US3483825A

US3483825A - Gear pump with abrasive resistant sealing elements

Info

Publication number: US3483825A
Application number: US724912A
Authority: US
Inventors: Le Roy A Difford; Charles W Grennan; David L Moorcroft
Original assignee: Chandler Evans Inc
Current assignee: Chandler Evans Inc
Priority date: 1968-04-29
Filing date: 1968-04-29
Publication date: 1969-12-16
Anticipated expiration: 1986-12-16
Also published as: DE1921342A1; FR2007249A1; GB1234692A

Description

Dec. 16, 1969 LE ROY Av DIFFORD ETAL 3, 5

GEAR PUMP WITH ABRASIVE RESISTANT SEALING ELEMENTS Filed April 29, 1968 2 Sheets-Sheet l FIG-2 Dec. 16, 1969 LE ROY A DIFFORD ETAL 3,483,825

GEAR PUMP WITH ABRASIVE RESISTANT SEALING ELEMENTS Filed April 29, 1968 2 Sheets-Sheet 2 %C3 3 FEG.4

nited States Patent O US. Cl. 103-426 8 Claims ABSTRACT OF THE DISCLOSURE A gear pump for pumping fluids containing highly abrasive contaminants, each tooth having an abrasive resistant refractory metal insert extending longitudinally across the tip and radially down from the tip along both lateral faces of each tooth, each insert sealingly engaging the mating arcuate surface of the abrasive resistant refractory metal member of a movable sealing unit to provide an abrasive resistant sealing engagement of the complete sealingly engaged perimeter of each gear tooth insert, with the refractory metal member of the movable sealing unit having a T-shaped configuration cooperatively engaging a mating T-shaped form such that the slip planes provided to accommodate differential expansion intersect at the geometric center of the T-shaped form.

BACKGROUND OF THE INVENTION This invention pertains to gear pumps capable of delivering high output pressures at exceptionally high volurnetric efficiencies when pumping a fluid containing a highly abrasive contaminant.

When the inlet port of a gear pump containing an intermeshing pair of gears is connected to a source of fluid, rotation of the gears in one direction will cause the liquid to be drawn through the inlet port into the housing and carried around in a pocket between the adjacent teeth of both gears and the housing and thence be discharged through the outlet port. The liquid is drawn into the housing due to the increasing free space between the housing adjacent the inlet port as the teeth of the two gears move out of engagement, and is discharged due to the decreasing free space within the housing adjacent the outlet port as the teeth move into engagement, inlet and outlet ports being substantailly isolated from one another by the small clearances between the teeth and the housing.

The volumetric efliciency of such a gear pump depends upon the closeness of the fit between the tips of the gear teeth and the enclosing housing. When such a gear pump is utilized to pump a fluid containing a highly abrasive contaminant, the clearances between the tips of the gear teeth and the surrounding housing rapidly become enlarged and the pump volumetric efiiciency falls oif.

One well known method of providing a solution to this problem of rapid high wear is to insert a wear block in the pump housin adjacent the pump outlet. This Wear block is urged by discharge ressure into engagement with the periphery of the gear teeth adjacent the pump dis- 3,483,825 Patented Dec. 16, 1969 charge area. It has been customary to manufacture the Wear block and the gear teeth of an extremely hard wear resistant material, such as tungsten carbide. The peripheral engagement of the gear teeth and the mating arcuate wiping surfaces of the Wear block present a surface that can withstand the highly abrasive action of the contaminant fluid.

However, the use of tungsten carbide gears and tungsten carbide Wear blocks imposes an excessive weight penalty because of the high specific gravity of tungsten carbide relative to tool steel coupled with the high percentage of the total pump mass represented by the gears and wear block alone.

Further, tungsten carbide displays extremely poor structural fatigue life and notch sensitivity characteristics relative to the tool steels normally used for pump gears. Thus, while tungsten carbide gears may extend the Wear life of a pump operated in a fluid containing highly abrasive contaminants, the individual gear teeth have a tendency to break off as a result of bending fatigue stresses existing across the critical flank section when the gear tooth is analyzed as a beam.

To date, attempts to provide a wear resistant coating of refractory metals on the surface of a tool steel gear by means of flame or plasma arc spray deposition have not been successful due to the inability to obtain a uniform thickness of the coating over the entire tooth form.

SUMMARY OF THE INVENTION This invention pertains to a gear pump that has a separate movable sealing element or wear block engaging the periphery of each gear and incorporating sideplates positioned adjacent each lateral face of the gears and their associated movable elements to provide a pump capable of delivering high output pressures at extremely high volumetric efliciency when pumping a fluid containing a highly abrasive contaminant.

The gear pump organization of the instant invention incorporates tool steel gears having tungsten carbide inserts extending longitudinally across the tips of each gear and radially down from the tip of each gear along both lateral faces of each tooth. The movable sealing element or wear block comprises a two-piece structure having a tungsten carbide element with an arcuate surface that mates with the tips of the gear teeth to provide an abrasive resistant sealing engagement surface between the tips of the gear teeth and the movable wear block. The second element of the movable wear block is a tool steel member having a T-shaped configuration that cooperatively engages a mating T-shaped form on the tungsten carbide Wear block to produce a geometric configuration such that the slip planes generated by the differential expansion of the tungsten carbide and tool steel elements intersect at the geometric center of the T-Shaped form. Thus, this configuration produces an organization whereby the mating sealing surfaces are of tungsten carbide, which is particularly suitable for its wear resistant properties, but includes a structure where the bulk of the gear and the wear block mass are composed of the less dense tool steel thereby providing a configuration of considerably less weight. Additionally, the T-shaped mechanically connected two-element wear block wherein one element is composed of tungsten carbide, and the other element is composed of tool steel forms a structure whereby the regions subjected to high bending stresses are composed of the tool steel and the sealing surfrace exposed to wear is composed of tungsten carbide.

An object of this invention is to substantially reduce the weight penalty associated with the use of tungsten carbide to reduce the wear associated with pumping fluids containing a highly abrasive contaminant by joining tungsten carbide inserts to a portion of the perimeter of each gear tooth and running the carbide inserts against a mating tungsten carbide wear block element to provide a highly abrasive resistant sealing engagement between the tips of the gear teeth and the mating wear block.

Another object is to provide a wear block unit with a tungsten carbide movable sealing element to sealingly engage the tungsten carbide inserts of the gear teeth Wherein the wear block unit incorporates a mechanically connected tool steel element that engages the tungsten carbide wear block element such that the maximum bending stresses associated with the movable wear block unit occur in the tool steel element.

Another object of this invention is to provide a multielement movable wear block unit wherein one element comprises a tungsten carbide configuration engaging the tungsten carbide insert of the gear teeth, and the second element comprises a tool steel substructure joined to the tungsten carbide wear element by a T-shaped connection so constructed that slip planes provided to accommodate differential expansion of the first and second wear block elements intersect at the geometric center of the held member thereby placing tool steel where needed to resist fatigue and high bending stresses and placing tungsten carbide where required for high Wear resistance when pumping fluids containing highly abrasive contaminants.

It is another object of this invention to provide a light weight gear pump for pumping fluids containing a highly abrasive contaminant wherein the gears incorporate a tool steel tungsten carbide composite configuration, and the wear blocks comprise a similar tool steel-tungsten carbide configuration so constructed that the pump is suitable for operation in a broad thermal spectrum.

Many other advantages and features of this invention will become manifest to those versed in the art by making reference to the detailed specification and drawings which follow.

DESCRIPTION OF THE DRAWINGS The following is a brief description of the drawings accompanying the detailed description of the preferred embodiment of the instant invention.

FIGURE 1 is a front View of one form of a pump incorporating the instant invention.

FIGURE 2 is a longitudinal sectional view taken along line 22.

FIGURE 3 is a section taken along line 3-3.

FIGURE 4 is a section of a first alternate form of sealing block construction similar to that shown in FIGURE 3.

FIGURE 6 is an enlarged fragmentary view of a portion of FIGURE 4.

FIGURE 7 is a perspective view of a single gear tooth showing the arrangement of the refractory metal insert.

FIGURE 8 is a perspective view showing one form of a refractory metal gear tooth insert.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings and first generally to all of the forms shown; in the following general description like parts are designated throughout by like reference numerals.

Referring now to the example shown in FIGURES 1, 2 and 3, there is provided a pump having a housing 1 defining therein a cavity 2 and a pair of sideplates 3 and 4 positioned on opposite sides of housing 1 and secured in fluid tight relationship to said housing and cover by means of a plurality of bolts 6. Rotatably mounted about axes of rotation 7 and 8 in cavity 2 of housing 1 are a pair of intermeshing gears 9 and 10 engaging one another and an area of intermesh shown generally at 11 to form an inlet chamber shown generally at 12 and an outlet chamber shown generally at 13. Discharge flow is routed from discharge chamber 13 through passageway 14 in loading member 15 to chamber 16 and thence through interconnected outlet 17 in the pump housing.

Shafts

18 and 19 are journalled in

bearings

20, 21, 22 and 23 respectively in housing 1 with a close running fit such that axes of rotation 7 and 8 are maintained substantially parallel. Loading member 15 has an upper portion that mechanically engages

inserts

24 and 25, said inserts having arcuate surfaces that engage the periphery of the tips of at least two teeth of each gear. Loading member 15 has an upper portion having straight flat edges parallel to the lateral faces of gears 9 and 10. Similarly,

inserts

24 and 25 have straight flat parallel faces that are spaced apart a distance identical to the thickness of gears 9 and 10 such that sideplates 3 and 4 will simultaneously sealingly engage the lateral faces of gears 9 and 10, the lateral faces of

inserts

24 and 25, and the straight flat parallel faces of loading member 15.

Inserts

24 and 25 have T-

shaped protuberances

26 and 27 that are disposed in mating T-

shaped recesses

28 and 29 of loading member 15. The

inclined surfaces

30, 31, 32 and 33 of insert 24 engage the mating

inclined surfaces

34, 35, 36 and 37 of loading member 15 such that the differential expansion between the carbide insert 24 and the tool steel loading member 15 will cause the diagonally opposite slip surfaces to form a common plane such that the two slip planes intersect at the point 38 of insert 24. Similarly, the T-shaped protuberance 27 of insert 25 has inclined surfaces that engage mating inclined surfaces of loading platform 15 such that the two diagonally opposite slip surfaces form a common plane that intersects at the center of the T-shaped protuberance of insert 25.

FIGURE 6 discloses an alternate arrangement of the carbide insert and tool steel loading member whereby the T-shaped protuberance 48 of loading element 15 is disposed in a T-shaped recess 49 of insert 24 with the

inclined surfaces

50, 51, 52 and 53 engaging the mating

inclined surfaces

54, 55, 56 and 57 respectively of recess 49 such that the diagonally opposite slip surfaces form a common plane whereby the two slip planes intersect at the point 58 at the center of protuberance 48 in a manner similar to that described in detail above for the loading member 15 having a T-shaped recess receiving a T-shaped protuberance of the insert.

The form shown in FIGURE 5 is the preferred construction in that the critical bending section shown at 59 occurs in the tool steel member as opposed to the critical bending section shown at 60 in FIGURE 6 which occurs in the tungsten carbide member, since tungsten carbide does not possess the bending stress characteristics of tool steel.

Referring now to FIGURE 7, a groove is formed across the tip of each gear tooth and is extended radially inward from the tip of the gear tooth along each lateral face to form a U-shaped recess shown generally at 61 in FIG- URE 7. A U-shaped refractory metal insert shown generally at 62 in FIGURE 8 composed of a material such as sintered tungsten carbide is inserted into each channel of each gear tooth and joined to the tool steel base metal of gears 9 and 10 by any suitable means, such as brazing, electron beam welding, or a refractory metal adhesive. The tooth profile and the lateral faces of the gears are finished ground subsequent to the joining operation to form a unitary structure wherein the refractory metal insert protrudes a small distance such that the tungsten carbide inserts shown generally at 62 of gears 9 and IQ engage the

tungsten carbide inserts

24 and 25 of the movable peripheral sealing means to thereby provide abrasive resistant gear tooth peripheral sealing engagement over the entire arcuate sealing surface.

It is to be understood that the refractory metal insert 62 shown in FIGURE 8 is but one form of insert that may be used. The insert may be alternately constructed of three separate pieces or an Lshaped piece and a single straight piece, any of which alternates may be suitably secured to the channel formed in the gear tooth to provide a final gear tooth form having a refractory metal insert similar in construction to that described in detail for FIGURES 7 and 8.

Further, it has been found that the acute wear problem is at the tip of each gear tooth due to the high peripheral velocity and contact stresses imposed upon the gear tips at the point of engagement with the arcuate wiping surface of the movable peripheral sealing member. The problem of Wear on the lateral surfaces of the gear has been found to be minimal. Since the use of carbide elements imposes an excessive weight penalty, because of the high specific gravity of tungsten carbide relative to tool steel, an alternate form is to construct a carbide insert that extends only across the tip of the gear tooth and does not extend radially downward from the tip along the lateral faces of the gear tooth. It is to be understood that this alternate form of construction will permit a tungsten carbide insert on each gear tooth to engage a mating tungsten carbide surface on the movable peripheral sealing element to thereby provide an abrasive resistant refractory metal peripheral wiping surface while providing for engagement of tool steel sideplates with the lateral surfaces of the gears at the less critical gear tooth lateral surface engagement area.

Several alternate configurations for providing abrasive resistant refractory metal wiping surface engagements and concurrent configurations to reduce the risk of structural failure of mating elements of dissimilar material due to differential expansion have been shown herein. These specific embodiments are set out by Way of illustration rather than by limitation of the invention.

While one embodiment of the present invention and some specific modifications thereof have been disclosed in detail, it will be understood that other embodiments and modifications of the invention are contemplated, It is, therefore, the intention to include in the invention all such modifications and embodiments of the invention.

What we claim is:

1. A gear pump for pumping fluids containing highly abrasive contaminants at elevated temperatures comprising a housing having a bore and end closures, a pair of intermeshing geads, said gears disposed in said bore and journalled in said housing such that the axes of rotation of said gears are positioned substantially parallel, movable peripheral sealing means having an abrasive resistant refractory metal portion sealingly engaging a portion of the tips of a plurality of teeth of each of said gears, said gears having an abrasive resistant refractory metal insert positioned in each gear tooth such that said inserts sealingly engage the mating arcuate abrasive resistant refractory metal wiping surface portion of said movable peripheral sealing means to provide an abrasive resistant gear tooth peripheral sealing engagement over the entire arcuate sealing surface.

2. A gear pump for pumping fluids containing highly abrasive contaminants including a housing enclosing a chamber, a pair of intermeshing gears supported on parallel axes of rotation in said chamber, pressure loaded sideplates urged into engagement with the lateral faces of said gears, movable means including a refractory metal element urged into engagement with a select portion of the perimeter of a plurality of teeth of said gears, each tooth of said gear having a slot formed on a portion of its perimeter, a refractory metal insert sealingly disposed in each of said slots, said inserts cooperatively engaging said sideplates and the refractory metal element of said movable means to form an abrasive resistant fluid sealing engagement between said perimeter portion of said gears and the mating surfaces of said sideplates and movable element.

3. A gear pump, as claimed in claim 2, wherein said refractory metal insert comprises a tungsten carbide ele ment sealingly secured in each of said slots by metallurgical bonding, such as welding or brazing.

4. A gear pump, as claimed in claim 2, wherein said refractory metal insert comprises a tungsten carbide element sealingly secured to each of said slots by chemical bonding with a refractory adhesive.

5. A gear pump, as claimed in claim 2, wherein said movable means includes at least one first member and at least one second member having different coefficients of expansion, said first member being formed of tungsten carbide and having an arcuate surface in sealing engagement with the tips of a plurality of the teeth of said gears and including a generally T-shaped slot positioned opposite said arcuate surface with the surfaces of said T-shaped slot having a position normally substantially parallel to the plane of said arcuate surface being inclined with respect to said plane, said second member having a T-shaped protuberance disposed in said T-shaped slot with inclined surfaces engaging the corresponding inclined surfaces of said T-shaped slot such that the center of the slip plane generated by the differential expansion of said first and said second elements intersects at the geometric center of the T-shaped portion of said second member to thereby preclude any change in the fit of the mating portions of said first and said second members of said movable means.

6. A gear pump, as claimed in claim 3, wherein said movable means includes at least one first member and at least one second member having definite coefficients of expansion, said first member being formed of tungsten carbide and having an arcuate surface in sealing engagement with the tips of a plurality of the teeth of said gears and including a generally T-shaped slot positioned opposite said arcuate surface with the surfaces of said T-shaped slot having a position normally substantially parallel to the plane of said arcuate surface being inclined with respect to said plane, said second member having a T-shaped protuberance disposed in said T- shaped slot with inclined surfaces engaging the corresponding inclined surfaces of said T-shaped slot such that the center of the slip plane generated by the difierential expansion of said first and said second elements intersects at the geometric center of the T-shaped portion of said second member to thereby preclude any change in the fit of the mating portions of said first and said second members of said movable means.

7. A gear pump, as claimed in claim 2, wherein said movable means includes at least one first member and at least one second member having different coefiicients of expansion, said first member being formed of tungsten carbide and having an arcuate surface of sealing engagement with the tips of a plurality of teeth of said gears and including a generally T-shaped protuberance positioned opposite said arcuate sealing surface with the surfaces of said Tshaped protuberance having a position normally substantially parallel to the plane of said arcuate surface being inclined with respect to said plane, said second member having a T-shaped recess receiving said T- shaped protuberance and having inclined surfaces engaging the corresponding mating inclined surfaces of said T-shaped recess such that the center of the slip plane generated by the differential expansion of said first and said second elements intersects at the geometric center of the T-shaped portion of said first member to thereby preclude any change in the fit of the mating portions of said first and said second members of said movable means.

8. A gear pump, as claimed in claim 3, wherein said movable means includes at least one first member and at least one second member having different coeflicients of expansion, said first member being formed of tungsten carbide and having an arcuate surface of sealing engagement with the tips of a plurality of teeth of said gears and including a generally T-shaped protuberance positioned opposite said arcuate sealing surface with the surfaces of said T-shaped protuberance having a position normally substantially parallel to the plane of said arcuate surface being inclined with respect to said plane, said second member having a T-shaped recess receiving said T-shaped protuberance and having inclined surfaces engaging the corresponding mating inclined surfaces of said T -shaped recess such that the center of the slip plane generated by the diiferential expansion of said first and said second elements intersects at the geometric center of the T -shaped portion of said first member to thereby preclude any change in the fit of the mating portions of said first and said second members of said movable means.

References Cited DONLEY I. STOCKING, Primary Examiner W. J. GOODLIN, Assistant Examiner US. Cl. X.R.

22 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3483825 Dated December 16, 1969 Inventor) Leroy Uifford, Charles Grennen, David Moorcroft It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

zlolumn 3, insert between line 60 and line ()1 the following Flgure 5 is an enlarged fragmentary View of a portion of Figure 3 SIGNED AND SEALED MAY 1 21970 QSEAL) Attest:

Edward M. Fletcher, It. WILLIAM E. 'SOHUYLER, JR.

Commissioner of Patents Attesting Officer