DD296024A5 - SCHLEIFFBLATTMATERIAL - Google Patents

Abstract

The invention relates to an abrasive sheet material. The inventive solution is to provide an abrasive sheet material which allows improved grinding performance. According to the invention, this is achieved by the abrasive sheet material consisting of a carrier layer and an abrasive layer, the abrasive layer having a contact layer and a layer of a plurality of preformed fibrous abrasive particles having a substantially uniform cross-section adhered to the backing pad by the contact layer, and that the abrasive particles have a substantially uniform cross-section with each other and a length ratio of at least 1: 1 and consist of sintered a-alumina crystals whose size is preferably 2 mm and at most 10 mm. Fig. 1 {abrasive sheet material; Traegerschicht; Contact layer; Abrasive layer; fibrous abrasive particles; uniform cross-section; Laengenverhaeltnis; a-alumina crystal}

Description

For this 9 pages drawings

Sanding sheet material

This invention relates to an abrasive sheet material. Since their introduction several years ago, sol-gel corundum abrasives have demonstrated significant advantages over other premium abrasives in wide ranges of application to abrasive sheet materials. It is known to produce such abrasives by drying and sintering an aluminum hydroxide gel, which may also contain varying amounts of additives such as MgO or ZrO2. The dried material is crushed either before or after sintering to obtain irregular, boulder-shaped polycrystalline abrasive grains of a desired size range. Subsequently, the abrasive particles can be incorporated into abrasive sheet materials such as round abrasive sheets or abrasive belts. It is known from US-P 4,314,827 to produce abrasive grains in which the sintered abrasive grains contain irregular "snowflake-like" shaped Al ₂ O ₃ crystals whose diameter is from 5 to ЮЮt. The space between the arms of a "snowflake" and between adjacent "snowflakes" is occupied by other phases, such as a fine crystalline alumina magnesia spinel.

U.S. Patent No. 4,623,364, issued November 18, 1986 and assigned to Norton Company, teaches a sol-gel process for the production of alumina abrasive grits and non-abrasive grit products such as coatings, thin films, fibers, rods, or small-sized parts having improved properties known. According to this patent, the conversion of the aluminum hydroxide to a-alumina is facilitated by introducing seed into the gel or gel precursors before drying. This may be combined with wet vibration milling of the gel or gel precursor with ct alumina binders or with direct addition of high purity seed particles in powder or other form. This a-alumina obtained in this way (hereinafter often referred to as SG grain) has a very fine, uniform crystallite structure, in which the size of all crystallites is substantially less than about 1 μιτι. Somewhat larger crystallites can be achieved by prolonged firing, but this is generally undesirable. For the production of abrasive grains, the seeded gel is dried, crushed and fired. The abrasive grains thus produced can be used for the production of abrasive products such as round abrasive sheets and abrasive wheels. For the production of moldings or rods, the material may also be profiled or formed by extrusion prior to firing. When bars are extruded, the bars are later cut or broken into the appropriate lengths. The invention has for its object to provide an abrasive sheet material with which an improved grinding performance is achieved.

According to the invention, the object is achieved in that the abrasive sheet material consists of a backing and an abrasive layer, wherein the abrasive layer has a contact layer and a layer of a plurality of preformed, fibrous abrasive particles having a substantially uniform cross-section which adhere to the backing by the contact layer and in that the abrasive particles have a substantially uniform cross-section and an aspect ratio of at least 1: 1 relative to one another and consist of sintered α-aluminum oxide crystals whose size is preferably 2 μm and at most 10 μm.

The abrasive particles have a minimum hardness of 14, better 16 and in the most preferred embodiment 18GPa and / or an average aspect ratio of at least about 1: 1, preferably 2: 1 and / or a preferred diameter of about 0.33mm. The aspect ratio is the ratio between length and cross section of the fibrous abrasive particles. Preferably, at least 80%, better still 95% of said alumina abrasive fibrous particles appear as generally equiaxed crystals having a size of at most 0.5%, preferably 0.4%. Further features of the solution according to the invention can be found in the dependent claims.

The solution according to the invention comprises an abrasive layer. The abrasive sheet material of the invention contains polycrystalline abrasive fibers. It ensures a long service life and requires less force for a given chip removal through the use of a special form of sol-gel alumina abrasive grain.

The abrasive sheet material of the invention also has better free-cutting properties and develops less heat during grinding.

With the abrasive sheet material according to the invention, a more uniform ablation is achieved, while giving the workpiece to be machined a more consistent surface quality over an unusually long life.

The present invention provides an abrasive sheet material in which the abrasive grain consists of sintered sol-gel-α-alumina fibers whose cross-section is substantially consistent over its length. On average, the abrasive fibers have an aspect ratio of at least about 1: 1, preferably at least 2: 1 to 9: 1, wherein a length ratio to 12: 1 and above is possible. Diea alumina fibers may contain additives such as MgO or other spinel alumina, ZrO ₂ or other compatible materials. They are prepared by a sol-gel method, preferably from a seeded SoI gel. The abrasive fibers are preferably at least 95%, more preferably at least 98%, of a-alumina crystallites and are substantially free of impurities which form amorphous or "glassy" substances upon firing.The crystallites are about 2μιτι in size, but the preferred fibers are crystallites contain μιη less than 1 and in the most preferred embodiment less than 0.5 \ in the are.

With a fiber end, the abrasive fibers are attached to a flexible backing by means of an adhesive contact layer.

In general, the abrasive fibers extend in a direction opposite to the backing and are advantageously coated with a make coat which reinforces their anchorage in the backing. As a backing, any known pad for abrasive sheet materials such as woven or malware, foil or paper is suitable. Depending on the application, all conventional methods and materials for sanding sheets can be used for the fabric finishing and paper finishing of the backing. Likewise, all known customary contact layers used in the production of coated abrasive sheets can be used.

If the aspect ratio of the abrasive fibers of the invention is relatively small, e.g. on average at least about 1: 1, preferably about 2: 1 to about 5: 1, the binder layer can be applied by the roll coating method known per se.

If the abrasive fibers have a greater aspect ratio, preference is given to other coating methods, such as spray coating, in which the fibers are not excessively pressed down. Also, the materials used for the make coat may be any of the known types used in the abrasive industry for abrasive sheet materials. It has been found that the abrasive products having the fibrous abrasive particles have a substantially longer life than those containing a crushed abrasive grain of the known type.

Compared to the abrasive sheet materials known per se, there is also a tendency for less unstable material removal and a less unstable surface finish of the machined workpiece over at least part of its tool life.

Surprisingly, it has also been found that the use of the abrasive sheet materials according to the invention produce particularly effective results when sanding at low pressure. A particular advantage of the invention is that not only abrasive products can be created in the form of abrasive sheet materials with fibrous abrasive particles of different desired length, but also the particle size distribution for a specific application as precise or as variable as may be required-one way which was previously not given with broken abrasive grain. Another advantage is that abrasive fibers can be used, which are cut into different lengths or lengths ratios to simulate a normal fiber mixture according to CAMI classification. Likewise, the abrasive sheet materials may contain a specified mixture of abrasive fibers having oversize, comparative, and fine grain diameters.

Another advantage of using abrasive particles of predetermined configuration to make abrasive sheet materials is that they are more economical and effective.

It is also advantageous that the abrasive products having a lower grain density on the surface often perform better than those having a higher number of grains per surface unit.

The abrasive sheet materials of the present invention can be made in a variety of shapes, such as tapes, round or polygonal abrasive sheets, and specialty finishes.

The tests used special circular sanding sheets and showed that they perform better in many sanding jobs.

It has also been found that the abrasive sheet materials according to the invention are particularly well suited for the effective use of grinding aids. Typically, these are applied to the surface of the abrasive in the form of a coating. In this case, the low profile limits the conventional abrasive grain, the applicable grinding aid amount, since the individual abrasive grains should not be covered. However, due to the high profile of the fibrous abrasive particles used in the present invention, it is possible to apply far more grinding aid, which gives extremely advantageous results. This also gives rise to the possibility of applying the grinding aid in a more reactive form, for example as a foam instead of a mixture in a resin layer.

The grinding aids may include all those whose effectiveness is known, such as. As KBF ₄ , K ₂ TiF, NaCl, sulfur and similar substances.

The invention will be explained in more detail by exemplary embodiments. In the accompanying drawing show

Fig. 1: the photograph of a plan view of a portion of an abrasive sheet material according to the invention with a

Abrasive layer of fibrous abrasive particles; Fig. 2 is a photograph of a cross-section through an abrasive sheet material of Fig. 1;

Fig. 3: the photograph of a cross section through another inventive abrasive sheet material, in which the

fibrous abrasive particles have a greater average aspect ratio than the abrasive particles in Fig. 2; Fig. 4: the photograph of a cross-section through an abrasive sheet material in which the fibrous abrasive particles are a bit

lower mean aspect ratio than the abrasive particles in Fig. 2; Fig. 5: the photograph of a cross section through an abrasive sheet material in a conventional manner by roll breaking

prepared abrasive grains; Figures 6 (a), (b), (c), (d), (e) and (f) are the photographs of roll-broken 50 grit sol-gel alumina abrasive grains (a), grit-type, broken-grain, electrocorundum grains 50 (b) and 50 grit spherical SoI gel abrasive particles having disordered (c) and increasing (d, e, f) mean aspect ratio

be used in the preparation of the abrasive sheet material according to the invention; Fig. 7: a graphical representation of the effect of increasing the length ratio of the fibrous abrasive particles

on the total removal with round sanding sheets; Fig. 8: a further graphic presen- tation of the effect of the aspect ratio of the fibrous abrasive particles on the

Ablation data of round abrasive sheets; 9 shows a scanning electron micrograph (100 × magnification) of the surface of an inventive device

Abrasive sheet material showing the embedding of the abrasive particles in a binder layer; Fig. 10: a 100-fold enlarged scanning electron micrograph of the surface of a product with itself

known broken, seeded sol-gel abrasive grain in a make coat; 11: a 50-fold enlarged scanning electron micrograph of the chip from the application of a

abrasive sheet material according to the invention shown in FIG. FIG. 12: a 50-times enlarged scanning electron micrograph of the chip from the application of a per se known grinding product according to FIG. 10.

In Fig. 1, an inventive abrasive sheet material 10 is shown, which has a support pad 12 and an abrasive layer 14 thereon. The structure of the abrasive sheet material 10 is shown in FIG. 2 clearly removed.

The abrasive layer 14 is formed by a contact layer 16 and adhering thereto fibrous abrasive particles 18 and abrasive fibers 18, wherein a binder layer 20 embedding the abrasive fibers 18 may be provided.

For the purposes of the invention, the term fibrous abrasive particles 18 or abrasive fibers 18 is used for elongated ceramic abrasive bodies, each having a generally uniform cross-section along its length and whose average length is preferably about twice the maximum dimension of the cross-section. However, this aspect ratio may be very different as described below depending on the conditions of use.

The abrasive fibers 18 may be bent or twisted so that the length is measured along the body rather than necessarily being straight.

In general, the abrasive fibers 18 are preferably made by extruding or spinning a preferably seeded aluminum hydroxide gel into continuous filaments, drying the filaments thus prepared, cutting or breaking them into the desired lengths and then firing the fibers at a temperature up to 1500 ^° C. Different sol-gel methods for making gels of aluminum hydroxide are described, for example, in US Pat. Nos. 4,314,827 and 4,623,364. As disclosed in said patents, in addition to the aluminum hydroxide, the sol may contain up to 10 to 15 parts by weight of spinel, muMt, manganese dioxide, titanium dioxide, magnesia, ceria, zirconia in powder form, or their precursors may also be present in larger quantities, e.g. B. 40% or more and other suitable additives or their precursors are added. It is preferred, however, that the gel be substantially free of substances that form an amorphous vitreous material upon firing. The fired sol-gel grain used for the abrasive sheet material according to the invention should therefore preferably consist of at least 95 parts by weight in% and better still at least 98 parts by weight in% a-alumina. In the most preferred embodiment, the sol or gel contains a dispersed submicroscopic crystalline seed or its precursor in an amount effective to facilitate conversion of the aluminum hydroxide particles to a-alumina upon sintering. This method is called an inoculated sol-gel method. The amount of inoculum should not exceed about 10 parts by weight in% of the aluminum hydroxide, and normally amounts above about 5% will not give any benefit. If the seed material is sufficiently fine, amounts of about 0.5% to 10% can be used, with 1 to 5% being the preferred range.

In general, with the addition of larger amounts of inoculum, for example, more alpha-alumina, the stability of the gel may be compromised and extrusion made very difficult. In addition, large amounts of a-alumina already contained in the extrudate require higher temperatures for sintering. However, as shown above, higher temperatures result in crystal growth, and such abrasive articles are generally inferior.

Examples of solid, microcrystalline seed materials are β-alumina, α-iron (III) oxide, α-alumina, γ-alumina, chromium oxide and other particulate which becomes the nucleation site for formation of the α-alumina crystal, with α-alumina being preferred becomes. The addition of the germs may also be in the form of a precursor such. As an iron (III) nitrate solution. In general, the seed material should have the same structure as α-alumina and similar dimensions of the crystal lattice (approximately within 15%) and be present in the dried gel at temperatures that convert to α-alumina (about 1000 to 1100 ° C ).

The green abrasive fibers can be formed by a variety of techniques such as extrusion or spinning from the gel. The extrusion is best suited for fibers of about 0.25 to 1.5 mm in diameter, which after drying and firing from the diameter in about the screen sizes for a separation of abrasive grains of grain size 100 to 24 correspond. Spinning is best suited for burned fibers with an approximate diameter of less than 100 μm.

Spinning already prepared abrasive fibers with a diameter up to 0.1 μιτ »(0.001 mm) were prepared according to the invention by means of spiders. On firing, the green fibers fade to about 50% of their extruded diameter.

The gels most suitable for extrusion have a solids content of about 30 to 65% and preferably about 45 to 64%. The optimum solids content changes in direct proportion to the diameter of the extruded fiber,

with about 60% solids being preferred for fibers whose burnt diameter is about the grain size of 50 grit broken abrasive grains (about 0.28 mm).

For spinning in accordance with the invention, a quantity of gel may be placed on a disk, which is then set in rapid rotation and ejects green abrasive fibers which air-dry almost immediately. Similarly, the gel can be in a solid bowl centrifuge with holes or slots in the wall bring, in which case the shaping of the fibers by rotation of the solid shell with, for example 5000U / min. For the shaping of the green fibers, other known methods for spinning can also be used. In spinning, the most favorable solids content is about 20 to 45%, with about 35 to 40% being the preferred range.

If the fibers are formed by spinning, it is advisable to add to the sol from which the gel is formed about 1 to 5% spin agent such as polyethylene oxide to give the gel the necessary viscoelastic properties for the formation of the abrasive fibers. The optimum amount of the spinning aid is in inverse proportion to the solids content of the gel. During calcining or firing, the spinning aid is burned out of the fibers. Since only very small amounts of the same must be added to the extruding usually nothing, the properties of the fired fibers are not significantly affected.

The extruded gel fibers can be given various predetermined shapes, in which are used in the extrusion mouthpieces whose cross section corresponds to the desired fiber cross-section, for example, square, star-shaped, oval, triangular or even hollow tubular. Have the gel fibers have a relatively large cross section or have been made of a gel prepared with a high water content, it may be necessary or advisable to dry them at a temperature below 100 ⁰ C for 24 to 72 hours before being heated above 100 ⁰ C be suspended. If the gel fibers have a relatively small cross-section or core and are made from very high solids gels, drying may be unnecessary.

The shaped continuous fibers are then broken or cut into lengths desired for the intended grinding task. In general, the necessary shaping and separating work for the production of individual fibers from the continuous fibers or to change their shape most advantageous in the gel or in the dried state, since this much lower expenses and costs are necessary than in the processing of much harder and firmer fibers after final firing. The continuous fibers emerging from the mouthpiece of the extruder during extrusion can be subdivided into fibers of desired length in a manner known per se. This can be done for example with a rotating wire cutter, which is arranged on the front side of the mouthpiece. The dried fibers can also be easily broken or ground and then classified into the desired length ranges.

After the gel fibers have the desired cross-sectional shape, cut or broken after drying, they are given their final fiber shape in a controlled firing process. By firing, substantially all of the alumina in the gel fibers is to be converted to crystalline alpha alumina, but excessive bake temperatures or times are to be avoided, as overburning can promote undesirable grain or crystal growth. In general, the firing is carried out at a temperature of 1200 ⁰ C to 135O ⁰ C over a period of 5 minutes to one hour. For coarser fibers, the firing is preferably preceded by drying at about 400 to 600 ^° C. for about 10 minutes to several hours to remove the residual volatiles and bound water which could cause cracking in the fibers upon firing , Especially with fibers formed from seeded gels, overburning rapidly results in larger grains absorbing most or even all of the smaller grains surrounding them, thereby reducing the uniformity of the microstructure in the abrasive article. The abrasive fibers according to the invention have an aspect ratio of at least 1: 1 and preferably of at least 2: 1. The aspect ratio is determined by the measure of the actual length of the abrasive fiber in relation to the dimension of its diameter or cross section perpendicular to the longitudinal direction. For a non-round cross-section, for example polygonal, the determination of the aspect ratio is based on the greatest dimension perpendicular to the longitudinal direction. The actual achievable aspect ratio in a particular batch of abrasive fibers may be dependent, to some extent, on the particular type of fiber separation. Thus, a particular lot may contain some abrasive fibers with aspect ratios less than 2: 1 and some with ratios greater than 2: 1. For the abrasive sheet material according to the invention, the abrasive fibers used should have on average an aspect ratio of preferably at least 2: 1.

A preferred range of aspect ratio is between 2: 1 and 8: 1. In this case, longer abrasive fibers can be useful in many applications. In general, abrasive sheet material with abrasive fibers whose aspect ratio is low is well suited for high pressure grinding, while higher aspect ratio abrasive fibers are more suitable for low pressure grinding. The most suitable abrasive fibers for use in the present invention have a hardness of at least 16GPa and preferably at least 18GPa (Vickers hardness 500g load) and a theoretical density of preferably at least 90%, most preferably at least 95%. In comparison, a pure, dense a-alumina has a hardness of about 20 to 21 GPa. It is also possible that the abrasive fibers used can be rotated in the longitudinal direction or slightly curved or bent.

It has been found that the abrasive sheet material according to the invention, with abrasive fibers, is far superior to the abrasive sheet material having broken abrasive grain known per se, even though material and microstructures as well as diameters are the same. The production of the abrasive sheet material 10 according to the invention can be carried out in different ways with traditional but also with technically advanced processes. The backing 12 may be made of any material currently used in the production of abrasive sheets. These include paper, foil, woven and stitched goods, those made of chemo silk, cotton, nylon and polyester, vulcanized fiber, dimensionally stable polyester film and the like. This backing may be finished with a finish or primer coating of different materials, essentially depending on the intended use. This primer coating may contain binders as well as fillers. In this case, starch, glue or a resin such as phenolaldehyde can be used. On this backing pad an abrasive layer 14 is arranged. This consists of a contact layer 16 and a plurality of preformed fibrous abrasive particles 18th

The bonding layer or contact layer 16 may be made of a resin wiez. As Phenoladelhyd, epoxy resin and similar substances. If necessary, this contact layer 16 may be covered by a further binder layer 20. When the binder layer 20 is made of a thermoset resin, the contact layer 16 may be made of an adhesive or a resin as needed. In these layers, the abrasive fibers 18 are embedded, whereby they penetrate each other. For example, a conventional contact adhesive consists of a solution containing 48% phenol-formaldehyde resin as a solid and 52% calcium carbonate filler. After applying the contact layer 16 on the support base 12, the resin of the contact layer 16, depending on the mixing approach in the usual manner, for example, 30 minutes at 107 ⁰ C are pre-cured. Thereafter, the abrasive fibers 18 are applied in a conventional electrostatic process, with upward spin or tumble being preferred. This can then be followed by the application of the binder layer 20, for which a conventional solution with 48% phenol-formaldehyde resin and 52% calcium carbonate filler is an example. Subsequently, the abrasive sheet material is subjected to a final curing usually at 107 ⁰ C for a period of 10 hours, so that the resin in the contact layer 16 and the binder layer 20 is cured in the desired manner. Normal radiation curable (Ε-radiation or UV) and resins used in the production of abrasive sheet materials may also be used as needed for some or all of the fabric-finishing or adhesive layers. In general, the application of the adhesive layers to the substrate by means of known coating methods, for. B. roll coating. However, if relatively long abrasive fibers 18 are used, it may be more convenient to apply the make coat 20 in a sprayed coating or other techniques other than roll coating so as to avoid undesirable breakage or depression of the abrasive fibers 18.

In Fig. 5 is comparatively a per se known abrasive sheet material 22 is shown, which contains abrasive grains 24, which were prepared in this known roll crushing method. It is easy to see the difference in structure compared to the abrasive sheet material according to the illustrations in Fig. 1 to 4 clearly. The different configuration of the abrasive fibers 18 used in the production of the abrasive sheet material according to the invention can be seen more clearly from FIGS. 6a to 6f. FIG. 6a shows irregularly three-dimensionally shaped abrasive grain 26 obtained by conventional roll breaking of sol-gel alumina abrasive. In terms of their shape, the irregularly shaped individual abrasive grains 26 are similar to corundum corundum 28 as shown in Fig. 6b made by conventional roll breaking techniques. In Figs. 6c; d; e; f, various lots of abrasive fibers 18 are illustrated which are used in the manufacture of the abrasive sheet material of the present invention. Fig. 6c shows a lot of abrasive fibers 18 with disordered length ratios, in which no classification of the abrasive fibers 18 was carried out according to their length. These abrasive fibers 18 have a mean aspect ratio of 4.1: 1. In Fig. 6d; 6e; 6f, the abrasive fibers 18 have average aspect ratios of 3.6: 1.5.1: 1 and 8.5: 1, respectively. It can be seen from Figs. 6c to 6f that the sol-gel abrasive fibers 18 have a substantially uniform circular cross-section along their length. In contrast, the roll-broken SoI-GeI abrasive grains 26 as well as the roll-broken, electrocorundum grains 28 have strongly irregular shapes. Some are relatively long and others have chunky shapes. From a consistent cross-sectional shape can be in any case the question.

FIGS. 9 and 10 clearly show the differences in the external appearance of the surface of the abrasive sheet material according to the invention and the embodiment known per se.

FIGS. 11 and 12 show the grinding waste produced by the structures shown in FIGS. 9 and 10. It can be seen that the abrasive sheet material according to the invention produces a smooth continuous waste, which reflects an excellent removal. In contrast, Fig. 12 shows a splintery grinding waste mixed with small molten metal balls, which is an indication of a relatively poor grinding performance. It has become clear that abrasive sheet materials according to the invention have clear advantages over the known design, in which the shapes are less regular and process the workpiece with a variety of configurations. Many advantages result directly from the shape of the abrasive grain. In grinding tests with a variety of pressures and sanding sheets in belt and bladder form, a close correlation between the performance improvement and the values for the length ratio of the abrasive fibers 18 was found. However, only up to a certain value, which was dependent on the type of abrasive sheet material, the pressure and other test conditions, did the overall cut increase with increasing aspect ratio. For example, increasing the aspect ratio to a value greater than 3: 1 did not increase the performance of the abrasive fibers 18 in a 80 psi (11,603 MPa) tape profile grinding test. With increasing aspect ratio values, the increase in performance did not continue indefinitely, as the longer length of the abrasive fiber 18 resulted in a larger moment arm on the grain base and the resulting internal stress very quickly resulted in breakage of the abrasive grain. For round leaves with Vulkanfiberunterlage and a lower pressure of about 5 psi (725.2MPa) resulted in a power loss only at a much higher aspect ratio.

It has been found that a higher aspect ratio affects the mechanisms of grinding performance in four ways by:

• to a wider distribution of the cutting edges;

• less contact points per unit area;

• to higher grinding chip distances;

• leads to mutual support or agglomeration of the abrasive fibers.

At higher aspect ratios, the cutting edges spread over a greater height or thickness above the backing, thereby providing the abrasive sheet with an abrasive layer having multiple groups of cutting edges at different heights and correspondingly grinding. Eventually, the first group of abrasive fibers with the largest aspect ratios will fail due to internal fiber stress, and a new set of shorter, uncut, abrasive fibers will be exposed and begin to cut. If the edge stresses locally exceed the stress on the abrasive fibers, the edges will splinter, resulting in new edges and a re-sharpening effect. First, the high aspect ratio abrasive fibers are effective primarily by exposing new abrasive grain; later, when the moment arm is reduced, a resharpening function becomes more prevalent for the edges.

This interpretation of the mechanism is supported by several experiments and examinations. During the tests, the mass loss per cycle increased with an increase in the aspect ratio from 2: 1 to 3: 1. In tests of low pressure circular abrasive sheets and high pressure abrasive belts in timed cycles to monitor grain wear and failure, the fracture operations described above occurred during grinding. The visual inspections as well as the profile measurements of the surface also showed that the grain tips in the abrasive sheet materials according to the invention are distributed over a greater height range than those with broken SG grain known per se and that the range increases with increasing aspect ratio. In addition, the surface quality (Ra or arithmetic mean roughness value) and working range increased with increasing aspect ratio. The work area is determined by finding the average of the highest and lowest peaks from ten different cycles and making the difference. With the work area can be better expressed how much material over the binder layer for the grinding work available.

For identical granules, an abrasive sheet material according to the present invention has a more "open" coating, ie fewer abrasive grains per unit area on the backing, since the peaks are distributed over a greater height and each abrasive grain is heavier.The lower number of potential points of contact per unit area results in a higher force per each When the abrasive grain is able to withstand the increased load, a deeper and thus cooler and more efficient cut occurs, with each grain edge removing more material than a broken pyramidal grain tip, the abrasive grain containing a broken abrasive grain cuts with a greater number of grain tips, resulting in greater grain size initial abrading is about the same or the broken abrasive grain initially even has a somewhat higher erosion, whereas the abrasive grains in the form of abrasive fibers are used in the abrasive sheet material according to the invention, a higher erosion and the life of the abrasive grains is longer. By noting that larger, broader particles are contained in the grinding waste, this mechanism is confirmed (see, for example, Figures 11 and 12). Profile measurements also demonstrated that the peak density (number of peaks / cm) decreases with increasing aspect ratio. Furthermore, the third mechanism is effective which results in larger abrasive chip spacings due to the rougher and more open coating of the abrasive sheet material. In tests of cylindrical abrasive wheels having a backing made of vulcanized fiber and a large contact area, the length of the chips produced by the abrasive sheet material of the invention increases with increasing aspect ratio of the abrasive fibers due to the larger abrasive chip spacings. During the test, the vulcanized fiber circular discs did not show signs of smearing until the test was completed. Smearing means accumulation of metal on the abrasive layer. It hinders the cutting process and limits the service life.

As the aspect ratio increases, the abrasive fibers attach to each other and support each other, this process being equivalent to an agglomeration. During cutting, this helps the grain groups; Although they have a large mass, but the achieved surface quality of the workpiece is determined by the size of the cutting edges of the individual grinding grains.

With the higher aspect ratio alone, the superior performance of the fibrous abrasive grain or fibrous abrasive particle can not be fully explained. Even with a low average aspect ratio of 1.9: 1, the fibrous abrasive grains still had higher performance than conventional sol-gel abrasive grains known per se with only a slightly lower average aspect ratio of 1.5: 1. As a result, it is obvious that the regular cylindrical grain shape is also important for the grinding performance. The cylindrical shape affects the grinding performance in four ways:

• More abrasive grains with a rake angle of zero or near zero

• More uniform distribution of the stress in the abrasive grain

• Longer, more consistent cutting edges

• Chip removal controlled controlled from the cutting zone.

When properly aligned, the fibrous abrasive grains achieve a rake angle with respect to the workpiece to be machined and the grain cutting area of zero or near zero. The rake angle will also remain zero irrespective of the rotational orientation about the grain axis, as long as the fibrous abrasive grain has a radially symmetric shape. With a rake angle of zero, the grain can cut a strip-like chip, reducing heat, friction, and wear. The abrasive grain acts more like a miniature cutting tool than a known broken abrasive grain. The negative rake angle of the typical pyramidal crushed grain means that the grain tip breaks like a plow through the metal, resulting in melting, cracking and smearing and less cutting. According to many reports in the technical literature and observations of the metallurgical changes in the material of the workpiece, the temperatures and pressures developing during the grinding process are extremely high. Any mechanism that removes the grinding waste from the cutting zone means less cutting edge wear, longer life and longer tool life. In the scanning electron micrographs of Figs. 11 and 12, the differences between the cutting and the plow-like process are shown. Thus, it is confirmed that the fibrous abrasive grains in the abrasive sheet material of the present invention remove the workpiece material in a cutting process and not in a plow-like manner.

Properly oriented, the cylindrical grain shape helps steer the chips away from the cutting zone. Fig. 11 shows that the chips have a concave groove on the cut surface. The convex cylindrical grain surface wedges the chip, thereby limiting the movement of the chip with respect to the cutting edge and the workpiece. The regular cylindrical shape also results in a more uniform stress distribution compared to the very sharp, irregularly broken SG abrasive grain. As a convex cylindrical surface penetrates the workpiece, compressive stresses develop in some areas of the grain surface. Often, the per se known, broken sol-gel abrasive grain has concave surfaces and concave flake shapes due to its tendency to mussel fracture. When the concave shapes penetrate into the workpiece, tensile stresses often occur in some regions of the crushed abrasive grain. Ceramics can absorb much higher pressures under pressure than under tension. Consequently, the abrasive grain has a higher stability under compressive stress. Thus, the fibrous abrasive grains have a good life with a possible relatively low chip removal. In contrast, broken abrasive grains have on their surface

many cracks and notches or other imperfections that increase or concentrate stresses With the methods of fracturing known per se, it is not possible to exclude hollow surfaces and stress concentrating indentations Although in tests with abrasive belts the sharper edges of broken grains lead to an initially higher erosion, however, the broken abrasive grains are more likely to disintegrate under the action of the abrasive forces due to higher local stresses

The cylindrical abrasive grains used in the abrasive sheet material of the present invention have long, continuous cutting edges that create wider chips compared to the shorter, ragged edges of conventional cracked grains and spread wear over a longer working edge. The longer cutting edges dull relatively slowly and are therefore very strong stable Observations in the course of time-delayed grinding tests show that the wear plateaus at the top of the fibrous abrasive grains or abrasive particles are slower than the broken SG grain

The following examples illustrate certain specific embodiments of the invention, but they are given by way of illustration only and are not to be construed as limiting thereof

example 1

Evaluating the performance of abrasive fibers as compared to roll-broken sol-gel alumina beads In this example, round abrasive sheets were coated with alumina abrasive fibers made of seeded gel ("SG") having a mean diameter of 0.33 mm (0.013 ") a 50 grain size CAMI classification (0.35 mm 0.01369 "), as compared to alumina seed grits of seeded gel obtained by roll breaking the dried gel in a manner known per se. In each case, the crystallite size was less than one μηη (the measurement of all sizes of clumps mentioned herein is done with the intercept method.) The abrasive fibers were provided in different lengths and longitudes of about 2 1 to 12 1 in a manner approximating the different long distribution of abrasive grains obtained by roll breaking and classifying Nevertheless, it should be noted that the Schle iffasern are not really suitable for such a classification In the case of abrasive fibers, in contrast to conventional roll-broken grains, two of the dimensions of all the fibers are equal. The roll-broken gel material had a particle size distribution of +8.2 +3.1. Round abrasive sheets with a diameter of 177. 8 mm (7 ") and a hole with a diameter of 0 22.2 mm Ch) . Known methods were used. The support pad is a 0.76 mm (0.03") thick Vulkanfiberunterlage

The contact layer is comprised of a calcium carbonate filled resole base layer (48% resin, 52% filler) and resole binder layer (48% resin, 52% filler). The filler used in the binder layer, however, was cryolite After application of the abrasive fibers, the resin of the contact layer was pre-bake for 5 hours at 107,22 ⁰ C (225 ° F), followed by the application of the glue layer followed by a lugh-hour final curing also at 225 ° F (107,22 ° C) The coating was carried out using per se known rolling coating processes, the curing being carried out in a convection oven. The mass of the resin coating (wet basis) was 6.8 kg / ream (15 lbs / ream) for the contact layer and 10.4 kg for the binder layer / Ream (23 lbs / ream) A ream equivalent to 30.7 m ² (330 square feet) Coating surface The coating of the roll-broken abrasive grains and the fiber for The abrasive particles were applied by methods known per se using an electrostatic deposition process. Table 1 shows the amounts of abrasive layer for the various round abrasive papers tested

Table 1

Characteristics of the round abrasive sheets with a Vulkanfiberunterlage for the evaluation of fibrous abrasives compared with roll-broken grains

Sanding sheet no Type of grinding by means Electrostatic throw-up time (seconds) Mass of the abrasive (grams) 1 Roll Broken SG Corner (comparative) 5 52 2 Extruded SG fibers # 645 5 65 3 Extruded SG fibers # 645 ¹¹ 20 84-87

1 The normal cycle time for the electrostatic Kornbeschichtung.dh in the case of broken grains, amounts to 5 seconds After this coating time, however, it was found (sheet No. 2), that the layer was very open so that a second sample (sheet No. 3) with a coating time of 20 Seconds and was also tested

The roll-broken abrasive grains (comparative abrasive grains, sheet No. 1) had the following normal composition

Ingredient% by weight

Al ₂ O ₃ 99.58 SiO ₂ 0.12 Fe ₂ O ₃ 0.03 TiO ₂ 0.20 CaO 0.04 MgO 0.02 Na ₂ O 0.01

100.00

Other properties: Density 3.89 (water pycnometer); 3.88 (helium pycnometer); Hardness 20.7 (GPa); and medium

The abrasive fibers had the same normal composition at an aspect ratio of about 2: 1 to 12: 1 (average aspect ratio 6: 1 to 7: 1). As seen from the above data, the longer layover time resulted in a significant increase in the mass of the applied coating.

After cutting, the cured round sheets were first bent at 90 ° C normally with a rubber roll bender to crack the hard resin bond (contact and binder layer) in a controlled manner, followed by ripple correction by methods known in the art; then they were subjected to the usual blunting tests for the evaluation of round sanding sheets on a vulcanized fiber underlayer (112 DsIII) and high sanding pressure (112 Ds, 112 Dss). In general, such tests involve the mounting of the circular abrasive sheet on a medium hard rubber backing, which in turn is mounted on a horizontally mounted motor spindle assembly mounted on a carriage which rests freely in horizontal direction on frictionless inward bearings to and from a hydraulic sample holder can move away. The sample holder is designed to either have an angle in the dimensions 25.4mm x 25.4mm x 247.7mm x 3.2mm (1 "χ 1" χ 9 ³ A "χ Ve") or a plate in the dimensions 76.2mm χ 4.8mm x 381mm (3 "χ ³ / іб" x 15 "), it moves horizontally in the 90 ° direction to the spindle, making a reciprocating motion at a fixed speed over one The tester is mounted on a fixed steel table which ensures stability during operation To apply the grinding force, a dead load is attached to a roller system fixed to the moving carriage on which the motor spindle device with the abrasive sheet has been placed. Align the circular abrasive sheet with an angle deviating 10 ° from the parallel to the sample holder The 112Dsh test is a high pressure blunting test 2.25N lOlbsforce grit 50, 2.7Nf 12 lbs force grit 36), in which the round sanding sheet t with vulcanized fiber backing for sanding 3.2 mm of the (Ve ") thick edge of a carbon steel angle 1018 with the dimensions 25.4 mm χ 25.4 mm x 247.7 mm x 3.2 mm (1" χ 1 "χ 9 ³ A" x pce ") is used. First, the angle is weighed and then attached to the sample holder, which reciprocates over a distance of 247.7 mm (9 ³ Å) at 8V2 strokes / min and a longitudinal speed of 2.14 m / min (7ft./min) The grinding cycle rotates at 3450 rpm, the grinding cycle is two minutes, after which the angular sample is removed and the loss of mass is registered, after which this cycle is repeated with new angle samples according to the requirements, until a minimum of 10 g / min The data are recorded in grams (g) of removed material per 2-minute cycle, number of cycles to the end of the test, and total removal (g) of the round-paper to be evaluated Exam in% to a comparison sheet instructed.

Test 112 Dss-Test 112 Dss is identical to Test 112Dsh except that a 304 stainless steel angle is used as the sample instead of the 1018 carbon steel angle, the grinding cycle is one minute and the test is terminated after 10 cycles , In addition, the abrasive force is 1.5 lbs (7 lbs force) for 50 grit and 2.25 N (10lbs force) grit for 36 grit.

Test 112 DsIII - This test is similar to Test 112 Dsh except that it is a low abrasion test - 2.25 N (10 lbs.force) - and the sample is a cold drawn 1018 carbon steel sheet the dimensions 76.2 mm χ 4.8 mm x 381 mm (3 "/ ³ / ιβ" χ 15 "), which is mounted in the receptacle so that of the round abrasive sheet with Vulkanfiberunterlage the end face of 76.2 mm (3 ") long side of the sheet is processed. The grinding cycle is one minute and the test is terminated as soon as the abrasion falls below 3 g / min.

Table 2

Evaluation of the performance of the fibrous abrasive compared to broken grains Total (in grams)

Sheet number. Arid grinding by means 112Dsh steel angle 1018 112 Dss Rostfr. HONEYCOMB. 304 112DsIII 3 "sheet StahM018 (Lot B) 112DsIII 3 "sheet steel 1018 (lot C) 1. walzengebr. SG 5s superficial coating. 618 50 117 365 BK 2xtrudK! 4 # 645 5s superficial coating. 860 43 486 992 Third Extrud. SG # 645 20 s Aufwerfbeschichtg. 1192 - - 937

The low pressure test was carried out on two different steel lots (Lot Bund Lot C) which had been received at different times. As indicated, they show different grinding characteristics, which result from the total removal according to Table 2.

In the following Table 3, the results of the above-mentioned sanding tests are relative to the comparative sheet, i. Sheet no. 1 indicated.

Table 3

Percentage results of the cutting performance of the fibrous abrasive relative to roll broken grains

Sheet number. Type of grinding by means 112Dsh steel angle 1018 112DSS Rostfr. HONEYCOMB. 304 112DsIII 3 "sheet steel 1018 (lot B) 112DsIII 3 "sheet steel 1018 (lot C) 1. walzengebr. SG 5 s Aufwerfbeschichtg. 100% 100% 100% 100% Second Extrud.SG # 645 5 s lay-up coating. 139% 86% 400% 479% Third Extrud. SG # 645 20 s Aufwerfbeschichtg. 193% _1> _1) 264%

1 These tests were not performed due to the limited availability of prepared abrasive sheets.

From the results shown above, it is clear that for carbon steel 1018, the round sheets of vulcanized fiber underlayment and abrasive fibers contained therein exhibit significantly better grinding performance than the Norton Company inoculated gel-alumina abrasive grain made by conventional crushing techniques. Sheet No. 2 with 5 seconds of deposit coating gave 39% more erosion in the high pressure test and 179 to 300% more erosion in the low pressure test on steel sheet. In addition, the larger amount of abrasive fibers (Sheet No. 3) resulted in even better cutting performance with high pressure, while no improvement was observed in the low pressure test. From the overall results of the test shows that abrasive fibers are more durable during grinding under high pressure. With 1018 carbon steel and low pressure, they are also more versatile and have better free-cutting properties than roll-broken SG abrasive grains.

The fibrous abrasive was prepared by mixing 3.2 kg of Pural® NG aluminum monohydrate from Condea Chemie GmbH with 1.3 kg of mixed water and 22 g of alumina seed in a conventional V-jacketed mixer for 5 minutes until a substantially uniform sol was present was. Then 200g of 70% nitric acid were diluted to 750cm ³ of distilled water were added and mixing continued for another five minutes to obtain a gel having 59% solids and uniform seed distribution. Seedlings used in the gel were prepared by milling a batch of distilled water and 88% normal grain alumina abrasive (each 12 mm in diameter and 12 mm in length) from the Diamonite Products Company, Shreve, Ohio in a Model 45 Sweco mill until the particles (Alumina nuclei) in the water had a surface index of at least 100m ² / g.

The Pural® NG powder used had a purity of about 99.6% with small amounts of carbon, silica, magnesia and iron oxide.

Thereafter, the seeded gel was extruded through a soft-walled extruder die having multiple orifices whose openings had a diameter of 0.60 mm for producing the continuous gel fibers. After drying, the extruded fiber bundles were broken into lengths of 2 mm on average and then fired at 1320 ° C. for five minutes. After firing to convert the material of the abrasive fibers into α-alumina, the individual fibers had an average cross-section corresponding to a normal grain size 50 abrasive. At least some of the abrasive fibers were bent and twisted in length.

Essentially, the abrasive fibers consisted of pure a-alumina with an above average crystallite size of 0, ЗЗt and a hardness of about 16GPa.

Example 2

Comparison of Cutting Performance of Abrasive and Roll Broken Granules In this example, the cutting performance and surface finish of fused alumina gel abrasive particles is compared to SG abrasive grains obtained by per se known roll breaking. The fibrous abrasive particles had a mean diameter of 0.33 mm (0.013 "), which roughly corresponds to 50 grit abrasive grains, 0.35 mm (0.01369), and had unordered aspect ratios of about 2: 1 to 8: 1 However, the batchwise classification used resulted in some very long fibers and a disproportionately high proportion of fine grain. The abrasive grains and roll-broken SG comparison grains of grain size 50 had the same normal composition as stated in Example 1.

Results of the classification of roll-cut grains and abrasive fibers

Type of grain Serial number granulation classification Rolls broken 08D168.3 50 + 3.2 + 1.9 Abrasive fibers 08D168.7 50 -2.5 + 30.9

As can be seen from the table above, there were considerable differences between the classification of the two types of grain. The indication "+3.2 +1.9" means that the sample of broken abrasive grain contained 3.2% of excess grain and 1.9% of fine grain, as determined by the classification screen system according to CAMI. This is within the permissible

On the other hand, the indication "-2.5 +30.9" for the abrasive fiber sample indicates that with 2.5% too little excess grain and with 30.9% too much fines were included, giving a disproportionately high value The high specification for fines is the final result of the fact that all abrasive grains ("grains") are approximately the same diameter as under the sieve size of the comparative sieve for grain size 50. Round sanding sheets with vulcanized fiber backing were made as described in Example The coating compositions were approximately in contact layer 6.8kg / ream (15lbs / ream), make-up layer 104kg / ream (23lbs / ream), abrasive fibers 65g, roll-broken grains 52g

After the usual buckling, the round abrasive sheets with Vulkanfiberunterlage were first evaluated in the already described Abstumpfungsprufung with low grinding pressure (Examination DsIII) In the following Table 4, the removal and surface results are shown comparatively

Table 4

Comparison of the removal and the surface finish of fibrous abrasives and roll broken grains at 76.2 mm (3 ') sheet

removal GES fibrous form GES Surface quality pc faserformig rtm pc SG-Comp From- Grain size 50 From- SG-Comp Grain size 50 Grain size 50 tr Cut / tr Grain size 50 227 Surface quality 995 211 cycle Cut / (G) cycle (G) Surface quality 255 855 233 No cycle 29 20 163 Ra 757 156 55 (G) 37 Ra Rtm 115 386 82 (G) 94 20 68 103 125 268 73 1 29 119 16 92 164 1005 96 103 222 91 2 25 136 15 112 105,736 109 193 92 4 18 46 10 128 80 625 53 297 81 6 12 - 9 143 48 414 33 8th 8th - 8th 154 37,331 28 10 41 7 34 282 28 12 - 5 40 14 -

Ra = deviation from the center line inprn Rtm = mean roughness depth m Mm Pc = number of peaks

Typically, the surface finish of a metal work piece is indicated by the Ra and RT values measured at the grinding marks at different locations (eg, in the center, left, right edges) along the machined workpiece. The significance of these statistical parameters is good to those skilled in the art They are clearly defined in a publication titled "An Introduction to Surface Texture and Part Geometry" by the Industrial Metal Products Incorporated Company (IMPCO). In general, Ra is a measure of the average surface roughness This number is usually supplemented by other parameters measured on the same surface in metal topography. Rt is often used to complement the Ra measurement. The Rt value is a measure of the depth of Traces or scratches after the surfaces Processing may remain on the surface of the work piece. Pc is a number which generally indicates the scratch frequency. As can be seen from the above data, the circular abrasive sheets with abrasive fibers had a higher removal rate than those with per se known broken abrasive grain First cycles cut the abrasive sheet with the fibrous abrasives initially with a slightly lower removal, but then a removal was achieved over a much longer time The surface material produced with the abrasive fibers seems to correspond approximately to that produced with the broken abrasive grain Nevertheless, it should be referred again As noted above, the batchwise classification of the fibrous abrasive particles produced a disproportionate amount of fines and some very long abrasive fibers. A more controlled "classification" was expected to produce a yield other surface qualities

A further test (112DsI) was carried out to allow a comparison between the abrasion and the surface finish from the use of abrasive fibers on the one hand and roll-broken abrasive grains of granulations 50 and 36 on the other. Table 5 below shows the results. This test is similar to test DsIII except for the specimen, which had a 25.4mm ("1") thick endface

Table 5

Comparison of the abrasion and the surface finish of abrasive fibers and roll-cut abrasive grain on a 25.4mm I steel face

952 ¹¹ in uramm 31 SG V " 44 SG Vergl rtm pc Surface quality rtm pc SG Vergl 1 rtm pc Korng 189 Korng 256 grain 1053 214 952 ¹¹ 1455 149 grain Grain size 36 1181 163 50 41 419 36 526 852 195 Korng 1279 173 Surface 1079 224 Cycle total removal 215 640 779 Grain size 50 839 233 50 1019 179 840 177 removal No " 438 859 1001 Surface 1018 243 714 159 Ra 711 284 SG-V 627 1060 1 181 599 353 730 196 226 820 145 Korng 1 799 1 228 1334 Ra 420 320 581 230 205 526 179 50 5 880 1350 1437 152 254 100 Surface 423 152 135 534 181 10 926 1444 1506 154 - - 477 139 128 394 168 15 - 1496 1541 119 - - Ra 431 200 129 359 181 20 - 1532 - 136 - - 407 489 96 75 503 115 25 - 63 - - 196 347 90 73 - - 30 - = Deviation from the mean line in pm 41 158 54 35 1 abrasive fibers = mean roughness in μηη 41 136 70 40 Ra = = Number of peaks - 124 80 44 Rtm = - 92 - 48 Pc = - 80 - 87 48 73 65

As can be seen from the above results, the 50 grit abrasive fibers not only achieved better removal rates than the 50 grit abrasive grits, but the abrasion also corresponded to that of the control 36. Again, the abrasion of the abrasive grit was initially slightly lower than that of the grinded abrasive grits, however, it consistently continued for a longer time. In this 25.4mm ("1") thick sheet test, the fibrous abrasive particles produced a surface finish equal to the 36 score

Example 3

Comparison of Cutter Power with Increasing Ratio and Roll Broken Abrasive Grain In this example, round abrasive blanks with abrasive fibers of varying length are subjected to testing in comparison with roll-cut abrasive grains of similar composition to evaluate the effect of the long-wear rate on cutting performance

As already stated, seeded sol-gel abrasive was prepared and then extruded through a fine round-mouth stucco having a plurality of openings. The abrasive fibers were dried and easily broken in a jaw crusher to obtain different sized abrasive fibers. After firing, the lot was briefly sieved through various openings in order to separate different loop laser lengths. The mean long-term ratio given below is shown. Table 6 shows the results of the chemical analysis of the different samples and other physical properties

Table 6

Name of the sample 1015 ¹¹ 1016 1017 1018 Comparative sample Mass (lbs) 10 24 13.5 12.5 0.01

Chemical composition Na ₂ 0.01 0.01 0.01 0.01 0.02 mensetzung MgO 0.01 0.01 0.01 0.01 0.12 SiO ₂ 0.04 0.03 0.03 0.03 0.04 CaO 0.02 0.02 0.03 0.02 0.20 TiO ₂ 0.17 0.17 0.21 0.18 0.03 Fe ₂ O ₃ 0.15 0.21 0.11 0.12 3.89

Density (pycnomes) (helium pycnomes) 3.91 3.94 3.91 3.96 3.91 3.96 3.91 3.95 3,88 20,7 Hardness 19.6 20.1 20.4 19.6 0.17 Medium size crystal 0,139 0.135 0,125 0.135 Mittl Langenver haltnis 4.2 1 3.6 1 5.1 1 8.5 1

The mean grain diameter was 0.011 to 0.013 'for all 4 samples.

1 No sieving, d h full size range

2 parts by weight in%, rest AI ₂ O ₃

According to the method disclosed in Example 1, round abrasive sheets were prepared with vulcanized fiber underlay. The results of the previously described sanding tests are shown in Table 7 below.

Table 7

Results Körn. Length ratio LPD ¹ Exam 112 Dsh Exam 112 Dss Test 112 DsIII Mass loss of the leaves Exam 112 Ds Mass loss d. Round leaves with abrasive on backing 1.8g 100% 50 1.4: 1 180.7 rolled hot. Steel 1020 Rostfr. 304 steel Steel 1018 Test 112 DsIII 0.5 g 100% 6.2g 344% sheet 50 4.2: 1 189.2 705g 100% 48 g 100% 180g 100% 2.6 g 520% 3.8 g 211% SG-Comp. 50 3.6: 1 197.9 1434 g 203% 55 g 115% 624g 347% 1.5g 300% 7.2 g 400% SG-1015 50 5.1: 1 180.3 1185g 168% 57g 119% 401g 223% 2.3 g 460% 9.5 g 528% SG-1016 50 8.5: 1 163.9 1617g 56 g 117% 465 g 258% 2.7 g 540% SG-1017 1346 g 191% 53 g 110% 639 g 355% SG

1 LPD = grinding test with low grinding pressure

As indicated above, the round-bladed abrasive discs, in contrast to the control blade with roll-cut abrasive grains, have significantly better ablation in the 112Dsh and 112DsIII tests on 1020 and 1018 steels. However, the performance increase when grinding stainless steel (test 112 Dss) was comparatively much lower. As in the high pressure blunting test, the blades containing abrasive fibers appear to have high grinding efficiency with low grinding pressure. The Abrasive Abrasive Abrasive (Sample 1015) achieved a total wear of 347% in the 112 DsIII test as compared to the Abrasion of the control. As shown in Fig. 7 of the drawings, in the test 112 Dsh with hot rolled steel 1020, the removal increases to an aspect ratio of 5.1: 1 (sample 1017) and then decreases. During the test, flying away of abrasive fibers from the round abrasive sheet was observed. Without being limited to this, apparently, this is a result of the moment arm increasing and thus the stress levels in the abrasive grain, i. H. the abrasive fibers are changed. The abrasive fiber loss depending on the aspect ratio is confirmed by the values in Table 7. For example, in the Test 112Dsh, the weight loss of the coated abrasive sheet increases with increasing aspect ratio: 9.5g at a ratio of 8.5: 1 versus 3.8g at an aspect ratio of 3.6: 1. Nevertheless, Fig. 7 shows that at a mean aspect ratio of 8.5: 1, the sample 1018 still outperformed the comparative abrasive sheet with perimeter known abrasive broken abrasive grain. As also seen from Table 7, the aspect ratio does not appear to affect stainless steel cutting performance (Test 112Dss).

It can be seen from FIG. 8 that during the blunting test at low pressure (112DsIII), the removal increases with increasing aspect ratio, with the exception of the length ratio 4.1: 1 of the sample 1015 being a single peak in the ablation. This sample is the only one of a group of samples subjected to the test in this Example 3 in an unsized form. A small number of abrasive fibers, namely 25 pieces, were randomly selected from sample 1015, with their diameters optically determined. With these abrasive fibers, the aspect ratio moved between 2.58 and 12.66. Thus, it is believed that this erosion difference of the sample 1015 may be the result of the wider length distribution in the unsized sample while the other samples were all sieved. By sieving the length distribution is changed or reduced. With non-abrasive abrasive fibers, on the other hand, some long abrasive grains (fibers) touch each other, resulting in a higher unit pressure per grain. Although not expressly stated in Table 7, abrasive grind-off abrasive sheets initially have less than the comparative SG sample, as in the examples previously cited, but in any event retain higher abrading performance for a significantly longer time. The SG comparative abrasive sheet cut 10 g / min until the 8th cycle, while the 1015 sample achieved over 10 g / min until the 30th cycle.

Example 4

Cutting performance of abrasive sheets with 36 grit abrasive grains and 36 grit broken grains. In this example, a round abrasive sheet was evaluated with vulcanized fiber backing and seeded 36 grade sol-gel alumina abrasive, the composition given below being the same as for conventional abrasive grain preparation by normal roll breaking and fiber extrusion was:

component waxed Al ₂ O ₃ 99.52 Na ₂ O 0.01 MgO 0.01 SiO ₂ 0.06 CaO 0.04 TiO ₂ 0.19 Fe ₂ O ₃ 0.17

The broken abrasive grains and fibers had the following physical properties: Density (pycnometer, water) 3.89, density (pycnometer, helium) -3.92, Hard-20.3, Knall size (average) -0.149μπι This abrasive was cut to a diameter of 0.41 mm (0.016 ') extruded (about 36 grit) and cut into disordered lengths of about 0.8 mm to about 4 mm. Thus, the long ratios of these abrasive fibers were approximately between 2 1 and 10 1

Circular abrasive sheets were prepared with vulcanized fiber backing according to Example 1, but the coating compositions were contact layer 7.7 kg / ream (17 lbs / ream), binder layer 12.7 kg / ream (28 lbs / ream), abrasive grain fibers 27.2 kg / ream (60 lbs / ream). Ries)

The classification of the abrasive used and the resulting cutting performance are shown in Table 8

Table 8

medium granulation classification LPD ¹ Results of the test Gamm removal / time in% from the comparison sheet 112 Dss stainless steel 112DsIII 3 "sheet 112D's steel 1018 80/100 264/100 Verification 35 -0.7 + 13.2 185.1 1214/100 91/112 465/176 Abrasive fibers 35 -15.6 + 70.8 208.4 1842/152

1 blunting test with low sanding pressure

As with the tests already carried out at each test with the inventive abrasive on documents, the removal is initially lower than with the Vergleichskornern, but it is maintained over a much longer time According to an unfounded theory, such an initially low removal may be with the relatively In the stainless steel test, which is normally completed after 10 minutes, the comparative SG blade achieved a removal of six grams per minute, with a total stock removal of 80 grams. By contrast, at the end of the 10 minutes The abrasion of the sanding sheets with sanding fibers 8 grams per minute and the total abrasion was 91 grams The grinding with this round sanding sheet on Vulkanfiberunterlage was continued until the erosion to six grams per minute had dropped back for another 10 minutes grinding time and the total removal after 20 minutes was 163 grams

Although the solution according to the invention has been described with particular reference to abrasive fibers having an approximately circular cross-section, it will be understood that it is not limited thereto. The fibrous abrasives employed in the practice of this invention may have any desired cross-section, B, round, square, triangular, The main requirement is that these abrasives must have an elongated shape as previously disclosed. Such fibrous abrasives need not necessarily have a straight configuration. They may be rotated in their longitudinal direction or have other non-linear shapes if desired In addition, round abrasive sheets can be made with mixtures of abrasive fibers of different shapes or different sizes, so B can contain the abrasive sheet material round abrasive fibers with two different diameters n In addition, abrasive fibers can be mixed with conventionally broken abrasive grains. It is also possible to mix grinding fibers made of SoI-GeI-Al ₂ O ₃ with grinding bodies of a different composition, ζ B with sintered Al ₂ O ₃ , garnet, etc. Furthermore, the abrasive sheet material can also be used The basecoat can be prepared by following known separate coating techniques, followed by a cheaper abrasive grain or filler by drop coating and then the abrasive fibers by the electrostatic coating. Classified abrasives can be created by separate coating processes by first passing a fine grain through Case coating is applied, followed by the coarser abrasive fibers by means of electrostatic coating The erfmdungsgemaße solution has been set out in detail with reference to round abrasive sheets with Vulkanfiberunterlage, but is not limited to these Various Known abrasive sheet materials can be provided, B bands, rectangular abrasive sheets, profile and disc grinding wheels

Example 5

This example illustrates the effect of different crystal sizes on the performance of the abrasive fibers of the invention

The abrasive fibers were applied to 174.8 mm (7 ") diameter round abrasive sheets having the standard test procedure for abrasive papers 112 DsH, 112 DsIII, and 113 Dsl. The first two tests were

described. The 113 Dsl test is a medium-pressure test using the same equipment as the 112DsH test specimen and a 1018 steel rod with the dimensions 25.4mm χ 63.5mm χ 247.7mm (1 "χ 2Ѵг" х 9 ³ A ") The rod and the abrasive sheet are aligned with each other to grind the 25.4 mm (1") thick face of the rod. The grinding cycle is two minutes each; after each grinding, the bar is removed and weighed to determine mass loss. During the test, four bars are used alternately. In all other respects, the examination exam is 112 DsH. Table 9 below shows the results. The tested comparative sample is a normal commercial sol-gel seeded abrasive with chunky grains prepared by breaking and classifying.

Table 9

sample crystal lengths 112DsH * 112DsIII * 113DsI * size behave (Stole (3 "-steel (Stole (Μπι) nis 1018) sheet) 1018) Vergl.- Not Not 100% 100% 100% template available available (SG) 5-1 (Not 2.5: 1 14% 42% 8th% vaccinated) > 2 5-2 1.16 2.5: 1 127% 127% 119% 5-3 0.65 2.5: 1 148% 118% 109% 5-4 0.54 2.5: 1 156% 154% 108% 5-5 0.42 2.5: 1 158% 129% 118% 5-6 0.39 2.5: 1 193% 136% 134% 5-7 0.26 2.5: 1 211% 183% 151%

* expressed in% of the commercial reference sample

From the above data, the significant advantage of using the smallest possible crystal size in the abrasive particles becomes clear. It also becomes clear that good performance can not be achieved with a non-seeded abrasive.

Example 6

In this example, a product having a square cross-section abrasive grain is compared to a product made using the normal, broken SG abrasive grain. In each case, the abrasive grain was formed from seeded SoI GeI, wherein the crystallite size was less than 1 μηι. For the 80 grit SG abrasive grain and the abrasive sheet material of the present invention, square section abrasive wheels having a grain size of 80 were used. The aspect ratio was 4: 1.

The results are expressed in% relative to the performance of the SG comparative abrasive article. The results obtained were as follows:

112DsIII 3 "sheet 113DsI 1 "steel bar SG comparison sanding product (grain size 80) 100% 100% Abrasive fiber with a square cross-section (grain size 80) 339% 249%

This makes it clear that abrasive grain with cross-sections other than the round shapes described above in the abrasive sheet material according to the invention are effective.

Example 7

This example shows the effect of grain size on the effectiveness of a sanding product. A series of grinding operations were performed to evaluate the effect of different parameters on the grinding performance of abrasive products of the invention. The parameters investigated were the aspect ratio, the grain mass, mixtures of different grains and the method of grain application. Unless otherwise stated, the backing used was 2079 (7.3 oz.) Heavy duty polyester atlas with a surface finish of 775, the contact and binder layers were prepared by the following procedure:

contact layer 30.0% binder layer 27.3% Va reu m 2535 13.6% Varcum2535 14.4% BM-42 54.5% BM-42 49.1% Dura 0.25% cryolite 0.25% A-1100 1.6% A-1100 8.9% water water

Table 10 summarizes the abrasive products produced and the results of the sanding tests. Examination of the test results reveals that the highest performance abrasive products contained the aspect ratio. In addition, a positive effect was already achieved by simply reducing the amount of this abrasive grain in the product. For the product with the best results (308%), only 66% of the surface was coated with the abrasive fibers with an aspect ratio of 3.1: 1. The results obtained with the aspect ratio 2.1: 1 were not as salient as the length ratio 3.1: 1, but with 172% still much better than the comparison grain. Significantly, the same performance improvement was achieved by reducing the abrasive fibers with the aspect ratio 2.1: 1. Apparently, grain mass values between about 40 and 60% give the best results for each of the two weighted aspect ratios. Interestingly, the arrangement of abrasive fibers with a 2.1: 1 aspect ratio on the abrasive sheet material caused significant performance differences. For the abrasive sheet material 7-11, abrasive grains having a 3.1: 1 aspect ratio as the first layer and the grain size 50 grain SG as the second layer were coated, while the abrasive sheet material 7-12 as the first layer was used as the grain size 50 SG grain and second layer the abrasive fibers of the aspect ratio 3.1: 1. The results of the test 112 Ds (80) show that 7-11 had somewhat better performances (115%) than the control sample, while 7-12 reached 292% compared to the control grain. It should be noted that while the 3.1: 1 aspect ratio abrasives produced in this case had a particle diameter of 0.33 mm, which corresponds approximately to a grain size of 50, the performance of Coronet 36 (see 34 R984) in the test 112 Ds (80) by a factor of 2.5 and 2 times in the fixed-feed test.

Table 10

Schl.-

Procedures

1-Sch. 1-Sch. 1-Sch. 1-Sch.

Co rnart

total Prz.An- Results of window granulation part D. Exams in the feed lbs./ the Closed. Verhältniszum stole ream layer normal 4140 premium 122Ds grain size (80 / psi) lbs./ stole ream 1018

normal 1. SG, Kör 39 39 100% 100% 100% layer voltage (Sch.) 50 7-1 1-Sch. LV 3.1 55.8 55.8 100% 269% 450% 7-2 1-Sch. LV 3.1 47 47 84% 299% - 7-3 1-Sch. LV 3.1 37 37 66% 308% 406%

LV 2.1 LV 2.1 LV 2.1 LV 2.1

50 42 29 22.5

100% 84% 58% 45%

I.Sch. LV 3.1 28.2 2. Sch. SG-50 18.8 I.Sch. SG-50 21 2. Sch. LV 3.1 26

47

47

100%

100%

136% 151% 164% 172%

115%

292%

163%

184% 131%

7-8 1-Sch. LV 3,1 / EK 30.4 47.4 100% 261% 325% 7-9 1-Sch. LV 3,1 / EK 36 43.8 100% 256% 7-10 1-Sch. LV3,1 / EK 30.4 47.4 100% 191%

97%

7-14 1-Sch. LV2,1 / NZ 44 44 100% 138% 7-15 1-Sch. LV 2.1 26.8 41.8 100% 136% SiC

In each case, an electrostatic deposition process was used for the grain coating.

The 50 grit SG grains had a low density of 1.73 and contained +16.0 excess grain and -4.6 fines.

EK stands for a grade 50 electrocorundum abrasive. (This is not a premium grade) NZ stands for Norzon®-Körmer 50 from Norton Company. (This is a premium grade) SiC stands for 50 grit silicon carbide grains. (This is not premium grade) "Perc. Share d. the Closed. Layer "represents the percentage of the actual mass of the abrasive layer of the

highest possible mass of the abrasive layer.

From the results presented above it seems clear that if a fibrous grain is used, it should preferably be in the topsheet if multiple layers are used. Thereafter, it will be appreciated that to achieve optimum performance, a fibrous abrasive grain coating should preferably constitute only about 40 to 60 percent of a closed abrasive layer, the remainder being comprised of non-premium abrasive grain, or more preferably, air-filled clearance.

Example 8

This example illustrates the effect of in-situ production of the a-alumina in fibrous form as opposed to extruding the a-alumina particles in a suitable medium followed by sintering to form a coherent web.

Vaccinated sol-gel fibers were prepared by mixing boehmite ("Dispersal" from Condea), water and submicroscopic α-alumina with 1 weight% boehmite in a V-mixer for two minutes, then adding 18% by weight in% nitric acid solution, which resulted in a 7.2% by weight nitric acid solution based on the boehmite, and mixing was continued for another five minutes to produce a boehmite gel, followed by a series of abrasive products similar to those mentioned above for comparative purposes Except for the fact that more α-alumina (as a seed of the type used above) was added so that the total mixture contained much higher weight percent alumina, the boehmite was retained to make the mixture extrudable the mixture approaches described.

tables

batch to batch variation Solids content in% 70% Comparative sample A 30% a-alumina 70% Comparative sample B * 30% a-alumina 10% gel Comparative sample D 90% alpha alumina / 40% gel Comparative sample E 60% a-alumina / 40% gel Comparative sample F 60% a-alumina / 62% example 1 1% a alumina (germ) 58% Example 2 1% a alumina (germ) 59% Example 3 1% a alumina (germ)

* With additional ultrasonic mixing of the slurry.

Thereafter, these materials were extruded into fibers which were dried and sintered under the conditions described below. Higher temperatures were required for sintering the high alpha alumina comparative batches than for those prepared by the seeded sol-gel process. Subsequently, samples of abrasive fibers were tested for strength using a simple three-point method using an Instron tester with a crosshead speed of 0.2 cm / min. The abrasive fiber rested on two blades at a distance of 1 cm (0.9 cm for Comparative Samples C, D and E). In the middle between these two points, a downward pressure was applied with a cutting edge. Gradually, the pressure was increased until fiber breakage, and this pressure divided by the cross-sectional area of the abrasive fibers is reported in Table 12 below as the breaking strength.

Table 12

charge Brenntemper./ fiber breaking strength maximum burning time by kg / cm ² knife medium 7 465 (Mm) 6268 Vergl.A 1500 ° C 30 min 0.32 6831 6646 Vergl.B 1550 ⁰ C 30 min 0.3175 6162 4036 Vergl.C 1450 ⁰ C 60 min 1.00 5424 2436 Vergl.D 1300 ° C 6 min 0.88 3430 13 239 Vergl.E 1350 ⁰ C 6 min 0.87 2 378 15 986 Ex. 1 1370 ° C 4 min 0.054 11 197 17112 Ex. 2 1350 ⁰ C 30 min 0.043 14366 16 549 1350 ° C 5 min 0.046 14154 14859 1 325 ° C 30 min 0.046 14,296 18169 1350 ⁰ C 30 min 0.053 10281 Ex. 3 1350 ° C 30 min 0,020 16000

The shear fibers of the comparative batches were much stronger because it was extremely complicated to obtain finer dimensionally stable abrasive fibers by extrusion prior to firing. It has been found that higher levels of α-alumina further aggravate this problem.

As can be seen from the comparison of the above-mentioned data, the comparative fibers had much lower breaking strength, which is believed to be an expression of the weaker sintered bonds between the α-alumina crystals as a result of the sintering process. Therefore, the preferred fibers for use in the abrasives of the present invention have a breaking strength of at least 8,000 and preferably at least 10,000 kg / cm ²

Cross sectional area measured with the test described in Example 8. This is in contrast to abrasives made by sintering preformed α-alumina and having significantly lower strengths.

conversion table = 145,083MPa 1 psi = 2.54 cm Ilnch = 929.03 cm ² 1 square foot = 2.205 kg force A 0.102 N 11b. force = 0.4536 kg 11b. = 0.305 m / min 1 ft / min = 28.35 g 1oz. = 107.22 ⁰ C 225 ⁰ F

Claims (23)

An abrasive sheet material characterized in that it comprises a backing sheet (12) and an abrasive layer (14), the abrasive sheet (14) comprising a contact layer (16) and a layer of a plurality of preformed fibrous abrasive particles (18) has a substantially uniform cross-section which adhere to the support base (12) through the contact layer (16), and that the abrasive particles (18) have a substantially uniform cross-section and an aspect ratio of at least 1: 1 with each other and of sintered a Alumina crystals exist whose size is preferably 2μΓη. An abrasive sheet material according to claim 1, characterized in that the fibrous abrasive particles (18) consist of sol gel a-alumina crystals having a density of at least 90%, preferably 95%, of the theoretical density. 3. abrasive sheet material according to claim 1 or 2, characterized in that the fibrous abrasive particles (18) have a hardness of at least 16GPa. 4. grinding sheet material according to any one of the preceding claims, characterized in that the fibrous abrasive particles (18) have a round cross-section. 5. abrasive sheet material according to any one of the preceding claims, characterized in that the fibrous abrasive particles (18) on the support base (12) have an aspect ratio of at least 2: 1. Abrasive sheet material according to any one of the preceding claims, characterized in that the fibrous abrasive particles (18) have a hardness of at least 18GPa. 7. abrasive sheet material according to any one of the preceding claims, characterized in that each fibrous abrasive particles (18) has a diameter of about 0.05 to about 0.5 mm and / or the a-alumina crystals are seeded sol-gel crystals and a Size of at most about 1 цт. 8. abrasive sheet material according to any one of the preceding claims, characterized in that the fibrous abrasive particles (18) consist of alumina to at least 95% of generally equiaxed crystals whose crystal size is at most about 0.5Tit. 9. abrasive sheet material according to any one of the preceding claims, characterized in that the fibrous abrasive particles (18) have a breaking strength of at least 8000kg / cm ² . 10. Abrasive sheet material according to one of the preceding claims, characterized in that the preformed abrasive particles are formed as abrasive fibers (18) and contain up to 15 parts by weight in% of a constituent from the group consisting of spinel, mullite, manganese dioxide, titanium dioxide, magnesium oxide, ceria , Zirconium dioxide, precursors of oxides and mixtures thereof. 11. Abrasive sheet material according to any one of the preceding claims, characterized in that the a-aluminum crystals are seeded sol-gel-a-aluminum oxide crystals whose size is less than 1 μπι. 12. abrasive sheet material according to any one of the preceding claims, characterized in that at least some of the fibrous abrasive particles (18) are curved on alumina-based in its longitudinal dimension. 13. Abrasive sheet material according to one of the preceding claims, characterized in that at least some of the abrasive fibers (18) are twisted in their longitudinal dimension. 14. abrasive sheet material according to any one of the preceding claims, characterized in that the preformed abrasive particles are formed as abrasive fibers (18) with a circular cross section and each abrasive fiber (18) has a diameter of preferably about 0.33 mm. 15. abrasive sheet material according to any one of the preceding claims, characterized in that the surface of the support pad (12) between 40 and 60% of the theoretical mass of the formation of a closed abrasive medium layer (14) required fibrous abrasive particles (18) of sintered alumina receives. Abrasive sheet material according to any one of the preceding claims, characterized in that a plurality of abrasive layers are arranged and at least the last layer applied comprises fibrous abrasive particles (18). 17. abrasive sheet material according to any one of the preceding claims, characterized in that the abrasive layer (14) contains a mass fraction of up to 40% by weight of the existing abrasive of non-fibrous abrasive particles. Abrasive sheet material according to any one of the preceding claims, characterized in that at least a portion of the fibrous abrasive particles (18) in the application have a rake angle of approximately zero with respect to a workpiece. 19. Abrasive sheet material according to any one of the preceding claims, characterized in that at least a part of the abrasive fibers (18) is arranged in groups in which the respective abrasive fibers (18) abut each other and support each other. 20. abrasive sheet material according to any one of the preceding claims, characterized in that a grinding aid layer on the abrasive layer (14) is applied. 21. Abrasive sheet material according to one of the preceding claims, characterized in that a binder layer (20) after application of the fibrous abrasive particles (18) is applied and the contact layer (16) and the binder layer (20) contain a phenolic resin. 22. abrasive sheet material according to any one of the preceding claims, characterized in that the abrasive sheet is a round abrasive sheet and the carrier pad (12) consists of vulcanized fiber. 23. Abrasive sheet material according to one of the preceding claims, characterized in that the abrasive fibers (18) have an average aspect ratio of 2: 1 to 12: 1.