Fundamental Frequency values for Rexnord ZA-2115 bearing

Question

I am having difficulty coming to terms with the Rexnord ZA-2115 bearing technical specifications. This bearing is used in the NASA Bearing Dataset where the Rexnord bearings are tested at 2000 RPM under a 6000 pound load. My questions in particular are:

(A) The Vibration Frequency Fundamental Train, Inner Ring Defect, Outer Ring Defect, and Roller Spin values are specified as 0.0072, 0.1617, 0.1217, 0.0559 cps, respectively. I might assume these are somehow related to Fundamental Train Frequency (FTF), Ballpass frequency outer race (BPFO), Ballpass frequency inner race (BPFI), and Ball spin frequency (BSF).
$\begin{array}{lcl|} FTF &=&\frac{R}{2}\left(1-\frac{d}{D}\cos\phi\right)\\ BPFO&=&\frac{nR}{2}\left(1-\frac{d}{D}\cos\phi\right)\\ BPFI&=&\frac{nR}{2}\left(1+\frac{d}{D}\cos\phi\right)\\ BSF &=&\frac{DR}{2d}\left[1-\left(\frac{d}{D}\cos\phi\right)^2\right] \end{array}$ where $n$ is the number of balls, $R$ is rotational speed, and $\phi$ is the contact angle.

But how do I get (and/or should I be able to get) from the Rexnord values to the (FTF, BPFO, BPFI, BSF) 4-tuple? Do I need to multiply Rexnord values by shaft rotational frequency? For example, is 0.0072 x RPM/60 equal to FTF in Hertz?

(B) How can I determine the number of rolling elements in ZA-2115? Since BPFO and FTF only differ by a factor $n$, then I might think that $n$ should equal BPFO / FTF (regardless of RPM). However, when I calculate 0.1217 / 0.0072, I get approximately 16.9 ... shouldn't I get an integer? Or are the values derived empirically using actual test data and a PSD?

Some PSD-Welch calculations suggests peaks at the following locations for $x$ axis
$\begin{array}{cc} 492.95775 \;Hz& 2.1302751\\ 985.91549 \;Hz& 3.6660246\\ 4201.87793 \;Hz& 1.4599044\\ 5164.31925 \;Hz& 1.5721200\\ 7018.77934 \;Hz& 1.3078587\\ 9061.03286 \;Hz& 1.6893742 \end{array}$
and $y$ axis
$\begin{array}{cc} 492.957746 \;Hz& 1.497\\ 985.915493 \;Hz& 1.596\\ 5164.319249 \;Hz& 1.024\\ 7136.150235 \;Hz& 0.979\\ 8990.610329 \;Hz& 2.115 \end{array}$

Answer 1

the BPFO is 236.4Hz. You can reference some of the publications that used this dataset like: DOI: 10.1016/j.jsv.2005.03.007

Page 19 gives the design parameters to calculate the fault frequencies of the Rexnord ZA-2115 used in the test. ” Four Rexnord ZA-2115 double row bearings were installed on one shaft as shown in Fig. 16. The bearings have 16 rollers in each row, a pitch diameter of 2.815 in., roller diameter of 0.331 in., and a tapered contact angle of 15.171. “

You can use this information and a simple bearing fault frequency calculator to determine the BPFO, FTF, BPFI and BSF at different running speeds. [![Fault frequencies of ZA-2115][1]][1] [1]: https://i.sstatic.net/9lIt8.jpg

Hope this helps. Let me know if you have anything else you'll like to discuss concerning this dataset.