Electrolysis: processes – compositions used therein – and methods – Electrolytic erosion of a workpiece for shape or surface... – Electrolyte composition or defined electrolyte
Reexamination Certificate
2000-02-02
2001-08-21
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic erosion of a workpiece for shape or surface...
Electrolyte composition or defined electrolyte
C205S680000, C205S681000, C204S22400M, C204S22400M, C204S272000
Reexamination Certificate
active
06277264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to electropolishing processes, and more particularly to a system and method for electropolishing the inner surface of a pipe. Even more particularly, the present invention relates to a system and method for maintaining process parameters (e.g., the electrode-pipe gap voltage within acceptable limits.
2. Description of the Background Art
FIG. 1
is a block diagram of a typical electropolishing system
100
for polishing the inner surface of a pipe
102
. Electropolishing system
100
includes a power a power supply
104
having a first voltage supply terminal
106
and a second voltage supply terminal
108
, a cable
110
, an electrode
112
, and an electrical lead
114
. Electrode
112
is coupled to first voltage supply terminal
112
via cable
110
, and pipe
102
is coupled to second voltage supply terminal
108
via electrical lead
114
. An electrolyte solution (not shown) is circulated through pipe
102
during the electropolishing process by an electrolyte pumping system (not shown).
Power supply
104
asserts a first voltage, via first voltage supply terminal
106
and cable
110
, on electrode
112
, and a second voltage, via second voltage supply terminal
108
and electrical lead
114
, on pipe
102
. The voltage difference between electrode
112
and pipe
102
causes electrical current to flow from electrode
112
, through the electrolyte solution (e.g., phosphoric acid or sulfuric acid solution), to pipe
102
. The electrical current selectively removes microscopically raised points from the inner surface of pipe
102
(including any deposits thereon), into the electrolyte solution in the form of a soluble salt, effectively polishing the inner surface of pipe
102
.
The amount of electrical current, and thus the amount of material removed from the inner wall of pipe
102
, depends on the voltage difference between electrode
112
and pipe
102
. When electrode
112
is in position W, close to the connection between pipe
102
and lead
114
, the resistance of pipe
102
is negligible, so that the voltage difference between electrode
112
and pipe
102
is essentially equal to the voltage difference between first supply terminal
106
and second supply terminal
108
. However, during the electropolishing process, electrode
112
is drawn through pipe
102
from position W to position X, to position Y, and finally to position Z. As electrode
112
is drawn away from position W the resistance of pipe
102
becomes a factor, reducing the voltage difference between electrode
122
and pipe
102
. The changing voltage between electrode
112
and pipe
102
results in the nonuniform electropolishing of the inner surface of pipe
102
.
FIG. 2
is a chart
200
showing the increased resistance of pipe
102
, and the associated change in voltage across the electrolyte gap, as electrode
112
is drawn through pipe
102
. The electrode positions (W, X, Y, Z) shown in chart
200
correspond to the positions illustrated in FIG.
1
. The resistance (R) of pipe
102
was determined by the equation:
R
=&rgr;(
D/A
), (Eq. 1)
where R is the resistance of pipe
102
, &rgr; is the resistivity of the material of which pipe
102
is constructed, L is the length of pipe between the particular position and position W, and A is the cross-sectional area of pipe
102
. For purposes of this example, &rgr; is taken as 2.362 micro-ohms per foot, the resistivity of type
304
stainless steel, and the cross-sectional area of pipe
102
is 0.0655 square feet. The voltage drop (V) through a particular section of pipe
102
is calculated using Ohm's law:
V=IR,
(Eq. 2)
where (I) is the process current and (R) is the resistance of the relevant section of pipe
102
.
The voltage between electrode
112
and pipe
102
(the gap voltage) is determined by subtracting the voltage drop across the particular pipe section from the voltage between first supply terminal
106
and second supply terminal
108
(the process voltage). Chart
200
shows that as the distance between electrode
112
and the junction between pipe
102
and lead
114
(position W) increases, the gap voltage decreases. The decreasing gap voltage results in the nonuniform electropolishing of the inner surface of pipe
102
.
What is needed is an electropolishing system and method, wherein the gap voltage may be maintained within a desired range to achieve the uniform electropolishing of the inner surface of a pipe.
SUMMARY
The present invention overcomes the problems associated with the prior art by providing a novel system and method for uniformly electropolishing the inner surface of a pipe. The invention helps maintain the process voltage within a desired range by utilizing a plurality of electrical leads to achieve uniform electropolishing of the pipe. Coupling the pipe to a common voltage source with a plurality of electrical leads reduces the electrical resistance through the pipe by reducing the length of pipe through which the current must flow.
The embodiment of the present invention includes an electrode for placement within the pipe, a plurality of electrical leads, and a power supply having first and second voltage supply terminals. Each of the electrical leads is adapted to electrically couple a separate portion of the pipe to a common voltage source. The second voltage supply terminal of the power supply is also adapted to couple to the common voltage source. A cable electrically couples the electrode with the first voltage supply terminal of the power supply and draws the electrode through the pipe. In a particular embodiment the common voltage source is ground. In a more particular embodiment the electrical leads and/or the second voltage supply terminal of the power supply are adapted to facilitate separate grounding.
In another embodiment the plurality of electrical leads are adapted to couple to a single common voltage source, and in a more particular embodiment, the electrical leads are embodied in a single, electrically conductive cable. In an alternate embodiment, each of the electrical leads comprises an electrically conductive cable with a first end adapted to couple to the pipe to be electropolished and a second end adapted to couple to the common voltage source (e.g. a water pipe, grounded machinery, etc.). In a particular embodiment the first end of each of the leads is stripped of insulation and wrapped around the pipe to be electropolished. Alternatively, the first end of each of the leads includes a clamp for electrically engaging the pipe to be electropolished. In another particular embodiment the second end of each of the leads is stripped and wrapped around the common voltage source. Alternatively, the second end of each of the leads includes a clamp for electrically engaging the common voltage source.
A method for electropolishing the inner surface of a pipe is also disclosed. The method includes steps for placing an electrode within the pipe, attaching the pipe to a common voltage source with a plurality of electrical leads, coupling the electrode to the first voltage supply terminal of a power supply, coupling the common voltage source to a second voltage supply terminal of the power supply, and drawing the electrode through the pipe.
In a particular method the spacing between the electrical leads is dependent on the resistivity (&rgr;) of the pipe material and an acceptable variation in the voltage (&Dgr;V
gap
) between the electrode and the pipe. In a more particular embodiment the spacing (L) between each of the leads is obtained by the equation L≦(4A&Dgr;V
gap
)/(&rgr;I) where (I) is the process current and (A) is the cross sectional area of the pipe. Optionally, the leads are equally spaced.
According to one method, the common voltage source is maintained at ground. Optionally, each of the leads, and/or the second voltage supply terminal of the power supply are separately grounded.
In a particular method, the step of attaching the pipe to the common voltage source in
Henneman & Saunders
Henneman, Jr. Larry E.
Phasge Arun S,.
Therma Corporation, Inc.
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