Method of making multi-carbide spherical grinding media

Abstract

Grinding media, including shaped media such as spheres or rods ranging in size from about 0.5 micron to 100 mm in diameter, are formed from a multi-carbide material consisting essentially of two or more carbide-forming elements and carbon, with or without carbide-forming elements in their free elemental state. The media have extremely high mass density, extreme hardness, and extreme mechanical toughness.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority from U.S. Provisional Application Ser. No. 60 / 453,427 filed on Mar. 11, 2003 and entitled SPHERES IMPARTING HIGH WEAR RATES, incorporated herein by reference.FIELD OF THE INVENTION [0002] This invention relates generally to the field of grinding media composition, and more specifically to multi-carbide materials for use as grinding media formed in the shape of spheres or other shaped media. BACKGROUND OF THE INVENTION [0003] Carbide materials are well known in the art of material science. They include a range of compounds composed of carbon and one or more carbide-forming elements such as chromium, hafnium, molybdenum, niobium, rhenium, tantalum, thallium, titanium, tungsten, vanadium, zirconium, and others. Carbides are known for their extreme hardness with high temperature tolerance, properties rendering them well-suited for applications as cutting tools, drilling bits, and similar uses. Multi-element ...

AI Technical Summary

Problems solved by technology

Spheres and solid bodies of other specific shapes, whether of carbide or multi-carbide, are difficult to manufacture due to the very properties that make them useful.

Their high melting point necessitates a powerful energy source with difficulty in temperature regulation and effect, and their hardness makes them costly to machine.

This process is effective in fusing the materials, but causes inconsistent mixing of the elements in the compound and some uncontrolled loss of material due to vaporization, phenomena that can greatly compromise the properties of the resulting compound in uncontrolled and unpredictable ways.

Hardness is also a challenge, as the manufacturing process results in an irregularly-shaped lump of resulting compound that is generally a few inches in diameter, colorfully known as a “cow chip”.

These processes leave small cracks in the finished product that greatly reduce both its hardness and its mechanical toughness.

Re-melting of the material after crushing imposes high cost, and cannot efficiently achieve regular particle sizes or shapes.

Consequently, although carbide is available in small spheres and other preferred shapes, those spheres are not optimally composed, they are irregularly sized, they are expensive, and they are lacking in effectiveness.

The known art currently does not have a process whereby multi-carbide materials can be formed into small and regular shapes without loss of optimized properties due to process variation in manufacture or degradation of material during shaping.

Just as stone wheel grinding could not reliably provide the powders needed for earlier industrial processes, current media mills and similar technologies cannot reliably provide the ultra-fine and ultra-regular particles now required for certain applications.

Variation of the shape of the grinding media generally affects the regularity of particle size, the efficiency of the milling process, the total cost to achieve a given size reduction, and other factors.

Extremely small particle sizes are proving to be useful for many new applications. however, the size reduction and regularity necessary for standardized, acceptable results cannot be achieved by any current milling methods.

Production now requires alternate particle fabrication methods such as chemical precipitation, either at a fast rate with unacceptable process variation, or at very slow rates, with unacceptable time and expense.

Various metal media have relatively high mass density, but low mechanical toughness.

Carbides showed extreme hardness and mass density, even in small dimensions, but with unavoidable media failures that cause unacceptable product contamination and more general process failures that are incompatible with many applications.

Duplication of his example showed his invention to cause contamination of the milled product, as longer-term and higher-volume production attempts failed due to lack of mechanical toughness that caused metallic and other contamination of product material.

These materials changed the nature of but did not resolve the product material contaminant issue, and did not solve the mechanical toughness problem.

Rather, these materials tended to fail by degradation into hard, fine and irregular shards that acted as abrasives in the media mill, contaminating the product and on one occasion seriously damaging the mill itself.

While these materials are acceptably hard, and show greater mechanical toughness than those disclosed in Kaliski, they lack adequate density for many applications or for optimum efficiency in others.

This grinding media fractured due to insufficient mechanical toughness, contaminating the product and extensively damaging the media mill.

Tungsten carbide failed due to the lack of mechanical toughness despite experimental variation of media velocity, flow rate, material volume, and other milling variables.

In all attempts with all materials supplied to the Kaliski specification, the level of product contamination was a limitation on usefulness.

However, they show low hardness and density relative to ceramics.

Polymer grinding media thus can be useful in milling relatively soft product materials that are sensitive to product contamination, and in industries that are relatively insensitive to processing cost, such as in drug processing or in dispersing biological cells for analysis, but they are not appropriate for the majority of industrial applications.

Although the multi-carbides disclosed showed a combination of hardness, density and mechanical toughness that promised to be useful for milling, the known geometries for available multi-carbide materials rendered them incompatible with such use.

Difficulties included the large size of multi-carbide material that is produced by current manufacturing methods, and difficulty in machining or otherwise manipulating the material into sizes and shapes useful for milling due in part to its hardness and mechanical toughness.

This fact has greatly inhibited research into multi-carbide elements.

As summarized above, the grinding media of the prior art all suffer some technical disadvantage resulting in a proliferation of grinding media materials creating a significant economic burden and also resulting in technically inferior milled products due to contamination.

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