The opinion of the court was delivered by: KIRKPATRICK
This suit in equity for infringement involves United States patent to Aram, No. 1,558,215, and its reissue No. 17,416. The patent relates to mechanical underfeed stockers of the inclined type and the industrial field in which this controversy arises is the manufacture of the largest and most expensive type of such stockers, particularly designed for use in electric power plants.
The claims in issue are claim 2 of the reissue, which is identical with claim 5 of the original patent, and claims 9, 10, and 11 of the reissue.
Claim 2 of the reissue (arranged for convenience) is as follows:
"In an underfeed stoker having a combustion grate formed of alternately disposed tuyeres and retorts,
"(1) Front and rear supports for the grate,
"(2) A plurality of tie members extending between and connected to said supports,
"(3) Plates forming the side and bottom walls of said retorts secured to said tie members, and
"(4) Tuyers bridging the spaces between and supported upon said retorts."
The claim does not specify a stoker of the inclined type, but the specification and drawing embody that type of construction.
The plaintiff and the defendant advance widely divergent views as to the essence of the patent as embodied in this claim. The plaintiff says that it is the idea of marking the walls of the retorts composite, using beams (called "tie members" in the claim) and vertical plates bolted to them in such manner as to form side walls for the retorts, thus protecting the supports from the fire and at the same time making it possible to build stokers of much greater length than could be obtained by using unitary walls. The defendant says (emphasizing the thought which he finds in the words "tie members") that it is the idea of making the whole stoker a rigid grid composed of front and rear transverse castings firmly tied together by the members which form the sides of the retorts. Our first aim will be to find from all the evidence, including the history and development of the art, which of these views is correct.
In the type of stoker manufactured by the plaintiff until about 1920, the beam members were firmly secured to both front and rear transverse supports, but the rear (lower) transverse support itself rested upon its bed or subsupport by gravity only, and consequently the entire structure could move rearwardly if elongated by heat expansion. In the type manufactured by the defendant up to 1926 the whole construction was rigid, and there does not appear to have been any provision for rearward expansion of the structure or for absorbing the forces set up by the action of the rams upon the coal in the retorts.
In the practical operation of these early types considerable difficulty was encountered by reason of the cracking of the sides of the retorts (or, as the witnesses sometimes called them, the tuyers boxes). It is not necessary to go fully into just what combination of forces and heat caused this cracking or just how serious a matter it was. cracks, when they occurred, had to be attended to promptly; if not, they might develop into holes burned in the sides of the retorts, or might even result in a breakdown of the entire support and a consequent collapse of a part of the stoker. Sometimes the repair work was quite simple. At other times it involved the ...