N122-107 TITLE: Improved Bearing Material for Aircraft Carrier Arresting Gear Components

TECHNOLOGY AREAS: Materials/Processes

OBJECTIVE: Develop a dynamic bearing material (aka "slipper") to replace the current material used in the various subsystems of the carrier based arresting gear system that has improved service life with emphasis on galling and embedding resistance over the current material.

DESCRIPTION: Carrier aviation is dependent on the ability to recover aircraft expeditiously and safely aboard ship. The system that arrests the aircraft, the Arresting Gear system, utilizes slippers or bearing materials between moving components. The current slippers material conforms to specification MIL-P-5431 or commercial product Spaulding T-768. This material is a cotton-fabric reinforced graphite phenolic-based composite material. It is currently sole source procurement, and swells when exposed to ethylene glycol, which causes clearance issues in the operating equipment. When this material is used as packing, galling of material results in unwanted leakage, necessitating replacement prior to scheduled maintenance. Maintenance involving replacement of the slippers is a labor intensive, expensive process.

The Navy is seeking a material for the slippers that is more wear resistant than the current material. Improving the life of the slippers will result in labor savings and greater equipment availability.

The slipper materials bear the weight of the various arresting gear components: main engine cylinder piston, crosshead, accumulator piston, and sheave damper piston. The slippers are the sliding medium between arresting gear components to allow free movement during arrestments, therefore the static and dynamic frictional characteristics of the slippers are significant. The slippers bear the weight of the components both statically and dynamically during arrestments. Static loading on slippers varies from 10 psi to 530 psi. The dynamic loading has not been resolved. The slippers are subject to immersion in ethylene-glycol based hydraulic fluid, humid air, and various greases and lubricants. The slippers must maintain dimensional stability throughout their lifetime, and have low wear rates compared to the existing material. System operating temperature is ambient to 200 degrees F. Acceleration of components varies from 0 to 18 G’s during an arrestment. Total linear movement of the slippers during an arrestment is from 0 in. to 112 in. Velocity of the slippers during an arrestment ranges from 0 in/s to a peak of 540 in/s. It is desired for the slippers to have a life of 20,000 arrestments, with no shelf life limitations. The slippers are presently machined to shape, and some are required to be custom fitted and machined in situ during replacement. It is desired, but not required, for the same material to be used in all applications.

The Navy will consider proposals for new materials, application of existing materials, or novel approaches to slipper materials, but the solution must be a drop-in replacement for the current material. No proposals that require arresting gear component re-design will be considered.

PHASE I: Develop a concept for an improved "slipper" material including an approach for manufacturing the "slipper" material. Demonstrate feasibility of the approach through limited testing.

PHASE II: Fully develop the concept conceived under Phase I into a prototype "slipper" material for use in the various arresting gear system applications. Demonstrate the ability of the system to provide the required life under operational conditions along with the ability to produce the material in a repeatable fashion.

PHASE III: Perform qualification testing and transition the "slipper" material to the fleet.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Developed materials have broad application as wear and bearing materials, as well as intermediate material between two metal surfaces that slide relative to each other for any industrial application.

REFERENCES:
1. Sketches of Crosshead, Sheave Damper Crosshead, Accumulator slipper cage, MEC slipper cage sketch (to be posted in SITIS during Pre-Release).

2. Slipper location, contamination factors, risks, suggested testing and change methods spreadsheet (to be posted in SITIS during Pre-Release).

3. Locations where slippers are currently used, as well as mating material and bearing material information, including surface finish, and lubrication used. (Posted in SITIS 5/15/12.)

KEYWORDS: Arresting Gear; bearing material; Wear; slipper; dynamic and static friction; Composite

** TOPIC AUTHOR (TPOC) **

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