Intellectual Property Rights

Graver Tank & Manufacturing Co. v. Linde Air Products Co.

339 U.S. 605 (1950)

Facts

Linde owned a patent relating to an electric-welding composition or flux.
The patent described a flux containing silicates of certain alkaline-earth metals, including magnesium.
Graver Tank manufactured a competing welding composition.
Its product substituted manganese silicate for the magnesium silicate described in the patent.
Graver argued that manganese was not literally included within the wording of the relevant patent claim.
Linde accepted that literal infringement was doubtful but relied upon the doctrine of equivalents.
Evidence showed that persons skilled in welding chemistry regarded manganese and magnesium silicates as interchangeable for the relevant purpose.
The dispute reached the United States Supreme Court.

Whether an accused product can infringe even though it falls outside the literal wording of a patent claim.
Whether substituting manganese for magnesium was merely an insubstantial variation.
What factors determine equivalence.

The doctrine of equivalents prevents an infringer from escaping liability through an insignificant alteration.
A product may infringe where it performs:
substantially the same function;
in substantially the same way;
to obtain substantially the same result.
Equivalence is assessed in the context of:
the patent;
prior art;
the purpose of the claimed element;
knowledge of skilled persons;
known interchangeability.
Equivalence does not mean that every device producing the same result infringes.
The doctrine cannot erase meaningful claim limitations or extend the patent over prior art.
Whether a difference is substantial is ordinarily a factual question.

The claimed flux and Graver’s flux were both used in electric welding.
Both performed the same technical role in stabilising the welding process and producing a satisfactory weld.
Graver’s use of manganese silicate did not produce a fundamentally different operating method.
Expert evidence indicated that magnesium and manganese were recognised substitutes in welding compositions.
The accused product therefore performed substantially the same function, through substantially the same chemical operation, to produce substantially the same result.
The Court emphasised why literal wording alone could be inadequate.
A copier could otherwise take the substance of an invention, change one minor ingredient and avoid the patent.
Such a rule would make patent protection ineffective and encourage deliberate evasion.
At the same time, the Court did not treat similarity of result alone as sufficient.
Equivalence had to be assessed element by element and with reference to what skilled workers understood at the relevant time.
The substitution was not a later-developed technology radically different from the patented teaching.
It was a known and direct chemical equivalent.
The trial court’s factual finding of equivalence was therefore supported by the evidence.
The Court also noted that the doctrine must be applied carefully because claims provide public notice of the patent’s boundary.
It should protect the invention’s substance without creating a monopoly that the patentee never disclosed.

The Supreme Court held that Graver’s manganese-silicate composition infringed under the doctrine of equivalents.
The substitution was insubstantial and involved a known interchangeable material.
The decision established the influential function–way–result approach.
Use this case for: an accused product may infringe despite avoiding the literal claim where its substituted element is insubstantially different and performs the same function in the same way for the same result.