Patent Publication Number: US-6668694-B2

Title: Die cutter blanket locking arrangement

Description:
This invention relates to die cutter blankets used to cover anvils in a sheet material die cutting apparatus. 
     Die cutter blankets are thermoset molded urethane material that wrap about steel circular cylindrical anvils. The anvils typically have a channel in the surface thereof extending along the anvil longitudinal axis. The blankets are wrapped about the anvil and have locking projections in some embodiments. The blankets are sheet material with opposing end edges at which the locking projections are located. The ends are complementary and the locking projections engage when inserted into the channel. The locking projections interlock when inserted into the anvil channel, locking the edges to the blanket, locking the blanket to the anvil and preclude the blanket from rotating about the anvil. 
     U.S. Pat. No. 3,765,329 discloses one aspect of a blanket with such projections. The plastic blanket has a sheet metal inner liner. The locking projections form a two part snap in construction in which a female part receives a male part, the female part depending from the blanket at one end edge thereof with a longitudinal rounded groove and the male part is complementary to the groove and snaps into the groove. The male part may be made of metal. The female part has a metal support. The male and female parts depend from the blanket edge for insertion into the anvil channel. 
     Other complementary locking structures are shown in U.S. Pat. Nos. 4,848,204, 3,885,486, 4,867,024, 5,078,535 and 5,758,560. All of the above patents use inerlocking complementary depending structures which fit into the anvil channel and cooperate with each other and the anvil channel to lock the blanket ends together. 
     Another locking arrangement for locking blanket ends together employs interlocking interdigitated fingers which are somewhat dovetail in shape. U.S. Pat. Nos. 4,075,918, 4,791,846 and 3,577,822 disclose this type of interlocking arrangement for use with a die cutter blanket. The interlocking fingers are in the same plane as the blanket sheet material and overlie the anvil. The anvil has a channel. The interlocking fingers, in some embodiments, may overlie the channel. The blanket interlocking finger end portions or other portions of the blanket have a depending projection which fits within the anvil channel to preclude the blanket from rotating relative to the anvil. The blanket is generally of uniform thickness except for the depending projections which add considerable thickness to the blanket at the anvil channel. The blanket is formed of molded urethane and in some embodiments is supported by a woven nylon or fiberglass fabric. The blanket thus comprises two materials, urethane forming the blanket structure and the support woven fabric to which the blanket is molded. 
     A problem with this construction is that the blanket eventually exhibits a recessed flat portion over the anvil channel during use. This recessed flat portion creates a problem with the product die cut by the apparatus. The die cutters cut into the sheet material being die cut, typically corrugated or pressed cardboard. The cutters also cut somewhat into the blanket. Because of the resiliency of the blanket material the blanket wears uniformly except at the anvil channel and depending projection which results in the recessed flat portion. Because of this recess flat portion, the dies eventually do not cut uniformly through the blank sheet material at this location causing the premature production of poor product. The recessed portion does not permit the dies at this location to cut cleanly through the product sheet material. 
     The present inventor attributes the recessed flat portion to the greater thickness of the urethane material at the projection region depending into the anvil channel. The present inventor recognizes the source of the problem not heretofore recognized by those of ordinary skill in this industry. The present inventor believes that since the material is resilient, the thicker material at the anvil channel exhibits non-linear increasingly greater resiliency than the sheet blanket material over the rest of the anvil. The present inventor believes that this greater resiliency results in excessive wear of the blanket material at this location as compared to the rest of the blanket surface. That is, the die cutters cut away more material from the blanket at this location than in the rest of the blanket for a given time period of use due to the increased resiliency of the material at the anvil channel region. This problem is only present with the interlocking finger construction which uses solid urethane material at the anvil channel. 
     According to the present invention, the above problems are minimized by a die cutter blanket for use with an anvil having an axially extending channel in the surface thereof comprising a urethane sheet member blanket having first and second ends, the blanket for wrapping about the anvil. A plurality of complementary interlocking fingers are at the first and second ends for selective interlocking engagement with each other to secure the blanket to the anvil. A first projection depends from and is integral one piece with the sheet member blanket of the same material as the blanket at at least one of the ends for complementary engagement with the channel, the material forming the projection and blanket having a first given property such that the blanket exhibits excessive surface wear at the first projection during use in comparison to the rest of the blanket surface unless otherwise precluded. An insert is embedded in the blanket at at least one of the ends overlying at least the first projection, the insert having a second given property different than the first given property for substantially precluding the excessive wear. 
     In one aspect the insert is urethane and in another aspect the insert forms a portion of the fingers. 
     In a further aspect, the insert is sheet material with a second projection depending therefrom forming a portion of the first projection. 
     In a further aspect, a woven sheet support member is included to which the blanket is secured. 
     In a further aspect, the insert has a plurality of through bores, a portion of the material of the blanket being embedded in the through bores. 
     Preferably, the through bores have a chamfered end region. 
     In a further aspect, the support member has a depending portion extending into the first projection from the plane of the support material. 
     Preferably, the blanket has a working surface for facing the cutting dies, the support member being uniformly spaced from the working surface of the blanket throughout the blanket. 
     Preferably the insert is a sheet member. In a further aspect, the sheet member has a projection depending therefrom. Preferably, the sheet member insert is approximately rectangular in plan view having opposing end edges and lateral opposing edges, the projection extending transversely across the sheet member medially the end edges to the opposing lateral edges. 
     In a further aspect, the blanket first property is a durometer of about 85 and the insert second property is a durometer of about 90 
     In a still further aspect, the first and second properties are the values of cut and tear resistance of the material wherein the blanket exhibits less resistant to cut and tears than the insert for a given load thereon. 
     In a further aspect, the first and second properties are the values of rebound of the material wherein the blanket exhibits a higher rebound value than the insert. 
     In a further aspect, the first and second properties are the modulus values of the material wherein the blanket exhibits a higher modulus than the insert. 
    
    
     IN THE DRAWING 
     FIG. 1 is an end sectional elevation view of a blanket and anvil assembly according to an embodiment of the present invention; 
     FIG. 2 is a top plan view of the assembly of FIG. 1 showing the interlocking finger joints of the blanket; 
     FIG. 3 is a more detailed fragmented view of a portion of an interlock joint of a representative set of fingers of FIG. 2; 
     FIG. 4 is a sectional elevation view of the assembly of FIG. 2 taken along lines  4 — 4  according to one embodiment of the present invention; 
     FIG. 5 is a sectional elevation view of the embodiment of FIG. 6 taken along lines  5 — 5  of FIG. 6; 
     FIG. 6 is a fragmented top plan view of an anvil blanket end according to a second embodiment of the present invention; 
     FIG. 7 is an end sectional fragmented view of a blanket locking portion according to a third embodiment; 
     FIG. 8 is a more detailed view of the embodiment of FIG. 7 taken at region  8 ; 
     FIG. 9 is a top plan view of a blanket insert according to one embodiment; 
     FIG. 10 is a sectional elevation of the embodiment of FIG. 9 taken along lines  10 — 10 ; 
     FIG. 11 is a top plan view of a blanket insert according to a second embodiment; 
     FIG. 12 is a sectional elevation of the embodiment of FIG. 11 taken along lines  12 — 12 ; 
     FIG. 13 is an isometric view of the locking fingers of the embodiment of FIGS. 5 and 6; 
     FIG. 14 is a plan view of the end interlocking finger portion of a blanket according to a further embodiment; and 
     FIG. 15 is a sectional view of the embodiment of FIG. 14 taken along lines  15 — 15 . 
    
    
     In FIG. 1, assembly  10  in the present embodiment comprises a steel circular cylindrical anvil  12  and a die cutter blanket assembly  14 . The assembly is provided the anvil in an apparatus in which dies cut sheet material moving over the rotating anvil and blanket. The dies penetrate somewhat into the blanket material. The material is resilient, but over a period of time exhibits wear at the die areas impacting the blanket. 
     The anvil  12  has a channel  16  that extends for the length of the anvil along the anvil axis into the sheet of the drawing. The channel is square or rectangular depending upon the implementation. The blanket assembly  14  has a projection  18  that is complementary with the channel and secures the assembly  14  from rotation relative to the anvil as the anvil rotates during the die cutting process wherein blank sheet material is die cut, such as cardboard and the like. In the prior art, the projection and sheet portion of the blanket are molded of urethane material and typically molded to a support formed by a woven fiberglass or other fibrous material. 
     In FIG. 2, the blanket assembly  14  is formed with a plurality of interlocking fingers  20  and  22  which are complementary configured dovetail shapes An insert  24  of molded urethane material is embedded in the blanket  26  of assembly  14 . 
     In FIGS. 9 and 10, insert  24  of a first embodiment is a molded rectangular shape as seen in FIG.  9 . The insert  24  has a plurality of through bores  28  formed therein. The insert  24  has a second plurality of through bores  30 . Bores  28  are countersunk with a tapered portion  32 , FIG.  10 . The bores  30  are uniform throughout. 
     The insert  24  is formed with a depending projection  34 . The bores  30  penetrate through a portion of the projection  34 . The rest of the insert  24  extending from the projection  34  in opposite directions therefrom are of substantially uniform thickness sheet material. The insert has a flat surface at central region  36  and has two sheet material mirror image portions  38 ,  40  of the same thickness and which are inclined at about 6° from the plane of region  36 . Two edge regions  42 ,  44  are chamfered somewhat on the top surfaces  46 . The inclination of the portions The insert  24  inclined portions  38 ,  40  and region  36  approximate the curvature of the blanket when the blanket is secured to the anvil  12 . The insert  24  length dimension from left to right, FIG. 9, extends transversely across the blanket  26 . The insert has a durometer of about 90 shore hardness and the blanket has a durometer of about 85 shore hardness. However these values are nominal and may vary in the range of about +/−2 durometer. The hardness of the insert however is always greater than that of the blanket material regardless the hardness values which may vary somewhat from the above values. The insert is thus harder than the blanket, although both are made of thermoset molded urethane material. The reason for this difference in properties will be explained below. 
     The insert may differ from the blanket in respect of other properties according to a given implementation. Such properties include cut and tear resistance, i.e., the ability of the material to resist cutting and tearing in response to cuts formed by an edge and tearing in response to a tearing force, rebound, in which the ability of the material returns to its acquiescent position in response to deformation forces and is a measure of the rate of return, and the material modulus, material elongation in response to a tensile load, i.e., the amount of elongation for a given load. Any or any combination of these properties may contribute to defects in the blanket during use at the projection region located in the anvil channel as will be explained below. 
     In FIG. 4, the insert  24  is shown molded embedded into the blanket  26  material. The insert extends across the blanket within about ¼ inch (6.4 mm) from the blanket edges  46 ,  48 , FIG.  2 . The bores  28  are filled with the blanket material during the molding process. The chamfered portions  32  (FIG. 10) fill with the blanket material also and lock the insert to the blanket due to the flanges  50  of blanket material formed by the chamfered portions. The bores  30  (not shown in FIG. 4) secure the insert  24  projection  34  to the blanket and do not have similar flanges. The insert  24  is embedded in the blanket  26  at the blanket lower surface  52  and the two materials may have coplanar surfaces. The insert  24 , portions  38 , and  40 , and bottom surfaces  54  are thus coplanar with the blanket lower surface  52 . 
     A conventional woven sheet fiberglass fabric  56  or other fabric as used in the industry is molded to the blanket  26  and to the insert  24  which are molded together as the blanket is molded. The fabric  56  is somewhat U-shaped at the projection  18  and depends into the projection as shown in FIG. 4, below and adjacent to the insert  24  projection  34 . 
     The blanket assembly  14  is initially formed as a molded circular cylinder with the insert  24  embedded therein. The fingers  20  and  22  in the cylinder are then formed, FIGS. 2 and 3, by die cutting the cylinder (not shown). This is a typical commercially known process for forming such fingers in this art. In FIG. 3, fingers  20  and  22  have a length l′. The position of the fingers  20  and  22  is shown in FIG. 4 by the dimension l′. The tips of fingers  20  extend from a side  58  of projection  18  to a side  60  of the insert  24  projection  34  adjacent to the side  62  of projection  18 . Thus, a major portion of projection  18  forms the fingers and the entire portion of the insert projection  34  is within projection  18 . 
     In operation, the blanket assembly  14  is attached to the anvil  12  in conventional fashion by insertion of the projection  18  into the anvil channel  16  and interlocking the fingers  20  and  22 . However, the projection  18  has a large mass of insert projection  34  therein. The mass of the insert projection has a greater hardness than that of the blanket material projection  18 . The resiliency of the urethane material is non-linear, which means the greater the thickness the greater the resiliency in non-linear increasing fashion. The thicker material thus exhibits an increasingly greater resilience than a thinner material of the same properties. 
     The harder insert material resists the tendency of the blanket surface  64 , FIG. 4, to deflect for a given cutter load as compared to a blanket formed solely of one type of urethane in the projection and thus provides a support at this location for the blanket. It is believed that in the prior art the thicker projection permits the surface to deflect more at the projection region than at the non-projection regions for a given die cutter load. This greater deflection results in the formation of an undesirable flat recess in the projection and anvil channel region discussed in the introductory portion. That is, excess wear of the blanket surface  64  occurs in the anvil-projection region than in the remaining blanket surface region due to the greater deflection of the surface in response to impact of the cutter dies. 
     By reinforcing the projection  18  region of greater urethane thickness with a stiffer harder material formed by the insert  24  or of other different enhancing property, the surface  64  deflection is normalized to that which occurs at the rest of the surface  64  beyond the anvil channel region and beyond the region of the projection  18 . This normalized deflection thus results in more uniform wear of the surface  64 . This minimizes the occurrence of defects in the die cut sheets of cardboard material and thus provides longer life of the blanket. This reduces the cost of blanket replacements and of rejected poor product formed by the cutting apparatus, providing lower cost to the product. 
     The various different properties of the insert mentioned above may also contribute to minimizing the wear of the blanket surface at the thicker projection region in accordance with a given implementation. The various properties other than hardness as noted above herein may in certain cases be a primary cause of surface defects in the blanket due to wear. The effect of the different properties is determined empirically in a case by case basis. 
     FIGS. 11 and 12 shown an insert  66  of a different configuration. Insert  66  is substantially the same as insert  24  but has no projection. Insert  66  has chamfered through bores  68  and non-chamfered through bores  70 . Bores  70  over lie the projection region of the mating blanket and thus the anvil channel. The bores  68  are located in section portions  72  and  74  of the insert. The upper surface  76  is shaped the same as that of the insert  24  described above. The insert  66  has the same properties as described above for insert  24 . The insert  66  is rectangular in plan view in FIG.  11 . It is somewhat angular to accommodate the curvature of the blanket as described above for insert  24 . However, insert  66  is substantially sheet material notwithstanding its somewhat bent configuration. 
     In FIGS. 5 and 6, in a further embodiment, blanket assembly  104  comprises a blanket sheet  105  in which there is embedded an insert  106  and a woven fabric layer  108 . The sheet  105  is molded with a depending projection  112 . The sheet  105  has a top layer  105 ′ over and abutting the fabric layer  108 , which is over and abutting the insert  106 . The insert  106  has a depending projection  110  embedded in the projection  112 . The insert  106  serves the same function as the insert  24 . FIG.  4 . The assembly  104  has fingers  114  defined by length l. The finger  114  shown terminates at extended crest edge  116 . The finger  114  terminates at root  118 . Edge  116  extends beyond the surface  120  of the projection  112 . The projection  112  has a side surface  122 . 
     In FIG. 7, blanket assembly  78  includes insert  66  located somewhat symmetrically with projection  80  of blanket  82 . In FIG. 8, the insert  66  is substantially coplanar with the blanket  82  and embedded therein. The insert  66  is adjacent to the lower surface  84  of the blanket and is molded integrally therewith. A woven fiberglass support  86  is molded or otherwise bonded to the lower surface of the blanket  82 . In this case the support extends coextensive across the projection  80  of the blanket  82  which projection depends from the fabric support  86 . The fingers  88  (represented by dashed lines  88 ′) are formed in the region of the projection  80  and overly the projection  80 . In this embodiment, the properties of the insert are of such value that the insert need not depend into the projection  80  in order to minimize surface defects in the blanket  82 . As in the embodiment of FIGS. 4 and 9, the insert  66  and blanket  82  are molded as a circular cylinder initially. Later, the fingers  88  are die cut formed in the molded cylinder blanket assembly  78  as in commercially known processes. 
     In FIGS. 13-15, a further embodiment is shown. Blanket assembly  90  comprises a blanket  92  of molded urethane supported on a fiberglass woven support  94 . A molded urethane of harder material insert  96  is bonded to the underside of the woven support  94 . Insert  96  is of the shape and configuration of insert  24 , FIGS. 9 and 10. The difference between the embodiment of FIG.  4  and that of FIG. 13 is that the woven fabric support  94  is molded in the interior of the blanket  92  as best seen in FIG. 15, rather than at the bottom surface as shown in the embodiments of FIGS. 4 and 8. The projections  98  thus comprise the blanket material on the top surface and at the bottom surface of the fingers  100 . The fabric support  94  is embedded in the blanket material. The insert  96  is embedded beneath the fabric support and above the blanket material in the fingers  100 . The fingers  100  have a length l″. The fingers  100  of one blanket end terminate at their roots  102  in the projection  98  region as best seen in FIG.  14 . In this way the fingers are formed entirely of the projection  98  layers. The fingers of the mating blanket mirror image end may be constructed similarly. 
     It will occur to one of ordinary skill in this art that various modifications may be made to the disclosed embodiment without departing from the spirit and scope of the invention. The disclosed embodiment is for illustration and not limitation. The invention is defined by the appended claims.