US 3824887 A
A cutting edge is carried by a knife body and formed with a series of teeth, each of which has a root merging into said knife body and a tip spaced from said knife body. Adjacent ones of said tips are spaced 0.5-5 millimeters apart. Each of said teeth has a depth of up to 5 millimeters, measured from its tip to its root. Each of said teeth increases in hardness from its tip to its root. Each of said teeth has at its root at least the same hardness as the adjacent portion of said tooth body.
Description (OCR text may contain errors)
United States Patent [191 Marchard 1 July 23, 1974 1 STAMPING KNIFE  Inventor: Gustav Marchard, Waidhofen/Ybbs,
Austria  Assignee: Gebr. Boehler C0. AG, Kapfenberg,
Austria  Filed: Sept. 15, 1972 21 Appl. No.: 289,752
 Foreign Application Priority Data Nov. 26, 1971 Austria 10187/71 Oct. 22, 1971 Germany 2152622  US. Cl 83/679, 83/697, 83/701, 30/355, 76/107 C, 76/101 SM  Int. Cl B261 l/44  Field of Search 83/835, 846, 847, 697,
83/679, 701; 30/355, 112; 76/101 SM, 107, 107 C; 408/144  References Cited UNITED STATES PATENTS 1,669,623 5/1928 Messer 83/679 2,422,561 6/1947 Pavitt 76/112 X 2,858,718 11/1958 Kohler 408/144 3,203,295 8/1965 Sauer 30/355 Primary ExaminerDonald R. Schran Attorney, Agent, or Firm-Arthur O. Klein  ABSTRACT 4 Claims, 4 Drawing Figures 55HRc P es-4mm:
STAMPING KNIFE This invention relates to stamping knives which have a serrated cutting edge and are used for punching parts of any desired configuration out of textile fabrics, plastics materials, leather, rubber, paper, carton, cellulose and the like.
Stamping knives having a straight cutting edge are usually made from sheet steel which consists of 0.40-1 percent C, 0.25-0.60 percent Si, 0.25-1 percent Mn, up to 1 percent chromium, up to 1 percent Ni, up to 0.60 percent Mo and/or W and/or V, balance iron and inevitable impurities.
Stamping knives of this kind are made with different hardness values, and the back of the knife has a lower hardness than the cutting edge of the knife. Suitable hardening processes have been adopted to impart a hardness of HRC 50-55 to the cutting edges and a hardness of only HRC 35-45 to the remaining part of the knife.
In addition to the quality of the steel being used, the configuration of the cutting edge has a considerable influence on the cutting performance of a stamping knife.
Another important characteristic of a stamping tool is its flexibility. Stamping knives having optimum flexibility characteristics have been provided by the use of favorable cross-sectional shapes of the knife and by a localized hardening of the cutting edges.
The development of novel material in the garment industry has created a need for processing tools meeting increasingly high requirements. Stamping knives having an extremely high cutting performance and edge life are required to process plastics material fibers such as Perlon, Dralon, nylon, etc.
A knife has a good cutting performance ifa relatively small stamping pressure will cause the knife to cut entirely through the material to be cut.'ln a stamping operation, using a conventional stamping knife, which has a straight cutting edge, the knife first compresses the material to be stamped and then cuts through the same as the pressure applied by the knife against the backing is increased. During this operation, the stamping knife penetrates more or less into the backingto form a groove therein. During the next stamping operation, the presence of this groove gives rise to the undesired effect that the material to be stamped is no longer cut through entirely in that groove unless the knife penetrates into the backing to an even larger depth. As a result, the stamping pressures required for satisfactory cuts become progressively higher. These stresses increase the wear of the stamping knife and result in a premature destruction of the backing by the formation of new and progressively deeper grooves so that the backing becomes useless.
It has been attempted to improve the cutting performance by using knives having cutting edges which are harder and have a specially selected cutting angle. These attempts have not given satisfactory results because the stamping pressures required for a given stamping performance are only slightly decreased. The improvement has been observed only during the first few cuts and when the backing was repeatedly replaced.
Serrated cutting knives have been used to cut reed and cane, and to cut wood, e.g., to machine wood and to sever plates and boards.
The experience made with serrated machine knives of this kind have led to experiments in which textile fabrics were cut with stamping knives provided with serrations.
For use in experiments in which fabrics were stamped which consisted of synthetic fibers and were severable only with difficulty, three stamping knives having different serrations were made.
In the accompanying drawings,
FIG. 1 is a diagrammatic view showing the tooth shape of three teeth of a stamping knife.
FIG. 2 shows another stamping knife according to the invention.
FIG. 3 is a transverse sectional view along line A-B showing a portion of a preferred stamping knife embodying the invention.
FIG. 4 is a diagrammatic view showing the change of the hardness in a stamping knife according to the invention.
FIG. 1 shows the tooth shape of stamping knives according to the invention. The tooth tip spacing defined as the distance between adjacent tooth tips is designated t and the depth of the tooth is designated h in FIG. 1.
Stamping knife I had a tooth tip spacing of 1.5 millimeters and a tooth depth of 0.75 millimeter.
Stamping knife II had a tooth tip spacing of 2 millimeters and a tooth depth of 1 millimeter.
Stamping knife III had a tooth tip spacing of 3 millimeters and tooth height of 1 millimeter.
All knives were hardened to a body hardness of HRC 38-40. The tooth tips were locally hardened to HRC 49-51. The knives were made as square knives having a side length of 100 millimeters and a radius of about 2 millimeters at the corners.
The stamping knives described hereinbefore were used in a test under production conditions using a conventional hydraulic press, which was provided with a device for measuring the required punching pressure under extreme conditions. To provide extreme operating conditions, the knives were used to stamp tubing made of crimped Perlon filaments. Before the tests, it had been possible to stamp these textile products only with restrictions and in small quantities and if the backing was continually renewed.
The use of the novel knives permitted of a considerable decrease of the stamping pressure. Besides, the life of the backing was much increased because contrary to stamping knives having straight cutting edges the stamping knives according to the invention did not fonn notchlike grooves in the backing but resulted only in a punctiform penetration into the backing.
These advantages were observed to the same extent with all three knives. For a given cutting operation, the following stamping pressures were to be applied to the three knives:
Knife I: 62-67 kg per cm of length of knife Knife II: -75 kg per cm of length of knife Knife III: 74-80 kg per cm of length of knife.
Where stamping knives having straight cutting edges were used, stamping pressures between and l 10 kilograms per centimeter of the length of the knife had to beused to obtain cuts having the same quality.
All stamping operations were carried out on a cast nylon backing.
The knives became useless because the tips of the teeth were bent and broken. This was observed with Knife I after 927 stamping operations, with Knife II after v1008 stamping operations and with Knife III after 1234 stamping operations.
Even these improved performance figures are not sufficient for an economical mass production in the textile industry.
Additional experiments involved a variation of the hardness of the tooth tips and produced the surprising result that knives in which the teeth were softer at the tips than at the roots had edge lives which were a multiple of those of knives which had been conventionally hardened. I
For instance, a stamping knife having the geometrical configuration described hereinbefore and the same tooth pattern as knife I but had'been hardened to a hardness of HRC 46 at the tips and a hardness of HRC 51 at the roots of the teeth could be used for 2,500 stamping operations on the same material without exhibiting any substantial wear. After, 2,500 stamping operations, the experiment was terminated to save time.
Stamping knives according to the invention are also shown in FIG. 2. With stamping knives of this general kind, best results were obtained if the teeth had a diamond-shaped cross-section in their upper one-third, as is shown in FIG. 3.
The ability of these knives to bend around very small of a festoon-shaped edge portion between the roots of adjacent teeth.
This festoon-shaped edge portion between adjacent teeth is designated c in FIG. 2.
The hardness pattern in a stamping knife according to the invention is shown in FIG. 4. The hardness increases from the tip to the root of each tooth.
Part A of FIG. 4 is a sectional view taken through a tooth tip, which had been hardened to a hardness of HRC 43, which increases toward the root of the tooth to HRC 47 and in the transitional region between the tooth and the knife body reaches a value of HRC 48 and may even increase there up to HRC 55. This is indicated in Part B of FIG. 4.
. Part B of FIG. 4 is a sectional view taken through the knife body which has been hardened to the pattern according to the invention. The hardened zone comprises the tooth of the root and the transitional region between the tooth and the tooth body. This hardened zone is designated Pos. C. in Part B of FIG. 4.
Any desired known hardening process may be used in making the stamping knives according to the invention. For the performance of the stamping knives acradii of 1-2 millimeters was improved .by the provision cording to the invention, the hardening process itself is significant only inasmuch as the specified hardness pattern must be obtained. For instance, such knives may be made by flame hardening, induction hardening, plasma hardening or electron beam hardening.
Thus, the invention provides stamping knives having a serrated cutting edge for punching parts of any desired configuration from textile fabrics, plastics materials, leather, rubber, paper, cellulose and the like, and the invention resides in that the cutting edge is provided with teeth having a tip spacing of 0.5-5 millimeters, each tooth has a depth of at most 5 millimeters and the knives are hardened so that the hardness of each tooth increases from its tip to its root and decreases or remains constant from the root of each tooth to the body of the knife.
The tips of the teeth may be faceted in various ways, like the cutting edges of conventional stamping knives.
Although the invention is illustrated and described with reference to a plurality of preferred embodiments thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a plurality of preferred embodiments, but is capable of numerous modifications within the scope of the appended claims.
l. A stamping knife, which comprises a knife body and a cutting edge which is carried by said knife body and formed with a series of teeth, each of which has a root merging into said knife body and a tip spaced from said knife body,
adjacent ones of said tips being spaced 0.5-5 millimeters apart,
each of said teeth having a depth of up to 5 millimeters, measured from its tip to its root,
each of said teeth increasing in hardness from its tip to its root,
each of said teeth having at its root at least the same hardness as the adjacent portion of said tooth body.
between the tips of adjacent teeth.