US2252869A - Hacksaw blade - Google Patents

Description

g- 1941- w. H. SHORTELL ETA L 2,869

HACKSAW BLADE Eiled April 28, 1937 IN V EN TORS Hskwwww ATTOR Y.

Patented Aug. 19, 1941' UNITED STATE s" PATENT OFFICE I HACKSAW BLADE William H.- Shortell, Greenfield, and Leslie D.

Hawkridge, Newton, Mass, assi gnors of onehalf to Millers Falls Company, Greenfield, Mass, a corporation of Massachusetts, and onehalf to Hawkridge Brothers Company, Boston,

, Mass, a corporation of Massachusetts Application April 28, 1937, Serial No. 139,434

3 Claims.

In accordance with the present invention, there is provided an improved hack-saw blade which is adapted to render satisfactory service under the most severe operating conditions while cutting materials of wide diversification of properties. O 1

In attempting to cut materials characterized v by their extreme hardness, which materials find wide application in the industrial arts, great difficulty has been encountered in the production of a hack-saw blade that .will stand-up under the extremely severe'conditions of service to which such bladesv may be subjected, especially in operating upon materials such as-hard alloy I steels, including tool steels, drill rods, and tempered automobile springs, as well as in the rapid sawing of the thin sheet steel from which automobile bodies are made, or in the cutting of gutter pipe or the like; for, in order to produce a satisfactory blade for such purposes it must have a combined hardness and toughness to enable the blade to penetrate the work without breaking the blade or stripping the teeth.

The combination of these properties has been impossible to attain prior to the present invention, although many attempts have been made to produce a hack- -saw blade which will meet the requirements. The difficulties which are encountered arise from the fact that hardness'in the blade is accompanied by brittleness which causes the blade to break or the teeth of the blade to be stripped during service; or, when efforts are made to overcomethe brittleness by toughening the blade by tempering operations, the increase in toughness or strength is accompanied by decreasing. hardness, so that the resistance to breakage, when attained, is largely offset by the blade being too soft for operating upon anything but the ,softest materials such as brass, copper,

aluminum, and very soft steel. A

Efiorts to overcome these defects haveresulted in only indifferent success, although several types of so-called non-breakable hack-saw blades have been produced and placed upon the market. The present inventionhasfor one of its objects to provide a cutting tool which may be illustrated as a hack-saw blade, which will obviate the above-mentioneddefects, and which is adapted for operating upon both thin and heavy crosssections of virtually any range of hardness;

A further object of the invention is to provide a hack-saw blade which not only is substantially non-breakable under severe conditions of use; but

which also will operate with equal satisfaction upon both hard alloys such as tool steel, drill rod, and

-the1ike, and soft materials such as copper, brass,

aluminum, or the like, and which performs satisfactorily upon thin sections, tubing, sheet metal, gutter pipe, electric casings, orthe like.

A still further object of the invention is to provide a. hack-saw blade which is free from qualities of weakness under any conditions where a hack-saw blade may be used;

Further objects and advantages of the present improved construction will become apparent as the description proceeds, and the features of novelty will be pointed out in the appended claims and the invention accordingly comprises the features of cbnstruction and combination of elements which will be exemplified in the construction hereinafter set forth, and the scope of the application of which will be indicated in the claims. 4

In theaccomp'anying drawing, the single figure represents a hack-saw blade in side elevation, .the blade being made of the improved composition and having the above-described, and other, improved properties.

The drawing is self-explanatory, the body of the blade being represented by the'numeral 2, which is provided with the teeth 4; and while the drawing illustrates a hack-saw blade, the

present invention contemplates, in general, any I within the following ranges:

- 1 Per cent Carbon 0.50 to 1.00 Manganese 0.50 to 1.00 Silic0n 0.10 to 0.50 Chromium 0.10 to 0.50 Molybdenum 0.50 to 1.00 Iron Balance As a typical specific illustration. the toolsteel U which is employed in the production of the improved tools of the present invention may com- "prise:

Per cent Carbon.. 0.65 Manganese 0.80 Molybdenum- 0.85

It will be seen from the above percentages s'tituents, ferrite (carbon-free iron) and that the typical composition, as well as the major portion of the preferred composition, is that of carbon. In exceptionally puresteel, a little more carbon may be required to cause the complete disappearance of ferrite, while in the presence of much impurity, a smaller percentage may be sufiicient. 7

Steel made up" exclusively of pearlite is some- I times said to be saturated, and it is also called eutectic, or 'eutectoid, steel. If the steel contains less than 0.85% carbon, and, therefore, an excess of ferrite (carbon-free iron), it is called under-saturatedor hypo-eutectoid steel. The use of the terms eutectic and eutectoid implies that steel is considered as an alloy of two concementite (iron carbide, FeaC) which, upon cooling, gives rise to the formation of a third constituent, pearl-ite, made up of small particles of both components.

Wheresteel contains more than approximately .85% carbon, that is more than enough to produce an entirely pearlitic structure, the excess is in the form of cementite, which excess cementite improves the resistance of the steel to abrasive wear but with amarked decrease in its toughness. Such steel containing over .85% carbon is described as hyper-eutectoid.

After forming the blade, the teeth-or any other desired edge-are formed on the blades in the usual or any suitable way. The blade is then heat treated in order to harden the same.

The heat treatment employed for hardening implements of the above-indicated compositions embraced in the present invention comprises heating the blade to a minimum hardening temperature from within the thermal critical range to a maximum hardening temperature ofapproximately 250" F, above the thermal critical range, and quenching in any liquid medium suchas oil, water and brine.

Following this treatment, the material may be tempered to a temperature as high as 600 F. or as low as 200 F. far various lengths of time depending upon the type of implement, hardness and the use to which the implement is to be put.

A typical example of heat-treating saw blades of the composition as indicated above is to heat I to 1450 F., oil quench and temper at 40 F. for

various lengths of time, 30 minutes being usually suiiicient for normal purposes.

Prior to this invention it was generally believed to be necessary to make hack-saw blades and other tools requiring a keen, long lasting cutting edge of hyper-eutectoid steel in order'to from hyper-eutectoid steel; and the explanation ting material.

, 0.5:0.5:1 (Mn:Mo:C).

for this fact is not known with an entire degree of deflniteness. However, the novel and superior properties of the tools produced from the above indicated compositions may be attributed to the balanced proportions of carbon, manganese, and molybdenum, which impart certain essential characteristics necessary to the life of any out- The proportion of these elements-manganese and molybdenum to the carbon contentare usually in an approximate ratio of 1:121 (MnzMozC), but never less than These balanced proportions of the elements create a transformation temperature interval, since manganese lowers the thermal critical range (A3) and molybdenum raises it, and consequently, upon rapid cooling,

the proportion of manganese present within the steel creates a tough, wear-resistant austenitic matrix which is dispersed with the hard complex carbides of molybdenum and iron. Thus, any work application such as cutting, abrasion, friction, etc., will convert the tough, wear-resistant austenitic matrix into a harder, tougher, more stable abrasion resistant martensitic condition which is essential in all cutting material. Furthermore, not only does manganese lower the thermal critical range and increase the amount of retained austenite at room temperature, but it also forms distinct carbides of itsown during the conversion of theretained austenite to mar tensite by the application of cold work, tempering or aging, and, as a result, it imparts addi tional wear-resistant qualities to the already hard, wear-resistant material. I

The development of the above blade resulted from investigations regarding specially tempered blades for sawing rapidly through the thin steel of which automobile bodies are made, the thin sections of which caused considerable diiiiculty because of the fact that the teeth of the blades would-be broken out of either the regular, all hard, or flexible types of blades, manufactured in accordance with the previously outlined procedure described above in this specification. In attempting to overcome this difliculty, all hard blades. were drawn to a higher temper, which reduced their hardness to .about that of a wood cutting or butcher saw blade, but it increased the toughness or strength so that the teeth would not break out nor the blade itself break under the twisting or extreme vibration to which they are subjected in cutting operations of this character. The breakage of the blades frequently occurs because of the fact that the thinness of the section being cut affords insufi'icient support for the teeth of the blade, the material being out.

' would be produced a blade which would be able to resist breakage and which would secure more cuts on the body work; and also that the blade would be suitable for cutting machinery steel solids, thereby increasing its scope of usefulness. Experimentation for the accomplishment of this aim produced the alloy described above, and

blades produced from this alloy by the abovedescribed procedure were found to have a toughness equal to, if not greater than, the spring tempered blade, and additionally there wasobage, it holds its teeth under the most severe operating conditions, and is applicable both to e'xx tremely hard and diflicultly-cut materials as well as to soft metals.

It will be understoodthat the invention i's not limited, necessarily, to the specific details asare herein specifically illustratedfanddescribed, but it will be apparent that such details are subject to various modifications which become apparent readily to one skilled in'the art, without departing from the spirit of the invention; and it will be understood, therefore, that it is intended and desired to include within the scope of the invention such modifications and changes as may be uses. 11; is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as amatter' of lz'tnguage,

might besaid to fall therebetween.

What is claimed is: a

1. As a new article of manufacture, a hack sawblade composed of steel containing approximately ..50-'1.50% carbon, .50-l. 50% manganese, fill-1.50% molybdenum, and .10.50% silicon, the remainder being essentially iron and the propOrtions of manganese 'and'fmolybdenum being approximately equal.-

2. As a new article of manufacture; a hack saw blade composed of steel containing approximately .50- -1% carbon, .50-1% manganese, .50-1% molybdenum and .10.50% silicon, the remainder be:- ing essentially iron' and the proportions of manganese" and molybdenum being approximately equal.-

' a 3.'As a new article of manufacture, a. hack saw blade composed oi steel containing approximately .50-1.% carbon, .50-1% manganese, .50'

1%- molybdenum, .10-'50% silicon and .10.50% chromium, the remainder being essentially iron and the proportions of manganese and molybdenurn; being approximately equal;

necessary to adapt it to varying conditions and 30 -W]LLIAM H. SHORTELL. I LESLIE D. I-LAWKRIDGE.

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