I’ll probably repeat what others said but here’s my two cents.
1) Typically, I've read that the NDE bearing takes the thrust load, and the DE bearing is more of a guide bearing.
Among large vertical motors (let’s say above 250hp), it’s fairly common that the NDE takes the downthrust (which is typically larger) and the DE takes the upthrust (which is often smaller and/or momentary). It is equivalent to what you’d call a “cross locating” arrangement if the machine were vertical. I’d say this vertical cross locating arrangement is more common in large motors than an arrangement where the upper bearing takes both directions of thrust.
Can DE bearing take the load and NDE bearing as the guide bearing?
Yes. We have a family of motors where the DE takes both directions of thrust load, including the downthrust which is the larger load. So the lower bearing is a fixed bearing (back to back angle contact) and the upper bearing is a floating bearing (deep groove loose in the housing).
2) In horizontal motors, typically, DE bearing is the locating bearing and NDE bearing has a wave washer to allow for shaft thermal expansion. This is to prevent the shaft thermal growth towards DE because you don't want to put strain on customer's coupling. In vertical motors for pump applications, if the NDE bearing takes the thrust, then you need to fix the NDE. Does that mean DE floats and the thermal growth will go toward the customer's coupling
Yes thermal growth would affect positioning of the pump. Typically the amount of movement is small in comparison with the available clearances especially if pump is positioned in the middle of those clearances.
As an interesting aside, the growth would not necessarily be toward the pump because the rotor is not the only component growing, the stator is growing as well. Since the vertical motor is supported at the bottom, if the stator and rotor both grew by the same amount then there would be no change in pump position. So what is relevant is the differential growth. Maybe you have an intuition that the structural components of the stator are not growing as much as structural components of rotor… that was my intuition as well
until I was proven wrong by one of our vertical motor families. The vertical motor in question was what I called above the vertical version of a cross locating arrangement. Specifically a spherical roller bearing on top took downthrust, while a deep groove on bottom took any momentary upthrust. During refurbishment of these motors, we set the endplay to 0.010” (We didn’t realize at the time but the factory endplay setting was much larger). We did this for 6 motors. About 10 years later we had a bad lower bearing degradation event that we investigated. Examination of the lower bearing showed it had clearly been in an upthrust condition for most of its life (which is strange because any upthrust should only be momentary). We are lucky enough to have continuous temperature monitoring on these motors. Examination of the trends showed the lower bearing temperature went up after we refurbished (and reduced the endplay) on every one of these motors. Later we ended up setting the endplay to 0.025” and the lower bearing temperature went back down. What had happened was the stator was thermally expanding more than the rotor and eating up the 0.010” room temperature endplay to create a tension that loaded the lower bearing against the upper bearing. The upper bearing was a lot beefier and had no problem but the lower bearing coulnd’t handle it.
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(2B)+(2B)' ?
