Note: Descriptions are shown in the official language in which they were submitted.
371~.{3'~
~CENTRIFl~J~AL P~5P }IAVING WEAR RB~I~TAN~I! CO~POl~IEN~8'~
DE:~CRIPTION
The present invention relates generally to a
centrifu~al pump having wear resistant elements mounted
on opposing wear prone faces of an impeller shroud and
a pump housing.
Centrifugal slurry pumps are known which include
replaceable wear plates on the front and rear internal
surfaces of the pump housing. Such replaceable wear
plates are generally formed of hard, abrasion resistant
material such as a hardened steel alloy.
A cantilevered centrifugal pump is disclosed in
U.S. Patent No. 4,655,684 in which internal faces of the
pump housing are case hardened ~or increased wear
resistance.
The present invention provides a centri~ugal pump
having reduced wear characteristics and a prolonged life
by providing replaceable wear resistant components at the
most wear prone locations in the pump. The invention also
provides a centrlfugal pump operable at optimum
efficiency by controlling recirculation or leakage loss.
The pump according to the present invention also reduces
maintenance time required for impeller adjustment
~7~''3'7
--2--
and for replacement of worn parts to obtain optimum pump
performance. The invention provides an economical
solution to wear in slurry pumps.
These and other objects and advantages of the
present invention are obtained in a centrifugal pump
having a shaft mounted impeller rotatably disposed within
a housing wherein a first wear resistant member, or
insert, is mounted in a wear prone face at a front
internal surface within the housing and a second wear
resistant member is mounted in an opposing wear prone
face of a front shroud of the impeller. The wear
resistant members are preferably formed of an extremely
hard, abrasion resistant material mounted in compression
in the respective impeller shroud and housing surfaces.
Such material is preferably a super hard ceramic
composite. The members, or inserts, are also preferably
replaceable to extend the life o~ the pump.
In a centrifugal slurry pump, the area of greatest
wear is the region adjacent the inlet where the impeller
face is closely adjacent a stationary face of the pump
housing. A recirculating, or leakage, flow occurs in this
area as the result of reduced pressure at the inlet of
the pump and increased pressure at the impeller outlet
at opposite sides of this area. A forced flow through the
~ '7
3--
area, potentially carrying abrasive solids from the
slurry, thus, occurs. Wear in this region is, for
example, three times greater than the wear occurring in
the next most wear prone region of the pump.
The present invantion provides replaceable inserts
of extremely hard material in the regions of greatest
wear on the front face, or shroud, of the impeller and
on an opposing region in a wear face in the pump housing.
The inserts of the present invention are provided in the
region of closest running clearance at the suction side
o~ the impeller. With hard wear resistant inserts
according to the invention, the wear life of the front
wear plate in the pump nousing and the front shroud face
of the impeller is prolonged to at least equal the wear
life of the next most wear prone portion in the pump
housing, which generally is a rear wear plate.
In one embodiment, the centrifugal pump is a
cantilevered pump in which shaft runout, or lateral
movement, is possible due to radial hydraulic forces
operating on the impeller, the impeller being mounted on
a sha~t supported in bearings spaced ~rom the impeller.
In such application, the wear face diameter of the
stationary wear resistant insert is greater than ~he
~ 3'~f3'7
diameter of the rotating wear r sistant insert in the
impeller.
The wear resistant inserts, or elements, of the
instant invention are preferably mounted in compression
and, therefore, materials can be used which are hard and
strong in compression but relatively weak in tension.
Such wear resistant materials may include, but are not
limited to, ceramic composites such as ceramic composites
in the family of silicon carbide with a metal bonding
matrix. Other materials, su~h as alloys or composites may
be used in some applications.
ON ~HE DRA~ING8
Figure 1 is a cross section generally in an axial
direction of a centriEugal pump according to the present
invention and including wear resistant inserts;
Figure 2 is an enlarged fragmentary view of the
impeller mounted within the pump housing from Figure 1
having the annular wear resistant inserts;
Figure 3 is a perspective view of a wear
resistant insert for use in the impeller shroud of the
centrifugal pump shown in Figures 1 and 2; and
Figure 4 is a perspective view of a second wear
resistant insert for mountiny opposite the insert of
~ 7~ ~'7
Figure 3 in the centrifugal pump of Figures 1 and 2
according to the present invention.
A centrifugal slurry pump according to the
principles of the present invention is shown in cross
section in Figure 1, including a horizontal drive
shaft 10 driven by a drive motor 12 and connec~ed
through a coupling 14 to a pump shaft 16. The drive
shaft 16 is rotatably mounted in a pair of spaced
bearing assemblies 18 and 20 along the shaft 16. Each
of the bearings assemblies 18 and 20 include
respective bearings 22 and 24 and are conn~cted by
brackets 26 and 28 to a stationary mounting location
such as a horizontal mounting plate 29, which together
with the brackets 26 and 28 form a mounting pedestal.
At a free end of the pump shaft 16 is a pump
housing 30 including a seal mounting flange 32 having
a plurality of seals 34 extending between the seal
flange 32 and a sleeve 36 on the pump drive shaft 16.
A front portion of the pump housing 30 forms a volute
chamber 38 within which is rotatably disposed an
impeller 40 mounted on the free end o~ the pump drive
shaft 16. A hub cover 42 is threaded over a threaded
extension 43 of the pump drive sha~t 16 to hold the
impeller 40 in place and a key 45 assures tha~ the
'7~'7
impeller 40 rotates with the shaft 16. In the
illustrated embodiment, an inlet housing 44 is mounted
at the end o~ the pump housing 30 for connection to an
inlet pipe (not shown).
In more detail, the preferred embodiment of the
centrifugal slurry pump has a replaceable rear wear
plate 46 forming a rear face of the volute impeller
chamber 38 and a replaceable front wear plate 48
forming a front interior surface of the volute chamber
38. A plurality of bolts 50, one of which is shown in
Figure 1, mount the rear wear plate 46 in the pump
housing 30. A plura~ity of bolts 83 and 84 as shown,
hold the components together and permit disassembly
for maintenance.
The impeller 40, when driven by the drive motor
12, rotates within the volute chamber 38 between the
rear wear plate 46 and the front wear plate 48. The
impeller 40 includes a plurality of impeller blades 54
extending substantially radially between a front
impeller shroud 56 and a rear impeller shroud 58. The
rotational motion of the impeller 40 within the volute
chamber 38 generates a centrifugal force which draws
liquid and/or slurry material through a centrally
disposed inlet 60 in the inlet housing 4~ and into the
~ ~3
volute impeller chamber 38. As is known, the volute
chamber 38 includes an outlet (not shown) through
which pressurized liquid material is pumped. Although
a single volute chamber is shown, it is, of course,
possible that the pump chamber can be a double volute
chamber. It is also possible that the impeller can
have other shapes than that shown in Figure l.
During operation of the present pump, portions
of the pump are subject to wear, particularly when a
slurry or other liquid/solid mixture is being pumped.
A centrifugal pump of the type shown has the greatest
rate of wear on the inner portions of the ~ront
surfaces of the front impeller shroud 56 and on the
opposing surface portions of the front wear plate 48.
To reduce the rate of wear on these particular surface
portions, the present invention provides inserts 62
and 64 of highly abrasion resistant material in the
impeller 40 and the front wear plate 48 at these most
wear prone locations in the centrifugal pump~
The operation of the drive motor 12 causes the
pump sha~t 16 to rotate the impeller 40 within the
volute chamber 38, thereby ~enerating a flow o~ liquid
through the pump. When the liquid contains solid
particles, such as, ~or example, when a slurry iB
~ s7
being pumped, then the liquid-carried solids wear down
the surfaces in contact with the flow. The higher the
flow rate, the higher the wear rate. Wear occurs on
the impeller 40 itself, on the rear wear plate ~6, and
on the front wear plate 48. However, the rate of wear
on the ~ront wear plate 48 ~or an exemplary
centrifugal pump is approximately three times greater
than the wear rate on the rear wear plate 46. This is
due to a recirculation, or leakage, flow between the
suction side of the impeller 40 and the outlet side of
the impeller 40 which is caused by the high pressure
differential. On the front wear plate 48, the region
having the greatest wear rate is an area 65 of closest
running tolerance between the face of the front
impeller shroud 56 and an annular surface region of
the front wear plate 48 immediately adjacent the inlet
opening 60~
Referring to Figure 2, the rear wear plate 46
and the front wear plate 48 as well as the impeller 40
are generally formed of relatively durahle, wear
resistant materials, such as hardened steel and the
like. However, even materials such as hardened steel
undergo wear at a relatively ~a~t rate in the region
65 in some slurry-pumping uses. Therefore, the inserts
~ 7
62 and 64 of the present invention are formed of an
extremely hard and durable ceramic composition so that
the wear rate at the region 65 at least approximates
that in other areas of the pump. Since ceramics in
general, and particularly those which have the
requisite hardness and durability for use in the
present application, are expensive and quite difficult
to form into complex shapes, the present invention
provides that the quantity of material used for the
present inserts is minimal and that the shapes are as
simple as possible.
A further ~onsideration is that such extremely
hard ceramics generally are brittle and do not have
sufficient strength in tension to withstand the
stresses which occur inside a pump, particularly
during pumping of a slurry. As such, the present
inserts 62 and 64 are mounted at the wear prone region
65 in compression. More specifically, the front
insert 64 is preferably of a continuous annular shape
of rectangular cross section and is mounted in
compression in a similar size annular notch or channel
66 formed in the front wear plate 48. An outside
surface 68 of the insert 64 tiyhtly abuts a radially
inwardly directed notch face 70 of the notch 66 to
~ ~3~
--10--
maintain the ceramic insert 64 in a stable, compressed
condition. Irregularities in the notch 66 and insert
64, such as in shape and surface condition, should be
eliminated to assure that the compression forces are
substantially equal about the entire circumference o~
the annular insert 64.
When mounted as described, the insert 64
presents a wear face 72 directed toward the impeller
40O Fluid pressures in the region 65 act to compress
lo the insert 64 axially against an axially directed
notch face 74. Thus, the insert is in compression both
radially and axially during operation o~ the pump.
The insert 62 is provided at an opposing face of
the front impeller shroud 56 and i5 likewise mounted
in compression. The insert 62 is of a continuous
annular shape but differs from the insert 64 in that
it has an "~-shaped" cross section. An axially
directed leg 76 of the "L" is mounted in compression
in an annular channel or notch 78 ~ormed in the front
shroud 56 of the impeller 40. The impeller insert 62
also includes a radially extending ~lange or leg 80 of
the l'L'I extending across the front o~ the frant shroud
56 and in axial compression due to fluid pressures ln
the region 65 acting on a face 82 of the insert 62.
~b~ '7
It is preferred that the inserts ~2 and 64 ~e
mounted in compression in the pump of the present
invention since a preferred material of which the
inserts are formed is a hard ceramic material. One
possibility for this hardened ceramic material is in
the family of silicon carbide with a metal bonding
matrix as made by Alanx Products, L.P. Such ceramic
materials offer the advantages of extreme abrasion
resistance and strength in compression, although
weakness in tension. Of course, inserts of a material
which does not require mounting in compression may be
used, so long as resistance to abrasion and wear are
provided.
An alternate means for mounting the inserts 62 and
64 is to provide a somewhat looser fit between the
inserts 62 and 64 and the corresponding notches 78 and
66 and instead to bond the inserts 62 and 64 therein,
such as by an epoxy adhesive. Other means for mounting
the inserts 62 and 64 are also contemplated, including
rivets or threaded fasteners.
Referring to Figures 3 and 4, the inserts 62 and
64 are shown before insertion in the respective
notches 7~ and 66 in the pump. They each have a
relatively simple shape and are made with minimal
amount of the abrasion resistant material and are
therefore economical. When the inserts 62 and 64
become worn or damaged, they can be easily replac~d so
that the efficiency of the pump is maintained without
costly replacement of the impeller 40 and housing
parts. However, due to the extreme hardness of the
inserts 62 and 64, the wear rate is reduced
considerably and replacement is much less frequent
than with known devices.
As can be seen in Figure 1, the drive shaft 16
rides on the bearings 24 which are spaced from the
impeller 40 so that the impeller 40 is of a
cantilevered design. A cantilevered centrifugal pump
design permits larger solids to pass through the pump
without damaging the impeller 40 and other pump
components during pump being of a heavy slurry, for
example. However, the impeller 40 is subject to
lateral movements due, in part, to radial hydraulic
forces and/or solids in the fluid flow acting on the
impeller 40. Therefore, the front insert 64 of the
preferred embodiment has the wear face 72 of greater
diametrical extent then the opposing front face 82 of
the insert 62 in the front shroud 56 o~ the impeller
40 to accommodate shaft runout or ~lexure due to the
-~ ~'r~ 7
-13
cantilevered design of the disclosed pump. As a
result, wear is prevented beyond the outside ~dge of
the wear face 72, which preferably extends at least to
the maximum foreseeable lateral position of the wear
face 82.
~ hus, there is disclosed and shown an improved
centrifugal slurry pump of a cantilevered design
having wear resistant annular inserts 62 and 64 in the
front shroud 56 o~ the impeller 40 and in the ~ront
wear face 48 in the pump housing 30. ~he disclosed
pump provides optimum efficiency by controlling
recirculation or leakage loss in the region 65 and,
therefore, reducing energy costs in the operation of
the pump~ The present pump also reduces the
maintenance time and cost in adjusti~g the impeller
for optimum performance by axial adjustment of the
bearings 24 in the housing 20, and in replacing worn
parts of the impeller 40 and pump housing 30.
Although other modifications and changes may be
suggasted by those skilled in the art, it is the
intention of the inventors to embody within the patent
warranted hereon all changes and modifications as
reasonably and properly come within the scope of their
contribution to the art.
