Centricut, Llc v. The Esab Group, Inc.

United States Court of Appeals for the Federal Circuit

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CENTRICUT, LLC (New Hampshire),

Plaintiff/Counterclaim Defendant-
Appellant,
and

CENTRICUT, LLC (Delaware),

Counterclaim Defendant-Appellant,

v.

THE ESAB GROUP, INC.,

Defendant/Counterclaimant-
Cross Appellant.

Edward A. Haffer, Sheehan Phinney Bass & Green, PA, of Manchester, New
Hampshire, argued for plaintiffs/counterclaim defendants-appellants. With him on the
brief were Michael J. Bujold and Neal E. Friedman, Davis & Bujold, P.L.L.C., of
Manchester, New Hampshire.

Blas P. Arroyo, Alston & Bird, LLP, of Charlotte, North Carolina, argued for
defendant/counterclaimant-cross appellant. With him on the brief was Richard M.
McDermott.

Appealed from: U.S. District Court for the District of New Hampshire

Judge Steven J. McAuliffe
 United States Court of Appeals for the Federal Circuit

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CENTRICUT, LLC (New Hampshire),

Plaintiff/Counterclaim Defendant-
Appellant,
and

CENTRICUT, LLC (Delaware),

Counterclaim Defendant-Appellant,

v.

THE ESAB GROUP, INC.,

Defendant/Counterclaimant-
Cross Appellant.

___________________________

DECIDED: December 6, 2004
___________________________

Before MICHEL, CLEVENGER, and DYK, Circuit Judges.

DYK, Circuit Judge.

Centricut, LLC (New Hampshire) and Centricut, LLC (Delaware) (collectively

“Centricut”) appeal the judgment of the United States District Court for the District of

New Hampshire, finding that Centricut infringed U.S. Patent No. 5,023,425 (the “’425

patent”) and assessing damages in favor of The Esab Group, Inc. (“Esab”), the

assignee of the ’425 patent. Esab cross appeals the damages award. We hold that

Esab did not meet its burden in proving infringement, reverse the judgment of

infringement, and dismiss the cross appeal as moot.
 BACKGROUND

The central issue in this case is whether the absence of relevant expert

testimony resulted in a failure of proof.

I

Esab and Centricut are competitors in the plasma arc cutting torch market. Both

companies manufacture and sell electrodes used in plasma arc torches. The electrodes

must be replaced periodically. Centricut manufactures replacement electrodes. Esab is

the assignee of the ’425 patent, which claims an electrode for plasma arc torches and a

method of fabricating the electrode. Centricut filed for a declaratory judgment that its

product did not infringe the ’425 patent. Centricut also sought a declaration that the

’425 patent was invalid and unenforceable. Esab counterclaimed, alleging that

Centricut had infringed, inter alia, claims 1 and 8 of the ’425 patent.

II

Plasma arc torches use an electric arc to superheat a stream of gas to

temperatures of around 30,000 degrees Kelvin. This heated, ionized gas, or plasma, is

used to cut metal. Different gasses are used to cut metals of different types and

thicknesses. Oxygen gas is particularly suitable for cutting carbon steel up to one and

one-half inches thick. However, cutting with oxygen is difficult because its use leads to

frequent electrode failures and short electrode life.

Most prior art plasma arc torch electrodes consist of two parts: an emissive insert

and a holder. The electric arc (that heats the gas) knits off of the emissive insert and

runs between the electrode and the metal being cut. The emissive insert is commonly

made of a metal such as hafnium, zirconium, or tungsten, or an alloy of these metals.

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The emissive insert is embedded in the holder. The holder is commonly made of a high

thermal conductivity metal such as copper or an alloy of copper, and apparently cools

the emissive insert with means such as circulating water.

The electrode of the ’425 patent renders the plasma arc cutting of carbon steel

by use of oxygen gas more economical as compared to prior art electrodes. The ’425

patent discloses a three-part electrode that comprises an emissive insert, a holder, and

a sleeve positioned between the emissive insert and the holder. The emissive insert

and holder of the ’425 patent’s electrode are composed of the same materials as prior

art electrodes. ’425 patent, col. 3, ll. 4-46. The ’425 patent states that prior art

electrodes operating in an oxidizing environment, such as oxygen or air, fail when the

copper holder oxidizes and begins to support the arc in preference to the emissive

insert. Id. at col. 1, ll. 33-43. This occurs because oxidized copper has a lower “work

function” than non-oxidized copper. Id.

What is different about the ’425 patent is the sleeve. The sleeve is made of a

material, such as silver, with a high “work function” relative to the emissive insert. Id. at

cols. 1-2. The addition of the sleeve keeps the arc on the emissive insert even as the

copper holder becomes oxidized and thus increases the electrode’s useful life. Id. at

col. 2, ll. 23-28. Therefore, according to the ’425 patent, the improved performance of

the electrode is a result of the relative “work functions” of the emissive insert, the holder,

and the sleeve.

Claim 1 of the ’425 patent is stated in terms of “work function” and reads:

1. An electrode adapted for supporting an arc in a plasma arc torch
and comprising
a metallic holder having a front end, and a cavity in said front end,
and

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 an insert assembly mounted in said cavity and comprising an
emissive insert composed of a metallic material having a relatively low
work function, and a sleeve surrounding said emissive insert so as to
separate said emissive insert from contact with said holder, said sleeve
having a radial thickness of at least 0.1 inches at said front-end and being
composed of a metallic material having a work function which is greater
than that of the material of said emissive insert, and said sleeve being
composed of a metal which is selected from the group consisting of silver,
gold, platinum, rhodium, iridium, palladium, nickel, and alloys wherein at
least 50% of the composition of the alloy consists of one or more of said
metals and
whereby said sleeve acts to resist movement of the arc attachment
point from said insert to said holder.

Id. at col. 7, ll. 26-47 (emphases added).1

By agreement of the parties, the district court construed the term “‘work function’

as ‘the potential step, measured in electron volts, which permits thermionic emission

1
Claim 8 provides:
8. An electrode adapted for supporting an arc in a plasma arc torch
and comprising
a metallic tubular holder defining a longitudinal axis and having a
front end and a rear end, and a transverse end wall closing said front end,
said transverse end wall having a substantially planar outer front face
which is perpendicular to said longitudinal axis, and a cavity formed in said
front face and which extends rearwardly along said longitudinal axis, and
an insert assembly mounted in said cavity and comprising
(a) a generally cylindrical emissive insert disposed coaxially along
said longitudinal axis and having an outer end face lying in the plane of
said front face of said holder, said emissive insert being composed of a
metallic material having a relatively low work function so as to be adapted
to readily emit electrons upon an electric potential being applied thereto,
and
(b) a sleeve positioned in said cavity coaxially about said emissive
insert, said sleeve having a radial thickness of at least about 0.1 inches at
said front end and being composed of a metallic material having a work
function which is greater than that of the material of said holder and
greater than that of the material of said emissive insert, said metallic
sleeve being selected from the group consisting of silver, gold, platinum,
rhodium, iridium, palladium, nickel, and alloys wherein at least 50% of the
composition of the alloy consists of one or more of said metals, and
whereby said sleeve acts to resist movement of the arc attachment
point from said insert to said holder.
’425 patent, col. 8, ll. 27-61 (emphases added).

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from the surface of a metal at a given temperature.’” Centricut, LLC v. Esab Group,

Inc., No. 99-CV-39, slip op. at 9 (D.N.H. Feb. 7, 2002). “Work function is an energy. It’s

the energy that’s required to remove an electron from inside the material to outside the

material.” (J.A. at 645.) By definition it is easier to move an electron from a low work-

function surface than a high work-function surface.

Centricut’s accused electrode is similar to Esab’s patented electrode. It

comprises an emissive insert composed of hafnium or hafnium alloy, a holder

composed of copper or copper alloy, and a ring or washer (which Esab viewed as

satisfying the “sleeve” requirement) composed of silver or silver alloy positioned

between the emissive insert and the holder.2 Like Esab’s electrode, the Centricut

electrode exhibits significantly reduced electrode failure and a longer useful life than

prior art electrodes when used with oxygen gas.

III

The district court held a bench trial to determine (1) whether Centricut’s accused

device infringed claims 1 and 8 of the ’425 patent; (2) whether the ’425 patent was

invalid due to anticipation or obviousness; and (3) what, if any, damages should be

awarded if the ’425 patent was in fact valid and infringed. There was no dispute

2
The ’425 patent includes several limitations, in addition to work function,
that Centricut argues its accused device does not meet. First, Centricut contends that
the “sleeve” limitation is not met because the accused device has a ring or washer
surrounding only the front portion of the emissive insert, while the sleeve of the patent
surrounds substantially all of the emissive insert. Second, Centricut contends that the
“cavity” limitation is not met because the hole into which the emissive insert and sleeve
of the accused device are mounted is a through-hole (i.e., it does not have a back end)
while the patent calls for a blind cavity. The district court held in favor of Esab on both
of these claim construction issues. On appeal, Centricut urges that the district court’s
construction of these claim limitations was also erroneous. In view of our disposition,
we do not reach these issues, and accordingly do not discuss them further.

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concerning the district court’s claim construction of the work-function limitation. The

question was whether the accused device satisfied the limitation. Both parties called

witnesses to testify on infringement and with respect to work function, although

Centricut was the only party to introduce expert testimony. Neither party introduced any

evidence of tests conducted to directly measure the work function of the materials used

in the accused device. Indeed, neither party introduced evidence of tests or other

evidence concerning the exact materials used in the accused device. The only test

evidence that Esab introduced concerning the accused device concerned the useful life.

In that test, Esab used prior art electrodes and the accused device for long periods of

time, usually until the point of failure. The tests showed that the accused device had an

average useful life over four times longer than prior art electrodes.

Centricut’s expert, physics professor Dr. Marten denBoer, testified that it was not

possible to determine the relative work functions of the sleeve and the emissive insert of

the accused device without direct testing because many factors affect the work function

of a surface. In support of this testimony he submitted tables from various reference

texts reporting the work functions of samples of various pure elements, but concluded

that these tables established nothing about the relative work function of the sleeve and

emissive insert of the accused device. This is because work function is not an intrinsic

property of a metal, but is rather a property of specific surfaces under specific

conditions. The tables were therefore not representative of the torch under actual

operating conditions.

In contrast, Esab argued that the tables showed the Centricut electrode infringed

because the work-function values recorded in the tables for hafnium were lower than

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almost all of those recorded for silver. Esab argued alternatively that the useful life

testing was a surrogate for relative work function and that, because Centricut’s accused

electrode displayed a significantly longer useful life than prior art electrodes, it must be

because the sleeve had a higher work function than the emissive insert. Finally, Esab

argued that the relative work functions of hafnium and silver could be inferred from

hafnium’s use in emissive inserts and silver’s nonuse in emissive inserts. As discussed

in greater detail below, Esab introduced no expert testimony in support of any of these

three alternative theories.

Claims 1 and 8 of the ’425 patent differ in that claim 1 requires the sleeve to have

a work function higher than that of the emissive insert, whereas claim 8 requires the

sleeve to have a work function higher than that of both the emissive insert and the

holder. The district court concluded that Centricut had infringed claim 1, and indicated

that the work-function limitation of claim 1 had been satisfied.

The district court noted Esab’s argument that the long useful life of the accused

electrode must be due to the relative work functions of the sleeve and emissive insert.

Centricut, LLC v. Esab Group, Inc., No. 99-CV-39, slip op. at 6 (D.N.H. July 9, 2003).

However, although the district court mentioned the useful life theory, it did not adopt it.

Instead, the district court held that the work-function limitation of claim 1 was met by the

accused device by relying upon the tables3 originally submitted by Centricut’s expert,

stating:

3
The work-function tables reported work-function values for numerous
elements. Many of the tables before the court provided data on multiple samples of the
same element using multiple methods for measuring work function. For example, one
table reports sixteen work-function values for silver ranging from 3.08-4.81eV. (J.A. at
1361.) The same table reported a single value of 3.53eV for hafnium. (Id. at 1362.) On

03-1574, -1614 7
 Centricut established that physical circumstances could be
manipulated in such a way that some silver could indeed have a work
function lower than that of some halfnium [sic]. At the same time,
however, it is clear from the scientific references excerpted in Esab’s
Exhibit 25 [the tables] that silver commonly has a higher work function
than halfnium [sic]. Nothing in the record suggests that Centricut made its
silver sleeves from one of the relatively few low-work-function forms of
silver. It is more likely than not that the accused electrodes’ sleeves were
made from common forms of silver having a higher work function than
halfnium [sic].

Id. at 8 (footnote omitted). Thus, the district court found that Centricut’s insert was

made of hafnium and its sleeve was made of silver, and, because the tables commonly

disclosed higher work-function values for silver than hafnium, Centricut’s electrode

probably infringed. The district court defended its use of the work-function tables by

concluding that although the tables “might not establish to a physical certainty that the

silver used by Centricut has a higher work function than the halfnium [sic] in its inserts,

those standard references are sufficiently persuasive to support that finding by a

preponderance of the evidence.” Id. at 8 n.4.

In contrast, the district court held that Centricut did not infringe claim 8 because

“the readily available work-function tables disclose too great an overlap in relative work-

function values for silver and copper to give rise to a reliable inference one way or the

other.” Id. at 10. The district court refused to find infringement under the doctrine of

equivalents, holding that “Esab’s admittedly imprecise description of the physics of

plasma arc torch operation is fatal to its claim of infringement under the doctrine of

equivalents.” Id. at 11. The district court further held that claim 1 of the ’425 patent was

not invalid due to anticipation or obviousness. Based upon its finding of infringement of

this table, one of the work-function values reported for silver was less than the work-
function value reported for hafnium.

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claim 1 of the ’425 patent, the district court ordered Centricut to pay $2,182,972.24 in

damages plus prejudgment interest, and enjoined Centricut from infringing claim 1 of

the ’425 patent. Centricut appeals.4 Esab cross appeals the damages award. We

have jurisdiction pursuant to 28 U.S.C. § 1295(a)(1).

DISCUSSION

This case presents the question whether Esab satisfied the burden of proof on

infringement in the absence of expert testimony comparing the claims as construed with

the accused device. We hold that Esab failed to carry its burden.

I

The district court’s determination of infringement is a question of fact that we

review for clear error. Apex Inc. v. Raritan Computer, Inc., 325 F.3d 1364, 1371 (Fed.

Cir. 2003). “A finding is ‘clearly erroneous’ when although there is evidence to support

it, the reviewing court on the entire evidence is left with the definite and firm conviction

that a mistake has been committed.” United States v. United States Gypsum Co., 333

U.S. 364, 395 (1948).

II

The patentee has the burden of proving infringement by a preponderance of the

evidence. Seal-Flex, Inc. v. Athletic Track and Ct. Constr., 172 F.3d 836, 842 (Fed. Cir.

1999). Centricut argues that Esab did not satisfy its burden of proof on infringement

because it did not show that the accused device satisfied the work-function limitation.

Esab argues that it did, for three reasons. None of these theories was supported by

expert testimony.

4
The district court’s holding that the ’425 patent was not invalid has not
been appealed.

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 First, Esab urges (a little half-heartedly) that the district court’s reasoning was

correct. As noted above, the district court found the work-function tables showed that

the accused device met the work-function limitation by a preponderance of the

evidence, even though the only expert testimony directly contradicted this conclusion.

Centricut called as its witness Dr. Marten denBoer, a physics professor who was

qualified as an expert witness on the issue of work function. He filed an expert report to

which a number of work-function tables from various scientific reference books were

appended. The tables reported the measured work functions of samples of various

pure metals, including silver and hafnium. In the report, Dr. denBoer attempted to rank

the work functions of copper, hafnium, and silver. He concluded that “tabulated values

of . . . work function are . . . of limited value in attempting to rank work functions of

specific materials” because many factors affect the work function of a surface. (J.A. at

1335.) Dr. denBoer’s subsequent testimony and affidavits supported his conclusion in

the report that reference to work-function tables is an unreliable way to rank the work

functions of specific materials. In particular, he testified that work function is a property

of specific surfaces, not of specific elements as represented in the tables. He also

testified that the tables were prepared under much different conditions than a torch in

operation and that these differences in conditions greatly impact the work function

measurement. He concluded that the tables were not probative as to the relative work

functions in the actual accused device.

Esab barely mentions the work-function tables in its brief. Esab points to no

expert testimony or contrary testimony supporting the use of the tables.

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 III

Alternatively Esab urges that it satisfied its burden of proof on the work-function

issue by showing that the accused device had a longer useful life than devices without

the sleeve and that the extended useful life was attributable to work function. Esab’s

sole testimony attempting to show that useful life is a surrogate for work function was

the testimony of the inventor, Wayne Severance. His testimony can be read to support

Esab’s theory. Severance provided an explanation for why useful life is probative of

work function. He testified that the failure of an electrode usually occurs when the arc

moves off of the hafnium insert and onto the copper holder. When this occurs, the

holder rapidly deteriorates and the electrode is destroyed. He theorized that the arc

moves because the copper holder oxidizes to the point where its work function is lower

than that of the hafnium insert. He further theorized that the silver sleeve resists the

movement of the arc from the insert to the holder because the sleeve has a higher work

function, and, therefore, the arc is less likely to knit off of the sleeve. When asked about

other properties that might explain the longer useful life, Severance testified that work

function was the only explanation.

However, Centricut presented extensive expert testimony by Dr. denBoer that

longer useful life could be attributed to a number of different factors, including

temperature, the geometry of the electrode, the thermal and electrical conductivity of the

sleeve, or the sleeve’s resistance to oxidation, and that it was not reasonable to

conclude that longer useful life was attributable to work function. Dr. denBoer,

Centricut’s work-function expert, stated unequivocally that, while he did not know why

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the sleeve affects useful life, the useful life tests conducted by Esab told him “absolutely

nothing about work function.” (J.A. at 679.)

As with the first theory, there was no supporting expert testimony. Severance,

the inventor, was not qualified as an expert witness on any matter under Rule 702 of the

Federal Rules of Evidence. More to the point, he admitted that he was not an expert on

the issue of work function. He admitted that he had not studied the subject at college,

and had no graduate degree. He also did not claim to have acquired an expert’s

knowledge of work function during the course of his employment. In short, he offered

no foundation for offering reliable testimony on work function.

IV

Esab offers a final theory as to why the accused device reads on claim 1 of the

’425 patent. Esab asserts that testimony regarding the general properties of hafnium

and silver, and their use within the plasma arc torch field, was sufficient to prove that the

work-function limitation was satisfied. Esab argues that it is generally known that

hafnium is highly emissive and that its use in emissive inserts proves this, while silver is

a poor emitter, and that its nonuse in emissive inserts proves this. Esab theorizes that

emissivity and work function are the same.

Again the district court made no finding supporting such a theory, and again the

theory was not supported by expert testimony. There was no expert testimony that

emissivity and work function are the same. The only expert witness to address the

issue, Dr. denBoer, testified that although they are related, work function and emissivity

are not the same. None of the witnesses upon which Esab relies for the contrary view

had an expert knowledge of work function. Charles Landry identified himself as

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Centricut’s director of engineering and technical support, but affirmatively disclaimed

expert knowledge of work function. Daniel O’Hara was Centricut’s plasma arc cutting

torch expert, but he too admitted to having “a limited understanding of work function.”

(J.A. at 278.) Richard Couch, CEO of Centricut’s parent company Hypertherm, testified

that, although he was skilled in the art of plasma arc torches, he was familiar with work

function only “in a very general sort of way.” (J.A. at 908.) Patrick Byrne, the former

president, CEO, and chairman of the board of Centricut, testified that someone

explained work function to him during his first day at Centricut, but that he never

discussed work function again in the three years he was there, nor did he have any sort

of scientific training. Severance, a senior staff engineer at Esab and the inventor of the

’425 patent, cannot be considered an expert on work function for the reasons already

discussed. In summary, all of the witnesses upon which Esab relies to support this

argument lacked expert knowledge of work function.

Thus, each of Esab’s three theories suffers from the same deficiency: none is

supported by expert testimony. The first theory, adopted by the district court, rests on

the district court’s own interpretation of the evidence. The latter two theories rest on the

testimony of witnesses who were admittedly not experts on work function.

V

In many patent cases expert testimony will not be necessary because the

technology will be “easily understandable without the need for expert explanatory

testimony.” Union Carbide Corp. v. Am. Can Co., 724 F.2d 1567, 1573 (Fed. Cir. 1984);

see also Bernhardt, L.L.C. v. Collezione Europa USA, Inc., 386 F.2d 1371, 1384 (Fed.

Cir. 2004). But there is no claim that this is such a case. Indeed, in this case the

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technology involved was complex. The district court concluded that “the field of

technology from which [the invention] sprang is so poorly understood that it qualifies as

a ‘black art.’” Centricut, LLC v. Esab Group, Inc., No. 99-CV-39, slip op. at 20 n.6

(D.N.H. July 9, 2003).

In other areas of the law courts have held that relevant expert testimony

regarding matters beyond the comprehension of laypersons is sometimes essential.5

Expert testimony may be similarly important in patent cases involving complex

technology such as this one. Where the field or art is complex, we have repeatedly

approved the use of expert testimony to establish infringement. See, e.g., Ultradent

Prods., Inc. v. Life-Like Cosmetics, Inc., 127 F.3d 1065, 1070 (Fed. Cir. 1997). We

have also noted that “typically” expert testimony will be necessary in cases involving

complex technology. Schumer v. Lab. Computer Sys., Inc., 308 F.3d 1304, 1315 (Fed.

Cir. 2002).

We do not state a per se rule that expert testimony is required to prove

infringement when the art is complex. Suffice it to say that in a case involving complex

5
See, e.g., Wills v. Amerada Hess Corp., 379 F.3d 32, 36-37, 41 (2d Cir.
2004) (estate of a deceased seaman suing under the Jones Act claimed that long-term
exposure to toxic chemicals caused the decedent’s death; held “that: . . . expert
testimony on the issue of causation is necessary in Jones Act cases where a lay juror
could not be expected to intuit the causal relationship between the acts in question and
the injury”); Allison v. McGhan Med. Corp., 184 F.3d 1300, 1320 (11th Cir. 1999),
(“expert testimony was essential to prove causation” in products liability case); Mitchell
v. United States, 141 F.3d 8, 13 (1st Cir. 1998) (“Under Massachusetts tort law . . . a
plaintiff in a medical malpractice action may carry his or her burden of proof on the
issues of negligence and causation only with the assistance of expert testimony.”)
(citations omitted); Whelan Assocs. Inc. v. Jaslow Dental Labs., Inc., 797 F.2d 1222,
1232-33 (3d Cir. 1986) (“expert testimony is essential to even the most fundamental
understanding of” computer programs that were the subject of the copyright
infringement case); Carroll v. Beto, 421 F.2d 1065, 1068 (5th Cir. 1970) (lay testimony
not sufficient to establish competence to stand trial; “expert testimony [is] essential” to
the determination of accused’s competence to stand trial).

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technology, where the accused infringer offers expert testimony negating infringement,

the patentee cannot satisfy its burden of proof by relying only on testimony from those

who are admittedly not expert in the field. That is what happened here, and the

patentee thus failed to satisfy its burden of proof. This case stands as an apt example

of what may befall a patent law plaintiff who presents complex subject matter without

inputs from experts qualified on the relevant points in issue when the accused infringer

has negated infringement with its own expert.

Esab does not argue that a remand is necessary or appropriate to determine

infringement under the doctrine of equivalents. Esab’s cross appeal of the district

court’s damages award is dismissed as moot.

CONCLUSION

The decision of the district court is

REVERSED.

COSTS

No costs.

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