Flexible abrasive body

Details Flexible abrasive body Flexible abrasive body

1999-12-21

2002-05-07

Banks, Derris H. (Department: 3723)

Abrading

Flexible-member tool, per se

C451S533000

Reexamination Certificate

active

06383064

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a flexible abrasive body including a flexible abrasive medium having a pliable backing which exhibits one layer made from a pliable substrate on one side of which there is a full-coverage first metal coating in which the abrasive material is at least partly embedded.
BACKGROUND OF THE INVENTION
Flexible abrasive bodies include, for example, abrasives on underlays, like endless abrasive belts or abrasive sheets fitted to a pliable support. Crucial to the durability of such flexible abrasive bodies is that their pliable support resists the tensile, compressive and shear forces without impairment during the grinding process and that when in use the vital abrasive grain does not become detached too quickly from the composite material. In addition, the thermal stability of the flexible abrasive body with respect to fixing of the grain and load-carrying capacity of the support must be sufficient to withstand the high temperatures that occur during grinding especially in dry-grinding operations. The super cutting materials diamond and CBN (cubic boron nitride), distinguished by their high thermal conductance and extremely high hardness, require the grain embedment to exhibit a particularly high heat resistance. Owing to the good cutting ability of those abrasive grains, even when used to grind the very hardest of materials, it is particularly necessary that the heat generated at the grain by the grinding process be conducted to the grain bonding agent layer and into the pliable support in order to avoid excessive, damaging temperatures in the workpiece and severe heat-induced grain damage. To accomplish this it is known to electrostatically embed the abrasive grain in thermally stable, durable metal, primarily nickel; cf. DE 1 059 794, EP 276 946, EP 0 263 785, EP 0 280 653, EP 0 013 486, DE 39 15 810, which are described in more detail in the following.
The electrostatic abrasive coating has only one layer of abrasive. The layer of metal or nickel building up from the support interlocks with the grains which are being progressively spread in parallel fashion, whereby tee depth of embedment of the required cutting grain can be controlled exactly via the duration of the electrodeposition process. Owing to the single-coat nature of the abrasive layer, electrostatically bonded abrasive grain cannot be dressed; at best it is possible to compensate for differences in the height of the grain peaks by way of spot-grinding. This inability to rework electrostatically bonded abrasive bodies leads to a typical feature, namely that the compactness of the abrasive layer is at best only as good as the compactness permitted by the underlying support. For the relevant grain sizes (e.g. 20-600 &mgr;m with corresponding electrostatic embedment depths, e.g. 50-80%), a full-coverage, electrostatic metal bonding agent layer already exhibits a thickness which gives the planar structure the physical character of sheet metal. The thinner such layers, the higher is their flexibility or their fatigue strength under bending stress reversal because the relative difference between compressing and stretching the two sides of the planar structure decreases and the fatigue rupture under alternating loads is delayed. However such thin metal bonding agent layers just a few microns thick only have the ability to adequately anchor grain sizes of this order of magnitude. The strength and flexibility of electrostatic coatings may vary greatly, from stiff to brittle, almost to the suppleness of stress-free annealed rolled sheets, depending on bath composition, temperature, current densities and rate of deposition. Typically though, metal layers as thin as foil always exhibit a high sensitivity to impacts and buckling loads as well as low resistance to tear-propagation loads, which can be attributed to the low elastic deformability of the metal. Such irreversible, plastic deformations in a full-coverage, electrostatic grain bonding agent layer rule out its use as a highly durable, flexible abrasive body.
From DE 1 059 794 it is known to form a pliable support in the form of a metal layer on a flexible, endless steel belt which circulates in an electroplating solution and is wired as a cathode; spread over The surface of said belt is an abrasive grain bonded by means of an electrodeposited metal layer. This method creates a serviceable abrasive belt in the form of a metal foil with partly embedded abrasive grain when this abrasive coating is removed from the steel belt. The level of strength and the aforementioned problem of thin metal foils restrict the use of such abrasive belts to the very lightest of grinding operations or, owing to the limited flexibility, only the very thinnest electrostatic grain bonding agent layers and the very finest abrasive grits can be processed in this way to form flexible abrasive bodies. This abrasive coating can be laminated onto an abrasive support as a metallic coating. Although laminating the full-coverage electrostatic abrasive coating reduces the buckling susceptibility and raises the tearing strength, laminated flexible abrasive belts in continuous use generally suffer again and again from the problem that the extension ratios and the extension behaviour of the bonded layers differ. For instance, the use of laminated belts on grinding machines in which reversal and straight-running take place in dynamic alternation, the layer facing outwards is constantly subjected to tension and loading whereas at the same time the inner layer is constantly subjected to compression and relief. These differing longitudinal ratios must be compensated for elastically by the laminating adhesive. Furthermore, the extension behaviour of the different materials used for inner and outer layers differs considerably, like in the case of the electrostatic metal grain layer laminated onto an abrasive support discussed here. Durable laminated flexible abrasive bodies are only obtainable when the reversing radii are as large as possible and the laminated product is not too thick, because otherwise inner and outer belt lengths differ too greatly and adhesives that exhibit a mediating extension ability need to be employed. As a rule, the adhesive represents the weakest link in the planar composite system, meaning that just localized damage to the electrostatic abrasive coating leads to peeling and delamination of the whole coherent abrasive coating. To solve the problem of the lack of flexibility and the sensitivity of full-coverage, thin metal layers or metallic grain bonding agent layers in flexible abrasive media, various proposals have been made whose common feature is to refrain from using a full-coverage electrostatic abrasive coating on the surface of the flexible abrasive medium and instead to form the abrasive coating only at discrete, separate positions, i.e. isolated islands of abrasive coating arranged in regular patterns on a flexible substrate, e.g. cloth, whereby these isolated abrasive coatings are positioned on the surface offset with respect to each other in such a way that, in the direction of use, they overlap or abut. The interruption of the electrostatic coating, which becomes more and more rigid as the grain size and thickness of the layer increases, leads to the desired flexibility being essentially dependent on the underlying substrate because this has the chance to bend between the regularly arranged, discrete zones of abrasive coating.
For instance, a flexible abrasive medium is known from EP 0 280 657 in which a thin metal foil, copper in particular, is laminated onto a flexible, electrically non-conductive substrate so that a backing in the form of a planar composite material is obtained, one side of which is electrically conductive over its entire surface and the other side is electrically isolated. First, an electrically non-conductive mask with discrete openings is placed on the electrically conductive side and then metal, preferably nickel, is electrodeposited onto this together with the abrasive grain. During the electrodeposition pro

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