Title of Invention	A COATED SUBSTRATE FOR USE IN A COAL AUGER DRILL BIT
Abstract	A coated substrate for use in a coal auger drill bit comprising a metallic body (1), such as herein described, at least one shaped seat (3) provided on said metallic body, at least one shaped support (2) held to the said seat (3), a refractory metal based ceramic layer, or coating, on the working surface of the said support.

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FIELD OF INVENTION This invention relates to a coated substrate. By way of example, but without implying any limitation thereto, the coated substrate may advantageously be employed as a ceramic coated coal auger drill bit. BACKGROUND OF INVENTION Drilling in hand section coal mining increases, the production of coal, if uninterrupted drilling is accomplished. The capability of drilling depends on the cutting edge and the cutting surface of the drill. Thus, the drill bit attached to the drill rod plays an important role in the rate of penetration in the coal and its ability to remain in a cold condition and maintain a sharpness of the cutting edge, and assist easy flow of debris over the cutting surface and the flutes. Such a sharpness of the cutting edge is more critical in instances of hard coal and coal seam with stone bands or drilling in roof with stone or shale or in development section containing stone or coal seam with stone band. In the know art, drill bits are fabricated from strong and stable cutting edge of carbides, and particularly tungsten carbide with the substrate being the body of the drill bit. However, such drill bits are unable to maintain a sharp cutting edge, especially while drilling in coal seam with stone band or in stone or in roof drilling. It has been found that when the drill bit contacts hard coal or shale or coal seam during a drilling operation, the cutting edge gets blunt and immediately breaks and with the consequence that a penetration or drilling by the drill bit is adversely affected. In such an instance, debris are no longer formed. Simultaneously, the drill bit continues to drill at the same location resulting in a generation of heat at the cutting edge. Such a presence of heat, which often is higher than the brazing temperature of tungsten carbide results in a softening of the joint between tungsten carbide and seat of the body. In order to obviate such a disadvantage, the known art has employed a high content of tungsten carbide in the cutting edge and cutting surface. However, the tungsten carbide content increases the brittleness, which results in cracking or breaking of the tungsten carbide tips. In both of the aforesaid instances, the edges are subjected to the step of resharpening resulting in a loss of the tungsten carbide tip. Further, a drilling operation is discontinued for change of the blunt or broken tip or losing the tip itself which chips off into the debris, and thereby reducing coal production. OBJECTS OF THE INVENTION An object of this invention is to propose an improved coal auger drilling bit. Another object of this invention is to propose a coal auger drilling bit, which obviates the disadvantages of the prior art. Still another object of this invention is to propose a coal auger drilling bit, which avoids the numerous breakages or cracks associated with the drilling bits of the known art. Yet another object of this invention is to propose a coal auger drilling bit which avoids subjecting the drill bit to frequent changes. A further object of this invention is to propose a coal auger drilling bit which avoids constant resharpening of the drill bit. A still further object of this invention is to propose a coal auger drilling bit having a higher hardness, sharpness and toughness in comparison to that of the prior art. DESCRIPTION OF INVENTION According to this invention there is provided a coated substrate which may, for example, be advantageously employed in a coal auger drill bit comprising I. a metallic body II. at least one shaped support held to a support seat provided on said metallic body, and III. a refractory metal based ceramic layer or coating on the working surface and working edge of said support. The present invention resides in the provision of a ceramic layer on the support. As described hereinabove, reference to a coated substrate is intended to include a coal auger drill bit. Thus, one of the advantageous applications of the coated substrate is that of a ceramic-coated coal drill auger bit. When the drill bit of the known art contacted hard coal or coal seam with stone bands, the cutting surface and cutting edge would crack or break, and the initiation of the crack propagated beyond the cutting edge and into the body of cutting surface of tungsten carbide. To obviate such a disadvantage, it is known to add 4 to 6%. by weight of cobalt powder to tungsten carbide powder, which is then compacted and formed into a shape and finally sintered to form cemented carbide. The presence of cobalt is to reduce the hardness of tungsten carbide. It is recognized that if tungsten carbide has a high value of hardness, it becomes brittle and which is one of the factors that contribute to the formation of cracks. The presence of cobalt, which is a comparatively soft material, firstly bonds tungsten carbide powder and, secondly, reduces the hardness value of tungsten carbide. Simultaneously, it was recognized in the prior art, that the addition of a greater amount of cobalt would considerably reduce the hardness value of tungsten carbide, which is not a desired feature as in the known art the tungsten carbide constituted the cutting surface and edge. In distinction, the present invention no longer has a cutting surface or cutting edge of tungsten carbide as known from the prior art. Instead, the tungsten carbide forms only a shaped support for the cutting surface or cutting edge. As the tungsten carbide forms now only a support for the cutting surface and cutting edge, it has now been found that upto 18% of a toughening agent may be added to tungsten carbide to form the support. Though the support does not by itself form the cutting surface and cutting edge, it must simultaneously have sufficient strength to withstand the tensile forces acting on it during a drilling operation and suitably act a support for the cutting surface and cutting edge. Accordingly, it has now been found that the hardness value of tungsten carbide need not be as high as when it was used as a cutting surface and cutting edge, and also not too low so as not to be capable of supporting the cutting surface and cutting edge during a drilling operation. In accordance with the present, 8 to 12% by weight of a toughening agent is preferably added to tungsten carbide. It has been found that the presence of 8 to 12% by weight of the toughening agent in tungsten carbide removes inherent brittleness of tungsten carbide, but has sufficient strength to act as a physical support for the cutting surface and cutting edge during a drilling operation. Yet another function of the support is to form a metallurgical bond between the ceramic cutting surface and cutting edge, and thereby metallurgically increasing its own hardness at the interface. The support comprises a shaped body formed by powdered metallurgy or casting. Further, the support comprises essentially of tungsten carbide, though other metals may alternatively be used. Such other metals are selected from nickel, chromium, vanadium, molybdenum, cobalt, titanium and their alloys or their carbides, or both the combination of alloys, carbides, nitrides, oxides and boxides. Further, if tungsten carbide is used as the primary metal, then the alloying element can be selected from any one or more of the aforesaid metals. The support should have a thickness of at least 2 mm. Preferably, the support can have a thickness of upto 8 mm, though higher thickness could be employed but which would then constitute a waste. The support is held to the seats of the bit by the step of silver alloy brazing. The alloy employed for the step of brazing comprises essentially of silver, for example 40 to 60% by weight of silver, and the balance being selected from cadmium, copper, manganese and nickel. The brazing alloy is employed in the form of shim, film or thin plate and having a thickness of 0.1 to 0.5 mm. The process consists in applying the brazing flux to the support or the seat of the drill bit or both, which is then heated in a high frequency induction heater so as to allow the alloy to melt and fuses the silver brazing alloy. In accordance with this invention, the cutting surface and cutting edge comprises a refractory metal ceramic coating or layer applied over the working surface of the support. Preferably, such a ceramic coating is applied over the entire exposed surface of the support. Such a refractory metal based ceramic layer functions to increase the hardness of the support. The ceramic layer or coating is selected from refractory metals comprising titanium, vanadium, chromium tungsten cobalt or molybdenum and present in the metallic form or as nitrate, carbide, oxide or boride presently singularly or in any combination. In accordance with this invention, the ceramic coating or film has a thickness of 5 to 10 microns and may be deposited by any known method, such as physical vapour deposition or chemical vapour deposition. Such a ceramic layer substantially increases the hardness of the cutting surface and edges and improves the cutting properties and performance. Further, the ceramic coating has a smooth cutting surface and cutting edge and a low coefficient of friction and in comparison to the tungsten carbide of the known art. Such a low coefficient of friction assists free flow of debris formed during drilling without any flow restriction. This free flow of debris dissipates the heat generated during drilling and keeps the cutting edge cool and prevents build up of mug at the cutting edge. In the known art, tungsten carbide has high coefficient of friction in comparison to the present ceramic film. In the old art tungsten carbide formed the cutting edge and cutting surface and in direct contact with the coal, or coal seam with stone band or hard coal or shale. Hence, heat generated was not dissipated fast and the cutting edge was not cooled and there was more chance of a mug formation in the cutting edge which reduced the efficiency of cutting and ultimately contributed to the breaking/loosening the brazing joint and loss of tungsten carbide tips. DESCRIPTIOIN OF INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS Fig. 1 shows the ceramic coated coal drill bit anger body 1 as it is in east form by investment casting process. Body 1 is a NET SHAPE obtained from casting stage itself from molten eliminating forging, machining operations etc. Fig.2 shows a sectional view along line XY of Fig. 1. The bit auger body 1, which may be of steel, has a support 2 held in seat 3 by a silver brazing alloy 4. A ceramic coating 5 is deposited on the cutting surface 6 and cutting edge 7. Fig. 3 shows a comparative graphic representation of the hardness, and Fig.4 shows a comparison of the output of the bit of the present invention with that of the known art. I CLAIM: 1. A coated substrate for use in a coal auger drill bit comprising a metallic body (1), such as herein described, at least one shaped seat (3) provided on said metallic body, at least one shaped support (2) held to the said seat (3), a refractory metal based ceramic layer, or coating, on the working surface of the said support. 2. A coated substrate as claimed in claim 1 wherein said ceramic coating comprises at least one refractory metal selected from titanium, vanadium, chromium, tungsten, cobalt and molybdenum group. 3. A coated substrate as claimed in claim 2 wherein said coating is selected from a nitrate, carbide, oxide or boride or any combination thereof. 4. A coated substrate as claimed in claim 1 wherein said support is a metal selected from aluminium, chromium, nickel, vanadium, molybdenum, cobalt, tungsten, titanium and their alloys present singularly or in any combination or their carbides or both the combination of alloys, carbides, nitrides, oxides and borides or any combination thereof and includes super alloy. 5. A coated substrate as claimed in claim 1 wherein the support is held to the seat by a silver alloy flux. 6. A coated substrate as claimed in claim 5 wherein said silver alloy contains silver, copper, zinc, cadmium, manganese and nickel or any combination of these elements. 7. A coated substrate as claimed in claim 5 wherein said silver alloy is a thin sheet or film of 0.5 mm to 0.1 mm thickness. 8. A coated substrate as claimed in claim 1 wherein said coating has a thickness of 5 to 10 microns. 9. A coated substrate substantially as herein described and illustrated. A coated substrate for use in a coal auger drill bit comprising a metallic body (1), such as herein described, at least one shaped seat (3) provided on said metallic body, at least one shaped support (2) held to the said seat (3), a refractory metal based ceramic layer, or coating, on the working surface of the said support.

Documents:

52-cal-2002-granted-abstract.pdf

52-cal-2002-granted-claims.pdf

52-cal-2002-granted-correspondence.pdf

52-cal-2002-granted-description (complete).pdf

52-cal-2002-granted-drawings.pdf

52-cal-2002-granted-examination report.pdf

52-cal-2002-granted-form 1.pdf

52-cal-2002-granted-form 18.pdf

52-cal-2002-granted-form 2.pdf

52-cal-2002-granted-form 26.pdf

52-cal-2002-granted-form 3.pdf

52-cal-2002-granted-reply to examination report.pdf

52-cal-2002-granted-specification.pdf