I have taken over a legacy design of which we are having trouble with a hot running system.
It is an outboard motor type set-up where I have a vertical outer shaft containing an internal needle roller bearing and Viton oil seal running on an inner shaft. The inner shaft is running at 2600rpm and has light grade motorcycle gearbox oil running between the shafts. The gap between the two shafts is 2.1mm and the diameter of the inner shaft is 28mm. Using temperature strips on the outer shaft I have found that over the needle roller and oil seal we are getting temps of 80degreesC, whereas 80mm above we are seeing temps of 54degreesC.
Any ideas why the oil seal is running hot? I should add that no load is being put through the system yet.
Image below should help.
Thanks, Roberto
Last edited by GIRoberto; 09-01-2015 at 05:26 AM.
Since this is a legacy design the first thing I would do, if you have not already done so, is to review the seal assembly design for the seal to shaft interference fit with the seal manufacturer. At the same time, check to see that you have the recommended surface finish on the seal contact area of the shaft.
As an addendum to my above post, just to be dilligent, I would also recommend that you contact the gearbox lubricant manufacturer to verify the compatibility of Viton with their product; and, did you lubricate the seal when you assembled your unit.
Additionally, you say this a legacy design (I assume that means you are working with an already designed and operating unit); if so, then what is the reason for your current testing, is this a design modification, a newly identified problem or an investigation into an existing one?
80 degrees C should not be over temp for Viton, and should be able to operate up to 200 degrees C.
Oil seal's create drag and is required to seal, this drag translates into heat. There will always be localized heating around an oil seal.
Patrick Adair
deVries International
There will be some sliding in the roller bearing as well as the on the seal lip. Since the high temperature is occurring both in the bearing area and the seal consider that the bearing may be generating some friction.
Consider a caged roller bearing if the current unit consists of a full compliment of rollers (your rollers may be skewed and sliding) or try a bronze bushing with an oil groove.
Things that spring to mind:
- Review shaft and seal lip fit with manufacturer.
- Review shaft material and finish requirements with seal manufacture.
- Improve the oil flow to the seal and bearing, perhaps a dedicated oil channel is needed or increase the clearance between the concentric shafts to increase oil volume.
- Change the seal lip geometry to reduce heating. I've seen seals with inboard pumping spirals cut into the lip to improve oil flow and reduce friction. Again your best speaking to a seal specialist.
- If its a legacy system maybe its always run hot?
May be Deviation in H7/H6
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