Abrasive belt grinding product

Abstract

An abrasive belt is provided which comprises a textile fabric being formed of interconnected yarns, and a coherent abrasive area formed on one side of the textile fabric, wherein the abrasive belt further comprises a plurality of regularly distributed openings in the form of through holes. The abrasive belt allows for a homogenous distribution of the abrasive material and thus an even sanding finish as well as for an appropriate dust removal and appropriate mechanical properties.

Claims

1. An abrasive belt comprising: a textile fabric being formed of interconnected fabric yarns, the textile fabric being defined by beams, each of the beams being defined by multiple ones of the interconnected fabric yarns, the beams extending between and defining connection regions in which different ones of the beams connect with each other, the interconnected fabric yarns in each one of the beams being knitted, stitched, or woven between the connection regions; and a coherent abrasive area that is a single, interconnected abrasive area that is continuous, wherein the coherent abrasive area is configured to sand or abrade a work piece, wherein the coherent abrasive area is formed on one side of the textile fabric, wherein the coherent abrasive area comprises a plurality of regularly distributed openings in the form of through holes, each perimeter portion of each respective one of the through holes being defined by one of the connection regions or by the interconnected fabric yarns that are knitted, stitched, or woven in one of the beams extending between two of the connection regions that define perimeter portions of the respective one of the through holes, whereby the coherent abrasive area defines a uniform thickness of the abrasive belt, whereby the abrasive belt promotes an even sanding finish of the work piece.

2. The abrasive belt according to claim 1, wherein the openings are arranged in lines that are perpendicular to a machine direction of the abrasive belt, the machine direction being defined by a direction in which the abrasive belt is driven to circulate, each respective one of the lines has multiple ones of the openings disposed along the respective one of the lines, wherein the multiple ones of the openings are regularly spaced apart from each other along the respective one of the lines, each of the multiple ones of the openings are offset from each one of the openings in another one of the lines when viewed along the machine direction of the abrasive belt, and a distance between each pair of sequential openings in the machine direction equals a distance between each pair of sequential openings in each respective one of the lines.

3. The abrasive belt according to claim 2, wherein the other one of the lines is adjacent to the respective one of the lines.

4. The abrasive belt according to claim 1, wherein a ratio of a volume of the fabric yarns to a volume of the abrasive belt, not including the openings, is 0.1:1 to 0.9:1.

5. The abrasive belt according to claim 1, wherein the coherent abrasive area on the one side of the textile fabric comprises a coating applied to the one side of the textile fabric.

6. The abrasive belt according to claim 1, wherein the thickness of each of the fabric yarns is between 5 to 4000 dtex.

7. The abrasive belt according to claim 1, wherein the openings have the form of an equilateral quadrilateral or are of hexagonal shape.

8. The abrasive belt according to claim 1, wherein the openings have a long dimension and a short dimension, the long dimension extending in a machine direction of the abrasive belt.

9. The abrasive belt according to claim 1, wherein a largest diameter of the openings is 0.3 mm to 20 mm.

10. The abrasive belt according to claim 1, wherein the beams separate neighboring openings and are arranged such that the beams extend in a direction intersecting a machine direction of the abrasive belt.

11. The abrasive belt according to claim 1, wherein a number of fabric yarns crossing at the connection regions of the interconnected fabric yarns is constant throughout the abrasive belt.

12. The abrasive belt according to claim 1, wherein the textile fabric has an atlas or cord structure.

13. The abrasive belt according to claim 1, further comprising reinforcing yarns worked into the textile fabric, the reinforcing yarns having a different thickness than the fabric yarns.

14. The abrasive belt according to claim 13, wherein the reinforcing yarns are worked into the textile fabric in the form of a pillar stitch.

15. The abrasive belt according to claim 13, wherein each of the reinforcing yarns have a thickness of 1/20 times the thickness of each of the fabric yarns or between 1 and 1/20 times the thickness of each of the fabric yarns.

16. The abrasive belt according to claim 13, wherein the reinforcing yarns are worked into beams.

17. The abrasive belt according to claim 1, wherein the textile fabric is impregnated with an impregnation and the textile fabric is tensed when applying and/or curing the impregnation.

18. The abrasive belt according to claim 1, wherein a total area of the openings is 0.1 to 10 times a total surface area of a total coherent abrasive area.

19. The abrasive belt according to claim 1, wherein, when a force of 100N per 50 mm width of a sample length of 200 mm is applied to the abrasive belt along a machine direction of the abrasive belt, an elongation along the machine direction of the abrasive belt is less than 1%.

20. An abrasive belt comprising a plurality of openings in the form of through holes, wherein the abrasive belt comprises a textile fabric being formed of interconnected fabric yarns and has a uniform thickness, a coherent abrasive area is formed on one side of the textile fabric, the plurality of openings are arranged in the coherent abrasive area in lines perpendicular to a machine direction of the abrasive belt, the machine direction being defined by a direction in which the abrasive belt is driven to circulate, the plurality of openings are regularly spaced along a direction that follows the lines, subsequent lines are offset from one another with respect to the position of their openings, wherein the textile fabric is defined by beams, each of the beams being defined by multiple ones of the interconnected fabric yarns, the beams extending between and defining connection regions in which different ones of the beams connect with each other, the interconnected fabric yarns in each one of the beams being knitted, stitched, or woven between the connection regions, whereby the abrasive belt promotes an even sanding finish of a work piece.

21. The abrasive belt according to claim 20, wherein the offset between subsequent lines is such that the plurality of openings of every second line align in the machine direction.

22. The abrasive belt of claim 1, wherein an entirety of the textile fabric is defined by only the beams, all of the beams of the textile fabric being transverse to a machine direction of the abrasive belt, the machine direction being defined by a direction in which the abrasive belt is driven to circulate.

23. The abrasive belt of claim 1, wherein the interconnected fabric yarns in each respective one of the beams are knitted, stitched, or woven along an entirety of the respective one of the beams between the connection regions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention may be better understood by reference to the following specification disclosed in preferred embodiments thereof and taken in conjunction with the following accompanying drawings.

(2) FIG. 1 schematically shows a section of an abrasive belt in different stages of the production process of the abrasive belt according to one embodiment.

(3) FIG. 2 schematically shows a cross section of the abrasive belt according to a preferred embodiment.

(4) FIGS. 3A and 3B schematically show the silhouette of the structure of the abrasive belt in a top view according to preferred embodiments.

(5) FIG. 4 shows an example of a knitting pattern according to a preferred embodiment.

(6) FIG. 5 shows another example of a knitting pattern according to a preferred embodiment.

(7) FIG. 6 shows another example of a knitting pattern according to a preferred embodiment.

(8) FIG. 7 shows another example of a knitting pattern according to another embodiment.

(9) FIG. 8 shows an example of a reinforced knitting pattern according to a preferred embodiment.

(10) FIG. 9 shows an example of a reinforced knitting pattern according to a preferred embodiment.

(11) FIG. 10 shows another example of a reinforced knitting pattern according to a preferred embodiment.

(12) FIGS. 11A to 11C show SEM-images of cuts through grinding products.

(13) The description and the accompanying drawings are to be construed by ways of example and not of limitation.

DESCRIPTION PREFERRED EMBODIMENTS

(14) In the following, preferred embodiments are described in detail with reference to the drawings.

(15) FIG. 1 shows a section of an abrasive belt 1 according to an embodiment. The different layers that are shown in FIG. 1 illustrate the abrasive belt 1 in different stages of its manufacturing process. As can be inferred form stage one, the textile fabric 2 of the abrasive belt 1 comprises a plurality of interconnected fabric yarns 20. Preferably, the textile fabric 2 has the form of a knitted textile fabric which can be produced on a textile producing machine by warp-knitting, for instance. In stage two, the textile fabric 2 is physically fixated by applying an impregnation 30. In stage three, the impregnated textile fabric 2 has been coated with a coating 40. Further, abrasive material or abrasives 50 have been applied, optionally by using a suitable binding system. Thereby, a coherent abrasive area 60 is formed, wherein the abrasives 50 are evenly distributed over the abrasive belt 1. Stage three can be referred to as the final precursor stage before further conversions and process stages are carried out to convert the material into a functional abrasive product. It is to be noted that the impregnation is not mandatory and that the impregnation step may also be omitted. In addition the abrasives may directly be applied onto the textile fabric or the impregnation, i.e., without any coating.

(16) The type of interconnection between the fabric yarns 20 is, in general, of minor relevance as long as the conflicting requirements as identified for abrasive belts can be fulfilled: combing a small elongation under load with an open structure and the ability to achieve an even sanding result.

(17) To this end, as can be inferred from the cross-sectional view in FIG. 2, the number of crossings of the fabric yarns 20 at interconnecting points of the fabric yarns 20 is preferably uniform throughout the textile fabric 2. As shown at FIGS. 1, 2, and 4-10, the textile fabric is defined by only a homogeneous fabric structure throughout the textile fabric. For example, the knitted fabric structure shown in FIGS. 1, 2, and 4-10 extends throughout the entirety of the textile fabric in a continuous manner. Specifically, in FIG. 2, the number of crossings of the fabric yarns 20 at interconnection points is two.

(18) This ensures that the local enrichment of the yarns 20 due to the interconnections is limited. Enrichment of the yarns refers to the fact that in the textile fabric 2, an interconnection of the fabric yarns 20 is necessary in order to produce a coherent and physically stable material. Without interconnecting stitches only loose fabric yarns 20 would be produced but no textile fabric 2 would be created. In theory and in practical terms, a warp knitted or other type of textile needs a minimum of one point of interconnection per stitch. When, however, more than two fabric yarns 20 are crossing at such an interconnection point, more than the minimum amount of fabric yarns 20 for creating such an interconnection point is present. Such yarn crossings involving more than two fabric yarns 20 per interconnection point thus lead to minor elevations in the textile fabric 2 when the level of the interconnection points is compared with the other parts of the textile fabric 2.

(19) The uniform number of crossings throughout the textile fabric 2 ensures a uniform height of the abrasive belt 1 that is preferably of the order of 1.5 to 5 times the diameter of the individual fabric yarns 20. It is also not desired that certain surface areas are on a lower level than other surfaces as this would result in uneven sanding results and the formation of stripes on the sanded surfaces.

(20) FIGS. 3A and 3B schematically show the silhouette of the structure of the abrasive belt in a top view. The silhouette of the belt 1 is thereby essentially identical to the abrasive area 60. As can be taken from this illustration, the openings 10 are highly symmetric with respect to the machine direction M1 and perpendicular thereto. This is preferable, as such structures ensure that the abrasive regions between adjacent openings 10 are as uniform as possible, which in turn leads to a regularly and evenly distributed abrasive area 60 throughout the belt 1. With other words this means that the local density of the abrasive area, which may be measured in abrasive area per unit area, is essentially constant throughout the abrasive belt 1 (at least on length scales of said unit area, which are larger than or equal to two opening diameters).

(21) Moreover, the openings 10 are arranged in lines L1, L2 perpendicular to the machine direction M1 of the abrasive belt 1 and subsequent lines L1, L2 are offset form one another with respect to the position of their openings 10.

(22) Further, the width of the openings and the width of the region between two openings (i.e. the connection region) are of the same order in cross-direction (i.e. in a direction perpendicular in the machine direction), which further promotes an even sanding finish. For instance, if the width of the openings is 1.5 mm, the width of the connection region may be 0.3 mm to 5.0 mm, which still guarantees a sufficient overlap of the openings of subsequent rows. Even more preferable would be a width of the connection region may between 1 mm to 2.0 mm for a width of the openings of 1.5 mm.

(23) Strands or beams 21 of interconnected fabric yarns 20, which separate neighboring openings 10, run at a given angle with respect to the machine direction M1. The term beams of yarns shall refer to the overall shape or direction which is described by the fabric yarns when they proceed in the textile fabric. Accordingly, the beams 21 of fabric yarns 20 will form mirror images of each other seen from a plane crossing the connection points in the longitudinal direction of the belt 1 (FIG. 3). Examples for suchlike geometries of the openings are presented in FIGS. 3A and 3B, wherein FIG. 3A shows essentially equilateral quadrilateral openings 10 and FIG. 3B shows essentially hexagonal openings 10.

(24) The evenness of the abrasive area 60 for the symmetric openings 10 that are illustrated in FIGS. 3A and 3B can be further exemplified by a virtual projection of the abrasive area of two consecutive lines of openings 10 on a line perpendicular to the machine direction, which will be in both cases highly uniform and entail a good sanding area balance. Thus, the sanding area balance might be seen as a measure for deviations in the physical area of the abrasive area within in one repetition of the pattern, i.e. within two consecutive lines L1, L2.

(25) In this regard, the equilateral openings 10 may provide a sanding area balance that is even better as in the case of the hexagonal openings 10 if the machine direction is as indicated in FIGS. 3A and 3B. Interconnection points between the single hexagonal openings 10 shall in that case be kept as short as possible as such areas will disrupt the sanding area balance between the areas coated with abrasives 50.

(26) As regards the beams 21, the number of fabric yarns 20 per beam 21 is preferably two as this ensures a uniform thickness of the belt 1.

(27) If the textile fabric is formed of knitted yarns, preferred knitting patterns are shown in FIGS. 4 and 5. Another preferred knitting pattern is illustrated in FIG. 6.

(28) Turning first to FIGS. 4 and 5, one possible structure is based on a textile fabric with open (FIG. 4) or closed atlas binding (FIG. 5).

(29) The term open atlas binding refers to a knitting pattern on a warp-knitting machine which proceeds over two or more rows. Hereby, the intermediate stitches between the stitches which induce a directional change can either be open, closed or a combination thereof. An open stitch pattern is for instance based on the following warp-knitting structure type: 1-0/1-2/2-3/2-1// (FIG. 4). Thereby the notation 1-0/1-2/2-3/2-1// is the notation according to the ISO 8388:1998-standard (page 76, B4 Chain Notation).

(30) The term closed atlas binding refers as well to the intermediate stitches between the directional changes in the knitting pattern. In contrast to the example of the open atlas binding, a closed atlas binding follows for instance the following knitting structure type: 0-1/2-1/3-2/1-2// (FIG. 5).

(31) In case of an atlas binding, the beams 21 of interconnected yarns 20 generally may be seen as obliquely protruding with respect to the machine direction M1 of the belt 1.

(32) Preferably, a two-row atlas structure is used. In this regard, the number of rows refers to the number of stitches which proceed into one direction before the knitting proceeds into the opposite direction. Another definition is by referring to the repeat height of the pattern. In this case the number of rows equals half of the repeat height. For instance, in case of an atlas repeat height of four, the number of rows consequently equals two. In this context, the term course may be used which, in the field of warp knitting, refers to the number of stitches needed until the pattern which is to be knitted begins to repeat itself. Consequently a pattern having a repeat height of four requires four courses until the next repeat begins.

(33) Structures based on two rows provide openings 10 which are equilateral quadrilateral. Accordingly, all the surfaces located in between the openings 10 in the textile fabric 2 have exactly the same area. This ensures an even distribution of the abrasive area throughout the abrasive belt 1. At the same time, the enrichment of the fabric yarns 20 at the interconnecting points can be kept low. Moreover, the openings 10 are arranged in lines L1, L2 perpendicular to the machine direction M1 of the abrasive belt 1 and subsequent lines are offset form one another with respect to the position of their openings 10. Therefore, when used as an abrasive belt 1, such structures will provide an equal rate of removal throughout the entire sanding surface. In turn, the formation of stripes or similar structures on the work piece can be avoided.

(34) Moreover, the openings 10 are elongated in the machine direction M1, which is beneficial for the general resistance of the textile fabric against elongation in the machine direction M1.

(35) Preferably, the binding direction is alternating for every needle. The binding proceeds in the same direction in each second needle in this structure, and it is also possible to use an atlas fillet binding with more than two rows, like for instance three, four or more rows, but these structures are more prone to induce stripes on the work piece.

(36) As mentioned, another example for a preferred knitting pattern is the cord stitch as shown in FIG. 6. Thereby, the cord stitch may form a net structure with similar quadrilateral openings 10 as in the previously mentioned two row atlas structure (c.f. FIG. 6).

(37) Such a structure would follow a lapping pattern of e.g. the type 1-0/2-3// (FIG. 6). Also this pattern will result in a structure possessing a low enrichment of yarns in the interconnection points, such as the previously described atlas binding.

(38) Structures with low enrichment of fabric yarns 20 as the ones that are shown in FIGS. 4 to 6 will as such allow the fabric yarns 20 to be as much as possible on a similar height level on both the front and backside of the textile fabric 2, which is preferable for many applications of the abrasive belts. In this case, the front side of the textile fabric 2 will carry the abrasive materials 50 and the back side of the textile fabric 2 will bear and distribute the pressure from the backing device as evenly as possible.

(39) Also for the cord stitch, the openings 10 are highly symmetric and the abrasive areas between adjacent openings are highly uniform throughout the abrasive belt 1. Moreover, adjacent openings 10 are offset with respect to one another in the machine direction M1 of the belt 1. This will ensure a sanding result which does not cause stripes on the sanded article.

(40) Although with the atlas binding and the cord stitch two preferred knitting patterns have been described, it should be noted that the present invention is not limited to these structures. Other knitting patterns might also be suited for achieving the desired properties in terms of mechanical stability, permeability of the belt for dust and other particles and an even sanding result. One additional example is shown in FIG. 7, in which a warp knitting structure of the type 10/12/10/12/23/34/45/43/45/43/32/21// is shown. Accordingly, a more closed product with less dust extraction capability but very high mechanical strength in machine direction results. However, the sanding result might be more uneven as compared to the aforementioned structures.

(41) Textile fabrics which are in principle suitable are defined in ISO 8388 and comprise weft-knitted jersey-based fabrics, weft-knitted double layer jersey-based fabrics, weft-knitted rib-based fabrics, weft-knitted purl-based fabrics, warp-knitted jersey-based fabrics, warp-knitted double layer jersey-based fabrics, warp-knitted rib-based fabrics, warp-knitted purl-based fabrics, combined warp- and weft-knitted jersey-based fabrics and others.

(42) It is also conceivable to transfer the patterns and shapes of the openings to other base materials, like woven textile fabrics or even paper-backings and films. Moreover, it is also possible to manufacture structures with various threadings to achieve different opening sizes and surface area ratios between openings and abrasive areas.

(43) In order to further promote the mechanical stability and, in particular, the resistance of the textile fabric 2 against an elongation in the machine direction when tensed, it is preferable to integrate a reinforcing inlay or generally reinforcements into the belt 1. Preferably, these inlays consist of reinforcing yarns 25 that are worked into the structure of the belt 1.

(44) Preferably, a pillar stitch or an inlay can be integrated as reinforcements in the machine direction. FIG. 8 shows an example of a possible knitting structure that is reinforced by reinforcing yarns 25. Thereby, the reinforcing yarns 25 are shown in dark color. By way of example, the reinforcement yarns 25 shown in FIG. 8 are worked into a two row atlas binding. The resulting structure possesses predominantly quadrilateral openings with minimal yarn enrichment in the connection points. The use of a pillar stitch for longitudinal reinforcement of the textile fabric leads to an additional enrichment of yarn in this specific structure.

(45) A preferred integration of an inlay of reinforcing yarns 25 into an atlas structure consists of the use of an open or closed pillar stitch proceeding over two rows as shown in FIG. 8. In such a configuration, the reinforcing pillar stitch of the type 1-0/0-1// or 0-1/1-0// will protrude along the general direction of the atlas binding and, therefore, will not lead to a partial coverage of the openings. With other words, the reinforcing yarns generally follow the beams of the interconnected fabric yarns. Such reinforcement is also worked into the basic binding by stitches in the way that it is mechanically bound by stitches to the base textile fabric and thus only allows a certain, limited stretchability (FIG. 8).

(46) Self-speaking the above atlas structure may also be reinforced in various different ways in order to reduce its elongation along the knitting direction of the textile fabric 2. One other example is shown in FIG. 9, in which the atlas binding of FIG. 4 is reinforced by an inlay binding of 0-0/1-1/ /. In addition, in an atlas structure with a two rows net structure, open or closed stitches plus inlay 0-0/0-0// are also suited to reduce the elongation along the knitting direction of the textile fabric. However, such a reinforcement type might lead to partial coverage of the openings in the textile. Another type of reinforcement is the incorporation of an inlay of the type 1-1/0-0 which will follow the structure of the atlas binding more closely.

(47) Also for the cord binding, it is possible to integrate a pillar stitch in order to improve the mechanical properties of the material. An example is shown in FIG. 10, in which a pillar stitch of the type 1-0/0-1// or 0-1/1-0// is applied.

(48) An alternative to using a pillar stitch is to use an inlay yarn which protrudes along the machine direction through the material and leads to a similar reinforcement as the previously described pillar stitch reinforcement.

(49) Noteworthy, yarns which are either inserted as an inlay, a warp yarn or as a knitted pillar stitch lead to very low values of mechanical displacement when longitudinal forces are applied. The structure as described is nonetheless prone to stretch in transverse direction. This circumstance can be utilized for controlling the size and shape of the openings 10 in the textile fabric 2 during the impregnation process by stretching the textile fabric 2 and allowing the formation of larger or smaller openings 10 in the material.

(50) The inserted knitting structure, inlay-yarns or reinforcing yarns 25 need to be sufficiently thin in order to avoid the creation of height differences in the final textile fabric surface and, at the same time, sufficiently strong to withstand tensile forces.

(51) Preferably, the reinforcing yarns 25 have a maximum thickness of approximately 0.05-2.00 mm. More preferably, the thickness is in the range of 0.1-0.5 mm. In relation to the thickness of the fabric yarn 20 of the base textile fabric 2, a thickness ratio of base fabric yarn to reinforcing yarn of approximately 1:1 to 20:1 is applicable wherein a range of 7 10:1 to 2:1 is in most cases preferred. With such a thickness for the reinforcing yarns 25, it can be ensured that the uniform height distribution of the textile fabric 2 is not too much affected by the integration of the reinforcing yarns 25.

(52) In this context, it should be noted that small height differences might be re-balanced in a later process step. This may include that, for instance during coating of the abrasive articles, printing technologies maybe applicable such as screen print, ink-jet, gravure roller coating and the like, in order to apply a coating in a fashion which enables the abrasive articles 50 to be strewn in such a manner that these only occupy a defined area of the textile fabric. In addition, the coated surface may be machined by an abrading or sanding process in order to obtain an even surface finish. In such a way, an inequality in sanding area balance of the impregnated textile fabric structure can be compensated during the coating process.

(53) The same applies for a facultative second coating (not shown) that is applied on the backside of the belt. Accordingly, the second coating can be used for leveling the backside of the belt (i.e. the side that does not come into contact with the work piece).

(54) The fabric yarns 20 for the base textile fabric 2 of the abrasive belts 1 as well as the reinforcement yarns 25 are typically texturized or flat yarns of polyester or polyamide due to their suitable tensile properties and low costs. However, yarns based on natural fiber such as cotton, hemp or similar fiber may also be suitable. This includes in more general terms the use of so called staple fiber or multifilament yarns based on synthetic or natural fibers which can be used for the base structure or the reinforcement of the textile fabric. Twisted yarns being single or plied yarns can optionally also be used. Elastic yarns may be applicable in certain applications when the textile fabric shall be stretched in a specific way, e.g., when a change in shape of the openings into a special shape is desired.

(55) The term texturized yarn, commonly known as DTY (Drawn Texturized Yarn), is a multifilament yarn which has been treated by thermal or mechanical methods or combinations thereof in a way that the yarn filaments are coiled, crimped or looped. There are various texturizing methods which can be applied, such as air texturized, knife edge texturizing, false twist friction texturizing, stuffer box texturizing or gear crimped yarn.

(56) The term flat yarn is commonly known under the abbreviation FDY, which is so called Fully Drawn Yarn. Such FDY's can be of various buildup types based on mono- or multifilament. These yarns can also be either bright, semi dull or full dull in respect to their appearance, which are the most common types. However also various shapes of yarns, filaments and their cross sections are available which amongst others can be for instance of the type round, trilobal, multi-edged or of any other type of shape.

(57) Yarns of either type, such as texturized or flat yarn, can apart from their type of texturization, or shape and appearance additionally also be twisted. Twisting refers to turning the yarn into two different directions which are commonly referred to as S and Z directions. These directions of twist only refer to the direction in which the yarns are twisted; so that S and Z twisted yarns resemble mirror images of each other. Such twisting of yarn has in most cases barely any technical relevance in warp knitting, but leads to different optical effects in the final textile fabric.

(58) The fabric yarn 20 for the base textile fabric 2 as well as the reinforcing yarns 25 may be monofilament or multifilament yarns.

(59) The term monofilament yarn refers to a man-made, endless spun yarn which is built up of a single filament of material. A yarn of a certain thickness as e.g. 20 dtex is not separated into other substructures but consists of only one filament. A multifilament yarn consequently consists of several substructures (filaments) in contrast to a monofilament yarn. Hereby, yarns can be distinguished by the number of filaments that the yarn consists of. As an example, a 20 dtex multifilament yarn can consist of for instance two or more filaments.

(60) A plied yarn typically consists of multifilament yarns, which can be twisted or non-twisted yarns, texturized or non-texturized yarns, as well as intermingled or non-intermingled yarns. Whereas typically twisted yarns are not intermingled. These previously described single yarns can then in the following be joined together to form a new, thicker, yarn which is referred to as being plied. Such a plied yarn consequently consists of at least two or more single yarns which have been plied together.

(61) The term natural fibers refers to fibers which have an origin in renewable sources. These refer to fiber formed materials such as cotton, hemp, wool, silk or similar materials which are directly obtained from plants or animals.

(62) The term man-made fiber is referring to all other fibers than natural fibers. Man-made fibers can be synthetically produced from petrochemicals, bio-based polymers or organic raw materials. Regenerated fibers are one subgroup under man-made fibers. Those are made of natural materials like plants by going through chemical and mechanical process. These kinds of fibers are e.g. Viscose, Bamboo and Modal type yarns which are made of cellulose. Synthetic fibers can be made of petrochemicals e.g. polyester, vinyl acetate, nylon, aramid and carbon. This category also includes chemically modified fiber formed materials and fibers manufactured from polymers of bio-based building blocks like for instance, lactic acid, amino acids or propylene dioxide based materials.

(63) Another important property of an abrasive belt 1 may be the electrical conductivity of the final abrasive product which may include the incorporation of carbon fibers or yarns of similar materials which provide conductive properties. Examples of such modified yarns are metal-coated yarns or yarns which have a conductive core or are treated with other treatments.

(64) This does not exclude that the base textile fabric 2 even may solely be composed of carbon or other conductive yarns. In order to achieve a highly conductive material, this naturally shall also apply in regard of the resin used for impregnation of the textile fabric. The resin may also contain conductive elements such as carbon, metals, metal ions and the like, in order to achieve conductive properties of the composite of textile base and resin impregnation.

(65) Examples of other potential yarns for textile based belts include fibers of ultrahigh molecular weight polyethylene (UHMWPE), polypropylene (PP) and aramid yarns. These can be used for the base structure of the textile fabric or solely for the reinforcement of the material.

(66) The thickness of flat or texturized yarn may range from 5 to 4000 dtex, depending on the desired tensile and elongation values of the textile fabric as backing material, as well as the desired size of the abrasive grains or the end use of the final product. The unit dtex is by definition the weight in grams per 10,000 m of yarn. A typical thickness for the atlas base yarn is between 150 to 900 dtex and between 15 to 450 dtex for the reinforcing yarns.

(67) When a knitted structureeven if reinforced by reinforcing yarnsis exposed to forces in the longitudinal direction, this may result in a small but still undesired elongation. This can be avoided if the textile fabric 2 is already exposed to longitudinal stretching at the time when the material is impregnated with a resin or coated with the coating or the second coating prior to the application of the abrasives. Due to this stretching of the textile fabric during impregnation, the mechanically displaceable parts are set under tension. By consequence, the yarns are still under strain when the impregnation 30/coating 40 is cured and the textile fabric 2 can withstand longitudinal forces better and further stretching is reduced.

(68) Additionally, it is possible to control the stretchability of the textile fabric 2 in a transverse direction after final curing of the impregnation 30. Hereby, a more extensive stretching of the textile fabric 2 will lead to the formation of larger openings 10 but will also reduce the transverse elongation of the impregnated material after curing is complete. Such a more extensive stretching during impregnation prevents the final textile fabric 2 from stretching excessively in the transverse direction when the material is used as an abrasive belt, as during its use also transverse forces may occur (though the forces in transverse direction are typically of significantly lower magnitude than the forces occurring in longitudinal direction).

(69) Different types of impregnations 30 and coatings 40 may be applied for the textile fabric 2. The same applies for the second coating on the backside of the belt. The types of resins used for impregnations and coatings may consist of phenolic, urea or latex as well as blends thereof as described in EP 0 779 851. The belt may be coated by using roller coating, spray coating, curtain coating, by printing methods such as screen printing or gravure rollers, transfer foil or similar methods resulting in coatings referred to as a make- and size-coat. Further on, also radiation curable impregnation resins such as epoxides, acrylates, or similar resins may also be applied. Also thermally curable epoxies, acrylates, isocyanides or similar resins and mixtures thereof may be utilized for the mechanical stabilization of the textile fabric. The resins may include fillers and additives such as surface active substances like fatty acid ethoxylates, fillers or various kinds such as fibers, aluminum trihydroxide, kaolin, calcium carbonates, talc and the like.

(70) The textile fabric 2 of the belt 1 may furthermore be subject to any kind of surface modifications from either technical front- or backside of the textile like also described in EP 0 779 851.

(71) The abrasive areas 60 may in the same or separate processes be strewn or coated with abrasive articles 50 such as silicon carbide, aluminum oxide of various types or mixtures thereof such as brown, pink, white, or high temperature treated species. Hereby also high performance abrasives such as ceramic coated or similar grains as well as diamonds, CBN or other particles commonly referred to as super-abrasives can be applied.

(72) FIGS. 11A, 11B, and 11C show SEM-images of a cut through the cross section of the impregnated fabric. The cut runs perpendicular to the previously defined machine direction of the fabric and at the same time perpendicularly to the front and back sides.

(73) In the original SEM-images (FIGS. 11A and 11B) the fabric yarns can easily be distinguished from the surrounding impregnation resin. FIG. 11B shows a cross cut section which was embedded into a mold resin (which is unrelated to the actual product and merely applied for imaging purposes) prior to cutting in order to achieve a planar cut and have the possibility to determine the area ratio between fabric yarns and surrounding impregnation resin by photographical analysis methods. The surrounding area of the mold resin is hereby taken into account and reduced from the total cross-section area.

(74) In order to calculate the volume fraction ratio of the yarns and impregnation resin the same analysis is performed on several repeated cuts (>5) in the machine direction in order to obtain a statistically relevant result.

(75) The fibers are identified either manually or by means of an image recognition algorithm and the associated number of pixels is extracted (FIG. 11C). The image for extracting the number of pixels of the yarn area is shown in FIG. 11C. A similar colored or color inverted picture is used to determine the area of pixels covered by the impregnation resin. The number of pixels from the yarn surface is then related to the total number of pixels of the cut surface of the product or the number of pixels of the impregnation resin.

(76) By calculating the average area fraction of the fabric yarns in relation to the average fraction of the impregnation resin for a statistically sufficient number of cuts this can be taken as a volume ratio between the yarn and impregnation resin. In the example that is shown in the FIGS. 11A to 11C, the volume fraction of fabric yarns to impregnation resin amounts to about 1.7 and, correspondingly, the volume fraction of fabric yarns to the total volume of the product (excluding the openings) is about 0.6.

(77) It is also possible to determine the weight fraction ratio of the fabric and the impregnated fabric by relating the weight of the fabric and the impregnated fabric after curing. This ratio lies between 0.05 and 0.9, whereas it preferably lies between 0.1 and 0.7 and even more preferably between 0.2 and 0.4. An abrasive belt with sufficient mechanical properties can be formed within these ratios.

(78) At the same time, a certain amount of resin ensures that the irregularities stemming from the textile fabric backing (in terms of enrichment points of the fabric yarns) can be balanced out.

(79) Although, in the above example, a sample has been investigated in which only impregnation resin is present, the above analysis can equally well be applied for products that are (additionally) coated. In that case the values are corresponding volume/weight ratios of fabric yarn to resin wherein the resin fraction is then either formed by impregnation resin plus coating or merely coating.

(80) In even more general terms, if additional components are present, the above analysis will lead to volume/weight ratios of the fabric yarns to the volume/weight of the overall product (not including the openings) and/or to the applied coatings and combinations thereof.

(81) The requirements for abrasive belts are demanding. The embodiments described above allow for a homogenous distribution of the grains as well as for an appropriate dust removal and sufficient tensile properties. Moreover, the open structure is extremely useful in certain types of belt sanding machines where the transparency of the belt gives the machine operator a significantly better possibility to control the sanding process, like for instance in the case of stroke sanders.