Flywheel Bearing Pocket Wear
Flywheel Bearing Pocket Wear
(OP)
I have a line of fitness equipment that has had a small issue for some time, and now that all the bigger issues are out of the way it is time to tackle the small stuff. We have noticed that the belt side of the flywheel housing is being worn out after about a year's worth of service on a small percentage of units. The flywheel is spinning less than 500RPM. The bearings are 6001ZZ. The flywheels are cut on CNC, balanced, and inspected. Most of the radial load is coming from belt tension alone, but some comes from the eddy current resistance. This unit does not product a lot of resistance as it is a cardio piece. After the housing becomes worn the unit will make all sorts of bear rattle noises and if left unchecked, it eventually creates a thin wall condition with the belt grooves and brakes the flange lip right at the centerline of the bearing essentially locking the unit up completely. The bearings feel completely fine when removed so I do not think it stems from a bearing failure. I believe we have narrowed down the what; the bearing not initially being a tight fit even though it passed inspections. But I am still foggy as to the exact why. The exact why I think would be either the bearing bore was too loose all together (should not have passed inspection), allowing the bearing to walk slightly in the pocket. This would slowly wear away the casting. My other thought is the the surface finish is too rough in the bearing pocket, so it would be like pressing a bearing into a very fine threaded body. This would not hold the bearing well and could eventually wear the housing. The few things I can think of to help stop this from happening are; increase the wall thickness at that bearing site, increase the surface finish, add bearing loctite (similar to loctite 641) only on the outer race, and source a longer bearing so that there is more bearing surface between the bearing and flywheel.
Now to my main question. Does this sound like the correct direction or maybe someone has seen similar issues that they could shed some light on some possibilities that I have not thought of? Any incite would be much appreciated.





Now to my main question. Does this sound like the correct direction or maybe someone has seen similar issues that they could shed some light on some possibilities that I have not thought of? Any incite would be much appreciated.





RE: Flywheel Bearing Pocket Wear
RE: Flywheel Bearing Pocket Wear
My gut says you may want to check both diameter and circularity of the bearing bore, but bearing fits are outside of my area of expertise so I could be off base there.
RE: Flywheel Bearing Pocket Wear
Stick. - I always second guess our Chinese factories at least a little. Even if they say they are doing x, y, and z it is impossible to really verify unless I fly over there. And due to Covid I have not been able to visit our factories in a year and a half and I used to go nearly every month. That said we are going to look into having the used flywheels CMM'ed for concentricity between the two bearing bores (probably will check their balance as well), but I am unsure if that will give much usable data. Most of the bore is worn away and I wonder if the small portion that is not in contact is slightly larger now from the wear and vibration during use. If we wanted to check new flywheels, that would be quite timely and costly as the failure rate for this failure mode is less than 1% and it would be like finding a needle in the haystack. I am also in the process of verifying their whole process the best I can from a distance. I would still like to do some modifications like I had discussed (or any other ideas others propose that seem viable) to help solve this. Reason being is that these machines are made to a price point and to hit the rate it becomes very timely and costly to have them machined as if they were going into a racecar.
Thank you for reply's so far Tug and Stick. Any ideas or incite helps in one way or another.
RE: Flywheel Bearing Pocket Wear
You could also substitute a bushing. Bushings run quieter than rolling bearings. There are a few options for low friction dry running bushings. Some extra design consideration will be necessary for the shaft in regards to wear resistance.
I do suggest using rubber sealed bearings. Your speed is low and they will hold lubricant longer in this app.
RE: Flywheel Bearing Pocket Wear
RE: Flywheel Bearing Pocket Wear
RE: Flywheel Bearing Pocket Wear
RE: Flywheel Bearing Pocket Wear
Tug - Free float with a light wave spring to keep a little positive pressure. If I hold any bearings positively in a situation like this, they always get a sleeve in between so there are no axial loads on the bearings.
RE: Flywheel Bearing Pocket Wear
If you're willing to use the try it and see approach, I suggest applying some retaining compound to the outer race. Loctite 609 or 635 are commonly available options.
RE: Flywheel Bearing Pocket Wear
All - Thank you for all of your input and helping with this sanity check. If there are any other possibilities I am open to just about anything.
RE: Flywheel Bearing Pocket Wear