Abrasive article containing an inorganic metal orthophosphate

Details Abrasive article containing an inorganic metal orthophosphate Abrasive article containing an inorganic metal orthophosphate

1999-06-25

2001-08-07

Marcheschi, Michael (Department: 1755)

Abrasive tool making process, material, or composition

Impregnating or coating an abrasive tool

C051S298000, C051S307000, C051S309000, C428S330000

Reexamination Certificate

active

06270543

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to abrasive products comprising abrasive particles, binder, and an inorganic metal orthophosphate salt, and to methods of making and using same. These abrasive products include bonded abrasives, coated abrasives, and nonwoven abrasives.
2. Description of the Related Art
In the competitive and economically significant field of abrasive products, a continuing desire exists to reduce manufacturing costs and increase performance of such products in efforts to seek and acquire competitive edge.
Abrasive products are generally known having abrasive particles adherently bonded to a sheet-like backing. It is generally known to stratify the abrasive grains and binders into separate layers that are serially formed upon a sheet-form substrate, such as in coated abrasive articles, in such a way as to basically segregate the abrasive grains as a particulate monolayer sandwiched between underlying and overlaying binder layers.
More specifically, coated abrasive products typically have a backing substrate, abrasive grains, and a bonding system which operates to hold the abrasive grains to the backing. In a typical coated abrasive product, the backing is first coated with a layer of adhesive, commonly referred to as a “make coat”, and then the abrasive grains are applied to the adhesive coating. The application of the abrasive grains to the make coat involves electrostatic deposition or a mechanical process which maximizes the probability that the individual abrasive particles are positioned with its major axis oriented perpendicular to the backing surface. As so applied, the abrasive particles optimally are at least partially embedded in the make coat. The resulting adhesive/abrasive grain layer is then generally solidified or set (such as by a series of drying or curing ovens) sufficient to retain the adhesion of abrasive grains to the backing. After curing or setting the make coat, a second layer of adhesive, commonly referred to as a “size coat”, is applied over the surface of the make coat and abrasive particles, and, upon setting, it further supports the particles and enhances the anchorage of the particles to the backing. Optionally, a “supersize” coat, which may contain grinding aids, can be applied over the cured size coat. In any event, once the size coat and supersize coat, if used, has been cured, the resulting coated abrasive product can be converted into a variety of convenient forms such as sheets, rolls, belts, and discs. As an optional supersize enhancement, to mitigate any anticipated loading or clogging of the abrasive product with swarf (i.e., debris liberated from the workpiece during the abrading operation), a coating of anti-stick stcaratc also can be applied as supersize over the exterior of the abrasive coating, once formed, as suggested in
Kirk
-
Othmer Encyclopedia of Chemical Technology
, Fourth Ed., Vol. 1, (p. 29).
In many abrasive articles the binder includes a particulate filler as an adjuvant. Typically, the binder will comprise between 40 to 70 percent by weight particulate filler. The addition of the filler either increases the toughness and hardness of the binder and/or reduces the cost of the finished article, e.g., by decreasing the amount of binder required. The filler is typically an inorganic particulate material, generally having a particle size less than about 40 micrometers. Examples of common fillers in the abrasive industry include calcium carbonate, calcium oxide, calcium metasilicate, alumina trihydrate, silica, kaolin, quartz, and glass.
There exists a subclass of fillers, referred to as grinding aids, cutting aids, or generically as “active fillers”. An active filler is typically a particulate material the addition of which to the binder has a significant affect on the chemical and physical processes of abrading which leads to improved performance. It is believed that active fillers will either (1) decrease the friction between the abrasive grains and the workpiece being abraded, and/or (2) prevent the abrasive grains from “capping”, i.e. prevent metal particles from becoming welded to the tops of the abrasive grains, and/or (3) decrease the interface temperature between the abrasive grains and the workpiece, and/or (4) decrease the required grinding force.
Grinding aids can be especially effective in abrading stainless steel, exotic metal alloys, titanium, metals slow to oxidize, and so forth. In some instances, a coated abrasive product containing a grinding aid in the binder can abrade up to 100% more stainless steel than a corresponding coated abrasive product in which the binder is devoid of a grinding aid. The reason, in theory, being that the activity of grinding metal by abrasive articles produces freshly formed, hot, and uncontaminated metal surfaces. If the newly formed, uncontaminated metal surface is not rapidly “contaminated”, metal will transfer and adhere to the abrasive particle surface(s) causing “capping” which decreases grinding performance. One purpose and function of grinding aids is to prevent capping by rapidly contaminating the freshly formed metal surface. Grinding aids are normally incorporated into the bond resin(s) of the abrasive article. Grinding aids (active fillers) can be classified as physically active or chemically active. Cryolite, sodium chloride, and potassium tetrafluoroborate are known physically active grinding aids that melt between 500 and 1,000° C. which can form thin films on freshly formed metal. Chemically active grinding aids include iron pyrite, polyvinyl chloride, and polyvinylidene chloride which decompose when heated forming chemicals that rapidly react with the freshly formed metal surface.
Also, combinations of grinding aids in abrasive articles (grinding wheels) may produce more than a cumulative grinding effect. U.S. patents describing use of the combination of a sulfide salt and an alkali metal salt include U.S. Pat. Nos. 2,408,319; 2,811,430; 2,939,777; 3,246,970; and 5,061,295. Other patents that combine an inorganic salt containing fluorine, c.g. cryolite, and a salt such as ammonium chloride include U.S. Pat. Nos. 2,949,351 and 2,952,529.
Another type of grinding aid enhancement is described in U.S. Pat. No. 5,441,549 (Helmin) wherein the grinding aid effect of potassium tetrafluoroborate is enhanced by the addition of specific thermoplastics.
Other descriptions of grinding aids include:
U.S. Pat. No. 2,216,135 (Rainier), which teaches a grinding wheel having as a grinding aid an anhydrous, water-soluble non oxidizing inorganic alkali or alkaline earth metal salts whose melting points are within the range of 700 to 1200° C. These materials include sodium chloride, potassium chloride, anhydrous sodium carbonate, sodium sulfate, potassium sulfate, lithium sulfate, sodium pyrophosphate, potassium pyrophosphate, calcium chloride, calcium bromide, magnesium sulfate, barium chloride, barium bromide, magnesium chloride, magnesium bromide or strontium chloride.
U.S. Pat. No. 2,243,049 (Kistler), which teaches an abrasive body (grinding wheels) containing finely divided strongly acidic or potentially acidic inorganic compounds. Acid sulfates, phosphates or pyrophosphates are satisfactory, as are the ammonium, sodium, potassium, calcium, or barium salts thereof. Phosphorus pentoxide is also possible. The grinding aid constitutes about 7% of the bond. is When used on metal work surfaces, the grinding aid reduces loading and increases the grain efficiency 40 to 100%.
U.S. Pat. No. 3,502,453 (Baratto) discloses abrasive articles containing hollow spheriles filled with lubricant, which spherules rupture during grinding to release the lubricant. In one example, Baratto discloses a formulation molded into a wheel for titanium snagging, where the formulation includes silicon carbide, bonding resin, trisodium phosphate, and encapsulated lubricant.
U.S. Pat. No. 2,690,385 (Richlin), which teaches a metal cleaning cloth or felt impregnated with abrasive, sodium bisulfate and a humectant. Substitutes for the sodium bisulfate i

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