Do we really have a so capable 4 points contact brg ? 1

[FreddyMusic]

See below specification from a reputable brg manufacturer catalog

Cr (KN) Co (KN) d X D X B (mm)
4P QJ 308 = 86.5 68 40X90X23
DAC 3308 B = 62 45 40X90X36.5
AC 7308 B = 50 32.5 40X90X23

4 points (4 P) has higher load capacity as a double row angular contact (DAC)?
It seems like 4 P is a kind of DAC, but two row race share one row of balls.

Then see this,
4 points (4 P) has higher Load capacity than angular contact (AC) with same OD. ID. Width.?

What about we put the same load (only one direction axial load) on both brgs and do test life?
I assume P = 50 KN, from Life equation L10 = (C/P)^3
We have conclusion, 4P is 5.18 times longer life than AC.
Under same load, with same dimension and material,
Is 4 points so capable on life, with a not super finished outer race?

Did anyone really test 4 points brg life ?
or have some application experience ?
What is 4 points brg ? DJ what do you think ?

 

[diamondjim]

A four point contact bearing
is basically a gothic arch design
having angular contact.
Each race makes 2 point contact
with the balls.
If you can imagine a bearing ring of
x width. If you removed or cut
the ring in the middle of width
and put the two halves back together
there would be a gothic arch formed
and the width would become x-(saw cut width).
You would have to move the gothic
arch out radially to encompass the balls.

 

[diamondjim]

Also see Tedric Harris
and Zaretsky's works.

 

[FreddyMusic]

OK. I try to get a Tedric Harris first.
Also, Amazon has together sales.

Applied Tribology : Bearing Design and Lubrication
Michael M. Khonsari, E. Richard Booser

Any comments for this works ?

 

[Mendit]

The unique feature of a 4 point bearing is the inner race is split circumfrencially(yes 2 separate rings) This feature allows the manufacturer to put in more balls and a better support cage usually brass. The races do not need to be offset to assemble the bearing and it does not require a fill slot. A QJ209 bearing has more balls than a 6209 but is equal in size. Also during the manufacture the shoulder of the inner race is larger providing better axial support.
Point to note this bearing must be secured with a nut, or other securing device whan fixing to the shaft, retaining rings will not do.

 

[FreddyMusic]

Mendit, I am afraid, you descripted brg is called 3-points contact
* jim descripted is called 4-points contact.

4 points brg can assembly bigger dia. balls and more quantity of balls than Deep groove ball brg. (I can understand.)
But angular contact ball can also assembly with bigger Dia. balls and more quantity of balls.

What I don’t understand is,
Why 4 points brg are more capable than a angular contact ball ?

Therefore, raise a question.
Is the 4 points contact brg really are working at 4 points contact on race?

 

[diamondjim]

The unknown in the formula or
ratings listed do not show the
contact angles for these bearings.
O degree contact angle bearings
have greater radial capacity than
15 degree contact angle bearings
assuming that the number of balls
are the same in each bearing.

It is true that bearings which
are not conrad style can have
more balls assembled in them.
To get a full picture of the
ratings would require the
axial load ratings shown as
well.

As Mendit points out a 4 point
contact bearing could have a
filler plug or have split rings
for assembly purposes to allow
more balls in the bearing.

The conrad style bearing by
design allows only 1/2 the number
of balls for it to be assembled.
It further restricts the contact
angle to avoid edge loading because
of its cross section.

The 4 point contact bearing allows
thrust or axial loading and also
overturning moment which is there
advantage by design.

 

[Mendit]

Check here for more details, there is no fill slot. Picture and all. Good luck

http://www.fag.com/content/en/produ...tact_bearings/four_point_contact_bearings.jsp

 

[sujithvs]

Hello everybody,

I have been reading the threads related 4-point contact ball bearings. I have a customer who wants a 4-point contact bb for a steering geardrive. I'm reaching a dead end understanding 2 important things related to these type of bb's.
i)radial clearence and endplay
ii) Static and dynamic ratings
can anybody throw a light on how to calculate them for a 4-point bb?? The question raised by someone on the ratings of these bb's is very valid: even if you put in the increased no. of balls into the calculation, you wouldn' get the same rating value; its specified to be higher. Is there a factor in there for ex 1.51 X single row AC rating???

 

[diamondjim]

Radial clearance is the max clearance
that the ring can shift radially from
tight to maximum clearance.
The end play is also defined as axial
clearance.
Basically a conrad style bearing can
only accomodate 1/2 the number of balls
in a bearing that a full complement
bearing would have. Because of separators
being used in most bearings, a rough
estimate would be 80 percent to 87 percent
of a full complement bearing.
Full complement bearings are used in
primarily static applications where high
revolutions are not required.
The static rating would be a direct
relationship to the number of balls
whereas the dynamic capacity is based
on the number of balls to the .7 power.