KR0153252B1 - Chemically bonded superabrasive grit, method of making the same and tool thereof - Google Patents

Abstract

The present invention relates to a method of chemically bonding a coating such as tungsten to a diamond or CBN superabrasive grit attached to a substrate that provides superabrasive cutters such as blades, grinding, wheels, perforated bits and the like.

Description

Coated superabrasive grit, manufacturing method thereof and apparatus containing the same

The present invention relates to coated superabrasive grit useful for making improved abrasives or cutters. It is within the scope of the present invention to include instruments comprising coated grit.

Superabrasive grit (eg diamond and CBN) attached to the support is widely used to remove material. Typical applications include, for example, sawing, drilling, dressing, grinding, lapping and polishing.

In typical applications, the grit is fixed to a suitable matrix and attached to a toolbody. The grit can be basically fixed by mechanical means, for example by enclosing the grit with a matrix material. The method of attachment is simple and practical but has limitations because its exposure must be limited so that the grit does not weaken the mechanical cohesion of the surrounding matrix. As a result, the cutting speed is limited due to the small grit exposure. In addition, because the matrix wears out, the retention force becomes insufficient, so that the grit can escape and disappear. For example, in conventional lumber blade articles, the average exposure of diamond grit is less than 20% of the total grit length, and the grit is often lost because it leaves off when worn to about one third of its original size. After some use of the saw blade, about one third of the original grit size is typically lost, as evidenced by the empty pockets on the blade.

In order to overcome this problem, a method of increasing the bonding strength by coating the grit has been proposed. US Pat. No. 3,650,714 (Farkas) describes a method of coating diamond grit as described above. Commercially available coated abrasive products include DeBeer Co.'s titanated products for grit material and General Electric Co.'s CBN grit titanated products. For all metal matrix superabrasives, the only commercially available grit coating is a titanated product.

However, titanated products, in particular for diamond grit, are not effective in increasing adhesion strength. The performance of the titanated grit, i.e., the residual rate and the cut rate, in the lumber blade article was not significantly improved. One of the problems with titanated products is the lack of resistance to oxidation. It is known that Ti or TiC can be oxidized at most material blade manufacturing conditions. Oxidation can break the bond between the grit and the coating and between the coating and the matrix. Another problem faced by titanized products is the thickness of the coating. Titanized products typically include Ti or TiC having a thickness of less than 1 μm. Such thin coatings do not prevent dissolution or removal of the coatings from the grit surface by the matrix material during the process of fabricating the instrument. U.S. Patent Nos. 3,757,878 and 3,757,879 (Wilder) describe a method for encapsulating diamond particles. However, the patent document provides a method for mechanically enclosing the grit, but does not provide a chemical bond.

It is an object of the present invention to provide a chemically coated superabrasive grit.

Another object of the present invention is to firmly attach the grit to the matrix body of the instrument.

It is still another object of the present invention to provide a continuous thickness coating having a thickness of 1 μm or more on the superabrasive grit to completely maintain the coating after the fabrication process.

It is a further object of the present invention to provide a coating which is substantially inert to oxidation during the instrument building process.

It is yet another object of the present invention to provide a grinder or cutter comprising a coated superabrasive chemically bonded for improved material removal function.

It is yet another object of the present invention to provide a mechanism having a chemically coated abrasive grit that exhibits better grit retention, greater grit protrusion and more free cutting action. Such mechanisms include, for example, lumber blades, grinding wheels, piercing tools, drilling bits and lapping tools.

The term superabrasive as used herein refers to natural and synthetic diamond and cubic boron nitride (CBN).

As used herein, the term chemical bonding is distinguished from mechanical bonding. In the case of mechanical bonding, there is no reaction between the two binding sources. In the case of chemical bonds, the reaction takes place in the contact region between the two sources. The reaction can be, for example, the formation of a solution by carbide formation, boride formation, nitride formation or by inter-diffusion between two binding sources.

As used herein, the term drill bit includes drilling bits, which are machinery, as well as drilling bits and core bits, such as those commonly used for rock drilling in the quarrying and petroleum industries.

According to the present invention there is provided a superabrasive grit coated with a substantially non-oxidizing metal having a thickness of at least 1 μm, which is strongly bonded to the surface of the grit by chemical bonding. In short, the grit is coated with a highly non-oxidizing metal selected from W, Ta, Mo, Nb or alloys thereof. The coated grit is then heat treated before or during the instrument fabrication process to form a strong chemical bond between the grit and the coating, such as, for example, a carbide layer in the case of diamond grit. Tungsten is the preferred metal for coating. The surface of the grit is optionally roughened by chemical or mechanical means prior to coating to strengthen subsequent bonding. The matrix composition is miscible with the coating selected for the grit so that, under processing conditions for making the instrument, the matrix will chemically bond to the coating. The product is a chemically bonded coated superabrasive grit strongly attached to the instrument matrix.

Contact areas between the superabrasive grit and the coating and contact areas between the coating and the matrix are formed by strong chemical bonds. This is first distinguished from the prior art in which the grit is mechanically attached by the surrounding matrix material. The coated superabrasive grit included in the apparatus according to the present invention has a longer service life due to the deviation of the grit smaller than (1); Higher cutting rate due to larger protrusion of grit than (2); And (3) more free cutting, with smaller force, smaller work and smaller heat generation due to the greater degree of protrusion of the grit.

The superabrasive coated according to the present invention may be a member of a cutter having a particular physical form, such as, for example, round, oval, winged, or the like; Or is particularly suitable for grit in perforated bits, such as the actual cutter member itself, such as when the grit is incorporated into a virtual matrix of bits, which protrudes from the surface and wears off and exposes other portions of the grit attached to the matrix. . This is particularly suitable for core bits, and other bits for hard products can likewise be manufactured.

According to the invention, the superabrasive grit surface is first roughened by mechanical or chemical means. This coarsening process provides a non-uniform surface that improves the adhesion of the grit to the coating to be applied later. This improved adhesion is the result of increased chemical reactivity of the grit surface due to very high surface instability. In addition, the number of unbonded electrons of carbon on the surface increases, thereby increasing the reactivity between the grit and the cladding. In addition, the nonuniformity of the surface may enhance the mechanical adhesion of the grit to the coating because of the larger surface area in intimate contact.

In the practice of the present invention, the grit is first roughened arbitrarily. The preferred coarsening process is to form a uniformly polished surface. This coarsening process can be carried out using mechanical means such as, for example, milling with other superabrasive powders, or using chemical means such as oxidation or etching.

For example, the grit is oxidized uniformly on all surfaces by tumbling at high temperatures under an air or oxygen rich atmosphere. In order to obtain the desired result, either a chemical vapor deposition (CVD) system or a circulating furnace of the fluidized bed can be advantageously used. In the chemical etching process, an oxidizing agent such as potassium dichromate or potassium nitride can be optionally used. When using the above methods, the weight loss of the grit during the surface roughening process should be adjusted to less than 5% (W / W).

Although the surface roughening process is an important step according to the invention, in some cases it may be an unnecessary process. For example, for smaller sized grit articles for grinding fabric using fine powder, the coarsening process can be omitted.

After performing the surface-roughening treatment, the grit is washed and chemically clarified by methods known in the art to remove surface impurities. For example, most of the surface impurities can be removed by washing the grit with an inorganic acid (eg nitric acid or hydrochloric acid solution) or by heating the grit under a nitrogen atmosphere.

After cleaning the surface, the grit is coated with a material that is a carbide forming material (e.g., W, Ta, Mo, and Nb, or alloys thereof) that forms a continuous layer that is quite antioxidant and has a thickness of at least 1 μm. The coating thickness can vary from about 1 to about 50 μm, preferably from about 1 to about 30 μm. Such coatings are readily distinguished from coatings known in the art. For example, a coating obtained according to the technique of US Pat. No. 3,650,714 (Farkas) has a very thin thickness of less than 1 μm. This difference is also found in other commercially available titanated products.

In the case of using diamond grit, carbide can be formed between the grit and the coating by heating the coated grit to the carbide forming temperature. When using CBN, nitride bonds are formed. Suitable alloy coatings can for example be W-NiB.

After applying the first coating to the grit, the coating of the second coating or additional layer can optionally be spread over the first layer. The purpose of coating the multiple layers is to further prevent the first coating from being oxidized in the air or dissolved in the matrix material during the instrument fabrication process and / or the cutting action of the instrument. The outer layer coating may also provide better metal connection points with the matrix binder to form diffusely bonded covalent surfaces. In most cases, the outer layer coating does not need to include a carbide formation. For example, an electroless copper outer layer coating may be used to bond with a particular matrix material.

The coating is typically applied by known methods, such as chemical vapor deposition as described in US Pat. No. 3,757,878 to Wilder. Using this method, a mechanical layer is typically applied that does not contain an antioxidant carbide forming material.

Chemical bonding between the grit and the coating can be obtained in different ways depending on the desired final product. For example, when the grit is included in the lumber blade, the processing conditions for forming the blade, in particular the temperature required to form the blade, should be sufficient to form a chemical bond. On the other hand, when the desired final product is formed under different processing conditions that do not result in sufficient chemical bonding, the coated grit can be pretreated under conditions such as, for example, in a furnace under an effective carbide formation temperature (eg, about 850 ° C.). Form chemical bonds in the final product before using the grit.

After the coating is applied to the grit, the coated grit can be used together with the uncoated grit in a continuous process for making the device. For example, in the manufacture of a lumber blade, the grit is mixed with a well mixed matrix metal powder and then hot-compressed into the molding at about 800 to 1,000 ° C. or a binder alloy is introduced. As a result, a material blade having grit chemically bonded to the coating material and a coating material chemically bonded to the matrix material is produced. In short, all covalent surfaces are connected by chemical bonds.

In another aspect of the invention, the coated grit is packed to form a mass of very high viscosity. For example, using vibrating filling means, a constant size grit (size of 500 μm) can reach a filling rate of about 55% (the remaining 45% is void). When a second size (70 μm) grit corresponding to about 1/7 of the first size is added, the filling rate may increase to about 77%. Again adding a third size grit, equivalent to about 1/7 of the second size, would result in a filling rate of at least 83% of the total aggregate. After filling the grit, an alloy having a melting point below the deformation temperature of the super abrasive grit is introduced into the aggregate. When diamond grit is used, the temperature is limited to less than about 1,100 ° C. for synthetic grit and less than about 1,300 ° C. for natural grit, depending on the quality. Due to the presence of the coating, the binder alloy is fairly easily injected into the aggregates of the high-filled superabrasive grit. In the absence of a coating, most binder alloys cannot be introduced into the above-described aggregates.

The above-described embodiment is carried out to obtain a superabrasive-metal composite such as a diamond-metal composite called so-called Diamet. Such composites have greater impact resistance than conventional polycrystalline superabrasive aggregates due to the presence of metal binders. For example, when the impact test is performed on diamond aggregates and polycrystalline diamond (PCD) materials, it can be obtained that the diamond aggregates are stronger than PCD materials.

The diamond material can easily bind to the bonded WC substrate to form a useful cutter, for example, as a drill bit for rock drilling articles. When a cutter having such a support is tested in a laboratory, the cutting result is comparable to that of a cutter made of a green compact such as a geoset.

The method according to the invention provides many advantages. For example, since the method of the present invention does not require the use of the high pressure required to make polycrystalline superabrasive aggregates such as PCD, the cost of producing such composites can be much less than in the prior art methods. The size and shape of these substrates are also not limited by the conditions of the high pressure chamber and are more flexible.

To describe embodiments of the invention in more detail, reference is made to the following examples.

Example 1

Natural diamond grit, marketed under the trade name EMBS by DeVer, having a size of D602 in FEP A designation (30/40 US mesh), is coated with a tungsten layer using a fluidized bed CVD method. The diamond grit is then immersed in an acid solution containing hydrofluoric acid and nitric acid for 1 minute. It is then rinsed in deionized water for 15 minutes, washed in NaOH dilution for 2 minutes and then further rinsed in deionized water. The cleaned grit is dried in an oven. The dried diamond grit is placed in a chemical vapor deposition (CVD) reactor containing a graphite tube. After the diamond grit is placed in the reactor, argon is introduced into the reaction chamber for about 30 minutes under a pressure of about 5 torr. Thereafter, the pressure is changed to 0.5torr to evaporate the water. The reactor was then heated to 900 ° C. and 900 ° C. in 16 minutes while introducing gas containing Ar, He, H ₂ in a ratio of 1: 1: 1 into the reaction chamber at a flow rate of 0.21 L / min under a pressure of 5 torr. Fix for 30 minutes at. After the temperature was lowered to 700 ° C. in 3 minutes, the pressure was increased to 12 torr. Increasing the flow rate of the gas causes the diamond grit to flow in the reactor. At the same time, WF6 (tungsten hexafluoride) was introduced to deposit tungsten on the diamond to a thickness of up to 11 μm in about 75 minutes. Finally, only argon flow is introduced to cool the reactor to room temperature. The thickness of the tungsten coating on the product is 7.75 μm. The coated grit is made into the material fraction by hot pressing into a matrix material consisting of 80% Cu—Sn alloy and 20% bonded tungsten carbide grit. This fraction is used to cut an abrasive concrete sample comprising silica rock grain. The results indicate that the grating departure loss on the cut plane after testing was reduced to less than 10%. This low departure loss is in stark contrast to the 40% departure loss as a result of the corresponding tests performed with uncoated grit under the same conditions.

Example 2

A synthetic diamond grit, marketed under the trade name SDA 100 by Devier, having a size of D602 in the F.E.P.A designation, was coated with a tungsten layer of about 10 μm thickness as in Example 1. The coated grit is dispersed to form a densely packed single layer surface in a matrix powder made of tungsten carbide. The aggregate is precompressed into a molding and then hot pressed at a temperature of 815 ° C. and a pressure of 3,500 psi. Hot pressurized aggregates are of dog-bone shape. The tensile test (uniaxial tensile test) is then performed with the tensile test specimen. As a result, it was found that coated grit having this geometry can support a tensile strength of 15 KSI. Under the same test conditions, the uncoated grit was found to have virtually no tensile strength.

The coated grit was also recoated with a layer of deposited electroless nickel-boron, about 30 μm thick, according to the method used at the Allied-Kelite branch of Witco Corp. Let's do it. A solution comprising nickel-boron, commercially available from witco corporation, is used. In the first coating step, using a solution such as the Niklad Alprep 230 solution available from Witco Corporation, the solution is heated to 65.5 ° C. and cleaned by immersing the diamond grit in the solution for 5 minutes. The diamond grit is then rinsed with tap water until foaming stops. A photoresist commercially available from Wittco Corporation as Niklad 261 is applied to the diamond grit surface, where the grit is immersed in the photoresist at 224 ° C. for 2 minutes. The diamond grit is then rinsed with deionized water. A catalyst commercially available under the trade name Niklad 262 is then applied to the diamond grit surface, where the diamond grit is immersed in the catalyst for 4 minutes at 43 ° C. under a pH of 1.9 to 3. The diamond grit is then rinsed with deionized water. The treated diamond grit is dried and immersed in a commercially available Ni-B solution with Niklad 752 solution at a temperature of 80 ° C. under a pH of about 6. Here, the nickel layer contains about 3% boron. Tensile strength under the same test conditions as Example I was 20 KSI.

In a control test, grit of the same type is first roughened and then coated with the same bilayer. The surface is roughened by milling into fine diamond powder in a water medium. If milling is continued for 24 hours, the final weight loss of the grit is about 0.7%. Tensile strength under the test conditions described above was found to increase to 35 KSI.

Example 3

The tungsten-coated fine diamond powder produced by the method of Example I, which is 500 µm and 60 µm in size, is filled by vibration to form uniformly distributed aggregates at a filling rate of 80%. The alloy is then charged with an alloy consisting of copper, manganese and titanium at 1,050 ° C. for 20 minutes under vacuum. The diamond is made into a cutter and the granite log is cut using the cutter containing the coolant. Abrasion resistance is tested and tested for other commercial PCD materials under the same conditions. The wear resistance of diamond is comparable to the high-set PCD available from General Electric Company. The high-set PCD products are manufactured in the diamond stable region under high pressure conditions. In addition, a corrosion test is performed by injecting an abrasive containing impurities to the same diamond sample as described above. Corrosion resistance has been found to be comparable to injected tungsten carbide slugs commonly used as the surface of the matrix bit body. A diamond material having a large wear resistance and corrosion resistance as described above is useful for making a cutter in a drill bit for rock drilling. Perforated bits known in the art use PCD (e.g., gossett) or tungsten carbide inserts.

Example 4

It is brazed into bit bodies according to a conventional brazing process known in the art, using a diamond cut 8-1 / 2 gas prepared according to Example 3.

Claims (14)

Selected from the group consisting of diamond and CBN, and after cleaning the surface, a substantially continuous metal coating (first metal coating) selected from the group consisting of W, Mo, Ta, Nb and alloys thereof A coated super abrasive grit capable of supporting a tensile strength of 2.3 kg / cm 2 (15 KSI), characterized in that it comprises super coated grit particles coated in a chemically bonded state in thickness. The coated superabrasive grit of claim 1, further comprising superabrasive grit particles having a rough surface. 3. The method of claim 1 or 2, further comprising a second substantially continuous metal coating comprising nickel or copper on top of the first metal coating, wherein the total thickness of the first metal coating and the second metal coating is Coated superabrasive grit in the range of 1-50 μm. The coated superabrasive grit of claim 3, wherein the first metal coating is tungsten. The coated superabrasive grit of claim 3, wherein the second metal coating comprises nickel. The coated superabrasive grit of claim 3, wherein the metal coating comprises NiB. 4. The coated superabrasive grit of claim 3, wherein the first metal coating is tungsten and the second metal coating comprises NiB. The coated superabrasive grit of claim 3, wherein the first metal coating has a thickness of 10 μm and the second metal coating has a thickness of 30 μm. Rinsing the grit selected from diamond and CBN with deionized water to clean the surface of the grit and cleaned to a thickness of 1 to 50 μm using an easily oxidized metal selected from W, Ta, Mo, Nb or their alloys Coating the grit and forming the coated grit between a grit particle surface selected from diamond and CBN and a metal coating selected from the group consisting of W, Mo, Ta, Nb and alloys thereof Heat-treating at a temperature for forming a strong chemical bond between the coating and the grit, wherein the coated abrasive grit comprises super abrasive grit particles selected from the group consisting of diamond and CBN. An instrument comprising the coated superabrasive grit as claimed in claim 1 which is in contact with a matrix bonded to a tool body. The instrument of claim 10 which is a saw blade. The instrument of claim 10 which is a drill bit. 13. The appliance according to claim 11 or 12, wherein the filling rate of the grit is at least 70% by volume. A cutter comprising the coated superabrasive grit as claimed in claim 1 as a cutting member as an integral component of the appliance.