Cutlery – Blades – Metallurgical feature
Reexamination Certificate
2000-03-15
2001-12-18
Watts, Douglas (Department: 3724)
Cutlery
Blades
Metallurgical feature
C030S346540, C076S104100
Reexamination Certificate
active
06330750
ABSTRACT:
This invention relates to scalpel blades and their production and, more particularly, to such blades having high toughness and a high sharpness that is retained for an extended period of use.
BACKGROUND OF THE INVENTION
A scalpel is a small knife, typically with a removable blade, that is used in medical, veterinary, biological, and other procedures to cut a workpiece. Scalpel blades used in medical, veterinary, and biological procedures must be very sharp so as to inflict as little damage as possible to the tissue being cut. They must retain that sharpness for as long as possible during a procedure to minimize the number of instrument changes during the procedure.
Conventional scalpel blades are made of a surgical grade stainless steel that is hardened to a Rockwell C hardness of about 54-62 in order to retain the sharpness of their cutting edges throughout a procedure. They are sharpened to an included blade angle that is typically about 26 degrees. It would be desirable to reduce the included blade angle so as to increase the sharpness of the scalpel blade. The result of such a reduction of the included blade angle is to increase the tendency of the blade to bend and roll over, rendering it ineffective. The blade also has a tendency to break during a procedure, because the high hardness results in a low ductility and toughness that render the very thin blade susceptible to brittle failure. Brittle failure is of particular concern during surgery because the broken piece of the scalpel blade is difficult to find and may be retained within the body of the patient. The reduction in the included blade angle of conventional scalpel blades also causes the blades to become dulled very quickly during service.
On the other hand, the stainless steel may be annealed to reduce the Rockwell C hardness to a level where the blade has reasonable toughness and a reduced tendency to brittle fracture. The result is that the tapered region of the blade still has a rollover tendency that can render it ineffective. Further, because the steel is softer and does not hold an edge as well, the service life of the sharp edge is greatly reduced so that only a few cuts may be made before the scalpel blade must be replaced.
There is a need for an improved scalpel and scalpel blade which has an increased sharpness that is retained for an extended period of time, yet is not susceptible to brittle fracture during a procedure. The present invention fulfills this need, and further provides related advantages.
SUMMARY OF THE INVENTION
The present invention provides a scalpel blade and a method for its manufacture. The scalpel blade has a high sharpness that is retained for an extended period of use in service. The scalpel blade is relatively ductile as compared with conventional scalpel blades, so that it has a reduced tendency to brittle fracture. The increased ductility also improves the consistency of performance of the scalpel blade in service. The scalpel blade of the invention is otherwise compatible with conventional scalpel blade holders and requires no changes to medical and other cutting procedures that use the scalpel blade. The manufacturing method produces scalpel blades of consistent structure and functionality.
A coated scalpel blade comprises a substrate having a body and a tapered region with an edge thereon. The tapered region desirably has an included angle of from about 10 to about 25 degrees, more preferably from about 10 to about 18 degrees. The substrate is made of steel, preferably first hardened to a Rockwell C hardness of at least 54 and then annealed back to a Rockwell C hardness of from about 46 to less than about 53. A coating overlies the tapered region. The coating has a thickness of from about 0.1 to about 2.5 micrometers, preferably from about 0.1 to about 1.0 micrometer, and most preferably about 0.3 micrometer. The coating comprises a first coating layer of a first metal, and a second coating layer overlying the first coating layer. The second coating layer comprises a chemical combination of a second metal selected from the group consisting of vanadium, chromium, zirconium, titanium, niobium, molybdenum, hafnium, tantalum, and tungsten, and combinations thereof, and a nonmetal selected from the group consisting of nitrogen and carbon, and combinations thereof. Most preferably, the first metal and the second metal are the same, and the coating has a first coating layer of zirconium and a second coating layer of zirconium nitride. The coated scalpel blade preferably has a coated edge thereon which is atomically serrated and atomically sharpened.
A method for preparing a coated scalpel blade includes the step of providing a substrate having a body and a tapered region with an edge thereon. The substrate is made of steel hardened to a Rockwell C hardness of at least 54. The substrate is thereafter annealed to reduce its hardness by at least about 5 points of Rockwell C hardness. A coating is deposited from a deposition source onto at least the tapered region of the substrate. The coating has a thickness of from about 0.1 to about 2.5 micrometers. The step of depositing comprises the steps of first depositing a first coating layer of a first metal, and thereafter second depositing a second coating layer overlying the first coating layer. The second coating layer comprises a chemical combination of a second metal selected from the group consisting of vanadium, chromium, zirconium, titanium, niobium, molybdenum, hafnium, tantalum, and tungsten, and combinations thereof, and a nonmetal selected from the group consisting of nitrogen and carbon, and combinations thereof. The step of second applying includes the step of applying a voltage more negative than about −70 volts to the substrate relative to the deposition source, in the latter portion near the end of the second applying step. This preparation process produces a scalpel blade that has excellent properties, and which are highly reproducible in production operations and yield consistent service performance.
Preferably, the step of annealing and the step of depositing are performed in the same apparatus. The deposition source is desirably a cathodic arc deposition source. The step of providing may include the step of providing a plurality of substrates, and the step of depositing includes the steps of stacking the plurality of substrates with their bodies adjacent to each other and their edges facing in a common direction, and orienting the edges facing toward the deposition source. Other features described above may be incorporated into the method.
The resulting scalpel blade is very sharp, both because it has a small included angle of the tapered region and because, in the preferred approach, it is atomically sharpened by the application of the large negative voltage toward the end of the deposition of the second coating layer. It is also relatively ductile and metallurgically tough, because the steel substrate is annealed. The presence of the coating allows the metal to be annealed and yet have the included blade angle small, because the coating strengthens the tapered region of the blade so that it resists bending and rollover of the blade more effectively. The resulting scalpel blade is tough and resistant to brittle fracture, so that there is a greatly reduced likelihood of breakage during the cutting procedure. The scalpel blade is also sharp, and it retains the sharpness for extended periods of use in service.
The structure and function of the scalpel blade are distinct from another commonly available sharp article, a razor blade. The razor blade is supported from a holder over the entire length of its cutting edge, and outwardly extends from the holder only a short distance. The scalpel blade, on the other hand, is cantilevered from its handle by a relatively large amount. The sharp end of the scalpel blade may be used for cutting, and must withstand both conventional cutting action and impacts against hard objects. It requires a substantially greater toughness than the razor blade.
REFERENCES:
patent: 3874900
Molecular Metallurgy, Inc.
Nydegger & Associates
Watts Douglas
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