A bearing is to be designed to carry a radial load of 150 lb from a shaft having a minimum acceptable diameter of 1.50 in and rotating at 500 rpm. Design the bearing to operate under boundary-lubrication conditions.

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Accepted Answer

We will use the design procedure previously outlined.
Step 1. Trial diameter: Try [latex]D = D_min = 1.50[/latex] in.
Steps 2–4. Try [latex]L/D = 1.0[/latex]. Then [latex]L = D = 1.50[/latex] in.
Step 5. Bearing pressure:
[latex]p = F/LD[/latex] = (150 lb)/(1.50 in)(1.50 in) = 66.7 psi

Step 6. Journal speed:
[latex]V = πDn/12 = π(1.50)(500)/12 = 196[/latex] ft/min
Step 7. [latex]pV[/latex] factor:
[latex]pV[/latex] = (66.7 psi)(196 fpm) = 13 100 psi-fpm

Step 8. Design value of [latex]pV[/latex] = 2(13 100) = 26 200 psi-fpm.
Step 9. From Table 16–1, we could use a bearing made from high tin babbitt having a rated value of [latex]pV[/latex] of 30 000 psi-fpm.
Steps 10–11. Nominal diametral clearance: From Figure 16–4, we can recommend a minimum [latex]C_d[/latex] = 0.002 in based on [latex]D[/latex] = 1.50 in and [latex]n[/latex] = 500 rpm. Other design details are dependent on the system into which the bearing will be placed.

TABLE 16–1 Typical Performance Parameters for Bearing Materials in Boundary Lubrication at Room Temperature
Material	pV
Material	psi-fpm	MPa-m/s
Vespel® SP-21 polyimide	300000	10.500	Trademark of DuPont Co.
DP11™, oiled	286000	10.020	GGB Bearing Technology
Manganese bronze (C86200)	150000	5.250	Also called SAE 430A
Aluminum bronze (C95400)	125000	4.375	Also called SAE 68A
DX®10, dry or oiled	80000	2.800	GGB Bearing Technology
Leaded tin bronze (C93800)	75000	2.625	Also called SAE 660
DU®	51400	1.800	GGB Bearing Technology
BU dry lubricant bearing	51400	1.785	See note 1
Porous bronze/oil impregnated	50000	1.750
Babbitt: high tin content (89%)	30000	1.050
DP11™, dry	28600	1.000	GGB Bearing Technology
Babbitt: low tin content (10%)	18000	0.630
Graphite/Metallized	15000	0.525	Graphite Metallizing Corp
Rulon® PTFE: 641	10000	0.350	Food and drug applications (see note 2)
Rulon® PTFE: J	7500	0.263	Filled PTFE
Polyurethane: UHMW	4000	0.140	Ultra-high molecular weight
Nylon® 101	3000	0.105	Trademark of DuPont Co.

Question 16.1: A bearing is to be designed to carry a radial load of 150 lb...

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