WO2001031075A1 - Cemented carbide tool for woodworking - Google Patents

Abstract

The present invention relates to a cemented carbide with excellent properties for tools for woodworking. This has been achieved by using a WC powder with extremely fine grain size and cobalt and/or nickel powders made from the polyol process. The cemented carbide is particularly useful for the machining of chip board, particle board and medium and high density fibreboard (MDF/HDF).

Description

Cemented carbide tool for woodworking

The present invention relates to a cemented carbide with excellent properties for use as tool for woodworking. More particularly, the invention relates to a sintered, very fine-grained cemented carbide material in which a corrosion and oxidation resistant phase has been distributed in a monophase binder based on nickel and cobalt and of one or more of the following metals : chromium, molybdenum, iron and vanadium. Most particularly, the binder is based on nickel and/or cobalt powders made by the polyol process .

Cemented carbide is usually manufactured by blending the WC, Ni, Co and other powderous sources and an organic binder (typically wax-based) and mixing these in a ball mill before spray-drying the slurry into a flowable ready-to-press powder. But most of the powder sources of Ni and Co are made from calcinated oxalates or hydroxides subsequently reduced in a hydrogen atmosphere. These powders usually have a broad particle size distribution and strongly agglomerated particles . The particles are difficult to deagglomerate, even by ball milling. This may lead to Co-lakes and a heterogeneous cemented carbide microstructure resulting in varying physical and chemical properties.

Polyol cobalt and nickel powders made according to US patent no.4,539,041 contain predominately near- spherical grains with little agglomeration and a submicron average particle size. The use of polyol powders as binders in cemented carbides is described in US patent 5,441,693. By using polyol powder sources the microstructure becomes more homogeneous through better dispersion of the binder phase particles. Thereby fewer binder phase-lakes are present after sintering and further the sintering temperature may be decreased. Cemented carbide is one of the most common materials currently being used in the wood industry for woodworking tools. In the quest for extended lifetime of the woodworking tools and for cutting quality it is important to optimise specific properties of the cutting tool material. Two of the most important properties of the woodworking tool are the resistance to corrosion and oxidation and the hardness .

Since these tools are used for working solid wood, such as logs etc. but also man-made products based on wood particles, fibres or chips, such as chipboard, particle board and medium and high density fibre boards (MDF/HDF) , the different types of corrosion are important : • Solid wood contains organic acids and other compounds that degrade the binder in the tool material and cause outbreak of the hard WC-particle from the matrix and thus wear the tool material .

• Man-made wood products contain organic binder material, based on compounds such as urea, formaldehyde, wax, glue fillers etc. and possibly laminated with plastic layers, such as melamine . The temperature may get very high (>500°C) when working these wood products and then the content of the product will degrade into corrosive compounds chemically attacking the cemented carbide binder. Furthermore the high temperature may result in oxidation of the cemented carbide binder, also degrading and wearing the cutting edge. The hardness usually should be as high as possible in order to retain a sharp and wear resistant cutting edge. The factors determining the hardness are predominately grain size and binder content. The lower the grain size and/or the binder content the higher hardness usually will be. Usually, a compromise has to be reached between grain size and binder content in order to get optimal sinterability, e.g. low porosity of the sintered compact and low sintering temperature. A very fine grain size usually necessitates a higher binder content than slightly higher grain size in order to have the WC grains wet properly and homogeneously by the binder constituents. The influence of grain size in a Ni- based corrosion resistant cemented carbide for woodworking is discussed in EP0568584. The problem is to produce a cemented carbide with very fine grain size and low binder phase content avoiding a heterogeneous microstructure, sintered porosity and property differences within the material when using the highly agglomerated standard Ni- and Co- powder sources.

In order for the cemented carbide material to work optimal it is important that the microstructure be as homogeneous as possible. Polyol binder phase elements will promote the optimal distribution of the binder phase around the ultra-fine WC grains and make it possible to combine very fine WC grain size and a low binder .

The invention is primarily concerned with the use of near-spherical, submicron nickel and/or cobalt powders manufactured by the polyol process in cemented carbide grades particularly for woodworking having a corrosion and oxidation resistant monophase binder phase. The said polyol Ni- and Co-powders shall be produced separately by the polyol process, preferably as a mixture of Ni and Co by the polyol process . The total content of said binder phase varies between 0.5 and 30 wt%, preferably between 1 and 10 wt%, most preferably between 1.5 and 5 wt%, the remainder being tungsten carbide. The composition of said binder phase shall be 30 to 80 wt% Co, max 5 wt% Mo, max 15 wt% Cr, max 10 wt% V, max 20 wt% Fe, balance Ni . The average sintered WC grain size shall be less than 0.7 μm, preferably less than 0.5 μm, most preferably less than 0.3 μm.

In a preferred embodiment particularly useful for machining of chip board, particle board and medium and high density fibreboard (MDF/HDF) , the cemented carbide consists of 2.3 wt% Co, 0.9 wt% Ni and 0.3 wt% Cr, the rest being tungsten carbide. The average sintered WC grain size is <0.5 μm, preferably <0.3 μm. The invention also relates to the use of a cemented carbide with very fine sintered grain size and with a binder phase containing Ni and Co produced by the polyol process as a tool, such as saw tips or indexable inserts, for cutting and machining of wood and wood- based products, particularly chipboard, particle boards and medium or high density fibre boards (MDF/HDF) .

The present invention further relates to a method of making a cemented carbide body based on tungsten carbide and a binder phase based on Ni and Co and any of the following constituents: Mo, Cr, Fe and V, by powder metallurgical methods by milling, pressing and sintering of powders forming hard constituents and binder phase whereby said binder phase contains Ni and/or Co made by the polyol process. Preferably sintering is performed gas pressure sintering also referred to a sinter-HIP. The advantages offered by the use of polyol Ni or/and Co are as mentioned a more homogeneous microstructure and hence improved physical and chemical properties .

Example

An alloy (A) consisting of 2.3 wt% Co, 0.9 wt% Ni and 0.3 wt% Cr, the rest being tungsten carbide with an average sintered grain size of 0.2μm was tested against an alloy (B) containing 1.9 wt% Co, 0.7 wt% Ni, 0.3 wt% Cr and 0.1 wt% Mo, the remainder being WC with an average sintered grain size of 0.8 μm. The determination of the average sintered WC grain size was made on scanning electron micrographs made in an instrument equipped with a field emission gun. The evaluation was made using a semiautomatic equipment and taking geometry effects into consideration.

Both grades were manufactured by conventional cemented carbide techniques . In the prior art powder Co and Ni-powders were made by reduction of Co-and Ni- oxalate; in the invention powder Co and Ni-powders were made from Co-and Ni-hydroxide thermally reduced in polyol thus obtaining powders with a submicron average particle size. The test comprised machining particleboard plates with a top cutter containing three identical indexable inserts. The cutting speed was 18000 rpm, feed rate lm/min and cutting depth 2 mm.

Cutting Wear A, Wear B,

Distance invention prior art

(m) (μm) (μm)

1300 36 45

4000 58 72

It is clear from the test results that the wear of the alloy made according to the invention decreases by up to 20% compared to prior art.

Claims

Claims

1. Cemented carbide for wood working containing 0.5 to 30 wt% Ni- and Co-based binder phase and the remainder tungsten carbide with an average sintered grain size of less than 0.7 μm, preferably less than 0.5 μm, most preferably less than 0.3 μm c h a r a c t e r i s e d in that the Ni and/or Co- sources of said binder phase are powders made by the polyol-process as Ni and Co separately, preferably as a Ni- and Co-mixture.

2. Cemented carbide according to the preceding claim c h a r a c t e r i s e d in that the binder phase contains 30 to 80 wt% Co.

3. Cemented carbide according to the preceding claim c h a r a c t e r i s e d in that the binder phase contains max 5 wt% Mo, max 15 wt% Cr, max 10 wt% V and max 20 wt% Fe.

4. Cemented carbide according to the preceding claim c h a r a c t e r i s e d in that the binder phase content is 1 to 10 wt% .

5. Cemented carbide according to the preceding claim c h a r a c t e r i s e d in that the binder phase content is 1.5 to 5 wt% .

6. Use of a cemented carbide with ultrafine tungsten carbide and 0.5 to 30 wt% Ni-Co-based binder phase containing Co and Ni made by the polyol-process and possibly Mo, Cr, V and/or Fe as a tool for cutting and machining of wood or wood-based products, particularly chip board, particle board and medium and high density fibreboard (MDF/HDF) .