GB1563728A

GB1563728A - Brazing tools

Info

Publication number: GB1563728A
Application number: GB3839576A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1976-09-16
Filing date: 1976-09-16
Publication date: 1980-03-26

Description

(54) IMPROVEMENTS IN OR RELATING TO BRAZING TOOLS (71) We, GENERAL ELECTRIC COMPANY, a corporation organised and existing under the laws of the State of New York, United States of America, of 1 River Road, Schenectady, State of New York United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The grinding of high strength, hard or abrasion resistant materials such as metals, cermets, stones, ceramics, filled polymers and rubber is generally performed by the use of metal bonded abrasive tools. These tools include a core on which are bonded high strength crystals such as diamonds or cubic boron nitride crystals. These crystals are normally bonded to the core by electroplating or brazing.These methods, however, result in voids between the crystals which trap grinding swarf and promote tool glazing, loading and uncontrollable premature tool failure.

Additionally, during use the crystals are pulled out of the bond due to their strength thus reducing the efficiency of the tool.

In the past, the only methods used to overcome these problems of premature failure and pullout were to heavily overplate or layer the brazing alloy. However, the thickened bond layer produced by these methods promoted smearing of the alloy over the cutting crystals during use and thus rendered the tool useless. Moreover, since these tools were monolayer composites, dressing of the abrasive crystals was not practical.

According to the invention a composite abrasive tool comprises: a carrier member, a plurality of abrasive crystals of diamond and/or cubic boron nitride crystals, a metallic layer bonded to said carrier member, said crystals being partially embedded in said metallic layer and a non-metallic laver overcoating said metallic layer and partially surrounding said crystals, said crystals being exposed from said non-metallic layer at the ends thereof opposite said carrier member.

The metallic layer may include nickel or , copper.

The invention is illustrated by way of example in the accompanying diagrammatic drawings wherein: Figure 1 is a perspective view, with certain portions broken away for clarity of illustration, of an abrasive grinding tool of the present invention; and Figure 2 is an enlarged fragmentary view of the tool in Figure 1 illustrating the bonding layers.

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will hereinafter be described in detail a preferred embodiment in many different forms, there is shown in the drawings and will hereinafter be described in detail a preferred embodiment of the invention, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.

Figure 1 illustrates an abrasive grinding tool 10 of the present invention. Tool 10 is of the wheel type and includes a cylindrical core 12 formed of steel or carbide and a .reduced diameter, steel or carbide arbor 14 extending from the core. Arbor 14 is inserted into and held by a chuck to rotate the tool.

As best illustrated in Figure 2, a multiplicity of crystals 16 is arranged about the periphery of the surface of core 12. Crystals 16 may be diamonds or cubic boron nitride crystals and are bonded to the core by a retaining layer 18. Layer 18 is 25% of the diamond thickness and may be produced by electroplating or brazing as described below. Overlying layer 18 and surrounding crystals 16 is an outer or overcoat nonmetallic layer 20 of filled epoxy or phenolic resin. Thus the non-metallic layer 20 has an exposed cylindrical surface and the ends of the crystals 16 and the exposed surface of the layer 20 together form an exposed tool surface for engagement with a work piece.

Tool 10 is illustrated as a cylindrical tool but it will be appreciated that other tool shapes for example mounted point, may also be utilized.

The tool 10 may be prepared by either a brazing technique or an electroplating technique. In the brazing technique the core 10 is prepared by vapor degreasing or similar cleaning technique. The core is then coated with a brazing flux paste which is tacky.

The abrasive crystals are sprinkled on the fluxed core surface to form a single layer of crystals and the tacky flux is thus utilized to hold the crystals in position on the core. The brazing and flux composition is preferably a mixture of Borax and water with L. M.

Nicrobraze Powder, 325 U. S. Standard mesh, available commercially from Wall Colmonoy, Detroit, Michigan.

The crystals may be uncoated or coated preferably with a composition of 1 to 1-1/2 weight per cent nickel produced by electroless deposition sodium hypophosphate (nickel with 5-10% phosphorus), electroless nickel phosphorus, additionally electrolytically overcoated with 13 to 14 w/o Ni-Co, nickel cobalt (30-45%). The method of overcoating the individual crystals is well known in the art. See, e.g., U.K. Patent No.

1,154,598.

The assembly of core, flux and diamond crystals is heated in a high temperature furnace, utilizing a nitrogen or hydrogen atmosphere at about 1050"C for a period of time ranging from about 2 to 30 minutes and brazed. The period of heating is a function of tool size and geometry.

After brazing, the tool is cleaned of surface boron gloss generated by the flux.

Subsequently, the tool (crystals) are overco ated with a fff SiC filled high temperature epoxy or other resin and cured in a conven tional resin curing oven. "fff" means triple fine i.e. 30 CL or less.

The final step is to dress off the excess resin surface thereby exposing the abrasive crystals.

For electroplating, the core is first cleaned in a strong alkali electrolytic clean ing solution. After cleaning, the core is flashed with electrolytic copper then rinsed in water to remove the copper salt strike solution.

The flashed tool is then placed in a diamond or cubic boron nitride crysal bed and the tool and bed are immersed in a Watts electrolytic nickel plating solution.

The crystals are thus initially tacked down to the core using the conventional electroplating technique. After initial tackdown, the tool is removed from the bed and solution and inspected for plating uniformity, reflashed with copper and overplated to 25% crystal height in a nickel bath solution at 20 ' amperes per square foot current density.

The thus plated tool is finally overcoated with epoxy or phenolic resin and dressed as described above.

Diamond crystals may be bonded to the core with either the brazing or electroplating process. Cubic boron nitride crystals are preferably bonded with the electroplating method since they tend to float during the brazing process thus militating against a good bond to the core.

The use of the non-metallic reinforcing layer of filled epoxy or phenolic resin with the metal bond permits nearly complete use of the abrasive crystals without bond interference or loading. Additionally, the metal bond layer 18 provides an excellent heat sink which cooperates with the crystal to defined good thermal paths for tools cooling by the core mass, and much better than in a conventional resin bonded which where the thermal paths are more terminus or ill defined.

A tool in accordance with the present invention thus provides a three-fold advance of the prior tools. The metallic layer firmly affixes the crystals to the tool core or carrier, and the non-metallic overcoat, which fills the spaces between crystals, supports each crystal against substantial fracture and also prevents wheel loading from workpiece debris. This unique combination permits the crystals to fracture at the limited area of the working surface during use to provide a highly abrasive surface and the non-metallic, layer chips away at the fracture to avoid premature failure or glazing of the abrasive surface.

Although two resinous compositions for the non-metallic layer have been described, those skilled in the art will be able to utilize other non-metallic reinforcing layer compositions to optimize performance of the grinding wheels without departing from the scope of the present invention as pointed out in the appended claims.

WHAT WE CLAIM IS: 1. A composite abrasive tool comprising: a carrier member, a plurality of abrasive crystals of diamond and/or cubic boron nitride crystals, a metallic layer bonded to said carrier member, said crystals being partially embedded in said metallic layer and a non-metallic layer overcoating said metallic layer and partially surrounding said crystals, said crystals being exposed from

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. diamond thickness and may be produced by electroplating or brazing as described below. Overlying layer 18 and surrounding crystals 16 is an outer or overcoat nonmetallic layer 20 of filled epoxy or phenolic resin. Thus the non-metallic layer 20 has an exposed cylindrical surface and the ends of the crystals 16 and the exposed surface of the layer 20 together form an exposed tool surface for engagement with a work piece. Tool 10 is illustrated as a cylindrical tool but it will be appreciated that other tool shapes for example mounted point, may also be utilized. The tool 10 may be prepared by either a brazing technique or an electroplating technique. In the brazing technique the core 10 is prepared by vapor degreasing or similar cleaning technique. The core is then coated with a brazing flux paste which is tacky. The abrasive crystals are sprinkled on the fluxed core surface to form a single layer of crystals and the tacky flux is thus utilized to hold the crystals in position on the core. The brazing and flux composition is preferably a mixture of Borax and water with L. M. Nicrobraze Powder, 325 U. S. Standard mesh, available commercially from Wall Colmonoy, Detroit, Michigan. The crystals may be uncoated or coated preferably with a composition of 1 to 1-1/2 weight per cent nickel produced by electroless deposition sodium hypophosphate (nickel with 5-10% phosphorus), electroless nickel phosphorus, additionally electrolytically overcoated with 13 to 14 w/o Ni-Co, nickel cobalt (30-45%). The method of overcoating the individual crystals is well known in the art. See, e.g., U.K. Patent No. 1,154,598. The assembly of core, flux and diamond crystals is heated in a high temperature furnace, utilizing a nitrogen or hydrogen atmosphere at about 1050"C for a period of time ranging from about 2 to 30 minutes and brazed. The period of heating is a function of tool size and geometry. After brazing, the tool is cleaned of surface boron gloss generated by the flux. Subsequently, the tool (crystals) are overco ated with a fff SiC filled high temperature epoxy or other resin and cured in a conven tional resin curing oven. "fff" means triple fine i.e. 30 CL or less. The final step is to dress off the excess resin surface thereby exposing the abrasive crystals. For electroplating, the core is first cleaned in a strong alkali electrolytic clean ing solution. After cleaning, the core is flashed with electrolytic copper then rinsed in water to remove the copper salt strike solution. The flashed tool is then placed in a diamond or cubic boron nitride crysal bed and the tool and bed are immersed in a Watts electrolytic nickel plating solution. The crystals are thus initially tacked down to the core using the conventional electroplating technique. After initial tackdown, the tool is removed from the bed and solution and inspected for plating uniformity, reflashed with copper and overplated to 25% crystal height in a nickel bath solution at 20 ' amperes per square foot current density. The thus plated tool is finally overcoated with epoxy or phenolic resin and dressed as described above. Diamond crystals may be bonded to the core with either the brazing or electroplating process. Cubic boron nitride crystals are preferably bonded with the electroplating method since they tend to float during the brazing process thus militating against a good bond to the core. The use of the non-metallic reinforcing layer of filled epoxy or phenolic resin with the metal bond permits nearly complete use of the abrasive crystals without bond interference or loading. Additionally, the metal bond layer 18 provides an excellent heat sink which cooperates with the crystal to defined good thermal paths for tools cooling by the core mass, and much better than in a conventional resin bonded which where the thermal paths are more terminus or ill defined. A tool in accordance with the present invention thus provides a three-fold advance of the prior tools. The metallic layer firmly affixes the crystals to the tool core or carrier, and the non-metallic overcoat, which fills the spaces between crystals, supports each crystal against substantial fracture and also prevents wheel loading from workpiece debris. This unique combination permits the crystals to fracture at the limited area of the working surface during use to provide a highly abrasive surface and the non-metallic, layer chips away at the fracture to avoid premature failure or glazing of the abrasive surface. Although two resinous compositions for the non-metallic layer have been described, those skilled in the art will be able to utilize other non-metallic reinforcing layer compositions to optimize performance of the grinding wheels without departing from the scope of the present invention as pointed out in the appended claims. WHAT WE CLAIM IS:

1. A composite abrasive tool comprising: a carrier member, a plurality of abrasive crystals of diamond and/or cubic boron nitride crystals, a metallic layer bonded to said carrier member, said crystals being partially embedded in said metallic layer and a non-metallic layer overcoating said metallic layer and partially surrounding said crystals, said crystals being exposed from

said non-metallic layer at the ends thereof opposite said carrier member.

2. A tool of Claim 1, wherein said metallic layer includes nickel.

3. A tool of Claim 1, wherein said metallic layer includes copper.

4. A tool of Claims 1-3, wherein said metallic layer thickness is about 25% of the thickness of the crystals.

5. A tool of Claims 1-4, wherein said crystals are diamond crystals.

6. A tool of Claims 1-4, wherein said crystals are cubic boron nitride crystals.

7. A tool of Claims 1-6, wherein said crystals are individually coated with a composition of 1 to 1-1/2 w/o electrolessly deposited nickel.

8. A tool of Claims 1-7, wherein said tool is a grinding tool.

9. ~ A tool of Claims 1-8, wherein said non-metallic layer is a resinous composition.

10. A tool of Claim 9, wherein said resinous composition is a filled epoxy resin.

11. A tool of Claims 9 or 10, wherein said resinous composition is a phenolic resin.

12. The tool of Claims 1-11, wherein said non-metallic layer is a resin layer and has an exposed surface, said exposed ends of said crystals and said exposed resin surface together forming an exposed tool surface for engagement with a workpiece.

13. The tool of Claim 12 wherein said abrasive crystals are disposed about said carrier in a single layer of crystals.

14. A method of fabricating a composite abrasive tool according to claim 1 comprising: bonding a plurality of abrasive crystals onto a core with a metallic layer; and overcoating said metallic bond layer and filling the interstices between crystals with a non-metallic reinforcing layer to reinforce said crystals.

15. The method of Claim 14 wherein said non-metallic reinforcing layer is a resinous composition.

16. An abrasive tool substantially as described.

17. A method of fabricating a composite abrasive tool substantially as described.