Patent Publication Number: US-3874126-A

Title: Flexible hand held abrading tool

Description:
United States Patent [191 Catlin et al.  
 [ *Apr. 1,1975  
 [ FLEXIBLE HAND HELD ABRADING TOOL [73] Assignee: Remington Arms Company, Inc.,  
 Bridgeport, Conn.  
 [*1 Notice: The portion of the term of this patent subsequent to Nov. 27, 1990 has been disclaimed.  
 [22] Filed: Nov. 23, I973 [21] Appl. No.: 418,498  
 Related U.S. Application Data [63] Continuation-impart of Ser. No, 189,786, Oct. 15, 1971, Pat. No. 3,774,355, which is a continuation of Ser. No. 803,561, March 3, 1969, abandoned.  
 3,774,355 11/1973 Dawson ct al. 51/395 FOREIGN PATENTS OR APPLICATIONS 151,172 8/1955 Sweden 29/80 Primary Examiner-Othell M. Simpson Attorney, Agent, or Firm-,Iohn H. Lewis, Jr.; Nicholas Skovran [57] ABSTRACT A flexible base metal strip has a strong, tough and adherent abrasive armoring coating produced thereon in situ from abrasive particles of hard, high melting material selected from the group consisting of metal carbides, borides, nitrides, silicides and combinations thereof, and particles of a matrix metal, said matrix metal particles being in said armoring coating and fusion bonded to each other, to the base metal strip and to the abrasive particles to anchor and partially embed the abrasive particles therein with the particles projecting therefrom in the form of a seris of sharp cutting edges. Attachment means are provided at each end of the coated strip for attachment of the strip to a suitable frame such as a standard hack saw frame. When properly secured and tensioned in such a frame, a small, flexible hand held abrading tool is formed which is suitable for hand working materials having a high hardness so as to be unsuitable to be worked by prior art abrading tools.  
 8 Claims, 8 Drawing Figures ATENTEU 3.874126 sum 1 0f 2 FLEXIBLE HAND HELD ABRADING TOOL This is a continuation-in-part of our copending application Ser. No. 189,786, filed Oct. 15. I971 US. Pat. No. 3.774.355, which is in turn a continuation of our application Ser. No. 803,561,, filed Mar. 3. 196 now abandoned.  
  This invention pertains to armored abrading tools and the production thereof. comprising a structural base member composed of a base metal, such as steel, alloy steel or other metal or alloy characterized inherently by high strength. hardness and toughness or heat treatable to such, said structural base member having a hard wearing, ductile and abrasive surface coating produced in situ from powdered metal particles of a hard, refractory brazing or matrix metal or metal alloy, such as a nickel-base or cobalt-base alloy, and abrasive particles of a hard, high melting material. such as metal carbides, borides, nitrides, silicides or equivalent diamond substitute materials, said matrix metal particles being fusion bonded to each other, to said abrasive particles and to said base metal, and said abrasive particles being partially embedded oranchored in said. ma trix metal and projecting therefrom to provide a multiplicity of sharp cutting edges.  
 The invention provides a new tool of the above type and methods of producing the same. These tools have a new field of utility, namely, a flexible, hand held file band tool having surface portions armored as above, the tool being particularly adapted for hand filing and surface abrading of such refractory materials and metals as glass, fiber glass, ceramics, cement asbestos, tiles, high temperature alloys, such as chrome-nickel alloys, titanium and titanium base alloys and the like.  
 Small hand held filing or abrading tools have long been commercially available. The most common tool of this type is characterized by the conventional metal file which generally comprises a relatively thick piece of suitably shaped steel with its surfaces grooved in a pattern to produce raised cutting points for effecting the abrading or filing action. Similar tools have recently been manufactured by securing minute cutting elements to the steel bar by a copper braze instead of scoring the surface. Such tools are disclosed in US. Pat. No. 2,906,612, issued to Myron L. Anthony et al. on Sept. 29, 1959. Prior art hand held abrading devices may be used only for surface grinding of relatively soft materials, such as wood or other cellulosic products, unreinforced plastics, relatively soft metals such as aluminum, brass, mild steel and the like. Additionally,  
 they are inherently rigid, rendering. them much less readily adaptable to work in the contouring of surfaces.  
  in accordance with this invention, a metallic strip of suitable length is mounted at its end portions to an appropriate frame, such as a hack saw frame. Tension of the file band may thus be adjusted to provide any desired degree of flexibility for abrading work.  
  The armoring coating of the tile band is preferably so applied that the abrading grit particles are anchored in weldments of the matrix metal which are individual thereto and which may be spaced apart as desired for enhancing the flexibility and fatigue life of the file band. A preferred method for applying the armoring coating to the substrate band stock consists first in precoating the abrasive particles with a fluxing agent, such as borax, and with the brazing metal powders, the brazing metal powders being advantageously of much smaller particle size than the abrasive particles A thin adhesive coating is next applied to the surface portion or portions of the substrate to be armored, preferably vby a printing operation, employing printer&#39;s ink or other adhesives as the coating materials. Before this coating becomes dry, the so-printed surface of the substrate is passed beneath a falling curtain of the precoated abrasive particles at a rate of application adjusted to provide a preselected average spacing between the particlesfalling upon and adhering to the printed surface portions. non-adhering particles being removed thence by such means as an air blast or vacuum. In this way, the precoated abrasive particles may be applied to the printed surface portions in as dense or sparse a distribution as desired. depending on the character of the substrate being armored. For armoring thefile band stock of this invention, a relatively sparse distribution is desired as has been previously mentioned.  
  The thus armored tool or substrate band stock is then allowed to travel for some distance, or through a drying unit, until the adhesive coating is dryed and thence is passed next through an induction heating coil energized from a high frequency alternating current source for rapidly heating the tool or file band stock to temperatures sufficiently high to melt the brazing metal powders coating each grit particle whereby the molten matrix metal flows about the base of each grit particle and onto the base metal substrate and by capillary action coalesces into a cup-like molten pool partially immersing the grit particle therein. with said particle projecting therefrom.  
  The file band stock is next subjected to rapid cooling in an inert atmosphere or fluid until cooled to temperatures such that the molten cup of brazing metal surrounding the base of each grit particle solidifies and thus permanently anchors the grit base therein in bonded relation to the grit particle and to the substrate base metal. This heating and cooling may also be such as to austenitize and thence transform to martensite the micro-structure of this steel substrate which is thereafter subjected to a tempering treatment.  
  The file band is then punched and cut into suitable lengths for mounting on the desired frame.  
  Numerous advantages result from individually precoating the grit particles, each with its own supply of brazing metal and fluxing agent. The amount of brazing metal for each grit particle can be accurately controlled to partially embed the same only to an extent desired and to assure that each grit particle will project therefrom to provide a sharp, exposed cutting edge. The brazing metal for each grit particle bonds only to the grit particle coated thereby and also only to a relatively small area of the substrate base metal. This is a particular advantage in armoring applications requiring a flexible substrate with optimum fatigue properties as in the file band of this invention. This is further facilitated by the fact that the precoated grit particles may be applied to the substrate with a controlled average spacing between the particles such that the bonded particles may be spaced apart sufficiently as not to impair the flexibility and fatigue life of the substrate band stock. The precoating also facilitates application of the armoring coating in spaced patterns if such is desired for a particular application. The precoating of the grit particles is particularly efficacious where such particles are relatively large. Small grit particles are, however, more difficult to precoat and, with respect to such, a  
 satisfactory file band can be produced without preeoating.  
  The advantages resulting from precoating the grit particles are less readily obtainable with other methods for applying an armoring coating, such as that wherein there is first applied to the substrate a thin layer of paste flux, then a layer of brazing metal powders and finally an overlayer of the carbide grit particles, or that wherein a paste flux and the brazing metal powders are premixed and applied as an initial coating on the substrate base metal and an overcoating of the grit particles superimposed thereon. Such techniques tend to produce a layer of brazing metal which covers the substrate in varying thickness throughout the armored area, depending on the amount of brazing metal initially applied and wherein it is difficult to control the extent of embedment of the grit particles. Also, where flexible substrate is required, as in the case of the tile band, a continuous layer of brazing metal reduces the flexibility and fatigue life because the physical properties of the brazing metal may not be compatible with those of the substrate. Also, the procedure for applying the flux, brazing metal and grit particles in two or three separate operations results in increased labor costs, while the excess braze metal not actually employed for anchoring the grit particles increases the material cost as compared to the grit precoating technique of this invention.  
  Having thus described the invention in general terms, reference will now be had for a more detailed description to the accompanying drawings, wherein:  
  FIG. 1 is a perspective view of a hand held abrading tool constructed by mounting a file band of this invention in a suitable frame;  
  FIG. 2 is a plan view of a fragmentary portion of steel or alloy steel flexible strip stock which is continuously armored on one surface longitudinally thereof in accordance with the preferred embodiment ofthis invention;  
  FIG. 3 is an enlarged sectional view of FIG. 2 taken along the line 33 thereof;  
  FIG. 4 is a plan view similar to FIG. 2 wherein the base stock is armored in spaced-rectangular areas in accordance with another embodiment of this invention;  
  FIG. 5 is a diagrammatic showing in flow sheet form illustrative of a method and apparatus for producing the armored grinding stock of this invention;  
  FIG. 6 is an enlarged view in elevation of a tungsten carbide particle coated with a flux such as borax and matrix metal particles;  
  FIG. 7 is a view in elevation of the coated carbide particle of FIG. 6 after fusion bonding to the base metal strip; and  
  FIG. 8 is a plan view of base metal strip as punched prior to coating in accordance with one embodiment of this invention.  
  Referring now to the drawings, FlG. 1 illustrates an abrading tool I] in accordance with this invention having a suitable frame 12 such as, in this case, a hack saw frame which is provided with a pair of opposed mounting brackets 14 which are adapted for securing thereto a file band 15 of this invention. In the preferred embodiment, the file band I5 is provided with a hole 15a positioned at each end portion thereof to accommodate standard mounting means such as those generally used for the securing of a hack saw blade in the frame 12. lfdesired, any other type of attachment means may be provided at or secured to the end portions of the file band 15. It should be noted that the mounting brackets 14 are preferably rotated in the frame 12 to the position shown in FIG. I, so that one side of the file band 15 will be in working position, facing outwardly from the frame, as distinguished from a saw wherein an edge of the blade is so positioned.  
  The file band 15 (FIG. 2) preferably comprises a flexible strip of base metal, such as a steel or alloy steel strip 16 which is provided with an armoring coating 17 extending continuously in the longitudinal direction. End portions, however, may remain uncoated in a manner and for reasons to be further described in detail. Referring to FIG. 3, the armoring coating 17 comprises a myriad of tungsten carbide or other diamond substitute abrasive particles 19 each of said particles being partially embedded in and bonded to a substantially meniscus shaped anchoring layer 20 of a matrix metal, such as a high melting, refractory, nickel-base or cobalt-base alloy, which anchoring layer of matrix metal is in turn bonded to and alloyed with the base metal 16.  
  FIG. 4 illustrates how the armoring coating may be, if desired, applied to the base stock 16 in longitudinally spaced rectangular areas 21. Such a configuration may be preferable in certain applications to the continuous coating illustrated in FIG. 2 and may be accomplished in a manner set forth herein and described in greater detail in our above-mentioned Patent application Ser. No. I89,786.  
  Referring to FIG. 5, the following is a suitable sequence of manufacturing operation for the production of armored file bands in accordance with this invention. A coil of for example AlSl 6150 alloy steel strip 0.025 in. thick by l in. wide is mounted on an unwind wheel 30. By way of example, this coil may contain approximately l,()()() ft. of strip. A frictional drag mechanism of conventional construction (not shown) restrains the unwind wheel from turning prematurely in response to the spring energy contained in the wound up steel strip. The strip passes thence between a pair of rubber covered wheels 31, 32, which frictionally engage the strip in the upper roll of which is driven in order to move it forward against the resistance of the frictional drag mechanism. Thus, the upper roll 31 is driven by a variable speed electric motor 33 and geared head speed reducer 34 while the lower roll 32 functions as an idling back up roll.  
  The strip then passes between a pair of rolls 35, 36 of an industrial roll type printing machine 37. This machine prints a desired pattern as shown, for example, in either FIG. 2 or FIG. 4, on the top side of the strip using a viscous coating medium, as hereinafter described. The printing machine is driven via a chain drive 38 by the same motor and speed reducer 33, 34 that powers the drive wheel 3] so that the printing speed and strip speed are synchronized.  
  While the printed pattern is still wet, the strip passes under a vibratory feed hopper 39, electromagnetically actuated in conventional fashion. This feed hopper covers the entire strip with a thin layer, as&#39;at 40, of tungsten carbide or other abrasive particles which have been preeoated with a suitable flux such as borax and brazing metal powders, as described below. By controlling the relationship between the operating rate of the feed hopper 39 and the rate of travel of the strip 16, the particle density and distribution of the grit particles can be well controlled to leave any desired average spacing between adjacent abrasive particles.  
  This strip covered with the thus precoated tungsten carbide particles travels next to the air blower 4]. The blower removes the abrasive particles from all areas of the band other than those which stick to the printed pattern. If desired. a vacuum may be used so that grit particles may be readily collected. Depending on such factors as strip speed or spacing between the feed hopper and the air blower, it may be necessary in some instances to include a dryer between the hopper and the air blower. Alternatively such a dryer, for example. as an infrared ray drying unit 42 may be disposed following passage of the strip past the air blower 41.  
  The strip with the abrasively coated pattern passes next through a high frequency induction coil 43 encrgized from a high frequency current source 44. as for example of about 5.2 megacycles per second. This coil heats the strip to approximately l,9()() F. to austenitize the steel of the substrate strip and to braze the tungsten carbide grit to the strip by causing the steel band to be inductively heated. this heat then by induction and ra diation causing the matrix metal particles coating each carbide particle to melt and flow to and about the base of each particle in the manner shown in FIG. 3, as is more fully explained hereinafter with reference to FIGS. 6 and 7.  
  The strip passes next through an atmosphere chamber 45 and thence through a slotted, water cooled chill block 46 extending therefrom. As the strip passes out of the magnetic field of the induction coil and into the atmosphere chamber, the matrix metal cools and solidifies thereby permanently to anchor the grit particles therein and to bond the matrix metal to the grit particles and to the base metal substrate. The chill block further cools the heated strip quickly to a temperature below that of martensitic transformation of the steel substrate, thus to quench harden the same. The chill block is not required if the strip stock is made of a steel which hardens on air cooling from the austenitic state. If desired. the atmosphere chamber 45 and chill block 46 may be replaced by a fluid quenching system.  
  The atmosphere chamber is supplied with a circulating flow of nitrogen gas to minimize scaling or oxidation of the steel strip substrate until it is cooled below scaling or oxidizing temperature. The strip passes out of the chill block 46 through a slot 47. thence over an idler support roller 48 and through a tempering oven 49, wherein the strip is tempered at a suitable temperature which may be. for example, about 950 F. The strip passes next past a counter 50, which continuously records the number of blade segments, total length in feet or otherwise of the strip processed. The strip is next engaged by a take-up reel 51 driven by a motor 52. The motor may be controlled by a friction clutch or. as illustrated, be structured so that the take-up reel exerts only an intermittent pull on the band. It is,intermittently activated by a loaded tension arm 52:: resting on the band stock It), and applies tension when needed for coiling but avoids excessive pull which could stretch the file band at the point where it is red hot and a weakly plastic in the induction heating coil.  
  Details of construction of particular structures referred to with reference to FIG. 5, such as the printing machine 37, atmosphere chamber 45, and chill block 46. are described in detail in our above-mentioned U.S. Pat. application Ser. No. I89,786 which is expressly incorporated herein for that purpose.  
  The band stock 16 on the take-up reel 51 may be later unwound and cut into sections of suitable length for use as a file band 15 and the holes I511 may also be punched at that time. As an alternative, the take-up reel 51 may be omitted and in its place. suitable cutting and punching means may be provided to cut and punch file bands immediately after the band stock has been coated as described above.  
  Asa further alternative, the steel strip 16 may be prepunched at spaced intervals in the manner shown in FIG. 8 prior to coating the strip. In this way the holes 15! and a pair of cutouts 54 are formed prior to coating so that. after the coating process has been completed. only a small bridging portion 55 between adjacent file band segments need be severed to produce a finished product.  
  Regardless of the manner adapted for cutting the individual file hands. it is preferable that the portions which must be cut or punched remain uncoated as the cutting of abrasive coated band stock would cause a high degree of wear and tear and a resultingly short life for the tooling utilized. Referring to FIG. 5. sufficient uncoated portions 56 may be provided at properly spaced intervals along the coated steel strip by proper patterning of the roll 35 of the printing machine 47. This can be accomplished whether the tile band 15 is provided with a continuous armoring coating 17 as shown in FIG. 2 or with spaced areas of abrasive coat ing 21 as shown in FIG. 4.  
  The coating liquid may be conventional printers ink minus the coloring matter, compositions for which are described in standard texts, such as Chemical and Metallurgical Engineering 47.544 I940), Kingzetts &#34;Chemical Encyclopaedia. I940 Ed.. page 520, and Shreves &#34;Chemical Process Industries.&#34; I945 Ed., page 509. As stated in these publications. printing ink consists essentially of a suspension of pigments. such as paint pigments, in a drying oil. such as linseed oil. or petroleum oils. to which may be added various natural or synthetic resins, waxes, gums, water insoluble soaps, driers. antioxidants, bitumen, asphalt. or stearin pitch, etc.  
  In addition to the conventional printing inks, applicants have found the following adhesive printing admixtures to be suitable for purposes of this invention.  
 EXAMPLE I Admix 7 /2 oz. Nicrobraf Flux. 8t) milliliters Corn Syrup, l0 milliliters Lube Well D-IOO. water soluble oil used as an emulsifier and to promote wetting, 2O milliliters ethylene glycol to slow up drying action, and 25 milliliters water.  
 EXAMPLE II Admix 7 oz. Nicrobraz Flux with milliliters glycerin.  
  The flux is used in the above examples as the solid in suspension to prevent squeegee action during printing which otherwise causes the adhesive to push out around the print pattern thus destroying the precise pattern. The addition of extra solids makes room between the printer and the surface being printed so that an adequate thickness of adhesive material may be applied. Flux is compatible with the process where many other types of solids for the purpose leave harmful inclusions in the finished product. The Nicrobraz Flux referred to in the examples is a boride-fluoride flux put out under that designation by the Wall Colmonoy Company, Detroit, Mich.  
  As above stated, the preferred material applied to the steel or alloy steel base metal band stock for purposes of armoring comprises tungsten carbide particles precoated with a suitable flux, such as borax, and also with the brazing metal powders. The materials employed for the brazing metal are preferably powders of hard. refractory alloys, such as nickel-base or cobalt-base alloys, capable of providing a matrix metal which wets the surfaces of and bonds to the tungsten carbide or other diamond substitute particles and also which fusion bonds to and alloys with the steel or alloy steel base metal band stock. Suitable such brazing alloys are Stcllitef a cobalt-chromium tungsten alloy of well known composition; also that sold by the Wall Colomony Corporation, as LM Nicrobraz comprising an alloy consisting of 13.571 Cr, 3.5% B, 4.57! Si, 2.5% Fe and the balance nickel. A suitable particle size for the brazing metal powders is 300 mesh. A suitable particle size for the carbide particles is that which passes through a 30 mesh screen but is held on a 40 mesh screen. Thus, the particle size of the carbide particles is considerably greater than for the brazing metal powders.  
  The following is a suitable procedure for precoating the tungsten carbide or other abrasive grit particles with a tluxing agent and with the matrix metal powders, although the proportions given below may be varied within fairly wide limits with satisfactory results. Assuming tungsten carbide grit of relatively coarse grit size, for example 3040 mesh (U.S. standard, i.e., about 0.0l650.0232 inch), is required, the procedure is to admix in a container approximately 1 1b. tungsten carbide grits, l .4 oz. Oxweld Brazo Flux (borax), 4 oz. 300 (0.0019 inch) mesh braze alloy ranules and 50 ml. water. Where relatively fine (70-100 mesh) 0.008270.00587 inch tungsten carbide grits are required, an admixture in approximately the following proportions is suitable, 1 lb. tungsten carbide grits, 1.4 oz. Oxweld Brazo Flux (borax), 4 oz. 300 mesh braze alloy granules and 65 ml. water. In either case, the water is boiled off until a thick slurry is formed while stirring continuously to keep the solids from sticking to the bottom and sides of the container. The slurry is then spread on a flat surface and trowelled to a thickness of 3/16 inch, which is sliced into small squares and allowed to dry to a solid cake. The dry cake is crushed and screened through a sieve of a mesh adapted to pass single tungsten carbide grits coated with brazing alloy, but not to pass a multiplicity of such grits stuck together. The larger crushed dry cake particles retained on the sieve are recrushed and rescreened. This procedure is repeated until all of the dry cake particles are crushed adequately to pass through the sieve. Any excessive braze alloy granules which do not adhere to the .tungsten carbide grits are screened out on a sieve size substantially smaller than the coated tungsten carbide grits. The adherence of the brazing alloy granules to the tungsten carbide grits may be improved by gently hand mixing shellac with the small dried cake squares prior to crushing. For this purpose. approximately 12 milliliters of shellac may suitably be used for each pound of coarse (30-40 mesh) tungsten carbide grits in the original mixture, or 15 ml. of shellac for each pound of fine (70-100 mesh) tungsten carbide grits in the original mixture. After the shellac dries, the remaining procedure is the same as above described.  
  A so-eoated carbide particle is shown in enlarged view in FIG. 6, wherein the grit particle is shown at 60, the flux coating at 61 and the brazing or matrix metal particles at 62. As the soeoated carbide particle passes through the high frequenev induction coil, the matrix metal powders become molten and under the fluxing action of the borax and How to and about the base of the carbide particle and against the base metal in the manner illustrated in FIG. 7, wherein the carbide particle is shown at 60, the fused brazing metal at 64 and the base metal at 65. On subsequent cooling, the matrix metal solidifies and alloys with the base metal and also bonds to the carbide particle. thereby permanently anchoring the base of the carbide particle in the matrix metal, with the carbide particle projecting therefrom to provide exposed sharp cutting or abrading edges. as at 66.  
  The use of precoated grit particles provides securement of the particles to the substrate by individual weldments as shown in FIG. 3. The particles 19 are spaced with uncoated metal generally exposed between adjacent regions of the anchoring layer 20. It will be readily apparent that, with such an arrangement, the flexibility of tile band 15 is substantially the same as that of the uncoated strip 16.  
  Referring again to FIG. 1, to assemble an abrading tool 11 in accordance with this invention with a suitable tile band 15, the frame 12 is selected of an appropriate size to accommodate the file band or, if adjustable as is the hack saw frame illustrated, is adjusted to an appropriate size to accommodate the tile band. With the mounting brackets 14 oriented in the proper direction, the file band is secured to the mounting brackets and, through the use of a suitable tensioning means 67, such as the wing nut illustrated, the file band is tightened to a tension suitable for the job to be accomplished.  
  In accordance with this invention, the tile band 15 is not supported between its end portions so that it maintains a high degree of flexibility. This is of great advantage in working many of the materials suitable for the abrading tool 11. When filing metals and other hard materials, portions of the material to be filed may be too hard to be removed by the action of a single abrasive particle 19 (FIG. 3). Were the file band 15 rigid, in the manner of prior art tiles, the abrasive particles 19 could become rigidly interlocked with portions of the material to be filed thus causing the abrading tool to split or skip and producing an excessive amount of wear to the tool. With the flexible file band of this invention, if an abrasive particle 19 is unable to move a portion of material which it abuts, it will be moved, with the file band, away from and over the material so that the abrading tool 11 continues to move smoothly and other abrasive particles 19 can engage the material in similar manners until it has been successfully removed.  
  The flexibility of the file band 15, particularly when coupled with adjustability provided by tensioning means 67, greatly eases the task of shaping materials such as fiber glass and ceramics in that the file band 15 is deformable into a somewhat curved shape to accommodate the curvature of the item being shaped for greater ease and smoothness of filing. Further, the spacings between adjacent abrasive particles coupled with the flexible nature of the file band enables the tool to be virtually self-cleaning. This prevents the clogging which has been known to generally disable prior art abrading devices.  
 We claim:  
  I. An abrading tool comprising a flexible strip of hardenable and temperable steel having end portions and having. over at least a surface portion thereof. a strong, tough and adherent abrasive armoring coating produced in situ from abrasive particles of hard. high melting point, refractory mctal-carbides precoated with particles of a high melting and tough brazing metal selected from the group consisting of cobalt-base and nickel-base alloys and combinations thereof. said brazing metal particles being fusion bonded to each other and to said steel strip and alloyed therewith into weld ments individual to and partially embedding said abrasive particles. with said abrasive particles projecting from said weldments to form sharp cutting edges. and bolder means for engaging the end portions of said strip and holding said strip under tension.  
  2. The abrading tool of claim I wherein said strip is unsupported between said end portions.  
  3. The abrading tool of claim 2 wherein said holder means includes a spaced pair of opposed mounting brackets for engaging the end portions of said strip and tensioning means at one of said mounting brackets for controlling the tension of said strip.  
  4. The abrading tool of claim 2 wherein said holder means is a hack saw frame.  
  5. A flexible file band for an abrading tool. said file band comprising a flexible strip of hardenable and tentperable steel having over at least a surface portion thereof. a strong. tough and adherent abrasive armoring coating produced in situ from abrasive particles of hard. high melting point. refractory metal-carbides. prccoated with particles of a high melting and tough brazing metal selected from the group consisting of cobalt-base and nickel-base alloys and combinations thereof. said brazing metal particles being fusion bonded to each other and to said steel strip and alloyed therewith into weldments individual to and partially embedding said abrasive particles with said abrasive particles projecting from said weldments to form sharp cutting edges, said strip having end portions engageable by a suitable frame for freely supporting said band under tension.  
  6. The file band of claim 5 wherein said abrasive coating is continuous.  
  7. The file band of claim 5 wherein said abrasive coating comprises a plurality of spaced coated areas.  
  8. The file band of claim 5 wherein the end portions of said strip are uneoated.