US3926585A - Abrasive sheet containing a grain-size binder with wax particles - Google Patents

Abstract

The loading of an abrasive belt with particles of a soft metal during grinding or polishing of the latter is sharply reduced, the amount of metal removed per unit time greatly increased, and the useful life of the belt improved if the abrasive grains on the belt are covered with an intimate mixture of a solid binder with finely dispersed wax particles.

Description

United States Patent Lukowski Dec. 16, 1975 1 ABRASIVE SHEET CONTAINING A [56] References Cited GRAIN-SIZE BINDER WITH WAX UNITED STATES PATENTS PARTICLES 2,881,065 4/1959 Reuter 51/305 [75] Inventor: Heinz Lukowski, Wesseling, 2,899,290 8/19 Riegler 4 4 5l/305 Germany 3,102,010 8/1963 Lang .1 51/298 3,195,993 7/1965 Gladstone 51/295 [73] Asstgnee: Feldmuhle Anlagenund 3,205,054 9/1965 Tucker 1 1 5l/298 Produktionsgesellschaft mit 3,331,667 7/1967 Schnabel... 51/298 beschrankter Haflung, 3,676,092 7/1972 Buell 51/298 Duesseldorf-Oberkassel, Germany 1 Primary Examiner-Donald J .1 Arnold [22] Flled 1974 Attorney, Agent, or FirmHans Berman [21] App]. No.: 447,789

- 57 ABSTRACT Foreign Application Priority Data The loading of an abrasive belt with particles of a soft Mar. 10,1973 Germany 2312052 metal during grinding or polishing of the latter is sharply reduced, the amount of metal removed per [52] US. Cl. 51/295; 51/298; 51/301; unit time greatly increased, and the useful life of the 51/305; 51/306 belt improved if the abrasive grains on the belt are [51] Int. Cl. B24D 11/02; C08] 5/ 14 covered with an intimate mixture of a solid binder [58] Field of Search 51/295, 298, 305, 301, with finely dispersed wax particles.

9 Claims, N0 Drawings ABRASIVE SHEET CONTAINING A GRAIN-SIZE BINDER WITH WAX PARTICLES This invention relates to abrasive sheet material, and particularly to an improved abrasive sheet material suitable for fine-grinding and polishing soft, non-ferrous metals such as copper, aluminum, and their soft alloys.

The term abrasive sheet material, as employed herein, covers paper and fabric sheets and belts coated with abrasive grains which are bonded to the fibrous, flexible base by a layer of binder material. When such abrasive sheet material is employed for removing sur* face layers of soft, particularly non-ferrous metal, the metal tends to drag and to load the abrasive sheet, that is, particles of the soft metal tend to clog the interstices between the abrasive grains on the surface of the flexible base. It is impractical to remove the metal from the abrasive sheet, and it is not unusual to discard abrasive belts or flat sheets before much of the abrasive material is lost from the base. The problem is of minor consequence in rough-grinding, but increases in importance as the size of the abrasive particles decreases. This invention is concerned primarily with improving abrasive sheet material in which the abrasive grains have a size smaller than 100 grit, but its advantages are available, at least to some extent, in coarser abrasive sheets.

It has been usual practice to apply a greasy lubricant, such as tallow, to an abrasive belt, particularly when the belt travels at the high end of the usual grinding and polishing range of 5,000 to 10,000 ft./min. The improvement achieved is relatively modest, and it is necessary continuously to replenish the lubricant which is thrown from the belt by centrifugal forces and contaminates the work area. The use of solid chloroparaffin lubricant, which has been proposed in US. Pat. No. 3,676,092, overcomes some of the disadvantages of tallow, but the rate of material removal from a soft metal work piece is improved only by about 50 percent.

Polytetrafluoroethylene has been proposed as a lubricant coating for abrasive material in US. Pat. No. 3,042,508, and has been shown to provide greatly improved grinding efficiency, but it is not practical to apply a continuous and coherent fluorocarbon layer to abrasive grains on a fibrous substrate such as paper or cloth because the fluorocarbon layer must be consolidated at temperatures well beyond the decomposition temperature of the usual flexible base materials.

Only minor improvements in grinding efi'lciency were achieved by the method of US. Pat. No. 2,893,854 in which granular abrasive is coated with a layer of ethyl cellulose, metal soaps, and fillers. The added layer can retard loading of the abrasive grains with soft metal particles only for a very limited time.

The object of the invention is the provision of an improved grinding or polishing material of the type in which one of the major faces of a flexible base of sheet material carries a layer of binder material, and a multiplicity of abrasive grains are secured to the base by the binder material.

The improved grinding or polishing material of the invention includes an exposed covering layer covering the abrasive grains and essentially consisting of an intimate mixture of a second binder material and wax. The wax is present in the mixture in the form of particles having an average size of less than 500 microns, and the second binder material is solid and shape-retaining at least at 25C when traveling at 10,000 ft/min. in a circular path of 4 inch diameter. The weight ratio between the second binder material to the wax in the mixture is between 1:5 and 2:1, and preferably between 1:1 and 2:3.

The term wax is employed herein according to modern usage, as defined by l-llackhs Chemical Dictionary (McGraw-l-lill Book Company, New York, 1969), to encompass substances characterized by a crystalline to microcrystalline structure, the capacity of acquiring gloss when rubbed, the capacity to produce pastes or gels with suitable solvents or when mixed with other waxes, a low viscosity at just about the melting point, and low solubility in solvents for fats at room temperature. A wax, for the purpose of this invention, thus may be a mineral wax, an animal or vegetal wax, or a synthetic wax. Beeswax, carnauba wax, ouricuri wax, paraffin, ceresin, polyolefin waxes, and amide waxes are merely representative of suitable waxes.

The binder materials employed for securing the abrasive grains to the flexible base are conventional and include synthetic resin compositions, but also water soluble glue, such as hide glue. The second binder material which is mixed with the wax in the covering layer must be strong enough to prevent loss of wax by centrifugal force generated typically when an abrasive belt travels at 10,000 ft./min. in a circularly arcuate path about a pulley 4 inches in diameter, but greater strength, of course, is desirable as far as it is consistent with the necessary flexibility of the abrasive sheet material.

Binder materials combined with the wax particles in the covering layer thus may be synthetic resin compositions including phenolic, urea, epoxy, polyester, polyurethane, and alkyd resins, but. also water soluble glue.

It is normally most advantageous to hold the weight ratio of binder material and wax in the covering layer between 1:1 and 2:3. No advantages can be achieved by deviating from this ratio. When the binder material amounts to less than about 16 percent of the mixture (a ratio of 1:5), the adhesion of the covering layer to the abrasive grains is normally too small, and the covering layer is released from the grinding sheet in a relatively short time. When the binder material exceeds about 66 percent of the mixture (a ratio of 2:1), the improvement achieved by the presence of the wax is normally unsatisfactory. As a general rule, and particularly when using amide waxes, the best results are achieved at an approximate ratio of one part binder to 1.35 part wax.

The preferred amide waxes are derivatives of ethylenediamine in which two acyl radicals of fatty acids, particularly of stearic, palmitic, and oleic acid, are attached to at least one amine nitrogen, and more specifically the distearoylethylenediamines. The commercial products which are nominally distearoylethylenediamines are mixtures of the N,N- and N,N'-isomers, and may contain minor amounts of impurities. The specific location of the acyl groups and the presence of minor amounts of impurities have not been found significantly to affect the performance of the amide waxes.

The effectiveness of a covering layer in the abrasive sheet material of the invention is not impaired by the presence of a pulverulent, inorganic or organic filler which is softer than the abrasive grains employed if it does not amount to more than 60 percent of the weight of the covering layer. Calcium carbonate is typical of inexpensive filler materials readily available.

The weight of the covering layer may vary between 5 and 1,000 g/m and will be selected according to the mesh or grit of the abrasive grains. Coarse abrasive generally requires a heavier covering layer than finer abrasive grain. For abrasive grains smaller than 100 grit, which benefit most from the improvement of this invention, a covering layer of 5 to g/m is adequate.

The greatest improvement in grinding performance as compared to abrasive material without a wax-bearing covering layer has been achieved so far in an abrasive belt in which the grains of abrasive material are bonded to the fibrous base by means of water soluble animal glue (hide glue), the covering layer consists of amide wax and a cured epoxy resin, and a layer of cured phenol-formaldehyde resin is interposed between the grains and the exposed covering layer.

The following Examples further illustrate the invention:

EXAMPLE 1 An endless belt of cotton twill having two major faces 50 mm wide and 3,500 mm long was coated on a roller coater with a commercial, water-bearing, A-stage phenol formaldehyde resin composition having a nominal viscosity of 800 cp to 1,000 cp, a pH of 8.0 to 9.0, and a density of about 1.25 at C. The resin composition was capable of conversion to the B-stage in about 5 minutes at 120C without significant loss of formaldehyde;

The coated base of textile sheet material was covered with 120-grit emery grains from an electrostatic spray gun, and the abrasive grains were bonded to the base by heating to 90C until the resin layer solidified. The grains then were covered with a surface layer prepared by dispersing 10 parts micronized amide wax and 4 parts calcium carbonate powder in 20 parts of another commercial, A-stage phenol formaldehyde composition and depositing the mixture by means of a roller coater, all parts herein being by weight unless stated otherwise.

The amide wax was Hoechst Wax C, a commercial product essentially consisting of di-octadecanoylethylenediamine, the stearoyl groups being bound to the nitrogen atoms of the diamine. The wax employed had a nominal dropping point of 139 to 144C, an acid number of 3 7, a saponification number of 3 10, a density of 0.99 1.01 at 20C, and was free from measurable amounts of ash.

The A-stage phenolic resin employed as a binder material in the covering or surface layer had nominal properties of 900 to 1,100 cp viscosity, a pH of 8.0 to 8.5, a density of 1.26 at 20C, and it converted to the B-stage in about 10 minutes at 120C.

The laminar belt structure so obtained was cured in an oven at a temperature gradually raised to 120C, and held at 120C for 2 hours.

Additional belts were prepared from otherwise the same materials employing 220, 320, and 400 grit emery. A second set of four abrasive belts was prepared for comparison purposes without the amide wax under otherwise identical conditions.

The weight ratio of first binder layer, abrasive grains, and covering layer were as shown in Table 1 which also lists weight ratios for abrasive grit not employed in this Example, but referred to hereinbelow. The Table applies to all Examples unless stated otherwise.

TABLE 1 Weight, g/m

Grit 1st Binder Abrasive Coverq Layer TABLE 2 Weight loss, g Grit With wax Without wax EXAMPLE 2 A fabric belt of the type and dimensions described in Example 1 was coated with hide glue in a conventional manner and covered with grit emery grains as in Example 1. After drying of the glue layer, a phenolic resin layer was deposited and was cured as in Example 1. The weight of this layer, when cured, was 40 g/cm The A-stage phenol-formaldehyde composition employed was identical with that used as a first binder between the abrasive grains and the base in Example 1.

The belt so prepared was tested as described in Example 1. It removed 30 g aluminum from a test body in the standard testing period of 60 minutes, and did not contain wax in a covering layer.

EXAMPLE 3 A belt prepared as in Example 2 was further coated with a covering layer prepared by intimately mixing 134 parts micronized Hoechst Wax C with 100 parts of a liquid epoxy resin composition containing a hardener, and curing the covering layer.

The amount of aluminum removed by the modified belt from a test body under conditions otherwise identical with those used in Example 2 increased from 30 g to 227 g.

EXAMPLE 4 In the otherwise unchanged procedure of Example 3, Hoechst Wax C was replaced by an equal amount of an amide wax commercially available as Glockem Wax D2S, chemically closely similar to Hoechst Wax C, and having a similar range of physical properties including a dropping point of 142 147C, an acid number of 2 6, a saponification number of less than 6, a density of 0.997 at 20C, and an ash content of 0.018 percent.

The belt so prepared removed 207 g aluminum from the test body.

EXAMPLE 5 It removed 207 g aluminum from the standard test body.

EXAMPLE 6 134 Parts paraffin was dissolved in benzene, and the benzene solution was mixed with the liquid, catalyzed epoxy resin composition employed in Examples 3 and 4 by means of a high speed mixer which caused small paraffin particles to be uniformly dispersed in the resin composition. The mixture so obtained was applied to a belt prepared as in Example 2, and the coated belt was stored until the resin was fully cured.

214 g Aluminum were removed by the cured belt from the standard aluminum body in the grinding test described in Example 1.

When polypropylene wax was substituted for the paraffin, the belt was capable of removing 162 g aluminum in the standard test.

EXAMPLE 7 A belt prepared as in Example 2 was coated with a covering layer initially consisting of an intimate mixture of 100 parts liquid epoxy resin composition containing a hardener and identical with the composition employed in Examples 3 and 4, 134 parts micronized Hoechst Wax C, and parts calcium carbonate powder.

The belt, when tested after complete cure of the resin, removed 24] g aluminum from the test body. The improvement apparently due to the presence of the filler material cannot be fully explained at this time.

When the amount of calcium carbonate was increased to 50 parts under otherwise unchanged conditions, the amount of removed aluminum was reduced to 227 g, and a further reduction to 216 g occurred when the calcium carbonate was further increased to 200 parts.

EXAMPLE 8 In a procedure otherwise unchanged from that of Example 7, the calcium carbonate in the covering layer was replaced by 10 parts powdered cryolite (Na AlF The aluminum removed in the standard test of Example 1 amounted to 231 g.

When the cryolite was increased to 50 parts, aluminum removal remained approximately unchanged at 228 g. It was reduced to 208 g when the cryolite was further increased to 150 parts.

EXAMPLE 9 The procedure of Example 2 was repeated using 320 grit emery and a correspondingly reduced layer of glue (see Table 1). The thickness of the phenolic resin layer applied over the abrasive grains also was reduced to g/m The belt so prepared removed 4 g aluminum from the test body in the standard grinding test of Example 1.

Application of a covering layer of epoxy resin composition and amide wax, as in Example 3, improved the test result to 36 g aluminum.

EXAMPLE 10 A twill belt was coated with a first binder layer of A-stage phenolic resin composition and with grit emery as in Example 1. After partial curing of the first binder layer, the grit was covered with enough additional A-stage phenol-formaldehyde resin to make the second or intermediate layer 50 g/m after curing. As a covering or surface layer, the: mixture of epoxy resin composition and amide wax described in Example ,3 was applied. A control sample lacking the covering layer was also prepared.

Y A test block of structural steel having a tensile strength between 37 and 45 kplmm a carbon content of less than 0.20 percent, a phosphorous content of less than 0.06 percent, and a sulfur content of less than 0.05 percent was ground on a commercial belt grinder at a speed of 6,000 ft./min. and at a pressure of 6 kg by means of the two belts. The control belt removed 306 g steel and lost 3.5 g of its abrasive grains after 30 minutes grinding. The belt according to the invention removed only 269 g steel and lost 6.1 g abrasive material, being thus clearly inferior to the control.

When an aluminum test body (99 percent Al) was ground on the same machine at a pressure of 4 kg with the two belts, the control removed only 56 g aluminum and lost 2.2 g abrasive, while the belt according to the invention removed 166 g aluminum, losing 6.6 g abrasive grains.

Additional belts were prepared from 220 grit emery with correspondingly reduced thicknesses of bonding material and covering layer, and employed in tests on bodies of the above-mentioned mild structural steel, an austenitic stainless steel, commercial aluminum (99 percent Al), brass (58 percent Cu), phosphorbronze, copper, melamine formaldehyde resin, and nylon 6. The belt according to this invention was superior to the control belt in grinding aluminum, copper, nylon, stainless steel, melamin resin, and brass, in that order, and inferior to the control belt on the harder metal of the structural steel and phosphorbronze.

These results could be duplicated, at least in a qualitative manner, using other commercial belt grinders at different contact pressures, belt speeds, abrasive grits. Substitution of paper as a base material did not have a significant effect on the results. Limited tests with other abrasives (silicon carbide, quartz sand) showed that the nature of the abrasive has no bearing on the advantages of the abrasive sheet material of the invention.

It should be understood, of course, that the foregoing disclosure relates only to preferred embodiments of the invention, and that it is intended to cover all changes and modifications of the Examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

What is claimed is:

1. In a grinding or polishing material having a flexible base of sheet material, a layer of a first binder material on one of the major faces of said base, and a multiplicity of abrasive grains secured by said binder material to said base, the improvement which comprises a covering layer covering said grains and said first binder material and essentially consisting of an intimate mixture of a second binder material and a wax, said wax being pre= ent in said mixture in the form of particles having an average size of less than 500' microns, said secofl binder material being solid and shape-retaining at 25 when traveling at 10,000 ft./min. in a circular arc of 4 inch diameter, the weight ratio of said second binder material to said wax in said mixture being between 1:5 and 2:1, said second binder material securing said particles to said grains, said first binder material, and said base, said binder materials being members of the group consisting of phenol formaldehyde resin, urea formaldehyde resin, epoxy resin, polyester resin, polyurethane resin, alkyd resin, and water soluble glue.

2. In a material as set forth in claim 1, the weight ratio of said second binder material to said wax being between 1:1 and 2:3.

3. In a material as set forth in claim 2, said covering layer containing up to 60 percent by weight of a solid, particulate filler having a hardness substantially smaller than the hardness of said grains.

4. In a material as set forth in claim 1, a layer of cured phenol-formaldehyde resin composition interposed between said grains and said covering layer.

5. In a material as set forth in claim 4, said first binder material essentially consisting of water-soluble glue, said Second binder material being a cured epoxy resin composition, and said wax is an amide of a fatty acid.

6. In a material as set forth in claim 1, the size of said abrasive grains being smaller than 100 grit.

7, In a material as set forth in claim 1, said wax being distea'roylethylenediamine.

8. In a material as set forth in claim 2, said second binder material being a cured epoxy or phenol formaldehyde resin, and said wax being an amide of a fatty acid.

9. In a material as set forth in claim 1 and said wax being a member selected from the group consisting of beeswax, carnauba wax, ouricouri wax, paraffin, ceresin, polyolefin wax, and amide wax.

Claims (9)

1. IN A GRINDING OR POLISHING MATERIAL HAVING A FLEXIBLE BASE OF SHEET MATERIAL, A LAYER OF A FIRST BINDER MATERIAL ON ONE OF THE MAJOR FACES OF SAID BASE, AND A MULTIPLICITY OF ABRASIVE GRAINS SECURED BY SAID BINDER MATERIAL TO SAID BASE, THE IMPROVEMENT WHICH COMPRISES A COVERING LAYER COVERING SAID GRAINS AND SAID FIRST BINDER MATERIAL ESSENTIALLY CONSISTING OF AN INTIMATE MIXTURE OF A SECOND BINDER MATERIAL AND A EAX SAID WAX BEING PRESENT IN SAID MIXTURE IN THE FORM OF PARTICLES HAVING AN AVERAGE SIZE OF LESS THAN 500 MICRONS, SAID SECOND BINDER MATERIAL BEING SOLID AND SHAPE-RETAINING AT 25*C WHEN TRAVELING AT 10,000FT/MIN. IN A CIRCULAR ARC OF 4 INCH DIAMETER, THE WEIGHT RATIO OF SAID SECOND BINDER MATERIAL TO SAID WAX IN SAID MIXTURE BEING BETWEEN 1:5 AND 2:1, SAID SECOND BINDER MATERIAL SECURING SAID PARTICLES TO SAID GRAINS, SAID FIRST BINDE MATERIAL, AND SAID BASE, SAID BINDER MATERIALS BEING MEMBERS OF THE GROUP CONSISTING OF PHENOL FORMALDEHYDE RESIN, UREA FORMALDEHYDE RESIN, EXPOY RESIN, POLYESTER RESIN, POLYURETHANE RESIN, ALKYD RESIN AND WATER SOLUBLE GLUE.

2. In a material as set forth in claim 1, the weight ratio of said second binder material to said wax being between 1:1 and 2: 3.

3. In a material as set forth in claim 2, said covering layer containing up to 60 percent by weight of a solid, particulate filler having a hardness substantially smaller than the hardness of said grains.

4. In a material as set forth in claim 1, a layer of cured phenol-formaldehyde resin composition interposed between said grains and said covering layer.

5. In a material as set forth in claim 4, said first binder material essentially consisting of water-soluble glue, said second binder material being a cured epoxy resin composition, and said wax is an amide of a fatty acid.

6. In a material as set forth in claim 1, the size of said abrasive grains being smaller than 100 grit.

7. In a material as set forth in claim 1, said wax being distearoylethylenediamine.

8. In a material as set forth in claim 2, said second binder material being a cured epoxy or phenol formaldehyde resin, and said wax being an amide of a fatty acid.

9. In a material as set forth in claim 1 and said wax being a member selected from the group consisting of beeswax, carnauba wax, ouricouri wax, paraffin, ceresin, polyolefin wax, and amide wax.