lubrication.
Aaron Tanzer
www.lehightesting.com
RE: Splined Shaft Wear
RE: Splined Shaft Wear
But I believe that the large amount of fretting that has taken place is not the root cause.
The fretting appears to have occurred as a result of initial wear.
A decrease in tooth thickness, as a result of wear, causes an increase in backlash. Increased backlash in a system that is experiencing torsional vibration will increase the risk of fretting due to the impacting nature of the contact.
"Adhesive wear occurs on sliding surfaces"
While I agree with this statement, the statement isn't really adequate to help explain what it is that's going on in a splined joint.
Keep in mind that, in a properly aligned splined joint that is fixed, there would be no sliding contact. The contact is compressive in nature only.
Sliding contact in a splined joint will only occur if there is any misalignment between the mating components.
Angular misalignment generates a small oscillatory movement, between mating spline teeth, which traces the path of a figure of 8.
In the initial stage of damage; these small oscillatory movements generally result in some kind of fretting taking place but the amount of fretting, at this stage, rarely results in any form of destructive damage. A good example of this can be seen on the crowned/barrelled teeth of a gear coupling.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Splined Shaft Wear
I agree that this spline has suffered from severe fretting erosion, and you give a fairly good explanation of the situation. However, for fretting damage to occur there does not necessarily need to be sliding contact. Fretting damage can also occur from excessive cyclic contact loading, where two faying surfaces come in and out of contact. This type of fretting damage is common on the OD of rolling element bearing races that don't have a proper bore fit. I can imagine a similar situation occurring at the spline tooth flank contacts, where extreme torsional oscillations cause the flanks to come in and out of contact.
The mechanism behind fretting is basically a repeated process of diffusion bonding and breaking between contacting metal surface asperity tips. Over numerous cycles, this results in a transfer of material from one surface to the other. The surface that loses material has the typical pitting seen with fretting. The metal diffusion bonding effect that causes fretting can be inhibited by providing a surface film that is non-reactive, such as oil, grease, plating, dry films, etc. (picture trying to MIG weld two pieces of steel that are greasy or oily). Unless these materials are continually replenished at the contact interface, they no longer provide protection once displaced.
Interesting topic of discussion.
Terry
RE: Splined Shaft Wear
I still think the mechanism of damage at the time the spline was removed was adhesive wear. But I also see the scenario where problems started under fretting. Roughening of contact surfaces and the presence of fretting debris could have provided the asperities to then created nonuniform loading across the contact surface, starting the adhesive wear process outlined previously. This mechanism then predominated from the relatively large displacement contact.
Under this scenario, fretting actually would be the primary failure mechanism (adhesive wear/galling were secondary since they would not have happened without fretting first occurring). We really do not know the relative direction of movement between surfaces during the fretting phase because subsequent radially-oriented galling obliterated that evidence. Using this scenario, issues which could cause fretting contact during service (including alignment and design) would need to be examined. However, fretting situations are not corrected through lubrication because the lubricant film simply is displaced by contact unless lubricant can be continuously applied. Fretting can be reduced though by applying a hardening carburizing or nitriding surface treatment.
Finally, you may want to consider having metallurgical analysis performed of the worn spline to confirm failure mechanism(s). Microscopic examination of both the damaged contact surface both directly and in cross-section can better illuminate whatever happened.
Aaron Tanzer
www.lehightesting.com
RE: Splined Shaft Wear
Please explain what in the metallurgical analysis what evidence one would be expecting to visually find?
Gearcutter
"if the correct size spline coupling is installed" & if periodic maintenance is done like greasing with with Zerk fittings, I believe this would help the situation. this is done for automotive drive shaft splined connections. as long as the connections are sealed correctly. High velocity shafts are sealed units with grease.
I can see if the the unit are open to the environment, adding grease is like adding an attraction for dust, dirt debris, which is like adding sand or lapping compound.
Would it not depend on the design of the unit.
at first I thought maybe this post was getting a little long but now I realize there's more to this post. it's a sleeper issue.
nice going every one, it's a very Interesting & great responces by all.
Mfgenggear
RE: Splined Shaft Wear
First one should look at the loaded tooth faces using a stereobinocular microscope. All of our opinions are based on macro photos but binocular views may tell a different story and in any case will provide more detailed information on wear mode as well as some confirmation that discoloration around the damage is in fact consistent with fretting debris. It is also easier to differentiate fretting from galling wear at magnification.
A cross-section through a tooth will also be useful. Microstructure will be able to show differences between the contact surface and the matrix. One indication of adhesive wear involves plastic deformation at the contact surface. You will also be able to see if the contact surface shows a rehardened layer (such as untempered martensite) and adjacent plastic deformation of the structures, both consistent with adhesive wear. Fretting usually does not affect surface structure because the particles abrasively machine away the surface. Etched structure will also show whether the spline had been given a carburizing or nitride hardening treatment.
The cross-section should also be used for microhardness testing. Specifically, hardness should be measured by the surface both in the damaged area and in a non-contact area (such as a tooth root), in the middle of a contacted tooth, and in base metal away from the teeth. This information will shed light on the failure mechanism by identifying work hardening (if any) associated with wear, surface hardening of the as-manufactured spline (for example, from carburizing), and possible softening that may be found in the teeth that may have also occurred from wear.
Aaron Tanzer
www.lehightesting.com
RE: Splined Shaft Wear
Excellent comments. I don't have any formal training in metallurgy or tribology, so I'm learning something from your posts.
Just one comment about the presence of red iron oxides. The pictures of the internal spline seem to show significant rust outside the area of the spline flanks. It looks like the whole spline joint was exposed to moisture, and moisture penetration may have been the cause of the iron oxide on the flank surfaces.
With grease lubed splines and bearings, moisture can be a problem even with a sealed environment. If there is sufficient air volume and humidity within the housing, repeated heating and cooling cycles can cause the moisture to condense out onto surfaces and wick into gaps like those between the spline teeth. Ideally, grease lubed splines should have some sort of dam or shield that keeps the grease tightly packed around the spline joint to minimize such moisture intrusion.
Terry
RE: Splined Shaft Wear
Thanks to both of you for the excellent information and descriptions.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Splined Shaft Wear
Fretting wear contact generates small metal particles. In the case of steels and irons, these particles oxidize instantly to form hematite, Fe2O3. This is the same oxide associated primarily with low temperature corrosion/oxidation of steel. This is also why some people call this fretting corrosion. I think that is a misleading term since the oxide is generated from a wear mechanism. The red-brown discoloration surrounding the wear contact areas is consistent with steel fretting debris and the basis for the opinion expressed by many (myself included) in this thread that there is evidence of fretting. There are a couple of clues in the first set of pictures indicating this discoloration is from fretting contact rather than corrosion. First, the red oxide is concentrated around the worn contact areas and disappears away from it. In addition, you will note that discolored non-contact areas still clearly show original tooling marks, which means the surfaces are not yet corroding.
Aaron Tanzer
www.lehightesting.com
RE: Splined Shaft Wear
Thanks again for taking some time to elaborate on the subject!
Terry