Relationship to Copendinα Applications

This application is a continuation-in-part of copending applications Serial No. 07/875,889 filed April 29, 1992, Serial No. 07/868,080 filed April 13, 1992, Serial No. 07/735,920 filed July 25, 1991 and Serial No. 07/738,007 filed July 30, 1991, the latter two of which, in turn, are continuations-in-part of application Serial No. 07/595,420 filed October 11, 1990, now abandoned. The entire contents of all of the above applications are hereby incorporated by reference.

Technical Field

This invention relates to sealing devices for rotating shafts and more particularly to seals located between a rotating shaft and a housing of a pump, pressure vessel or the like in which fluid is contained under pressure. Such fluids may include liquids, gases, or slurries including fluids containing corrosive chemicals.

Background Art

In industries with manufacturing processes involving fluids, numerous pumps and other rotary shaft devices are required for the transport and handling of fluids such as slurries and chemical solutions. The flushing water requirements of these seals for seal lubrication and radical or fugitive emission suppression greatly increased operational water requirements and increased the volumes of liquid wastes requiring treatment to remove environmental pollutants.

Our rotary seals are developed to solve these problems. These seals are believed to rely on mixed boundary asperity lubrication between a resilient seal member and a hard smooth surface of an opposed sealing member, the pressure at the contact surface between these two members being sufficient to minimize flow of liquid between their sealing faces. The normally high friction

between such elastomeric materials and hard surfaces would appear to so severely limit the useful life of such seals that they would not be practical. One would expect that a significant flow of liquid lubricants would be required to reduce this friction.

However, we have found that if the contact area of the resilient member is minimized, the resilient materials at the contact area are stress hardened, the polymeric components aligned in a direction parallel to the hard sealing surface, and heat transfer elements are provided to remove heat from the sealing contact surfaces, the life of such seals are greatly extended and satisfy industrial requirements, without conventional thin film liquid lubrication. These "dry faced" seals require negligible flow f product for lubrication, unlike conventional mechanical seals. The liquid product in the stuffing box has a primary function of removing heat. Remaining heat is removed by conduction through the stationary sealing member.

We have also observed that the failure rate for rotary seals increases if the seals are operated in the absence of process liquid since the liquid functions a seal coolant. This can occur when a pump is activated without a liquid supply or through failure of liquid supply during operation.

Disclosure of the Invention

It is an object of this invention to provide a dry face seal with a long operational life without requiring flushing liquid lubrication during operation, and which can be used with rotary pumps and other devices operating with all types of liquids and suspensions.

It is a principal object of this invention to provide a sealing method and apparatus using a resilient sealing member with a minimized sealing contact area and with an auxiliary liquid coolant, the coolant providing sufficient

heat transfer to maintain the temperature at the sealing surface below destructive levels during all phases of operation.

It is another object of this invention to provide a dry face seal which reduces the volume of water used in manufacturing facilities and released therefrom into the environment, and which can be used with liquids containing or producing gaseous components without releasing hazardous amounts of the gaseous components into the environment.

It is a further object of this invention to provide liquid between tandem rotary seals according to this invention, the liquid providing the functions of removing heat from the seals, seal lubrication, and a further barrier to escape of gaseous components.

In summary, the tandem dry face rotary sealing device of this invention is adapted to be mounted on a rotary shaft. The sealing device comprises an annular auxiliary liquid chamber, the axial limits thereof being defined by first and second annular rotary sealing means. The first annular rotary sealing means constitutes means for preventing escape of process liquid along the rotary shaft in one direction and escape of auxiliary liquid from the auxiliary liquid chamber along the rotary shaft in the opposite direction. The second annular rotary sealing means constitutes means for preventing escape of auxiliary liquid from the auxiliary liquid chamber along the rotary shaft. Each rotary sealing means comprises a seal combination of an annular rigid seal having a smooth sealing surface and an annular resilient seal having an annular projecting edge means for contacting the smooth sealing surface under a biased pressure to form a seal in conjunction therewith, one of the rigid seal and the resilient seal of each seal combination being adapted for attachment to a rotary shaft and the other of the rigid seal and the resilient seal of each combination being

adapted to be secured to a structural casing surrounding the rotary shaft. Each of said resilient seals has a breaking elongation of at least about 90 percent of its original length. Each seal can be stretched at least about 15 percent and preferably from 20 to 40 percent of its breaking elongation in a direction substantially parallel to the smooth sealing surface.

In use, the projecting edge of each seal combination is pressed in an axial direction against the respective smooth sealing surface with a pressure which is sufficient to effect a seal therebetween under operating conditions of the seal but which will not cause destruction of the seal during its normal operating life.

Preferably, the width of each projecting edge in contact with the corresponding smooth sealing surface in the radial direction is less than about 2 mm and each resilient seal has a durometer hardness of from about 85 to about 95. The preferred resilient seals comprise a thermally and chemically resistant elasto eric polymer.

The improved method of this invention comprises use of the above structure to prevent escape of process liquid along the rotary shaft in one direction and to prevent escape of auxiliary liquid from the auxiliary liquid chamber along the rotary shaft in the opposite direction. The first and second annular seals prevent escape of auxiliary liquid from the auxiliary liquid chamber along the rotary shaft. The auxiliary chamber liquid removes heat from the seals and provides lubrication to the seals.

Brief Description of the Drawings

Fig. 1 is a view of a cross-section of a tandem seal of this invention taken along the central axis of the seal.

Fig. 2 is a cross-sectional view of the tandem seal of Fig. 1 taken along the line II-II.

Fig. 3 is an cut-away isometric view of the tandem seal of Fig. 1.

Fig. 4 is an isometric exploded view of the tandem seal of Fig. 3.

Best Mode For Carrying Out The Invention

The devices of this invention are suitable for use with rotary shaft devices used in process and mining industries. For purposes of example and not by way of limitation, the invention is described hereinafter using an embodiment which is particularly adapted for use with slurry pumps. The same basic configurations can be used for other pumps used in chemical manufacturing, and other industries requiring pumping of suspensions and chemical process solutions.

The term "breaking elongation", as used herein, is defined as the percentage of stretch under tension of an elastomer from its relaxed condition to its breaking point.

Seals known prior to our inventions require a constant and substantial flow of liquid between sealing surfaces. The seals of this invention comprises a flat, annular smooth rigid surface and an opposed annular resilient projection which forms a seal therewith. One of the sealing components rotates, and the other is stationary. In the seals of this invention, negligible flow of lubricating and cooling liquid takes place from one side, through and between, to the other side of the sealing surfaces during normal operation of the seal. Hence, the seals of this invention are described as "dry face seals". The term "dry face seal", as used herein, is defined to denote seals which are characterized by the absence of any significant flow of liquid through the seal during normal operation, and little, if any, of liquid from one side of the seal is detectable on the other side. Since the seals of this invention are in constant contact with liquid.

however, minute amounts of liquid may be present between the sealing surfaces, and this liquid, if present, may be involved in an asperity lubrication or elastohydrodynamic lubrication of the seals. The invention and the term "dry face seal" is intended to include seals of the structure described herein whether or not liquid is present between the sealing surfaces during normal operation.

The tandem dry face rotary sealing device of this invention is adapted to be mounted on a rotary shaft. The sealing device comprises an annular auxiliary liquid chamber, the axial limits thereof being defined by first and second annular rotary sealing means. The first annular rotary sealing means constitutes means for preventing escape of process liquid along the rotary shaft in one direction and escape of auxiliary liquid from the auxiliary liquid chamber along the rotary shaft in the opposite direction. The second annular rotary sealing means constitutes means for preventing escape of auxiliary liquid from the auxiliary liquid chamber along the rotary shaft to the external or bearing side of the seal. Each rotary sealing means comprises a seal combination of an annular rigid seal having a smooth sealing surface and an annular resilient seal having an annular projecting edge means for contacting the smooth sealing surface under a biased pressure to form a seal in conjunction therewith, one of the rigid seal and the resilient seal of each seal combination being adapted for attachment to a rotary shaft and the other of the rigid seal and the resilient seal of each combination being adapted to be secured to a structural casing surrounding the rotary shaft. Each of said resilient seals has a breaking elongation of at least about 90 percent of its original length. Each of said resilient seals can be stretched at least about 15 percent and preferably from 20 percent up to about 40 percent of its breaking elongation in a direction substantially parallel to the smooth sealing surface whereby the friction

between the projecting edge and the smooth sealing surface is stabilized.

The auxiliary liquid which is contained between the tandem seals provides a source of cooling liquid for both seals and can be used to remove heat from the seals during normal operation and particularly when liquid is not present on the pressure side of the seal, for example is a pump is energized without liquid in the pumping chamber.

These critical features yield a dry face seal with a surprisingly long useful life. The stress hardening of the contact surface, alignment of the polymers and smoothing of the contact surface of the resilient element provides an effective seal with a minimum contact area even at high operating pressures. The source of auxiliary liquid insures long life even when the seals are engaged in the absence of adequate cooling liquid on the pressure side of the seal.

Referring to the drawings, Fig. 1 is a view of a cross-section of a tandem seal of this invention taken along the central axis of the seal. Fig. 3 is an cut-away isometric view of the tandem seal of Fig. 1 and Fig. 4 is an isometric exploded view of the tandem seal of Fig. 3. Referring to these figures, the tandem seal of this invention comprises a front gland 2 adapted to be mounted on a pump or similar housing in which a rotary shaft is to be mounted and a rear gland 4 adapted to be secured to proximal face of the front gland 2 by socket head screws 6. Mounted on the inner surface of the gland 2 are a distal stationary sealing element 8 (on the pressure side of the seal, distal as viewed from a position exterior of the housing,) and proximal stationary sealing element 10 (on the ambient side of the seal) . Each of these sealing elements is an annular rigid ring such as silicon carbide with a smooth sealing surface sealed to the inner surface of the gland by O-rings 12 and bonded to the forward gland

with a conventional adhesive such as an epoxy resin, for example.

The sleeve 14 is adapted to be secured to a rotary shaft (not shown) for rotation therewith by advancing set screws 16 positioned in threaded holes extending through the sleeve toward the shaft. O-ring 18 seals the sleeve to the rotary shaft. Forward or distal resilient annular rotary seal 20 is positioned in an annular groove 22 in the sleeve 14, and rearward or proximal resilient annular rotary seal 24 is positioned in a corresponding annular groove 26 in the sleeve 14.

Three equally spaced (120° spacing) compression bolts 30 pass through an annular array of openings in sleeve flange 34 for threaded engagement with opposing threaded holes in the rear gland 4. Advancement of compression bolts 30 move the sleeve 14 in the distal direction, thereby advancing the annular stationary seals 8 and 10 against the corresponding opposed surfaces of the respective rotary seals 20 and 24 to establish the sealing engagement of each stationary and rotary seal pair. This "locks" the position of the gland. Three equally spaced (120° spacing) decompression bolts 32 are threadingly engaged with a threaded hole through the sleeve flange 34, the end of each bolt contacting an opposed surface of the rear gland 4. Advancement of decompression bolts 32 move the sleeve 14 in the proximal direction, thereby withdrawing the annular stationary seals 8 and 10 in a direction away from the corresponding opposed surfaces of the respective rotary seals 20 and 24 to adjust the sealing engagement of each stationary and rotary seal pair. The bolts 30 and 32 are used to precisely adjust the engagement of the stationary and rotary sealing components around their entire circular sealing contact area and to maintain a rigid relationship between the core of the gland and sleeve to facilitate installation. This mechanism provides a means to assure

the rotary and stationary elements are parallel and axially concentric.

The elastomeric resilient seal component is made of a chemical resistant elastomer. Preferred materials include chemically and thermally resistant elastomers sold under the trademarks VITON, AFLAS, EPDM and HNBR. Further details about the construction and relative interactions of the resilient rotary seal and the stationary rigid sealing components are described in copending application Serial No. 07/868,080 filed April 13, 1992, the entire contents of which are incorporated by reference.

The seals are formed by contact between the distal stationary seal 8 and corresponding opposed rotary seal 20, and by contact between the proximal stationary seal 10 and the corresponding opposed rotary seal 24. The forward or distal rotary seal 20 and stationary sealing ring 8 are exposed to liquid on the pressure side of the housing during normal operation and are partially cooled by such liquid. The rearward or proximal stationary sealing ring 10 is encased in the forward gland 2 and is not exposed to liquid on the pressure side of the housing. To provide liquid coolant even when liquid is absent from the pressure side of the housing, an annular auxiliary liquid chamber 36 between the sleeve 14 and the forward gland 2 is defined between the sealing pairs 8,20 and 10,24. The sealing surfaces defined between the distal sealing elements 8 and 20 and between the proximal sealing elements 10 and 24 are both exposed to liquid in the liquid chamber 36.

Fig. 2 is a cross-sectional view of the tandem seal of Fig. 1 taken along the line II-II. Auxiliary threaded liquid ports 38 and 40 communicating with the auxiliary liquid chamber 36 can be used either to fill the chamber in a closed cooling configuration or can be coupled with a cooling water recirculating system wherein one port is the inlet connected with a cooling liquid and the other port is

an outlet connected with the cooling liquid return. In the closed cooling system, the ports 37 and 38 are closed with suitable threaded plugs (not shown) .

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will make themselves know without departing from the spirit and scope of the invention. The disclosure and the description herein are purely illustrative and are not intended to be in any sense limiting.