Metal treatment – Process of modifying or maintaining internal physical... – Heating or cooling of solid metal
Reexamination Certificate
2000-12-01
2003-10-14
Kastler, Scott (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Heating or cooling of solid metal
C101S167000
Reexamination Certificate
active
06632301
ABSTRACT:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention includes bainitic steel doctor blades, bainitic steel coating blades, bainitic steel creping blades and bainitic steel rule die knives ed in gravure printing, flexographic printing, paper making, die cutting of materials, such as, paper, plastic, foam, leather, etc. Other uses include printing processes such as pad printing and electrostatic printing, glue application arid other uses which will be apparent to those skilled in the art. This invention also relates to the process for producing bainite strip steel.
2. Discussion of Related Art
Various commercial industrial processes require metallic components that have extremely high straightness characteristics, high wear resistance and, in some cases, are also capable of being bent around small radii of bending. These components include doctor blades, used in such processes as flexographic and photogravure or gravure printing. Flexographic printing, formerly called analine printing, comprises a method of rotary printing utilizing flexible rubber plates and rapid drying fluid inks. Gravure printing is a printing technique wherein intaglio engravings of an image which are to be printed on a substrate, such as paper, are formed by known techniques on the surface of a gravure cylinder. Intaglio engravings are those where the elements to be printed are below the surface of the gravure cylinder, having been cut or etched into the metallic cylinder to form ink retaining cells. During printing, the gravure cylinder is immersed in fluid ink. As the cylinder rotates, ink fills tiny cells and covers the surface of the cylinder. The surface of the cylinder is wiped with a doctor blade, leaving the non-imaging area clean while the ink remains in the recessed cells in the cylinder. A substrate, such as paper stock, is brought into contact with the image carrier with the help of an impression roll. At the point of contact, ink is drawn out of the cells onto the substrate by capillary action.
Rule die knives are used in the cutting, creasing and perforating of various substrates such as, paper, cardboard, plastic, leather and foam.
Coating and creping blades are used in the manufacture of paper of various types wherein the blades are used to separate paper webs from calendar surfaces and used to apply coatings to the paper stock. Coating blades are also used to apply coatings, glue and protective films to a variety of substrates used in many different industrial processes.
While commercial tolerances of strip steel may generally have a straightness, referred to as camber, of about 0.375 inch per four feet, doctor blades and rule die knives used in the flexographic and gravure printing processes require a camber of a maximum of about 0.040 inch per ten feet and preferably about 0.024 inch per ten feet. This requirement is nearly one-hundred times more stringent than the tolerances in commercially supplied strip steel. Presently, there are very few manufacturers, none of which manufacture in the United States, that produce strip steel for the manufacture of these products. As a result of the limited suppliers and their foreign residences, these components are not only expensive, but are also susceptible to periods of unavailability.
In addition to low tolerances for straightness, it is desirable that doctor blades and rule die knives have relatively long useful service lives. Gravure and flexographic printing equipment are universally recognized to be expensive, and the labor costs associated with running these printing operations are significant. Printing pressmen are highly skilled and command high labor costs. It should readily be appreciated that anytime a gravure press or flexographic press is not operating during periods when it is supposed to be producing a printed substrate (downtime), significant costs are expended. Such costs are not likely to be recouped. Downtime may also result in the failure to meet printing deadlines. Thus, it is highly desirable to use doctor blades and rule die knives that require as few replacements as possible because such components can only be replaced during downtime.
These components are presently made of high carbon steel containing about 0.80% to 1.25% carbon by weight that is hardened and tempered to a martensitic structure. Martensite, a very hard and brittle microstructure in steel, has a fine, needlelike appearance under a microscope. While there is some correlation between higher hardness of this type of steel and better wear resistance, there is a limit to increases in hardness of martensitic steels to improve wear resistance due to the added brittleness that accompanies higher hardness. A practical limit of 54 Rockwell C is generally acknowledged, above which the parts become too brittle for use in printing press applications. A hardness of Rockwell of 48-52 Rockwell C is preferable.
Factors that contribute to the wear of doctor blades include a combination of abrasive wear, adhesive wear and wet impingement wear. Depending on the specific application any one or more than one of these types of wear may significantly contribute to reducing the wear life of doctor blades.
Attempts to improve wear properties of these components have included coating the wear surface with metallic materials such as chromium and non-metallic materials such as TiN, diamond, nitrides, SiO
2
and sprayed ceramic. There also has been some use of edge hardening on alloy steels. While these methods improve wear resistance, they are expensive to apply and do little or nothing to change the camber. In certain instances, these processes actually can be deleterious to camber due to the high temperatures encountered in the particular process causing stress relief or thermal distortion,
In attempts to solve some of the technical problems associated with martensitic steel, the a use of cold rolled eutectic carbon steels with tensile strengths in excess of 300,000 psi has met with some success in gravure printing with water based inks. Cold rolled austenitic stainless steels were used for some time, but have been replaced by martensitic stainless steels.
Some have offered alloy steels and special high carbon steels such as SAE 52100, but these alternatives still contain martensitic structures. These special high carbon steel components therefore have the drawbacks of being expensive and/or show little improvement in useful wear life. Notably, none of these martensitic steels have answered the problem of long-term camber being greater than desired.
Coating and creping blades used in paper manufacturing have similar requirements to those of doctor blades. Because these blades are usually made of thicker material in the range of 0.024-0.060 inch there seems to be less problem with camber, but wear problems persist.
Rule die knives have requirements similar to those of doctor blades in that they must be very straight and durable. They must be sufficiently hard to permit edge sharpening, and they also must exhibit good sharpness retention when used to cut abrasive materials including kraft paper, coated stock and abrasive plastics. In addition, however, rule die knives also must be capable of being bent with small radii of bending.
In the past, this requirement has been met by various means including employing a softer metal, hardening the cutting edge, decarburizing the outer surfaces of the blade to depths of 0.003-0.006 inches, laser hardening of the cutting surface only and induction hardening after bending. All of these means are expensive.
It is believed that martensitic steel has not been successful with respect to camber requirements of doctor blades and die knife blades because of distortions that occur as a result of the austenitizing, quenching and tempering operations used in manufacturing the martensite. Quenching is the rapid cooling process in which the heated steel is plunged into a liquid or other medium to harden the me
Benton Rufus C.
Krauss George
Voorhees Steven C.
Benton Graphics, Inc.
Gibbons Del Deo Dolan Griffinger & Vecchione
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