A Model Configuration For Studying Stationary Grease Bleed In Rolling Bearings

Figures & data

Fig. 1. Schematic representation (not to scale) of static grease bleeding in a ball bearing (cross-sectional view), assuming inner ring rotation. 1: Outer ring; 2: inner ring; 3:seal; 4: grease under the cage; 5: static grease reservoir and 6: oil film

Fig. 2. a) A schematic representation of the test configuration (not to scale). b) Top-view snapshots of CaS/MS grease during bleeding. Dark circle in the center: the grease patch; solid blue lines: intensity contrast ($I/I_{bg}$) profile of the oil stain; dashed blue lines: the effective intensity contrast profile

Table 1. Properties of the commercial greases and their bled oils; and the values of the fit-parameters obtained from the grease bleeding tests, the oil drop spreading tests and the initial-stage capillary rise tests.

Grease	Li/M	Li/SS	LiC/PAO	PU/e	CaS/M
Color code	Teal	Cyan	Pink	Olive	Purple
Thickener
Type	Lithium soap	Lithium soap	Lithium soap/ Calcium soap	Polyurea	Calcium sulfonate/ Calcium carbonate
Microstructure	Fibrous	Fibrous	Fibrous	Fibrous /platelets	Agglomerated particles
Base oil
Type	Mineral oil	Semi-synthetic mineral oil	Polyalphaolefin	Ester oil	Mineral/synthetic oil
Density$(kg/m^3)$	900	910	850	910	900
Volume fraction$(\%,v/v)$	86	84	81	76	74
Viscosity$(Pa·s,{20}^{°}C)$	0.35	0.10	0.27	0.19	0.24
Surface tension $(mN/m,{20}^{°}C)$	32.3 ± 0.0	32.3 ± 0.3	31.2 ± 0.3	28.9 ± 0.2	31.8 ± 0.2
Refractive index$({20}^{°}C)$	1.49	1.47	1.47	1.48	1.49
NLGI	3	2-3	2-3	2-3	1-2
Worked penetration $(mm/10,60s\mathit{trokes})$	207	270	230-260	283	280-310
Oil separation (DIN 51817) ($7d,{40}^{°}C)$	2.10%	4.90%	0.50%	0.50%	1.10%
Calibration coefficients
$c_1{A}_{px}(m{m}^2)$	26.6 ± 2.6	22.6 ± 3.0	25.7 ± 1.6	21.8 ± 1.3	22.5 ± 2.0
c2	1.80	1.80	1.90	1.70	1.75
Fit-parameters
Grease bleeding $a_b^2/t_b ({10}^{-4} m{m}^2/s)$	126 ± 2	588 ± 92	32 ± 4	69 ± 4	21 ± 0
Oil drop spreading $a_s^2/t_s (m{m}^2/s)$	0.08 ± 0.00	0.27 ± 0.02	0.06 ± 0.01	0.14 ± 0.02	0.07 ± 0.02
Capillary rise $w (mm·s^{-1/2})$	0.130 ± 0.003	0.241 ± 0.009	0.117 ± 0.007	0.168 ± 0.003	0.125 ± 0.012

Fig. 3. a) Effective radius of the oil stain R versus square-root of time $\sqrt{t}$ resulting from bleeding of greases; b) normalized effective radius R/a of the oil stain as a function of normalised time $t/t_b,$ or the square-root of normalized time $\sqrt{t/t_b}$ (inset) collapsed onto a single master curve. The colored symbols represent the experimental data (from left to right, cyan: Li/SS; teal: Li/M; olive: PU/e; pink: LiC/PAO; and purple: CaS/M). Dashed lines represent the best fitting model curves

Fig. 4 a-e) Effective radius of the oil stain R versus square-root of time $\sqrt{t}$ resulting from spreading of bled oil drops of various volume; f) normalized effective radius R/a of the oil stain versus normalised the square-root of time $\sqrt{t/t_b}$ or normalized time (inset) collapsed onto a single master curve. The colored symbols represent the experimental data (cyan: Li/SS; teal: Li/M; olive: PU/e; pink: LiC/PAO; and purple: CaS/M). Dashed lines represent the best fitting model curves

Fig. 5 a) Height of the rising front of bled oils h versus square-root of time $\sqrt{t};$ the linear dependence confirms that the data are collected in a time range shorter than the characteristic rise time. b) h versus $\sqrt{t/\eta }.$ Excluding the influence of bled oil viscosity η, bled oils Li/SS, Li/M and PU/e rise faster than LiC/PAO and CaS/M. Cyan: Li/SS; teal: Li/M; olive: PU/e; pink: LiC/PAO; and purple: CaS/M

Fig. 6. a) Values of $kp\Delta p_p$ determined by the initial-stage capillary rise test (red) and by the oil spreading tests (blue); b) values of $\mu (a_s^2/t_s-a_b^2/t_b)$ (red), which is proportional to the absolute values of $\Delta p_g$ estimated using k_p = 0.16 μm² (blue)

Fig. 7. Capillary rise of the bled oil of PU/e grease (blue) and that of the polyurea grease taken from (31). Height of the rising front is plotted versus a) time and b)square-root of time. Scatters indicate experimental data and dashed lines are the best fits at various local minima. The fit-parameters ($h_{\infty }$ and t_r) and the corresponding paper properties ($\Delta p_p$ and k_p of the fits are given in c)

Zhang, Q., Mugele, F., Lugt, P., and van den Ende, D. (2020), “Characterizing the fluid-matrix affinity in an organogel from the growth dynamics of oil stains on blotting paper,” Soft Matter, 16, pp 4200–4209. doi:https://doi.org/10.1039/c9sm01965k

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