Patent Application
20090277098
The invention generally relates to an abrasive wherein abrasive grains are embedded in a matrix of a binder and wherein a contact surface covered by abrasive grains is configured for abrasion of a workpiece.
Ever since the start in the development of such abrasives it is known to fabricate their abrasive composites in an homogenous structure. For this purpose originally, use was made of non-elastic binders, but elastically compliant binders have since been employed for decades. One example of such an abrasive composite using non-elastic binders is a grindstone. Examples of abrasive composites employing elastically compliant binders are compact composites e.g. in the form of a cube or also other abrasive compacts formed e.g. as an abrasive wheel. Known in this respect are both cellular and non-cellular embodiments. These known abrasive compacts were and still are cast as a whole as practiced by the applicant with a more than 40 year proven record of success.
These known abrasives employing elastically compliant binders for the abrasive grains have hitherto been regularly fabricated without the substance integrated in the abrasive because of their configuration as abrasive compacts. By contrast, with abrasives having a non-elastic binder, “backed abrasives” termed as such in the branch are in a class of their own since decades.
The invention relates furthermore specially to abrasives having a non-cellular, particularly non-foamed binder in said contrast to the cellular, particularly foamed binder.
With reference to the German Plastics Handbook, “Saechtling Kunststoff Taschenbuch, 28th Edition, by Karl Oberbach, published by Verlag Hansa, see page 555, FIG. 4.18” it is clear that a distinction is made generally between foamed materials and non-cellular binders in any case where PUR (polyurethane) is concerned, but also as regards all other foaming binders.
In this case the non-cellular PUR types particularly substantial to the invention belong to the group:
solid polyurethanes
cast and spray elastomers
thermoplastic elastomers
rubber
The elastically compliant compacts cited initially as prior art and “solid” composites in the cited grouping respectively are special cast elastomers, the abrasives in accordance with the invention also using particularly cast elastomers.
When the binders are fabricated foamed a distinction is made between materials foamed physically and mechanically by the application of air and materials foamed chemically by the application of blowing agents.
Abrasives having a non-cellular binder, to which the invention relates, are characterized by being targeted foamed neither physically nor chemically by the corresponding concrete handling of the process. The target instead is to avoid expansion within the scope of being maximum possible, although in practice remnant cellular formations can never be totally avoided. This is why—at least in describing the abrasive product as fabricated concretely designed for the market—it appears best to make reference to the real and theoretical densities as compared to actual practice.
For foaming binders this comparison is best illustrated by way of PUR, as an example. As it reads from the cited German Plastics Handbook “Saechtling Kunststoff Taschenbuch, 28th Edition, by Karl Oberbach, published by Verlag Hansa, see page 554 et seq” a distinction is made between molded foams 30-300 kg/m3), rigid foams 30-90 kg/m3) and open-celled foams 20-40 kg/m3).
In accordance with the invention the PUR is employed, particularly with a density of no less than 800 kg/m3 which adequately describes the minimum porosity.
Backed binders in which the abrasive composite features a cellular and particularly foamed binder are already known for example from German patents DE 31 14 001 A1 and DE 19 07 983 A1.
The invention relates in conclusion particularly to the abrasives, the composite of which comprises a thermosetting binder of the abrasive grains. Here the invention recourses to the thermosetting plastics, such as for example of polyurethane, known as such as binders for abrasive grains of composites, although rubber may also be used in the scope of the invention as the binder for the abrasive grains.
One example of a thermoplastic binder for the abrasive grains in the form of a plasticized colloxyline reads from the German patent DD 106 585 A which different to the thermosetting plastics employed in the scope of the invention additionally requires the use of a plasticizer in roughly equal proportion 1:1 or 0.8:1.). Also required to prevent loading of the abrasive is a proportion of at least 60% by weight of the abrasive powder in the abrasive composite, a corresponding proportion of abrasive powder exceeding 80% being incidentally viewed as being detrimental for bonding the abrasive composite. This known abrasive composite is specially devised for configuring the abrasive composite as an extremely thin layer of abrasive in the range of 10 μm to maximum 40 μm thick as measured perpendicular to the backing.
Just for the sake of completeness reference is further made to a more exotic known abrasive, the binder of which for the abrasive grains is kneadable is thus alleging to adapt to the profile of a workpiece surface for abrasion (German patent DD 255 903 A1).
In the course of the technical development of the abrasives as presently involved the working speeds, e.g. in rotating or oscillating operation at the side of the abrasive tools or machines are becoming faster all the time, having resulted in since decades homogenous abrasives having elastically compliant binders becoming incapable of standing up to the resulting forces of acceleration and traction including centrifugal forces which, without special measures culminated in the matrix of the abrasive formed by the elastically compliant binder being prematurely ruined. One of these special measures used in conjunction with abrasive wheels involves dimensioning the abrasive coating of a solid core of the abrasive wheel forming the abrasive thinner and thinner, resulting in the useful life being relatively short. For endless abrasive belts it was also considered even almost half a century ago to coat an endless belt serving as the backing with strip-shaped abrasive composites, the matrix of which containing the abrasive grains is formed in each case by a compliant foam of polyurethane, whereby these abrasive grains were secured to the endless belt by means of a separate adhesive (see British patent GB B 821929, particularly page 2, lines 3 to 7). However, the gist of this invention necessitates an unreasonably complicated method in series production because of having to blank the abrasive composites and the separate bonding involved, this being the reason why this failed to find acceptance in practice.
For conventional erosive abrasion it has always been usual to bond the abrasive grains—the grain size of which is selected in accordance with the desired result—directly to a backing by means of a non-elastic binder, such as initially hide glue and now man-made resin. This backing absorbs the traction and centrifugal forces resulting in the machine. In this conventional case the abrasive grains are attached to the backing in just a single layer and jut from the surface in abrasive contact with the workpiece by abrasive protuberances. As soon as these protuberances have become worn down in abrasion, resulted in the binder coming into friction contact with the workpiece, the effectiveness in abrasion is significantly diminished and the nuisance of the binder loading the abraded surface of the workpiece occurs.
With an abrasive whose abrasive grains are homogenously arranged in a matrix of a radiation-cured non-elastic binder on a backing bonded via the binder, the matrix is divided into a plurality of matrix bodies dispersed mutually interspaced featuring in the direction the free contact surface with the workpiece with the workpiece to the backing an increasing cross-section parallel to the backing (German patent T2 692 10 221).
In other words, in erosive abrasion abrasive portions of abrasive grains protrude from the contact surface, the finish of the abraded surface being all the better the smaller the size of the abrasive grains. In this respect a distinction is needed as to finishing comparable to honing or lapping no longer involving substantially erosive abrasion but a reduction in the peak-to-valley height of the surface.
For use in modern abrasive machines it is now usual to provide abrasive non-wovens as the finishing abrasive. As it reads from German patent DE-T2 69609709 (particularly claim 4) a plurality of abrasive particles is bonded to an open loose fabric of organic fibers via a binder system. Finishing done therewith resulted in scabs in the surface being machined being bent out of the way or broken. Imperfections in the finished surface of the workpiece, such as scratches and scrapes are merely glossed over and not really eliminated
The invention is based on the object of providing an abrasive of the kind as it reads from the preamble of claim 1 which is suitable as an article for rational mass production for use as a finishing tool on modern abrasive machines in combining a long useful life with high consistency in finishing quality.
This object is achieved by an abrasive having the features of claim 1.
In the abrasive in accordance with the invention when new, a contact surface covered with abrasive grains is provided which as may be necessary needs to be exposed in the last phase of the production process by releasing a covering skin of the matrix binders resulted in portions of the abrasive grains protruding from the original first contact surface with the workpiece. When implementing finishing these protruding portions of the abrasive grains are impressed fully or near fully into the matrix in thus substantially eliminating an erosive abrasive action with the workpiece. Loading of the abraded surface of the workpiece is avoided or at least minimized in that during wear down of the abrasive grain covering of the matrix the previously surrounding resident binder does not come into loading contact with the abraded surface of the workpiece, it instead abrading like a rubber eraser. In this arrangement the abrasive grains are not worn down as such, but drop off bit by bit from the current contact surface. This loss of abrasive grains is regenerated continuously from the depth of the matrix so that during finishing, despite consumption of the matrix the finishing quality remains consistent. Indeed, this applies even up to total consumption of the matrix in its connection to the backing. In this arrangement the backing ensures a consistent working quality no matter to what degree the matrix is consumed even with high working parameters such as rotative speed, belt speed or ratings of an oscillation, whilst achieving rational and cost-effective fabrication of the abrasive in accordance with the invention in just a few working steps.
Particularly also to be emphasized is the finish achievable with the abrasive in accordance with the invention in conjunction with modern finishing machines as an improvement over what was possible hitherto. Thus the finish in accordance with the invention achievable with abrasive non-wovens is associated with a further additional minimally erosive effect of the abrasive grains as compared to the abrasive non-wovens whereby in accordance with the invention imperfection in the abrasive surface can now be not only concealed but abraded away or at least corrected. This now surprisingly makes it possible to subsequently chrome workpieces suitable therefor without further finishing being needed.
The abrasion is substantially determined by the selection of the binder, any fillers as may be employed and the type of grain of the abrasive grains. For machining the various materials, such as e.g. brass, aluminum or stainless steel the birder can be tailored thereto. The abrasive in accordance with the invention is particularly effective in finishing relatively rough workpiece surfaces. These can now be finished to extremely fine surfaces with no imperfections even when the abrasive grains are relatively coarse in the abrasive in accordance with the invention.
All this is achieved in a departure from the current development tendency by making a novel recourse to elastically compliant binders in the matrix after decades of being ignored.
Claims 2 to 43 relate to advantageous further embodiments of the abrasive in accordance with the invention and claims 44 to 49 relate to a preferred device for fabricating the abrasive in accordance with the invention.
In the sub-claims reference is made, as far as generalizing terms are used, to the terminology as usual in the branch supported by physical data and the technologies as usual to this extent as standardized.
What is particularly to be highlighted is that with the abrasive in accordance with the invention an abrasive composite whose elastically compliant matrix comprises a noncellular thermosetting binder is now applied to a flexibly configured backing in forming an integral composite directly, i.e. without the promotion of a separate bonding layer, whereby in consumption of the abrasive the grains continually worn out are replaced from the depth of the matrix, this applying continued until total or near total wear out of the abrasive composites down to the flexible backing without loss of abrasion quality. In this arrangement the elastically compliant configuration in the abrasive composites comprising matrix and abrasive grains can endow the complete abrasive in conjunction with the flexibility of the backing a native flexibility which can be tailored to the particular application. In addition to this, it is now possible to make available to the customer the same abrasive, irrespective of this at his end needing to be flexible or not in abrading in thus no longer making it necessary in many applications to stock a wealth of different abrasives for such applications having differing requirements on the flexibility of the abrasive.
Claims 2 and 3 relate to preferred upper and lower limits for the density of the binder in the matrix and abrasive composite respectively.
Claims 4 to 8 relate to preferred selection criteria as regards the elastically compliable configuration of the matrix with reference to elasticity (claims 4 and 5), hardness (claims 6 and 7) and ultimate elongation (claim 8).
The limiting values cited in the claims 2 to 8 for the ranges of density (claims 2 and 3), elasticity (claims 4 and 5), hardness (claims 6 and 7) and ultimate elongation (claim 8) are established standardized, particularly on the basis of German DIN standards or the worldwide valid ISO standards, each relating to the other as follows:
density: DIN 53479 and ISO 1183 (claims 2 and 3) respectively
elasticity: DIN 53513 and ISO 527-2 (claims 4 and 5) respectively
hardness: DIN 53505 and ISO 868 (claims 6 and 7) respectively
ultimate elongation: DIN 53504 and ISO 527-1 (claim 8) respectively.
Claim 9 recites preferred criteria under which the backing of the matrix or of the abrasive composite is claimed to be flexible.
Claims 10 and 11 relate to preferred dimensions for the thickness of the matrix perpendicular to the backing as claimed minimally (claim 10) and maximally (claim 11). Currently, the thicknesses as preferred for application are 1000 μm, i.e. 1.0 mm and 1500 μm, i.e. 1.5 mm. One application of the invention particularly highlighted is in this sense the fabrication of the abrasive as flat material, especially as web material.
Claims 12 and 13 relate to preferred dimensions for the ratio of the percentage by volume of the abrasive grains and of the binder of the matrix in claiming a lower limit (claim 12) and an upper limit (claim 13).
Claim 14 recites preferred grain size ranges of the abrasive grains.
Claim 15 recites preferred ranges for the Shore hardness of the abrasive.
Claims 16 to 20 relate to preferred materials for the non-cellular thermosetting binder which as claimed in claim 21 may be filled as usual in the branch whilst claims 22 and 23 recite special formulations.
Claim 24 relates to a special formulation for the case of the binder being foamable which in the scope of the invention is to be avoided as best possible. For this purpose claim 24 recites use especially of a foam inhibitor as an additive to the binder.
Claims 25 and 27 relate to preferred selections as to the type of abrasive grains.
Claims 28 to 30 relate to preferred arrays of the abrasive grains in the matrix.
Claims 31 to 34 relate to preferred sub-divisionings of the matrix into individual matrix bodies.
Claims 35 to 38 relate to preferred configurations of the backing.
Claims 39 to 42 relate to preferred geometric configurations of the abrasive for various abrasive tools.
Claim 43 in conclusion relates to a preferred configuration of the original contact surface of the abrasive in its configuration as marketed prior to its use on the abrasive tool.
Of particularly interest is the variant as recited in claim 39 in which the abrasive in accordance with the invention is configured as an endless belt, in this configuration its effect on the workpiece for the same abrasive can also be varied according to the location of the endless belt resulting in the effect on the workpiece. The locations particularly preferably for the effect are, on the one hand, on a contact wheel and, on the other, on a free side of the endless belt whereby also the hardness of the contact wheel and the belt speed may serve as influencing factors.
The invention relates also to methods of fabricating the abrasive in accordance with the invention as claimed in claims 44 to 49.
One method known as such reads from U.S. Pat. No. 5,562,745.
The invention will now be detailed by way of a special example embodiment with reference to the
In the abrasive as shown in all of the FIGs. a flexible supporting backing 2 is bonded to a matrix 4 (shown dotted in
Configured on the side of the matrix 4 facing away from the backing 2 is a free contact surface 10 parallel to the backing 2. When the abrasive is not in use free scabs of the abrasive grains 8 slightly protrude from the contact surface 10 (not shown) subject to the return force of the elastically compliant binder 6. When in use, the abrasive grains in the region of the contact surface 10 interact with a workpiece (not shown) against the return force of the elastically compliant binder 6 in becoming fully, or near fully impressed into the matrix 4. However, in its original condition or prior to use of the abrasive the abrasive grains 8 jut from the contact surface only sufficiently to form a microstructure together with the binder 6 of the matrix 4 at the contact surface 10.
In addition, the special embodiment as illustrated features the following special aspect:
In a full-length backing 2 the matrix 4 is divided into a plurality of the regular hexagonal matrix bodies 4a whose defining surfaces at the hexagonal profile are oriented perpendicular to the backing 2 so that no matter how worn the matrix 4 becomes the same regular hexagonal cross-section of each matrix body 4a to each backing 2 or parallel to the contact surface 10 remains.
Each single matrix body 4a juts from the backing 2 with a full-length interspace 12 dimensioned consistently inbetween and extending from the backing 2 to the region of the contact surface 10.
The interspaces 12 can be used for air or liquid cooling of the workpiece (not shown).
As shown, the matrix bodies 4a form a homogenously honeycomb structure of the matrix 4. In this arrangement the abrasion direction 16 is selected so that it is oriented along the imaginary line connecting the two opposing corners of a matrix body 4a, these in turn being arranged mutually staggered in forming a gap so that even when a matrix body 4a is destabilized mutual support by a neighboring non-destabilized matrix body 4a is assured.
Irrespective of the special hexagonal configuration of the individual matrix bodies 4a as shown in this case, their configuration and array in the matrix 4 are selected so that the connection of the matrix 4 resolved into individual matrix bodies 4a with the backing 2 enhances the flexibility of the abrasive composite as a whole. This is particularly and especially of advantage when the abrasive is an endless belt (not shown).
Test Example:
Test Parameters:
tubestock belt grinder: Flex LBR 1506 VRA, 1200 Watt
Belt length (endless belt): 40 mm×618 mm
Cutting speed: 14 m/s
Workpiece: stainless steel tubestock, material No. 1.4301,
dimension: 50 mm.×2.5 mm
handling: machine guided by hand over tubestock
Test Preparation:
The stainless steel tubestock is firstly rough ground on a centerless abrasive machine with an abrasive belt grain size P 80. The average peak-to-valley height after the rough cut is approx Ra=2.6 μm.
Test Implementation:
For stainless steel railings or frontings an average peak-to-valley height of Ra=0.5 μm is normally specified. This is usually achieved by using the following grain sequence: P120-P180-P280. The abrasive belts employed are e.g. standard abrasive belts CS 310 XF (flexible cotton backing approx. 320 g/m2, abrasive grain aluminum oxide, phenolic resin binder). To achieve the specified finish at least three runs with the machine (grain P120-P180-P280) were needed.
For comparison an endless belt in accordance with the invention was used in the same test configuration and with same test preparation, the characteristics of the belt being as follows: flexible cotton backing approx. 320 g/m2, polyurethane as non-cellular thermosetting binder with a layer thickness of 1200 μm, abrasive grain silicon carbide P60 homogenously dispersed in the binder.
The average peak-to-valley height of Ra=0.5 μm was achieved in just a single run.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 058 710.8 | Dec 2004 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2005/012637 | 11/25/2005 | WO | 00 | 6/1/2007 |
