Laminated Rubber Bearings, Heavy Duty Composites for Aerospace and Undersea
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Laminated Rubber Bearings
Heavy Duty Composites for Aerospace and Undersea
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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
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(Seen from above,
moving up on picture)
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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
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(Seen from above,
moving up on picture)
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Laminated Rubber / Elastomeric Bearings
•Easily handle tons of CF •Oscillate at high frequency•No lubrication•NR for high resilience
Used on most helicopters now
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Enstrom – First with Elastomeric Bearings
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Enstrom Bearing Design
• 2-1/4" in diameter
• More than100 rubber
& brass layers each
• All layers 0.002” thick
• 18,000 lbs. CF
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Small Wind Turbines
• Blade pitch angle variable with wind
• Increase efficiency
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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
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One-inch Square Laminate Pads
• 40 layers .002’ brass• 39 layers .002” NR
• Bendable
• RIGID
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• 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
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Planar & Chevron
• Planar
- angular oscillation & lateral movement
- easier to make – no metal forming
• Chevron
- precludes lateral shifting
- permits taller bearing for given load
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Conical
• Combined radial & thrust loads
• Angular motion about axis
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Cylindrical (Radial) Bearing
• Circular & axial motion
• Wrapped around shaft
• Axial thermal expansion of shaft
• Silicone rubber for heat
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Spherical Bearings
• 3D angular motion about center
- rotation about longitudinal axis
- tilting L/R and in/out of screen
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Helicopter Spherical Bearing
• Many large helicopters
• Ordinary pitch oscillation
• Also lead-lag & flapping
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Design Factors
• Diametral dimensions
• Height
• Load forces
• Torsional stiffness
• Oscillatory torsional shear strain
• Fatigue life
• Angular range.
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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
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Bearing-Seals
• A more recent development by RRC
• New design opportunities
for undersea craft
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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!
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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!
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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.
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• 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
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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
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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
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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
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Laminated Rubber Bearing Technology
• Simplicity
• Low cost
• No lubrication
• Reliability
• Long life
For vehicles that Probe the sky and depths of the sea