Design World

  • Home
  • Technologies
    • ELECTRONICS • ELECTRICAL
    • Fastening • joining
    • FLUID POWER
    • LINEAR MOTION
    • MOTION CONTROL
    • SENSORS
    • TEST & MEASUREMENT
    • Factory automation
    • Warehouse automation
    • DIGITAL TRANSFORMATION
  • Learn
    • Tech Toolboxes
    • Learning center
    • eBooks • Tech Tips
    • Podcasts
    • Videos
    • Webinars • general engineering
    • Webinars • Automated warehousing
    • Voices
  • LEAP Awards
  • 2025 Leadership
    • 2024 Winners
    • 2023 Winners
    • 2022 Winners
    • 2021 Winners
  • Design Guides
  • Resources
    • Subscribe
    • 3D Cad Models
      • PARTsolutions
      • TraceParts
    • Digital Issues
      • Design World
      • EE World
    • Engineering diversity
    • Trends
  • Supplier Listings
  • Advertise
  • Subscribe

Modern Mechanical Carbon Materials for Aircraft Seal Applications

By Editor | September 17, 2013

Oil-free, self-lubricating mechanical carbon materials possess a combination of characteristics that make them suitable for use in both commercial and military aircraft seal applications.

The materials are self-lubricating, self-polishing, and dimensionally stable, which insures a good sealing mate. They are heat resistant and have a high thermal conductivity, which helps conduct frictional heat away from the sliding surface. In addition, these materials are readily machinable to exacting aerospace dimensional tolerances, and they can be supplied lapped and polished to a flatness specification of one helium light band. In aerospace applications, modern mechanical carbon materials are being used in aircraft gear boxes, air turbine motor starters, and main shaft seals for both aircraft turbine engines and aircraft auxiliary power units (APUs).

The materials are self-lubricating, self-polishing, and dimensionally stable, which insures a good sealing mate

These self-lubricating materials are composed of fine-grained, electrographite substances that are impregnated with proprietary inorganic chemicals to improve their lubricating qualities and their oxidation resistance. They have a low coefficient of friction, low wear rate at high sliding speed, high thermal conductivity, and they resist oxidation in high temperature air. These properties also suit other high speed, rotating equipment, such as high-speed rotary gas compressors and steam turbines.

Aircraft gearboxes reduce the main engine shaft’s rotational speed from as high as 26,000 rpm down to about 3,400 rpm, so the shaft can drive such system components as hydraulic pumps, generators, and air conditioning compressors. To seal the oil lubricant within the gearbox and protect it from leaking out at the point where the shaft enters and exits the gearbox, most aircraft gearboxes use face seals. The face seals usually contain a carbon-graphite stationary ring and a silicon carbide or tungsten carbide rotating ring. The rings that make the dynamic face seal are both lapped flat and are held together with springs or magnets so that liquids cannot flow between the ring faces even though they are spinning against each other at high speed.

The two rings in relative motion that make the dynamic seal are sealed to the shaft or the gear box housing with static seal rings such as polymeric O-rings. Seal designers use spiral grooves, straight grooves, and wedges to channel or pump a thin film of air or oil between the two sliding sealing faces. This creates aerodynamic or hydrodynamic lift, which reduces the friction and wear of the seal faces.

For example, Metcar Grade M-45, manufactured by Metallized Carbon Corporation, is often used successfully as the stationary ring. This material is suited for these shaft seals because it is impermeable and thus able to support an aerodynamic film. It also has the ability to run at high speed with low friction and low wear.

Air turbine motor starters typically use the same carbon-graphite versus silicon carbide or tungsten carbide dynamic face seal materials used in gearbox seals, but the sliding speed is much higher. These air turbine motor starters are actually small turbines that use the exhaust gas from the auxiliary power unit to create the power necessary to start the main engines. The shaft speed on air motor starters can be as high as 180,000 rpm, or a sliding speed of about 1000 feet/second, which is nearly the speed of sound. The seals are designed by aircraft seal manufactures with wedges and gas flow passages to produce aerodynamic or hydrodynamic lift-off. Metcar Grade M-45 is used in air motor starter seals because of its outstanding self-lubricating qualities at the required operating conditions.

Face seal rings, with carbon-graphite primary rings, and carbon-graphite circumferential seal rings are used in aircraft engine main shaft seals to control the air flow and combustion gas flow inside the engine. They also seal the oil lubricant in the main engine bearings that allow the compressor shaft and the combustion gas turbine shaft to rotate freely. Both circumferential and face type seal ring are used.

For circumferential main shaft seal rings, carbon-graphite segments that fit with close end clearance in slots in the stationary housing are used. The carbon-graphite segments are tensioned against a ceramic or hard metal coating on the rotating shaft using a “garter” spring.

Lifting wedges and machined configurations are used to create lift so that these seals run on an aerodynamic or hydrodynamic film. Rotating speeds can be as high as 26,000 rpm, and temperatures in the seal rings can reach as high as 800 degrees Fahrenheit.

Metallized Carbon Corporation
www.metcar.com

You Might Also Like


Filed Under: Aerospace + defense, Seals • gaskets • O rings, Material handling • converting, MORE INDUSTRIES
Tagged With: metallized carbon corporation
 

LEARNING CENTER

Design World Learning Center
“dw
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for Design Engineering Professionals.
Motor University

Design World Digital Edition

cover

Browse the most current issue of Design World and back issues in an easy to use high quality format. Clip, share and download with the leading design engineering magazine today.

EDABoard the Forum for Electronics

Top global problem solving EE forum covering Microcontrollers, DSP, Networking, Analog and Digital Design, RF, Power Electronics, PCB Routing and much more

EDABoard: Forum for electronics

Sponsored Content

  • Sustainability, Innovation and Safety, Central to Our Approach
  • Why off-highway is the sweet spot for AC electrification technology
  • Looking to 2025: Past Success Guides Future Achievements
  • North American Companies Seek Stronger Ties with Italian OEMs
  • Adapt and Evolve
  • Sustainable Practices for a Sustainable World
View More >>
Engineering Exchange

The Engineering Exchange is a global educational networking community for engineers.

Connect, share, and learn today »

Design World
  • About us
  • Contact
  • Manage your Design World Subscription
  • Subscribe
  • Design World Digital Network
  • Control Engineering
  • Consulting-Specifying Engineer
  • Plant Engineering
  • Engineering White Papers
  • Leap Awards

Copyright © 2025 WTWH Media LLC. All Rights Reserved. The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media
Privacy Policy | Advertising | About Us

Search Design World

  • Home
  • Technologies
    • ELECTRONICS • ELECTRICAL
    • Fastening • joining
    • FLUID POWER
    • LINEAR MOTION
    • MOTION CONTROL
    • SENSORS
    • TEST & MEASUREMENT
    • Factory automation
    • Warehouse automation
    • DIGITAL TRANSFORMATION
  • Learn
    • Tech Toolboxes
    • Learning center
    • eBooks • Tech Tips
    • Podcasts
    • Videos
    • Webinars • general engineering
    • Webinars • Automated warehousing
    • Voices
  • LEAP Awards
  • 2025 Leadership
    • 2024 Winners
    • 2023 Winners
    • 2022 Winners
    • 2021 Winners
  • Design Guides
  • Resources
    • Subscribe
    • 3D Cad Models
      • PARTsolutions
      • TraceParts
    • Digital Issues
      • Design World
      • EE World
    • Engineering diversity
    • Trends
  • Supplier Listings
  • Advertise
  • Subscribe
We use cookies to personalize content and ads, to provide social media features, and to analyze our traffic. We share information about your use of our site with our social media, advertising, and analytics partners who may combine it with other information you’ve provided to them or that they’ve collected from your use of their services. You consent to our cookies if you continue to use this website.OkNoRead more