Coated abrasives

Details Coated abrasives Coated abrasives

2002-05-14

2004-09-28

Turner, Archene (Department: 1775)

Abrasive tool making process, material, or composition

With synthetic resin

C051S307000, C428S323000

Reexamination Certificate

active

06797023

ABSTRACT:

BACKGROUND TO THE INVENTION
The present invention relates to coated abrasives and particularly to abrasive products adapted to perform in an improved fashion when used under moderate to low pressure grinding conditions.
In the production of coated abrasives a backing material, which may be treated to modify the absorptive properties, is provided with a make coat comprising a curable binder resin and abrasive grains are deposited on the make coat before the binder is at least partially cured. Thereafter a size coat comprising a curable binder resin is deposited over the abrasive grain to ensure the grains are securely anchored to the backing.
When the coated abrasive is used to abrade a workpiece, the tips of the abrasive grains lying in the plane of the surface contact the workpiece and begin the work of abrasion. The grains thus contacting the workpiece are subjected to great stresses and, if the grain is not adequately held by the size coat it can be plucked from the surface before it has completed abrading. The bond therefore should hold the grain securely. As abrading continues the grain can become polished, in which case significant frictional heat is generated and little removal of the workpiece occurs. In addition the stresses build up further and eventually the grain is either plucked out completely of it fractures so that a large portion is lost. This however generates new sharp edges such that abrading can resume. Ideally the mode of fracture should be as small as possible such that each grain will last a long time. This is achieved using sol-gel alumina abrasive grains which each comprises micron-sized or smaller crystallites which, under grinding conditions, can break off to reveal new cutting edges. However this occurs under moderate to heavy grinding pressure and only a reduced amount of self-sharpening occurs at lower pressure grinding conditions. There is therefore a need for a highly effective abrasive particle that operates very efficiently at moderate to low pressure grinding conditions.
One option that has been explored is the use of agglomerated abrasive grains in which an abrasive particle made up of a number of finer abrasive particles is held together by a bond material that can be organic or vitreous in nature. Because the bond is in general more friable than the abrasive particles, the bond fractures under grinding conditions that would otherwise lead to polishing or wholesale fracture of the abrasive grain.
Agglomerated abrasive grain generally permit the use of smaller particle (grit) sizes to achieve the same grinding efficiency as a larger abrasive grit size. Agglomerated abrasive grains have also been reported to improve grinding efficiency.
U.S. Pat. No. 2,194,472 to Jackson discloses coated abrasive tools made with agglomerates of a plurality of relatively fine abrasive grain and any of the bonds normally used in coated or bonded abrasive tools. Organic bonds are used to adhere the agglomerates to the backing of the coated abrasives. The agglomerates lend an open-coat face to coated abrasives made with relatively fine grain. The coated abrasives made with the agglomerates in place of individual abrasive grains are characterized as being relatively fast cutting, long-lived and suitable for preparing a fine surface finish quality in the work-piece.
U.S. Pat. No. 2,216,728 to Benner discloses abrasive grain/bond agglomerates made from any type of bond. The object of the agglomerates is to achieve very dense wheel structures for retaining diamond or CBN grain during grinding operations. If the agglomerates are made with a porous structure, then it is for the purpose of allowing the inter-agglomerate bond materials to flow into the pores of the agglomerates and fully densify the structure during firing. The agglomerates allow the use of abrasive grain fines otherwise lost in production.
U.S. Pat. No. 3,048,482 to Hurst discloses shaped abrasive micro-segments of agglomerated abrasive grains and organic bond materials in the form of pyramids or other tapered shapes. The shaped abrasive micro-segments are adhered to a fibrous backing and used to make coated abrasives and to line the surface of thin grinding wheels. The invention is characterized as yielding a longer cutting life, controlled flexibility of the tool, high strength and speed safety, resilient action and highly efficient cutting action relative to tools made without agglomerated abrasive grain micro-segments.
U.S. Pat. No. 3,982,359 to Elbel teaches the formation of resin bond and abrasive grain agglomerates having a hardness greater than that of the resin bond used to bond the agglomerates within an abrasive tool. Faster grinding rates and longer tool life are achieved in rubber bonded wheels containing the agglomerates.
U.S. Pat. No. 4,355,489 to Heyer discloses an abrasive article (wheel, disc, belt, sheet, block and the like) made of a matrix of undulated filaments bonded together at points of manual contact and abrasive agglomerates, having a void volume of about 70-97%. The agglomerates may be made with vitrified or resin bonds and any abrasive grain.
U.S. Pat. No. 4,364,746 to Bitzer discloses abrasive tools comprising different abrasive agglomerates having different strengths. The agglomerates are made from abrasive grain and resin binders, and may contain other materials, such as chopped fibers, for added strength or hardness.
U.S. Pat. No. 4,393,021 to Eisenberg, et al, discloses a method for making abrasive agglomerates from abrasive grain and a resin binder utilizing a sieve web and rolling a paste of the grain and binder through the web to make worm-like extrusions. The extrusions are hardened by heating and then crushed to form agglomerates.
U.S. Pat. No. 4,799,939 to Bloecher teaches erodable agglomerates of abrasive grain, hollow bodies and organic binder and the use of these agglomerates in coated abrasives and bonded abrasives. Higher stock removal, extended life and utility in wet grinding conditions are claimed for abrasive articles comprising the agglomerates. The agglomerates are preferably 150-3,000 microns in largest dimension. To make the agglomerates, the hollow bodies, grain, binder and water are mixed as a slurry, the slurry is solidified by heat or radiation to remove the water, and the solid mixture is crushed in a jaw or roll crusher and screened.
U.S. Pat. No. 5,129,189 to Wetscher discloses abrasive tools having a resin bond matrix containing conglomerates of abrasive grain and resin and filler material, such as cryolite.
U.S. Pat. No. 5,651,729 to Benguerel teaches a grinding wheel having a core and an abrasive rim made from a resin bond and crushed agglomerates of diamond or CBN abrasive grain with a metal or ceramic bond. The stated benefits of the wheels made with the agglomerates include high chip clearance spaces, high wear resistance, self-sharpening characteristics, high mechanical resistance of the wheel and the ability to directly bond the abrasive rim to the core of the wheel. In one embodiment, used diamond or CBN bonded grinding rims are crushed to a size of 0.2 to 3 mm to form the agglomerates.
U.S. Pat. No. 4,311,489 to Kressner discloses agglomerates of fine (≦200 micron) abrasive grain and cryolite, optionally with a silicate binder, and their use in making coated abrasive tools.
U.S. Pat. No. 4,541,842 to Rostoker discloses coated abrasives and abrasive wheels made with agglomerates of abrasive grain and a foam made from a mixture of vitrified bond materials with other raw materials, such as carbon black or carbonates, suitable for foaming during firing of the agglomerates. The agglomerate “pellets” contain a larger percentage of bond than grain on a volume percentage basis. Pellets used to make abrasive wheels are sintered at 900° C. (to a density of 70 lbs/cu. ft.; 1.134 g/cc) and the vitrified bond used to make the wheel is fired at 880° C. Wheels made with 16 volume % pellets performed in grinding with an efficiency similar to that of comparative wheels made with 46 volume % abrasive grain. The pellets contain open cells within th

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