U.S. patent application number 11/858388 was filed with the patent office on 2008-03-20 for process for hardfacing a progressing cavity pump/motor rotor.
This patent application is currently assigned to KUDU INDUSTRIES INC.. Invention is credited to James COULAS.
Application Number | 20080069715 11/858388 |
Document ID | / |
Family ID | 39188809 |
Filed Date | 2008-03-20 |
United States Patent
Application |
20080069715 |
Kind Code |
A1 |
COULAS; James |
March 20, 2008 |
PROCESS FOR HARDFACING A PROGRESSING CAVITY PUMP/MOTOR ROTOR
Abstract
A method of hardfacing a metal body, including the steps of
flame spraying a metallic material onto a surface of the metal body
to produce a layer of the metallic material on the metal body and
fusing the layer of metallic material to provide a hardfacing
layer, is improved by roughening the surface of the metal body
prior to the step of flame spraying to provide a mechanical bond
between the metal body and the hardfacing layer. The roughening is
carried out to achieve a surface roughness adjusted to the
thickness of the hardcoating. The surface roughness is preferably
40%-90% of the thickness of the hardfacing layer. A rotor for a
progressing cavity pump/motor, including a metallic rotor body
having a surface, and a layer of hardfacing on the surface, the
hardfacing comprising of fused flame sprayed metallic material, the
surface of the rotor body having an average surface roughness of at
least substantially 6 mils with irregular protrusions for providing
a mechanical bond between the rotor body and the hardfacing.
Inventors: |
COULAS; James; (Calgary,
CA) |
Correspondence
Address: |
Dennis R. Haszko;Patent Law Office of D.R.Haszko
499 MOSHER HILL ROAD
FARMINGTON
ME
04938-5405
US
|
Assignee: |
KUDU INDUSTRIES INC.
9112 - 40th Street, S.E.
Calgary
CA
T2C 2P3
|
Family ID: |
39188809 |
Appl. No.: |
11/858388 |
Filed: |
September 20, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60826369 |
Sep 20, 2006 |
|
|
|
Current U.S.
Class: |
418/179 ;
427/450; 427/455; 427/456 |
Current CPC
Class: |
C23C 4/067 20160101;
F04C 2240/20 20130101; C23C 4/06 20130101; F04C 2/1073 20130101;
F04C 2230/91 20130101; F04C 2230/92 20130101; F04C 2/084 20130101;
C23C 4/129 20160101 |
Class at
Publication: |
418/179 ;
427/450; 427/455; 427/456 |
International
Class: |
F04C 2/107 20060101
F04C002/107; C23C 4/06 20060101 C23C004/06; C23C 4/10 20060101
C23C004/10 |
Claims
1. In a method of hardfacing a metal body, including the steps of
flame spraying a metallic coating material onto a surface of the
metal body to produce a metallic coating having a coating thickness
and fusing the metallic coating to provide a hardfacing layer, the
improvement comprising the step of roughening the surface of the
metal body prior to the flame spraying for generating a surface
roughness equal to at least 40% and at most 90% of the coating
thickness.
2. The method of claim 1, wherein the step of roughening the
surface of the metal body comprises the step of forming a
multiplicity of jagged irregular projections and indentations,
substantially covering the surface of the metal body.
3. The method of claim 1, wherein the step of roughening the
surface of the metal body comprises grit blasting.
4. The method of claim 3, wherein the grit blasting comprises
blasting with steel grit having a hardness at least equal to a
hardness of the metal body.
5. The method of claim 4, wherein the grit blasting comprises
blasting with steel grit having a hardness between about 20 and
about 50 Rockwell.
6. The method of claim 3, wherein the grit blasting comprises
blasting with grit at an air pressure of between about 80 psi and
about 150 psi.
7. The method of claim 1, wherein the minimum surface roughness is
8 mil.
8. The method of claim 1, wherein the metallic material is selected
from the group consisting of chromium, molybdenum and nickel and
alloys thereof.
9. The method of claim 7, wherein the thickness of the layer of
metallic material is substantially uniform.
10. The method of claim 1, wherein the metallic material comprises
between about 30 wt. % and 80 wt. % metal carbide powder.
11. The method of claim 10, wherein the metal carbide powder is
selected from the group consisting of the carbides of tungsten,
titanium, tantalum, columbium, vanadium and molybdenum.
12. The method of claim 11, further comprising, prior to the step
of flame spraying the metallic material onto the metal body, the
steps of: (a) predicting the approximate expected grain size of an
abrading substance to be encountered by the metal body when the
metal body is placed into service; and (b) selecting a grain size
for the metal carbide powder that is finer than the grain size of
the abrading substance.
13. The method of claim 1, wherein the step of fusing the layer of
hardfacing comprises heating by inductive heating.
14. The method of claim 1, wherein the metal body is a rotor for a
progressing cavity pump/motor.
15. A rotor for a progressing cavity pump/motor, comprising: (a) a
metallic rotor body having a surface; and (b) a layer of hardfacing
on the surface, the hardfacing consisting of flame sprayed and
fused metallic material applied at a coating thickness, the surface
of the rotor body having a surface roughness with irregular
protrusions for providing a mechanical bond between the rotor body
and the hardfacing, the surface roughness having a depth equal to
40-90% of the coating thickness.
16. The rotor of claim 15, wherein the flame sprayed metallic
material is selected from the group consisting of chromium,
molybdenum and nickel and alloys thereof.
17. The rotor of claim 15, wherein the irregular protrusions are
formed by a multiplicity of jagged irregular projections and
indentations in the surface of the rotor body.
18. The rotor of claim 15, wherein the surface of the metal body
has a surface roughness of 60-90% of the coating thickness.
19. The rotor of claim 15, wherein the surface of the metal body
has a surface roughness of 70-90% of the coating thickness.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Patent
Application Ser. No. 60/826,369, entitled Process for Hardfacing a
Progressing Cavity Pump/Motor Rotor, the contents of which are
incorporated herein in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to wear-resistant
hardfacings for movable parts. More particularly, the present
invention relates to hardfacings for rotors of progressing cavity
pumps/motors.
BACKGROUND OF THE INVENTION
[0003] Progressing cavity pumps have been used in water wells for
many years. More recently, such pumps have been found to be well
suited for the pumping of viscous or thick fluids such as crude oil
laden with sand. Progressing cavity pumps include a stator which is
attached to a production tubing and a rotor which is attached to
the bottom end of a pump drive string and is made of metallic
material, usually high strength steel.
[0004] Progressing cavity motors are used to provide rotary power
sections for use in horizontal and directional drilling.
Progressing cavity motors include a stator which is connected with
a drillpipe and a rotor which is attached to a drill bit. Drilling
fluid is forced down the drillpipe causing rotation of the rotor
and operation of the motor to rotate the drill bit.
[0005] The rotor is usually electroplated with chrome to resist
abrasion. However, the corrosive and abrasive properties of the
fluids produced in oil wells or utilized for drilling fluid
frequently cause increased wear and premature failure of the rotor.
Since it is important for efficient operation of the pump/motor
that a high pressure differential be maintained across the rotor,
only small variations in the rotor's dimensions are tolerable. This
means that excessively worn rotors must be replaced immediately.
However, replacement of the rotor requires pulling the whole
pump/motor drive string from the well which is costly, especially
in the deep oil well applications which are common for progressing
cavity pumps/motors. Consequently, rotors with increased wear
resistance and, thus, a longer service life are desired to decrease
well drilling and operating costs.
[0006] Various hardfacing methods have been used in the past to
increase the wear resistance of metal surfaces.
[0007] A number of progressing cavity pump/motor manufacturers
chrome electroplate the rotors to increase wear resistance. Chrome
electroplating does provide increased wear resistance, but is
susceptible to corrosion in the harsh environment of downhole
production and drilling.
[0008] Another way of increasing wear resistance is to deposit a
coating or layer of material onto the rotor by thermal spraying.
Conventional flame spraying uses a relatively low flame temperature
and particle velocity (such as less than about 40 m/s), and results
in coatings with high porosity and permeability as well as low bond
strength. Nevertheless, it allows the spraying of a layer with much
smaller thickness variations, overcoming the problem of
uncontrollable thickness variations experienced with other thermal
spraying techniques.
[0009] U.S. Pat. No. 3,310,423 to Ingham makes reference to
conventional flame spraying usually requiring severe mechanical
roughening for example by sand or grit blasting or machine
roughening which forms key-like cavities, and that a light
sand-blasting is insufficient. Ingham also makes reference to
fusing after flame spraying to increase the density and bond.
[0010] U.S. Pat. No. 4,004,042 to Fairbairn teaches a method for
coating with a mixture of tungsten carbide powder and nickel chrome
boron powder. The surface is cleaned by grit blasting using
aluminum oxide particles, for example. Then the coating is applied
by a "stream of energy" such as provided by a plasma generating
gun, covered with a protective film (using boric acid or boric
oxide) and fused at elevated temperature.
[0011] U.S. Pat. No. 4,013,453 to Patel teaches flame spraying a
powder containing WC to obtain a wear resistant coating, including
the step of fusing the coating after deposition by bringing a torch
tip within about 1'' of the coating until the coating melts and
bonds metallurgically to the substrate.
[0012] U.S. Pat. No. 4,161,555 to Appleman teaches a flame spraying
process for materials requiring fusion, in which a particular
method of fusing is taught using a removable siliceous film.
[0013] U.S. Pat. No. 4,241,110 to Ueda et al. teaches a rotor blade
having a coating of at least one coat each of Ni--Cr--B--Si alloy
and WC applied by spraying and fusing. The surface to be treated is
cleaned by grid blasting or the like. Then, powders of a
Ni--Cr--B--Si alloy and WC are fed in succession into and melted or
heated by a flame, e.g. an oxyacetylene flame. For greater joining
strength, the coats formed by spraying are heated, e.g. by an
oxyacetylene flame up to the melting point of the alloy to fuse the
particles solidly onto the surface.
[0014] U.S. Pat. No. 4,517,726 to Yokoshima et al. teaches shot
blasting to clean the surface to be coated, followed by plasma
spraying in a method of producing a seal ring.
[0015] U.S. Pat. No. 5,455,078 to Kanzaki teaches a method of
coating an aluminum or aluminum alloy valve lifter with iron,
including the steps of primary blasting to form a rough surface
having larger irregularities (using preferably grit), secondary
blasting to form smaller irregularities, and forming a coating
layer of wear resistant material on the surface (preferably by
thermal spraying) thereby increasing the adhesion strength of the
coated layer.
[0016] U.S. Pat. No. 5,395,221 to Tucker et al. teaches a
progressive cavity pump/motor rotor with a coating of metal carbide
with a metal alloy using thermal spray processes which include
detonation gun deposition, oxy-fuel flame spraying, high velocity
oxy-fuel deposition, and plasma spray, and also teaches that the
coating particle size must be less than the size of the particles
in the fluid or the fluid particles will abrade and wear off the
coating particles. Tucker et al. teaches the use of a sealant to
address the porosity challenge.
[0017] U.S. Pat. No. 6,425,745 to Lavin teaches a surface treatment
for helically profiled rotors, such as progressing cavity
pump/motor rotors by high velocity oxygen fuel (HVOF) spraying of a
WC/ceramic composite coating onto the surface of a rotor by
traversing the axis of the rotor while the rotor is rotated in
synchronism to maintain the proper position of the spray relative
to the surface of the rotor, to give a desired coating thickness
profile.
[0018] In general, conventional flame spraying techniques result in
coatings with high porosity and permeability as well as low bond
strength, although they do allow the spraying of a layer of
sufficiently consistent thickness. Thickness variations on the
other hand are a major problem with other coating techniques, such
as high velocity oxygen fuel (HVOF) or detonation gun (D-gun)
coating. Furthermore, those coating techniques cannot always be
used to produce a sufficiently thick coating. In order to prevent
failure of the coating during use, the thickness of the coating
must be equal to at least 50% of the diameter of any particles to
which the coating is exposed during use. Moreover, sufficiently
thick coatings, even if achievable are subject to pitting and
spalling during use, due to insufficient bond strength with the
underlying metal layer.
[0019] It is, therefore, desirable to provide a method for
hardfacing a rotor for a progressing cavity pump/motor which
overcomes the problems associated with conventional flame spraying
and chrome coatings.
SUMMARY OF THE INVENTION
[0020] It is an object of the present invention to obviate or
mitigate at least one disadvantage of previous methods for
hardfacing and of rotors for progressing cavity pumps/motors.
[0021] In conventional hardcoating processes using flame spraying,
the coating is fused to reduce the high porosity and permeability
of the sprayed-on layer. The underlying substrate may be roughened
prior to flame spraying to provide increased bond strength. The
result is a lower porosity, lower permeability coating with a
stronger bond to the substrate. However, sprayed-on and fused
coatings are still subject to pitting and spalling upon flexing and
impact, even when the surface to be coated is roughened prior to
application of the hardcoating.
[0022] It has now been surprisingly found by the applicant that the
bond strength of the coating with the underlying substrate can be
significantly increased and pitting and spalling substantially
prevented, even on impact and flexing, if the surface is not only
roughened prior to hardcoating, but if the surface roughness is
coordinated with the coating thickness. In particular, superior
bond strength is achieved when the substrate is roughened prior to
spray coating by grit blasting, preferably metal grit blasting, to
achieve a surface roughness, the depth of which is adjusted to at
least 40% of the intended coating thickness. The result is a
sufficiently deep inter-penetration of the coating and the
substrate to achieve a superior bond strength, even for relatively
thick coatings. The inter-penetration of the substrate and the
coating to such a large degree also results in a bond strength of
the coating which is substantially equal to the strength of the
substrate. The maximum surface roughness is preferably 90% of the
coating thickness, to avoid exposure of the substrate upon
polishing of the coating or premature exposure of the substrate
during use. For example, for a coating of 10 mil thickness, the
surface roughness should be at least 4 mil and at most 9 mil.
[0023] The concept of surface roughness or rugosity is well
understood by the art skilled person and is a measurement of the
small-scale irregularities in a physical surface. The term "surface
roughness" generally refers to the depth of a surface profile or
texture measured as the peak to valley height of individual surface
features in the surface profile or texture.
[0024] Coatings providing the desired wear resistance and improved
corrosion resistance are selected to increase service life.
[0025] In a first aspect, the present invention provides a method
of hardfacing a metal body, with the steps of flame spraying a
metallic coating material onto a surface of the metal body to
produce a metallic coating having a coating thickness and fusing
the metallic coating to provide a hardfacing layer, and the
additional step of roughening the surface of the metal body prior
to the flame spraying step for generating a surface roughness of at
least 40% and at most 90% of the coating thickness.
[0026] In a second aspect, the invention provides a method of
hardfacing a metal body with a coating layer having an intended
coating thickness, comprising the steps of roughening a surface of
the metal body to a surface roughness, the depth of which equals at
least 40% and at most 90% of the intended coating thickness, flame
spraying a metallic coating material onto the roughened surface of
the metal body until the intended coating thickness is achieved and
fusing the layer of metallic material to provide a hardfacing
layer.
[0027] In a third aspect, the invention provides a rotor for a
progressing cavity pump/motor, comprising a metallic rotor body
having a surface, and a layer of hardfacing on the surface, the
hardfacing consisting of flame sprayed and fused metallic material
applied at a coating thickness, the surface of the rotor body
having a surface roughness with irregular protrusions for providing
a mechanical bond between the rotor body and the hardfacing, the
surface roughness of the irregular protrusions being equal to
40-90% of the coating thickness.
[0028] Preferably, the surface roughness is between 50% and 90%,
more preferably between 60% and 90%, most preferably between 70%
and 90% of the intended coating thickness.
[0029] Preferably, the step of roughening the surface of the metal
body is achieved by grit blasting. The grit is preferably metal
grit selected to have a hardness at least equal to that of the
metal body. The grit hardness is preferably between about 20 and 50
Rockwell. The step of grit blasting preferably is carried out at an
air pressure between about 80 and 150 psi. The surface roughness is
preferably at least 6 mil, more preferably at least 8 mil.
[0030] The step of roughening the surface of the metal body
preferably creates a multiplicity of jagged irregular projections
and indentations, substantially covering the surface of the metal
body.
[0031] Preferably, the hardfacing method includes additional steps
prior to the step of flame spraying the metallic material onto the
metal body, namely, the steps of predicting the approximate
expected grain size of an abrading substance, to be encountered by
the metal body when the metal body is placed into service, and
selecting a grain size for the metal carbide powder that is finer
than the expected grain size of the abrading substance.
[0032] The layer of metallic material is preferably fused by
inductive heating to produce the hardfacing layer. The layer of
metallic material is preferably applied at a thickness of at least
9 mil and is preferably applied at a substantially uniform
thickness. The metallic material is preferably selected from the
group consisting of chromium, molybdenum and nickel and alloys
thereof. Most preferably, the metallic material includes a NiCr
alloy. The metallic material preferably includes between about 30
wt. % and 80 wt. % metal carbide powder. The metal carbide powder
is preferably selected from the group consisting of the carbides of
tungsten, titanium, tantalum, columbium, vanadium and molybdenum.
Most preferably, the metal carbide powder includes tungsten
carbide.
[0033] In a further aspect, the present invention provides a
downhole progressing cavity pump/motor, including a pump rotor in
accordance with the invention and a pump stator.
[0034] Other aspects and features of the present invention will
become apparent to those ordinarily skilled in the art upon review
of the following description of specific embodiments of the
invention in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] Embodiments of the present invention will now be described,
by way of example only, with reference to the attached drawings,
wherein:
[0036] FIG. 1 shows the principal components of a progressing
cavity pump/motor;
[0037] FIG. 2 schematically illustrates a roughened surface of the
progressing cavity pump/motor; and
[0038] FIG. 3 schematically illustrates a hardfacing layer applied
to the progressing cavity pump/motor.
DETAILED DESCRIPTION
[0039] The present invention in general is directed to a method of
hardfacing a metal body which includes the steps of flame spraying
a metallic coating material onto a surface of the metal body to
produce a metallic coating having a coating thickness and fusing
the metallic coating to provide a hardfacing layer, wherein the
method also includes the step of roughening the surface of the
metal body prior to the flame spraying step for generating a
surface roughness, the depth of which is at least 40% and at most
90% of the coating thickness.
[0040] In the preferred embodiment, the hardfacing in accordance
with the present invention is applied to the rotor of a progressing
cavity pump/motor 10 as shown in FIG. 1 by roughening the surface
of the rotor body, flame spraying a metallic coating material onto
the roughened surface to achieve a metallic coating of a selected
coating fluidness, and fusing the metallic coating. In the
roughening step, the surface of the rotor body is roughened for
generating a surface rougheness of at least 40% of the thickness of
the metallic coating to be subsequently applied.
[0041] Progressing cavity pumps/motors include a helical rotor 12
made of ferrous metal, usually high strength steel, and a stator
having a generally double helical rotor receiving bore 15 of twice
the pitch length. The dimensions of the rotor and stator are
coordinated such that the rotor tightly fits into the bore 15 and a
number of individual pockets or cavities 13 are formed which are
inwardly defined by the rotor 12 and outwardly by the stator 14.
Upon rotation of the rotor 12 in the operating direction, the
cavities 13 and their contents are pushed spirally about the axis
of the stator 14 to the output end of the pump. The seal between
the cavities is made possible by an interference fit between the
rotor and the elastomeric material of the stator 14. The rotor 12
and stator 14 are at all times in tight contact in the areas
between the cavities which results in the wear of both components
and in particular the rotor, especially when sand-laden and
corrosive liquids are pumped as is often the case in deep oil well
applications.
[0042] In the preferred embodiment, the surface of the rotor 12 is
mechanically roughened by grit blasting to provide increased bond
strength. The grit blasting involves impinging the rotor 12 with
steel grit formed of angular particles, delivered upon the surface
of the rotor 12 through the use of pneumatics (such as through the
use of air or an inert or other substance), or other methods known
to those skilled in the art of surface blasting.
[0043] The grit is selected to have a hardness greater than or
equal to the hardness of the rotor 12. The grit blasting forms a
multiplicity of jagged or irregular projections and indentations,
substantially covering the surface of the rotor body. The roughness
of the grit blasted surface is adjusted to be at least 40% of the
intended thickness of the metallic coating. To achieve superior
bond strength, the grit blasting is preferably carried out under
conditions which will generate a surface roughness of 40-90% of the
intended coating thickness, preferably 60-90% and most preferably
70-90%. Although surface roughening by shot blasting is known as
well, such roughening is not preferred for the present invention.
Shot blasting produces rounded indentations. As a result, the
mechanical connection between the metallic coating and the rotor
may not be sufficient to guarantee a long service life for the
rotor. Grit blasting produces jagged and irregular projections and
indentations in the rotor body surface. Thus, roughening by grit
blasting produces superior bonding strength between the rotor and
the metallic coating due to the mechanical interlocking connection
between the metallic coating and the rotor body.
[0044] After the surface of the rotor 12 is roughened, it may be
cleaned to remove any grit blasting residue, for example by
pneumatic cleaning.
[0045] A metallic material layer is flame-sprayed onto the
roughened surface of the rotor, or onto a bond coating on the
rotor, by way of a flame spray gun. Flame spray coating processes
and apparatus are well known in the art. In brief, the flame spray
process uses a chemical combustion reaction (flame) from oxygen and
a fuel (such as acetylene or hydrogen) to produce a heat source
which creates a gas stream. The coating material to be flame
sprayed is fed into the flame in the form of a wire or a powder.
The powder is heated by the flame to a molten or plastic condition
and projected onto the base metal part to be coated by a compressed
gas (such as air). Upon impact, a bond is formed at the interface
between the molten or plastic powder and the base metal part.
[0046] The metallic material may be chromium (Cr), molybdenum,
nickel (Ni) or alloys thereof. In the preferred embodiment, the
metallic material is a NiCr alloy. The metallic material may be
applied in a single layer, or may be applied in a plurality of
layers to form a coating of the metallic material on the rotor
body. The average thickness of the layer of metallic material can
be about 9 mils to about 100 mils. This can be accomplished in a
single layer or single pass. Flame spraying generally provides a
substantially uniform coating thickness.
[0047] The metallic material may further include between about 30
wt. % and 80 wt. % metal carbide powder. The metal carbide may be
carbides of tungsten, titanium, tantalum, columbium, vanadium, and
molybdenum. In the preferred embodiment, the metal carbide is
tungsten carbide (WC).
[0048] As an example, a typical progressing cavity pump/motor rotor
may be hardfaced in accordance with the present invention, as
follows. First, the surface is roughened by grit blasting with grit
having a hardness of 30 Rockwell, using an air pressure of 130 psi.
Then, a layer of NiCr with 40% WC is applied using flame
spraying.
[0049] In contrast with a plasma gun type thermal spray, the flame
spraying of the present invention provides that the WC is not
plasticized as it would be with plasma spray, but instead is
cemented in place on the rotor body by the metallic material (e.g.
NiCr). In a typical downhole application, there is some expectation
or prediction of what abrading substances may be encountered, for
example sand is a well known and expected abrading substance.
Typically, the metal carbide powder (e.g. WC) is selected to have a
finer grain size than that of the expected abrading substance, so
that the hardness of the metal carbide will resist abrasion by the
abrading material. If the abrading substance is finer than the
metal carbide, the metallic material (e.g. NiCr) will be abraded
and the metal carbide will delaminate or fall off.
[0050] After application, the surface of the metallic material is
fused to reduce porosity and permeability of the coating. Fusing
involves bringing the surface of the metallic material almost to,
but just short of, its melting point. Typically this is done
through electric induction heating. However, those skilled in the
art recognize there are many ways to fuse the bond, and are skilled
in the recognition of the appropriate temperature. Typically fusing
is done manually with visual recognition of the appropriate level
or degree of fusion.
EXAMPLE I
[0051] For an intended metallic coating thickness of 9 mils, the
surface of a progressing cavity pump was roughened by grit blasting
and subsequently hardfaced by flame spraying a WC containing
metallic material onto the roughened surface. Typically, only that
portion of the rotor surface which comes into contact with the
fluids to be pumped is roughened and provided with a hardfacing
layer. The grit used was steel grit with a hardness of 30 Rockwell
and was blown at the rotor using an air pressure of 85 psi.
EXAMPLE II
[0052] A metallic coating thickness of 15 mils was applied and all
other conditions were identical to those described in Example
I.
EXAMPLE III
[0053] A metallic coating of 15 to 20 mils was applied to a surface
which was roughened by grit blasting to a surface roughness of 10
to 12 mils. The grit had a hardness of 40 Rockwell and was blown at
the rotor using an air pressure of 95 psi.
EXAMPLE IV
[0054] A metallic coating of 25 mils was applied to a rotor surface
roughened by grit blasting with grit of about 50 Rockwell and at an
air pressure of 105 psi to achieve a surface roughness of 14 mils.
Thicker coatings can be equally applied to a surface having a
surface roughness of 14 mils.
[0055] Although the hardfacing method and progressing cavity
pump/motor rotor of the present invention was described in detail
only for the application of a metallic material such as an alloy of
NiCr, a person skilled in the art will readily appreciate that
other metallic materials can be used such as chrome, molybdenum and
nickel, especially chrome/molybdenum and nickel/chromium alloys.
Similarly, although described in detail only for the application of
a metal carbide, such as WC, a person skilled in the art will
readily appreciate that other metal carbides can be used, such as
the carbides of tungsten, tantalum, titanium, columbium, vanadium
and molybdenum. Furthermore, any conventional fusing process
adapted to fuse the coating material and the rotor can be used for
the application of the top layer.
[0056] The above-described embodiments of the present invention are
intended to be examples only. Alterations, modifications and
variations may be effected to the particular embodiments by those
of skill in the art without departing from the scope of the
invention, which is defined solely by the claims appended
hereto.
* * * * *