Timken - SNT Plummer Block

SNT SPLIT PLUMMER BLOCKS
Engineering • Mounting, Fitting, Setting and Installation
EXAMPLE #1 –
Calculating RIC Reduction Using a Spherical Roller Bearing with Tapered Bore
Given bearing number 22328K C3 (140 mm bore with C3 clearance)
is to be mounted on a tapered shaft. Using a set of feeler gages,
RIC is measured at (see fig. E-3):
RIC = 0.178 mm
Suggested reduction of RIC due to installation =
0.064 mm – 0.089 mm, found in table E-5 on page E-10.
Calculate the clearance after mounting (see fig. E-4):
0.178 mm – 0.076 mm = 0.102 mm
For this example, the value of 0.076 mm was obtained by taking the mid-range value of
the upper and lower limits found in the tables on page E-10.
Therefore, the locknut should be tightened until ric reaches
0.102 mm.
It also should be noted that the value obtained by reading the
suggested ric after installation directly from the table is 0.056 mm.
Observations:
• Bearing 22230EM, nominal 150 mm bore and 270 mm O.D.,
standard class, operating at 1200 RPM.
• Float bearing position so the stationary O.D. should be free
to move in SNT housing, with the locating ring removed.
• With shaft/inner ring rotation and the moderate loading
0.09C, the bore should be tight fit.
We can use the nominal fit charts in table E-6 on page E-15 (shaft
fit) to help guide our ISO fit selection.
Shaft Fit at 150 mm Bore: ISO p6
From the shaft fit chart at 150 mm nominal bore at p6 (table E-8,
page E-20), the shaft tolerance is nominal +0.043 to +0.068 mm.
Therefore we have the following bore range:
max. shaft = 150.068 mm
min. shaft = 150.043 mm
This yields a shaft fit:
max. fit = max. shaft - min. bore
= 150.068 - 149.075
= 0.093 mm tight
min. fit = min. shaft - max. bore
= 150.043 - 150.000
= 0.043 mm tight
For the primary selection of RIC, the major parameters are the
bearing speed and the fits. For our example, we know that the
shaft fit is 0.043 mm tight to 0.093 mm tight. We know the housing
Fig. E-3. Measure RIC before
installation.
Fig. E-4. During mounting, the
RIC should be checked at the
unloaded roller.
This differs from the value calculated in the example. The value
taken directly from the table is provided as a minimum value.
It is not suggested to use a calculated value that falls below
this minimum.
EXAMPLE #2 –
Calculating RIC Reduction Using a Spherical Roller Bearing with Cylindrical Bore
fit is loose. We also know that the bearing speed is 1200 RPM or
60 percent of the speed rating.
As a general rule of thumb, we increase the clearance for
operating speeds that exceed 70 percent of the speed rating, due
to concerns over internal heat generation and thermal growth.
In this case, we are at 60 percent of the speed rating, so normal
clearance, ISO CO or the SNT standard C3, can be selected.
Observing the RIC chart on page E-9, we find for 150 mm nominal
bore at CO, the RIC will be 0.110 mm to 0.170 mm. We also note
that the minimum recommended RIC (installed) is 0.056 mm.
Also from page E-9, we note that we get an approximate reduction of
ric that is 80 percent of interference fit on a solid housing. Since we
have a loose housing fit, there will be no ric reduction from that fit.
Shaft fit RIC reductions and clearance:
For a 150 mm nominal bore at C3, the RIC will be 0.115 mm to
0.165 mm. Recalculating shaft fit RIC reduction and clearance:
max. clearance = max. RIC - min. fit reduction
= 0.165 - 0.034 = 0.131 mm
min. clearance = min. RIC - max. fit reduction
= 0.115 - 0.074 = 0.041 mm
Since the minimum mounted clearance is less than the minimum
suggested RIC of 0.056 mm, the C3 RIC clearance limit needs to
be reevaluated.
TIMKEN ® HOUSED UNIT CataloG • Download 3D Models and 2D Drawings at cad.timken.com E-11