Bearings – Rotary bearing – Water lubricated propellor shaft or well shaft
Reexamination Certificate
2001-08-23
2003-11-18
Lavinder, Jack (Department: 3683)
Bearings
Rotary bearing
Water lubricated propellor shaft or well shaft
C384S295000
Reexamination Certificate
active
06648510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a bearing assembly, and more particularly, to a new and novel cost-effective bearing assembly for use in supporting a water-lubricated propeller shaft such as in large ships, the bearing assembly having low bearing wear and greatly reduced shaft wear.
2. Description of the Prior Art
The need for lower first-cost and longer-lived components in marine propulsion shaft systems is always important because of the cost of acquiring and operating such systems. The challenge that confronts the rudder and main propulsion shaft water-lubricated bearings supplier is how to reduce the total bearing system wear. System wear life reduction concerns shaft/sleeve wear as well as bearing wear. There have been many attempts at producing a bearing with a low coefficient of friction to reduce the bearing wear. However, a low coefficient of friction does not guarantee low system wear. Shaft wear may be excessive while bearing wear is low.
In the prior art, bearing assemblies utilizing a combination of load bearing elements known as staves lining the interior of the bearing housing are well known. The staves have generally been made out of wood or elastomeric materials. Many patents exist for different arrangements of the staves within the bearing housing and materials used for the staves. Each of the various bearing arrangements seek to reduce the coefficient of friction between the bearing surface of the staves and the propeller shaft and to reduce the wear thereon of both members, primarily of the bearing material.
For example, U.S. Pat. No. 2,382,270 issued to Enz relates to a bearing assembly having staves therein and a keeper strip which is formed of laminated fibrous material such as paper, cloth, fabric, fiberglass, etc., impregnated with a resinous binder such as phenolic, urea, vinyl, and the like.
U.S. Pat. No. 3,497,278 issued to Orndorff, Jr., relates to a shaft bearing wherein the bearing surface is formed of strips of elastomeric material which line the inner periphery of a cylindrical housing between radially inwardly projecting lugs with each strip being secured therein by a locking bar inserted into a longitudinal groove in the strip.
U.S. Pat. No. 3,561,830 issued to Orndorff, Jr., relates to a resilient elastomeric insert for bearings of the type used for marine propeller shafts wherein the insert is formed of a low hardness elastomeric material and has rigid backing strips inserted in the elastomer spaced closely adjacent to the bearing surfaces.
U.S. Pat. No. 3,826,547 issued to Finefrock relates to the demountable water-lubricated bearing wherein a housing is formed with a cylindrical bore in which a plurality of symmetrically spaced keys are mounted. A complement of staves formed entirely of elastomeric material are positioned in the bore and directly compressed by a removable compression head to cause tight engagement between the bore and keys. Removal of the compression head allows the staves to assume their unstressed condition in which clearance is provided with respect to both the bore and the keyways.
U.S. Pat. No. 4,607,964 issued to Kramer et al. discloses a water-lubricated bearing assembly having a plurality of circumferentially spaced first set of bearing elements with substantially flat surfaces and water courses therebetween supporting a shaft for rotation. Certain ones or all of such bearing elements support a second set of bearing elements that are movable radially into supporting engagement with the shaft such that either the first set or second set of bearing elements are the prime supports for the shaft and wherein such first and second set of bearing elements have different coefficients of friction.
Heretofore, the material the staves in these bearing assemblies was composed of an elastomeric material such as natural rubber or a synthetic rubber, such as nitrile rubber, or a combination of these materials that could be vulcanized to exhibit both low wear and a low coefficient of friction when lubricated with water. A physical property called “hydrodynamic lubrication” occurs under certain conditions with bearings made from these materials and lubricated with water. When hydrodynamic lubrication occurs, a very thin film of water is pumped constantly between the bearing surface and the propeller shaft by the rotating propeller shaft, resulting in very low friction between the two surfaces.
The new super demountable designs combine the best features of the demountable designs with the performance advantages of the new Slippery Polymer Alloy (SPA). SPA is the subject matter patented in U.S. Pat. No. 4,735,982 issued to Orndorff, Jr.
There already exists one patent for a bearing assembly using the new Slippery Polymer Alloy (SPA). U.S. Pat. No. 5,932,049 issued to Orndorff, Jr., provides a top layer of SPA provided on the stave element. SPA exhibits superior system wear resistance properties at all shaft speeds.
In a paper entitled “Lubrication in a Sea-Water Environment,” Naval Engineers Journal (1963), pp. 841-854, the authors commented on judging the performance of propeller shaft bearings and said that static and running friction, noise-producing tendencies and life are very relevant. Cost must be added today in the case of both naval and commercial vessels. Their list of the factors believed to be of concern in bearing and shaft sleeve life are listed below:
1. Load
2. Rubbing Velocity
3. Velocity-Time Interactions
4. Time at Zero Velocity
5. Total Operating Time
6. Shaft and Bearing Roughness
7. Type and Amount of Abrasive
8. Uniformity of Loading
9. Shaft and Bearing Materials
All of these factors must be considered in bearing and shaft sleeve design. For example, the life of most materials is adversely affected by increases in pressure either by adding extra radial load or by shortening of the bearing. When their paper was written, the best water-lubricated bearing designs they considered were made of harder rubber brass-backed staves having machined bearing surfaces and overthick rubber with improper land edges, all of which contributed to unpredictable and intermittent hydrodynamic operation. Excessive time at zero velocity, commonly called dwell time, results in an elevated breakaway coefficient of friction at shaft start-up for many bearing materials. The desired operating time and operating profile (number of start-ups, time spent at low shaft speed) is very important especially in military operations. Shaft and bearing roughness must have the correct finish and texture combination. The possibility of operating in abrasive conditions must be considered. The uniformity of loading is strongly affected by such things as shaft alignment and bearing length, as well as the compressive stiffness of the bearing material. Finally, shaft and bearing materials are listed last, but not the least in importance even when there were only a limited number of suitable material candidates for water-lubricated bearings.
A history of water-lubricated bearings will help to further understand the invention described below.
In 1956 John Penn described to the Institution of Mechanical Engineers his series of experiments running different bearing materials in a tank of water. These experiments led to his invention of the first successful (lignum vitae) water-lubricated bearings. Over the years, various other wood bearings have been developed, such as oil-impregnated maple, which has found a niche in certain types of agricultural machinery where the lubricant is particularly aggressive. Glass bearings were tried as were various ceramic combinations, some of which are still used today. Many types of plastics have been tried with water lubrication over the years. One that has lasted into modern times has been phenolic, a thermosetting plastic reinforced with various natural and manmade fibers. Lignum vitae bearings were in wide use in commercial and international naval vessels until the 1960's. One of the most well-known applications of lignum vitae bearings was the main sha
Orndorff, Jr. Roy L.
Spangler Richard C.
Duramax Marine, LLC
Hochberg D. Peter
Lavinder Jack
Mellino Sean
Vieyra Katherine R.
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