Splined Shaft Coupling Issues 8

[TugboatEng]

I am having repeat failures of a splined coupling. The system consists of belts and a pulley driving a splined input hydraulic pump through an adapter that is flanged on one end for the pulley and female splined on the opposite for the pump. The splines keep fretting away to nothing. The system came packed with a moly paste type lubricant that quickly gets hammered out of the connection. We switched to an EP grease which quickly gets centrifuged into base oil and thickener. We tried a gear coupling grease, Kop-Flex KSG, which was too thin and passed through the coupling too quickly. There are no seals. We have settled on Mobilgrease 28 which has enough viscosity to stay in the coupling and is stabil enough to make it to a reasonable lubrication interval. We are still getting some random failures here and there, though.

One thing I have noticed is that the female spline is not hardened. A center punch leaves an indentation similar to A36 steel. We are thinking about making our own adapters and matching the hardness of the pump shaft.

However, I have seen that it might be possible to use an anaerobic adhesive to make the coupling rigid and eliminate fretting corrosion. I am interested in pursuing this route and just wanted to see if there was any experience with it here.

 

[CouplingGuru]

I am with Strong, you definitely have a vibratory torque condition, but I don't see how you can eliminate it being that the drive train is set. I go back to the fit on the spline hub, clearance or run-out variance will cause the spline to just grind itself away under vibratory torque conditions.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[MikeHalloran]

Well, sure you have vibratory torque with a Diesel prime mover, even absent resonance.
Maybe some compliance would help.
For instance:
A small accumulator on the pump discharge.
A spring loaded idler on the drive belt, on the driving side.
A slightly flexible, hollow, toothed idler sprocket, inserted between the belt runs, free floating, i.e. with no bearing or pin or fixed support. (This may have been patented; I don't know if it has been commercialized; I haven't seen it much in the wild. It would probably need flanges to keep it from riding out of the belt, and the flanges would have to be segmental to maintain the flexibility of the sprocket.)



Mike Halloran
Pembroke Pines, FL, USA

 

[TugboatEng]

It's a variable displacement axial piston pump, Rexroth A4V 125 displacement code, with an additional gear pump ganged on the back. The gear pump is probably around 10hp consistently. The variable displacement pump spends most time in the 0 flow position and has a soft start and stop by pulsing the servo piston solenoids. It's operating a slewing gear.

 

[Tmoose]

Does The OEM "grease" solution happen to be one of the Kluber assembly pastes? One of those was a pretty effective solution on a machine tool spline situation I'm aware of involving hundreds of precision spindles a few decades back. Those splines were very precisely manufactured and located.

Some of the pictures appear rather dry and lots of red fretting debris is present. I wonder if weekly re-lubrication is possible, or an oil bath or even total-loss oil lube could be arranged.

I know one experienced spline person on this board maintains there are situations when lubrication is to be avoided.

 

[Strong]

You mentioned that the pump runs most often at low/no load. A conventional gear drive operating at low load with a torsional resonance present can cause the gears to chatter. If this is the case with the spline shaft, then I doubt lubrication change would be the answer to the problem. In the case of a diesel powered fishing vessel with two brand-new engines and and transmissions, I recommended a flywheel be installed on the problem starboard drive engine that solved the vibration problem. A good set of vibration measurements possibly including torsional vibrations and sound pressure (for belt vibrations) would really help get to the root cause of the problem.

Walt

 

[CouplingGuru]

It think it was mentioned that it is spinning at 2400 rpm in a previously deleted post. That lends me to believe that any type of grease will be ineffective. At those speeds grease just is centripetally forced away from the contact surfaces, especially since the fit allows for clearance.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[mfgenggear]

My opinion the male and female spline are of in adequate design, based on the type of material and the type of heat treat. the male spline should be crown lead to allow for misalignment. both splines should be case harden premium steels and coated with drylube. the splines should be similar to ANSI b92.1 class 4 splines. there should be adequate process control with manufacturing and heat treating.

 

[mfgenggear]

in addition if better alignment is required a major diameter fit spline, in addition with a crown major diameter on the male spline.

 

[TugboatEng]

I thought I added it but the pump shaft is a DIN 5480 40x2x30x18x9g.

 

[TugboatEng]

Ok, got the pieces hardness tested. The driver is 29 HRC, possibly 4140, and the pump shaft is 50 HRC.

 

[CouplingGuru]

If it is 4140, then you could just take the replacement part and have it hardened to 40-42 HRC. But I definitely think going about 45 HRC could expose your pump shaft to significant wear.

When it comes to couplings we are always here to help.

http://WWW.PSCCOUPLINGS.COM

 

[TugboatEng]

The heat treatment shop recommended going to 40 HRC and broaching after heat treatment. Any higher and the machine shops won't touch it.

 

[mfgenggear]

hmmmm I still believe the surfaces need to be case harden for wear, if AISI 9310 is uses the parts can be normalized and harden while in the bar stock condition to 27-36 HRc which perfect for machining and broaching.
then carburized and harden with a .020-.025 effective case depth, core hardness of 33-43 HRc, then lap with cast iron. to obtain size. & od grind any close tolerance diameters.
the surface will be wear resistance (Hertz) and the core will allow for over torque or vibration. or the desired yield and ultimate tensile.
or use 300M or 4340M same as above but instead harden to 50 HRc by vacuum gas 2 or more Bar quench. the problem with soft splines is excessive wear. then it self destructs.
300M will not distort with a high bar quench.
Important!!!!
the spline P.D.'s must be concentric to the registered diameters within .0015 TIR max.

 

[TugboatEng]

Under $1100 is my target cost for each driver. Lapping sounds expensive? Grinding is expensive out here, too. It's $600 for the bore of the driver housing.

 

[mfgenggear]

send quotes to gear shops and see what the cost will be. at that price,it is why there are failures. cheap parts.
add the cost of down time plus parts and labor, I bet it's more than $1100 . just saying. a spline lapping operation is a simple and quick operation if broach correctly.

though harden parts is the most cost effective method but does not wear as long. I would highly recommend a crowned spline. it is simple to manufacture.
and coat it with dry film lube.

 

[TugboatEng]

I did find a local gear shop so the RFQ is in.