KEVOS® MAKEOS · Power Transmission
Flat Plate Thrust Bearing Design (Pad Layout, Unit Load, Friction Loss, Oil Flow, Chamfer Depth)
For a flat plate (parallel surface) thrust bearing carrying an axial load, what outside diameter, pad width, number and length of pads, actual unit load and pitch-line speed result, what friction power and oil flow does it need for my temperature rise, and how deep must the feed chamfers be to pass that oil?
Flat plate thrust bearing design by the handbook procedure: outside diameter D2 = √(4W ÷ (π Kg p) + D1²), radial pad width a = (D2 − D1) ÷ 2, pitch-line circumference B = π(D2 − a), approximate number of pads B ÷ (a + s), pad length b = (B − i s) ÷ i, actual unit load W ÷ (i a b), pitch-line velocity U = B N ÷ 12, friction power Pf = i a b M with M read from the handbook’s friction-loss chart, oil flow Q = 42.4 Pf ÷ (c t), film flow QF = 1.5 × 10⁵ i V h³ ps ÷ Z2 (h taken as 0.002 in), flow per chamfer Qc = share × Q ÷ i, uncorrected flow Q0c = Qc ÷ κ with the kinetic energy factor κ from the chart, and chamfer depth g = ⁴√(Q0c l Z2 ÷ (4.74 × 10⁴ ps)).
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Axial load | N | Axial (thrust) load on the bearing. |
| Inside diameter D1 | mm | Inside diameter of the thrust face, set by the shaft and its clearance. |
| Design unit load p | kPa | Unit load the bearing is designed for; the handbook gives about 75 psi (517 kPa) normal and 150 psi (1034 kPa) maximum for parallel surface bearings. |
| Fraction of the circumference occupied by pads Kg | Fraction of the circumference occupied by pads; usually 0.8. | |
| Outside diameter chosen D2 | mm | Outside diameter you choose, at least the diameter required (often rounded up). |
| Oil groove width s | mm | Width of each oil groove between pads. |
| Number of pads chosen | pads | Number of pads you choose, near the approximate number shown and usually even. |
| Speed N | rpm | Shaft speed. |
| Friction and oil | ||
| Friction loss M from the handbook chart (Fig. 3) | hp/in² | Friction horsepower per square inch of pad read from the handbook’s Fig. 3 at the pitch-line speed and unit load shown. |
| Oil density | kg/m³ | Density of the oil. |
| Oil specific heat | kJ/(kg·K) | Specific heat of the oil. |
| Oil temperature rise allowed | °C | Temperature rise of the oil you allow; the handbook gives 50 °F (27.8 °C) as an acceptable maximum. |
| Oil viscosity at the outlet temperature | cP | Oil viscosity in centipoises at the outlet temperature (inlet plus the rise). |
| Film thickness for the film flow (handbook: 0.002 in) | mm | Film thickness used for the film flow; the handbook says to use 0.002 in because it cannot be calculated for this bearing. |
| Oil supply pressure | kPa | Oil supply pressure. |
| Share of the oil flow passed by the chamfers | Share of the required oil flow to pass through the chamfers; the handbook recommends at least one-half. | |
| Chamfer length l | mm | Length of each feed chamfer. |
| Kinetic energy correction factor κ from the chart (Fig. 4) | Kinetic energy correction factor read from the handbook’s Fig. 4 at Z2 × l and the flow per chamfer. | |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Axial load
- What it is
- Axial (thrust) load carried by the bearing.
- Units and format
- Enter a number in N: newtons. The form accepts 0.000001 N to 10000000 N. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4003.4 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the outside diameter required and the unit load.
- Get it right
- Include any hydraulic or gear thrust on the shaft.
What this means: Inside diameter D1
- What it is
- Inside diameter of the thrust face.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 3000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 76.2 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger bore needs a larger outside diameter.
- Get it right
- Set by the shaft diameter plus running clearance.
What this means: Design unit load p
- What it is
- Unit load the thrust face is designed to carry.
- Units and format
- Enter a number in kPa: kilopascals. The form accepts 0.000001 kPa to 10000 kPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 517.11 kPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A lower design load needs a larger outside diameter.
- Get it right
- About 517 kPa (75 psi) normal and 1034 kPa (150 psi) maximum for flat plate bearings.
What this means: Fraction of the circumference occupied by pads…
- What it is
- Fraction of the pitch circumference occupied by pads rather than grooves.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.8 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller fraction needs a larger outside diameter.
- Get it right
- Usually 0.8, leaving a fifth of the circumference for oil grooves.
What this means: Outside diameter chosen D2
- What it is
- Outside diameter of the thrust face you choose.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 3000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 139.7 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the pad width and pitch circumference.
- Get it right
- Round up from the diameter required.
What this means: Oil groove width s
- What it is
- Width of each oil groove between the pads.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 200 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4.7625 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Wider grooves shorten the pads.
- Get it right
- The handbook example uses 3/16 in (4.8 mm).
What this means: Number of pads chosen
- What it is
- Number of pads around the thrust face.
- Units and format
- Enter a number in pads: pads. The form accepts 2 pads to 100 pads. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 10 pads as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the pad length and the flow per chamfer.
- Get it right
- Take an even number near the approximate number shown, so pads are about square.
What this means: Speed N
- What it is
- Rotational speed of the shaft.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 4000 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the pitch-line velocity for the friction chart.
- Get it right
- Use the running speed at full load.
Friction and oil
What this means: Friction loss M from the handbook chart (Fig. 3)
- What it is
- Friction horsepower per square inch of pad, read from the handbook chart.
- Units and format
- Enter a number in hp/in²: hp/in². The form accepts 0.000001 hp/in² to 10 hp/in². Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.19 hp/in² as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Friction power and the oil flow required rise in proportion.
- Get it right
- Enter Fig. 3 at the pitch-line velocity and unit load shown.
What this means: Oil density
- What it is
- Density of the lubricating oil.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 2000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 880 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- With the specific heat, sets the heat the oil carries per litre.
- Get it right
- About 850 to 900 kg/m³ for mineral oils.
What this means: Oil specific heat
- What it is
- Specific heat of the lubricating oil.
- Units and format
- Enter a number in kJ/(kg·K): kilojoules per kilogram per kelvin. The form accepts 0.000001 kJ/(kg·K) to 10 kJ/(kg·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.9953 kJ/(kg·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A higher specific heat needs less oil flow.
- Get it right
- About 1.9 to 2.0 kJ/(kg·K) for mineral oils.
What this means: Oil temperature rise allowed
- What it is
- Temperature rise of the oil through the bearing you allow.
- Units and format
- Enter a number in °C: degrees Celsius. The form accepts 0.000001 °C to 100 °C. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 22.222 °C as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller rise needs more oil.
- Get it right
- The handbook gives 27.8 °C (50 °F) as an acceptable maximum.
What this means: Oil viscosity at the outlet temperature
- What it is
- Viscosity of the oil in centipoises at the outlet temperature.
- Units and format
- Enter a number in cP: cP. The form accepts 0.000001 cP to 10000 cP. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 9.6 cP as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Higher viscosity lowers the film flow and deepens the chamfer.
- Get it right
- Inlet temperature plus the allowed rise, from the oil’s viscosity chart.
What this means: Film thickness for the film flow (handbook: 0.0…
- What it is
- Film thickness used to estimate the film flow of a flat plate bearing.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 1 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.0508 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Film flow rises with its cube.
- Get it right
- The handbook says to use 0.002 in (0.0508 mm) because it cannot be calculated.
What this means: Oil supply pressure
- What it is
- Pressure at which oil is supplied to the bearing.
- Units and format
- Enter a number in kPa: kilopascals. The form accepts 0.000001 kPa to 100000 kPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 206.84 kPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the film flow and allows a shallower chamfer.
- Get it right
- Measure at the bearing inlet.
What this means: Share of the oil flow passed by the chamfers
- What it is
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the flow per chamfer and its depth.
- Get it right
- The handbook recommends at least one-half; the example puts all the flow through them.
What this means: Chamfer length l
- What it is
- Length of each feed chamfer along the pad edge.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 3.175 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A longer chamfer needs a slightly deeper cut.
- Get it right
- The handbook example uses 1/8 in (3.2 mm).
What this means: Kinetic energy correction factor κ from the cha…
- What it is
- Kinetic energy correction factor for the chamfer flow, read from the handbook chart.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.44 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller factor raises the uncorrected flow and the chamfer depth.
- Get it right
- Enter Fig. 4 at Z2 × l and the flow per chamfer shown.
Method and formulas
- D2 = √(4W ÷ (π Kg p) + D1²); a = (D2 − D1) ÷ 2; B = π(D2 − a); approximate pads B ÷ (a + s).
- b = (B − i s) ÷ i; p = W ÷ (i a b); U = B N ÷ 12 ft/min.
- Pf = i a b M hp; Q = 42.4 Pf ÷ (c t) gpm with c in Btu/gal °F.
- QF = 1.5 × 10⁵ i (a/b) h³ ps ÷ Z2 gpm; Qc = share × Q ÷ i; Q0c = Qc ÷ κ; g = ⁴√(Q0c l Z2 ÷ (4.74 × 10⁴ ps)) in.
- Inputs are converted to inches, pounds, psi and °F for the handbook constants; results are shown in SI with the inch values.
- Example: 10 pads of 31.75 × 29.151 mm carry 432.55 kPa; the bearing needs 3.125 L/min and chamfers 0.50667 mm deep.
Limitations
- Friction loss M and the kinetic energy factor κ come from the handbook’s charts; read them at the pitch-line speed, unit load and flow shown.
- The film thickness of a flat plate bearing cannot be calculated; the film flow uses the handbook’s 0.002 in.
- Flat plate bearings suit light or occasional loads; use step, tapered land or tilting pad bearings for higher loads.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Lay out a parallel-surface thrust bearing for a light or occasional load
- Find the oil flow and chamfer size that keep the temperature rise acceptable
- Check the unit load of an existing thrust face
Who it is for
- Machine designers
- Pump and gearbox engineers
- Students
What you get
- Outside diameter required
- Pad width, pitch-line circumference, approximate number of pads and pad length
- Actual unit load and pitch-line velocity
- Friction power and oil flow required
- Film flow, flow per chamfer and chamfer depth
Interpreting the result
- Most of the oil must pass the chamfers because the film flow is small.
- A deeper chamfer passes more oil at the same supply pressure.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2338–2344. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Useful alongside · KEVOS® original book
Thrust bearings
In Plain Bearings by the Numbers
What it covers: Check a thrust face's area, unit load, sliding speed and PV, estimate its friction heat and oil flow with the KEVOS® thrust tools, and see why tapered lands and tilting pads carry load.
KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.