Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
  • B24D3/02—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent
  • B24D3/20—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially organic
  • B24D3/28—Resins or natural or synthetic macromolecular compounds
  • B24D3/30—Resins or natural or synthetic macromolecular compounds for close-grained structure
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
  • B24D3/02—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent
  • B24D3/20—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially organic
  • B24D3/28—Resins or natural or synthetic macromolecular compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
  • B24B5/00—Machines or devices designed for grinding surfaces of revolution on work, including those which also grind adjacent plane surfaces; Accessories therefor
  • B24B5/18—Machines or devices designed for grinding surfaces of revolution on work, including those which also grind adjacent plane surfaces; Accessories therefor involving centreless means for supporting, guiding, floating or rotating work
  • B24B5/22—Machines or devices designed for grinding surfaces of revolution on work, including those which also grind adjacent plane surfaces; Accessories therefor involving centreless means for supporting, guiding, floating or rotating work for grinding cylindrical surfaces, e.g. on bolts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
  • B24D3/02—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent
  • B24D3/04—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic
  • B24D3/06—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic metallic or mixture of metals with ceramic materials, e.g. hard metals, "cermets", cements
  • B24D3/10—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents the constituent being used as bonding agent and being essentially inorganic metallic or mixture of metals with ceramic materials, e.g. hard metals, "cermets", cements for porous or cellular structure, e.g. for use with diamonds as abrasives
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
  • B24D3/34—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents characterised by additives enhancing special physical properties, e.g. wear resistance, electric conductivity, self-cleaning properties
  • B24D3/342—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents characterised by additives enhancing special physical properties, e.g. wear resistance, electric conductivity, self-cleaning properties incorporated in the bonding agent
  • B24D3/344—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents characterised by additives enhancing special physical properties, e.g. wear resistance, electric conductivity, self-cleaning properties incorporated in the bonding agent the bonding agent being organic
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
  • B24D3/00—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents
  • B24D3/34—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents characterised by additives enhancing special physical properties, e.g. wear resistance, electric conductivity, self-cleaning properties
  • B24D3/346—Physical features of abrasive bodies, or sheets, e.g. abrasive surfaces of special nature; Abrasive bodies or sheets characterised by their constituents characterised by additives enhancing special physical properties, e.g. wear resistance, electric conductivity, self-cleaning properties utilised during polishing, or grinding operation

Definitions

• Polycrystalline diamond compacts include a polycrystalline diamond layer bonded to a tungsten carbide substrate.
• the polycrystalline diamond layer provides high hardness and abrasion resistance, while the tungsten carbide layer improves the toughness of the composite.
• PDC's are often employed as the cutting tips for boring bits used to drill into the earth for natural resources.
• Resin bond grinding wheels with diamond abrasive particles can be used to grind and finish PDC to its final specified dimensions.
• PDC is extremely difficult to grind because of the interface of the two dissimilar hardness materials.
• the diamond abrasive in the resin bonded grinding wheel dulls very quickly.
• the tungsten carbide substrate loads the grinding wheel reducing the ability of the abrasive wheel to further grind the
• the invention resides in a method of grinding comprising: contacting a polycrystalline diamond compact with a grinding wheel; the grinding wheel comprising diamonds, a resin binder, and a mixture of hard filler particles and soft filler particles; and wherein the diamonds comprise a diamond concentration from 175 percent to 225 percent based on volume, the resin binder comprises 30 percent to 40 percent based on volume, a ratio of hard filler particles to soft filler particles in the mixture is from 85: 15 to 15:85, and the mixture of hard filler particles and soft filler particles comprises 5 percent to 30 percent based on volume.
• the invention resides in an abrasive article comprising: a grinding wheel, the grinding wheel comprising diamonds, a resin binder, and a mixture of hard filler particles and soft filler particles; and wherein the diamonds comprise a diamond concentration from 175 percent to 225 percent based on volume, the resin binder comprises 30 percent to 40 percent based on volume, a ratio of hard filler particles to soft filler particles in the mixture is from 85: 15 to 15:85, and the mixture of hard filler particles and soft filler particles comprises 5 percent to 30 percent based on volume.
• FIG. 1 shows a centerless grinding process with a resin bonded grinding wheel operating to grind a PDC to its final diameter.
• FIG. 2 shows the grinding results for the inventive resin bonded grinding wheel versus the comparative resin bonded grinding wheel with different dressing frequency.
• the centerless grinder includes a resin bonded grinding wheel 12, a regulating wheel 14, and a support 16 for holding a PDC 18 between the two wheels.
• the PDC includes a polycrystalline diamond layer 20 bonded to a tungsten carbide substrate 22.
• the speed at which the PDC will traverse through the grinding interface between the two wheels is controlled by the helix angle a between the axis of the resin bonded grinding wheel 12 and the axis of the regulating wheel 14 in combination with the rotational speed of the regulating wheel.
• Prior art resin bonded grinding wheels require constant dressing of the outer surface 26 with a carborundum stone to maintain the ability of the resin bonded grinding wheel to grind the polycrystalline diamond layer.
• the high concentration diamond portion can be an outer annulus of the grinding wheel, a segmented portion thereof, or the entire grinding wheel.
• Suitable diamonds for use in the abrasive wheel include, for example, natural diamond, synthetic diamond, resin bond diamonds, metal bond diamonds, diamond abrasive powder, resin bonded or vitrified bonded diamond agglomerates of the foregoing, and combinations of all of the foregoing.
• the diamond concentration is very high.
• the diamond concentration as a volume percent of the total volume of the high concentration diamond portion of the grinding wheel is from 175% to 225% or from 180% to 200%. Diamond concentrations less than 175% do not reduce the need for dressing and concentrations greater than 225% become difficult to bond with sufficient integrity.
• the diamonds may be coated or uncoated with a metal such as nickel or copper.
• the coating weight percent should be less than 40%>, or less than or equal to 30%. Excessive coating amounts reduces the diamond concentration to too low of a level and does not result in reduced dressing of the resin bonded grinding wheel during use.
• the size of the diamonds, if not agglomerated, should be between 60/80 mesh size to 200/230 mesh size. Ranges above and below these limits do not provide the requisite packing density to achieve the desired diamond concentration.
• Resin bond diamonds may be suitable, especially if agglomerated, the diamonds are preferred to be metal bond diamonds.
• Resin bond diamonds are generally too weak and friable to be used in a resin bonded grinding wheel to grind PDC.
• Metal bond diamonds are available in strengths from friable (weaker) to less friable (stronger). Such strength rating is qualified by various suppliers using different designations. In order to expose fresh diamonds more effectively, weaker metal bond diamonds are preferred. For example, if using diamonds from ABC Superabrasives, the strength is rated on a scale from ABS 2 (weak) to ABS 9 (strong). When using ABC Superabrasive diamonds, the diamonds are desirably ABS 2 or ABS 3.
• Suitable strength diamonds can include WSG 200, WSG300, WSG400, and WSG500.
• LANDS Superabrasives has strengths designated as LS200, LS230, LS250, LS260, LS270, and LS290.
• Suitable strength diamonds can include LS200, LS230, and LS240. In general, the bottom 50% of the strength scale for a given supplier's metal bond diamonds are suitable.
• Suitable resin binders for use with the diamond abrasive particles include formaldehyde-containing resins, such as phenol formaldehyde, novolac phenolics and especially those with added crosslinking agent (e.g., hexamethylenetetramine), phenoplasts, and aminoplasts; unsaturated polyester resins; vinyl ester resins; alkyd resins, allyl resins; furan resins; epoxies; polyurethanes; cyanate esters; and polyimides.
• the amount of binder resin used in the resin bonded grinding wheel is from about 30% to about 40% by volume such as approximately 35% by volume of the high concentration diamond portion.
• the amount of resin should be sufficient to fully wet the surfaces of all the individual particles during manufacturing such that a continuous resin structure, substantially devoid of porosity, is formed with the inorganic components discretely bonded throughout, which comprises the mechanical structure of the grinding wheel.
• Suitable filler additives can include reinforcing particles, grinding aids, dessicants, colorants, and lubricants. As mentioned, both hard and soft filler particles are used in addition to the diamonds to reinforce and control the breakdown rate of the grinding wheel.
• Hard filler particles (excluding diamonds) are those having a Mohs hardness of 7 or greater.
• Suitable hard filler particles include aluminum oxide, silicon carbide, zirconia, ceramic alpha alumina particles typically derived from boehmite sol gels, or other abrasive particles having the requisite Mohs hardness.
• Soft filler particles have a Mohs hardness of 5 or less.
• Suitable soft fillers include petroleum coke, pyrophyllite, cryolite, lime, graphite, refractory grog, ball clay, copper, or talc.
• the volume ratio of the hard to soft filler particles is from (can be)15:85 to 85: 15, or from 30:70 to 70:30, or from 40:60 to 60:40.
• Suitable hard filler particle sizes include sizes equal to or less than about 30 microns, such as 600, 800, or 1000 ANSI mesh equivalents.
• Suitable soft filler particles sizes include 100 mesh or finer.
• the soft particles can have a fine fraction and coarse fraction if desired. The fine fraction can be finer than 280 mesh and the coarse fraction can be from 100 to 180 mesh.
• volume fraction of the coarse to fine particles can be 50:50 to 70:30. Too large a volume fraction of hard filler particles impedes breakdown leading to heat buildup and glazing of the grinding wheel, and too large a volume fraction of soft filler particles undesirably increase the wear rate of the grinding wheel.
• the volume percent of a mixture of hard filler particles and soft filler particles used in the resin bonded grinding wheel is from 5% to 30%, or from 8% to 20% of the high concentration diamond portion.
• fillers can include fibrous and plate-like materials such as carbon or glass whiskers and mica.
• Grinding aids such as cryolite, potassium tetrafluoroborate (KBF4), polyvinyl chloride, lignosulfonates, and blends thereof.
• Colorants such as organic or inorganic pigments or dies may be incorporated into the grinding wheel.
• Example 1 The grinding wheels of Examples 1 , 7, 9 to 14 and Comparative Examples 1A to 6 A were prepared and tested to evaluate their grinding performance on PDC. Examples 1 and Comparative Example 1 A were evaluated under different grinding wheel dressing procedures. The weight percentage compositions of the various grinding wheels are shown in Table 2.
• Each composition listed in Table 2 was thoroughly mixed for 4 hours in a 1000 ml polyethylene mixing jar and a roller mill stand (2-Bar Tumbler Base, C&M Topline Inc., Goleta CA) set at approximately 180 rpm.
• the die cavity in the five-piece, ring-punch double-compaction steel mold was filled with the mixed abrasive composition by rotating the die assembly on a circular table while pouring the abrasive powder mixture into the annular cavity around the core.
• the powder was then smoothed and leveled with a plastic straightedge tool, and the filled mold was closed with the upper ring punch.
• the filled mold was placed in a 200-ton heated-platen hydraulic press with the platen set point temperature set at 350 degrees F. The press platens were closed to bring the ring-punch surfaces flush against the mold shell. A magnetic thermometer was attached to the side of the mold shell and the mold temperature was monitored. When the mold shell reached 350 degree F, the mold was held closed under pressure for 20 minutes.
• the mold assembly was removed from the heated-platen press and placed on a water-cooled steel table and allowed to cool to room temperature.
• the mold shell was stripped from the formed wheel section using a 50-ton hydraulic press and steel spacers.
• the formed wheel sections were cured in air according the following schedule. One hour ramp to 150 degree F, one hour soak at 150 degree F, 4 hour ramp to 350 degree F, seven hour soak at 350 degree F, followed by 3 hour cool to room temperature.
• the wheel sections were surface ground to thickness and then two sections were bonded together using epoxy adhesive.
• the bonded structure was then trued and dressed using a 40/60 grit SiC grinding wheel on a 3M E228 truing and dressing machine to make the final test grinding wheels
• Example 1 and Comparative Example A were ground using a centerless grinder (Acme Model 47 Centerless Grinder, Acme Manufacturing Company, Auburn Hills, Michigan) using the 8" diameter x 2.5" wide resin bond diamond wheels of Example 1 and Comparative Example A.
• the PDCs were mounted in a spring-loaded fixture to hold them during the grinding process.
• the grinding wheel speed was about 4000 SFPM and the regulating wheel speed was about 55 SFPM and the helix angle of the regulating wheel was set to about 3 degrees. This provided a grinding contact time of about 5.5 seconds per load of PDC.
• testing was performed using either 2 PDCs per load or 3 PDCs per load as noted below:
• Comparative Example 1 A is a prior art resin bonded grinding wheel sold by 3M having part number MMMRBDW26435-R. Comparative Examples 2A and 3A utilized non-agglomerated resin bond diamonds, which were too friable and sheared off on the outer surface of the grinding wheels when grinding PDC leading to excessive glazing and poor cut. Comparative Example 4A used the same diamond concentration of Comparative Example 1 A of approximately 125% and a brittle soft filler particles instead of ductile soft filler particles. The need for dressing was reduced, but not significantly. Comparative Example 6 A used the same 125% diamond concentration but the fine grade diamonds were replaced with courser grades. No significant performance difference was noted. Example 1 (185%), Example 7 (225%), Example 9 (200%), and Example 10
• the cut rate of the inventive grinding wheel was significantly greater than that of the comparative grinding wheel when dressing was employed every pass (0.0027 cubic inches versus 0.0023 cubic inches), and the inventive wheel had a good level of cut rate when dressing was employed only every 10 th pass (0.0013 cubic inches versus 0.0008 cubic inches).
• the cut rate of the inventive wheel with only every 10 th path dressing was approximately 48% of the single pass cut rate versus approximately 35% for the comparative wheel 1 A.
• Example 1 was evaluated at a customer who produces PDC's using centerless grinding.
• the centerless grinding application reduced the outside diameter of the PDC's to the final required diameter/tolerance and was conducted under a coolant flood.
• the existing grinding wheel that was previously used by the customer required frequent or substantially continuous abrasive media dressing to maintain stock removal with the existing diamond abrasive grinding wheel.
• the Example 1 grinding wheel was installed on the centerless grinder, the PDC's were processed using the same previous grinding conditions of the prior existing diamond abrasive grinding wheel. No external abrasive dressing media was used on the Example 1 grinding wheel during the centerless grinding of the PDC's.
• the centerless grinding operations were able to continue to produce PDC's to the required finished size using the existing process parameters while achieving the same production rates without the use of abrasive wheel dressing or conditioning media on the surface of the Example 1 grinding wheel during the production of the PDC's.
• the total absence of dressing media while grinding PDC's had not been previously possible under the existing process conditions for any prior grinding wheel used.
• the Example 1 grinding wheels were fully consumed to the core while grinding the PDC's and did not become glazed over or inoperative at any point in the grinding process.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Inorganic Chemistry (AREA)
• Polishing Bodies And Polishing Tools (AREA)

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• 2012
  • 2012-04-17 CA CA2833342A patent/CA2833342C/en active Active
  • 2012-04-17 EP EP12774388.8A patent/EP2699387B1/en active Active
  • 2012-04-17 US US14/111,280 patent/US20140057534A1/en not_active Abandoned
  • 2012-04-17 BR BR112013026817A patent/BR112013026817A2/pt not_active Application Discontinuation
  • 2012-04-17 RU RU2013146357/02A patent/RU2567165C2/ru not_active IP Right Cessation
  • 2012-04-17 WO PCT/US2012/033880 patent/WO2012145284A2/en active Application Filing
  • 2012-04-17 CN CN201280018778.4A patent/CN103492126B/zh active Active

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