Design a boundary-lubricated plain surface bearing to carry a radial load of 2.50 kN from a shaft rotating at 1150 rpm. The nominal minimum diameter of the journal is 65 mm.

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Accepted Answer

We will use the design procedure previously outlined.
Step 1. Trial diameter: Try D = 15 mm.
Steps 2-4. Try L/D = 1.0. Then L = D = 15 mm.

Step 5. Bearing pressure:
p = F/LD = (2500 N)/(75 mm)(75 mm) = 0.444 [latex]N/mm^2[/latex]

Converting to kPa, we have
p = 0.444 [latex]N/mm^2[/latex] ([latex]10^3[/latex] kPa)/([latex]N/mm^2[/latex]) = 444 kPa

Step 6. Journal speed:
[latex]V = πD_n/(60 000) =π(75)( 1150)/(60 000) = 4.52 m/s[/latex]

Step 7. pV factor:

pV = (444 kPa)(4.52 m/s) = 2008 kPa.m/s

Step 8. Design value for pV = 2(2008) = 4016 kPa- m/s.
Step 9. From Table 16-1, we can specify aluminum bronze (C95200) having pV ratingof4375 kPa-m/s.

TABLE 16-1 Typical performance parameters for bearing materials in boundary
lubrication at room temperature
	pV
Material	psi-fpm	kPa-m/s
[latex]Vespel^{\circledR}[/latex] SP-21 polyimide	300 000	10 500	Trademark of DuPont Co.
Manganese bronze ( C86200)	150 000	5250	Also called SAE 430A
Aluminum bronze ( C95200)	125 000	4375	Also called SAE 68A
Leaded tin bronze (C93200)	75 000	2625	Also called SAE 660
KU dry lubricant bearing	51 000	1785	See note 1
Porous bronze/oil impregnated	50 000	1750
Babbitt: high tin content (89%)	30 000	1050
[latex]Rulon^{\circledR}[/latex] PTFE: M-liner	25 000	875	Metal backed
[latex]Rulon^{\circledR}[/latex] PTFE: FCJ	20 000	700	Oscillatory and linear motion
Babbitt: low tin content (10%)	18 000	630
Graphite/Metallized	15 000	525	Graphite Metallizing Corp.
[latex]Rulon^{\circledR}[/latex] PTFE: 641	10 000	350	Food and drug applications (see note 2 )
[latex]Rulon^{\circledR}[/latex] PTFE: J	7500	263	Filled PTFE
Polyurethane: UHMW	4000	140	Ultra high molecular weight
[latex]Nylon^{\circledR}[/latex] 101	3000	105	Trademark of DuPont Co.
Source: Bunting Bearings Corp., Holland. OH 1KU Bearings consist of bonded layers of a steel backing and a porous bronze matrix overlaid with PTFE/lead bearing material. A film from the bearing material is transferred to the journal during operation. 2[latex]Rulon^{\circledR}[/latex] is a registered trademark of Saint-Gobain Performance Plastics Company. Bearings are made from [latex]Rulon^{\circledR}[/latex]PTFE (polytetrafluoroethylene) material in a variety of formulations and physical constructions.

Steps 10-11. From Figure 16-3, we can recommend a minimum [latex]C_d= 100 \ μm[/latex] (0.100mm or 0.004 in) based on D = 75 mm and 1150 rpm.

Alternate design: The pV factor for the initial design, while satisfactory, is somewhat high and may require careful lubrication. Consider the following alternate design having a larger bearing diameter.

Step 1. Try D = 150 mm.
Step 2. Let L/D = 1.25.
Step 3. Then

L = D(L/D) = (150mm)(1.25) = 187.5 mm

Step 4. Let's use the more convenient value of 175 mm for L.
Step 5. Bearing pressure:

[latex]p = F/LD = (2500 N)/(175 mm)( 150 mm) = 0.095 N/mm^2 = 95[/latex] kPa

Step 6. Journal speed :

[latex]V = πD_n/(60 000) = π( 150)( 1150)/(60 000) = 9.03[/latex] m/s

Step 7. pV factor:

[latex]pV = (95 \ kPa)(9.03 \ m/s) = 860 \ kPa.m/s = 860 \ kW/m^2[/latex]

Step 8. Design value of [latex]pV = 2(860) = 1720 \ kW/m^2.[/latex]

Step 9. From Table 16-1, we can specify an oil impregnated porous bronze bearing having a pV rating of 1750 kPa-m/s or a KU dry lubricated bearing having a pV rating of 1785 kPa-m/s.

Steps 10-11. From Figure 16-3, we can recommend a minimum [latex]C_d = 150 / μm[/latex] (0.150mm or 0.006 in) based on D = 150 mm and 1150 rpm. Other design details are dependent on the systemin into which the bearing will be placed.

Question 16.2: Design a boundary-lubricated plain surface bearing to carry ...

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