GRAVER TANK & MFG. CO. V. LINDE AIR PRODUCTS CO. (GRAVER TANK II) 339 U.S. 605 (1950)
FACTS
There are two electric wielding compositions or fluxes: the patented composition (Unionmelt Grade 20) and the accused composition (Lincolnweld 660).
The patent under which Unionmelt has made a claim is essentially a combination of alkaline earth metal silicate and calcium fluoride (silicates of calcium and magnesium)
Licolnweld’s composition is similar to Unionmelt’s, except that it substitutes silicates of calcium and manganese-the latter not an alkaline earth metal – for silicates of calcium and magnesium. In all other respects, the two compositions are alike.
The mechanical methods in which these compositions are employed are similar. They are identical in operation and produce the same kind and quality of weld.
PROCEDURAL HISTORY
The plaintiff (Linde Air Products Co.) owned a patent for an electronic welding process, and sued defendants including the Graver Company for infringing the patent.
The defendants asserted that they were not infringing the patent because the patented welding process used a welding composition made of alkaline earth metal silicate and calcium fluoride (usually expressed as silicates of calcium and magnesium), while the purported infringers substituted a similar element, manganese, for the patentee's magnesium. -The United States district court found infringement, and the Court of Appeals affirmed the infringement claim.
ISSUE
Whether the substitution of the manganese, which is not an alkaline earth metal, for magnesium, which is, under the circumstances of this case, and in view of the technology and and the prior art, is a change of such substance as to make the doctrine of equivalents inapplicable; or, conversely whether, under the circumstances, the change was so insubstantial that the trial court’s invocation of doctrine of equivalents was justified?
HELD
Court raised the doctrine of equivalents. It noted that if another party could use a process exactly the same as one that is patented, but escape infringement by making some obvious substitution of materials, it would deprive the patentee of the exclusive control meant to come with a patent. This would undermine the profitability of the patent, which would go against the policy of encouraging inventors to invent by giving the opportunity to profit from the labor of invention.
Court also outlined how the doctrine should be used, noting that "what constitutes equivalency must be determined against the context of the patent, the prior art, and the particular circumstances of the case."
Court laid out two possible tests to determine equivalency. Under the first of these ("triple identity" test), something is deemed equivalent if: -
It performs substantially the same function –
in substantially the same way –
to yield substantially the same result.
Under the second test, something is deemed equivalent if there is only an "insubstantial change" between each of the features of the accused device or process and the patent claim.
In this case, the Court gave particular weight to the determination of "whether persons reasonably skilled in the art would have known of the interchangeability of an ingredient not contained in the patent with one that was." Finding that the substitution of magnesium for manganese was both obvious to anyone working in the field, and was an insubstantial change, the Court upheld the finding of patent infringement.
In the current case, disclosures of prior art made it clear that manganese silicate was a useful ingredient in welding compositions. Also specialists familiar with the problems of welding compositions understood that manganese was equivalent to, and could be substituted for magnesium in the composition of the patented flux and their observations were confirmed by the literature of chemistry. Hence the substitution in the accused composition of manganese silicate for magnesium silicate, where the two compositions were substantially identical in operation and result was so insubstantial in view of technology and prior art, that the patent was infringed under the doctrine of equivalents.