Armored Metal Tools

Abstract

Armored metal tools having a hard wearing, ductile, abrasive coating produced in situ from powdered matrix metal particles and abrasive particles of hard, high melting material, said tools comprising a structural base composed of a base metal, at least a portion of the surface of which is covered with a relatively thin, adherent and homogeneous layer of substantially uniform thickness, of said metal powders fusion bonded to each other and to said base metal and alloyed with said base metal throughout an interlayer between said base metal and coating layer, said coating layer of said fusion bonded metal powders having embedded therein and projecting from the surface thereof, a multiplicity of said abrasive particles forming projecting cutting edges and being composed of material selected from the group consisting of diamond substitute materials, such as metal carbides, borides, nitrides or silicides or mixtures thereof, said base metal being optionally composed of a heat treatable ferritic steel or alloy steel.

Parent Case Text

This application is a continuation-in-part of my copending application Ser. No. 638,998, filed May 16, 1967 (now U.S. Pat. No. 3,449,146), which is in turn a continuation-in-part of my copending application Ser. No. 177,558, filed Mar. 5, 1962 (now abandoned), which is in turn a continuation-in-part of my application Ser. No. 546,779, filed Nov. 14, 1955 (now U.S. Pat. No. 3,024,128), which in turn is a continuation-in-part of my application Ser. No. 379,100, filed Sept. 8, 1953 (now abandoned), and which in turn is a continuation of my application Ser. No. 41,180, filed July 28, 1948 (now abandoned). Application Ser. No. 548,915, filed Nov. 25, 1955 (now U.S. Pat. No. 3,023,490), is a continuation-in-part of my application Ser. No. 367,543, filed July 13, 1953 (now abandoned), and both are incorporated by reference in my aforesaid application Ser. No. 177,558. In addition, said application Ser. No. 367,543 is also a continuation-in-part of my said application Ser. No. 41,180.

Description

This invention pertains to improved armored metal tools and the production thereof, said tools having a hard wearing, ductile, abrasive coating produced in situ from powdered metal particles of a hard, refractory brazing or matrix metal alloy, such as nickel-base or cobalt-base alloys, and abrasive particles of hard, high melting material, such as metal carbides or equivalent diamond substitute materials, said tool comprising a structural base composed of a base metal, such as steel, alloy steel, etc., at least a portion of the surface of which is covered with a relatively thin, adherent and homogeneous layer of substantially uniform thickness, of said matrix metal powders fusion bonded to each other and to said base metal and alloyed or interdiffused with said base metal throughout an interlayer between said base metal and said matrix metal layer, said layer of said fusion bonded matrix metal powders having embedded therein and projecting from the surface thereof, a multiplicity of said abrasive particles to provide sharp cutting edges for cutting or abrading applications.

These improved tools may take the form of saws, files, rasps, sanding discs, abrasive sheets, and the like. All are characterized by a myriad of relatively small individual cutting teeth provided with exposed sharp edges of particles of diamond substitute materials, such as hard, refractory metal carbides, borides, nitrides and silicides. In each case, the cutting particles are supported from a metallic base, usually a heat treatable ferrous base metal or alloy, by a matrix of hard, refractory alloy, such as cobalt-base or nickel-base alloys, containing substantial amounts of one or more of chromium, tungsten, boron and silicon, which alloys are capable of wetting the surface of and metallurgically bonding to the cutting particles, and also capable of alloying by fusion with or diffusion into the surface layers of the underlying base metal and vice versa. The refractory alloy is also one which melts only at temperatures well above the upper transformation point of the base metal, such that the base can be heat treated by conventional techniques as by heating, quenching and tempering to develop desired combinations of strength, hardness and ductility, without affecting the ability of the matrix tenaciously to retain the cutting particles.

To assure that the diamond substitute particles project sufficiently beyond the layer of matrix metal to provide a myriad of said sharp cutting edges, the thickness of the matrix metal layer preferably does not exceed about one-half to two-thirds the average transverse dimensions of said abrasive particles, whereby said abrasive particles project beyond said layer to an average extent of at least about one-third to one-half their average transverse dimensions, as shown by the measurements and etched sections hereinafter presented and discussed.

The invention is directed in one of its aspects to improved saws and more especially band saws and band saw strip stock, and to the production thereof, said saws and saw stock being characterized by the application of armoring coatings of the character aforesaid to at least one edge and contiguous surface portions to form a cutting edge in which the cutting action is performed by the abrasive particles. For cutting heavy stock, the strip is preferably blanked out or gulleted at equispaced intervals to provide cutting teeth between the gullets, the teeth being armored in accordance with the invention. For cutting thin stock, the gullets may be omitted and the armoring applied continuously or intermittently along the cutting edge, as hereinafter described in detail.

For producing an armored metal tool in accordance with the invention, the tool base comprised of the base metal may first be coated over a selected surface area with an admixture of a suitable paste flux adhesive in admixture with the brazing metal powders in appropriate proportions, or alternatively a coating of the paste flux adhesive alone may first be applied and an overcoating of the brazing metal powders next applied. To the resultant coating applied by either procedure, there is applied a further overcoating of the abrasive metal particles; following which the coated surface is dried and the tool subjected preferably to high frequency electrical induction heating to temperature such as to fusion bond the matrix metal powders to one another and to the base metal, as to the latter by alloying therewith, and also partially to embed the abrasive metal particles therein. Immediately thereupon the tool is subjected to a cooling treatment to solidify the matrix metal layer thus permanently to embed the abrasive metal particles therein and to produce a solid state alloying layer between the matrix and base metals, thus permanently bonding the two together. Without interfering with the bonding of the matrix metal the cooling may be rapid enough to constitute quenching as part of the heat treatment of the base metal.

The paste flux adhesive employed must be such as to leave no residuum of unabsorbed material in the armor coating as this weakens the structure. The preferred paste flux adhesive is such as volatilizes in part on heating the tool to the brazing temperature and leaves a residuum which interdiffuses or alloys with the brazing and base metals. As pointed out more particularly below, paste flux adhesives of this character include those of boride-fluoride or organic base types. Silicate containing fluxes are undesirable because they leave a residuum of silica or silicates in the matrix metal layer, which weakens the armoring.

The base metal of the tool is preferably such as to be heat treatable to high hardness after heating to the brazing temperature of the matrix metal as by air cooling or more drastically quenching therefrom depending on the base metal employed, following which the tool may be tempered to a desired combination of lower hardness and ductility. Such metals include principally the ferritic steels and steel alloys.

It is a vitally important aspect of the novel process and product of the invention that the coating technique be so controlled that the abrasive particles are only partially embedded in the matrix metal layer and thus protrude beyond the same to form a myriad of sharp cutting edges. This may be accomplished by applying a relatively thin coating of the matrix metal powders, by employing a particle size for the matrix metal powders which is considerably less than that of the abrasive particles, and/or by superimposing the coating layer of abrasive particles on top of the coating layer of matrix metal powders.

The exact nature of the invention, as well as other objects and advantages thereof, will become more apparent from consideration of the following specification, referring to the attached drawings, illustrating various embodiments of the invention, as applied more particularly to the production of band saw strip stock, and in which:

FIG. 1 is an enlarged plan view of a portion of a band saw strip stock with arcuate gullets punched therein, while FIG. 2 is a similar view with somewhat elongated gullets punched therein.

FIG. 3 is a plan view of a portion of the gulleted band saw strip stock after armoring coating has been applied, while FIG. 4 is an enlarged plan view of one of the armored teeth of the FIG. 3 showing.

FIGS. 5 and 6 are plan views corresponding to FIG. 1, but wherein no gullets are cut into the band saw strip stock prior to armoring. In the FIG. 5 embodiment, the armoring is applied continuously along one edge of the strip stock, while in FIG. 6, it is applied intermittently at spaced intervals therealong.

FIG. 7 is a more or less diagrammatic showing in perspective illustrative of an apparatus and method for applying an armoring coating to an edge of the band saw strip stock, in accordance with one embodiment of the invention wherein the paste flux adhesive and brazing metal powders are premixed prior to application to the base metal strip stock and applied as a first coating thereto followed by overcoating with the abrasive particles.

FIG. 8 is a vertical longitudinal sectional view through an induction heating coil and subsequent controlled atmosphere, rapid cooling unit apparatus employed in the FIG. 7 sequence for purposes and in the manner described below.

FIG. 9 is a more or less diagrammatic fragmentary showing in perspective illustrative of a method and apparatus for applying an armoring coating to an edge of the band saw strip stock in accordance with another embodiment of the invention wherein the paste flux adhesive and brazing metal powders are separately and successively applied as coatings to the strip stock followed by overcoating with the abrasive particles.

FIG. 10 is a perspective view of a vibratory feeder operating on the principle of a "Syntron" vibrator, but of novel, spiral construction and which is employed in the apparatus sequences of FIGS. 7 and 9.

FIG. 11 is a view of a polished and etched section at about 40:1 magnification of gulleted, armored band saw strip stock, as taken longitudinally thereof, and as produced by the method of the FIG. 7 sequence wherein the paste flux and brazing metal powders are premixed prior to application to the strip stock base metal.

FIG. 12 is a view of a polished and etched section at about 40:1 magnification of gulleted, armored band saw strip stock, as taken transversely through one of the armored teeth thereof, and as produced by the method of the FIG. 9 sequence, wherein the paste flux and brazing metal powders are separately applied to the strip stock base metal.

Referring to FIGS. 1 and 2, the band saw strip stock 10, comprising, for example, a suitable grade of heat treatable alloy steel, such for example as SAE 6150 of approximate analysis 0.5% C, 0.8% Mn, 0.25% Si, 1% Cr, 0.15% V, balance Fe, is first gullet punched along one edge, as at 11, to punch out arcuately or elongated shaped gullets at equally spaced intervals, as at 12 and 12a. After the strip stock has been gulleted, it is wire brushed on both sides and thence grit blasted to remove any burrs produced along the gullet edges as a result of the punching operation.

The band saw strip stock 10, as thus prepared, is now ready for application to the gulleted edge, of a protective armoring coating as above generally described, and which preferably is accomplished by means of the method and apparatus sequence shown in FIG. 7. To this end the blanked strip 10 is fed progressively from a reel 50 thereof, and in vertically disposed position with reference to its height with the blanked edge at the top, first through a guide 51 and then beneath a feed roll 55 of an applicator unit 52 for applying to the upper edge of the strip a coating comprising an admixture of paste flux and brazing metal powders contained in a reservoir 53 and transferred thence to roll 55 via pickup and transfer rolls 54 and 54a, respectively.

A suitable paste flux for this purpose is that put out by Wall Colmonoy Corporation, Detroit, Michigan, under the designation "Nicrobraz Flux," as suitably thinned with water, and which is a boride-fluoride flux. Alternatively, an organic adhesive may be employed as described in my above mentioned U.S. Pat. Nos. 3,024,128 and 3,023,490.

Suitable brazing metal powders for admixture with the paste flux are powdered, hard, refractory alloys, such as nickel-base or cobalt-base alloys, capable of providing a matrix metal which wets the surface of and bonds to the tungsten carbide or other diamond substitute particles and also which fusion bonds to or alloys with the metallic base. Suitable such alloys are the cobalt-base or nickel-base alloys, such as the cobalt-chromium-tungsten "Stellite" alloys or the nickel-base alloys put out by the aforesaid Wall Colmonoy Corporation under the designation "Nicrobraz." A preferred such alloy is that put out by said company as "LM Nicrobraz" comprising an alloy consisting of about 13.5% Cr, 3.5% B, 4.5% Si, 2.5% Fe, 0.15% C and the balance Ni.

The strip as thus coated along its upper edge with the aforesaid admixture of flux paste and brazing metal powders, is now fed beneath the discharge lip 56, of an electromagnetically actuated vibratory feeder 57 of spiral construction. This unit, referring to FIG. 10 is vibrated at high frequency by conventional means (not shown) enclosed in the base housing 57a. The spiral trough 58 of the vibrating unit, contains a mass of diamond substitute abrasive particles 58a, which by virtue of the vibration of the unit, are fed upwardly along the spiral trough 58 and discharge over the discharge lip 56 thereof in a thin layer which falls as a curtain of the powdered particles transversely across the upper edge of the strip 10, as at 56a. A thin layer of the abrasive particles is thus deposited as an overcoating onto the coated upper edge of the strip, as limited, however, to the extent of the adherence of the carbide particles to said coated surfaces. The nonadhering excess of the particles fall into a return trough 56b which discharges these particles into a reservoir 56c thereof at the base of the spiral feed of the vibrator unit.

The strip is fed thence past an inspection station 59 consisting of an illuminated magnifying system 60 used in conjunction with a mirror 61 for inspection and quality control of the coated strip edge. The mirror is set at an angle of about 45.degree. to the vertical so that an observer may observe both the back as well as the front surfaces of the strip. Next, the coated strip is passed through a wiper assembly 62 comprising a pair of wipers 63, 64, mounted on an angle member 65 having a vertical slot therein as shown and carried by a second angle member 66 having threaded thereon a wing nut 67 for vertical adjustment of the wiper assembly.

The strip is fed next past an air blast unit 70, consisting essentially of a pair of nozzles 71, 72, adjustably positionable for blowing air at relatively low pressure against opposite sides of the strip below the coated edge thereof for removing loose tungsten carbide particles that may be deposited in the gullets or loosely adhering to the strip at this stage.

Next, the strip passes to a drive unit 73 and between a pair of pinch rolls 74, 75 thereat, driven by a motor 76 wherein the strip is pulled from the takeoff reel 50 and through the apparatus previously described. The strip passes thence through a troughlike, infrared ray heating unit 77, wherein the paste flux of the armoring coating is thoroughly dried.

Thence the strip passes between a pair of rolls 80, 81 of a tensioning unit 82 which tensions the strip at this point against the pull of the motor driven strip feed unit 109 at the end of the strip traverse. From the tensioning unit 82 the strip passes through an exhaust blower 83 for purposes described below.

The strip passes thence through an induction heating coil 86, supplied with high frequency electrical current, a suitable frequency being for example about 5.2 m.c.p.s., for heating the strip to temperature of about 1900.degree.-2000.degree. F., such as to cause the brazing metal powder to fuse and alloy with the base metal of the strip at the interface between them, also partially to embed the carbide particles therein and also to austenitize the alloy steel base metal of the strip. It has been found that the magnetic field of the induction heating coil has the effect of causing the carbide particles to project from the surface of the brazing metal and thereby enhance the cutting action of the so-armored tool.

Reverting now to the exhaust blower 83, its function is to draw air, smoke and flux vapor fumes from and through the induction heating coil 86, to prevent accumulation thereat of a conductive atmosphere such as might produce a flashover between the coil and the band saw strip stock.

The strip passes thence, referred to FIGS. 7 and 8, into a controlled atmosphere housing 87, through an entrance slot 88 therein and passes thence within the housing through a longitudinal slot 89 in a metal chill plate 90. The plate 90 is made of a metal of high thermal conductivity, such as copper or equivalent, and is chilled by circulation of a coolant, such as cold water, circulated therethrough by passages therein, as at 91, connected to inlet and outlet pipes, as at 92, 93, for supply and withdrawal of the coolant. As the strip passes along the slot in the chill plate it is held down by passage under a hold down roll 94, adjustably mounted for vertical displacement in a suitable supporting structure 95. The strip passes out of the housing 87 through an outlet 96. The housing is filled with a substantially inert atmosphere, such as nitrogen gas injected therein via a valved pipeline 97 but is admixed with a small fraction of oxygen containing gas, such as that supplied from the outer atmosphere which leaks in through the inlet and outlet strip feed ports 88, 96. The housing roof is provided with an adjustable gas exit vent 97a.

As the strip is fed along the slot in the chill plate it is subjected to a rapid cooling action for two purposes. One is to solidify the fused matrix metal, thereby to form the base metal and in which the carbide or other diamond substitute metal particles are partially and permanently embedded. The other purpose is to transform the high temperature austenitic structure of the steel alloy base metal into a hard, fully martensitic structure which may thereafter be tempered to a desired lower degree of hardness with accompanying increased ductility and toughness. However, in order to accomplish this the steel strip must be cooled from the austenitic phase with sufficient rapidity to temperature below the lowermost nose of the time-temperature-transformation or "TTT" curve of the steel as to prevent transformation of the austenite into any of the higher temperature transformation products such as pearlite, ferrite, bainite, etc. Since for SAE 6150 steel the lower nose of the "TTT" curve occurs at about 750.degree. F., it is necessary to cool the steel strip down to about 700.degree. f., with sufficient rapidity, i.e. in about 6 seconds, to get past the transformation curve while still retaining the steel in the fully austenitic state. Thereupon the steel is air cooled down to ambient temperature with transformation into a fully martensitic structure, with a minimum of quenching stress. In the normal cycle of operation of the FIG. 7 strip feed rate, several minutes is available for such air cooling for cooling the strip below about 200.degree. F. as it passes from the chill plate to a subsequent tempering furnace 107, FIG. 7 in which time the transformation of the austenite to martensite is substantially complete. The resultant hardness imparted to the steel strip is about "C" 60 Rockwell.

Referring to FIG. 7 the strip 10 next passes through a guide block 100 and under an inspection station 101, which is similar to inspection station 59, and thence through a tensioning unit 103. This unit is controlled by a hydraulic cylinder 104 for pressure actuating a movable brake shoe 105 toward a fixed brake shoe 106, with the strip 10 passing between said brake shoes. The strip 10 next passes through a tempering furnace 107 wherein it is given a short-time tempering treatment at about 950.degree. F. which tempers the base metal down to about "C" 40-45 Rockwell.

On leaving the tempering furnace 107, the strip passes between a cluster of straightening rollers 108, before passing through the rolls 109 of a drive unit like that of FIGS. 15-18 inc. The strip passes thence under a roller 110 of a counter 111 and thence onto a takeup reel 112 driven by a motor 113.

Since the untempered martensitic structure of the steel strip as it leaves the quenching unit 87 is quite brittle, it is desirable to avoid bending the strip prior to tempering. Hence the strip is fed in a straight path between units 87 and 107, and then is straightened in rollers 108.

The armor coating applied to the strip 10 as processed in accordance with the FIG. 7 sequence, has the appearance as shown in approximately actual size in FIG. 3 and in enlarged view in FIG. 4 at 115. Referring to FIG. 4 the base metal of the saw band is shown at 116. The overcoating of carbide particles are shown typically at 118 partially embedded in the brazing metal 119 and projecting therefrom as shown to form sharp cutting edges.

Referring now to FIG. 9 in the modification of the sequence therein shown, the paste flux and brazing metal powders are separately applied to the strip, in contrast to the FIG. 7 sequence above described, wherein these constituents are admixed and applied to the strip stock on one application. Thus, in the FIG. 9 sequence, the arcuately blanked strip stock 10 is fed from the takeoff reel 50 thence through guide 51 and thence beneath the grooved coating roll 55 of the coating unit 52. In this case, however, the hopper 53 of the coating unit contains only the paste flux adhesive, such, for example, as the "Nicrobraz" flux above described, whereby the coating roll 55 applies only the paste flux to the strip to about the depth shown at 115 in FIG. 3. The strip passes thence under the discharge lip 56 of the vibratory feeder 57, the spiral trough 58 of which in this instance contains only the brazing metal powder, such as powders of the "LM Nicrobraz" alloy above described. Due to the action of vibratory feeder 57, the brazing metal powder is thus progressively propelled in a thin layer over the discharge lip 56 thereof, and falls thence as a curtain of the powdered metal transversely across the strip. A thin layer of the metal powder is thus disposed on the paste flux coated surfaces of the strip, as limited, however, to the extent of adherence of the metal powder to the paste flux coating. The strip passes thence under the inspection unit 59 and thence through a spraying unit 301, for spraying a fine mist of an aqueous solution of glue onto the coated strip surfaces, which solution is applied over a pipeline 302, with the strayed excess falling into a container 303. The strip is fed thence beneath the discharge lip 304 of a second spiral type, vibratory feeder 305, like that of 57, the spiral trough 306 of which contains a supply 307 of the powdered metal carbide particles, such as tungsten carbide particles, or equivalent diamond substitute particles, which are propelled in a thin layer over the discharge lip 304 of the vibrator and fall thence in a curtain of powders transversely across the strip edge, causing a thin layer of said particles to adhere as an overcoating to the adhesively coated surfaces of the strip. The strip is fed thence past an air blast unit 308 supplied with a compressed air blast over pipelines 309, 310, which blows the strip gullets free of brazing metal and carbide powders. From this point on, the processing of the FIG. 26 embodiment is identical with that of FIG. 6 above described.

Reverting to FIGS. 5 and 6, the continuous armoring coating shown at 320 of FIG. 5 may be applied to the band saw strip stock 10 in either of the ways above described except that, referring to FIGS. 7 and 9, no air blast is directed against the coated strip as at 70 FIG. 7 or 308, FIG. 9. However, in producing the spaced armoring coatings as at 321 of FIG. 6, a continuous coating is first applied as at 320, FIG. 5, which coating is then blown off at spaced intervals, as at 322, by the air blast nozzles 70, FIG. 7 or 308, FIG. 9, which is this instance are supplied with intermittent or pulsating jets of air.

As a further alternative method, the coating unit 52 may be used to apply an alcohol solution of shellac or other organic adhesive, such as described in my above identified patents. Separate vibratory, hopper feeders may be used to apply a powdered cobalt base brazing alloy such as one of the Stellite compositions and a powdered flux such as borax or these two powders may be admixed with a shellac binder, baked and reground to prevent segregation while permitting feeding with a single hopper. If applied by separate hoppers, it may be desirable to wet the surface with a mist of alcohol after the application of the first powder to bring a sufficient amount of the shellac to the surface to again render the surface adhesive. The carbide particles may be similarly applied following a rewetting with an alcohol mist, or a composite cake of brazing alloy, powdered flux and carbide particles may be formed with shellac and reground for application from a single vibratory hopper feeder to a surface rendered adhesive with paste flux or organic adhesive.

Referring now to FIGS. 11 and 12, FIG. 11 as shown by the legend thereon, is a view of a polished and etched section of one tooth of gulleted, armored 1/2-inch band saw strip stock, as taken longitudinally, thereof, and as produced in accordance with the FIG. 7 sequence wherein the adhesive flux and brazing metal powders are premixed prior to application to the band saw strip stock and wherein the coating thus applied is overcoated with carbide particles of 50/70 mesh. FIG. 12, as shown by the legend thereon, is a view of a polished and etched section as taken transversely through one tooth of gulleted, armored 1/2-inch band saw strip stock, as produced in accordance with the FIG. 9 sequence wherein the paste flux adhesive and brazing metal powders are separately applied by first applying the paste flux adhesive and then overcoating the same with the brazing metal powders and finally overcoating the brazing metal powder coating with a coating of carbide particles of 50/70 mesh.

In the drawings the scales shown thereon give actual cross-sectional dimensions of the armor coatings. Comparing the two modes of production, it will be seen that each results in armored coatings in which the abrasive or carbide particles are partially embedded in a relatively thin layer of brazing metal and project considerably beyond the same to form a series of sharp cutting edges. The etched sections establish that the carbide particles project beyond the matrix metal layer to an average extent of at least about one-third to one-half their average transverse dimensions. The FIG. 11 embodiment wherein the flux and brazing metal powders are premixed prior to application to the base stock, results in thinner armored coatings than the FIG. 12 embodiment wherein the flux and brazing metal powders are separately applied. From FIGS. 11 and 12 it will be seen that the layer of brazing metal varies from about 0.002 to 0.01 inch in thickness and the carbide particles project therebeyond to a height of about 0.005 to 0.01 inch above the adjacent matrix metal. Also the carbide particles project above the base metal from about 0.005 to 0.025 inch. Examination of the etched sections at higher magnifications than shown in the drawings, establishes that the brazing metal is metallurgically bonded to the carbide particles and therefore "wets" the same at the brazing temperature. It further establishes that the brazing metal is alloyed with the base metal over a narrow zone shown by the so designated wavy line separating the two in each of FIGS. 11 and 12.

Accurate measurements and computations have established that the thickness of the brazing metal layer is not noticeably affected by the grain or grit size of the carbide particles embedded.

The following is the actual overall height of plain and armored bands coated with three different grit sizes of carbide particles embedded in brazing metal coatings, and as measured on a Jones & Lamson Optical Comparator at 10X magnification.

No grit 70/100 grit 50/70 grit 40/50 grit __________________________________________________________________________ Actual Height" 0.375" 0.385" 0.394"" __________________________________________________________________________

The following is the calculated height of the same three bands without the brazing alloy.

70/100 grit 50/70 grit 40/50 grit __________________________________________________________________________ Height of Band 0.375" 0.375" 0.375" Grit Size +0.008" +0.012" +0.017" __________________________________________________________________________ Calculated Height " 0.383" 0.387" 0.392" __________________________________________________________________________

The following is the indicated thickness of the braze layer based on the difference between the actual height as coated and the calculated height without brazing alloy.

70/100 grit 50/70 grit 40/50 grit __________________________________________________________________________ Actual Height 0.385" 0.389" 0.394" Calculated Height -0.383" -0.387" -0.392" __________________________________________________________________________ Indicated thickness 0.002" 0.002" 0.002" __________________________________________________________________________

In order to assure that the carbide particles will project beyond the matrix layer to form a series of sharp cutting or abrading edges, the carbide particles are of a grain size substantially exceeding the thickness of the matrix coating layer. Preferably, the thickness of the matrix coating layer does not exceed about one-half to two-thirds the average transverse dimensions of the abrasive particles, whereby said abrasive particles project beyond said coating layer to an average extent of about one-third to one-half their average transverse dimensions. The thickness of the matrix coating is controlled to some extent by the grain size of the brazing metal powders, which tend in the FIG. 9 process of application, to adhere in a single layer to the flux coated strip, with the excess sloughing off under gravity action. Hence, the carbide or other diamond substitute abrasive particles should substantially exceed in grain size, the dimensions of the brazing metal powders.

A suitable grain size for the brazing metal powders is about 150 mesh, i.e. 0.004 inch, or under. For the carbide or equivalent diamond substitute particles, a suitable size range is about 50-100 mesh, i.e., 0.0117-0.0059 inch, referring to mesh sizes as determined by the ASTM specification E11 of 1958. Preferred ranges for the diamond substitute particles are about -50/+70 mesh and -70/+100 mesh; 70 mesh is 0.0083 inch. In round numbers, the grain size of the matrix metal particles is about 0.004 inch and under and that for the abrasive particles about 0.006-0.012 inch and may range up to about 0.025 inch.

Tests have also indicated that the magnetic field set up by the induction heating coil 86, FIGS. 7 and 8, tends to attract the tungsten carbide particles, and hold them out from the matrix surface in the manner illustrated in FIGS. 11 and 12.

The brazing or matrix metal is preferably a hard, refractory metal alloy, of noneutectic character, having a substantial softening or plastic temperature range between liquidus and solidus points, below the melting point of the tool base metal and within the temperature range of about 1500.degree.-2400.degree. F. As above stated, suitable such alloys are of the cobalt-base or nickel-base types, such as the nickel-base alloys containing about 5%-15% Cr, 1%-3.5% B, 2%-5% Fe, without and with silicon up to about 5 to 10 percent, and carbon up to about 0.25 percent, having brazing temperatures within the range of about 1700.degree.-2200.degree. F. The cobalt-base "Stellite" alloys are also suitable, containing about 40%-80% Co, 20%-35% Cr, 0%-3% Si and 0.75%-2.5% C.

Although the invention has been particularly described as applied to the production of armored band saws and band saw stock, the same principles of production above described are similarly applicable to the production of other types of armored tools, such as cylindrical rod saws, hack saw blades, disc cutters, files, etc. As applied to each a thin coating of the paste flex adhesive alone or admixed with the matrix metal powder is first applied to the base metal of the tool over the area to be armored, and thereupon an overcoating of the abrasive metal particles applied. The armored portion, or alternatively the entire tool if the tool is to be heat treated, is thereupon rapidly heated to temperature sufficiently high to fuse the matrix metal powders into a thin coating layer and to alloy the same with the base metal and also partially to embed the abrasive particles therein. Thereupon the armored portion or the entire tool, as the case may be, is cooled to ambient temperature, permanently to bond the matrix metal layer to the base metal and permanently to embed the abrasive particles therein to the extent of their embedment in the matrix metal layer, and also to harden the tool base metal if it is to be heat treated.

Preferably, high frequency electrical induction heating is employed. Where only the armored portion requires heating, the frequency of induction heating is preferably just sufficiently high to penetrate into the base metal only to the required extent to fuse the matrix metal particles into a thin coating layer and to fusion bond the matrix metal layer to the base metal, and such heating is applied only for the duration required to accomplish the above, whereupon the current energization is abruptly terminated in order that the cool base metal will rapidly cool and solidify the matrix metal layer. Alternatively, if the base metal is to be concurrently heat treated, as in the case of a ferritic steel or alloy steel base, the frequency of induction heating and the arrangement of the induction heating means is made such that the entire body of the armored tool is heated above the fusion temperature of the matrix metal and thereupon cooled with sufficient rapidity to harden the tool base metal while solidifying the matrix metal.

With respect to small tools to be armored, such as rod saws, hack saws, files and the like, the armoring is best applied by first spraying or brushing onto the base metal, a thin coating of the paste flux adhesive. The matrix metal powders are next applied by feeding the so coated tool beneath a falling curtain of the matrix metal powders while rotating the tool about its axis if it is desired to coat all surface portions thereof, a glue spray is then applied, following which the final coating of abrasive particles is applied by the same technique as the matrix powders.

Where only a relatively flat surface of a tool base is to be armored, the paste flux adhesive is preferably first applied by spraying or brushing. The tool is then fed beneath a falling curtain of the matrix metal powders with the surface being armored, disposed at a sufficient angle of inclination to the horizontal that the excess of metal powders will fall off of the coated surface, leaving only a thin layer adhering thereto. A fine spray of an aqueous glue solution is next applied to the so coated surface and the final overcoating of abrasive particles applied by the same procedure as the matrix metal particles.

Claims

What is claimed is:

1. A metal cutting tool having a hard wearing, ductile and adherent, abrasive armor coating produced in situ from powdered brazing metal particles and abrasive particles of hard, high melting material, said tool comprising a structural base member consisting of a ferrous base metal of high strength and fracture resistance selected from the group consisting of heat treatable steels and alloy steels, at least a portion of the surface of which is covered with a relatively thin, flexible, ductile, and adherent coating layer of substantially uniform thickness, of said brazing metal powders fusion bonded to each other and to said base metal and into a substantially solid layer, said brazing metal being alloyed with said base metal throughout an interlayer of said alloy between said base metal and coating layer, said coating layer of said fusion bonded brazing metal powders having embedded therein and projecting from the surface thereof throughout said layer, a multiplicity of abrasive particles, of an average grain size exceeding the average thickness of said brazing metal layer, said abrasive particles forming sharp cutting edges and being composed of hard, high melting point, refractory metal carbides, said abrasive particles being metallurgically bonded to said brazing metal coating, and said brazing metal being selected from the group consisting of nickel-base and cobalt-base alloys containing about 40%-80% of said base metal and the balance principally elements selected from the group consisting of Cr, B, Fe, Si, W and Mo, said armor coating having an average maximum thickness of about 0.05 inch, and said brazing metal layer having an average thickness of about one-half to two-thirds the average transverse dimensions of said abrasive particles whereby said particles project beyond said brazing metal layer to an average extent of about one-half to two-thirds of their average transverse dimensions.

2. A tool according to claim 1 wherein the grain size of said matrix metal powders is 0.004 inch and under the grain size of said abrasive particles is about 0.006 to 0.025 inch.

3. An armored saw blade comprising a flexible strip of a ferrous base metal selected from the group consisting of heat treatable steels and alloy steels, said strip having adherently bonded to at least one longitudinal edge and contiguous surface portions thereof, a hard wearing, ductile, and abrasive armor coating, produced in situ from powdered brazing metal particles and abrasive particles of hard, high melting material, such coating comprising a relatively thin, flexible, ductile, and adherent layer of substantially uniform thickness of said brazing metal powders fusion bonded to each other and to said base metal and into a substantially solid layer, said brazing metal being alloyed with said base metal throughout an interlayer of said alloy between said base metal and coating layer, said coating layer of said fusion bonded brazing metal powders having embedded therein and projecting from the surface thereof throughout said layer, a multiplicity of abrasive particles, said abrasive particles forming sharp cutting edges and being composed of hard, high melting point, refractory metal carbides, said abrasive particles being metallurgically bonded to said brazing metal coating, and said brazing metal being selected from the group consisting of nickel-base and cobalt-base alloys containing about 40%-80% of said base metal and the balance principally elements selected from the group consisting of Cr, B, Fe, Si, W and Mo, said armor coating having an average maximum thickness of about 0.05 inch, and said brazing metal layer having an average thickness of about one-half to two-thirds the average transverse dimensions of said abrasive particles whereby said particles project beyond said brazing metal layer to an average extent of about one-half to two-thirds of their average transverse dimensions.

4. An armored saw blade according to claim 3 wherein the grain size of said matrix metal powders does not exceed about 0.004 inch and the grain size of said abrasive particles is about 0.005 to 0.025 inch.

5. An armored tool according to claim 1 wherein said layer of armor coating has a maximum thickness of about 0.025 inch.

6. An armored saw blade according to claim 3 wherein said layer of armor coating has a maximum thickness of about 0.025 inch.

7. An armored tool according to claim 1 wherein said structural base is of rod shaped configuration having said armor coating extending over a peripheral surface portion thereof.

8. An armored tool according to claim 1 wherein said structural base is of cylindrical configuration having said armor coating extending over a cylindrical surface portion thereof.

9. An armored tool according to claim 1 wherein said structural base has surface portions disposed at an angle of 90.degree. and under to one another and wherein said armor coating is applied to both said surface portions.

10. A tool according to claim 1 wherein said ferrous base metal has a microstructure of tempered martensite.

11. A tool according to claim 1, wherein said matrix metal layer has a thickness on the order of about 0.002 to 0.01 inch.

12. A tool according to claim 11, wherein said abrasive particles project beyond the adjacent matrix metal layer to an average extent of about 0.005 to 0.01 inch.

13. A tool according to claim 1, wherein said abrasive particles project beyond said base metal to the extent of about 0.01 to 0.025 inch.

14. An armored tool according to claim 1, wherein said matrix metal layer has a thickness on the order of 0.002 to 0.01 inch and wherein said abrasive particles project beyond the matrix metal adjacent thereto to an average extent of about 0.005 to 0.01 inch.

15. A saw blade according to claim 3, wherein the armored edge thereof is armored at spaced intervals to provide spaced armored teeth therealong.

16. A saw blade according to claim 3, wherein the armored edge is gulleted at spaced intervals.

17. A band saw blade according to claim 3, wherein said abrasive particles have a grain size of about 0.005 to 0.025 inch.

18. A saw blade according to claim 3, wherein said matrix metal layer has a thickness on the order of 0.002 to 0.01 inch and wherein said abrasive particles project beyond the matrix metal adjacent thereto to an average extent of about 0.005 to 0.01 inch.