Grinding aid material, method of producing it, use of it, and ab

Details Grinding aid material, method of producing it, use of it, and ab Grinding aid material, method of producing it, use of it, and ab

1997-04-18

1999-03-30

Jones, Deborah

Abrasive tool making process, material, or composition

With inorganic material

51309, B24D 334

Patent

active

058882588

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention concerns a grinding aid consisting of fluoride-containing inorganic compounds for use in an abrasive material comprising abrasive grains and a grinding aid, a method of producing it, use of it as well as an abrasive material containing it.
It is known to use cryolite as a grinding aid in the abrasive composition in abrasive materials, such as sandpaper, emery cloth and grinding wheels, cf. e.g. KIRKOTHMER: ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Third Edition, Vol. 10, 1980, line 672, and the mention of the prior art in WO 94/02562.
WO 94/02562 concerns abrasive grains having an outer surface to which a grinding aid material is bonded via interparticle attraction. A large number of materials, inter alia cryolite, including synthetic cryolite, are mentioned as a grinding aid material.
U.S. Pat. No. 5,078,753 concerns an abrasive material having on the abrading face, in addition to abrasive grains, erodable aggregates consisting of a finely ground filler and a resinous binder. The filler may be calcium carbonate, talc, glass, sodium sulfate, cryolite, fluoroborates, etc. Example V uses inter alia sodium cryolite.
EP Patent Application No. 8 868 describes abrasive materials consisting of brittle agglomerates of abrasive grains bonded in an inorganic matrix. The matrix may be based on natural cryolite, e.g. type S from KRYOLITSELSKABET .O slashed.RESUND A/S Danmark. These abrasive materials may be produced by melting natural cryolite, adding the abrasive grains, cooling and crushing the cooled material.
Grinding aids are used, because they have a positive influence on the utility properties of the abrasive materials, inter alia grinding rate and product life. No specific knowledge is available about the mechanism of the product improvement obtained. However, it is assumed that the effect of using cryolite as a grinding aid may be due to the circumstance that the chipping created by grinding locally takes place at very high temperatures, and that the cryolite acts as a flux in a melt produced by the chipping, whereby the viscosity of the melt is reduced. However, the effect of the cryolite may also be due to the circumstance that any tendency to block the gaps between the abrasive grains is diminished.
For many years KRYOLITSELSKABET .O slashed.RESUND A/S Danmark has supplied a ground natural cryolite for this purpose; thus, the company has supplied natural cryolite ground to -325 mesh, i.e. less than 45 micrometers, to the grinding disc industry.
After the termination of the mining of cryolite in Greenland, natural cryolite is today no longer available in the market. A few producers (from Russia) sell grades which they call natural cryolite, but tests have shown that it is precipitated cryolite types. There are deposits of natural cryolite in Russia, but, as far as is known, they are not suitable for working by flotation. Possibly, the Russian "natural cryolite" is made by extraction of such a deposit with subsequent precipitation.
Thus, in the mid-1990s the cryolite types available in the market are generally synthetic, i.e. produced by a wet precipitation process, and it has been found that none of these commercially available cryolite types are suitable as a grinding aid in abrasive compositions.
The difficulties involved by the use of synthetic cryolite appear to be of two types:
Firstly, there is an aesthetic problem, since the use of synthetic cryolite as a grinding aid results in undesirable stripes in the coating on sandpaper, especially on the finer types. Further, it has been observed that the synthetic cryolite absorbs more binder than the natural cryolite on both fine and coarse sandpaper types.
Secondly, there are productionally unacceptable variations in the course of a production of e.g. sandpaper, there being thus an increasing particle separation and particle agglomeration tendency during the course of the production.
Finally, it has been reported that users of the abrasive materials have experienced unspecified performance problems.
Through deta

REFERENCES:
patent: 4311489 (1982-01-01), Kressner
patent: 5078753 (1992-01-01), Broberg et al.

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