CORROSION-RESISTANT POSITION MEASUREMENT SYSTEM AND
METHOD OF FORMING SAME
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of United States Provisional Patent
Application No. 61/314,248, filed on March 16, 2010, which is hereby incorporated
by reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure generally relates to position measurement
systems and methods of forming position measurement systems.
BACKGROUND
[0003] Offshore drilling rigs often include direct-acting tensioners to
compensate for wave-induced motion. More specifically, the direct-acting tensioners
may include one or more massive hydraulic cylinders having a piston rod. The
hydraulic cylinders continuously dampen wave-induced motion and thereby balance
the drilling rig and/or stabilize the drill string. As such, dampening may be optimized
by measuring, monitoring, and adjusting a position of the piston rod within the
hydraulic cylinder. Moreover, the hydraulic cylinders are generally mounted below a
deck of the drilling rig, i.e., in a splash zone, and are therefore often exposed to an
extremely corrosive and wear-inducing environment from airborne salt spray, sea
water, ice, moving cables, and/or debris. Consequently, the piston rods of such
hydraulic cylinders must exhibit excellent corrosion-resistance and wear-resistance,
and must remain crack-free over a service life.
[0004] Other types of piston rods and hydraulic cylinders may actuate large
gate valves for applications including canals, locks, hydrodynamic power plants,
foundries, and metal processing facilities. Actuation of the gate valves may be
controlled by measuring and adjusting a position or displacement of the piston rods
within the hydraulic cylinders. Further, the piston rods may undergo thousands of
wear-inducing displacements and/or may experience impacts from moving
machinery, components, and seals during operation of the hydraulic cylinders.
SUMMARY
[0005] A method of forming a position measurement system includes melting
a surface of a substrate formed from a first material, wherein the surface defines at
least one groove therein and wherein the surface is melted within the at least one
groove. The method also includes, concurrent to melting, depositing a second
material into the at least one groove to form a mixture of the first material and the
second material. In addition, the method includes solidifying the mixture to form an
indicator material that is distinguishable from and metallurgically bonded to the first
material. The method also includes depositing an alloy onto the substrate to form a
corrosion-resistant cladding that covers the indicator material and the surface to
thereby form the position measurement system.
[0006] In one embodiment, the method includes machining a surface of a
substrate to define a plurality of grooves therein. The substrate is formed from a first
magnetic material and is a cylindrical rod having a longitudinal axis. Each of the
plurality of grooves is spaced apart from an adjacent one of the plurality of grooves
along the longitudinal axis, and the method includes melting the surface within each
of the plurality of grooves to thereby distribute the plurality of grooves evenly along
the longitudinal axis. Further, the method includes, concurrent to melting, depositing
a second non-magnetic material within each of the plurality of grooves to thereby
form a plurality of respective mixtures of the first magnetic material and the second
non-magnetic material. The method also includes solidifying each of the plurality of
respective mixtures to form a non-magnetic indicator material that is distinguishable
from and metallurgically bonded to the first magnetic material. In addition, the
method includes depositing a non-magnetic alloy onto the substrate to form a
corrosion-resistant cladding that covers and is metallurgically bonded to each of the
non-magnetic indicator material and the surface to thereby form the position
measurement system.
[0007] A position measurement system includes a substrate formed from a
first material and having a surface defining at least one groove therein. The position
measurement system further includes an indicator material disposed within the at least
one groove. The indicator material is formed from a mixture of the first material and
the second material, and is distinguishable from and metallurgically bonded to the
first material. In addition, the position measurement system includes a corrosionresistant
cladding formed from an alloy and disposed on the substrate so as to cover
the indicator material and the surface.
[0008] The above features and other features and advantages of the present
disclosure are readily apparent from the following detailed description of the best
modes for carrying out the disclosure when taken in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Figure 1 is a schematic perspective illustration of a position
measurement system;
[0010] Figure 2 is a schematic cross-sectional illustration of the position
measurement system of Figure 1 taken along section lines 2-2; and
[0011] Figure 3 is a schematic cross-sectional illustration of a plurality of
grooves of the position measurement system of Figures 1 and 2.
DETAILED DESCRIPTION
[0012] Referring to the Figures, wherein like reference numerals refer to like
elements, a method of forming a position measurement system 10 is described herein.
The position measurement system 10 may be useful for detecting a position of a
substrate 12 that operates in a corrosive environment. That is, the position
measurement system 10 exhibits excellent corrosion-resistance, and the position
measurement system 10 may be useful for determining a position or displacement of a
substrate 12 with respect to a reference position. As such, the position measurement
system 10 may be useful for marine applications, such as offshore drilling rigs, for
indicating a position of the substrate 12, e.g., a piston rod, within a hydraulic cylinder.
However, the position measurement system 10 may also be useful for non-marine
applications requiring position measurement and corrosion-resistance including, but
not limited to, canals, locks, hydrodynamic power plants, foundries, and metal
processing facilities.
[0013] Referring to Figure 1, the position measurement system 10 includes a
substrate 12 formed from a first material. In one non-limiting example, the substrate
12 may be a cylindrical rod having a longitudinal axis 14, as shown in Figure 1, such
as a piston rod for a hydraulic cylinder (not shown). Further, the substrate 1 may
have any suitable size according to a desired application. For example, for
applications requiring the substrate 12 to translate into and out of a sealed cylinder or
valve housing (not shown), the substrate 12 may have a length 16 of from about 1.5
meters to about 18 meters, and a diameter 18 of from about 120 mm to about 510 mm.
As such, the substrate 12 may be characterized as an extra-large (XL) hydraulic
cylinder piston rod.
[0014] The first material may be a metal. In addition, the first material may
be ferrous. Therefore, the first material may be magnetic, and may have a first
magnetic permeability. The first material may be selected from materials such as, but
not limited to, steel, carbon steel, alloy steel, stainless steel, tool steel, cast iron, and
combinations thereof. In one non-limiting example, the first material may be a heattreated,
low alloy, high strength steel such as SAE (Society of Automotive Engineers)
4130 steel or SAE 4340 steel. In another non-limiting example, the first material may
be a plain carbon steel, such as SAE 1045 steel.
[0015] Referring now to Figure 2, the substrate 12 has a surface 20 defining at
least one groove 22 therein. As shown in Figure 3, the at least one groove 22 may
have a V-shape and may define a substantially rounded vertex 24 having a radius of
from about 0.3 mm to about 0.7 mm, e.g., about 0.5 mm. Therefore, each side 26, 28
of the at least one groove 22 may define an angle 30 therebetween of from about 55°
to about 65°, e.g., about 60°. That is, each side 26, 28 of the at least one groove 22
may be sloped with respect to the surface 20. As such, rather than having a square
shape (not shown) or a sharp vertex (not shown) which may concentrate stress during
impact or wear-inducing events and cause cracking of the substrate 12, the groove 22
may have the substantially rounded vertex 24 configured to dissipate stress.
[0016] With continued reference to Figures 1 and 2, the surface 20 may define
a plurality of grooves 22 therein. Each of the plurality of grooves 22 may extend
from the surface 20 into the substrate 12 at a depth 32 (Figure 3) of from about 0.9
mm to about 1.3 mm, e.g., about 1.1 mm, and may have a groove width 34 (Figure 2)
of from about 1.9 mm to about 2.1 mm, e.g., about 2.0 mm. Further, as best shown in
Figure 3, two adjacent grooves 22 may define a gap 36 therebetween having a gap
width 38 of from about 1.9 mm to about 2.1 mm, e.g., about 2.0 mm, so that each of
the plurality of grooves 22 is spaced apart from an adjacent one of the plurality of
grooves 22 along the longitudinal axis 14 (Figure 1). Therefore, the surface 20 may
define the plurality of grooves 22 therein distributed evenly along the longitudinal
axis 14 (Figure 1). Stated differently, each gap 36 may be equidistantly spaced apart
from an adjacent gap 36 by a groove 22 so that a ratio between the groove width 34
(Figure 2) and the gap width 38 (Figure 3) may be about 1:1. Therefore, the total
width of one gap 36 and one groove 22 may be about 4.0 mm so that a period or pitch
40 of the position measurement system 10 may be about 4.0 mm. In addition, as
shown in Figure 1, each of the plurality of grooves 22 may be disposed substantially
perpendicular to the longitudinal axis 14. That is, the surface 20 may define
circumferential or radial grooves 22 in the substrate 12.
[0017] Referring again to Figure 2, the position measurement system 10 also
includes an indicator material 42 disposed within the at least one groove 22. The
indicator material 42 may indicate a position of the substrate 12 during operation, as
set forth in more detail below. The indicator material 42 is formed from a mixture of
the first material and a second material.
[0018] More specifically, the second material may be a filler metal for a laser
welding operation, as set forth in more detail below. Therefore, the second material
may be non-magnetic and may be provided as a powder or wire for injection and
melting by a laser (not shown). As such, the indicator material 42 may also be non
magnetic. In another non-limiting variation, the second material may be magnetic.
For this variation, the indicator material 42 may also be magnetic and may have a
second magnetic permeability that is different from the first magnetic permeability of
the first material set forth above.
[0019] For embodiments where the first material is low alloy, high strength
steel or plain carbon steel, the second material may be an alloy including an element
selected from the group of nickel, cobalt, and combinations thereof. Nickel and/or
cobalt may be present in the second material to provide corrosion-resistance to the
indicator material 42. More specifically, nickel and/or cobalt may be present in the
second material in an amount of from about 1 part to about 90 parts by weight based
on 100 parts by weight of the second material. For example, a suitable second
material for providing the indicator material 42 with excellent corrosion-resistance
may include about 65 parts by weight nickel, about 20 parts by weight chromium,
about 8 parts by weight molybdenum, about 3.5 parts by weight of a combination of
niobium and tantalum, and about 4.5 parts by weight of iron based on 100 parts by
weight of the metal alloy, and may be commercially available under the trade name
INCONEL ® 625 from Special Metals Corporation of New Hartford, New York.
Likewise, a suitable second material may include about 54 parts by weight cobalt,
about 26 parts by weight chromium, about 9 parts by weight nickel, about 5 parts by
weight molybdenum, about 3 parts by weight iron, about 2 parts by weight tungsten,
and about 1 part by weight of a combination of manganese, silicon, nitrogen, and
carbon, and may be commercially available under the trade name ULTIMET ® from
Haynes International, Inc. of Kokomo, Indiana. Further, other suitable non-limiting
examples of second materials may include alloys commercially available under the
trade names Micro-Melt® CCW alloy from Carpenter Technology Corporation of
Reading, Pennsylvania, Stellite® 2 1 from Stellite Coatings of Goshen, Indiana, and
Eatonite™ ABC-LI from Eaton Corporation of Cleveland, Ohio.
[0020] Alternatively, the second material may be a stainless steel. Suitable
stainless steels include, but are not limited to, 308-, 316-, 321-, and 347-grade
austenitic stainless steels. For some applications requiring excellent corrosionresistance
over a comparatively shorter service life, e.g., less than about 15 years, or
under comparatively less-corrosive operating environments, e.g., brackish water,
suitable second materials may alternatively include martensitic stainless steels, ferritic
stainless steels, super ferritic stainless steels, duplex stainless steels, super duplex
stainless steels, and combinations thereof.
[0021] Referring again to Figure 2, the indicator material 42 is distinguishable
from the first material. For example, since the indicator material 42 may be non
magnetic and the first material may be magnetic, the indicator material 42 may be
distinguishable, i.e., able to be sensed or detected, by a sensor (not shown), such as a
Hall effect sensor or transducer that is configured for varying output voltage in
response to changes in a magnetic field. In another non-limiting example, the
indicator material 42 may be distinguishable from the first material based on
differences between the second magnetic permeability of the indicator material 42 and
the first magnetic permeability of the first material. For example, each of the
indicator material 42 and the first material may be magnetic, but the indicator material
42 may have the second magnetic permeability that is different from the first
magnetic permeability of the first material. Therefore, the sensor may respond to the
difference between the second magnetic permeability and the first magnetic
permeability of the indicator material 42 and the first material, respectively. In yet
another non-limiting example, the indicator material 42 may be distinguishable from
the first material based on another property, such as density.
[0022] The indicator material 42 is also metallurgically bonded to the first
material. For example, the indicator material 42 may be weld bonded to the first
material. That is, since the indicator material 42 is formed from a mixture of the first
material and the second material, e.g., after melting, the indicator material 42 is
metallurgically bonded to the first material, as set forth in more detail below.
[0023] With continued reference to Figure 2, the position measurement system
10 also includes a corrosion-resistant cladding 44 formed from an alloy and disposed
on the substrate 12 so as to cover the indicator material 42 and the surface 20. The
corrosion-resistant cladding 44 may provide the position measurement system 10 with
excellent corrosion- and wear-resistance, as set forth in more detail below.
[0024] The alloy of the corrosion-resistant cladding 44 may be a metal alloy
for a laser cladding operation. Therefore, the alloy may be provided as a powder or
wire for injection and melting by a laser (not shown). In addition, the alloy and the
corrosion-resistant cladding 44 may be non-magnetic. Alternatively, the alloy and the
corrosion-resistant cladding 44 may be magnetic, but may have a magnetic
permeability that is different from the first magnetic permeability of the first material
set forth above.
[0025] The alloy of the corrosion-resistant cladding 44 may be similar to the
second material. For example, for applications where the second material is
INCONEL® 625, the alloy of the corrosion-resistant cladding 44 may also be
INCONEL® 625. Likewise, for applications where the second material is 316-grade
stainless steel, the alloy of the corrosion-resistant cladding 44 may also be 316-grade
stainless steel. Alternatively, the second material and the alloy of the corrosionresistant
cladding 44 may be dissimilar. For example, according to cost or weight
considerations, the second material may be 316-grade stainless steel, and the alloy of
the corrosion-resistant cladding 44 may be INCONEL® 625.
[0026] For embodiments where the first material is low alloy, high strength
steel or plain carbon steel, the alloy of the corrosion-resistant cladding 44 may include
an element selected from the group of nickel, cobalt, and combinations thereof.
Nickel and/or cobalt may be present in the alloy to provide corrosion-resistance to the
position measurement system 10. More specifically, nickel and/or cobalt may be
present in the alloy in an amount of from about 1 part to about 90 parts by weight
based on 100 parts by weight of the alloy. For example, a suitable alloy of the
corrosion-resistant cladding 44 may include about 65 parts by weight nickel, about 20
parts by weight chromium, about 8 parts by weight molybdenum, about 3.5 parts by
weight of a combination of niobium and tantalum, and about 4.5 parts by weight of
iron based on 100 parts by weight of the alloy, and may be commercially available
under the trade name INCONEL® 625 from Special Metals Corporation of New
Hartford, New York. Likewise, a suitable alloy of the corrosion-resistant cladding 44
may include about 54 parts by weight cobalt, about 26 parts by weight chromium,
about 9 parts by weight nickel, about 5 parts by weight molybdenum, about 3 parts by
weight iron, about 2 parts by weight tungsten, and about 1 part by weight of a
combination of manganese, silicon, nitrogen, and carbon, and may be commercially
available under the trade name ULTIMET® from Haynes International, Inc. of
Kokomo, Indiana. Further, other suitable non-limiting examples of alloys may be
commercially available under the trade names Micro-Melt® CCW alloy from
Carpenter Technology Corporation of Reading, Pennsylvania, Stellite® 2 1 from
Stellite Coatings of Goshen, Indiana, and Eatonite™ ABC-LI from Eaton
Corporation of Cleveland, Ohio.
[0027] Alternatively, the alloy of the corrosion-resistant cladding 44 may be a
stainless steel. Suitable stainless steels include, but are not limited to, 308-, 316-,
321-, and 347-grade austenitic stainless steels. For some applications, suitable alloys
may alternatively include martensitic stainless steels, ferritic stainless steels, super
ferritic stainless steels, duplex stainless steels, super duplex stainless steels, and
combinations thereof.
[0028] Since the alloy of the corrosion-resistant cladding 44 may include
nickel and/or cobalt, the corrosion-resistant cladding 44 exhibits excellent corrosionresistance.
More specifically, the corrosion-resistant cladding 44 may be substantially
resistant to corrosion from sea water at an ambient temperature of from about -40 °C
to about 50 °C. Stated differently, the corrosion-resistant cladding 44 minimizes
oxidation of the surface 20 of the substrate 12 in air after exposure to sea water. As
used herein, in contrast to fresh water, the terminology "sea water" refers to water
having a salinity of from about 31 parts by volume to about 40 parts by volume based
on 1 trillion parts by volume of sea water, i.e., about 3 1 ppt to about 40 ppt (about
3.1% to about 4%), and a density of about 1.025 g/ml at 4 °C. Further, sea water
includes dissolved salts of one or more ions selected from the group including
chloride, sodium, sulfate, magnesium, calcium, potassium, bicarbonate, bromide,
borate, strontium, fluoride, and combinations thereof. Sea water may include
brackish, saline water, and brine.
[0029] Additionally, the corrosion-resistant cladding 44 may exhibit a free
corrosion potential, Eco , of less than or equal to -0.200. As used herein, the
terminology "free corrosion potential" refers to an absence of net electrical current
flowing to or from the substrate 12 in sea water relative to a reference electrode.
Further, the corrosion-resistant cladding 44 may exhibit a corrosion rate of less than
or equal to about 0.000254 mm per year. As used herein, the terminology "corrosion
rate" refers to a change in the substrate 12 and/or corrosion-resistant cladding 44
caused by corrosion per unit of time and is expressed as an increase in corrosion depth
per year. Therefore, the corrosion-resistant cladding 44 may exhibit minimized
susceptibility to localized corrosion from, for example, pitting and/or crack
propagation.
[0030] As shown in Figure 2, the corrosion-resistant cladding 44 may have a
thickness 46 of from about 0.6 mm to about 1.6 mm, e.g., about 1.3 mm. Further, the
corrosion-resistant cladding 44 may define an external surface 48 thereof that is
substantially smooth. That is, the external surface 48 may have a surface roughness,
Ra, of from about 0.1 microns to about 0.15 microns, where 1 micron is equal to 1 x
10 6 meters. As used herein, the terminology "surface roughness, Ra" refers to a
measure of a texture of the external surface 48 of the corrosion-resistant cladding 44
and refers to an average distance between peaks and valleys (not shown) of the
external surface 48. More specifically, microscopic valleys on the external surface 48
of the corrosion-resistant cladding 44 correspond to a point on the external surface 48
that lies below an average line. Similarly, microscopic peaks on the external surface
48 of the corrosion-resistant cladding 44 correspond to a point on the external surface
48 that lies above an average line. Thus, measurements of distances between such
peaks and valleys determine the surface roughness, Ra. The surface roughness, Ra, of
the external surface 48 may be provided by polishing or finishing the corrosionresistant
cladding 44, as set forth in more detail below.
[0031] Comparatively rougher surfaces generally exhibit less wear-resistance
and wear more quickly as compared to relatively smoother surfaces, since
irregularities such as peaks and valleys in surfaces may form initiation sites for
cracks, stress zones, and/or corrosion. Therefore, since the external surface 48 is
substantially smooth, the corrosion-resistant cladding 44 exhibits excellent
smoothness and resulting wear- and corrosion-resistance.
[0032] Referring again to Figure 2, the corrosion-resistant cladding 44 covers
the indicator material 42 and the surface 20 of the substrate 12. More specifically, the
corrosion-resistant cladding 44 may be metallurgically bonded to each of the indicator
material 42 and the surface 20 at a bond strength of greater than about 70 MPa, e.g.,
greater than about 340 MPa, as measured in accordance with the ASTM Multistep
Shear Test for Bond Strength of Claddings. The aforementioned bond strength
minimizes delamination of the corrosion-resistant cladding 44 and may be especially
advantageous for applications requiring materials with minimized thermal expansion
upon repeated heating and cooling, e.g., from exposure to direct sunlight.
[0033] Referring now to the method, the method of forming the position
measurement system 10 is described with general reference to Figures 1-3. The
method includes melting the surface 20 of the substrate 12 formed from the first
material, wherein the surface 20 defines at least one groove 22 therein and wherein
the surface 20 is melted within the at least one groove 22. That is, the surface 20 is
melted within the at least one groove 22, i.e., at the location of the at least one groove
22. The surface 20 within the at least one groove 22, e.g., the plurality of grooves 22,
may be melted by any known process. For example, the surface 20 within the at least
one groove 22 may be melted by laser welding the surface 20 defining the at least one
groove 22 with a laser (not shown) having a spot size of about 2 mm.
[0034] Therefore, prior to melting, the method may include machining the
surface 20 to define the plurality of grooves 22 therein, wherein each of the plurality
of grooves 22 is disposed substantially perpendicular to the longitudinal axis 14
(Figure 1) and spaced apart from an adjacent one of the plurality of grooves 22 along
the longitudinal axis 14. The substrate 12 may be straightened and cleaned to prepare
the substrate 12 for machining. The surface 20 of the substrate 12 may then be
machined, e.g., with a lathe or cutting tool having a plurality of cutting inserts (not
shown), to define the plurality of grooves 22. Four, six, or more grooves 22 may be
machined into the surface 20 simultaneously. Referring to Figure 3, the plurality of
grooves 22 may result from machining the substrate 12, and may extend into the
substrate at the depth 32 set forth above, e.g., about 1.10 mm. As shown in Figure 3,
a machined width 50 of the groove 22 may be less than the final groove width 34 of
the groove 22 after melting. That is, the machined width 50 of the groove 22 may be
from about 1.8 mm to about 2.0 mm, e.g., about 1.9 mm, to allow for slight expansion
of the groove 22 during melting.
[0035] Referring again to Figure 2, the method also includes, concurrent to
melting, depositing the second material into the at least one groove 22 to form the
mixture of the first material and the second material. That is, melting and concurrent
depositing may be further defined as laser welding the surface 20 at the at least one
groove 22 so that the surface 20 within the at least one groove 22 melts as the second
material is deposited. Stated differently, the second material and the surface 20
defining the at least one groove 22 may be laser welded, i.e., fusion welded, so that a
portion of the at least one groove 22 melts and mixes with the second material to form
the mixture. For example, the second material in the form of powder or wire may be
injected into the melting groove 22 to form the mixture of the first material and the
second material. Laser welding may form a liquefied weld puddle within each groove
22, wherein the weld puddle is formed from the mixture of the first material and the
second material. A composition of the mixture may therefore be controlled by
varying an amount of the first material that is melted and an amount of second
material deposited or injected into the at least one groove 22.
[0036] Laser welding, i.e., melting the surface 20 of the at least one groove 22
and concurrently depositing the second material into the at least one groove 22, may
be carried out by a laser welding device (not shown) including a laser emitted from a
welding head. The laser welding device may also include a laser-structured light
seam tracker apparatus attached to the welding head to enable accurate, automatic
positioning of the welding head over the plurality of grooves 22. Such an apparatus
may minimize machining and positioning errors during machining.
[0037] The shape of the at least one groove 22 may minimize shrinkage
cracking and porosity of the mixture. As used herein, the terminology porosity refers
to an amount of void space within a material and is expressed as a percentage of the
total material. In addition, the at least one groove 22 minimizes an amount of the first
material that melts during laser welding, which in turn minimizes an amount of iron in
the resulting mixture of the first material and the second material. Such minimized
iron content of the mixture increases the corrosion-resistance of the position
measurement system 10.
[0038] Referring again to Figure 2, the method further includes solidifying the
mixture to form the indicator material 42 that is distinguishable from and
metallurgically bonded to the first material. That is, the mixture may harden after
completion of laser welding so as to solidify and form the indicator material 42 or
laser weld. Since the indicator material 42 is formed by solidifying the mixture of the
first material and the second material, the indicator material 42 is fusion welded to the
first material of the substrate 12. The aforementioned melting, concurrent depositing,
and solidifying of the mixture forms the indicator material 42 having excellent bond
strength and minimized porosity. That is, the bond strength of the indicator material
42 may be significantly greater than a bond strength of a comparative material (not
shown) formed by brazing, soldering, electroplating, and/or thermal spraying that may
exhibit a bond strength of from only about 13 MPa to about 69 MPa. The increased
bond strength of the indicator material 42 may be especially advantageous for
applications requiring materials with minimized thermal expansion upon repeated
heating and cooling, e.g., from exposure to direct sunlight.
[0039] With continued reference to Figure 2, the method also includes
depositing the alloy onto the substrate 12 to form the corrosion-resistant cladding 44
that covers the indicator material 42 and the surface 20 to thereby form the position
measurement system 10. That is, depositing the alloy may be further defined as laser
cladding the indicator material 42 and the surface 20 so that each of the indicator
material 42 and the surface 20 melts and metallurgically bonds to the corrosionresistant
cladding 44. Stated differently, the corrosion-resistant cladding 44 may be
laser clad, i.e., fusion welded to, the indicator material 42 and the surface 20 so that a
portion of the indicator material 42 and the surface 20 melts and mixes with the alloy
to form the corrosion-resistant cladding 44. Laser cladding may therefore fuse the
alloy with each of the substrate 12 and the indicator material 42 to form the corrosionresistant
cladding 44 on the substrate 12.
[0040] Laser cladding, i.e., depositing the alloy onto the substrate to form the
corrosion-resistant cladding 44, may be carried out by a laser cladding system (not
shown) including a laser emitted from a welding head. The corrosion-resistant
cladding 44 may be deposited onto the surface 20 and the indicator material 42 in a
tightly spiraling path along the longitudinal axis 14. For example, the substrate 12
may be rotated while the laser cladding system deposits the corrosion-resistant
cladding 44 onto the surface 20 and the indicator material 42 in the tightly spiraling
path.
[0041] The corrosion-resistant cladding 44 may be deposited directly onto the
indicator material 42 so as to cover the indicator material 42. Therefore, the method
does not require intermediate grinding or machining of the indicator material 42
before deposition of the alloy to form the corrosion-resistant cladding 44. The alloy
may be deposited so that the corrosion-resistant cladding 44 is a single layer having a
preliminary thickness (not shown) of from about 1.7 mm to about 2.0 mm, e.g., about
1.8 mm to about 1.9 mm. Subsequently, the corrosion-resistant cladding 44 may be
ground to the thickness 46 (Figure 2) of from about 0.6 mm to about 1.6 mm, e.g.,
about 1.3 mm.
[0042] It is to be appreciated that the alloy may be deposited onto the
substrate 12 after melting, concurrently depositing the second material, and
solidifying the mixture as set forth above. Alternatively, the method may include
concurrently melting, depositing the second material, and depositing the alloy. That
is, melting, depositing the second material, and depositing the alloy may be
concurrent. More specifically, the second material and the alloy may be of the same
composition, i.e., may be the same material, so that the second material may be
deposited into the at least one groove 22 as the alloy is deposited onto the substrate 12
to form the corrosion-resistant cladding 44.
[0043] The method may further include finishing the corrosion-resistant
cladding 44 to define the external surface 48 that is substantially smooth. For
example, the corrosion-resistant cladding 44 may be machined, ground, and/or
polished so that the external surface 48 has the surface roughness, Ra, of from about
0.1 microns to about 0.15 microns.
[0044] The method may also include increasing the bond strength between the
corrosion-resistant cladding 44 and each of the indicator material 42 and the first
material. That is, since the corrosion-resistant cladding 44 is formed from the alloy
deposited via laser cladding, the corrosion-resistant cladding 44 exhibits excellent
bond strength as set forth above.
[0045] In another embodiment, as described with reference to Figure 1, the
method of forming the position measurement system 10 includes machining the
surface 20 of the substrate 12 to define the plurality of grooves 22 therein, wherein the
substrate 12 is formed from the first magnetic material and is a cylindrical rod having
the longitudinal axis 14. Each of the plurality of grooves 22 is spaced apart from one
another along the longitudinal axis 14.
[0046] For this embodiment, the method also includes melting the surface 20
within each of the plurality of grooves 22 to thereby distribute the plurality of grooves
22 evenly along the longitudinal axis 14. That is, the surface 20 of each of the
plurality of grooves 22 may melt and thereby expand from the machined width 50 to
the groove width 34 to space each groove 22 apart from an adjacent groove 22 and
define the gap 36 therebetween. Therefore, melting may distribute the plurality of
grooves 22 evenly along the longitudinal axis 14 so that the ratio of the groove width
34 to the gap width 38 is about 1:1.
[0047] Concurrent to melting, the method includes depositing the second non
magnetic material within each of the plurality of grooves 22 to thereby form the
plurality of respective mixtures of the first magnetic material and the second non
magnetic material. The method also includes solidifying the plurality of respective
mixtures to form the non-magnetic indicator material 42 that is distinguishable from
and metallurgically bonded to the first magnetic material. The method additionally
includes depositing the non-metallic alloy onto the substrate 12 to form the corrosionresistant
cladding 44 that covers and is metallurgically bonded to each of the non
magnetic indicator material 42 and the surface 20 to thereby form the position
measurement system 10. It is to be appreciated that melting, depositing the second
non-magnetic material, and depositing the non-magnetic alloy may be concurrent.
The method may further include increasing the bond strength between the corrosionresistant
cladding 44 and each of the non-magnetic indicator material 42 and the first
magnetic material.
[0048] In operation, the position measurement system 10 may interact with
one or more sensors (not shown), e.g., one or more Hall effect sensors or magnetoresistance
sensors, to indicate the position of the substrate 12 with respect to a
reference position. For example, the sensors may continuously interrogate the
position measurement system 10 and detect the indicator material 42 disposed beneath
the corrosion-resistant cladding 44. In particular, as the position measurement system
10 translates past the sensors, e.g., extends or retracts within a hydraulic cylinder, the
sensors may detect a change in the magnetic field due to the presence of the
alternating magnetic first material and non-magnetic indicator material 42, and a
displacement of the position measurement system 10 with respect to a reference
position may be calculated. As the position measurement system 10 changes position,
the sensors may detect a position of the substrate 12 to an accuracy of about 1 mm. If
desired, the sensors may also include a pulse multiplier transducer (not shown) to
increase the sensitivity of the sensors. For example, in combination, the sensors and
the pulse multiplier transducer may detect a position of the substrate 12 to an accuracy
of about 0.1 mm. For redundancy during operation, the position measurement system
10 may interact with at least two sensors and two pulse multiplier transducers.
[0049] The aforementioned position measurement system 10 formed by the
method as described herein exhibits excellent corrosion-resistance as compared to
other systems (not shown) that include electroplated coatings such as nickelchromium
coatings; thermally-sprayed ceramic coatings such as chromia-titania
coatings and alumina-titania coatings; high velocity oxy-fuel gas (HVOF) thermallysprayed
ceramic coatings including hard particles such as tungsten carbide, chromium
carbide, oxides, and combinations thereof disposed in a cobalt, nickel-chromium, or
nickel binder phase; and plasma-sprayed coatings. Therefore, the position
measurement system 10 may be especially suitable for applications requiring
continuous corrosion-resistance over an extended service life, e.g., about 15 years or
more, such as piston rods for hydraulic cylinders in service within a saltwater splash
zone of an offshore drilling rig.
[0050] In addition, the corrosion-resistant cladding 44 and indicator material
42 each exhibit minimized porosity. For example, the corrosion-resistant cladding 44
may have a porosity of about 0.03 percent, which may contribute to reduced cracking
and increase corrosion-resistance. That is, the aforementioned porosity minimizes
formation of interconnected paths within the corrosion-resistant cladding 44. Such
interconnected paths may allow ingress of corrosive elements and compromise the
corrosion-resistance of the position measurement system 10. In contrast, HVOF
coatings may have a porosity of from about 0.5 percent to about 2.0 percent, and
plasma sprayed ceramic coatings may have a porosity of from about 3.0 percent to
about 10 percent, and may therefore exhibit reduced corrosion-resistance and spalling.
[0051] Further, the corrosion-resistant cladding 44 of the position
measurement system 10 may be ductile. Therefore, the corrosion-resistant cladding
44 may remain crack-free upon comparatively high-energy impacts. In contrast,
HVOF coatings and plasma sprayed coatings are generally brittle and may crack
severely upon comparatively low-energy impacts.
[0052] The position measurement systems 10 and related methods provide
corrosion-resistant claddings 44 having excellent hardness and corrosion-resistance.
Therefore, the position measurement systems 10 are suitable for exposure to sea
water, e.g., for applications requiring coated metal substrates 12 for operation within a
splash-zone of an offshore drilling rig. The corrosion-resistant claddings 44 are
smooth and exhibit excellent compressive residual stress. Therefore, the position
measurement systems 10 exhibit improved fatigue life and resistance to tensile stress,
and reduced infiltration and propagation of fatigue cracks, shrink cracks, and other
flaws. Further, the methods are cost-effective, and minimize discontinuities in the
corrosion-resistant claddings 44 and indicator material 42 such as cracks and/or pores.
[0053] While the best modes for carrying out the disclosure have been
described in detail, those familiar with the art to which this disclosure relates will
recognize various alternative designs and embodiments for practicing the disclosure
within the scope of the appended claims.
CLAIMS
1. A method of forming a position measurement system (10), the
method comprising:
melting a surface (20) of a substrate (12) formed from a first material,
wherein the surface (20) defines at least one groove (22) therein and wherein the
surface (20) is melted within the at least one groove (22);
concurrent to melting, depositing a second material into the at least one
groove (22) to form a mixture of the first material and the second material;
solidifying the mixture to form an indicator material (42) that is
distinguishable from and metallurgically bonded to the first material; and
depositing an alloy onto the substrate (12) to form a corrosion-resistant
cladding (44) that covers the indicator material (42) and the surface (20) to thereby
form the position measurement system (10).
2. The method of claim 1, wherein melting and concurrent
depositing is further defined as laser welding the surface (20) at the at least one
groove (22) so that the surface (20) within the at least one groove (22) melts as the
second material is deposited.
3. The method of claim 2, wherein depositing the alloy is further
defined as laser cladding the indicator material (42) and the surface (20) so that each
of the indicator material (42) and the surface (20) melts and metallurgically bonds to
the corrosion-resistant cladding (44).
4. The method of claim 1, further including machining the surface
(20) to define a plurality of grooves (22) therein, wherein the substrate (12) has a
longitudinal axis (14), and the plurality of grooves (22) is disposed substantially
perpendicular to the longitudinal axis (14), and wherein each of the plurality of
grooves (22) is spaced apart from an adjacent one of the plurality of grooves (22)
along the longitudinal axis (14).
5. The method of claim 4, further including increasing a bond
strength between the corrosion-resistant cladding (44) and each of the indicator
material (42) and the first material.
6. The method of claim 1, further including finishing the
corrosion-resistant cladding (44) to define an external surface (48) thereof, wherein
the external surface (48) is substantially smooth.
7. A method of forming a position measurement system (10), the
method comprising:
machining a surface (20) of a substrate (12) to define a plurality of
grooves (22) therein, wherein the substrate (12) is formed from a first magnetic
material and is a cylindrical rod having a longitudinal axis (14), and wherein each of
the plurality of grooves (22) is spaced apart from an adjacent one of the plurality of
grooves (22) along the longitudinal axis (14);
melting the surface (20) within each of the plurality of grooves (22) to
thereby distribute the plurality of grooves (22) evenly along the longitudinal axis (14);
concurrent to melting, depositing a second non-magnetic material
within each of the plurality of grooves (22) to thereby form a plurality of respective
mixtures of the first magnetic material and the second non-magnetic material;
solidifying the plurality of respective mixtures to form a non-magnetic
indicator material (42) that is distinguishable from and metallurgically bonded to the
first magnetic material; and
depositing a non-magnetic alloy onto the substrate (12) to form a
corrosion-resistant cladding (44) that covers and is metallurgically bonded to each of
the non-magnetic indicator material (42) and the surface (20) to thereby form the
position measurement system (10).
8. The method of claim 7, further including increasing a bond
strength between the corrosion-resistant cladding (44) and each of the non-magnetic
indicator material (42) and the first magnetic material.
9. A position measurement system (10) comprising:
a substrate (12) formed from a first material and having a surface (20)
defining at least one groove (22) therein;
an indicator material (42) disposed within the at least one groove (22),
wherein the indicator material (42) is formed from a mixture of the first material and a
second material, and is distinguishable from and metallurgically bonded to the first
material; and
a corrosion-resistant cladding (44) formed from an alloy and disposed
on the substrate (12) so as to cover the indicator material (42) and the surface (20).
10. The position measurement system (10) of claim 9, wherein the
corrosion-resistant cladding (44) is metallurgically bonded to each of the indicator
material (42) and the surface (20) at a bond strength of greater than about 70 MPa.
11. The position measurement system (10) of claim 9, wherein the
at least one groove (22) has a V-shape and defines a substantially rounded vertex (24)
having a radius of from about 0.3 mm to about 0.7 mm.
12. The position measurement system (10) of claim 9, wherein the
first material is magnetic and each of the corrosion-resistant cladding (44) and the
indicator material (42) is non-magnetic.
13. The position measurement system (10) of claim 9, wherein the
substrate (12) is a cylindrical rod having a longitudinal axis (14).
14. The position measurement system (10) of claim 13, wherein the
surface (20) defines a plurality of grooves (22) therein distributed evenly along the
longitudinal axis (14), and wherein each of the plurality of grooves (22) is disposed
substantially perpendicular to the longitudinal axis (14).
15. The position measurement system (10) of claim 14, wherein
each of the plurality of grooves (22) extends from the surface (20) into the substrate
(12) at a depth (32) of from about 0.09 mm to about 1.3 mm and has a groove width
(34) of from about 1.9 mm to about 2.1 mm, and wherein two adjacent grooves (22)
define a gap (36) therebetween having a gap width (38) of from about 1.9 mm to
about 2.1 mm.