Contour Saws, Inc. v. L. S. Starrett Co.

OPINION

WYZANSKI, Chief Judge.

This suit involves the validity and alleged infringement of claims 1 and 2 of reissue patent No. Re. 26,676, to R. A. Anderson and E. M. Connoy, dated September 30, 1969 for “Method of Making Band Saw Blade.”

Plaintiff, Contour Saws, Inc., an Illinois corporation, owns the patent. Defendant, L. S. Starrett Company, a Massachusetts corporation, is the alleged infringer.

The suit began upon patent No. 3,315,-548, issued April 25, 1967. The reissue occurred during the action, but the claims now in suit were in the original patent.

The patent in suit covers a method of making a band saw blade, and more particularly, a metal cutting band saw blade, having a body portion of tough, flexible, and inexpensive low alloy steel, such as SAE 6150, with a hardness of about 45 Rockwell C, and having tooth tips of high speed steel, such as M-2, hardened to about 65 Rockwell C.

What is claimed is:

1. The method of making a band saw blade wherein (1) a wire of high speed cutting tool steel is welded directly to one edge of a flexible alloy steel band of substantially uniform width and thickness to form a bimetal band, and

(2) after straightening and annealing, the resulting bimetal band has teeth of the desired size and shape formed in the edge thereof at which the tool steel wire is located to form a saw blade in which only the tips of the teeth are formed of the tool steel, said method being characterized by:

A. the use of an electron beam to weld the high speed steel wire to the edge of the band; and

B. simultaneously developing in the tool steel tooth tips the metallurgical characteristics of classically heat treated high speed steel along with maximum hardness, and bringing the remainder of the saw blade to a hardness on the order of 44-45 Rockwell C by

(1) passing the saw blade lengthwise once through the muffle of a heat treating furnace in which the final muffle temperature is maintained at a substantially constant level and at a selected value in the range of 2150°-2275°F.; and

(2) thereafter tempering the saw blade.

2. The method of claim 1, 'further characterized by the fact that the final muffle temperature is 2225 °F. and the tempering is done at 1050°F.

The need for a band saw blade having this combination of metals and hardness-es was due to the increased use since 1950 of high production band cut-off saws required for increased sawing of very hard metals.

For such purposes a blade backing or body material need be not only cheap, tough, and flexible, but also capable of being easily butt welded by means of the simple butt welder conventionally provided on band saws, to enable a strip of blade to be formed into a loop. The tooth tip material has to be hard and abrasion resistant on the finished blade, yet has to be soft enough to permit teeth to be formed by milling before the blade is heat treated. The tooth tip material should not be in an as-cast condition when applied to the band, but should retain the benefit of any previous working it has received. The bond between tooth tip material and band backing has to be straight even though its component metals have different coefficients of expansion. An especially difficult problem arose from the fact that high speed steel, the preferred tooth tip metal, has to be hardened by heat treatment at 2150° to 2275°F., whereas it had been the uniform teaching in the art that 6150 steel, the preferred backing body material, should not be heat treated at a temperature above 1650 °F., lest it acquire a coarse grain and poor fatigue resistance.

While bimetal hack saw blades were known before 1940, the art did not suggest a procedure by which a successful bimetal band saw blade could be made. In hack saw blades the band is substantially straight and unflexed; whereas a band saw blade is flexed many times per minute as it travels around the band wheels, and this flexing imposes severe demands upon a band saw blade with respect to fatigue resistance.

Before the patent in suit, several methods of bonding high speed steel to low alloy carbon steel were known. Included were resistance welding, puddling the high speed steel onto the low alloy steel with the use of an are, welding by a so-called Thermatool process, and electron beam welding.

The method shown in the claim in suit is by bonding a wire-like strip of high speed steel to a backing body of low alloy carbon steel like 6150 by the electron beam welding process, forming teeth in the tool steel edge portion of the composite band that have their gullets cut into the low alloy backing material, subjecting the toothed band to a single-pass heat treatment at 2150°-2275°F. (the hardening temperature for high speed steel), and then tempering the band. The key steps of this method are the use of electron beam welding for bonding the two metals together and the single-pass heat treatment at 2150°-2275°F.

The prior art does not disclose a process for making bimetal band saw blades that involves a combination of the two key steps just stated. It is true that Belgian patent No. 629,665 contains a disclosure of the use of an electron beam for joining materials in the making of saw blades; but it does not show how electron beam welding might be employed in the making of bimetal band saw blades, and it does not specify the particular metals to be joined in making the saw blades to which it does relate, nor how to treat them. Nor was there any prior art which suggested that low alloy carbon steel blade band stock such as 6150, when heated to 2150°-2275° F., would possess sufficient flexibility and fatigue resistance for the purposes of a band saw blade backing body. On the contrary, it was the uniform teaching of the prior art that such steel, heat treated at higher than about 1650°F., would possess an extremely coarse grain, and would therefore be unsuited for a band saw blade because of lack of flexibility and poor fatigue life.

No relevant disclosures were made in German patent No. 974,524 or Van Mater patent No. 3,231,433. The former relates to shaft tools such as milling cutters and to hack saw blades having a body of a steel alloyed with manganese or manganese and silicon, and that patent contains no disclosure of a 2150°-2275° F. heat treating temperature. The latter relates to a blade which is entirely of high speed steel.

The only bimetal band saw blades with high speed steel tooth tips that are now on the market are those made by the method of the patent in suit. Many well-known companies of strong financial position have taken licenses from plaintiff. Defendant’s own metallurgist recognized when plaintiff first marketed a bimetal blade made by the method of the patent in suit that “This band is a severe threat to our future in the high speed band market.”

Defendant’s 1963-1964 experiments with a bimetal blade stock of high speed steel and low alloy carbon steel did not teach the experimenter that low alloy carbon steel is suitable for band saw blade backing after heat treatment at 2150°-2275° F., inasmuch as the experimenter’s blade failed in fatigue from the back edge after only 20 hours of testing.

From the foregoing findings the Court concludes that claims 1 and 2 of Patent No. Re. 26,676 are valid.

Defendant sells “Powerband” bimetal band saw blades, the manufacture of which is charged to infringe the patent in suit.

The bimetal stock from which defendant’s blades are produced is purchased principally by defendant from Wallace Barnes Steel Division of Associated Spring Corporation, which makes it by electron beam welding a high speed steel wire to one edge of a band of alloy steel on the order of AISI or SAE 6150, to form bimetal band stock of substantially uniform width and thickness, and thereafter annealing and straightening the band thus formed. Defendant forms teeth in the high speed steel edge portion of the band stock, cutting the teeth to such depth that' only their tip portions consist of the high speed steel; and defendant then subjects the toothed band to a single-pass heat treatment at 2150°-2275°F., followed by quenching, and then tempers the band.

Defendant asserts that it is not infringing the patent in suit because it effects heat treatment of the toothed band stock by another means than a “muffle” furnace. There could be no plausible contention that the accused method fails to respond to the claims in suit in any other respect.

The furnace which defendant uses for the hardening heat treatment of the toothed stock that is to become its “Powerband” bimetal band saw blade is of a type generally regarded in the art as, and is indeed properly regarded as, being within the meaning of the claims, a “muffle” furnace.

Claims 1 and 2 of Patent No. Re. 26,-676 have been infringed by defendant in the manufacture of its “Powerband” bimetal band saw blade.