Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/14—Anti-slip materials; Abrasives
  • C09K3/1436—Composite particles, e.g. coated particles
  • C09K3/1445—Composite particles, e.g. coated particles the coating consisting exclusively of metals

Definitions

• Abrasive wheels containing diamonds in a polyimide binder have met with wide acceptance in industry, particularly for wet grinding cemented carbide. These polyimide grinding wheels have had significant advantage over the corresponding phenolic grinding wheels. Phenolic resin grinding wheels may be improved by using diamonds which have a smooth coating of a metal such as copper or nickel, and generally exhibit an improvement in grinding ratio of 80-100% as compared with a similar grinding wheel which contains uncoated diamonds. However, when these same smooth metal coated diamonds are incorporated into polyimide resin bonded grinding wheels only a modest improvement in grinding ratio of 10 to 20% is obtained.
• H. B. Dyer and A. R. ,Roy 1 indicate that four characteristics are considered in preparing a commercial synthetic diamond grit: (a) surface; (b) shape; (c) strength; (d) uniformity.
• Surface is defined as being of three types in which the diamonds have (1) flat smooth faces on single crystals, (2) nonflat smooth faces with re-entrant angles on single crystals, and (3) surfaces indicative of polycrystalline aggregates.
• Shape is defined as A New Synthetic Diamond Grit and Its Application to Heavier Carbide Grinding Operations in Diamond Abrasives and Tools, .1. Bur-ls, editor, Pergamon Press, Ltd, London, 1964, p. Ind.
• Diamonds having a Tyler screen size of from 50 to 200 generally are best for the present purpose.
• the metal coating can readily be applied to the diamonds by cleaning the diamonds such as with aqua regia.
• the diamonds are placed in a slowly rotating barrel containing a metal plating solution.
• the barrel is rotated and a suitable Voltage potential is applied to cause electrodeposition of the metal over the surface of the diamond crystals.
• the metal should be applied to give a 45 to percent increase in weight to the uncoated diamonds which results in an average increase in a linear dimension of the diamonds of from 10 to 15 percent.
• the resultant metal coating is barbed in character.
• the barbs vary from 0.3 to 15 microns in height and width at the base and due to their somewhat complex pyramidal t0 conical nature cover most of the surface of the diamond.
• the preferred metals for forming the coating are nickel, copper, tantalum, niobium and cobalt. A further description of metal coated diamonds may be found in Belgian Pat. No. 686,805.
• the polyimides used herein are powders of the aromatic polyimides. Generally, these aromatic polyimides have the formula I] H H o o o where R, R and R are organic radicals selected from the group consisting of aromatic, aromatic heterocyclic, bridged aromatic and substituted groups thereof.
• Preferred Rs include as @Q -Q wherein the bonds to the carbonyl groups shown are arranged in pairs with the carbonyl groups of each pair on adjacent or peri carbon atoms.
• Preferred R s include Q @mQw-Q- and When pyromellitic dianhydride is used at least 14 mole percent of the diamines used should contain two aromatic rings.
• Preferred R s include wherein the bonds to the carbonyl groups are arranged in pairs on adjacent or peri carbon atoms.
• R is selected from the group consisting of carbon 1n an alkylene group or perfluorinated alkylene group of from l-3 carbon atoms, oxygen, silicon in Si(R where R is lower alkyl or aryl and R is R or hydrogen.
• the polyimide powder should have a surface area of at least 0.1 square meter/ gram and preferably greater than 2 square meters/gram, as measured by adsorption of nitrogen from a gas stream of nitrogen and helium at liquid nitrogen temperature, using the technique described by F. M. Nelsen and F. T. Eggertson (Anal. Chem. 30, 1387 [1958]). Sample weights are in the order of 0.1- 3.5 g.
• the thermal conductivity detector is maintained at 40 C. and the flow rate is approximately 50 mL/min.
• the gas mixture used is parts by weight nitrogen and 90 parts by by weight helium.
• the polyimide should have an inherent viscosity of at least 0.1 and preferably from 0.3 to 5, as measured at 35 C. from a 0.5 percent by weight solution in 96% sulfuric acid. If the polyimide is not soluble to the extent of 0.5 percent in 96% sulfuric acid at 35 C. and a strong article can be coalesced therefrom it is assumed to have an inherent viscosity of greater than 0.1.
• the molded abrasive composition generally contains from 6 to 35 volume percent diamonds, from 3 to 17 /2 volume percent metal coating on the diamonds, and from 47 to 91 volume percent aromatic polyimide.
• part of the resin phase can be replaced with up to 50 volume percent as based on the resin phase of another abrasive such as silicon carbide, or aluminum oxide, or a filler such as glass, or a metal in the form of metal powder or metal fibers.
• the diamond containing composition is made up as a rim with the diamonds embedded in a coalesced polyimide matrix which rim is then mounted on a core.
• the core preferably is aluminum, but other materials such as aluminum filled phenol-formaldehyde resin may be used.
• the abrasive composition is further compacted at 50,000 p.s.i. while being maintained at 300 C. to make a preform.
• the resultant preform and mold is then removed from the press and heat-treated for 12 hours in a nitrogen atmosphere at 300 C. to complete imidization of the resin.
• the preform rim is then free sintered by heating at 450 C. for 25 minutes in a nitrogen atmosphere.
• the rim thus formed is fitted over an aluminum core coated C-7 epoxy adhesive made by Armstrong Products Company, and the adhesive is cured.
• the wheels are 6-inch diameter by inch wide DlAl peripheral wheels.
• the diamond-containing composition is prepared by admixing 25 volume percent of diamonds and 75 volume percent of metal coating and a mixture of grams of 400 grit silicon carbide and 42 grams of BRP 5727 medium flow novolac type phenol-formaldehyde resin useful as a wheel binder as made by Union Carbide Corporation. About 34.5 grams of this composition are placed in the cavity formed between a 6-inch diameter circular mold and a concentric 5% inch diameter core and the mold is placed in a press having platens heated to 177 C. A pressure of 3,000 p.s.i. is applied to the composition for 30 minutes during which time the composition is maintained at 177 C. The mold is removed from the press and the rim given a cure in air using the following cycle:
• the wheels are tested by mounting on a Gallmeyer and Livingston No. 28 grinder and, after truing and running-in on carbide, are used to surface grind a work piece of Walmet WA-S cemented carbide (C-5 grade) 2 inches by 9 inches or 4.2 inches by 11.2 inches under the following conditions:
• b the same diamonds as in a but with a smooth coating of nickel averaging in thickness approximately 1015% of the average linear dimension of the diamonds;
• c the diamonds of a but with a barbed coating of nickel averaging in thickness 1015% of the average linear dimension of the diamonds, which barbs are approximately 0.3 to 8 microns in diameter at the base and 0.3 to 8 microns in height with several smaller protrusions on each barb;
• e the d diamonds but with a barbed coating of nickel averaging in thickness -15% of the average linear dimension of the diamonds, which barbs are approximately to microns in diameter at the base with some small protrusions from each large barb.
• An abrasive composition comprising from 6 to 35 volume percent of '50 to 200 Tyler grit size synthetic diamonds, which diamonds are coated with a barbed metal coating which averages in thickness from 10 to 15 percent of the average linear dimension of the diamonds, and which barbs are from 0.3 to 15 microns in height and from 0.3 to 15 microns in width at the base, which metal coating comprises from 3 to 17 /2 volume percent of said abrasive composition, and from 47 to 91 volume percent a phase, at least 50 volume percent of which is a coalesced aromatic polyimide.
• composition of claim 1 wherein the composition is in the form of a grinding wheel.
• composition of claim 2 wherein the aromatic polyimide is prepared from 4,4'-oxydianiline and pyromellitic dianhydride.
• composition of claim 3 wherein said barbed metal coating is nickel.
• composition of claim metal coating is copper.
• composition of claim 3 wherein said barbed metal coating is tantalum.
• composition of claim metal coating is niobium.
• composition of claim metal coating is cobalt.

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• Chemical & Material Sciences (AREA)
• Composite Materials (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Polishing Bodies And Polishing Tools (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=25204807

Family Applications (1)

Country Status (4)

Cited By (6)

Families Citing this family (3)

• 1969
  • 1969-03-26 US US810826A patent/US3585013A/en not_active Expired - Lifetime
• 1970
  • 1970-03-24 JP JP45024164A patent/JPS4823597B1/ja active Pending
  • 1970-03-26 GB GB04821/70A patent/GB1268460A/en not_active Expired
  • 1970-03-26 DE DE7011371U patent/DE7011371U/de not_active Expired
  • 1970-03-26 DE DE2014863A patent/DE2014863C3/de not_active Expired

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