Alumina-based abrasive grains and method for preparing same

Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide

Patent

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Details

51298, 51295, 51308, B24D 304, B24D 328, C09K 314

Patent

active

06015442&

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention is concerned with the domain of alumina-based abrasive grains, such as electromolten corundum or corundum-zirconia grains or sintered bauxite grains intended for the production of cloth or abrasive paper as well as that of grinding wheels.


PRIOR ART

The search for abrasive materials of ever increasing performance has, in recent years, given rise to top grade products derived from highly complex ceramic technologies.
Thus, EP 0168606, EP 0171034 and EP 0291029 by NORTON, EP 0200487, EP 273569, EP 0373765 and EP 0471389 by 3M, EP 0263810 and EP 0368837 by TREIBACHER CHEMISCHE WERKE describe the production of polycrystalline sintered aluminum abrasives. As far as most of them are concerned, they are obtained through a combination of the advantages of synthesis methods derived from sol-gel techniques, crystallization initiation techniques wherein fine particles are seeded of the same type as the material to be produced, and ceramic composite production.
The properties of these materials are similar to those of microcrystalline ceramics with a high alumina content, usually above 95%, if the composites are not those with zirconia or titanium nitride dispersoids. Their micro-hardness and strength are greater than with electromolten products, and their abrasive power is clearly better.
However, the manufacturing cost of these materials which utilize relatively noble raw materials and which employ relatively complex synthesis processes is greater than that of electromolten products.
Moreover, EP 0304616 by LONZA describes alumina-based abrasive grains which have been subjected to surface treatment with a hygroscopic and/or hydrophillic substance. The purpose of this treatment is to improve the capability of the grains to rise within the electrostatic field used in order to orient the grains at the time when they are deposited on a cloth or piece of pre-coated paper. The capability of the grains to move within the electrostatic field, referred to as "rise within the field" is thus dependent on the amount of water absorbed, which, in turn, is very largely dependent on climatic conditions, to be more exact on the humidity of the atmosphere prevailing at the time of the depositing operation onto the sheet or paper.


SUMMARY OF THE INVENTION

It is an object of the invention to obtain, using conventional abrasive materials with moderate manufacturing costs such as electromolten brown or white corundum or corundum-zirconia or sintered bauxite or alumina, properties of use which are close to those of the top grade materials described hereinabove, and also to obtain a satisfactory capability to rise within the electrostatic field irrespective of the climatic conditions of the moment and place in the event.


OBJECT OF THE INVENTION

The invention is based on three factors observed by the applicant during research: of the humidity in the atmosphere can be obtained not by using a coating which is hygroscopic or hydrophillic but by using a coating which contains constitution water, i.e., wherein the water molecules form an integral part of the chemical composition of the product, e.g., in hydrate form, and which is either insensitive to water, i.e., insoluble in water and chemically inert to water, at least under normal conditions. its surface state, whether the support be organic, e.g., a resin on a sheet of paper, or inorganic as in the case of a vitrified grinding wheel. The coarser the material, the greater the number of anchorage points to the support for which it is intended. The physical property connected with this capability is the specific surface. material to form a chemical bond with the support.
The invention therefore relates to alumina-based abrasive grains such as grains of electromolten corundum or corundum-zirconia or sintered bauxite or alumina with a skin which consists essentially of a mixture of finely dispersed aluminum hydrate (5 to 95% by weight) and sodium silicate (5 to 95% by weight). This skin preferably represents 0.1 to 5% by weight of the grain.
The coated gra

REFERENCES:
patent: 2527044 (1950-10-01), Walton et al.
patent: 4472173 (1984-09-01), Bruning et al.
patent: 5042991 (1991-08-01), Kunz et al.
patent: 5213591 (1993-05-01), Celikkaya et al.

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