Laminated Rubber Bearings

Heavy Duty Composites for Aerospace and Undersea

Laminated Rubber Bearings(Elastomeric Bearings)

• Composite of elastomer and metal layers

• Support massive structures -Permit thermal expansion -Isolate bulidings from earthquakes -Big, maybe 1/2 inch thin

• Small & dynamic -Helicopters -Undersea

(Seen from above,

moving up on picture)

Heavy Duty for a Thrust Bearing

• Tons of CF while oscillating

+/- a few degrees

• Early failure of ball / roller bearings

-spalling, fretting corrosion

A New Idea was needed ---

Laminated Rubber Bearings

(Seen from above,

moving up on picture)

Laminated Rubber / Elastomeric Bearings

•Easily handle tons of CF •Oscillate at high frequency•No lubrication•NR for high resilience

Used on most helicopters now

Enstrom – First with Elastomeric Bearings

Enstrom Bearing Design

• 2-1/4" in diameter

• More than100 rubber

& brass layers each

• All layers 0.002” thick

• 18,000 lbs. CF

Small Wind Turbines

• Blade pitch angle variable with wind

• Increase efficiency

Compression Very Slight

• At 10,000 psi pressure on bearing - thinner by a few sheets of paper - about .010 of an inch

• Rubber layers can’t squeeze out - because rubber layers are very thin -only .002 of an inch thick

• Compression due to volume decrease

One-inch Square Laminate Pads

• 40 layers .002’ brass• 39 layers .002” NR

• Bendable

• RIGID

• RRC specializes in laminates with very thin layers

• Small helicopters• Chemical bond of NR to hi-tensile brass• Lack of adhesive reduces thickness

• Larger helicopters use thicker, fewer layers

Planar & Chevron

• Planar

- angular oscillation & lateral movement

- easier to make – no metal forming

• Chevron

- precludes lateral shifting

- permits taller bearing for given load

Conical

• Combined radial & thrust loads

• Angular motion about axis

Cylindrical (Radial) Bearing

• Circular & axial motion

• Wrapped around shaft

• Axial thermal expansion of shaft

• Silicone rubber for heat

Spherical Bearings

• 3D angular motion about center

- rotation about longitudinal axis

- tilting L/R and in/out of screen

Helicopter Spherical Bearing

• Many large helicopters

• Ordinary pitch oscillation

• Also lead-lag & flapping

Design Factors

• Diametral dimensions

• Height

• Load forces

• Torsional stiffness

• Oscillatory torsional shear strain

• Fatigue life

• Angular range.

Some Relationships• Torsional Stiffness - prop. to 4th power of diameter - inverse with height• Torsional Shear Strain for given angle - prop. to diameter - inverse with height• Fatigue Life - Max oscillatory torsional shear strain - internal pressure - other factors

Bearing-Seals

• A more recent development by RRC

• New design opportunities

for undersea craft

Undersea Bearing-Seal

-An ordinary laminated rubber bearing - Top and bottom enclosed•Circular body makes a hermetic seal - Seawater outside can't penetrate - Solid barrier around central hole

It’s the same thing!

Undersea Bearing-Seal

• Seals against immense pressure -tested to 17,000 psi• No flimsy sliding surfaces like lip or face• Immune to sand and grit• Torque remains constant with depth

It’s the same thing!

What can we do with a bearing-seal?

• Suppose we have a pressure vessel

- like a submarine

• And suppose we want to have a sealed shaft that extends from the inside of it to the outside

- like a diving plane shaft

• We can do that with a bearing-seal.

• Small autonomous robotic submarine • Looks like a torpedo, but leisurely• Loaded with sensors - pressure, temps, sonar, guidance• Pre-programmed for a mission over area• Military, Scientific, Offshore Oil & Gas - mine-hunting for the Navy - sensing ocean variables - inspect underwater oil & gas pipelines.

AUV

Application of Bearing-Seals

• Mount & seal external hydrofoils that can control AUV:

- direction by rudder - climb/descent by diving planes • Even “fishtail” propulsion - swivelling tail fin back & forth • Advantage of actuation in air environment - low cost, off shelf actuators - no worries about seawater corrosion

Typical Bearing-Seal• OD = 2.06", ID = 1", ht. = 1/2“

• 80 hi-tensile brass + 78 natural rubber layers, both .002" thick

• 10,000 psi water pressure outside

• +/- 15 degrees for 1,000,000 cycles

• Also cycled at max sea depth, 17,000 psi

Bearing-Seal application similar to helicopter use

• Bearing - as well as hermetic seal

• Angular movement/oscillation

+/-15 degrees

• High force -intense hydrostatic pressure

instead of centrifugal force

• Millions of cycles

Laminated Rubber Bearing Technology

• Simplicity

• Low cost

• No lubrication

• Reliability

• Long life

For vehicles that Probe the sky and depths of the sea