Patent Publication Number: US-8524138-B2

Title: Concrete block with beveled core opening edge

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of application Ser. No. 11/147,680, filed Jun. 7, 2005, which application is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to concrete blocks and methods of forming the same. More specifically, the invention relates to concrete blocks having core openings with beveled edges and methods and equipment for forming the beveled edges of the core openings. 
     BACKGROUND OF THE INVENTION 
     Concrete blocks have been a basic building material for many years. Concrete blocks have been designed for use in many applications, including concrete retaining wall blocks used to construct retaining walls. Concrete retaining wall blocks are typically dry stacked (i.e. no mortar is used) in ascending courses. 
     A concrete block is sometimes formed with one or more core openings. This lightens the block thereby make the manual handling of the block easier, and reduces the amount of material used to form the block thereby reducing material costs. The core opening(s) can extend entirely through the block from the top of the block to the bottom, or partially through the block (e.g. extending from the bottom of the block toward the top but not extending through the top). 
     An example of the formation of core openings in a concrete retaining wall block is disclosed in U.S. Pat. No. 5,827,015. As disclosed in that patent, and with reference to  FIG. 6  herein, a pair of concrete retaining wall blocks are formed face-to-face within a mold  100  that has an open top and an open bottom and is positioned on a pallet  102 . The tops of the resulting blocks rest on the pallet and the bottom of the blocks face upward. For each block, a pair of core forms  104  are positioned within the mold  100  to form a pair of core openings in each of the resulting blocks. Dry-cast concrete is then deposited in the mold  100 , the mold is vibrated to densify the dry-cast concrete, and a head  106  or “stripper-shoe” is brought down into the mold to compress the concrete in the mold and form the resulting bottom surfaces of the blocks. Thereafter, the blocks are stripped from the mold through relative vertical movement of the pallet  102  and mold  100  assisted by the head  106  pushing the blocks out of the mold. As the blocks are stripped from the mold, the core forms  104 , which are fixed to the mold, strip from the concrete, leaving behind the core openings in the blocks. 
     When a cored retaining wall block is stripped from the mold, a small ridge of concrete tends to be left around the edge of the core opening at what will be the bottom surface of the block (termed “feathering”). Similar feathering tends to occur along other edges of what will be the bottom surface of the block that are in contact with mold surfaces, for example the bottom side edges of the block. Once solidified, feathering can interfere with the block laying flat on other blocks when dry-stacked in a wall. 
     Attempts to remove the feathering have included the use of a rotating brush on the production line after the block is stripped from the mold to sweep away feathering that occurs. However, it has been found that the brush often leaves some of the feathering, particularly feathering that occurs along an edge that is perpendicular to the rotational axis of the brush. 
     There is a need for methods and equipment that minimize the feathering that occurs along bottom edges on concrete blocks as a result of the blocks being stripped from the mold. 
     SUMMARY OF THE INVENTION 
     The invention relates to a concrete block having at least one core opening with one or more beveled edges. The invention also relates to methods and equipment for forming the beveled edge(s) around the core opening. The formation of the beveled edge(s) eliminates the impact of feathering by reducing the amount of feathering that occurs and shifts any feathering that does occur away from the bottom surface so that the feathering does not prevent the block from laying flat on other blocks. 
     Any number of the core opening edges can be beveled as described herein. Only those edges of the core opening that tend to have residual feathering after passing by a rotating brush, for example edges of the core opening that are perpendicular to the rotational axis of the brush, may be beveled. Alternatively, all of the edges of the core opening may be beveled as described herein. 
     Similar beveling can be provided on the edges of the block at the intersection of the bottom surface of the block and the sides of the block to reduce feathering at the bottom side edges of the block and shift any feathering that does occur away from the bottom surface. 
     In one aspect of the invention, a stripper shoe is provided for use in forming a concrete block in a block mold. The stripper shoe is in the form of a plate having a first surface that in use faces the concrete block in the block mold. At least one core form opening is formed in the plate, where the core form opening is configured to allow passage therethrough of a core form that is used to form the core opening in the concrete block. In addition, a beveled ridge is formed on the first surface of the plate along at least a portion of the core form opening and projecting from the first surface toward the concrete block. The beveled ridge forms the beveled edge around the core opening. 
     In another aspect of the invention, a method of forming a core opening in a concrete block molded in a block mold is provided. In the method, during molding of the block and formation of the core opening, a beveled edge is molded around at least a portion of the perimeter of the core opening. 
     In yet another aspect of the invention, a method of forming at least one core opening in a concrete block is provided. The method includes providing a block mold having a plurality of side walls defining a mold cavity with an open top and an open bottom; positioning a pallet underneath the block mold to temporarily close the open bottom of the mold cavity; positioning a core form in the mold cavity at a location to form the core opening; depositing dry-cast concrete in the mold cavity; introducing a plate through the open top of the mold cavity to compact the dry-cast concrete in the mold cavity to form a pre-cured concrete block, the plate having a first surface that in use faces the mold cavity, the plate having a core form opening formed therein that is configured to allow passage therethrough of the core form, and the plate having a beveled ridge formed on the first surface of the plate along at least a portion of the core form opening and projecting from the first surface toward the mold cavity; reopening the temporarily-closed bottom of the mold cavity; discharging the pre-cured concrete block from the mold cavity through the reopened bottom of the mold cavity; and curing the pre-cured concrete block. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a bottom perspective view of a concrete block with core openings having beveled edges according to the invention. 
         FIG. 2  is a top view of a pre-split concrete workpiece comprising two concrete blocks molded face-to-face and oriented bottom-sides up. 
         FIG. 3  is a bottom view of a center stripper shoe and a pair of outside stripper shoes that are used to compact the concrete in the mold cavity and mold the top side of the work piece of  FIG. 2  (i.e. the bottoms of the resulting blocks). 
         FIGS. 4A and 4B  are cross-sectional views of the stripper shoes shown in  FIG. 3  taken along lines  4 A- 4 A and  4 B- 4 B, respectively. 
         FIG. 5  is detailed view of a portion of a core form and a core form opening in a stripper shoe. 
         FIG. 6  is an exploded perspective view of a prior art embodiment of a concrete block mold along with core support bars, core forms, outside stripper shoes and a center stripper shoe. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention relates to a concrete block  10  having at least one core opening  12  with one or more beveled edges  48 . The invention also relates to methods and equipment for forming the beveled edge(s)  48  around the core opening  12 . A stripper shoe is configured to form the beveled edge  48  during molding of the block  10 . The bevel helps to minimize a ridge of concrete (i.e. feathering) that tends to be left around the edge of the core opening once the block is stripped from the mold. Further, any feathering that is left is below the bottom surface of the block so that the block is more likely to lay flat when stacked into courses with other like blocks. 
     The block  10  will be described herein as having a pair of core openings  12 . However, the block could have a larger or smaller number of core openings. Further, the core openings  12  of the block  10  will be described herein as extending completely through the block from the bottom surface to the top surface. However, other arrangements of the core openings  12  are also possible. For example, the core openings  12  need not extend completely through the block; instead the core openings  12  could extend upwardly from the bottom surface toward the top surface, but stop short of the top surface so that the core openings do not extend through the top surface. 
       FIG. 1  illustrates the concrete block  10  having a pair of core openings  12  that extend completely through the block  10  from the bottom surface  16  of the block  10  to the top surface (not visible). The illustrated block  10  also includes a front surface  18 , a rear surface  20 , and side surfaces  22 ,  24  that extend from the front surface  18  to the rear surface  20  and that converge toward each other as the side surfaces approach the rear surface  20 . The bottom surface  16  is also provided with a locator flange  26  that projects from the bottom surface  16  adjacent the rear surface  20  of the block. A block of this configuration is the Anchor Diamond Pro™ block available from Anchor Block Company, Inc. of Minnetonka, Minn. 
     The front surface  18  of the block is provided with a rough texture resulting from, for example, a splitting process on a concrete workpiece  28 , shown in  FIG. 2 , comprising a pair of the blocks  10  formed face-to-face. The formation of concrete blocks by splitting a concrete workpiece is disclosed, for example, in U.S. Pat. No. 5,827,015 which is incorporated by reference herein in its entirety. 
     As disclosed in more detail in U.S. Pat. No. 5,827,015, and with reference to  FIG. 6  herein, the work piece is formed within a mold  100  having a plurality of side walls  108  defining a mold cavity  110  with an open top and an open bottom. A pallet  102  is positioned underneath the mold  100  to temporarily close the open bottom of the mold cavity. In addition, core forms  104  are fixed to core bars  112  that are connected to the mold so that the core forms  104  are positioned within the mold cavity  110  to form the core openings. Dry-cast concrete is then deposited into the mold cavity, and is compacted to densify it. 
     Densification is accomplished primarily through vibration of the dry cast concrete, in combination with the application of pressure exerted on the mass of dry cast concrete from above. With reference to  FIG. 6 , the pressure is exerted by one or more plates  106 , also called stripper shoes, that are brought down through the open top of the mold cavity  110  into contact with the top of the dry cast concrete in the cavity to compact the concrete. After the concrete is adequately densified, the temporarily-closed bottom of the mold cavity is reopened, the pre-cured concrete workpiece is discharged from the mold cavity through the reopened bottom of the mold cavity by lowering the pallet  102  relative to the mold while further lowering the stripper shoes  106  through the mold cavity to assist in stripping the pre-cured workpiece from the cavity. The stripper shoes  106  are then raised upward out of the mold cavity and the mold  100  is ready to repeat this production cycle. The pre-cured concrete workpiece is then transported from the mold for subsequent curing. After curing, the workpiece is split, resulting in a pair of concrete blocks. 
     As discussed above, in the past the work piece tended to have feathering that remained around the edges of the resulting core openings at the top of the work piece (i.e. bottom surfaces of the resulting blocks). The feathering is believed to be the result of adhesion between the dry cast concrete and the core forms that creates a ridge of concrete around the perimeter of the core opening as the workpiece is stripped from the mold. The feathering then needed to be removed, for example by a rotating brush on the production line, or manually, to enable the block to lay flat on other blocks when stacked in courses. 
     FIGS.  3  and  4 A- 4 B illustrate stripper shoes that minimize feathering around the core openings  12  and shift any feathering that does occur to below the top surface of the work piece  28  (i.e. the bottom surfaces  16  of the resulting blocks  10 ).  FIG. 3  illustrates a center stripper shoe  30  that is configured to compress the central portion of the workpiece during molding, and a pair of outside stripper shoes  32  that are configured to compress end regions of the workpiece during molding. The stripper shoes  30 ,  32  cooperate to compress the concrete in the mold cavity and to define the top surface of the work piece  28  (the bottom surfaces of the resulting blocks). 
     The stripper shoes  30 ,  32  each comprise a metal plate having a first surface  34  which in use faces toward the mold cavity and a second surface  36  opposite the first surface that faces away from the mold cavity. A plurality of core form openings  38  are formed in the shoes  30 ,  32 . The number of openings  38  can vary based on the number of core openings  12  to be formed in the workpiece  28  and block  10 . In the illustrated embodiment, two openings  38  are formed at each end of the shoe  30  and two openings  38  are formed at the end of the shoes  32  that face the respective ends of the shoe  30 . 
     The openings  38  in the shoe  30  combine with the openings  38  in the shoe  32  to form a pair of larger openings that are each configured to allow passage therethrough of a core form  50  (a portion of which is visible in  FIG. 5 ) that is used to form the respective core opening  12  in the concrete block  10 . During molding of the workpiece and subsequent stripping from the mold, the openings  38  allow the shoes  30 ,  32  to move up and down relative to the core forms  50  during compression of the concrete and subsequent stripping of the work piece. 
     The shoes  30 ,  32  are spaced from each other to provide a gap  39 . The gap  39  allows passage of a core bar  112 , shown in  FIG. 6 , to which the core forms  50  are attached. The core bar  112  creates a channel  17  in the bottom surface  16  of the block as shown in  FIGS. 1 and 2 . The gap  39  can be, for example, about 0.5 inch wide while the core bar has a width of, for example, about 0.375 inch, which allows for a gap of about 0.0625 inch between the sides of the core bar and the stripper shoes  30 ,  32 . 
     The surface  34  of each shoe  30 ,  32  has a beveled ridge  40  formed around the perimeter of the openings  38  and along the gaps  39  between the shoes  30 ,  32 . The ridge  40  projects toward the mold cavity and the concrete blocks to be molded therein.  FIG. 3  illustrates the ridges  40  extending around the perimeters of the openings  38  and along the gap between the shoes  30 ,  32 , while  FIGS. 4A and 4B  illustrate sectional views of the ridges  40 . The ridge  40  need not extend around the entire perimeter of the openings and gaps  39 . Instead, the ridge  40  could extend along select portions of the openings  38  and/or gaps  39  to bevel the edges at those select portions. 
     As illustrated in  FIGS. 4A ,  4 B and  5 , each ridge  40  includes a first section  42  that extends generally perpendicular to the surface  34  of the stripper shoes  30 ,  32  and generally parallel to, and forming an extension of, a wall  44  that forms the opening  38 . Each ridge  40  also includes a second section  46  that extends from the first section  42  to the surface  34  and which is disposed at an acute angle α relative to the direction of travel of the core form  50  through the core form opening  38  as the work piece  28  is being stripped from the mold. For example, the angle α can be about 45 degrees. The second section  46  faces generally away from the opening  38  that it is formed around, or faces generally away from the gap  39 . 
     As illustrated in  FIGS. 3 and 4B , the surface  34  of each of the outside shoes  32  also includes a recess  52  formed therein along the entire length of the shoe  32  that results in the creation of the flange  26  on the bottom surface of the block. 
     With reference to  FIG. 5 , during molding of the workpiece  28 , as the shoes  30 ,  32  are moved downward to compress the concrete in the mold cavity, the second section  46  of the ridge  40  creates a beveled edge  48  around the core opening that is formed by the core form  50 . The ridges  40  on the shoes  30 ,  32  inhibit the formation of a ridge of concrete around the perimeter of the core openings. In the event that residual feathering does result, the feathering will be present on the beveled edge  48  away from the bottom surface of the block. Therefore, any residual feathering is away from the bottom surface  16  of the block and would not prevent the block from laying flat on other blocks when stacked into courses with other blocks. 
     Similarly, the portion of the ridges  40  that face the gaps  39  inhibits the formation of feathering along the channel  17  and/or shifts the feathering away from the bottom surface by creating a bevel along the edges of the channel  17 . 
     Similar beveling can be provided along the bottom side edges  25  of the block where the side surfaces  22 ,  24  intersect the bottom surface  16 . To accomplish this, a ridge (not shown) similar to the ridge  40  can be provided along the sides  54  of the mold shoes  30 ,  32 . By providing such beveling, any residual feathering that may result from adhesion between the concrete and the side walls of the mold would be shifted away from the bottom surface  16 . If the bottom side edges  25  are beveled along with the core opening edges and the channel edges, the rotating brush on the production line to sweep away feathering is unnecessary.