Static and Dynamic Shaft Seal Assembly

This invention relates generally to mechanical equipment shaft sealing devices and more particularly concerns a shaft seal mechanism which seals effectively when a shaft is at rest, and which changes configurations so as to seal effectively but without friction when the shaft is rotating at an operating speed.

Bearings and mechanical seals may be responsible for up to 80% of rotating equipment failures. There is a close relationship between the life of these two critical components. The failure of a mechanical seal may cause the bearings to fail and poor bearing conditions can reduce seal life. It is estimated that only 10% of bearings achieve their minimum design life of from 24,000 to 40,000 hours (3 to 5 years). Rain, product leakage, debris, and wash-down water entering the bearing housing contaminate the bearing lubricant and have a catastrophic effect on bearing life. Very small amounts of water can compromise bearing life. A contamination level of 0.002% water in the lubricating oil can reduce bearing life by as much as 48%. As little as 0.10% water is reported to reduce bearing life by as much as 90%.

Auxiliary mechanical equipment shaft seals, sometimes called bearing isolators or sealing rings, have become increasingly important to modern mechanical equipment, especially for equipment called upon to operate in hostile applications. For example, mechanical power transmission units used in rock quarries are often subjected to highly abrasive dust particles. Elastomeric lip or O-ring shaft seals can quickly wear out and fail in environments such as these. Dust and exterior contaminants cannot be excluded from the interior of the transmission housing by a failed standard sealing device. Nor can oil or other fluids be prevented from leaking out of the transmission devices past a worn lip seal.

To prevent the ingress of corruption and the egress of lubricating fluids, a number of auxiliary or improved primary sealing arrangements and devices have been provided. Some of these sealing devices provide a physical engagement of the shaft and a wiping action while the shaft operates. Other devices provide an interengagement and wiping action between seal parts. But in both such arrangements, the inevitable friction causes inevitable part wear.

For example, lip seals, commonly known as oil seals, are a well-established method of protecting bearing housings from water, dust, chemical or steam contamination. Lip seals normally involve a stationary elastomeric lip or lips touching the rotating shaft or sleeve at an angle so that contaminants are excluded from the housing. While lip seals have a low initial cost, lip seals have a short protection life, approximately 3,000 hours, due to wear of the elastomer or the shaft itself.

Another type of seal is a labyrinth device which contains a tortuous path that makes it difficult for contaminants to enter the bearing housing to degrade lubricant effectiveness. The advantages of labyrinths are their non-wearing and self-venting features.

Some of these commercially successful seal devices do not require any actual physical interengagement of the sealing member parts. Among such devices which have met with considerable commercial acceptance are those disclosed in Orlowski U.S. Pat. No. 4,706,968; Orlowski 4,466,620; Orlowski 4,175,752; Orlowski 4,114,902; Orlowski 4,022,479; and Orlowski 4,832,350. The disadvantages of labyrinth seal devices include higher initial costs than lip seals, and the existence of an open path to the atmosphere that can allow the contamination of the lubricant by atmospheric condensate as the housing chamber "breathes" during temperature fluctuations in humid environments when the equipment cycles on and off.

The hollow O-ring seal disclosed in applicant's patent 4,989,833 provides static sealing action when the shaft is at rest, and non-contact dynamic sealing action when the shaft is rotating. The solid O-ring seal disclosed in applicant's parent application serial number 07/624,881 also provides static sealing action when the shaft is at rest and non-contact dynamic sealing action when the shaft is rotating. However, in some instances, a small percentage of these O-rings have insufficient lift-off from the stator during rotation of the shaft, such that the seal is subject to premature fatigue and failure due to heat and friction.

Therefore, it is the primary objective of the present invention to provide an improved static and dynamic seal for use with machinery having a housing through which a rotatable shaft protrudes, and which provides effective part-to-part contact static sealing action when the shaft is stationary and which provides effective non-contact dynamic sealing action when the shaft is rotating at operating speed.

It is another objective to provide a machinery seal of the type described in which a solid O-ring seal member engages both a seal stator and a seal rotor when the shaft is at rest, but in which the sealing member expands circumferentially so as to disengage from the stator when the shaft rotates at a normal operating speed.

Still another objective is to provide a seal of the type described which will provide a long, trouble-free service life.

To accomplish these objectives, an isolator mechanism is provided for use with a machinery housing and a rotatable shaft protruding through the housing. The isolator mechanism comprises a stator ring affixed to the housing and a rotor ring which is attached to the shaft. The stator and rotor are so shaped that the stator has a male cylindrical surface, and the rotor has a female cylindrical surface located radially outwardly of the stator male surface. A solid, yet stretchably deformable, annular seal member is mounted on the rotor female surface and engages the stator male surface when the rotor and seal member are at rest. However, the seal member is stretched by centrifugal force into a configuration out of engagement with the stator when the rotor and seal member are moving at operating speeds.

Other objects, advantages and embodiments of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. Throughout the drawings, like reference numerals refer to like parts.

FIG. 1 is a sectional view of a typical machinery housing, bearing, and protruding shaft upon which is mounted a novel seal of the present invention, with the shaft being at rest.

FIG. 2 is a sectional view similar to FIG. 1 showing the seal in further detail.

FIG. 3 is an exploded view of the seal of the present invention.

FIG. 4 is an enlarged sectional view showing portions of seal parts as they appear when the shaft is stationary.

FIG. 5 is an enlarged sectional view similar to FIG. 4 showing the bearing seal parts as they appear when the shaft is rotating at an operating speed .

While the invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to this embodiment. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention.

Turning first to FIG. 1, there is shown the novel seal or bearing isolator 10 as it appears when installed on and within a housing 12. A rotatable shaft 13 protrudes through this seal 10 and the housing 12. A bearing 14 is functionally interposed between the stationary housing 12 and the rotatable shaft 13 in known manner.

As shown in FIGS. 1, 2, and 3, the novel seal comprises, in general, a ring-like stator 20 which is affixed to the housing 12 and a mating rotor ring 22 which is secured to the shaft 13, and which follows the rotational motion of the shaft 13. The rotor and stator 20 and 22 can be formed of any suitable material such as bronze, steel or plastic of an appropriate formulation. The stator 20 is designed and sized to fit securely by means of a light metal-to-metal interference fit within a recess 24 formed in the housing 12. An O-ring seal 26 of known sort provides an effective and permanent seal between the stator 20 and the housing 12 so as to exclude dust and other corruption from the outside environment E, and to inhibit or prohibit the leakage of oil or other fluid from the housing inside I. As shown particularly in FIG. 3, the stator 20 is annular in general shape, but is formed so that its inner surface 28 is generally cylindrical in shape, and is sized to provide a modest clearance between that surface 28 and the adjacent outer surface of the shaft 13. Thus, the stator 20 is rigidly affixed to the housing 12 but does not engage the shaft 13.

To collect lubricating fluids and inhibit their passage down the shaft 13, an annular fluid catchment groove 30 can be formed in the interior of the stator 20. The illustrated groove 30 is provided with a first or downstream face 32 oriented generally perpendicularly to the axis A of the shaft 13, and a second opposed face 34 which is conical in shape. This groove configuration has been found to be effective in collecting oil or other fluids which may flow along the surface of the shaft 13 in a direction leading from the interior I of the equipment housing towards the exterior environment E. A return or drain groove 36 located at the bottom of the stator 20 is sloped toward the shaft axis and collects the accumulated oil or other fluid and encourages its return to the interior bottom of the housing 12.

The rotor 22 is affixed to and rotates with the shaft 13. To this end, the rotor 22 is provided with a restrictive recess 42 in which is mounted an O-ring 44 of known type. The O-ring 44 is sized and otherwise designed to be moderately compressed within the recess 42 and as to engage the shaft 13 with a modest amount of compressive pressure, in known manner.

To provide a static seal between the stator 20 and the stationary rotor 22 in accordance with the invention, the rotor 22 is formed with an axially-extending flange 50, and the stator 20 is provided with a mating recess 52. At their radially inner portions, the rotor flange 50 defines an axially-extending, cylindrical female surface 54 and the stator 20 has a mating, confronting, underlying, axially-extending surface 56. Between these surfaces 54 and 56 is interposed a solid, yet stretchable O-ring seal member 60, which engages both the stator 20 and the rotor 22 when the shaft 13 and rotor 22 are at rest.

In the preferred embodiment, this stretchable seal member 60 is disposed in a recess 62 formed in the rotor flange 50, and the seal member 60 is sized and shaped so as to engage the confronting and adjacent stator male surface 56 and the opposite side walls 63 of recess 62 when the rotor 22 and shaft 13 are not in motion. To improve seal-stator engagement and sealing contact when the seal and rotor are at rest, the stator surface 56 is interrupted by a groove 64 which is axially centered relative to the recess 62. This groove 64 defines two opposed shoulders 66, 68. The shoulders 66, 68 engage the resilient seal member 60 along two opposed annular lines of contact when the rotor 22 is not in motion. Thus, positive, physical seal engagement occurs between the sealing member 60 and the stator 20 along the two opposed annular shoulders 66, 68; and positive, physical engagement between the seal member 60 and the rotor 22 occurs at all times along annular lines of contact 69 between the seal 60 and the side walls 63 of the recess 62. A gap exists between seal 60 and the bottom wall 65 of recess 62 when the rotor is stationary. The at-rest configuration of the seal parts is shown in FIG. 4.

However, in further accordance with the invention, the solid seal member 60 centrifugates away from its engagement with the stator 20 when the rotor 22 and shaft 13 are turning at an operating speed, as shown particularly in FIG. 5. The excessive radial depth of recess 62 allows seal 60 to expand or stretch circumferentially during rotation, so that the seal disengages from surface 56 of stator 20. This lift-off or seal disengagement occurs because the centrifugal force applied to and experienced by the seal member 60 causes that seal member 60 to stretch radially as the member slides along the walls 63 of the recess 62 and away from the underlying stator male surface 56, as particularly shown in FIG. 5. Under these circumstances, there is no physical interengagement between any static portion of the seal and any rotating portion of the seal when the shaft is turning at its operating speed. Accordingly, the sealing member is dynamically effective to inhibit the ingress of corruption or the egress of fluids, yet it is frictionless and does not wear in operation.

As seen in FIGS. 4 and 5, the seal member 60 has a substantially circular cross section, both at rest and when rotated. When the shaft is at rest, there is, preferably and approximately, a 0.010 inch space between seal member 60 and the bottom wall 65 of recess 62. The gap allows a 0.010 inch lift-off of the seal member from stator surface 56, with a corresponding 0.020 inch increase in circumference of the seal member.

A lubricant, such as grease or the like, may be utilized in groove 64 so as to reduce the friction between the seal member and the stator at the initial rotational start up of shaft, before a sufficient operational speed is achieved to produce lift-off of the seal from the stator.

Preferably this resilient seal member 60 is a solid toroid formed from a nitrile or flora-elastomer material, such as viton, which is manufactured by Du Pont. The seal preferably has a low durometer hardness, shore A, ranging from 40-70 so that the seal is resiliently deformable.

As will be understood by those skilled in the relevant arts, the seal member 60 increasingly deforms and lifts away from engagement with the underlying stator as the centrifugal forces increase. These centrifugal forces increase in squared proportion to the linear speed of the moving sealing element 60.

In carrying out the invention, additional surface formations are provided in the stator recess 52 and mating rotor flange 50 to inhibit the ingress of corruption and the egress of fluids, especially when the shaft 13 is rotating. Here, the rotor flange 50 is formed so as to have a series of shoulders or corners 70-79 and annular collection grooves 80, 82. The stator recess 52 is likewise provided with a mating projection 84 and corners 90-94. These concentric stator and rotor rings define an annular, convoluted, labyrinth passage 96 of extended length and various sixes or thicknesses. This path is, at its thinnest portion, from 0.007 inches to 0.150 inches in radius or thickness. Consequently, the rotor can spin or rotate within the stator with practically zero friction between the respective surfaces. The labyrinth path effectively prevents lubricants from passing outwardly from the interior housing I to the exterior E, and also prevents the ingress of corruption from the exterior E of the interior I.

At the bottom of the stator 22 is located a radially-inwardly extending bore 100 which communicates with this collection groove 96. The bore 100 leads to the outside E of the machine housing 12, and permits corruption and other materials which may have collected within the collection groove 96 to expel out of and away from the seal device 10.

It will be observed that the manufacture of the stator 20, the rotor 22 and the solid seal 60 can be accomplished quickly and easily by known methods. When assembled, the stator and rotor do not physically engage one another and are interference-free both in configuration and in dynamic operation.

From the foregoing, it can be seen that the present invention accomplishes at least all of the stated objectives.