Abstract:
A method of manufacturing a blade of a cutting tool, the method including depositing a mixture including a hard material onto an edge of a movable steel strip to form a hard material coated steel strip; grinding the edge of the hard material coated steel strip; and subsequently to grinding, forming individual blades from the hard material coated steel strip.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority and benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/074,875, entitled “Cutting Tool Edge and Method”, filed on Jun. 23, 2008, the contents of which are incorporated herein in their entirety by reference. 
     
    
     FIELD 
       [0002]    The invention relates to a method of manufacturing a blade of a cutting tool. 
       BACKGROUND 
       [0003]    The use of tungsten carbide as cutting material is well known in the art. Tungsten carbide is used extensively in various cutting, drilling, milling and other abrasive operations due to its high abrasion resistant properties. Conventional cutting tools like power saw blades have tungsten carbide inserts brazed onto the blade teeth. This makes the actual cutting surface extremely hard and durable. However, brazing is not a suitable process for mounting tungsten carbide inserts on many cutting tools, such as utility knife blades, chisels and plane irons. 
       SUMMARY 
       [0004]    One aspect of the invention involves a method of manufacturing a blade having a hard coating deposited on its edge. The method includes depositing a hard material, e.g. tungsten carbide, onto the edge of a cutting tool and then sharpening the edge such that the surface is entirely made of the hard material, e.g. tungsten carbide, after sharpening. 
         [0005]    In an aspect of the invention, there is provided a method of manufacturing a blade of a cutting tool, the method including depositing a mixture including a hard material, e.g. tungsten carbide, onto an edge of a movable steel strip to form a hard material (e.g. tungsten carbide) coated steel strip; grinding the edge of the hard material (e.g. tungsten carbide) coated steel strip; and forming individual blades from the hard material (e.g. tungsten carbide) coated steel strip. 
         [0006]    These and other aspects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. As used in the specification and in the claims, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which: 
           [0008]      FIG. 1  shows a flowchart for manufacturing a blade of a cutting tool in accordance with an embodiment of the invention; 
           [0009]      FIG. 2  shows a steel strip in accordance with an embodiment of the invention; 
           [0010]      FIG. 3  shows a deposition station configured to deposit a hard metal (e.g. tungsten carbide) on an edge of a steel strip in accordance with an embodiment of the invention; 
           [0011]      FIG. 4  shows a dispenser for use in the apparatus of  FIG. 3  in accordance with an embodiment of the invention; 
           [0012]      FIG. 5  shows a deposition station configured to deposit a hard metal (e.g. tungsten carbide) on an edge of a steel strip in accordance with an embodiment of the invention; 
           [0013]      FIG. 6  shows a weld pool formed on a steel strip in accordance with an embodiment of the invention; 
           [0014]      FIG. 7  is a schematic representation of the steel strip after deposition of a hard metal (e.g. tungsten carbide) using a single head or nozzle; 
           [0015]      FIG. 8  is a schematic representation of the steel strip after deposition of a hard metal (e.g. tungsten carbide) using multiple deposition heads; and 
           [0016]      FIG. 9  shows a cross-section of a blade in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]      FIG. 1  is flow chart of a process of manufacturing a blade according to an embodiment of the present invention. In the process  10  of manufacturing a blade, a strip of steel blade stock material, from which a plurality of blades are produced, is provided at step  20 . In one embodiment, the steel is provided in a coil form, for example, to render the strip more compact to facilitate handling. In an embodiment of the invention, the steel material is a high carbon steel such as, for example, steel grade C1095 or a low alloy steel (e.g. AISI 4147), although it is contemplated that other types of materials could be used in other embodiments of the invention. The length of the strip in the coil can be as long as 1 km or more. The strip may also be provided in a multiple coils configuration, the multiple coils being welded end to end. The dimension of the strip can be selected according to desired dimensions of the blade. For example, the strip can have a width of 19 mm and a thickness of 0.6 mm. However, the strip can have other dimensions depending on the intended use of the blade that would be formed from the steel strip. In an embodiment of the invention, the steel strip is provided with a maximum hardness of about 300 HV. 
         [0018]    At step  30 , the steel strip material is delivered to a punch press where a plurality of openings are stamped into the strip to define attachment points employed to retain the blade in a cartridge or onto a blade carrier for utility knife. In addition, a brand name, logo or other indicia may also be stamped thereon. The steel strip is then scored at step  40  to form a plurality of axially spaced score lines, wherein each score line corresponds to a side edge of a respective blade and defines a breaking line for later snapping or cutting the scored strip into a plurality of blades.  FIG. 2  is a schematic representation of a portion of the steel strip  200  that shows the score lines  210 . The score lines define individual blades  205  that have a trapezoid shape. Other forms and shapes such as parallelogram blades, hook blades, etc. may also be obtained with a selection of an appropriate scoring configuration. 
         [0019]    In one embodiment, the scoring and piercing procedures of steps  30  and  40  can be combined into a single stamping operation. 
         [0020]    After scoring and piercing the steel strip, various options can be pursued for manufacturing the blade. For example, one option (“Option 1”) includes hardening the steel strip prior to depositing a hard material (e.g. tungsten carbide) and is represented by steps  50   a - 90   a  in  FIG. 1 . Another option (“Option 2”) includes depositing a hard material (e.g. tungsten carbide) prior to hardening the steel strip and is represented by steps  50   b - 90   b . Options 1 and 2 will be described in more detail hereinafter. 
         [0021]    Option 1: 
         [0022]    The coil of pressed steel strip of blade stock is then fed at step  50   a  through a heat treatment line to harden the steel strip material. In this process, the steel is run off of the coil and passed through a hardening furnace which heats the steel to a temperature above a transition temperature. The transition temperature is the temperature at which the structure of the steel changes from a body centred cubic structure, which is stable at room temperature, to a face centred cubic structure known as austenite (austenitic structure), which is stable at elevated temperatures, i.e. above the transition temperature. The transition temperature varies depending on the steel material used. In an embodiment of the invention, the heating to harden the steel strip is performed at a temperature between about 800° C. and 900° C. For example, for a grade C1095 steel, the transition temperature is approximately 820° C. (approximately 1508 F). In this instance, the heating to harden the steel strip is performed at a temperature above approximately 820° C. 
         [0023]    In an embodiment of the invention, the length of the hardening/heating furnace is approximately 26 feet (approximately 8 meters). The steel strip travels at a speed approximately between 16 and 22 feet per minute (approximately between 5 and 7 meters per minute). A controlled atmosphere of, for example, “cracked ammonia,” which contains essentially nitrogen and hydrogen, is provided in the furnace to prevent oxidation and discoloration of the steel strip. Although cracked ammonia may be used to prevent oxidation and discoloration other gases may be used, such as but not limited to, “a scrubbed endothermic gas” or “molecular sieved exothermic gas.” 
         [0024]    In an embodiment of the invention, the heating of the steel strip to harden the steel strip is performed for a time period between about 75 and 105 seconds. 
         [0025]    After exiting the heating (hardening) furnace, at step  60   a , the heat hardened steel strip is quenched. In an embodiment of the invention, the hardened steel strip is passed between liquid cooled conductive blocks disposed above and below the steel strip to quench the steel strip. In an embodiment of the invention, the heat hardened steel strip is passed through water-cooled brass blocks with carbide wear strips in contact with the steel strip to quench the steel. The brass blocks cool the steel strip from the hardening temperature, for example (approximately 820° C.), to ambient temperature (approximately 25° C.) at a speed above a critical rate of cooling. The critical rate of cooling is a rate at which the steel is cooled in order to ensure that the austenitic structure is transformed to martensitic structure. A martensitic structure is a body centred tetragonal structure. In the martensitic structure, the steel is highly stressed internally. This internal stress is responsible for the phenomenon known as hardening of the steel. After hardening, the hardness of the steel which was originally less than approximately 300 HV (before heat treatment) becomes approximately 850 HV (approximately 63 HRC). In an embodiment of the invention, the quenching of the steel strip is performed for about 2 to 4 seconds. In another embodiment of the invention, a gas or a liquid is used to quench the steel strip. 
         [0026]    At step  70   a , the hardened steel strip then passes through a tempering furnace which heats the steel to a temperature between 150° C. and 400° C. This process improves the toughness of the blade and reduces the blade hardness to HRc 62 to 55, depending on the tempering temperature selected. 
         [0027]    In an embodiment of the invention, the length of the tempering furnace is approximately 26 feet (approximately 8 meters). The steel strip travels at a speed approximately between 16 and 22 feet per minute (approximately between 5 and 7 meters per minute). A controlled atmosphere of, for example, “cracked ammonia”, which contains essentially nitrogen and hydrogen, is provided in the furnace to prevent oxidation and discoloration of the strip. Although cracked ammonia may be used to prevent oxidation and discoloration other gases may be used, such as but not limited to a “scrubbed endothermic gas” or “molecular sieved exothermic gas”. In the embodiment of the invention, the heating of the strip to temper the strip is performed for a time period between about 75 and 105 seconds. 
         [0028]    After exiting the heating (tempering) furnace, at step  80   a , the hardened and tempered steel strip is quenched. In an embodiment of the invention, the hardened and tempered steel strip is passed between liquid cooled conductive quench blocks disposed above and below the steel strip to quench the steel strip. In an embodiment of the invention, the heat hardened and tempered steel strip is passed through water-cooled brass blocks with carbide wear strips in contact with the steel strip to quench the steel. The brass blocks cool the steel strip from the tempering temperature, for example (approximately 150° C. to 400° C.), to ambient temperature (approximately 25° C.) at a speed above a critical rate of cooling to prevent oxidation of the steel surface. 
         [0029]    The coil of quenched steel strip is then continuously fed at step  90   a  to a hard material (e.g. tungsten carbide) deposition station that is configured to apply a coating of hard material (e.g. tungsten carbide) to an edge of the steel strip. The hard material has a hardness that is significantly greater than the steel strip. In one embodiment of the invention, the hardness of the hard material is at least 60 Rc. In one embodiment of the invention, the hardness of the hard material is in a range from about 70 to 80 Rc. 
         [0030]    Referring now more particularly to  FIG. 3 , this figure is a schematic representation of a deposition station, generally indicated at  300 , for depositing a coating of hard material, e.g. tungsten carbide, onto an edge  201  of the moving steel strip  200 , in accordance with an embodiment of the invention. The deposition station  300  includes a radiation source  305  configured to provide a beam of radiation  355  onto the steel strip  200 . The deposition station  300  further includes a projection system  325  configured to project and focus the beam of radiation  355  onto a target portion of the steel strip  200 . 
         [0031]    Option 2: 
         [0032]    In another embodiment, the deposition of the hard material (e.g. tungsten carbide/binder) powder takes place (step  50   b ) before the steel strip is hardened and tempered. The hardening and tempering operations are shown in steps  60   b - 90   b  and are substantially similar to those of steps  50   a - 80   a . Specifically, after depositing the hard material (e.g. tungsten carbide), the steel strip is hardened at step  60   b  and quenched at step  70   b . Then, the steel strip is tempered at step  80   b  and quenched at step  90   b.    
         [0033]    Referring back to  FIG. 3 , the radiation source  305  is configured to output a radiation beam with sufficient power and energy to melt the steel strip  200 . In one embodiment, the radiation source is a laser that outputs a beam of radiation in the infra-red (IR) range, with a wavelength of a few micrometers. An example of an IR laser that may be used is a CO 2  laser with the principal wavelength bands centering around 9.4 and 10.6 micrometers. The power of the CO 2  laser may be in the range of about a few kWatts, for example between 1 and 8 kWatts. In one embodiment, the power of the CO 2  laser is about 6 kWatts. Alternatively, a laser operating in the ultra-violet (UV) range could also be used in another embodiment of the invention such as, for example, a UV laser with a wavelength lower than 400 nm. Examples of UV lasers include excimer lasers. 
         [0034]    It will be appreciated that the source of radiation  305  is not limited to a light source. For example, in an embodiment of the invention, an electron beam source may also be used in the deposition station  300 . In this implementation, the electron beam source is configured to provide a beam of electrons with sufficient energy and power to melt the steel strip  200 . 
         [0035]    The beam of radiation  355  outputted by the radiation source  305  is directed to a projection system  325  that is configured to focus the beam onto the edge of the moving steel strip  200 . The energy of the projected beam  355  that is concentrated on the edge  201  of the steel strip  200  is used to melt the target portion of the steel strip, and when used, the binder within the feed powder  342 . The projection system  325  may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, to direct, shape, or control the radiation. In the event the radiation source is an electron beam source, electromagnetic lenses may be used to control and focus the beam  355 . 
         [0036]    It will be appreciated that the projection system  325  may be integral with the radiation source  305 . The projection system  325  is preferably mounted to a frame that is stationary, although it is contemplated that one or more optical elements of the projection system  325  may be movable to control the shape of the projected radiation beam  355 . 
         [0037]    A dispenser or deposition head  320 , arranged between the radiation source  305  and the steel strip  200 , is configured to supply a mixture  342  of hard material (e.g. tungsten carbide) and a binder element to the thin edge  201  of the steel strip  200 . The dispenser  320  has a generally hollow shape to allow the beam of radiation  355  to pass there-through. 
         [0038]      FIG. 4  shows a top view of the dispenser  320  in accordance with an embodiment of the invention. The dispenser  320  has a generally conical annular shape, although it is contemplated that other shapes (e.g. square, rectangular, oval, polygonal) could be used to dispense the mixture  342 . The dispenser  320  includes a series of conical annular cavities designed to deliver the powder  342 , inert shield gas  361  and laser beam to a single focus point F. In an embodiment of this invention, the shielding gas  361  is Argon. As shown in  FIG. 4 , the dispenser  320  includes an outer cone  370  and a gas inlet  371  through which the inert shield gas  361  is supplied. The dispenser  370  further includes an inner cone  373  and inlets  374   a - b  through which the mixture  342  is supplied. A central cone  375  defines a passage in the dispenser  320  to allow the projected radiation beam  355  to pass therethrough. The inner cone  373  is arranged between the central cone  375  and the outer cone  370  and defines a channel  376 . The inner cone  373  and the outer cone  370  define a channel  377  therebetween to allow the inert shield gas  361  to flow therethrough. It will be appreciated that other arrangements are contemplated. It will also be appreciated that additional or fewer channels may be used to supply the mixture  342  to the steel. strip  200 . 
         [0039]    The diameter of the periphery  362  of the central corn  375  is selected along with the distance D 1  separating the dispenser  320  from the steel strip  200  and the length of the channel  376  such that the particles of the mixture  342  fall under the action of gravity onto a predetermined portion of the steel strip  200 . In addition, or alternatively, the powder is placed into a hopper feed system, and the powder is stripped from the hopper and propelled through a plastic tube by a compressed gas (such as argon or helium). Such predetermined portion generally corresponds to the point of focus F of the beam of radiation  355  onto the steel strip  200 . The diameter of the inner periphery  362  is also selected in order to allow the radiation beam  355  to pass through the dispenser  320 . 
         [0040]    The inner shield gas  361  is configured to form a shield  346  around the mixture  342  at a location near the point of focus F, as shown in  FIG. 3 . The shield  346  provides a protective atmosphere during deposition of the mixture  342  of hard material (e.g. tungsten carbide) in order to prevent oxidation of the steel strip  200 . During use of the deposition station  300 , the inner shield gas  361  is flushed from the inlet  371  down the channel  377  to the steel strip in a manner that is such that the environment around the melted portion of the steel strip  200  is non-oxidizing. 
         [0041]    The dispenser  320  is fixedly mounted to a frame (not shown) of deposition station  300  and may be either stationary or moveable in at least three directions, e.g. x, y and z directions. A benefit of having a moveable dispenser  320  is that the position of the dispenser  320  relative to the steel strip  200  can be accurately controlled. Various motors and actuators, such as electric, electromagnetic and/or piezoelectric actuators, could be used to displace the dispenser  320 . 
         [0042]    Supply of the mixture  342  to the dispenser  320  is effected via the plurality of inlets  374   a - b . In one implementation, a container (not shown) is used to store the particles of mixture  342 . The container is arranged to communicate with the plurality of inlets  374   a - b  via one or more conduits  347  such that the mixture is conveyed to the predetermined portion of the steel strip  200  via the channel  376  under the action of gravity. In one embodiment of the invention, it is envisioned that the supply of the mixture  342  be mechanically assisted with, for example, a compressed gas as noted above or a mechanical pusher. 
         [0043]    It will be appreciated that alternative arrangements of the dispenser  320  could be used in other embodiments of the invention. For example, instead of using an annular shaped dispenser, one or more individual nozzles or deposition heads may be used to supply the particles to thin edge  201  of the steel strip  200 . This configuration is shown in  FIG. 5 . As shown in  FIG. 5 , a single power source  505  may be used in conjunction with individual deposition heads or dispensers  510   a - f . Each individual deposition head  510   a - f  may be similar to the deposition head  320  shown in  FIGS. 3-4 . The radiation beam (e.g. laser beam) provided by the power source  505  is directed to the individual deposition heads  510   a - f  such that each deposition head supplies its own radiation beam  511   a - f  on the thin edge  201  of the steel strip  200 . Power is individually controlled for each deposition head. Further, each deposition head is configured to individually supply its own mixture  512   a - f . In the embodiment of  FIG. 5 , the power source independently supports up to six laser deposition heads. It will be appreciated that additional or fewer deposition heads could be used in an embodiment of the invention. This configuration is greatly beneficial. Indeed, by independently controlling the power to each deposition head, it is possible to better control the shape of the deposited layer and deposit different compositions (e.g. different mixtures of materials or different compositions of the same mixture) at each deposition edge. In that way, it is possible to have multiple depositions from a single coating process without coiling and re-coating the steel strip  200 . In operation, the steel strip  200  moves along the x direction such that various layers can be coated on the thin edge  201  by the different deposition heads  20   a - f.    
         [0044]    As depicted in  FIG. 5 , the individual heads  510   a - f  are positioned along the edge of the thin edge  201  of the steel strip  200 . However, alternative arrangements are possible. For example, the individual deposition heads may be arranged around the predetermined portion of the steel strip  200  where the beam of radiation is focused (point F). Further, the one or more individual deposition heads may be stationary or moveable relative to the steel strip  200  in a similar manner as the deposition head or dispenser  320  and compressed gas may be used to convey the particles to the steel strip  200 . 
         [0045]    The dispenser  320  may also include one or more shutters (not shown) to prevent particles of mixture  342  from exiting the nozzles  360  after completing the deposition process. The shutters may be arranged on the inner periphery of the dispenser  320 , or within the channels or on the upper portion of the dispenser. 
         [0046]    Referring back to  FIG. 3 , the steel strip  200  may be moved in at least three directions, x, y and z, relative to the beam of radiation  355  with the aid of an actuator  335 . As shown in Figure, the movable steel strip  200  is moved under the radiation beam  355  along the x direction with the use of two rollers  344   a - b . The two rollers  344   a - b  can be positioned with the actuator  335 . One or more separate motors may be used to move the steel strip  200  in the at least three directions, x, y and z. Examples of actuators that may be used in an embodiment of the invention include electric and electromagnetic actuators. The position of the steel strip  200  may be controlled with the aid of dedicated electronics and servo control systems. To that effect, a measurement system (not shown) may be used to measure the position of the moving steel strip  200  under the radiation-beam  355 . 
         [0047]    It will be appreciated that deposition of the mixture  342  of hard material (e.g. tungsten carbide) and binder element could be carried out in a less protective environment. In this implementation, oxidation of the steel strip  200  will occur at the locations on the blade where the mixture  342  is deposited. The oxidation could then be mechanically or chemically removed after completing the deposition process. For example, it is contemplated that an in-line polishing process using a wire brushing be applied after deposition of the mixture  342  onto the steel strip  200 . 
         [0048]    An in-line measurement system  350  may be used to control the characteristics of the deposited mixture  342  onto the blade perform  10 . Preferably, the measurement system  350  is a non-destructive optical system, such as an ellipsometer, that controls the quality/composition and thickness of the film mixture  342 . The in-line measurement system  350  may include an emitter  351   a  and a detector  351   b . The emitter  351   a  is configured to illuminate the portions of the steel strip  200  with a radiation beam. The radiation beam is reflected by the steel strip  200  and then detected by the detector  351   b . The reflected radiation beam is subsequently analyzed with dedicated instrumentations in order to measure the characteristics of the coating of mixture  342 . Preferably, the measurements are performed by the in-line measurement system  350  after completing the deposition process. If the measured characteristics of the steel strip  200  are not within specification, the portion of the steel strip can be marked with a marker to indicate that the final blade should be rejected. 
         [0049]    As shown in  FIG. 3 , a controller  345  is used to control the deposition process. The controller  345  may be operatively connected to the dispenser  320 , the radiation source  305  and the actuator  335 . The controller  345  may be accessed by an operator to input the illumination settings, control the amount and flow of particles of the mixture  342  in the dispenser  320  and/or the desired positioning of the steel strip  200  during the deposition process. In the configuration where multiple deposition heads or nozzles are used, the operator can input to the controller  345  the desired composition in each deposition head. It will be appreciated that the positioning of the thin edge  201  of the steel strip  200  under the radiation beam  355 , the amount of particles of mixture  342  and the illumination settings of the radiation source  305  may substantially change depending on the geometry and nature of the steel strip  200 . 
         [0050]    In operation, the thin edge  201  of the steel strip  200  is continuously moved under the radiation beam  355 . Referring now to  FIG. 6 , this figure schematically depicts a view of the steel strip  200  during the deposition process. The x-direction represents the direction of movement of the steel strip  200  during deposition. As shown in  FIG. 6 , irradiation of the thin edge  201  of the steel strip  200  creates a weld pool  365  at the point of focus F of the beam of radiation  355 . Particles  367  of the mixture  342  are released by the dispenser  320  and fall freely within the weld pool under the action of gravity. The binder is irradiated and melted by the radiation beam  355  while falling on the steel strip  200 . As a result, substantially all the particles  367  are already melted when they reach the weld pool  365 . 
         [0051]    The binder element is selected to bind the hard material (e.g. tungsten carbide) to the melted material of the weld pool. All bonding between the particles  367  and the steel strip  200  is achieved by solidification of the hard material (e.g. tungsten carbide)/binder element within the weld pool. This results in a void free deposit of hard material (e.g. tungsten carbide)/binder onto the steel strip  200 . An example of binder that may be used in an embodiment of the invention includes cobalt. However, this is not limiting. It is contemplated that additional binders could be used in other embodiments of the invention. 
         [0052]    The thickness of the deposit is controlled by the particle feed rate, the particle size, the illumination settings of the radiation source (e.g. energy, power, frequency of the radiation pulses) and the rate of passage of the steel strip  200  beneath the focused beam of radiation  355 . These parameters are inputted and controlled by the controller  345 . The thickness of the deposit is measured by the measurement device  351 . 
         [0053]    The speed of displacement of the steel strip  200  is controlled such that the, thickness of the deposit remains within specification at all times. The speed of the steel strip  200  may vary depending on the characteristics of the beam of radiation (e.g. wavelength and frequency, energy and power of the pulses), the size of the focus spot and the materials constituting the steel strip  200 . 
         [0054]    Referring now to  FIG. 7 , this figure shows a schematic representation of the steel strip  200  after deposition of the mixture  342  using a single head or nozzle. As can be seen in this figure, a single layer  202  of the mixture  342  is coated on the thin edge  201  of the steel strip  200 .  FIG. 8  shows a schematic representation of the steel strip  200  after deposition of different mixtures using multiple heads or nozzles. In this embodiment, two heads are used and each head is configured to provide a different mixture composition. As shown in  FIG. 8 , two layers  203   a - b  are coated on the thin edge  201  of the steel strip  200 . It will be appreciated that more than two layers having the same or a different mixture composition could be coated on the thin edge  201 . Further, each of the layers may be coated with a different deposition head or nozzle. 
         [0055]    It will be appreciated that the deposition of the hard material (e.g. tungsten carbide) could be performed in a similar manner on the opposite side of the blade preform. 
         [0056]    Referring back to  FIG. 1 , after exiting the deposition station  300 , the steel strip  200  is delivered to a grinding machine. In an embodiment, at step  100 , the steel strip is recoiled and is transferred to a grinding machine for grinding an edge of the strip. A relatively shallow angle, such as between 10 to 32 degrees is ground onto the edge of the strip. This angle is ground on both sides of the blade, so that the blade is generally symmetrical relative to a longitudinal axis of the blade that bisects the edge, as can be appreciated from  FIG. 9 . In addition, the ground angle is measured relative to the longitudinal axis as can also be appreciated from  FIG. 9 . The angle is selected to be shallow to reduce the force that may be required to push the blade through the material it is cutting.  FIG. 9  shows a cross section of an example of a ground edge of a steel strip, according to an embodiment of the present invention. In this example, the angle of the ground edge  371  of the steel strip  200  is 22°±2°. 
         [0057]    It will be appreciated that the steel strip  200  can be further thermally processed after depositing the hard metal coating at step  90  in accordance with Option 1. For example, in one implementation, the steel strip  200  could be again hardened, quenched and tempered in a similar manner as described at steps,  50   a ,  60   a ,  70   a  and  80   a.    
         [0058]    In the grinding step, the blade edge may be ground with a single angle or with multiple angles. 
         [0059]    Finally, the processed steel strip is snapped along the length of the steel strip at each score line to break the steel strip along the score lines to produce a plurality of blades, at step  90 . An example of an embodiment of a blade obtained according to the manufacturing process of the present invention is shown with its various dimensions in  FIG. 9 . 
         [0060]      FIG. 9  shows a cross section of a blade  205  after grinding and sharpening the steel strip  200  The blade  205  includes a cutting edge  271  that is mainly made of a hard material (e.g. tungsten carbide)  272  while the remaining portion of the blade is made of the core material constituting the blade  205 , denoted as  273  in  FIG. 9 . As will be appreciated by one skilled in the art, the deposition of tungsten carbide in accordance with an embodiment of the invention provides a blade that has a surface of tungsten carbide that is flushed with the remaining surface of the blade. As can be seen in  FIG. 9 , the tungsten carbide is welded to the blade so as to form a seamless transition between the tungsten carbide and the core material  273  of the blade. 
         [0061]    While the principles of the invention have been made clear in the illustrative embodiments set forth above, it will be apparent to those skilled in the art that various modifications may be made to the structure, arrangement, proportion, elements, materials, and components used in the practice of the invention. 
         [0062]    It will thus be seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing preferred specific embodiments have been shown and described for the purpose of illustrating the functional and structural principles of this invention and are subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.