WO1994002297A1

WO1994002297A1 - Hard alloys for tools in the wood industry

Info

Publication number: WO1994002297A1
Application number: PCT/SE1993/000633
Authority: WO
Inventors: Enrico Galli
Original assignee: Sandvik Ab
Priority date: 1992-07-17
Filing date: 1993-07-16
Publication date: 1994-02-03
Also published as: SE9202194D0

Abstract

According to the invention there is now provided a sintered hard alloy for tools for cutting wood. The alloy according to the invention comprises 30-98 volume-% hard constituents in a binder-phase based on nickel and/or cobalt. The hard constituents comprise oxides, carbides, nitrides and/or borides of Al, Zr, Si and/or Ti, preferably Al2O3, ZrC, ZrO2, SiC, Si3N4 and/or TiB2 with a mean grain size < 1.5 νm, preferably < 1.0 νm. The binder-phase comprises in solution, in weight-%, Co max 90, Ni max 90, Cr 5-45.

Description

Hard allovs for tools in the wood industry

The present invention relates to new hard materials with excellent properties for tools in the wood indus- try. More particularly, the invention relates to hard materials in which a corrosion and oxidation resistant phase has been distributed in a corrosion and oxidation resistant monophase binder based on cobalt and/or nickel and chromium. Reconstituted wood products, such as medium density fibreboard and chipboard, are, together with solid wood, the main raw materials in the furniture industry. They are also used to some extent in the housing indus¬ try. These products are machined with a variety of tool materials, from high speed steel to cemented carbide to polycrystalline diamond. A leading role is being played by tools made with cemented carbide.

Cemented carbide grades used for woodworking tools consist generally of WC and cobalt as a binder to hold together the WC crystals. Sometimes small amounts of other carbides are added to improve control of the grain size distribution.

Abrasion has been thought to be the primary mecha- nism of tool wear when machining reconstituted wood products and solid wood. Recent work has proven that chemical mechanisms such as corrosion and oxidation play a significant role in the degradation of cutting edges, as the temperature increases dramatically during the machining process.

The chemical degradation of WC-Co tools is at least a two stage process when machining wood products.

At first the degradation occurs at a low tempera¬ ture (300-500°C) , in the early period of cutting. As the tool temperature rises, the wood products decompose and numerous chemicals are introduced in the cutting environment. Up to 213 different compounds have been identified upon the destructive distillation of wood. The machining of medium density fibreboard and particle board produces even more decomposition products. These products contain also a binder such urea, formaldehyde, wax and glue fillers and extenders and possibly chemi¬ cals added as flame retardants. The decomposition pro¬ ducts formed are highly corrosive and attack the co- bait-binder that holds the grains together. When this occurs, the WC-grains are removed by chemical action and the cutting edge loses its sharpness and its cut¬ ting capability.

As the temperature rises above 500°C, the decompo- sition products are volatilised and removed, but degra¬ dation of the cutting edge continues by oxidation of the WC grains and the cobalt matrix in air. The oxides formed are readily removed by mechanical action, re¬ sulting in a fast degradation of the sharpness of the cutting edge.

The present invention relates to new types of hard materials with excellent properties regarding corrosion and oxidation resistance particularly satisfying the different needs of the wood industry. Resistance to corrosion and oxidation has been achieved by alloying a cobalt and/or nickel and chro¬ mium binder and distribute in it hard constituents with fine grain size to permit an optimal anchorage of the grains to the binder. The material according to the invention comprises 30 to 98 vol-% of oxides, carbides, nitrides and/or borides of Al, Zr, Si and Ti, preferably AI2O3, ZrC, Zrθ2/ SiC, Si3N4 and/or TiB2. The mean grain size of said hard constituents is <1.5 μ , preferably <1.0 μ , most preferably <0.7 μ . The hard constituent grains are preferably pre-coated with cobalt and/or nickel. The binder comprises in solution in weight-%, Co max 95, Ni max 95 and Cr 5-45 and, in addition, WC max 30, ' Mo max 15, Al max 2, Mn max 10, Si max 2, Cu max 10, Fe max 20, Ag max 5.and Au max 10.

The materials according to the invention are manu¬ factured by powder metallurgical methods known per se namely milling, pressing and sintering. The alloy is preferably sintered under pressure. The material according to the invention is particu¬ larly useful for machining of particle board, chip board medium density fibre board and dry woods. For cutting of particle board, chip board and medium den¬ sity fibre board the binder phase content shall be <10 % by volume and for cutting of solid woods the binder phase content shall be 10-70 % by volume.

Example 1

An alloy consisting of 65 % by volume AI2O3 in a binder phase containing 19 % by volume Co, 14 % by volume Cr and 2 % by volume WC was tested against a straight WC-Co grade with 37 % by volume Co and a cor¬ rosion resistant cemented carbide containing 56 % by volume WC, 35 % by volume Co and 9 % by volume Cr. Chipboard 20 mm covered on both sides with a 0.16 mm layer of melamine was machined using a milling cut¬ ter and the following cutting data:

Diameter of the cutter 125 mm

Cutting depth 3 mm Cutting speed 40 m/s

Feed 6 m/min

Edge angle 55°

Rake angle 20°

Clearance angle 15° The edge wear and the surface finish of the chip¬ board were measured at 2000, 5000, 20000, 40000 and 60000 meters with the following result expressed as average wear in μm at different cutting lengths. Cutting length,

The material according to the invention shows sig¬ nificantly lower wear than the other two types of ce¬ mented carbide. The surface finish produced by the inserts in the material according to the invention was still accept¬ able after 60000 meters whereas for the other two types was found unacceptable after 40000 and 20000 meters, respectively.

Claims

1. Sintered hard alloy for tools for cutting wood comprising 30-98 volume-% hard constituents in a binder-phase based on Ni and/or Co c h a r a c t e r i z e d in that said hard consti¬ tuents comprise oxides, carbides, nitrides and/or borides of Al, Zr, Si and/or Ti, preferably AI2O3, ZrC, Zrθ2» SiC, and/or TiB2 with a mean grain size <1.5 μm, preferably <1.0 μm and that said binder-phase comprises in solution, in weight-%, Co max 95, Ni max 95, Cr 5-45.

2. Sintered hard alloy according to claim 1 c h a r a c t e r i z e d in that said binder-phase comprises in solution, in weight-%, WC max 30, Mo max 15.

3. Sintered hard alloy according to any of the pre¬ ceding claims c h a r a c t e r i z e d in that said binder-phase further comprises in solution, in weight- %, Al max 2, Mn max 10, Si max 2, Cu max 10, Fe max 20, Ag max 5 and Au max 10.

4. Sintered hard alloy according to any of the pre¬ ceding claims c h a r a c t e r i z e d in that the hard constituent grains are pre-coated with cobalt and/or nickel.

5. Use of the sintered hard alloy according to any of the preceding claims with a binder-phase content of max 10 vol-% for cutting of chipboard, medium density fibreboard and particle board.

6. Use of the sintered hard alloy according to any of claims 1-4 with a binder-phase content of 10-70 % by volume for cutting of solid dried wood.