More than 60% of the world’s production of tungsten is used to make cutting tools. It is the fundamental component of what we call «hard metal»
Hard metal is the basis of most of the tools we use for cutting in the industry. But: What is really the «hard metal»? How do we get it? Why it is used?. With this article we approach you to this material and its advantages in the machining of wood and derivatives.
What is the hard metal that is used in the cutting tools?
Hard metal is not a metal, nor an alloy of them. Actually it is a composite material . Its fundamental elements are:
- Ceramic materials or carbides, such as tungsten carbide, titanium carbide, tantalum carbide or chromium carbide.
- Binding metal, usually cobalt, nickel and / or iron..
How is it obtained?
As I have already explained it is not an alloy, therefore it is not obtained by melting the materials that compose it. It is obtained by a process called Sintering of tungsten carbide (Karl Heinrich Schroeter and Baumhauer 1923) resulting in what we know as «hard metal» or Widia (Krupp Hartmetall 1926).
The «Sintering» is a process of manufacturing molded solid parts, consisting of high pressure compacting several metallic powders and / or mixed ceramics. Once compacted, a thermal treatment is carried out at a temperature lower than that of fusion of the mixture of materials, obtaining a consolidated and compact piece. (source: wikipedia)
What are the advantages of this material?
The advantages are very varied and not only during the use of the tools. Since its manufacture already has huge advantages over other types of materials. Let’s see some of them:
- Tungsten is the metal with the highest melting point (3,410 ° C, 2870 ° C in the form of carbide), with the highest tensile strength and with the lowest coefficient of thermal expansion of all metals in pure state. Therefore it has great hardness, thermal resistance and chemical aggression.
- Using sintering, we combine advantages of metallic and ceramic materials. The casting of the same materials does not obtain the same results of hardness and strength.
- Complex shapes can be generated without machining, therefore without excess material, with less energy use and manufacturing time.
- The pieces obtained are porous, therefore: they are lighter, they can be coated with greater success and / or lubricants can be added in their manufacture.
- Its manufacturing process does not generate waste (vital with expensive and scarce materials such as wolfram) and is done at lower temperatures, with the consequent energy saving.
Why is it used for cutting tools?
As a result of the advantages of the material, the cutting tools manufactured with «hard metal»:
- High resistant to abrasion, therefore they last longer.
- High hardness and resistance to compression, which allows to work with composite materials, laminates, poly-laminates, etc.
- Higher working temperatures than high speed steel tools (HSS), so they can work at a much higher speed.
- They keep the sharp cutting edge better, so they provide a better finish.
Qualities, What is the best «hard metal» for wood cutting tools?
As in everything, there are different qualities according to their manufacturing process and the materials used in it. The «Hard Metal» components are manufactured in different processes and with specific requirements. Different properties are obtained depending on the composition and application. Fundamentally, the qualities differ according to the binder matrix, the percentage of the materials and the granulometry.
With different compositions we obtain the balance between hardness, wear resistance and tenacity that make «Hard Metal» so effective. As a fundamental point in the quality, we classify the MD according to the granulometry of the raw material, obtaining better performance (hardness and resistance to wear) the finer it is:
- Nanograin: carbide particles with a diameter of less than 200 nm (nanometers or a billionth of a meter).
- Ultrafine grain: particles between 200 and 500 nm.
- Micro grain: particles between 0.5 and 1 μm (microns or one millionth of a meter).
- Fine grain: particles of 1 to 1.3 μm.
- Medium grain: particles from 1.3 to 2.5 μm.
- Coarse grain: particles of 2.5 to 6.0 μm.
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