WO1997037774A1

WO1997037774A1 - Method of coating a cutting blade having improved wear characteristics

Info

Publication number: WO1997037774A1
Application number: PCT/US1997/005288
Authority: WO
Inventors: Metin Sakarcan
Original assignee: Diamant Boart Inc
Current assignee: Diamant Boart Inc
Priority date: 1996-04-04
Filing date: 1997-04-04
Publication date: 1997-10-16
Anticipated expiration: 1998-10-04
Also published as: AU2600197A

Abstract

A refractory coating (28) extends over a portion of a diamond cutting blade (10) comprising a disc-shaped body (12) having an edge on which is positioned one or more cutting segments (14). One or more grooves (40, 42) are located in the sides of the blade body. The coating (28) is created by spraying a liquid tungsten carbide mixture onto each side of the blade (10) at a speed of over 3000 fps. The tungsten carbide is directed at the blade (10), resulting in a solidified metal coating on each side of the body and which fills in any overhang of the segment(s) beyond the blade body and the grooves in the blade body.

Description

METHOD OF COATING A CUTTING BLADE HAVING IMPROVED WEAR CHARACTERISTICS

Field of the Invention

The present invention relates to a diamond cutting blade of the type having a central disc-shaped body and cutting segments located about the periphery of the body. More specifically, the invention relates to a cutting blade having a tungsten carbide coating covering a portion of the outer surfaces of the blade, and a method of forming this coating on the blade.

Background of the Invention

Diamond cutting blades are often utilized for cutting or sawing concrete, brick, and other abrasive materials. These cutting blades comprise a central disc-shaped body or cone having one or more cutting segments located on the peripheral edge of the body (See Figure 1) .

Due to cost considerations, the body of the blade is typically constructed from a material much less durable than the cutting segment, such as carbon-steel or similar material. The body is thin, has a circular outer shape, and a central mounting hole.

The cutting segment comprises diamond chips or a similar abrasive, durable material positioned in matrix form in a softer material. The cutting segment may be a single ring extending completely around the outer edge of the body, or individual segments spaced apart about the edge of the body. When multiple individual segments are employed, they are normally located between gullets or cut-outs in the body of the blade. Each cutting segment is attached to the peripheral edge of the body by welding, brazing or the like.

In use, the blade is mounted on a drive and rotated with respect to an axis extending perpendicular to the radial direction of the blade. The cutting segment(s) of the blade engage the material to be cut, movement of the durable diamond chips causing material removal.

Because the body is constructed of a less durable material than the segments, the body is not useful for cutting. Further, in order to reduce the drag which would otherwise be associated with the body rotating directly against the material being cut, the body normally has a thickness which is less than that of the cutting segments (see Figure 2) .

This blade configuration suffers from a significant drawback. When the blade is used it removes material from the base material being cut. Ultimately, most of this material is expelled from the slot being cut in the material by either the rotation of the blade, or in wet cutting operations, by being washed out of the slot.

A problem results from the fact that some of the cut, loose material is never expelled from and instead remains in the slot during cutting, and because much of the material which is ultimately expelled travels along the sides of the blade. This loose and often very abrasive material wears the body of the blade. This wear is most severe near the outer periphery of the body adjacent the segment/body interface.

In many instances, the wear is so great that the body is undercut to a point that it will no longer support the cutting segment (see Figure 3) . As a result, one or more of the segments, each of which subjected to large shearing forces, may be removed from the body during cutting. Once one or more of the segments are removed from the body, the blade is useless. This may be true even though the more valuable cutting segments are worn very little.

Some attempts to solve this problem have been to utilize kicker segments, recessed segments, vertical inserts, stellite cores or blade bodies, carbide inserts, and slurks. These and other attempts to solve the above-stated problem have met with relatively little success.

Summary of the Invention

In accordance with the present invention, a cutting blade is coated with a refractory metal coating to increase the wear characteristics of the blade.

The blade includes a disc-shaped body having an outer edge on which is mounted one or more cutting segments. A coating of tungsten carbide extends over a portion of each side of the blade.

Preferably, the coating extends over the sides of the cutting segments and radially inwardly over the sides of the body. The thickness of the coating at the edge of the body of the blade is preferably at least equal to the thickness or width of the cutting segment at the edge of the body. The thickness of the coating preferably decreases radially inwardly of the edge of the body. Concentric grooves are located in the body radially inward of the edge of the body. The coating fills the grooves.

The coating is preferably deposited utilizing a high- velocity oxy fuel gun. The gun burns liquid fuel creating a heated, high velocity gas stream. A powdered mixture of tungsten carbide plus chromium carbide and boride is fed into the gas stream, where it liquifies. The liquid tungsten carbide mixture is expelled from the gun at over 3000 feet per second and is deposited on a side of the blade at a rate between about 20 and 30 pounds per hour. The liquid tungsten carbide mixture cools into a compressed solid metal coating on the outside of the blade.

Further objects, features, and advantages of the present invention over the prior art will become apparent from the detailed description of the drawings which follows, when considered with the attached figures.

Description of the Drawings

FIGURE 1 is a perspective view of a cutting blade of the type known in the prior art;

FIGURE 2 is a cross-sectional view of the prior art cutting blade illustrated in Figure 1 through line 2-2;

FIGURE 3 is a cross-section view of the prior art cutting blade of Figure 2 after substantial undercutting of the segment has occurred;

FIGURE 4 is a cross-sectional view of a blade in accordance with a first embodiment of the present invention;

FIGURE 5 is a cross-sectional view of a blade in accordance with a second embodiment of the present invention; and

FIGURE 6 is a cross-section view of a blade in accordance with a third embodiment of the present invention.

Detailed Description of the Preferred Embodiment

Figure 3 illustrates a cutting blade 10 in accordance with the present invention. In general, the blade 10 comprises a central body or core 12 having a number of cutting segments 14 located thereon, and having a refractory coating 28 extending over at least a portion of the body 12. The body 12 of the blade is constructed of metal, such as steel, aluminum, or another similar material which has sufficient strength so as to support the cutting segments 14 during cutting. The body 12 is disc-shaped, having a first side 16, second side 18, and a peripheral edge 20 defining the outer circular shape of the body. The body 12 also includes a central aperture 22 for mounting the blade on the drive shaft (not shown) of a saw, as is well known in the art. The thickness and diameter of the body 12 of the blade 10 vary substantially depending on the type of blade and its application.

The cutting segments 14 comprise diamond (or other durable abrasive material) particles 24 located in a matrix material 26, the matrix material typically comprising iron, nickel, or a variety of other matrix materials well known in the art. The diamond particles 24 are bound to or embedded in the matrix material 26. The matrix material 26 is less durable than the diamond particles 24, so that during use of the blade 10, new particles 24 are continually exposed as the matrix material 26 is worn away. The composition of the matrix material 26 may vary widely depending on the desired rate of diamond chip 24 exposure for the material being cut.

Each cutting segment 14 has two outwardly facing sides 30, 32 and an outer end 34 which define cutting surfaces, and a base 36 which is preferably connected to the outer edge 20 of the body 12 of the blade 10 via welding, brazing or the like.

In accordance with the present invention, a durable or refractory coating 28 covers at least a portion of the body 12 of the blade 10. Preferably, the coating 28 comprises a coating which is primarily compressed, solidified tungsten carbide. As disclosed below, however, the coating 28 may comprise other refractory metal material(s), such as other metal carbides, borides, nitrides, suicides or oxides.

In a first preferred embodiment, illustrated in Figure 3, a first groove and second groove 40a, , 42a,b or other surface indentation or recess are preferably formed in each side 16,18 of the blade body 12. Preferably, the grooves 40a,b, 42a,b extend all the way around the body 12 adjacent the segments 14 in concentric fashion.

The coating 28 extends over a portion of each side 16,18 of the body 12. In particular, the coating 28 extends over each side 30,32 of the segment 14, and across where the body 12 meets the cutting segment 14 to a point radially inward therefrom. The coating 28 fills in at least part of, and preferably all of the grooves 40,42, aiding in adherence of the coating 28 to the blade 10.

As illustrated in Figure 3, the thickness of the coating 28 preferably decreases as its radial distance from the edge 20 of the body 12 increases. The coating 28 tapers in thickness, preferably at a relatively uniform rate, although the taper may alternatively be in step-wise fashion, with respect to its radial distance from the edge 20. It is desirable for the coating 28 to extend radially inwardly at least as far as the cutting depth of the blade. Alternatively, the coating may extend inwardly at least as far as the depth of the gullets or cut-outs in the blade 10, or across the encire body to the central aperture 22.

Most importantly, when the coating 28 has the above- described profile, it fills in the space between the portion of the base 36 of the cutting segment 14 which overhangs or extends beyond the respective side 16, 18 of the body 12 of the blade 10. The coating 28 thus forms a sort of "ramp" between the sides 16, 18 of the body 12 of the blade 10 and the corresponding sides 30, 32 of the cutting segments 14. The present invention includes a method for creating the above-described blade coating. First, as detailed above, at least one, and preferably two grooves 40,42 are formed (for example during molding or by machining) around and in the body 12 of the blade 10. The coating 28 is formed on the blade 10 by directing liquid tungsten carbide mixture at the blade 10 at a speed over 3000 feet per second.

Preferably, a high velocity oxy fuel (HVOF) gun, and more particularly a model JP5000 gun available from Hobart Tafa Technologies of Concord, New Hampshire, is utilized in this method. In this type of gun, liquid is burned in a combustion chamber and the resultant gases accelerate through a nozzle. A mixture of tungsten carbide, boride and chromium carbide in particulate or powder form is fed into the gas stream in the HVOF gun at a rate of approximately 25-30 pounds per hour. The particles liquify in the gas stream, and are expelled from the gun at rates of speed over 3000 feet per second. When the liquid metal particles are expelled at this high rate of speed, the resulting cooled and solidified metal coating is in compression, having a high icrohardness (900-1400 DPH (diamond pyramid hardness) at 300g) (as compared to coatings produced by spraying material from guns employing other processes and lower particle speeds, where the resulting coating has a much lower hardness (350-1000 DPH-300g) ) .

When using the JP5000 gun described above, coatings having a maximum thickness of .25 inches are achievable, as opposed to other similar coating processes where the coating may be limited to 20-40 mils or less.

To deposit the coating, the discharge end of the gun is directed at a side of the blade 10, with the liquid refractory coating material expelled from the gun and deposited on the blade. In the present method, the deposition rate is preferably over about 20 pounds/hour, achievable with the above-stated gun.

If it is desired to prevent the deposition of the coating 28 on the outside surfaces 30, 32, 34 of the cutting segments 14 and/or other areas of the body 12 of the blade 10, it is necessary to mask or divide off these areas.

The liquid refractory metal is directed towards the edge 20 of the body 12 for a longer period of time than those areas located radially inwardly from the edge 20, creating a coating 28 with its greatest thickness near the edge 20. Coating deposition continues until the coating profile described above is attained.

A second embodiment blade of the present invention is illustrated in Figure 5. In this embodiment, the coating 128 is located over all or a portion of each side 116,118 of the body 112 of the blade 110 and the sides 130,132 of the cutting segment(s) 114, just as described above. In this embodiment, however, no grooves are located in the body 112 of the blade 110.

A third embodiment blade 210 of the present invention is illustrated in Figure 6. In this embodiment, the coating 228 extends only over the sides 216,218 of the body 212 of the blade 210, and not over the sides 230,232 segment(s) 214. Here, the coating 228 extends from the edge 220 of the body 212 of the blade 210 radially inwardly. While not shown, this coating 238 profile may be utilized when one or more grooves are located in the body 212 of the blade 210.

In this embodiment, the thickness of the coating 228 varies with respect to its radial distance from the edge 220 of the body 212. Preferably, the thickness of the coating at the edge 220 of the body 212 is equal to the distance by which the segment extends axially outwardly from the respective sides 216,218 of the body 212. Thus, at the edge 220, the combined thickness of the body 220 and the coating 228 on each side thereof is approximately equal to the total thickness of the cutting segment 214.

This coating profile is desirable from the standpoint that it may eliminate the need to "dress" the blade before use. In particular, when using the blades 10,110 described above in which the coating extends over the outside surfaces of the segment(s), the coating must be removed before cutting will occur. This is normally accomplished by "dressing" the blade before use by removing the coating and exposing the cutting sides (and thus the cutting diamond particles) of the segment(s) .

On the other hand, this embodiment blade 210 makes more difficult the process of coating the blade 210. In particular, in the method of creating this coating it is necessary to mask off the sides 230,232 and top 234 of the segments 214 from the remainder of the blade to prevent coating deposition in these areas.

The coated blade of the present invention has significant advantages over the prior art blades. Foremost, the extremely hard coating on the sides of the blade significantly reduces the rate of blade body wear during use. Thus, the problems associated with segment undercutting are significantly reduced, greatly increasing the useful life of the blade.

When utilizing a coated blade of the preferred embodiment, the cause of the wear is also believed reduced. One of the reasons segment undercut is believed to occur is the build¬ up of removed material created as a result of cutting near the connection of the body and cutting segment. It is believed that material may become trapped in this area, increasing the rate of wear adjacent the cutting segment. In the preferred embodiment, the coating fills in the "overhang" where the base of the cutting segment extends outwardly beyond the sides of the thinner blade body. During use, removed material may not become trapped, believed to reduce the root cause of the wear.

In another form of the invention, the coating may be deposited in a uniform thickness and extend over all or a portion of the blade 10 or body 12. It is generally desirable that the thickness of the coating be chosen so that the thickness of the body of the blade in combination with the coating be less than the uncoated thickness of the cutting segment. If the combined thickness of the coating and body is equal to or greater than the cutting segment, the coated body portion of the blade may drag during cutting.

For the same reason, while it is possible for the coating to have thickness at any point where the combined thickness of the body or core and coating is greater than the cutting segment, this is generally undesirable.

It is contemplated that the coating 28,128,228 be used with blades 10,110,210 having individual cutting segments spaced about the edge of the body, or a single cutting segment which extends entirely around the perimeter of the body.

When utilizing a blade having spaced cutting segments, it is not necessary to coat the sides of the body where no cutting segment is located, as the problem of segment undercut does not occur there anyway. From a practicality standpoint, however, it may be easiest to place the coating around the entire edge of the body.

While tungsten carbide is the preferred coating material, other coatings are contemplated. Other materials which have refractory qualities (i.e. providing wear resistance to an underlying blade) and which may be positioned on the outside surface of an already formed blade in the profile and/or method as disclosed above are contemplated. The coating is preferably a cermet or ceramic in nature, however, formed from wear resistant metal carbides, borides, nitrides, suicides or oxides.

It is possible to coat only one side of the body and/or blade. This is generally undesirable in most applications, however, since it would normally result in the body of the blade still wearing on the uncoated side.

In the preferred embodiment blade 10 described above, other surface imperfections may be substituted for the grooves 40,42. As stated above, the grooves 40,42 are utilized to improve adherence of the coating 28 to the blade 10. The grooves may take a variety of other shapes. Small apertures or the like may pass into or entirely through the blade, the coating filling this space and possibly even forming a contiguous segment of material through the blade.

It will be understood that the above described arrangements of apparatus and the method therefrom are merely illustrative of applications of the principles of this invention and many other embodiments and modifications may be made without departing from the spirit and scope of the invention as defined in the claims.

Claims

1. A method of creating a cutting blade with improved wear characteristics, comprising: obtaining a cutting blade having a central disc-shaped body with an outer edge having at least one cutting segment positioned thereon; spraying a liquid refractory coating material towards said cutting blade; depositing said refractory coating material on at least a portion of a side of said body of said blade.

2. The method of Claim 1, wherein said refractory coating material comprises tungsten carbide.

3. The method of Claim 1, wherein said refractory coating material is sprayed from a HVOF gun.

4. The method of Claim l, further including the steps of burning a fuel -co create a heated gas, introducing solid refractory coating material into said gas, and liquifying said material.

5. The method of Claim 4, wherein said solid refractory coating material is in powder form.

6. The method of Claim l, wherein said liquid refractory coating material is sprayed at said blade at a speed over about 3000 feet per second.

7. The method of Claim 1, wherein said refractory coating material is sprayed at a rate over about 20 pounds per hour.

8. The method of Claim 1, further comprising the step of creating a solid refractory coating having a hardness of over about 900 DPH-300g.

9. The method of Claim 1, wherein said refractory coating material is deposited on both sides of said blade.

10. The method of Claim 1, wherein said refractory coating material is deposited only on said body.

11. The method of Claim 1, wherein said refractory coating material is deposited in a greater thickness at said outer edge of said body than a point radially inwardly therefrom.

12. The method of Claim 1 wherein said refractory coating material is deposited on said body at said outer edge in a thickness approximately equal to a distance by which an outer side of said segment extends beyond the side of said body on which said material is deposited.

13. The method of Claim 1, wherein said refractory coating material is deposited on both sides of said body and in a thickness whereby the total thickness of said coating and said body is approximately equal to a thickness of said segment at said outer edge.

14. The method of Claim 1, wherein said refractory coating material includes a metal containing boride, oxide, suicide, nitride or carbide.

15. The method of Claim 1, wherein said blade includes at least one groove in the body thereof, said deposition step at least partially filling said groove.

16. An improved cutting blade, said cutting blade having a central body with a first side, second side and outer edge and further including at least one cutting segment positioned on said outer edge, said cutting segment extending outwardly of said first and second sides of said body, said improvement comprising a refractory coating located on at least a side of said blade adjacent said outer edge, the thickness of said coating at said outer edge of said body of said blade being equal to a distance said segment extends outwardly from said side of said body at said outer edge.

17. The blade of Claim 16, wherein the thickness of said coating decreases radially inwardly of said outer edge of said body.

18. The blade of Claim 16, wherein said coating is positioned on each side of said body, said coating having a thickness such that the thickness of said coating on each side of said body and along with a thickness of said body is approximately equal to a thickness of said cutting segment at said outer edge.

19. The blade of Claim 16, wherein said coating comprises tungsten carbide.

20. The blade of Claim 16, wherein said coating has a hardness of over about 900 DPH-300g.

21. The blade of Claim 16, wherein said coating material is selected from the group consisting of: metal oxide, boride, nitride, carbide and suicide.

22. The blade of Claim 16, wherein at least one groove is located in the surface of each side of said blade body and said coating at least partially fills said groove.