14017

A preliminary selection needs the thrust load, maximum shaft diameter through the ring, collar speed, oil grade and inlet-oil temperature. After choosing the pad count and ring size, check both specific thrust pressure and sliding velocity against the appropriate pivot-condition limits.

Specific thrust pressure P, kN/m²

P = thrust load (kN) × 10⁶ / thrust surface area (mm²).

Sliding velocity V at mean pressure diameter, m/s

V = mean pressure diameter (mm) × shaft speed (rpm) / 19100.

• These relationships explain the selection quantities. Our engineers check the resulting oil-film thickness and operating temperature for the proposed duty.

Determine handing while looking in the direction of thrust at the whitemetal working faces.

In a double thrust bearing, if both shaft rotation and the axial direction of thrust reverse, the pads on the two faces have the same hand. If the axial thrust reverses while shaft rotation stays in one direction, the faces have opposite hands.

Handed pads are backed off to permit pivoting during reverse rotation, such as pump rundown. Describe the duration, speed and load of reverse duty so that it can be assessed separately from continuous operation.

Left-hand pads, L

For continuous anticlockwise shaft rotation under load from this viewpoint.

Right-hand pads, R

For continuous clockwise shaft rotation under load from this viewpoint.

Centre-pivoted pads, C

For continuous rotation in either direction under load.

Place the outlet at the top of the thrust housing so that air can escape and the bearing remains submerged. Shaft sealing rings or a bush retain the oil head. Feed oil towards the pad inside diameter, allowing the rotating collar to carry it outwards.

Arrange the inlet so the housing does not empty when the machine stops; retain a stationary oil level at least to the underside of the shaft. At high speeds, separate feeds and outlets for the two thrust rings can reduce the need for oil to pass across the collar rim.

Inlet sizing velocity

1.2–1.8 m/s.

Outlet sizing velocity

1.8–2.4 m/s.

Outlet restriction with sealing rings, all oil through restriction

Sizing basis 9.15–10.7 m/s.

Outlet restriction with sealing rings, restriction plus seal clearance

Sizing basis 2.4–4.6 m/s.

Outlet restriction without sealing rings

Sizing basis 4.9–6.1 m/s.

Inlet restrictor use

Only to reduce high delivery pressure to approximately 0.35–1.4 bar (5–20 psi) in the thrust housing.

Restrictor minimum diameter

2.4 mm.

Oil-drain maximum flow speed

Below 0.15 m/s.

• Outlet restrictions build a positive working pressure to limit air being drawn through shaft seals. Drains must allow oil to fall freely away from the outlet without backing up to the bearing.

The low-loss arrangement supplies oil to an annulus in the retaining-ring rim and through radial and axial holes to the pad leading edges. The housing allows hot oil to drain quickly from the collar. The high-speed discussion uses a mean sliding velocity greater than 60 m/s.

Low-loss supply pressure

Minimum 1.4 bar (20 psi) from an external oil system.

Oil-flow guide reference pressure

Specific thrust load 2500 kN/m².

Oil-flow guide thermal conditions

40°C inlet; 17°C inlet-to-outlet temperature rise; assumed effective oil temperature 90°C.

Oil-flow adjustment for another specific thrust pressure

Q₂ = Q₁ × √(P₂ / 2500), with P₂ in kN/m² and oil flow in litres/s.

Single versus double thrust face

For one thrust face, the low-loss power-loss guide gives 95% of the double-bearing value. In most cases the single-face oil flow is half the double-bearing guide value.

• Power-loss and oil-flow guides give approximate answers. Supply the actual duty for an engineering calculation of oil-film thickness, temperature, power loss and lubricant quantity.

Steel adjusting liners are normally supplied oversize for finish machining during installation. A composite option uses a steel liner with one 0.25 mm brass shim and two 0.125 mm brass shims. Confirm the required finished axial stack with our engineers.

Temperature can be monitored in the hot oil leaving the bearing or by thermocouples in the thrust pads. A pad-mounted probe must not interfere with the natural tilting action.

Pad count and size

06, 08, 11, 14 or 18 identifies the full-ring pad count; the following three digits identify the approximate pad width in millimetres.

N

The normal, non-equalised retaining-ring form.

F / D

F: flooded housing. D: directed, low-loss lubrication.

L / R / C

Left-hand, right-hand or centre-pivoted pads.

H / W

H: retaining ring in halves. W: whole retaining ring.

A / B

A: without adjusting liners. B: with liners or spacers.

B₁ / B₂ / B₃ / B₄

B₁: oversize steel liner for finish machining. B₂: B₁ with adjusting shims. B₃: finished steel liner. B₄: B₃ with adjusting shims.

Component suffix S / T

Production identification on the retaining ring: S denotes a ring stop fitted; T denotes no ring stop fitted.

• State whether the assembly is single thrust, double thrust, thrust with a smaller surge ring, or an axial-location arrangement. Include the duty and quantity for each ring; code meanings do not establish a complete supported combination.

DIN and ASTM materials are approximate equivalents to the British designations; differences in composition can exist. Screw threads follow ISO metric standards.

Retaining ring and steel adjusting liners

BS 970-070 M20 / Werkstoff No. 1.0724 / ASTM A576 AISI C1022; or BS 4360 GR43A / ASTM A284 GR B.

Thrust-pad steel

BS 4360 GR43A / ASTM A284 GR B; or BS 3146 CL A13 / AISI 4615.

Thrust-pad whitemetal

BS 3332/2 / DIN 1703 Lg Sn 89 / ASTM B23 GR2.

Brass adjusting shims

BS 2870/CZ108 / DIN 1785 K Ms 63 / ASTM B36/8.

Stops

Steel: BS 970-070 M20 / Werkstoff No. 1.0724 / ASTM A576 AISI C1022.