The present invention relates to cutting blades, such as saw blades, and processes of producing such blades, and is more particularly directed to improvements in blades with self-sharpening cutting edges.
Cutting and saw blades are used in a variety of household and industrial applications, including razors, knives, shears, agricultural implements, rotary cutters and slicers, chisels, power saws, band saws, and hand held hack saws.
Users desire cutting blades with sharp edges possessing long life and corrosion resistance. Typically, blades are initially sharpened to form a wedge shaped cutting edge and re-sharpened as needed, except in the case of razor blades which cannot be re-sharpened.
Sharpness of a cutting blade is measured in terms of "ultimate tip radius", which is different depending on the application. For kitchen knives, rotary cutters, and similar cutting instruments, ultimate tip radius may be several thousand Angstroms. In agricultural implements incorporating rotary blades that cut through the soil, axes, and in chisels, the cutting edge radius may be expressed in microns or even in millimeters rather than Angstroms. Shaving razor blades ordinarily have ultimate tip radii of about 1,500 Angstroms or less. This radius usually includes a layer of hard material coating applied to the wedge shaped base material of the razor blade.
Among cutting blades, razor blades incorporate the most stringent technological. requirements. Typically, a base material (usually a martensitic stainless steel strip) is ground and honed on one edge to a wedge shape with an included angle of 30 degrees or less, coated with a 200-900 Angstrom thick layer of hard material for improved life, and coated with up to 10 .mu.m thick layer of low friction coefficient organosiloxane gel, or a fluorocarbon polymer.
Many variations of the contemporary razor blade technology have been proposed. Polycrystalline ceramics were proposed as the base material by Kramer (U.S. Pat. Nos. 5,056,227 and 5,142,785) and by Hahn (U.S. Pat. No. 5,048,191). A totally glass razor was the subject of U.S. Pat. No. 4,702,004 to Haythornthwaite, and a compaction of hollow fibers was offered by Siegmund and Strack in their U.S. Pat. No. 3,805,387. As hard coatings, boron carbide (U.S. Pat. No. 5,129,289 by Boland et al.), diamond, and diamond-like carbon (DLC) coatings were offered in U.S. Pat. No. 5,142,785 by Kramer. Methods of application of fluorinated polymer films can be found in U.S. Pat. No. 5,088,202 to Boland et al., and in U.S. Pat. No. 4,330,576 to Dodd.
Like blades for knives and rotary cutters, razor blades are sharpened to ideal wedge angles and cutting tip radii in order to perform satisfactorily. Unfortunately, as soon as these blades are subjected to wear conditions in service, they begin to loose their sharpness. In other words, their ultimate performance can only occur at the beginning of their service life and their performance will continually diminish with time. This happens by loss of material from the blade tip which leads to increase of tip radius.
In most cases, cutting blades become dull by gradual loss of material due to wear of cutting edges. Wear mechanisms may include general and grain boundary corrosion, as well as chipping and loss of grains due to weak grain boundaries. In general, the harder the material, the more resistant it is to wear. However, if grain boundary weakness and loss of grains are part of the wear mechanism, hardness alone may not be the most important factor determining wear resistance.
Saw blades may be made of a single metallic material, or may have teeth with welded or bonded carbide tips. Initial sharpness of saw blades diminish with time and the blades must either be thrown away or re-sharpened. When a carbide tip wears, it must be reapplied, which consumes valuable time.
This invention provides a solution to the problem of blade edge dulling by providing self-sharpening blades with layered structures where the thickness of the most wear resistant layer determines the sharpness of the blade, and as the blade wears in service, cutting tip diameter, and therefore the blade sharpness, remains unchanged. Saw blades provided by this invention are similarly self-sharpening type blades.