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(11) | EP 0 699 506 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | An abrasive belt |
| (57) A continuous abrasive belt 31 for a power file or the like, wherein the belt 31 has
a substantially constant thickness throughout. The belt 31 is ideally seamless, being
formed from a tube of backing material coated with adhesive and abrasive particles
and cut to length. As a result of being seamless, and hence jointless, failure of
the belt 31 during use is less likely and "bumping" of the workpiece does not occur. |
[0001] This invention relates to abrasive belts, and in particular to belts for use with power files or the like.
[0002] Power files are well known which comprise two spaced rollers, one of which is driven by an electric motor, about which a continuous abrasive belt may run for sanding or polishing a workpiece, for example. The power files are generally hand-held and the two rollers are positioned to tension the continuous belt to produce smooth running of the belt about the two rollers.
[0003] Continuous belts for power files of the aforementioned type have been known for many years and have changed little. In general, the belts have been manufactured using a backing material of either paper, cloth or a combination of both with abrasive grit bonded to the front face using a number of resin or glue coats. The abrasive coated material is manufactured in jumbo rolls having a width of between 0.5 and 1.5 meters and lengths up to several hundred meters. The jumbo rolls are converted into lengths equal to the "developed" or final length of the belt and then formed into an endless loop by joining the two ends together. Once joined, the endless loop formed from the jumbo roll is slit down to the required width. Many methods exist for forming the joint, the two most favoured methods of manufacture being the "butt joint" and the "lapp and skieve joint".
[0004] A typical butt joint abrasive loop 1 is shown in Figure 1A of the accompanying drawings. The section taken along the line I-I in Figure 1A is shown in Figure 1B. As can be seen, the belt 1 comprises a backing material 3, which may be cloth including stabilising fillers, a make coat 5 (i.e. a primary adhesive coat), a size coat 7 (i.e. a secondary adhesive coat) and abrasive grain or particles 9. Once the two ends of the continuous belt 1 have been abutted, the jointing media 11, which is usually a polyester based tape, is applied to the inside of the belt 1 overlapping the two ends of the belt 1 as shown in Figure 1B. As a result, a continuous (or endless) abrasive belt is formed.
[0005] A measure of the discontinuity of a belt is provided by the arithmetic difference between the total thickness dimension D of the belt and the thickness d of the basic coated abrasive material, which in this instance results in a discontinuity (i.e. D - d) corresponding to the jointing tape 11 thickness. During use of the abrasive belt 1, the jointing tape 11 passes over the power file/sander running plate (not shown) and rollers (not shown) resulting in wear, which often becomes so severe that the jointing tape 11 can no longer carry the tension in the belt 1, thereby resulting in failure of the belt 1. Attempts to increase the life of the belt by increasing the tape thickness have been tried, but have been found to have detrimental effects on the belt performance as the increased "bump", when the jointing tape 11 passes over a roller, reduces the quality of the finish produced on a workpiece.
[0006] Figure 2 shows a typical continuous belt formed using a lap and skieve joint. As can be seen, the composition of the basic coated abrasive material is the same as that described with reference to Figure 1 of the drawings. In this instance, however, the ends of the material are spliced at an angle, overlapped, and then bonded together using an adhesive. The discontinuity of this joint (D - d) tends to be larger than that of the butt joint of Figure 1B and may vary from 0.2 mm to 0.3 mm, depending upon a manufacturer's preference and process capability.
[0007] Although continuous abrasive belts using butt joints or lap and skieve joints have been used for some years, as mentioned above, problems can occur with such belts, as follows:
(i) Premature failure due to separation of the two ends can arise during normal product usage. It has already been highlighted that the butt joint loses strength as the jointing tape 11 wears and failure occurs when the tension load exhibited by the sander (a requirement to drive the belt) exceeds the strength of the worn tape 11.
(ii) Repeated flexing of the belt over the drive and idler rollers of the sander of up to one hundred flexes per second (in the case of high speed machines) causes fatigue failure in both forms of joint.
(iii) The adhesive used in a joint is sometimes sensitive to liquids such as coolants and cutting fluids which are used in the metal working industry. This can reduce the strength of the joint, again resulting in premature failure.
(iv) The nature of the conventional jointing processes results in a belt discontinuity (as described above) which, if excessive, can create uneven sanding marks and coarse scratches on a workpiece and/or create excessive vibration as the belt "bumps" when the discontinuity passes between the workpiece and sander rubbing plate or roller.
(v) During usage, the belt may not run true or may show problems with tracking due to the poor alignment of the two ends of the belt during the jointing phase of manufacture.
[0008] In view of the foregoing, the present invention aims to improve upon the known prior art continuous abrasive belts by providing an abrasive belt having a negligible discontinuity throughout the length of the belt.
[0009] The present invention therefore provides a continuous abrasive belt for a power file or the like, wherein the belt has a substantially constant thickness throughout. More particularly, the belt is preferably seamless.
[0010] The belt preferably comprises a backing material, an adhesive layer on the backing material and an abrasive layer on the adhesive layer.
[0011] The backing material is preferably a cloth impregnated with a resin. Other suitable backing materials could, of course, alternatively be used.
[0012] A second adhesive layer is preferably applied to the abrasive layer to assist in retaining the abrasive layer on the backing material.
[0013] According to another aspect of the present invention, there is provided a method of forming a continuous abrasive belt comprising the steps of:
(a) forming a tube of backing material having a wall thickness which is substantially constant throughout;
(b) applying an adhesive layer to the exterior of the tube;
(c) applying abrasive particles to the adhesive layer; and
(d) cutting the tube to produce a continuous belt of required width.
[0014] Although the sequence of steps used in the method is preferably as set out above, in theory steps (b)-(d) could occur in any order after step (a).
[0015] Preferably, after step (c), a second adhesive layer is applied to the exterior of the tube overlaying the particle layer.
[0016] Before step (b), the backing material is preferably filled with resin and cured. More preferably, the backing material is of cloth.
[0017] In a particular method according to the present invention, the belt is baked in an oven between steps (c) and (d). Further, if a second adhesive layer is applied to the tube, the belt is also preferably baked in an oven after the application of the second adhesive layer.
[0018] The particle layer may be applied by an electrostatic coating process or using a gravity feed hopper. Other ways of applying the particle layer can, of course, alternatively be used.
[0019] Preferably the belt is flexed to crack the adhesive layer or layers prior to use of the belt. By doing this, loss of abrasive particles during use is less likely to occur.
[0020] Specific embodiments of the present invention are now described, by way of example only, with reference to the accompanying drawings, in which:
Figure 1A is a schematic perspective view of a continuous abrasive belt incorporating a butt joint;
Figure 1B is a sectional view in the direction I-I of Figure 1A;
Figure 2A is a schematic perspective view of a continuous abrasive belt incorporating a lap and skieve joint;
Figure 2B is a sectional view in the direction II-II in Figure 2A;
Figure 3A is a schematic perspective view of a continuous abrasive belt according to the present invention;
Figure 3B is a sectional view in the direction III-III of Figure 3A; and
Figure 4 is a schematic diagram showing some of the steps involved in a method of forming a continuous abrasive belt according to the present invention.
[0021] With reference to Figures 3A and 3B, a seamless, continuous, abrasive belt 31 according to the present invention comprises a backing material 33 of cotton cloth impregnated with resin, a make or primary adhesive coat 35, a layer of abrasive particles 37 and a size or secondary adhesive coat 39. Since there is no joint in the continuous belt, the thickness of the belt is substantially constant (within normal manufacturing tolerances) along its entire length. The discontinuity (D - d) of the belt is, therefore, negligible (i.e. essentially zero).
[0022] As a result of the continuous belt having no joint, the following advantages over the prior art belts arise:
(I) As there is no backing tape (as required by a butt joint) to wear during use nor adhesive joint (as in a lap and skieve joint), the belt or loop is equally strong across any cross-section and, therefore, the likelihood of premature failure is negated.
(II) Repeated flexing of the belt does not cause joint fatigue failures, as can occur with the prior art belts described above.
(III)The use of coolants or cutting fluids does not affect the belt joint, because a belt joint does not exist.
(IV) The avoidance of a joint eliminates the discontinuity witnessed in the prior art belts and, therefore, eliminates the "bumping" which can cause vibration and poor finishing on a workpiece.
(V) As a result of the belt not having a joint, the belt cannot experience the run out or tracking problems associated with the prior art belts due to misalignment when presenting the two ends of the belt for jointing.
[0023] Turning now to Figure 4 of the drawings, a method of manufacturing a seamless, continuous, abrasive belt according to the present invention is described.
[0024] A tube of cotton cloth 33 of known tensile strength is manufactured by weaving using processes developed in the cloth and hosiery industries. The tube 33, because of its nature of construction, is totally jointless and seamless. The tube diameter is simply chosen to correspond to the diameter of the required abrasive belt, whereas the length of the tube exceeds considerably the width of the final belt 31. In fact, the tube 33 is likely to be manufactured in lengths of several hundred meters; it will then be cut to a length which is practical to handle during manufacture, probably in the region of one meter. Once the abrasive coating stages of belt manufacture have been completed, however, the tube is cut or slit down to the required final belt width.
[0025] Once the tube of cotton cloth 33 has been produced, it is mounted onto a hub 41. The hub 41 is to take one of three formats, namely either (i) a solid drum which has a diameter equal to that required of the finished belt 31, (ii) a drum which is variable in diameter to accommodate a range of belt sizes, or (iii) two smaller diameter rollers separated by a variable size pitch, thereby allowing a range of tube sizes to be accommodated.
[0026] Once positioned on the hub 41, the tube 33 is subjected to the normal first stage of filling the cloth material with resin 43, etc, in order to stabilise the cloth 33 and reduce/eliminate the tendency for the cloth 33 to stretch or distort. Once cured, the filled cloth 33 has a make or primary adhesive coat 35 applied thereto by allowing the tube of cloth 33 to run in a bath 44 of adhesive. The adhesive is either a glue or resin, the thickness of the coat 35 being controlled with a scraper knife 45. Once the make coat 35 has been applied, the abrasive grit 37 is added via a gravity feed hopper (not shown) or an electrostatic coating device 47. The tube 33, now covered in make coat 35 and abrasive particles 37, is baked in an oven 49 at an elevated temperature to cure the make coat 35. The final adhesive or size coat 39 is applied after the curing process in oven 49. Again, application of the size coat 39 is achieved by running the tube 33 in a bath 51 of adhesive and removing the excess adhesive with a scraper knife 53. The final curing stage is then completed in a second baking oven 55.
[0027] When the meter length tubes 33 have been coated with the two adhesive/resin layers 35,39 and the abrasive particle layer 37, and the adhesive/resin layers 35,39 have cured, the tube 33 is cut diametrically to produce seamless, continuous abrasive belts having the required width. In this way, an abrasive belt 31 without a seam or joint is produced.
[0028] As is known with prior art belts, the make coat and size coat of an abrasive belt can result in a degree of rigidity being provided. Since this rigidity would adversely affect the performance of the abrasive belt due to the belt being incapable of deforming satisfactorily to meet even the slightest contour exhibited by a workpiece, it is normal for the abrasive bond to be "cracked" or broken in a controlled manner to improve flexibility of the belt. This process is called "flexing". If the flexing is not controlled correctly and is excessive, the adhesive bond will fail to hold the abrasive particles, thereby resulting in grit shed. In the light of this, it will be appreciated that a flexing of the finished abrasive belt 31 in a controlled manner would be beneficial, even for a belt 31 according to the present invention. Hence, a final step of flexing the belt prior to use should be undertaken.
(a) forming a tube of backing material having a wall thickness which is substantially constant throughout;
(b)applying an adhesive layer to the exterior of the tube;
(c)applying abrasive particles to the adhesive layer; and
(d)cutting the tube to produce a continuous belt of required width.