In this presentation by Bal Seal Engineering, we examine the challenges between seal design and gimbal performance, and suggest ways to achieve the elusive balance between low friction and sealing effectiveness.

1. Sealing Efficiency vs. Friction in
Gimbals, Pods & Pan-tilt Systems
James Mecredy, Global Market Manager
Karina Chavez, Applications Engineer
Bal Seal Engineering, Inc.

2. Slide 2
Common Gimbal Environments
• Aircraft –
fighter/helicopter/UAV
 High vibration, fast moving,
demand for more accuracy
• Shipboard
 Environmental concerns
• Land-based
 High rotational/speed
requirements

3. Slide 3
Common Applications
• C4ISR Gimbals/Pods
• High Energy Laser Turrets
• LaserComm Gimbals

4. Slide 4
Gimbal Seals: A Critical Element
• Protect sophisticated equipment in harsh
environments (radar, targeting, imaging)
• Enable precision targeting, regardless of craft
conditions (high speed, high vibration,
adverse weather conditions)

5. Slide 5
Sealing Factors That Impact Design
• Friction
 Drives actuator selection/sizing
 Impacts power usage
 Difficult to model
• Environmental sealing
 Moisture/dust/dirt prevention
 Inhibiting contamination, corrosion,
and condensation
• Pressure maintenance
 Pressure differential variance
 Use of Desiccants/Vents
• Lifetime maintenance
 Durability of seal
 Field maintenance requirements
 Use of lubricants

6. Slide 6
Sealing Factors That Impact Design:
A Closer Look
• Friction
 Highly non-linear behavior
 Function of rate
 Dramatic transition through zero rate
(stiction)
 Challenges for precision
pointing/stability
 Impacts max slew rates and
acceleration
 Highly dependent on temp, pressure,
surface finish, condition of materials
• Survivability
 Broad temp ranges (from -40 °C -
60 °C)
 Salt spray, dust, hydraulic fluid,
fuel, etc.
 Seal wear dependent on material
choices
 Pressure changes can change
friction profile dramatically

7. Slide 7
Sealing Factors That Impact Design:
A Closer Look
• Leak rate/contamination
 Compliance with mission
requirements
 Sealed versus breathable
design
 Desiccants or vents
 Leak rate allowance
• Pointing and stabilization
 Larger mass = stabilizing
inertial momentum
 Lower mass systems
dominated more by friction
 Dynamic pointing requires
friction compensation

8. Slide 8
Sealing Factors That Impact Design:
A Closer Look
• Sealing efficacy vs. sealing friction
 Preload amount trades sealing capability
with friction
 Directional seals
• Seal gland materials and surface
finish
 Gland must be compatible with the seal
 Gland surface finish affects friction
• Seal size vs. manufacturing precision
 Smaller seal cross section  greater
manufacturing precision required
 Tolerance stack-ups become very critical in
smaller systems
 Assembly process is crucial in achieving
housing tolerance geometry

9. Slide 9
Key Seal Design Considerations
• Low friction and low stiction
 Necessary for precision pointing and
stability
 Drives the selection of other system
components
• Sealing efficacy
 Sealing while still meeting friction
requirements is critical
 Prevention of environmental
contamination
 Sealing moisture, dirt, salt, dust, etc.
• Survivability
 Large temperature range, vibration
conditions, rotation, high speed
• Seal life
 Meet field maintenance requirements

10. Slide 10
Factors Affecting Seal Friction
• Seal material choice
 Filled PTFE with low friction coefficient
• Spring energizer
 Optimal force for balance of sealing effectiveness
• Seal profile
 Geometry that minimizes contact without
compromising sealing performance
• Seal size/diameter
 Low cross-section to diameter ratio
• The hardware
 Smooth surface finish*
 Material hardness to (30 Rc min.)
 Lubrication
• Additional factors
 Media type (dry, abrasive, lubricating)
 Seal usage after thermal cycling
 Pressure and speed
*Surface finish vs. friction
PTFE seal wear is proportional to frictional force
Improving surface finish reduces friction and provides greater
sealing contact between the seal and mating surface, thus
improving sealing ability

11. Slide 11
Optimizing the Seal Design
Requirements Solutions
• Low friction and
“stick slip”
• Resistant to various
environments and
chemicals
• Bal Seal® spring-energized seal made from
PTFE material
• Low coefficient of friction and low stick-
slip
• Large temperature range
• Polymer-filled PTFE material
• Increased wear resistance
• Friction not compromised
• Large gland height
tolerances
• 1 bar of pressure
differential or less
• Bi-directional
pressure
• Flexible seal lips
• Custom-engineered seal lips
• Bal Spring® canted coil spring energizer
• Precisely control forces (within 10% of
nominal)
• Accommodates large tolerance stack-up
• Wide temperature
variations
• Large diameter
relative to cross
section
• Bal Seal® face seal profile
Bal Seal cross section
with customized, low
friction geometry

12. Slide 12
Summary & Recommendations
• To eliminate costly mistakes and
delays, consider sealing
requirements as part of overall
system design
• In early design stages, collaborate
with Bal Seal Engineering to:
 Custom design a seal that meets all
your system/application requirements
 Produce high-quality seal prototypes
 Perform seal testing to verify
performance
 Friction testing
 Dynamic leak vs. friction testing
 Pressure
 Spray-down
 Transition successful prototype to full
production - 100 to 1M+ unitsBal Seal Engineering’s Friction &
Leak RateTesting Fixture

13. Slide 13
Resources & Contact Information
James Mecredy
Global Market Manager, Aerospace & Defense
Bal Seal Engineering, Inc.
jmecredy@balseal.com
Karina Chavez, EE
Applications Engineer
Bal Seal Engineering, Inc.
kchavez@balseal.com
sales@balseal.com www.balseal.com +1 949.460.2100 Design request form

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