Can opener with helically mounted blade
United States Patent 1191 1111 3,874,078 Raque Apr. 1, 1975 1 CAN OPENER WITH HELICALLY 1,789,729 1/1931 Coyle 30/4 A MOUNTED BLADE 2,677,881 5/l954 Anderson..... 75 I R b G R L K 3,215,017 11/1965 Rutz 83/696 x l 1 l f FOREIGN PATENTS OR APPLICATIONS [731 Asslgnee FMC Cmpmmn, San Jose Callf- 52,870 9/1910 Switzerland 30/55 [22] Filed: July 2, 1973 Primary ExaminerAl Lawrence Sm1th [21] Appl&#39; 375,400 Assistant Examiner-Gary L. Smith Related U.S. Application Data Attorney, h Firm-C PP [63] Continuation-impart of Ser. No. 301,594, Oct. 27,  
 1972, abandoned. [57] ABSTRACT A power operated, single stroke can opener includes a [52] U.S. C1. 30/5.5, 30/4 A r i lly r cipr ble r m hat carries a sawtoothed [51] Int. Cl B67b 7/30 nif ving own ardly direct d points lying in a he- [58] Field of Search 30/4 A, 5.5, 316, 329, lical path to sequentially puncture the top of a can 30/355; 83/689, 696 being opened. A cam ring encircling the knife engages the sharp cut edge of the rim of the top remaining in [56] Referenc Cited the can and bends it down to a safe position adjacent UNITED STATES PATENTS the side wall of the can. A particular feature is an im- 1,255,684 2/1918 Anderson et al. 30/5.5 proved kmfe and kmfe moummg Structure&#39; 1,317,001 9/1919 Clymer 30/4 A 5 Claims, 5 Drawing Figures CAN OPENER WITH I-IELICALLY MOUNTED BLADE This is a continuation in part of my copending application Scr. No. 301,594, filed Oct. 27, 1972 and now abandoned.  
 BACKGROUND OF THE INVENTION The present invention concerns can openers, and more specifically, full circle can openers of the single stroke plunge-cutting type, in contrast to openers of the rotary type.  
  Plunge-cutting can openers usually employ a circular cutting knife having depending saw teeth which are forced downward through the lid of a can. An early example of this type of can opener is disclosed in U.S. Pat. No. 602,455, issued Apr. 14, 1898. In the patented device, the cutting knife is provided with alternately long and short saw teeth to minimize the initial force required to puncture the lid of the can.  
  In later patents such as U.S. Pat. Nos. 1,481,546, issued Jan. 22, 1924; 1,789,729, issued Jan. 20, 1931; and 2,656,598, issued Oct. 27, 1953, it was further recognized that cutting knife teeth of elongate, elevational profile are more effective because the long, inclined cut by the long edge will gradually progress circumferentially according to the depth of the knife teeth through the lid of the can. A gradual cutting effect was also obtained by forming the cutting teeth with a nonsymmetrical profile having a long sharpened edge and a short edge. While the prior art indicates that a cutting knife might be improved by having both non-uniform length teeth, and teeth of non-symmetrical profile, to combine both features in a single cutting knife will result in an expensive construction for an element which does not have infinite life, and must be periodically replaced.  
  Thus, the general problem to which the present invention is directed is an economically practical cutting knife, for a plunge-cutting can opener, which is easy to force into the can lid and which attains the advantages that result in progressive puncturing of the can lid, followed by a relatively gradual progressive circumferential severing of the lid.  
 SUMMARY OF THE INVENTION A circular cutting knife is provided in the form of a split resilient ring of uniform axial width and having a series of uniformly shaped cutting teeth, each asymmetric, with an elongate sharpened edge. An annular back up member or wedge ring is provided for the smooth upper edge of the knife. The back up member is in the form of a thin split ring having non-parallel upper and lower surfaces so that it presents a substantially tapered or wedge-shaped profile. The upper edge of the back up member or wedge ring seats against the planar end surface of a knife mounting chuck. The knife is installed by springing it axially to seat against the lower edge of the wedge ring, and then locked in that position. This results in the knifeassuming a one turn helical configuration with the pointed lower ends of the cutting teeth lying in a helical path so that the teeth successively penetrate the can lid, one by one, when the mounting chuck descends against the lid of a can, and the elongate sharpened edges effect a gradual circular severance of the lid.  
  A basic aspect of the present invention, therefore, is that a cylindrical knife of uniform axial width and having uniform, asymmetrical teeth can be employed to achieve progressive puncturing of the can lid. as well as gradual circumferential cutting of the lid by the individual cutting teeth.  
  Thus, one object of this invention is to provide a plunge-cutting type of can opener with a multi-pointed knife arranged so that the force of puncturing and cutting a can lid is minimized, and wherein the knife can be made with a uniform width and identical cutting teeth each requiring only one sharpened edge.  
 BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:  
  FIG. 1 is a perspective view of the improved power operated can opener.  
  FIG. 2 is a side elevation, partly in section, of the knife and knife holding chuck mounted on the operating ram of the can opener.  
  FIG. 3 is an exploded perspective of the cutting knife, a locking ring and tapered knife backup ring used in the assembly shown in FIG. 2.  
  FIG. 4 is a section through one edge of the knife and adjacent parts of the chuck, and a portion of a can lid being severed from a can.  
 FIG. 5 is a side elevation of a modified form of the knife.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS In the form of the invention illustrated, the can opener is power operated, but it can be manually operated by usisng lever arms and linkages known in the art. The can opener comprises a base 10 on which is mounted an upright pedestal 12 that supports a power cylinder 14, preferably pneumatically operated. Conventional controls, not shown, may include separate, interlocked push buttons requiring two hand operation for operator safety. The power cylinder or ram 14 includes a piston rod 16 carrying a chuck 18 which mounts the improved can opener knife 20 inn position to engage the top of a can C. The can is positioned for opening by placing it on the base 10 between angled guide strips 22 that center the can with the chuck 18.  
  As shown in FIG. 2, the chuck 18 includes an upwardly directed internally threaded boss 24 that is attached to the lower end of the piston rod 16. The chuck 18 has a downwardly open shallow cylindrical recess, including a flat circular surface 26, bounded by a rim or lip 28, a cut edge camming ring 30, the knife 20, a knife backup or wedge ring 32, and a knife locking ring 34. All of these rings, plus the knife, are split so that they may be radially expanded into solid frictional contact with one another, and against the downwardly directed lip 28 of the chuck 18, as will presently be described.  
  With reference to FIGS. 2and 3, the knife 20 is formed of a resilient narrow metal strip or body of uniform width in the form of an interrupted cylinder. FIG. 3 illustrates the knife in its relaxed, uninstalled condition. A gap 40 between the ends of the knife allows one end of the knife to be axially offset from the other end, whereby the portions of the knife between the ends will assume a smooth helical configuration. As presently described, the ends of the knife are axially offset, when the knife is installed, in the order of one quarter of an Teeth 42 are formed on the lower edge of the knife 20, with a long edge 44 of each tooth sharpened and terminating in a short undercut edge 46. In the 6 inches can size illustrated, the point 48 of each tooth extends about seven-sixteenths inch past the sharpened edge 44 of the adjacent tooth and there are about 9 full teeth, and the ends of the knife at the gap 40 are parallel, one end representing a continuation of a short edge 46. Thus, the ends of the knife at the gap are inclined to the knife axis so that the cutting edge formed by the individual sharpened edges 44 is continuous, as viewed from the bottom or cutting edge.  
  The split back up or wedge ring 32 for the knife (FIG. 3) is in the form of a circular, axially tapered wedge having a planar upper surface 50, with the ends 51a and 51b of the ring, adjacent the gap 52, having an axial dimensional difference that provides the previously mentioned axial offset of about one quarter of an inch for the ends of the knife 20. FIG. 3 shows the wedge ring 32 before installation, with the upper surface 50 planar, and the lower surface 54 forming a smooth helix between the ends 51a and 51b adjacent the gap 52. With continued reference to FIG. 3, the split locking ring 34 is provided with beveled ends 55a and 55b, defining a gap 56, which are arranged to be cammed apart and expand the locking ring upon the installation of a wedge bolt 58 having a conical head 60 movable upward into the gap 56.  
  Referring to FIG. 2, when the knife 20 is installed in the chuck 18, the cut edge camming ring 30 is manually seated against the flat surface 26 of the chuck recess. Then, the wedge ring 32 is similarly seated against the surface 26, inside the camming ring 30, with the gap 52 diametrically opposite a threaded socket 62 for the wedge bolt 58. The knife 20 is rotatively positioned so that its gap 40 is aligned with the gap 52 of the wedge ring 32. To complete this assembly, the locking ring 34 is placed inside the knife 20, and the wedge bolt 58 is loosely installed. The knife 20 is then axially sprung to seat firmly against the wedge ring 32, and with the knife held in that position the wedge bolt 58 is tightened to 30, 32 open the locking ring 34. The assembled rings 30,32 and the knife 20 are thus clamped against the rim 28 of the chuck 18.  
  It will be clearly seen by referring to the horizontal plane H relative to the teeth points 48 (FIG. 2), that the helical arrangement of the teeth due to the axially sprung condition of the knife 20 will cause the teeth to progressively puncture the lid of a can when the chuck 18 is lowered by the ram 14, and that the cutting of the lid by the sharpened edge 44 of each tooth gradually progresses around a segment of a circular path. These desirable, cooperative results, however, are obtained with an easily formed knife blade having uniform width and uniform cutting teeth with only one edge of each tooth sharpened, thus minimizing the cost of an element which must be periodically replaced.  
  Any severed can lids L that remain wedged in the knife 20 (FIG. 4) as the piston rod 16 moves upwardly after severing the lid, are ejected near the top of the ram stroke by a pair of knockout bolts 64 (FIG. 2) that are slidable in diametrically located bosses 68 on the upper side of the chuck 18. The knockout bolts 64 are held in a retracted position by helical springs 70 compressed between the upper surfaces of the bosses 68 and blind nuts 72, to bring the heads 73 of the bolts up against the chuck face 26. As the ram 16 approaches the upper limit of its stroke, the nuts 72 strike the under surface of a lower end plate 74 (FIG. 1) of the power cylinder 14 and arrest the bolts 64 while the knife and chuck complete their upward motion. The knockout bolts thus eject those can lids L, which remain in the knife as the knife moves up. Ordinarily, however, the knife is raised so rapidly that a momentary vacuum is drawn between the contents of the can and the severed lid, thereby pulling the lid out of the knife and leaving it atop the can.  
  To eliminate the sharp edges of the rim portion of the top left on the can body after the lid L is removed, the rim of the lid is automatically bent down to a safe position against the side wall of the can during the can opening operation. This is accomplished by providing a beveled edge 76 (FIG. 4) on the lower edge of camming ring 30. After the knife 20 has penetrated and&#39; severed the lid L from the can, the beveled edge 76 bends the remaining rim portion 80 of the can top&#39; down to a position lying along and in contact with the sidewall of the can.  
  FIG. 5 illustrates a modified knife construction which achieves the same improved results noted for the knife 20, but which is of even further simplified construction in that no undercuts are required for the cutting teeth 42a. The sharpened edges 44a have intermediate short edges 46a which are axial, or perpendicular to one longitudinal edge of the knife, and the ends of the knife adjacent a gap 40a are also axial, and as before, the blade width is uniform. With reference to the tooth 42a which includes the dotted reference line 43, the short edge 46a and the long edge 44a respectively represent the short leg and the hypotenuse of a substantially right triangle. When the knife 20a is installed, in the same way described for the knife 20, it is sprung into continuous contact with the back up or wedge ring 32 so that its teeth points 48a lie in a helical path. The fact that the blade has a helical form, and that the sharpened edges 44a then incline downward (relative to their inclination before the blade is installed) from the thick end of the back up ring to the thin end, causes the teeth points 48a to mask the adjacent ends of the sharpened edges 44a because the short edges 46a are not truly vertical after the blade is sprung. In this manner, the benefits of an undercut blade are achieved with the simplified blade 20a.  
  Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention.  
 What is claimed is:  
  l. A cutting head for a plunger-type can opener comprising a chuck including a circular rim defining a downwardly open recess with a planar bottom face, a split cylindrical camming ring mounted in said recess and having an external beveled lower edge, a tapered split wedge ring mounted inside said camming ring and seated against the bottom face of said recess, a cylindrical split knife blade axially sprung into seating engagemcnt against said wedgc ring, the gaps in said knife blade and said wedge ring being vertically aligned, said knife blade being of uniform basic width and having downwardly facing uniform cutting teeth, a split locking ring mounted within said knife blade and said wedge ring, the adjacent end surfaces of said wedge ring converging upward, and a conical head wedge bolt threaded into the chuck with the head forcing the converging end surfaces of said locking ring apart to radially expand all of said rings and said knife blade against the rim of said chuck, the pointed ends of said cutting teeth being vertically offset by said wedge ring to lie in a helical path for sequentially. puncturing a can lid when the cutting head is forced.  
  2. In a plunger type can opener of the type comprising a chuck, a thin, split cylindrical knife blade of uniform width and having teeth along one edge thereof, and means for detachably retaining said knife blade in the chuck; the improvement comprising an axially tapered knife blade back up member in said chuck, said knife blade retaining means holding the edge of the knife blade that is opposite said teeth against said back up member so that the said teeth lie in a generally helical configuration.  
  3. The can opener of claim 2, wherein said chuck has a peripheral lip, said knife blade having a smooth edge opposite its toothed edge, said back up member comprising a split wedge ring having substantially the same thickness as that of said knife blade, said retaining means being radially expanded against said knife blade for retaining both the knife blade and the wedge ring within the peripheral lip of said chuck and with the smooth edge of said knife blade engaging said wedge ring.  
  4. The can opener of claim 2, wherein the split in said knife blade is substantially aligned with the split in said wedge ring with the teeth on said knife blade forming one turn of a helix.  
  5. In a cutting blade assembly for a plunger-type can opener of the type including a knife holding chuck defining a downwardly open cylindrical recess with a knife mounting surface parallel to the upper end of a can supported beneath the chuck, a split, resilient, cylindrical toothed knife blade in said chuck, and means for detachably retaining said knife blade in the chuck; the improvement wherein said knife blade is of uniform basic width having one smooth edge and cutting teeth on the other edge, and an axially tapered wedge ring seated against the knife mounting surface of said chuck and against the smooth edge of said knife blade, said knife blade retaining means holding said knife blade in an axially sprung condition against the wedge ring so that its cutting teeth define one turn of a helix.