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1. (WO2018165754) TRÉPAN À DIAMANTS ET PROCÉDÉ DE PRODUCTION D'UN TRÉPAN À DIAMANTS
Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

DIAMOND DRILL BIT AND METHOD OF PRODUCING A DIAMOND DRILL BIT

CROSS-REFERENCE DATA

The present application claims the priority of United States provisional patent application No. 62/471,142 filed on March 14, 2017.

FIELD OF THE INVENTION

The present invention relates to the ground drilling operations, and more particularly to a diamond drill bit composition for a drilling machine and a method of producing the diamond drill bit.

BACKGROUND OF THE INVENTION

Long-reach drilling machines are used in the mining industry to explore the ground for specific mineral formations. This exploration is accomplished by drilling very long boreholes that can be up to about 5000 meters long (about 16 250 feet long) to extract in-depth core mineral samples from the ground. These mineral samples can then be studied and evaluated to identify their mineral composition to determine if mining operations will take place where the mineral sample was retrieved. This type of exploration drilling is also called core drilling.

A long-reach drilling machines comprises a series of drill rods that each measure but several feet in length, but that will be assembled to form a drill string that can be thousands of feet long. The drill string is rotated by means of a drill rig, the machine that will hold and rotate the uppermost drill rod and allow the addition of drills rods as the drill string increases in length to accommodate the borehole that also increases in length. The drill rods are hollow.

At the end of the drill string opposite the drill rig is located the core bit, a ring-shaped bit that is impregnated with diamonds and, typically, tungsten or tungsten carbide powder to make it easier to cut the rock. The core bit is also often called the diamond drill bit, or simply the drill bit. The drill bit cuts the core sample out of the rock by rotating at a high speed and with a certain amount of pressure being applied to the drill bit against the ground to cut away the earth, stone and other minerals. This drill bit is attached to a reaming shell that reams the borehole to the desired diameter size. The reaming shell may also be impregnated with diamonds or tungsten carbide. The reaming shell also helps to stabilize the core bit drilling process to help avoid the drilling direction to undesirably change.

The reaming shell is attached to the wireline core barrel, the part of the equipment that will collect the core sample. A wireline core barrel includes three components: an inner tube assembly, an outer tube assembly and the overshot. The inner tube assembly includes the head assembly and the inner tube. The inner tube is the piece that will actually hold the core sample during the drilling process. The inner tube does not rotate within the outer tube assembly.

The wireline core barrel is connected to drill rods. The deeper the bore hole, the more drill rods are needed. Drill rods transfer the torque, feed, force and rotation speed required to drill into the rock, from the drill rig to the drill bit. A drill's pressure pump is used to pump drilling fluids into the hollow drill rods of the drill string all the way down to the drill bit. The fluids will flush the rock cuttings away from the bit and carry them to the surface and will cool the drill bit at the same time.

Core samples can be retrieved from the core barrel as drill rods are added to drill deeper into the ground. This is accomplished by retrieving the inner tube with a harpoon that attaches to the overshot, and then pulling the inner tube loaded with a ground sample out of the outer tube assembly and all the way up through the drill rods to the drill rig with a winch and a metal cable. There, the inner tube will be manually retrieved and the ground sample will be removed from the inner tube for testing.

The drill bits 10 themselves, shown in Figure 1, comprise a matrix 30 mounted to a blank 20 with a backing 40. The matrix 30 comprises teeth the shape of which is optimised for the drilling operation. The exact shape and configuration of the drill bits can and will vary depending on the type of ground that is being bored.

The matrix is made of a mixed metal powder, typically comprising tungsten in significant proportion, in which synthetic or natural diamonds are dispersed. This composition is then compressed to form the matrix before additional tungsten backing powder and a metallic alloy - also called the infiltrant - are added. The composition is then heated at high temperature, such as 1000 °C, until the metallic alloy melts and infiltrates the powder, giving the name to the process known as the infiltration process. Depending on the type of alloy being used, sealed kiln chambers wherein hydrogen or another inert gas is injected can be used, to deoxidize the alloy and promote the infiltration.

Prior art drill bits are also produced by a sintering process instead of an infiltration process, especially in other domains such as oil drilling. This process differs from the infiltration process, notably in that the matrix is formed with the tungsten powder being mixed with the diamonds and the metallic alloy at the outset; and the matrix is then compressed at high temperatures with the metallic alloy already added to the tungsten powder. The sintering process yields drill bits having different mechanical properties. Notably, the sintering-produced drill bit will have a greater resistance to wear. While this is desirable in certain applications such as oil drilling, a lower resistance to wear can be advantageous in the long reach drilling for mining exploration when harder ground is encountered and the prior art sintering process is consequently not ideal to obtain such matrixes, as explained hereinbelow.

Drill bits having different mechanical properties are desirable depending on the type of ground being bored through. To obtain these different mechanical properties, the composition of the drill bit can be adjusted, and the method of producing the drill bit can be selected.

For softer ground, harder metallic alloys are usually desirable to allow the matrix to wear out more slowly, increasing the drill bit life expectancy.

For harder ground however, softer metallic alloys are usually desirable to allow the drill bit to wear out more quickly. This quicker wear of the drill bit has the advantage of exposing new unworn diamonds at a quicker pace. These new diamonds have sharper edges than the worn diamonds that have been exposed for some time and have had their edges become blunt under repeated wear on the ground being bored.

So depending on the type of ground being drilled, a matrix will be selected with mechanical properties that will allow it to wear out at a desired pace, more or less quickly. This will allow the diamonds to fall from the matrix as the metallic alloy wears out, approximately at a rhythm corresponding to the diamonds themselves becoming worn out, to expose new sharper diamonds. Drill bit compositions and

methods of production are consequently selected to obtain drill bits with customized mechanical properties to fit different ground compositions.

Matrix compositions usually include tungsten, tungsten carbide, molybdenum and/or niobium powders that are used in the infiltration process to create the drill bit matrix. Tungsten powders, including in the form of carbide tungsten, is the most frequently used among those. More particularly, the tungsten, molybdenum and/or niobium powders will be admixed with the diamonds before a binding metallic alloy is poured into the mix, as mentioned above. This binding metallic alloy typically comprises brass, copper and silver; or copper, silver and nickel.

The purpose of the tungsten powder in the drill bit matrix is to increase the hardness and resistance to wear of the drill bit.

An important problem with prior art drill bits is their cost. Tungsten, molybdenum and/or niobium powders, and silver are all expensive materials.

However, replacing tungsten in particular has proven unsuccessful because of its very effective resistance to wear.

There have been some attempts in prior art drilling tools to replace the tungsten with ferrous powder to form the matrix of the drill bit. One advantage of using ferrous powders is its lower cost. It however has shown to yield tools with a much lower resistance to wear, and further the tool is prone to deforming more easily during use during which its temperature will increase as it rotates due to friction with the ground, which is problematic for recuperation of the cylindrical mineral sample, the structural integrity of which can be affected by the deformed tool.

SUMMARY OF THE INVENTION

There is consequently a need to provide a matrix composition for diamond drill bits that does not affect its mechanical properties beyond acceptable thresholds, while however being produced at lower cost. However, the challenge lies in that the known prior art matrixes including tungsten in particular, and alloys including silver in particular, have proven over time to be efficient compositions providing the desired mechanical properties.

In view of this desired goal, the present invention relates to a diamond drill bit comprising a steel powder comprising iron in a non-zero proportion of up to 99,6 % and carbon in a proportion between 0,03% and 2,14%, coated diamonds impregnated in said steel powder, and a metallic infiltrant alloy comprising copper and one of tin, silver and both tin and silver; wherein said diamond drill bit is produced by an infiltration process.

In one embodiment, said steel powder further comprises one or more of the following metals: manganese, silicon, phosphorus, sulfur, copper, nickel, chromium, aluminium, titanium, boron, molybdenum and vanadium.

In one embodiment, said steel powder further comprises tungsten.

In one embodiment, said infiltrant alloy comprises 50-92% copper and 2-50% silver.

In one embodiment, said infiltrant alloy comprises between 75-95% copper and 5-25% tin.

In one embodiment, said infiltrant alloy further comprises zinc.

In one embodiment, said infiltrant alloy further comprises bismuth.

In one embodiment, said steel powder comprises iron particles of a size between 1 and 300 microns.

The present invention also relates to a method of producing a diamond drill bit as defined hereinabove by an infiltration process, comprising:

· providing the steel powder to form a matrix;

• dispersing the coated diamonds in said steel powder;

• compressing said matrix comprising said steel powder and said coated diamond at a cold-compression temperature;

• after the step of compressing said matrix, adding to said matrix an infiltrant alloy comprising copper and one of tin and silver to form a drill bit mixture; and

• heating the drill bit mixture at or above a fusion temperature of said infiltrant alloy, for allowing said infiltrant alloy to melt, wherein said infiltrant alloy infiltrates said matrix and binds it.

In one embodiment, the step of providing the steel powder comprises providing a ferrous-based powder and graphite that comprises carbon, and wherein before the step of heating the mixture at or above a fusion temperature of said infiltrant alloy, said method further comprising the step of heating said drill bit mixture at or above a diffusion temperature of the carbon in the iron but below the fusion temperature of said infiltrant alloy for allowing the carbon to migrate into said iron.

BRIEF DESCRIPTION OF THE DRAWINGS

In the annexed drawings:

Figure 1 is a perspective view of a diamond drill bit according to the present invention;

Figure 2 is a table showing different steel compositions that can be used for providing the steel powder composing the matrix of the drill bit; and

Figure 3 is a graphic showing the results of three-point flexion tests for three different drill bit matrix samples having respective compositions.

DETAILED DESCRIPTION OF THE EMBODIMENTS

According to the present invention, a diamond drill bit has been developed including a matrix composition that offers lower production costs while yielding similar and comparable mechanical properties than those of conventional prior art matrixes that include tungsten powder admixed with a metallic infiltrant and diamonds.

The diamond drill bit of the present invention has been developed comprising a matrix impregnated with diamonds and infiltrated with a metallic alloy according to an infiltration process, with the matrix comprising steel powder.

More particularly, the matrix comprises a steel powder having a nonzero proportion of iron of up to 99,6% iron. The steel powder also comprises a minimum of 0,03% Carbon and up to 2,14% Carbon. Figure 2 shows a number of steel compositions that have been used to produce the steel powder used in the diamond drill bit matrix. The matrix composition can comprise, for example, about 70 grams of steel powder for 200 grams of metallic alloy, plus about 14 grams of diamonds.

The dimension of the steel powder particles that will compose the steel powder will influence the resistance to wear of the matrix. Steel powder particles size between 1 and 300 microns have been tested to be particularly advantageous. So depending on the type of ground being bored through and the desired rate at which the matrix should wear out, different sizes of steel powder particles can be used.

According to the present invention, the metallic infiltrant alloy can be either a copper-silver alloy or a copper-tin alloy, or a copper-silver-tin alloy.

In the embodiment where it is a copper-silver alloy, the composition of the infiltrant can be 50-92% copper and 2-50% silver. In an embodiment where a copper-tin alloy is employed, the composition of the infiltrant can be between 75-95% copper and 5-25% tin.

Nickel has been used as an optional additive in a copper-silver infiltrant to provide advantageous results. Nickel increases the wettability of the steel powder particles, making the alloy more fluid.

The following exemplary matrix compositions have been successfully produced:

1) 60%Cu-40%Ag

2) 74%Cu-18%Ag-8%Ni

3) 73%Cu-25%Ag-2%Ni

4) 76.8%Cu-19.2%Ag-4%Ni

5) 78.4%Cu-19.6%Ag-2%Ni

6) 80%Cu-15%Ag-5%Ni

7) 58% Cu-37% Ni-5% Ag

8) 84,5%Cu - 14%Sn - l,5%Zn

9) 83%Cu - 14%Sn - l,5%Zn - l,5%Bi

10) 84%Cu - 14%Sn - l,5%Zn - 0,5%Bi

In one embodiment, the infiltrant alloy comprises zinc in addition to copper and tin. The addition of zinc helps increase the structural harness of the bronze matrix composition.

In one embodiment, the alloy further comprises bismuth in addition to the copper, tin and zinc combination. Bismuth has been found to decrease resistance to wear, so it is advantageously used in circumstances where a higher wear rate of the matrix is desired.

The drill bit composition described in the present invention has been tested and found to provide mechanical properties that are equivalent or similar to those of the prior art compositions, albeit at a cheaper price.

Figure 3 indeed shows the results of three-point flexion tests for three different drill bit matrix samples having respective compositions. For all three drill bit matrix compositions, a copper-silver-nickel alloy was used. Curve 50 is obtained from a matrix comprising tungsten powder per the prior art. Curve 52 is obtained from a matrix comprising steel powder according to the present invention. Curve 54 is obtained from a matrix comprising pure iron powder.

It can be seen from the results of Figure 3 that the behavior of the steel powder matrix shown in curve 52 is very similar to that of the tungsten powder reference matrix 50. The pure iron powder has however shown to be too ductile, and furthermore pure iron powder-based matrixes have shown significant wear compared to steel powder matrixes. As also noted above, pure iron matrixes have shown to produce tools that deform during use under friction-induced heat, which is undesirable.

It can consequently be seen from the Figure 3 graphic that pure iron powder matrixes are not desirable, whereas steel powder matrixes formed by infiltration process

provide similar mechanical properties than that of tungsten powder matrixes. This was a surprising and unexpected result, and leads to the conclusion that steel matrixes can be used to produce a diamond drill bit in an infiltration process to obtain diamond drill bits that have comparable mechanical properties albeit at a much lower price. It is understood that diamond drill bits produced by infiltration process do not have the same mechanical properties at that of the diamond drill bits made with other production processes, such as a sintering process; and this is a feature, not a drawback, as it is known as noted in the Background of the Invention section to use diamond drill bits with different mechanical properties depending on the type of ground being drilled. The diamond drill bit of the present invention is produced with an infiltration process specifically, and it is not intended to compare, nor will it compare, to diamond drill bits produced with other processes such as a sintering process.

It is possible to use sealed kiln chambers wherein hydrogen or another inert gas is injected to deoxidize the alloy and promote the infiltration.

In the present specification, reference to compositions comprising percentages of certain elements, refers to percentages in mass.

The method of producing a diamond drill bit per the invention by an infiltration process consequently notably comprises providing the steel powder to form the matrix. It is noted that while the steel powder comprises a nonzero proportion of iron, otherwise it would not be characterized as steel.

It is also noted that a certain proportion of steel can be replaced by tungsten. While this is not necessarily desirable on a cost-effectiveness basis, it would still yield acceptable results. Replacing tungsten by steel is the purpose of the invention to

obtain a more cost-effective drill bit, but if this is done only in a certain proportion, then the savings are consequently proportional.

The steel powder comprises a maximum of 99,6% iron. It has been determined that beyond this proportion, the diamond drill bit would become too ductile, and would be prone to deforming under use. In fact, it would then start to behave more like the pure iron sample shown at 54 than the steel sample shown at 52 in Figure 3.

The steel powder also comprises at least 0,03 % carbon. This minimum is required for the steel to acquire the necessary hardness, and not be too ductile, for the intended purpose of being used as a matrix for a diamond drill bit in an infiltration process. Carbon concentration should not go beyond 2,14% however because beyond that point cast iron will be formed instead of steel.

Other metals can be included in the matrix composition, for example one or more of the following metals: manganese, silicon, phosphorus, sulfur, copper, nickel, chromium, aluminium, titanium, boron, molybdenum, vanadium, tungsten, and any other element that is known to be part of certain steels.

The use of these metals, and others, to form steel with the iron and carbon is known in the art, and will be obvious for a metallurgist. It is further noted that the use of steel implicitly means that some of these metals can be used. In fact, if the upper threshold of 99,6% iron and the lower threshold of 0,03% carbon is used, then one or more other metals, including the above-mentioned metals or other metals, must be used. However, it is contemplated that the steel could be formed of only iron and carbon: then, the minimum proportion of carbon would have to be 0,4%, since the maximum portion of iron is 99,6%.

The method includes the step of dispersing coated diamonds in the steel powder. This is known in the industry of producing diamond drill bits, and diamonds of known dimensions and coated with known compounds can be used.

The method also comprises compressing the matrix comprising the steel powder and the coated diamond at a cold-compression temperature. This cold-compression temperature can be, for example, at room temperature, or any other suitable temperature that will be obvious for someone skilled in the art.

After the compressing, the method comprises adding to the matrix an infiltrant alloy comprising copper and one of tin and silver, or both, as noted above, with possible additional metals as further noted above.

The method also comprises heating the mixture of steel powder, coated diamonds and infiltrant alloy at a fusion temperature or more, for allowing the infiltrant alloy to melt, wherein the infiltrant alloy infiltrates the matrix and binds it. The fusion temperature will of course depend on the infltrant being used. The fusion temperature of some infiltrant alloys is for example 1000°C: in this exemplary case, the step of heating would then occur at 1000°C or more.

The steel powder can be provided from fully formed steel, or it can be provided with the iron and carbon particles independently of one another to then produce the steel during the infiltration process. Carbon is then provided in the form of graphite, while the iron can be provided in the form of a ferrous-based powder that includes iron and, optionally, other metals as noted above. The method of the invention would then include, before the step of heating the mixture at the fusion temperature or more, the step of heating the mixture at a diffusion temperature that is at least equal to a diffusion temperature of the carbon in the iron but inferior to the fusion temperature of the infiltrant alloy for allowing the carbon to migrate into the iron to form steel

particles.