WO2016076887A1

WO2016076887A1 - Coated abrasive with low packing density ceramic grits

Info

Publication number: WO2016076887A1
Application number: PCT/US2014/065704
Authority: WO
Inventors: Robert Seider; Angelo R. Angelone
Original assignee: Washington Mills Management, Inc.
Priority date: 2014-11-14
Filing date: 2014-11-14
Publication date: 2016-05-19

Abstract

A coated abrasive product including a sheet material having at least a first set of ceramic abrasive grain product at least partially embedded in at least a first bonding layer on the sheet material and at least second set of ceramic abrasive grain product at least partially embedded in at least a second bonding layer on the first set of ceramic abrasive grain product; wherein, the ceramic abrasive grain product contains at least fifty weight percent of abrasive grains having a uniform grain thickness of from 0.005 to 0.04 cm; wherein, the thickness is the smallest uniform dimension, and a length bigger than the thickness and the methods of abrading with the coated abrasive product and for manufacturing the coated abrasive product.

Description

COATED ABRASIVE WITH LOW PACKING DENSITY CERAMIC GRITS

Background of the Invention

[0001] This invention relates to the production of coated abrasives containing very low packing density ceramic abrasive grits (grains) and methods of making and using the same.

[0002] New superior very low density (VLD) abrasive grains have recently been developed as described in U.S. Patents 8,481.438; 8,685,125 and 8,795,400, incorporated herein by reference. Such patents further claim or describe coated abrasive products containing such grains. Such coated products, as shown by comparative data, provide greater cuts over the life of the coated product than previously known coated abrasive products from essentially the same chemical materials. The grains used in coated abrasive products, as described above, may be made from various known abrasive materials such as fused aluminum oxide, co-fused aluminum oxide-zirconium oxide or sintered sol gel aluminum oxide, all of which may or may not contain various supplementary oxides.

[0003] A usual abrasive particle can simplistically be represented by a double ended cone, whereby one end of the cone is bonded to the abrasive product base and the other end is contacting the steel workpiece. As the cone wears back from the tip of the cone, the wear flat is increasing in two directions and thus the wear flat area growth rate increases as a squared function of the wear back.

[0004] For use in abrasive applications, usual abrasive grains are produced in bulk form and are crushed to the desired grit size for use in coated or bonded abrasive products. Aluminum oxide abrasive can be made by refining bauxite in an arc furnace or by melting a Bayer type alumina in an arc furnace and pouring into large molds for cooling. The crude is then crushed into the desired grit size. Co-fused aluminum oxide zirconium oxide abrasive is also arc furnaced, but it is poured into molds which produce very rapid cooling. Such molds may be steel plates with small spacings (about 1/4") between them or molds which contain steel balls, whereby the melt flows into the interstitial spaces. This crude is then also crushed into desired grit sizes. Sol gel alumina is made in a water based system, usually extruded, dried, crushed into the desired grit sizes, calcined and fired into abrasive grit particles. [0005] In all of the above, crushing of the bulk material results in particles with a three dimensional shape, whereby the dimensions of the particles in the three axes of the grain are equivalent or nearly equivalent. Abrasive grits for heavy duty bonded applications are desired to have equal axes which indicates a "blocky" material and is indicative of a material with a high packing density. Abrasive grits for paper and cloth applications are desired to have unequal axes which indicates a "sharp" material and is indicative of a material with a lower packing density. The table below illustrates typical packing densities of various traditional bonded and coated abrasive grits.

TABLE I

Packing Density 36 Grit

Bonded Coated

es

Fused Aluminum Oxide 1.82 - 1.92 1.73 - 1.82

Sintered Sol Gel Aluminum Oxide 1.82 - 1.92 1.73 - 1.82

Co-Fused Aluminum Oxide-Zirconium Oxide 2.10 - 2.22 1.99 - 2.10

[0006] The co-fused aluminum oxide-zirconium oxide traditional particles have similar shapes to the fused aluminum oxide and sintered sol gel particles. The higher packing densities result from the higher true specific gravity of the alumina-zirconia (4.55) versus 3.94 - 3.92 for the fused aluminum and sol gel alumina.

[0007] Generally, the abrasive grits for traditional coated applications are extracted during the initial crushing of the crude material when the abrasive particles are sharper as indicated by a lower packing density.

[0008] Of particular interest are the packing densities of the traditional coated abrasive materials is that they are only slightly lower than the packing densities of the bonded abrasive materials. The coated abrasive packing densities are inherent from crushing a bulk material into abrasive grits. Lower packing density material than shown on the above Table I for coated abrasive applications is desirable but not attainable with the typical crushing of abrasive grits from bulk crude materials. Lower packing density abrasive may be associated with providing a longer life abrasive product in coated applications i.e. a higher total metal removal (cut) until removal rate is unacceptable. [0009] An abrasive disc or belt is discarded when the grinding operator considers that it has become dull, which means the metal removal rate has decreased to approximately 10-20% of the initial metal removal rate. The metal removal rate is a function of the penetration of the abrasive particles into the steel workpiece. The penetration of the particles into the steel is further dependent on the pressure the abrasive grits apply to the steel workpiece. The pressure of the abrasive grits on the steel workpiece is defined by the force of the abrasive particles on the steel divided by the wear flat area of the particles. As the wear flat area of the abrasive particles increases, the abrasive grit pressure applied to the steel workpiece decreases, the abrasive grit penetration decreases and the resulting metal removal rate decreases. When a grinding disc or belt is discarded, the wear flat area is very small, e.g. 0.013 to 0.026 cm² per 100 to 400 particles of abrasive grit per sq. cm. of coated material, depending on the type and shape of the steel being ground and the force applied to the abrasive products.

[0010] To improve the useful cutting life of a coated abrasive product, it is necessary to slow the abrasive grit wear flat growth rate. This may be accomplished with an abrasive grain more resistant to wear which results in a slower wear back growth rate and a resulting slower wear flat growth rate. Secondly, the abrasive particle shape can be changed to result in a slower wear flat growth rate as the particle wears back. Thirdly, the shape and consistency of the abrasive particle can be altered so that the abrasive particles with terminal wear flat areas can shed the wear flats and expose a new grinding surface or that the particle can break off below the grinding interface thereby also removing the terminal wear flat. This shedding or break-off phenomenon can be called self dressing. The terminal wear flat area is defined as that area which prevents the abrasive particles from significantly penetrating the steel surface with a particular applied force.

[0011] Ceramic hollow spheres (ceramic bubbles) have been known for some time and have many applications, one of which is to lower the density of abrasive products, especially bonded abrasive products. Such bubbles, e.g. alumina or alumina-zirconia bubbles, added to reduce product density generally do not provide sharp edges or corners that significantly improve grinding performance; although, some of such bubbles might partially or completely fracture during use of the abrasive product which conceivably could have some such effect, albeit minor. Such ceramic bubbles are well known as are their methods of manufacture, e.g. by atomizing fused ceramic material, e.g. fused alumina or alumina-zirconia mix with compressed gas, usually compressed air. Such products are readily available in the industry, e.g. from Washington Mills as DURALAM® hollow ceramic spheres, from Zircar Corporation as ZIRCAR® hollow ceramic spheres or from Treibacher Corporation as ALODUR® hollow ceramic spheres.

[0012] Such ceramic bubbles may also be made from other processes such as a sol gel processes as described in U.S. Patent 5,077,241.

[0013] It has also been known to introduce ceramic filaments or rods into abrasive products, e.g. as described in U.S. Patents 5, 194,072; 5,372,620; and 5, 876,470 with idea that the end portions of such filaments or rods would retain a certain sharpness. While this may in some respects have validity, use in actual practice can be difficult. This is because to have the appropriate effect, the rods or filaments have to be appropriately oriented, i.e. a side on exposure of such a rod or filament to a work piece does not act as a good cutting edge. Further, the ends of such rods or filaments may not actually have particularly sharp cutting edges since they might be no thinner than the diameter of the rod or filament itself.

[0014] In accordance with U.S. Patents 8,481.438; 8,685, 125 and 8,795,400, above described, very low packing density (VLD) abrasive grains are provided that have a low packing density due to grain shape.

[0015] Such grains have a relatively uniform grain thickness (edge) that is thin enough to permit a sharp edge regardless of wear.

[0016] Such grains may, for example be scoop shape so that they are able to gouge out portions to be removed from a workpiece.

[0017] Such abrasive grains may be abrasive grains in the form of thin curved sheets that are self sharpening in that they crack or break off as their edges wear to provide new sharp cutting edge surfaces and have greater strength due to curvature.

[0018] The above objects may be attained by using abrasive grains formed by crushing ceramic bubbles. Such grains are thin plates having a curvature following the curvature of the original ceramic bubble thus resulting in a "scoop" shaped edge. Such a geometric configuration is stronger than a flat plate of the same thickness thus permitting a very thin abrasive edge to be useful without premature cracking yet at the same time fracturing when a wear flat forms applying more effecting force to the grain. Brief Summary of the Invention

[0019] It has now been surprisingly discovered that superior life and cut of a coated abrasive product using VLD grains, as described in U.S. Patents 8,481.438; 8,685, 125 and 8,795,400, is unexpectedly even more improved by using a particular coating method. When the coating method of the present invention is employed, coated abrasive products employing grains described in U.S. Patents 8,481.438; 8,685,125 and 8,795,400 maybe even further improved and even more surprisingly when the coating method of the present invention is employed with traditional abrasive grains, essentially no improvement is obtained.

[0020] It is thus an object of the present invention to reduce the wear flat growth rate or shed the terminal wear flats and prolong the useful metal removal rate (cutting life) of abrasive products, especially coated abrasive products even more so than described in U.S. Patents 8,481.438, 8,685, 125 and 8,795,400 (very low packing density grain, VLD ) by double coating the VLD abrasive grain onto a backing to form the coated product.

[0021] More particularly, the invention includes a coated abrasive product including a sheet material having a first set of ceramic abrasive grain product at least partially embedded in a first bonding layer on the sheet material and a second set of ceramic abrasive grain product at least partially embedded in a second bonding layer on the first set of ceramic abrasive grain product; wherein, the ceramic abrasive grain product contains at least fifty weight percent of abrasive grains having a uniform grain thickness of from 0.002 to 0.016 inches (0.005 to 0.04 cm); wherein, the thickness is the smallest uniform dimension, and a length bigger than the thickness, and the grain is preferably at least partially embedded in the bonding layers so that the ceramic abrasive grain product is oriented so that the thickness of the grain may be exposed to a workpiece.

[0022] It is to be understood that more than two layers of ceramic abrasive grain, as described above, may be included in accordance with the invention.

[0023] The invention further includes the coated abrasive product, as described above, where the ceramic abrasive grain product contains at least 50 percent by weight of particles having an average particle size of 100 to 3000 micrometers, commonly 300 to 2500 micrometers, and an internal concave surface wall, an external convex surface wall and a thickness between the internal and external walls, said external wall being in the shape of a portion of an essentially spherical shape, essentially all of said particles of the ceramic abrasive grain product having a thickness less than twenty percent of the particle size dimensions of the ceramic abrasive grain product, the particles having irregular circumferential edges defined by circumferences of the internal and external walls.

[0024] The invention also includes a method for abrading an article comprising grinding or sanding the article with a coated abrasive product including a sheet material having a first set of ceramic abrasive grain product at least partially embedded in a first bonding layer on the sheet material and a second set of ceramic abrasive grain product at least partially embedded in a second bonding layer on the first set of ceramic abrasive grain product; wherein, the ceramic abrasive grain product contains at least fifty weight percent of abrasive grains having a uniform grain thickness of from 0.002 to 0.016 inches (0.05-0.4 mm); wherein, the thickness is the smallest uniform dimension, and a length bigger than the thickness, and the grain is preferably at least partially embedded in the bonding layers.

[0025] The invention also includes a method for manufacturing a coated abrasive product including the steps of:

[0026] 1) applying a first bonding layer to a sheet material, where such first bonding layer, when cured, is capable of holding ceramic abrasive grain product and where the ceramic abrasive grain product includes at least fifty percent of abrasive grains having a uniform grain thickness of from 0.002 to 0.016 inches (0.005 to 0.04 cm); where, the thickness is the smallest dimension, and a length and a width, bigger than the thickness, and the grain is at least partially embedded in the bonding layers;

[0027] 2) applying a first layer of ceramic abrasive grain product, as above described, to the first bonding layer,

[0028] 3) curing the first bonding layer to retain ceramic abrasive grain product and removing excess unretained ceramic abrasive grain product

[0029] 4) applying a second bonding layer to the retained ceramic abrasive grain product of the first layer to form a second bonding layer, where such second bonding layer, when cured, is capable of holding ceramic the ceramic abrasive grain product;

[0030] 5) applying a second layer of ceramic abrasive grain product, as above described, to the second bonding layer,

[0031] 6) curing the second bonding layer to retain ceramic abrasive grain product and removing excess unretained ceramic abrasive product,

[0032] 7) applying a third bonding layer to the second layer of ceramic abrasive grain product; and

[0033] 8) curing the third bonding composition.

[0034] The invention also includes the above described method of manufacture where the ceramic abrasive grain product comprises at least 50 percent by weight of particles having an average particle size of 100 to 3000 micrometers, commonly 300 to 2500 micrometers, and an internal concave surface wall, an external convex surface wall and a thickness between the internal and external walls, said external wall being in the shape of a portion of an essentially spherical shape, essentially all of said particles of the ceramic abrasive grain product having a thickness less than twenty percent of the particle size dimensions of the ceramic abrasive grain product, said particles having irregular circumferential edges defined by circumferences of the internal and external walls .

Brief Description of the Several Views of the Drawings

Figure 1 shows a photomicrograph of an embodiment of abrasive grain 16 made by crushing hollow alumina beads that may be used to make an embodiment of a multilayer coated abrasive product 12 in accordance with the present invention.

Figure 2 shows an SEM photomicrograph at 800X showing microcrytalline structure of an embodiment of a grain 16 that may be used to make an embodiment of a multilayer coated abrasive product 12 in accordance with the present invention.

Figure 3 shows a drawing of an embodiment of an abrasive grain 16 formed by crushing a hollow ceramic bubble that may be used to make an embodiment of a multilayer coated abrasive product 12 in accordance with the present invention. The drawing shows a thickness 20, a curved surface 22 and a sharp edge 24.

Figure 4 shows a perspective view of a prior art single layer abrasive product 10 coated with a single layer 17 of abrasive grain 16 in a bonding layer "make coat" 18 on a sheet backing 26 where the abrasive grain 16 is formed by crushing hollow ceramic bubbles.

Figure 5 shows the product of Figure 4 with an added bonding layer "size coat" 28 that protects the abrasive grains 16 from premature fracture.

Figure 6 shows an embodiment of the invention having a second layer 30 of abrasive grain 16 at least partially embedded in a second layer size coat 28 as shown in Figure 5.

Figure 7 shows an embodiment of the invention with a further bonding layer "size coat" 32 to protect the second layer 30 of abrasive grains 16 from premature fracture.

Figure 8 shows an abrasive grain in the form of a ribbon 34 that may be used to make an embodiment of a multilayer coated abrasive product 12 in accordance with the present invention.

Figure 9 shows a cross sectional view of an embodiment of a three layer coated abrasive product 12 in accordance with a preferred embodiment of the invention employing abrasive grains 16. The three layer coated abrasive product has a base sheet 26, a first bonding layer 18, first abrasive grain layer 17, second bonding layer 28, second abrasive grain layer 30 , third bonding layer 32, third abrasive layer 38 and fourth bonding layer 40. Figure 10 shows a diagram of an embodiment showing preparation of a multilayer abrasive product of the invention.

Figure 1 1 shows grains 16 in the form of rods or fibers 42. Detailed Description of the Invention

[0035] As used herein:

[0036] "Bonding layer" is a material that will bond ceramic abrasive grain to a sheet material or backing coat on the sheet material and/or to other abrasive grain, when cured. The term "bonding layer" may be used to refer to both cured and uncured forms depending upon context. Bonding layers usually are resin containing compositions that, when cured will bind ceramic abrasive grain product. Examples of such bonding materials include organic adhesives such as phenolic and epoxy resin containing compositions. The bonding layer may be in the form of a "make" layer or a "size" layer. A "make" layer which is initially applied to adhere ceramic abrasive grain to a sheet material or a pre-coat on a sheet material. The make layer is applied in the form of a make adhesive formula usually later cured by heat. A "size layer protects ceramic abrasive grains from premature fracture by adhering projecting portions of the ceramic abrasive grain to the make layer and/or to each other. A size layer is applied in the form of size adhesive formula which is also usually later cured by heat. Both make adhesive formulas and size adhesive formulas usually contain at least 25 weight percent of an organic resin, preferably a phenolic or epoxy resin due to strength, toughness, adhesive character, heat resistance and heat curability. Size adhesive formulas often contain potassium borotrifluoride (KBF₄) or cryolite ( a₃AlF₆) as a grinding aid. KBF₄ is often added to improve performance on stainless steel and a₃AlF₆ is often added to improve performance on carbon steel.

[0037] "Cure" is intended to mean treatment of a bonding layer so that it will bond ceramic abrasive grain and applies to both ceramic and resin materials. Curing usually is accomplished with heat but may also occur by other means such as by chemical cross linking.

[0038] "Sheet material" is a three dimensional film or fibrous material having a very thin thickness, e.g. 0.05 to 0.3 percent relative to length or width of the material.

[0039] "Backing coat" is a coating of resin and or very fine particulate material that may be applied to the sheet material. "Sheet material" is intended to include material with or without a backing coat.

[0040] "Article" or "workpiece" is intended to mean any article that is to be abraded. [0041] "Uniform thickness" means a thickness that varies by less than 30 % along a majority of the length or width of a ceramic abrasive grain particle in excess of 0.04 cm.

[0042] "Particle size" or "average particle size" means the average of median dimensions of the particles. The median dimension is the intermediately sized dimension of the three dimensions of the particle. The median dimension is determined by determining each of x, y and z mutually perpendicular dimensions through the geometric center of the particle, where the sum of x, y and z is maximized and taking the dimension (width) that that is intermediate in length between the other two dimensions, as the median dimension. In general, the geometric center is assumed to be determined by taking x as the maximum length from one edge of the particle to another edge of the particle and the sum of y and z is maximized through a single point on x.

[0043] "Essentially spherical shape" means a configuration having diameter lengths that deviate by less than 20 percent from each other.

[0044] The invention also includes the coated abrasive product, as above described where the ceramic abrasive grain product includes crushed ceramic bubbles formed from fused ceramic material atomized with compressed gas or crushed ceramic bubbles formed from blown and sintered sol gel ceramic material where the crushed ceramic bubbles may have a size of 400 to 4000 micrometers and the particle size of the ceramic abrasive grain product may be between about 100 and about 3000 micrometers, commonly 300 to 2500 micrometers.

[0045] The invention also includes the coated abrasive product as above described where the ceramic material of the ceramic abrasive grain product is selected from the group consisting of fused and solidified white alumina, fused and solidified brown alumina, fused and solidified alumina-zirconia ceramic alloy, fused and solidified alumina-titania ceramic alloy, and solidified and sintered alumina sol gel.

[0046] The invention also includes the coated abrasive product as above described where the bonding layers are selected from the group consisting of a ceramic matrix, a resin matrix and mixtures thereof.

[0047] The invention also includes the coated abrasive product as above described where the ceramic abrasive grain particles include crushed white or brown alumina bubbles having a packing density below 1.5 g/cm³ when the product has an average particle size of between 500 and 550 micrometers.

[0048] The invention also includes the coated abrasive product as above described where the abrasive grain particles have a packing density less than about 1.3 g/cm³ when the product has an average particle size of between 500 and 550 micrometers. [0049] The invention also includes the coated abrasive product as above described where the ceramic abrasive grain product contain over 3,000 particles per gram when the product has an average particle size of between 500 and 550 micrometers.

[0050] The invention also includes the above described abrading method where the ceramic abrasive grain product is as above described.

[0051] The invention also includes the above described method of manufacture wherein the first, second, and third resin containing compositions all contain at least 25 weight percent phenolic resin.

[0052] The invention also includes the method of manufacture, wherein particles of ceramic abrasive grain product are electrostatically oriented so that the thickness of the particles face a workpiece during use.

The following specific examples and tables serve to illustrate and not limit the present invention.

[0053] The grinding results described below were generated with 7" fiber discs coated via conventional techniques with 36 grit materials and using KBF₄ in the size coat. The discs were mounted to a horizontal turntable and rotated at 2500 rpm. Stainless steel (316) bars (3/16" x 1 " x 24") were positioned vertically in a holder above the disc with the 1 " direction of the steel bar facing across the disc, in line with the central axis. The resulting wear track on the disc had an outside diameter of 6.5 inches and an inside diameter of 4.5 inches. An auxiliary weight of 8.17 lbs. was set on a holder attached to the bar. A new bar, the auxiliary weight and the holder for the auxiliary weight attached to the bar was 9.71 lbs., which applied a pressure of 51.8 psi from the steel bar to the grinding disc. A total of 12 bars with their auxiliary weight holders were used for sequential grinding for 20 second intervals. The weight loss for each set of six bars was recorded as the weight loss during a two minute period. As the bars lost weight, an equivalent weight was added to the auxiliary weight to keep the pressure applied to the disc constant.

[0054] Table I shows the cut in grams of two 36 grit (average particle size 500 to 550 microns) NZ+ 1585 grains made into discs which is for use in coated applications. This grain was used for a control. Also shown is an NZ+ comparable abrasive grain, ATZ-II. This second grain was separated on a diamond shape table into various shape fractions to evaluate the effect of packing density (i.e. shape or sharpness) on the cut of 316 stainless steel. Table I

WEIGHT LOSS (CUT) OF 316SS BARS

NZ+ NZ+ ATZ

Shape Table Compartments NA NA 1-5 9 10 11 12

Packing Density g/cm³ 2.01 2.01 2.16 2.07 2.00 1.93 1.82

Time (Minutes) 2 25.6 23.9 16.1 22.8 28.6 32.8 35.0

4 13.8 13.4 9.8 14.4 14.8 19.6 22.7

6 12.4 8.2 6.5 10.7 11.5 15.6 17.7

8 8.6 6.9 6.0 7.8 8.9 12.0 13.3

10 6.8 5.3 5.7 6.5 6.8 9.3 1 1.6

12 5.3 4.6 5.1 5.1 5.2 7.8 9.7

Total Cut (grams) 2.5 62.3 49.2 67.3 75.8 97.1 1 10.0

Dist Wt. Loss (grams) 1.51 1.38 0 .90 1.18 1.40 1.73 1.86

Test Number 503 507 417 418 419 420 421

[0055] Table I illustrates the importance of using a low packing density (sharp) commercial abrasive material to obtain higher cuts. The packing densities are illustrative of lowest available packing densities for "sharp" grains of the prior art but are not nearly as low as packing densities of grains of the present invention. The discs weight loss correlates very well with the packing densities and cuts. The blockier grains (high packing density) have a shape which results in a larger wear flat area for a specific wear back compared to sharper elongated grains which would have a smaller wear flat area for the same wear back. Thus, the blocky material, which has a higher wear flat area growth rate, also has a more rapidly declining cutting rate and a lower total cut. The smaller wear back for the blocky grains results in a lower disc weight loss. The sharper grains cut more aggressively, have a greater wear back and probably also have wear flat grains breaking off which contribute to a higher disc weight loss. [0056] A description of the physical properties of alumina bubbles is necessary to explain the results on Table III and IIIA.

[0057] The shell thickness of alumina bubbles varies with the S1O2 content and the bubble size. Generally, bubbles blown from AI2O₃ fusions containing 0.3 to 0.7% S1O2 have the thinnest wall thickness. As the S1O2 level decreases or increases from that level, the wall thickness gradually increases. In addition, wall thickness decreases with decreasing bubble size as illustrated on the following Table II. As the bubble size decreases, the wall thickness decreases which results in a decreasing 36 grit packing density and an increasing number of particles per gram and fewer particles on the abrasive disc shown in Tables III and IIIA. Table II is for illustration only. The material is not the same material listed on Table III and IIIA.

TABLE II

36 GRIT (500 to 550 micrometers) FROM CRUSHED BUBBLES

Mesh Bubble Size +5 5/9 9/14 14/18

(> 4 mm) (2-4 mm) (1-2 mm) (0.8-1 mm)

.49% SiO 2

wall thickness - inches 0.008-0.015 0.004-0.008 0.002-0.004 Not

mm 0.2-0.4 0.1-0.2 0.05-0.10 Processed particles per gram 4096 5154 6639

36 grit packing density 1.20 1.10 0.89

.34% SiO?

wall thickness - inches 0.008-0.015 0.004-0. 0.002-0.004 0.002

mm 0.2-0.4 0.1-0.2 0.05-0.10 0.05 particles per gram 4135 4956 6443 8155

36 grit packing density 1.18 1.07 0.89 0.73

0% SiO 2

wall thickness -inches * * 0.002-0.006 0.002-0.004

mm 0.05-0.15 0.05-0.10 particles per gram 6055 6427

36 grit packing density 1.05 .97

* This size bubbles not available. [0058] Table III shows the cut in grams for 36 grit NZ+ 1585, which was used as a control. Also shown are 36 and 30 grit materials made from crushed 4/10 and 10/14 alumina bubbles. Also shown is a 36 grit material made from crushed 6/14 NZ+ comparable bubbles. The grinding test for each individual grain was terminated when the cut reached approximately 5 grams in a two minute period.

TABLE III

WEIGHT LOSS (CUT) OF 316SS BARS

FOR VARIOUS BUBBLE MATERIALS

36N+ 36 30 36 30 36AT

4/10 4/10 10/14 10/14 6/14

% Si0₂ 0.49 0.49 0.28 0.28

Grams of Size on 8" Disc 32.0 32.0 39.0 33.0 37.0 33.0

Grams of Grain on 7" Disc 22.4 13.4 13.5 10.6 10.7 20.8

Packing Density g/cm³ 2.01 1.01 .95 .86 .81 1.37

NZ+ & ATZ-II Packing Density* 1.59 1.15

Particles Per Gram 2028 4805 - 5712 - 3432

NZ+ & ATZ-II Part. Per Gram* 2563 4098

Time (Minutes) 2 25.6 14.8 12.4 10.5 11.2 22.6

4 13.8 14.2 13.0 1 1.2 13.5 17.3

6 12.4 13.4 12.2 12.1 13.2 12.7

8 8.6 1 1.7 10.6 1 1.3 12.3 11.0

10 6.8 9.7 10.0 10.7 11.9 9.7

12 5.3 8.9 9.2 9.9 11.1 8.9

14 8.0 8.8 9.9 10.4 7.9

16 7.2 8.2 9.6 10.1 7.7

18 6.3 7.7 9.1 9.8 7.5

20 5.7 7.1 8.9 9.3 6.5

22 6.9 8.4 8.7 6.3 24 6.3 8.3 8.4 5.8

26 6.1 8.1 7.9

28 5.6 8.1 7.9

30 5.5 7.8 7.2

32 7.5 6.9

34 7.3 6.6

36 7.1 6.4

38 7.0 5.9

40 6.7 5.6

42 6.5

44 6.3

46 6.2

48 5.7

Total Cut 72.5 99.9 129.6 204.2 184.3 129.4

Disc Wt. Loss 1.51 3.12 3.73 5.87 5.86 2.91

Test No. 503 562 558 565 564 568

36 4/10: 36 grit produced by crushing 4/10 alumina bubbles

30 4/10: 30 grit produced by crushing 4/10 alumina bubbles

36 10/14: 36 grit produced by crushing 10/14 alumina bubbles

30 10/14: 30 grit produced by crushing 10/14 alumina bubbles

36 ATZ: 36 grit produced by crushing 6/14 alumina-zirconia bubbles

30 ATZ: 30 grit produced by crushing 6/14 alumina-zirconia bubbles

* NZ+ and ATZ packing density and particles per gram adjusted to a specific gravity of 3.60, the same specific gravity of the alumina bubbles.

[0059] The grain crushed from bubbles (flakes) had a significantly higher cut than the

NZ+ control, cut for a longer time and had a higher weight loss. While not wishing to be bound by any particular theory, this phenomenon is believed to result from the following: [0060] First, it is believed that the flake shape particles have a slower wear flat growth rate with wear back as noted previously, and therefore grind for a longer time before reaching the terminal wear flat area when the grinding product is discarded.

[0061] Second, it is believed that because of the weaker shape, the wear flats may shed (ablate) as they increase in size and receive more friction force from the grinding operation, and

[0062] Third, it is believed that because of the weaker shape, the grains with wear flats may break off below the grinding surface and thus allow new grains to engage the steel surface.

[0063] Shedding or ablation and breakoff can be considered self dressing, and this concept is supported by the higher disc weight loss compared with NZ+. In all test results the higher cuts always correlate with higher disc weight loss.

[0064] The grain made from the 10/14 alumina bubbles had higher cuts than the grain made from 4/10 alumina bubbles. The grain made from the 10/14 bubbles had a lower packing density, thinner walls and a larger number of particles per gram, all of which improved the cut. The grain made from the alumina-zirconia bubbles had a higher packing density, a thicker shell wall .005" - .010" and fewer particles per gram. Thinner wall bubbles should achieve a higher cut.

[0065] Another important aspect of grain from crushed bubbles is that the steel surface finish is finer. The cutting edge of a grain produced from crushed bubbles is composed of micro crystals as asperites and results in a finer surface finish compared with a large single grain cutting point as in NZ+. The finer surface finish of steel using crushed bubbles allows coarser gradings to be used in the manufacture of belts and discs, i.e. 30 grit crushed alumina bubbles to replace 40 or possibly 50 grit NZ+. The surface roughness of the steel bars ground with 36 NZ+ and 30 10/14 was 2783 micro-inches and 1577 micro-inches respectively after 2 minutes of grinding and 1836 micro-inches and 730 micro-inches after 12 minutes of grinding.

[0066] From Table III, the improved performance of crushed alumina bubbles vs.

NZ+ can be calculated.

36 4/10 A O, Cut 99.9g x 22.4g of NZ+ on Disc = 2.30

NZ+ Cut 72.5g 13.4g of Grain on Disc That is, 36 grit from 4/10 crushed alumina bubbles has a performance 230% higher than NZ+.

Using the same procedure:

Performance %

Grain Above 36 NZ+

36 grit crushed 4/10 alumina 230

30 grit crushed 4/10 alumina 297

36 grit crushed 10/14 alumina 595

30 grit crushed 10/14 alumina 548

36 grit crushed 6/14 alumina-zirconia 192

[0067] Again, while not wishing to be bound by any particular theory, it is believed that the difference in the cut and disc weight loss phenomenon between NZ+ and the crushed bubble materials can be explained by wear flat areas. The NZ+ initially has sharper points, and therefore a smaller initial wear flat area and a higher cut. But the blockier NZ+ material has a more rapid wear flat area growth rate during wear back. In comparison, the flakes from the crushed alumina bubbles have an initial higher wear flat area, but the wear flat area growth rate is slower during wear back and/or self dressing occurs to reduce the wear flat growth rate.

[0068] Another test was designed to determine if the amount of size has an effect on cut.

In previous test coating runs (before Table III) to evaluate various abrasives, 28-30 grams of size was always applied to the 8" fiber discs in two coatings, based on data in a 3M patent 4,770,671. Because of the assumed fragile nature of the crushed alumina bubble shells, it was decided to increase the amount of size on the discs in Table III to provide improved or additional support.

[0069] Table IIIA includes the same lot of 10/14 material (.28% Si0₂) as in Table III with various weights of size. Included are two NZ+ discs with 21 and 28g of size. The results indicate that for crushed bubbles there is an optimum amount of size which gives optimum performance. The NZ+ results indicate that 21 or 28 (Table IIIA) of size has no effect on cut.

[0070] A second set of grains on Table IIIA are labeled 0% SiO2. The 25 and 28g of size on the 0% S1O2 grains had a higher cut than the 25 and 28g of size on the .28% S1O2 samples. This was unexpected because the 0% S1O2 material has a higher packing density, fewer particles per gram and slightly thicker shell walls. One explanation is that the absence of S1O2 improves performance. TABLE IIIA

WEIGHT LOSS (CUT) OF 316SS BARS

FOR VARIOUS MATERIALS

36 36 36 36 36 36 36 36 36

NZ+ NZ+ 10/14 10/14 10/14 10/14 10/14 10/14 10/14

% Si0₂ 0.28 0.28 0.28 0.28 0 0 0

Grams size on 8" disc 28 21 21 25 28 31 23 25 28

Grams grain per 7" disc 23.4 24.1 10.2 10.3 10.3 10.6 12.4 13.1 12.5

Packing density g/cm³ 2.01 2.01 0.86 0.86 0.86 0.86 1.05 1.05 1.05

Particles per gram 2028 2028 5712 5712 5712 5712 4910 4910 4910

Time (Minutes) 2 26.2 30.5 26.1 25.0 20.8 18.2 26.4 23.6 19.8

4 16.8 16.8 17.5 18.7 16.0 15.6 19.6 20.3 18.2

6 12.1 11.1 13.3 14.9 13.1 13.7 16.3 17.3 16.1

8 7.9 8.5 11.1 12.5 12.0 12.8 13.4 14.5 14.3

10 6.4 6.2 9.9 10.8 10.3 11.3 11.7 12.4 13.2

12 4.7 5.0 9.2 9.8 9.0 10.2 9.5 11.1 11.8

14 8.5 8.8 8.4 9.6 8.6 10.0 11.0

16 7.6 7.8 7.7 8.8 7.2 9.2 9.9

18 6.2 6.3 7.2 8.2 6.6 8.0 9.2

20 5.4 5.5 6.3 7.8 6.0 7.2 8.6

22 4.7 5.0 6.0 7.1 5.3 6.4 8.0

24 5.9 6.7 5.8 7.3

26 5.5 6.2 5.5 6.5

28 5.3 5.9 5.2 6.2

30 4.9 5.8 5.9

32 5.4 5.3

34 5.2

Total Cut (g) 74.1 78.1 119.5 125.1 138.4 158.5 130.6 146.5 171.3

Disc Wt. Loss (g) 1.46 1.68 3.55 3.57 3.87 4.36 3.75 4.03 4.71 Test No. 589 593 594 595 603 599 588 602 587

Performance % 100 - 370 384 424 472 333 353 433

[0071] The same concepts that were discussed for the fused alumina and fused alumina zirconia materials are applicable with respect to alumina sol gel here and will not be discussed again. Data will be presented which concurs and supports the concepts of the previous section.

[0072] In the first case, ribbons of composition 321 were extruded into various thicknesses, dried, crushed 18gg x 26gg; calcined at 650° C, fired at 1370 °C for 6 minutes and graded into 36 grit. The approximately extruded and fired thickness is shown below:

Extruded Thickness: .099" .058" .036" .027" .020"

(2.5 (1.5 (0.9 (0.7 (0.5

mm) mm) mm) mm) mm)

Fired Thickness: .015" .010" .0065" .005" .004"

(0.4 (0.25 (0.16 (0.13 (0.1

mm) mm) mm) mm) mm)

[0073] The various samples were made into coated discs via the same process as discussed previously and tested by grinding 316 stainless steel bars as discussed previously. The results are shown in Table IV. Included in the results are controls of a 3M commercial disc (985C) and 3M commercial grain (321) made into discs at the same time the ribbon discs were made.

[0074] The grinding test was terminated when the metal removal rate for a two minute interval decreased below 11 grams.

TABLE IV

WEIGHT LOSS (CUT) OF 316SS BARS

VIA 36 GRIT DISCS MADE WITH CRUSHED RIBBONS

3M 3M WM**

985C 321 321

Extruded Thickness - - - .099 .058 .036 .027 .020

Fired Thickness - - - .015 .010 .0065 .005 .004

Grams on Grain on Disc 19* 19 19 19 19 19 18 17

Packing Density g/cm 3

- 1.81 1.63 1.70 1.72 1.59 1.43 1.33

Particles Per Gram NA 2726 3050 2874 2842 3212 4000 4351

Time (Minutes) 2 54.2 40.2 54.7 31.2 40.0 45.5 40.1 43.5

4 20.1 26.0 36.8 22.8 29.4 30.6 33.6 32.2

6 12.3 22.7 24.5 20.2 25.2 27.0 29.2 27.3

8 8.7 16.4 19.0 19.9 23.6 24.9 24.9 26.5

10 8.1 12.2 13.2 16.5 18.4 23.1 20.9 23.3

12 7.8 9.4 11.2 17.1 16.0 18.2 19.1 20.9

14 10.0 12.5 13.2 15.6 17.7 18.4

16 12.2 11.4 12.4 14.7 15.8

18 10.4 9.7 10.5 12.8 15.0

20 10.5 13.2

22 11.6 g. Total Cut 111.2 126.9 169.4 162.8 186.9 207.8 224.1 247.^' g. Disc Wt. Loss 1.64 2.25 2.68 2.84 2.79 3.45 4.37 4.82

Test No. 404 521 393 500 502 512 519 528

Performance % 100 133 128 147 164 197 247

Approximately 30% of the grain on this disc was 40 grit fused brown aluminum oxide * A 3M 321 equivalent composition made by Washington Mills Electro Minerals [0075] The 985 C commercial disc had a high initial cut which is typical of a sharper grain. However, the 985 C disc had a very rapid cut decay and a very low weight loss which is typical of blocky grain. The packing density of the sol gel grain on this disc could not be determined because it was mixed with approximately 30% brown aluminum oxide.

[0076] The commercial 3M 321 grain was used as a control for the remaining grains in the series. The grain labeled WM 321 was an equivalent composition similar to the 3M 321 but was much sharper and crushed from the crude material via a special technique. This sharper grain resulted in a higher cut and also a higher disc weight loss.

[0077] As the extrusion thickness of the ribbon grain decreased, the packing density decreased the particles per gram increased, the cut increased and the disc weight loss increased. Thus when an abrasive disc or belt is made from .020" (0.05 mm) extruded material, the cut will be much higher and 20-30% of the abrasive will be consumed compared to 10-20% for discs or belts made with conventional abrasives.

[0078] The product made with the extruded ribbons had improved cut relative to commercial alumina abrasive products but the performance factor of the extruded ribbons was not nearly as good as the low performance factor of the bulk density ceramic bubble grain of the invention previously described.

[0079] In a further test, fine rods were extruded via a die with multiple holes of .031 "

(0.08 mm). The dried material was partially crushed, calcined at 650°C, then further crushed by hand rubbing on a 14 mesh (1.4 mm) round 8" U.S. standard screen. Below this 14 mesh screen was a screen stack, 20, 25, 30, 35, 40, 45, 50 Pan. The rods were then screen categorized and fired at 1370°C for six minutes. The rod diameter was approximately .007 (0.018 mm)

U.S. Screens Average Length Average Length

Inches mm

25-30 .080 - .090 0.20 - 0.23

30-35 .070 - .080 0.18 - 0.2

35-40 .060 - .070 0.15 - 0.18

40-45 .050 - .060 0.13 -.0.15

45-50 .030 - .050 0.07 -0.13 Pan [0080] The rods were used as the above fractions and were not graded into 36 grit. The grinding results are shown on Table V. Some discs were made with combinations of rods and ribbons and rods and 321 WM.

TABLE V

WEIGHT LOSS (CUT) OF 316SS BARS

VIA DISCS MADE WITH RODS OR RODS AND RIBBONS

Rod Size U.S. Sieves 3M 321 45-50 40-45 30-40 25-3(

Grams of Rods 19* 10.7 20.3 7.9 7.7 1 1.5 17.1

Grams of .020" Ribbons 9.1

Grams of WM 321 9.3 12.8 8.6

Packing Density of Rods 1.81 * 1.54 1.54 1.49 1.47

Time (Minutes) 2 40.2 29.6 17.0 36.1 27.1 31.9 24.0

4 26.0 26.6 19.9 33.0 24.9 29.0 21.3

6 22.7 23.6 20.4 27.2 20.6 26.9 18.6

8 16.4 21.8 18.8 23.7 19.6 24.4 17.4

10 12.2 20.4 19.0 23.5 17.8 21.5 14.6

12 9.4 18.6 15.8 23.2 17.0 21.3 12.9

14 18.1 16.0 21.6 16.7 19.2 12.9

16 15.0 14.7 18.9 15.9 18.0 13.7

18 14.0 13.8 17.1 15.7 17.6 13.8

20 12.1 13.5 16.0 15.1 16.1 12.9

22 1 1.5 12.3 14.3 14.0 16.5 11.1

24 9.8 11.2 12.2 13.9 16.0 11.0

26 10.5 10.8 13.4 15.5 10.6

28 13.4 14.1

30 13.6 13.7

32 13.0 13.4

34 13.2 12.0 36 1 1.8 1 1.2

38 10.9 10.7

Total Cut 126.9 221.0 202.9 277.6 307.7 348.0 209.5

Disc Wt. Loss 2.25 4.21 4.98 5.86 5.95 7.56 5.08

Test No. 521 548 549 550 554 555 575

Performance % 100 165 150 244 225 259 183

Performance calculated via cut and grams of grain on disc.

* grams and packing density of grain - not rods

[0081] In all cases, the cuts and disc weight losses were higher to much higher than the

3M 321 control shown in Table IV and V. Again, this cut was superior but still not as good as the crushed alumina and alumina-zirconia bubbles as previously described. The believed explanation is as before, slower wear flat growth rate and self dressing, both of which contribute to a longer life and higher cut.

[0082] Mixtures of rods and ribbons or rods and WM 321 had higher cuts than rods alone and also had the highest disc weight loss. This could be the result of ribbons and WM 321 providing support for the rods during grinding. There also may be a synergistic effect which promotes self dressing.

[0083] The discs in this series had extra size material which may have contributed a small amount to the higher disc weight loss.

[0084] VLD is an abrasive that is significantly different than traditional abrasive grain.

[0085] The differences are:

1. Packing Density

2. Shape

3. A smoother work piece finish

4. Total metal removed (cut) during the life of the abrasive product

5. A more uniform or constant metal removal rate during the life of the abrasive product 6. Self-dressing ability

[0086] Traditional abrasive grain is comprised of irregularly crushed particles with a shape that can be described as three dimensional cones or pyramids. [0087] Particle shape is important because it affects the growth rate of the wear flat area of the abrasive particles as they wear down during grinding. As the particles wear flat area increases, there is a reduction in the psi applied by the abrasive particles on the steel, a decrease in penetration of the steel by the abrasive particles and a decrease in the metal removal rate.

[0088] All traditional abrasive grain during grinding has an increasing wear flat area, becomes dull and ceases to grind effectively. At this point the metal removal rate is significantly reduced and grinding is stopped; this is called the terminal cut or terminal wear flat area. In traditional abrasive particles the terminal wear flat area is reached when approximately 15-20% of the abrasive is consumed. When the wear flat area increases sufficiently to reduce the metal removal rate to 20-30% of the initial rate, grinding is stopped and is termed the terminal cut and terminal wear flat area. A slower wear flat area growth rate results in a longer grinding time and a higher cut. The terminal cut and wear flat area of classic abrasive particles occurs when only 15-20% of the abrasive is consumed and much abrasive is wasted when the abrasive article is discarded.

[0089] In a traditional three dimensional abrasive particle, the wear flat area increases in two directions as the abrasive particle wears back from its tip. Thus the growth rate of the wear flat area of a traditional particle increases rapidly as a squared function of the linear wear back. VLD is not composed of splintery or elongated classic particles and therefore produces a smoother surface per a specific grit size. A 36 grit VLD produces an Ry surface roughness value of 550-700 micro inches which is comparable or slightly lower than the surface roughness produced by an 80 grit ceramic abrasive. Fifty and 80 grit VLD produce surface roughness values of approximately 450 and 350 Ry and comparable to classic abrasive grits of 100 and 120.

[0090] VLD particles have a unique shape and are self-dressing during grinding which means they do not achieve a terminal wear flat area, but maintain a constant wear flat area as the wear flats continually shed. VLD continues to grind until the backing is reached.

[0091] VLD particles can be considered as two dimensional because the third dimension

(thickness) is thin and constant throughout each particle. In VLD abrasive particles, the growth rate of the wear flat area is initially only linear with particle wear back. Ultimately, after all the particles in the abrasive article make contact with the work piece, the wear flat area no longer increases but remains constant. This is in contrast to the rapid wear flat area growth rate of traditional abrasive particles.

[0092] The VLD self-dressing nature allows two or more layers of abrasive particles to be applied to an abrasive backing material such as polyester fabric or fiber discs. This increases the cut (metal removed during grinding) and extend the grinding life of the abrasive article. In addition, polyester fabric is expensive and extended grinding time and cut would reduce grinding costs.

[0093] This self-dressing phenomenon allows two layers of VLD to be applied to a backing material thereby increasing the total cut with one belt of backing material. Higher cuts and longer life increase efficiency reduce down time and reduce costs. With classic abrasives, no increase in cut is obtained by applying two layers of abrasives.

[0094] Applying two layers is cost efficient because the backing material is expensive and costs approximately $28.00 for a 68" x 132" wide belt. The backing cost for a single layer VLD belt is approximately 33% of the total abrasive belt cost and only approximately 18% of the total two layer abrasive belt cost.

[0095] The total metal removal of VLD abrasives is high because all of the abrasive is consumed during grinding. Table VI lists the cuts of 7" discs of 36 VLD, 22/36 VLD, and 36 sol gel ceramic grain on 316 SS.

[0096] The initial cut of VLD abrasive products (discs and belts) is always somewhat lower than abrasive products made with classic abrasive particles which have sharper points and an initial low wear flat area. However, VLD products continue grinding for longer periods because of self-dressing.

[0097] The specific examples herein illustrate the surprising superiority of double coated abrasives where the abrasive material is a low packing density ceramic abrasive as described above. As previously mentioned, double coating of traditional higher packing density, "blocky" type abrasives provides no significant improvement. It must be understood that the specific examples and tables herein are for embodiments of the invention and are not intended to restrict other embodiments encompassed by the claims or apparent to those skilled in the art in view of the teachings herein.

[0098] While not wishing to be bound by any particular theory, upon the discovery of the unexpected improvement for double coated abrasive of the present invention, it is theorized that when traditional abrasive grains are used in double coating, the abrasive grains in the top coat wear down to cause wear flats that shut down cutting and protect the lower layer before it can be reached. By contrast, when low packing density abrasive grains are used in accordance with the invention, the grains continue to cut and do not develop wear flats that protect the lower layer of abrasive grains. [0099] Another advantage of VLD grain is the lower bulk density and resultant lighter weight which reduces the weight and cost of the of the VLD grain on the belt or disc. The chart below shows the g/cm² of various types of grain on a coated product.

Packing Pickup

Density g/cm³ g/cm²

Fused A1₂0₃ 1.73-1.82 0.67

Sol Gel A1₂0₃ (Ceramic 1.73-1.82 0.67

Alumina Zirconia 1.99-2.10 0.82

VLD 0.85-0.95 0.40

[0100] Table VII lists the cut of 80 grit sol gel ceramic 7" discs on 316SS versus the applied pressure and shows the rapid decline in cut.

[0101] Table VIII lists the performance of 3" x 132" belts of 22/36 VLD and 80 grit sol gel ceramic commercial belts on 316SS. Because 22/36 VLD produces an 80 grit surface finish, the VLD belt is tested against 80 grit sol gel ceramic belts.

Table VI- 7" Discs of 22/36 and 36 Grits Grams of Cut vs. Minutes

Minutes 36 VLD One 22/36 VLD Two 36 Grit Ceramic

Layer Layers Commercial

2 24.0 27.8 61.9

4 18.3 23.4 20.0

6 16.1 21.2 12.4

8 14.5 20.5 10.4

10 13.4 19.5 9.7

12 12.8 99.1 18.3 130.7 8.9

14 12.1 17.7 7.7 131.0

16 11.4 17.0

18 11.1 16.3

20 10.8 15.6

22 10.3 14.6

24 10.0 164.8 14.6 226.5

26 9.6 14.8

28 9.0 14.1

30 8.6 13.7

32 8.1 200.1 13.1

12.8

36 12.5 307.5

12.2

11.6

11.2 10.5

10.5

9.6 373

* 17.6

12.3

12.4

11.6

11.6 450.2

10.9

10.3

9.8

* 11.8

* 12.0

* 12.2 517.2

* 11.5

* 11.6

* 11.5

* 11.4

* 10.8

84 * 10.8 584.8

Test: 3/16 x 1" 316SS bars perpendicular to a 7" disc on a rotating track at

3850ft/min.

Applied pressure 52psi above except * where * = 60psi

Table VII- 80 Grit Ceramic Commercial 7" Discs on 316SS Grams of Cut vs. Minutes

Applied psi 19 24 30 52

Minutes

2 10.7 17.1 24.6 57.3

4 4.4 7.3 13.4 31.1

6 3.9 6.1 10.9 17.7

8 3.9 5.6 8.9 11.6

10 3.7 5.2 8.2 9.2

12 3.3 29.6 5.2 46.5 7.2 72.8 7.3 134.2 *

Excessive burn on this steel. 80 Grit samples are typically tested at 19-24psi Table VIII- 22/36 VLD and 80 Grit Ceramic 3" x 132" Belt Tests

80 Grit Sol Gel Ceramics

Pressure Psi 52 19* 24* 30

Initial Cut g/min 1 4** 30.6 35.5 43.2

Final Cut g/min 14 8.6 8.0 8.0

Total Cut g 3005 485 776 1123

Grinding Min 214 30 38 52

Time

Average Cut g/min 14.0 16.2 20.2 21.6

Belt Test: 2" diameter x 0.156" wall seamless 316L SS tubing. Belt speed

7600ft/min

* The usual psi for grinding 80 grit classic abrasives is 19-24psi

** After the first 12 minutes. Preliminary tests with various size formulas indicate the cutting rate can be increased.

[0102] Table IX shows the grams of cut of 7" fiber discs on 316 stainless steel for various grits of one and two layers.

[0103] The cut of 80 grit commercial sol gel discs is shown on Table VII. Table VIII shows 3" x 132" belt tests at 7600FPM belt speed.

[0104] Finally, 3" x 132" belt grinding charts of 80 grit sol gel and 22/36 VLD on 316 stainless steel are included for comparison.

[0105] Note the rapid decline in cut of the 80 sol gel caused by a rapidly increasing wear flat area and a constant VLD cut resulting from a constant wear flat area combined with self- dressing.

Table IX

7" Discs-Metal Removed (Cut) of Various VLD Grits with One and Two Layers of Grain

Grit 1 Layer 2 Layer

Grams of Grams of grain on a 7" grain on a 7"

Cut Disc Cut Disc

80 154 6.7 343 12.2

50 191 7.6 440 15.3

36 200 9.7 518 20.7

22 305 12.0 - -

22/36 - - 704 23.3 * The test grinding machine rotates a 7" abrasive disc at 2675 RPM. The 316 stainless steel test bar (3/16 x 1" x 24" (starting length) is perpendicular to the abrasive disc and located to make a one inch wide wear track, 4.5" ID and 6.5" OD. The center of the wear track (5.5" ID) has a speed of 3850 FPM.

Manufacture of Coated Abrasive Discs with VLD Abrasives

[0106] Fiber discs (8" diameter) were purchased from Fibre Materials Corp., 40 Dupont St., Plainview, NY 1 1803.

[0107] The coating device was shop made and included a stand, counter top and a stationary lower stainless steel plate connected to the positive terminal of a high voltage power supply.

[0108] The grain to be applied to the fiber disc was sprinkled onto the stainless steel plate, inside of an 8 V₄" boundary. A "make" coat (approximately 7.5-8.5 grams) was applied to the fiber disc. The disc was then secured to the portable Aluminum plate with clips and placed over the lower plate so that the "make" coated fiber disc faced down and was one inch above the lower plate and the loose grain. The upper plate was attached to the negative lead. When the voltage (12,000-15.000 volts depending on grain size) was applied to the two plates, the abrasive particles projected upward and adhered to the "make" coating on the fiber disc.

[0109] Subsequently the disc was heated to 85°C for 2-3 hours to cure the "make" material and hold the abrasive particles to the fiber disc. After the disc was cooled a "size" material was applied which secured the abrasive particles to the fiber disc and contained a grinding aid

(KBF₄). The disc was cured at 85°C for 2-3 hours and then final cured at 115°C for seven hours.

Make Formula Size Formula

Phenolic Resin 48.8% Phenolic Resin 31.27

Span 0.4 Furfural 0.15

H₂0 10.9 H₂0 19.68

No. 70 CaCOs 39.9 KBF₄ 48.90

100.0 100.00 The above steps can be listed as follows for applying one layer of abrasive.

1. Apply "make"

2. Apply grain

3. Cure

4. Apply "size"

5. Cure

The steps for applying two layers are as follows:

1. Apply "make"

2. Apply grain

3. Cure

4. Apply a smaller amount of "size". Less than one half of normal.

5. Cure

6. Apply a small amount of "size" formula. This provides adherence for grain layer two.

7. Apply grain layer two

8. Cure

9. Apply final "size"

10. Cure

The specific values for 36 grit VLD one and two layers is as follows:

36 VLD one layer

Make 7.5g

Grain 13.0g

Cure

Size 28g

Cure

36 VLD two layers

Make 7.5g

Grain 13.0g

Cure

Size 12.0g approximately

Cure

Make (size formula) 12.0g approximately

Grain 14.0g approximately

Cure

Size 28g approximately

Cure

[0110] Finally after curing, the discs were flexed and cut to 7 inch diameters with a ⁷/₈" center hole. The discs were placed on a rotating turntable at approximately 2675 RPM. A set of six stainless steel bars (316L ³/i6" x 1" x 24"), one at a time were placed vertically in a holder above the disc with the 1" direction of the bar facing across the disc. The wear track on the abrasive disc was 1" wide with an inside diameter of 4.5" and an outside diameter of 6.5". The auxiliary weight applied to the top of the bar provided an approximate 51.8psi to the interface between the bar and disc when testing 36 grits. Each bar was ground for 20 seconds and the weight loss was recorded. As the test bars wore down, supplemental weights were added to the auxiliary weight on the top of the test bar to maintain a constant pressure. Lower pressures were used when testing finer grits.

[0111] The grinding results of one and two layers of various grits are shown on Table X.

Table X

Grit 1 Layer 2 Layer

Grams of Grams of grain on a 7" grain on a 7"

Cut Disc Cut Disc

80 154 6.7 343 12.2

50 191 7.6 440 15.3

36 200 9.7 518 20.7

22 305 12.0 - -

22/36 - - 704 23.3

Commercial Plant Manufacture of a Two Layer Coated Abrasive Product with VLD Abrasive

Grain

[0112] The following description of an embodiment for making a multilayer coated adhesive product may be better understood by reference to Figure 10. Such embodiment is intended to illustrate and limit other embodiments encompassed by the claims.

[0113] A sheet backing 26 in the form of a fabric belt 42 from a roll 41 of polyester cloth 42 (68" wide) was used for the manufacture of two layer VLD abrasive belts at an automated commercial facility.

[0114] The facility has an adhesive application station 44 that can be used for both a

"make" station and a size station. The adhesive application station is followed by a grain application station 46 which in turn is followed by a curing oven 48. Initially the adhesive application station 44 is used as a make application station to apply an adhesive layer 45 to the bottom of the fabric belt 42. This is accomplished by feeding fabric belt 42 from roll 41 between a top roller 50 and a bottom roller 52. Bottom roller 52 picks up adhesive 18 from tank 54 and applies it to the bottom of fabric belt 42. The amount of "make" adhesive applied to the belt can be controlled by a gap 56 between the rollers 50 and 52. [0115] The fabric belt 42 is then routed to a grain projection area 58 where the abrasive grain 16 is electrostatically projected onto the belt 42 from the grain belt 60 traveling below. Fabric belt 42 is positively charged by charging plate 62 and abrasive grain 16 is negatively charged on grain belt 60. Abrasive grains 16 thus jump from grain belt 60 to the bottom of fabric belt 42 and adheres to adhesive layer 45. The fabric belt 42 is then run through curing oven 48 to cure adhesive 18. Fabric belt 42 may then be rolled onto a roll 64 and transferred to be used as a roll 41 to repeat the process to apply another abrasive grain layer except that a "size" adhesive formula is used instead of a "make" adhesive formula. At the end of the process, the belt is run through curing oven 48.

[0116] To determine the amount of materials applied to the belt (make, grain and size),

5" circles are cut from the belt and weighed. The formula for the weight of the circle cut out produces a value in pounds/ream.

[0117] The values desired on the plant belt were based on the desired values from the known performance of the 8" discs. The factor is: 1 gram on an 8" disc is equal to 2.08 pounds per ream on a production belt.

[0118] The final cured belt was flexed and several wide belts were made (68" wide x

132" length). One wide belt was slit into 3" x 132" belts for testing on a belt grinder at 7600 feet per minute.

[0119] Previous to the two layer plant run, one and two layer belts were made in the lab by coating and sizing two 9" x 69" strips manually. The two strips were spliced end to end to make a 9" x 126" belt. This belt was then slit into three belts 2 ¾" x 126".

These results are shown below

Grinding

Time grams Cut Cut if

Date Mfg. Item Grit Layers Min 3" X 126 3" x 132

7- 29-08 Lab 1 36 83 1845 1933

8- 11-09 Lab 2 36 84 1617 1695

1-11-1 1 Lab 3 36 207 3436 3601

1-13-1 1 Lab 4 22 222 3322 3481

4-4-11 Lab 5 36 171 3065 3212

4- 7-11 Lab 6 36 169 3004 3148

5- 15-12 Plant 7 22/ 214 3005

36 [0120] The plant two layer belt had a cut slightly lower than expected. This is believed to result from less 36 grit deposited on the second or top layer due to insufficient 36 grit feed supplied to the grain belt.

[0121] The loading for the plant run is lower than previous lab made two layer belts. The loading includes the weight of various finished belts minus the backing material. Included is the abrasive grain, make and size.

Loading

Mfg Item Grit Layers g/in²

Lab 1 36 1 0.72

Lab 2 36 1 0.75

Lab 3 36/36 2 1.40

Lab 4 22/22 2 1.64

Lab 5 36/36 2 1.41

Plant 7 22/36 2 1.36

Claims

What is claimed is:

1. A coated abrasive product comprising a sheet material having at least a first set and a second set of ceramic abrasive grain product applied, said first set of ceramic abrasive grain product being at least partially embedded in a first bonding layer on the sheet material and a second set of ceramic abrasive grain product being at least partially embedded in a second bonding layer applied to the first set of ceramic abrasive grain product; characterized in that, the ceramic abrasive grain product comprises at least fifty percent of abrasive grains having a uniform grain thickness of from 0.005 to 0.04 cm; wherein, the thickness is the smallest uniform dimension, and a length, bigger than the thickness, and the grain is at least partially embedded in the bonding layers.

2. A coated abrasive product of claim 1 further characterized in that a majority of the grains having a uniform grain thickness are oriented so that the thickness of the grains may be exposed to a workpiece.

3. A coated abrasive product of claim 1 further characterized in that the ceramic abrasive grain product comprises at least 50 percent by weight of particles having an average particle size of 100 to 3,000 micrometers and an internal concave surface wall, an external convex surface wall and a thickness between the internal and external walls, said external wall being in the shape of a portion of an essentially spherical shape, essentially all of said particles of the ceramic abrasive grain product having a thickness less than twenty percent of length and width particle size dimensions of the ceramic abrasive grain product, said particles having irregular circumferential edges defined by circumferences of the internal and external walls.

5. A coated abrasive according to claim 2 further characterized in that a majority of the grains having a uniform grain thickness are oriented so that the thickness of the grains may be exposed to a workpiece.

6. The coated abrasive product of claim 3 further characterized in that the ceramic abrasive grain product comprises crushed ceramic bubbles formed from fused ceramic material atomized with compressed gas.

7. The coated abrasive product of claim 3 further characterized in that it comprises crushed ceramic bubbles formed from blown and sintered sol gel ceramic material. 8. The coated abrasive product of claim 1 further characterized in that the ceramic abrasive grain product is in the form of crushed hollow ceramic bubbles, said bubbles having a size of 400 to 4000 micrometers, said particles having an average particle size between about 0.005 to about 0.04 cm, said particles having irregular circumferential edges defined by circumferences of the internal and external surfaces.

9. The coated abrasive product of claim 1 further characterized in that the ceramic material of the ceramic abrasive grain product is selected from the group consisting of fused and solidified white alumina, fused and solidified brown alumina, fused and solidified alumina- zirconia ceramic alloy, fused and solidified alumina-titania ceramic alloy, and solidified and sintered alumina sol gel.

10. A coated abrasive product of claim 1 further characterized in that the ceramic abrasive grain product comprises at least 50 percent by weight of particles having an average particle size of 10 to 1500 micrometers, an internal concave surface wall, an external convex surface wall and a thickness between the internal and external walls of less than twenty percent of the particle size, said external wall being in the shape of a portion of an essentially spherical shape, said particles having irregular circumferential edges defined by circumferences of the internal and external walls; and a resin layer on the sheet material that partially embeds the abrasive grain particles.

11. The coated abrasive product of claim 1 further characterized in that the abrasive grain particles comprise crushed white or brown alumina bubbles having a packing density below 1.5 g/cm³ when the product has an average particle size of between 500 and 550 micrometers. 12. The coated abrasive product of claim 1 further characterized in that the ceramic abrasive grain particles have a packing density less than about 1.3 g/cm³ when the product has an average particle size of between 500 and 550 micrometers.

13. The coated abrasive product of claim 3 further characterized in that the abrasive grain particles have a packing density below 1.0 g/cm³ when the product has an average particle size of between 500 and 550 micrometers. 14. A method for abrading an article comprising grinding or sanding the article with a coated abrasive a sheet material characterized in that it has least a first set of ceramic abrasive grain product at least partially embedded in a first bonding layer on the sheet material and at least a second set of ceramic abrasive grain product partially embedded in a second bonding layer applied to the first set of ceramic abrasive grain product; wherein, the ceramic abrasive grain product comprises at least fifty percent of abrasive grains having an average particle size of 100 to 3000 micrometers, a uniform grain thickness of from 0.005 to 0.04 cm; wherein, the thickness is the smallest uniform dimension, and a length, bigger than the thickness.

15. The method of claim 14 further characterized in that a majority of the grain having a uniform thickness is at least partially embedded in the bonding layers such that the grain is oriented such that the thickness of the grain is exposed to a workpiece.

16. The method of claim 14 further characterized in that the ceramic abrasive grain product comprises crushed ceramic bubbles formed from blown and sintered sol gel ceramic material.

17. The method of claim 14 further characterized in that the particles of the ceramic abrasive grain product have an average particle size between about 500 and about 1500 micrometers.

18. The method of claim 14 further characterized in that the ceramic abrasive grain product is selected from the group consisting of fused and solidified white alumina, fused and solidified brown alumina, fused and solidified alumina-zirconia ceramic alloy, fused and solidified alumina-titania ceramic alloy, and solidified and sintered alumina sol gel.

19. A method for manufacturing a coated abrasive product characterized in that it comprises the steps of:

1) applying a first bonding layer to a sheet material, where such first bonding layer, when cured, is capable of holding ceramic abrasive grain product and where the ceramic abrasive grain product includes at least fifty percent of abrasive grains having a uniform grain thickness of from 0.005 to 0.04 cm, wherein the thickness is the smallest uniform dimension, and a length, bigger than the thickness, and the grain is at least partially embedded in the bonding layers;

2) applying a first layer of the ceramic abrasive grain product to the first bonding layer,

3) curing the first bonding layer to retain ceramic abrasive grain product and removing excess unretained ceramic abrasive grain product

4) applying a second bonding layer to the retained ceramic abrasive grain product of the first layer to form a second bonding layer, where such second bonding layer, when cured, is capable of holding ceramic the ceramic abrasive grain product;

5) applying a second layer of the ceramic abrasive grain product to the second bonding layer,

6) curing the second bonding layer to retain ceramic abrasive grain product and removing excess unretained ceramic abrasive product,

7) applying a third bonding layer to the second layer of ceramic abrasive grain product; and

8) curing the third bonding composition.

20. The method of claim 18 further characterized in that the ceramic abrasive grain product comprises at least 50 percent by weight of particles having an average particle size of 100 to 3000 micrometers and an internal concave surface wall, an external convex surface wall and a thickness between the internal and external walls, said external wall being in the shape of a portion of an essentially spherical shape, essentially all of said particles of the ceramic abrasive grain product having a thickness less than twenty percent of the particle size dimensions of the ceramic abrasive grain product, said particles having irregular circumferential edges defined by circumferences of the internal and external walls .

21. The method of claim 18, further characterized in that the first, second, and third resin containing compositions all contain at least 25 weight percent phenolic resin. 22. The method of claim 18, further characterized in that particles of ceramic abrasive grain product are electrostatically oriented so that the thickness of the particles face a workpiece during use.

23. The method of claim 18, further characterized in that subsequent to applying the third bonding layer, a further layer of ceramic abrasive grain is applied followed by the curing of the third bonding layer and yet another adhesive layer is applied as a size layer and is cured.

24. The method of claim 19 further characterized in that further alternating layers of ceramic abrasive grain product and bonding layers are applied prior to a final curing step.

25. The coated abrasive product of claim 1 further characterized in that there are a plurality of alternating bonding layers and sets of ceramic abrasive grain product.

26. The method of claim 19 further characterized in that after step 3) and before step 4) a first intermediate stabilizing bonding layer is applied and cured to stabilize the first set of ceramic abrasive grain product during further processing.