Tungsten Carbide Anvil Wear Mechanism (2/2)

Due to the structure of anvil has some complexity, it is difficult to obtain the stress distribution of tungsten carbide anvil under ultra-high pressure by a simple experiment. But it is also a crucial factor to analyze the wear mechanism, stress distribution and the relations of geometric parameters. So the related scholars and researchers use model simulation carbide anvil in the actual work of the forces by finite element analysis theory and related software. Through Finite element analysis model, it is known that acting on the top surface of the hammer cylinder radial preload from an interference fit between the anvil and the preload ring. Preload is essentially the contact pressure, and its main role is to provide lateral support for the anvil to improve stress distribution under actual working conditions.

From the point of view of stress distribution, preload distribution is very uneven, gradually decreasing from the bottom to the top. The stress in the four corners is relatively concentrated, but also the most likely to crack parts, which produces small cracks start from the stress concentration occurs at the micro cracks and gradually increased to the top surface of the anvil extension. These parts are neither covered within the scope of pyrophyllite, nor take advantage of the strengthening force top hammer steel ring, so in most cases they completely rely on their own strength to bear the stress.

Furthermore, tungsten carbide has certain fragility and poor shear resistance. It is normal that tensile stress and shear stress appear simultaneously in the process of anvil working, which will has a sharp increase of internal stress after loading. Especially, when the accumulated fatigue or load is too large, the internal material will yield and at the edge of the anvil surface crack formation under the action of shear stress; the radial shear stress will expand the cracks area and resulting in cemented carbide material in axial compression stress of sliding, eventually leading edge broken or crushed.

In order to reduce the wear and avoid the cracking and crushing of the anvil, the relevant researchers study from two aspects, one is the release of stress, the other is improve the interference fit. And the internal stress includes the stress of grinding and machining process. The anvil just after grinding is better to use after 3 month storing to ensure the release of the internal stress. Some academics have proposed that put the grinded anvil into muffle furnace and heat gradually cooled after 3-7h. However, this process requires high precision of vary parameters controlling, or the micro cracks will expand because of the heating and cooling; Anvil and increase the amount of interference with the steel ring will help improve the strength of the anvil, but it will increase the workload of the steel ring, reducing the strength of the tightening ring, its service life will be greatly shortened.

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