Bearings – Rotary bearing – Plain bearing
Patent
1995-12-20
1997-08-26
Hannon, Thomas R.
Bearings
Rotary bearing
Plain bearing
384206, 384909, 384913, F16C 2304, F16C 3324
Patent
active
056604823
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to bearings, especially sliding contact bearings used in aircraft landing gear and incorporating titanium components in surface-to-surface sliding contact.
Titanium is used in aircraft construction because it is lightweight compared with steel, but when used in bearings such as landing gear trunnion bearings that experience large shock loads, there can be problems with galling and seizure between titanium surfaces sliding on one another. It has been proposed in U.S. Pat. No. 4848934 to overcome this problem by coating the surface of one titanium bearing component with chromium oxide and forming the other component of copper. Although chromium oxide is a brittle material, it is considered satisfactory provided the complementary bearing surface with which it cooperates includes copper or copper alloys.
DISCLOSURE OF THE INVENTION
According to the present invention a sliding contact bearing comprises two bearing members composed of titanium or a titanium alloy with cooperating sliding surfaces, characterised in that a first one of said surfaces is chromium plated and the second one of said surfaces is coated with nickel and fluorocarbon polymer.
The nickel is preferably applied by an electroless plating process and provides a high level of wear and corrosion resistance. The fluorocarbon polymer is deposited on the metal surface so as to provide permanent lubrication between the two surfaces. A suitable nickel/fluorocarbon polymer coating may be provided by the General Magnaplate Corporation under their trade mark "NEDOX".
Comparative tests indicate that a bearing according to the invention offers comparable performance and durability to that of conventional bearings comprising a chromium plated steel member in sliding cooperation with an aluminium bronze member and superior performance compared to bearings involving chromium plated, or chromium oxide coated or bronze coated bearing surfaces. Further, bearings according to the invention offer the advantage of limiting the friction between the bearing surfaces due to the effect of the fluorocarbon polymer used.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diametral cross-section through an aircraft landing gear trunnion bearing according to the invention, and
FIG. 2 is a graph of friction against bearing life for a bearing as shown in FIG. 1 compared with a similar bearing in which the outer race is aluminium bronze and the inner spherical member is chromium plated steel.
MODE OF CARRYING OUT THE INVENTION
The aircraft landing gear trunnion bearing of FIG. 1 comprises an outer ring-shaped bearing race 1 with an inner bearing surface 2 formed on a sphere, and an inner ring-shaped bearing member 3 located within the outer bearing race 1 with an outer bearing surface 4 formed on a sphere so as to cooperate with the inner bearing surface 2 of the race 1 and allow relative rotary and sliding contact between the two bearing members 1, 3. The outer bearing race 1 is adapted for connection to one part of aircraft landing gear, and the inner bearing member 3 is formed with a bore 5 to receive the journal of a trunnion on the leg of the landing gear.
The two bearing members 1 and 3 are composed of titanium or titanium alloy, and to avoid galling between the cooperating surfaces of these bearing members, the inner surface 2 of the outer bearing race 1 is chromium plated, and the outer surface 4 of the inner bearing member 3 is coated with nickel and fluorocarbon polisher. The nickel is applied by an electroless plating process and the fluorocarbon polymer is subsequently infused into pores in the plating, and the coating is heat treated to create a smooth surface. This nickel/polymer coating is typically that provided by General Magnaplate Corporation under their trade mark "NEDOX". Typically, the coating is 0.025 to 0.041 mm thick and has a hardness in the range 750-1000 VPN.
For comparison purposes, the bearing as described above and a similar "standard" bearing with the outer bearing race 1 composed of chromium plated steel a
REFERENCES:
patent: 4846122 (1989-07-01), Kristof et al.
patent: 4848934 (1989-07-01), Blakely et al.
patent: 4938850 (1990-07-01), Rothschild et al.
patent: 5325732 (1994-07-01), Vogel
patent: 5328273 (1994-07-01), Nonaka et al.
Davies-Jones Alun
Newley Richard Andrew
Smith Paul Raymond
Dowty Aerospace Gloucester Limited
Hannon Thomas R.
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