Bearing Arrangement | Deep Groove + Cylindrical Roller Bearing Fitted Adjacent

Question

Bearing Arrangement | Deep Groove + Cylindrical Roller Bearing Fitted Adjacent

Vah1D (Mechanical)

(OP)

29 Jun 21 15:19

Hi Everyone,

The first picture (taken from a book titled "Power Mechanisms of Rotational and Cyclic Motions") shows a deep groove & cylindrical roller bearing combination acting is locating-side of a bearing system. The roller bearing supports only radial load and the deep groove ball bearing supports the axial load (hence the radial clearance in the housing around the outer ring of deep groove ball bearing.)

It also (although not very clear) shows a small gap (Z) between the cup (that holds the deep groove) and the cylindrical roller bearing to avoid transmission of any axial load to the roller bearing.

Now the author claims that the deep groove ball bearing can support axial load in both directions. However, I can only see how it can resist axial load when the load is applied to the shaft from right to left. If thrust applied from left to right, then because of the gap between the bearings, I can't see how the deep groove ball bearing can resist any axial load in this situation.

The only possible explanation I can think of is after thrust load is applied (from left to right to the shaft), the Z gap closes and that's when the load will transfer from roller bearing to the ball bearing. But that only happens if the roller bearing outer ring starts to slip in the housing? What am I'm missing?

Another idea (although this will contradict the author) is since the roller bearing has ribs on the right side, it can actually resist some axial load, so the system can resist axial load in both directions, but from left to right only by the roller bearing?

1#
https://files.engineering.com/getfile.aspx?folder=...

Description from the author about the picture (the first picture is continued on in the second picture)
https://files.engineering.com/getfile.aspx?folder=...
https://files.engineering.com/getfile.aspx?folder=...

Thanks!

JJPellin (Mechanical) · Answer 1 · 2021-06-29 15:53:54

It seems clear to me by the drawing that the author is correct. The outer race of the deep groove radial ball bearing is retained in both directions by parts number 23 and 24. It cannot move in either axial direction. So any imposed thrust from the shaft is transferred from the inner race, through the balls to the outer race which cannot move axially. The gap at Z is not relevant other than to prevent the roller bearing from taking any thrust force. Parts number 23 and 24 are retained in a groove in the housing, so they also cannot move axially in either direction. It seems like a strange configuration for bearings since a deep groove radial ball bearing is not capable of taking very much thrust load. But, it looks like it will work as described.

Perhaps you assumed that the gap Z also exists between the inner races of the two bearings. It does not. The inner races are clamped to the shaft with a spacer between them and no gap.

Johnny Pellin

Vah1D (Mechanical) · Answer 2 · 2021-06-29 16:30:03

Thanks JJ for your reply.

I think my thinking comes from the fact that I always assumed in order to properly transfer the axial load from the shaft you need to have a solid shoulder (or spacer or ring etc.) directly push against the ring of a deep groove bearing, but in this case, we don't have that (part 23 is solid and against the inner ring of bearing but it's not transferring the load directly from the shaft, since it's not connected to the shaft in any way)

What I'm inferring from your explanation is that in this case, the thrust force is transferred due to the "interference fit" between the shaft and inner ring and then from ball to part 24 and that's how the ball bearing is able to resist loads applied to the shaft from the left side. Am I correct?

Why can't the confirmation be similar to this picture from skf, which has no gap b/w the two bearings, so it can transfer the load through the inner ring of the roller bearing to the deep grove bearing?
https://files.engineering.com/getfile.aspx?folder=...

Thanks,
Vahid

JJPellin (Mechanical) · Answer 3 · 2021-06-29 17:05:08

Part number 23 is not in contact with the inner race of either bearing. Part number 23 is only in contact with the outer race of the ball bearing. The spacer ring between the two inner races is a separate part and is not numbered. The cross-hatching makes it look like this is all one part. It cannot be or the bearing would be locked in place and unable to turn. There is a solid shaft shoulder, the inner race of the roller bearing, a solid spacer ring, the inner race of the ball bearing and then an end plate, bolted to the shaft that clamps all of these in place against one another.

The drawing you posted is very fuzzy and poor quality. But, I believe I can see enough to confirm my description.

Johnny Pellin

Vah1D (Mechanical) · Answer 4 · 2021-06-29 17:17:03

JJ, I got what you are saying and you are absolutely correct, sorry about the picture quality, it was taken from google-books, not an actual electronics copy.
I did not notice the spacer between the two bearings due to the quality of the picture.
(You actually did mention that in your first reply too, but I neglected that, haste makes waste!)

Thank you so much.

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Bearing Arrangement | Deep Groove + Cylindrical Roller Bearing Fitted Adjacent