Abstract:
A method for dry casting concrete block using a resilient mold having a cavity for forming a block face and a form having a block body forming cavity. The form may be offset from the mold to provide steps where the block face joins the body for aligning stacked blocks. Alternately, the form cavity may have a dimension smaller that the height of the block face and can be offset to form a step between the block face and either the top or bottom of the block. Alternately, an insert may be placed in the form adjacent the mold for forming a downwardly projecting lip along the back of the block. Blocks are formed using a dry cast concrete block machine. After casting, the form is removed from the block. The block remains supported on the mold until after it has cured.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Applicants claim priority to U.S. Provisional Patent Application Ser. No. 61/357,963 filed Jun. 23, 2010. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     TECHNICAL FIELD 
     The invention relates to dry casting concrete blocks having at least one decorative face. 
     BACKGROUND OF THE INVENTION 
     Two methods are commonly used for casting concrete blocks: wet casting and dry casting. In a wet casting process, liquid concrete is poured into a block form cavity and remains in the cavity until the concrete has cured sufficiently to permit removal without damage to the cast block. During the cure time, the form cannot be used for casting additional blocks. When one or more surfaces of the block are to be decorative, one or more walls of the cavity may be lined with, for example, a urethane liner shaped to impart a desired texture or decoration to the cast block. This process may be used, for example, to form concrete blocks simulating natural stone with deep irregular fissures. 
     In a typical dry casting process, a form having an open top and an open bottom is places on a rigid support surface such as a pallet. The form is then filled to a desired level with a relatively dry cement mixture, which is not as fluid as in the cement used in wet casting. The cement mixture is then pressed into the form cavity with sufficient pressure to form a block which has sufficient rigidity to hold its shape when the form is removed. The block is then transferred to a curing station and the form can be immediately reused for casting additional blocks. The dry casting process is commonly used for casting concrete building foundation and wall blocks. However, it has in the past only been suitable for producing blocks having a decorative surface having a relatively shallow texture or pattern. Deeper patterns have not been achievable due to problems with the relatively soft uncured block breaking when separating the block from the mold which forms the decorative surface. 
     In operating prior art dry casting block machines, the forms have been provided with either straight sides or with a slight relief angle so that the form can be separated from the uncured blocks without breaking the blocks. This has prevented use of the forms for imparting projections and notches on the sides of the blocks. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the invention, a method is provided for dry casting concrete blocks which can have highly textured faces. The method also allows casting blocks which have either a top surface or a bottom surface which is offset relative to the face of the block, or both the top and bottom surfaces may be offset relative to the face of the block or a lip may be formed to extend below a back lower edge of the block to facilitate aligning the blocks when stacked. 
     The blocks are cast in a cavity defined at a bottom by a shaped resilient member which shapes the face of the block and a rigid form which shapes the body of the block. A back of the block is located at an open top of the cavity. 
     Various objects and advantages of the invention will become apparent from the following detailed description of the invention and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a wall block having a highly textured face and a step on the top of the block to the rear of the face according to a second embodiment of the invention; 
         FIG. 2  is a cross sectional view through a form and a resilient member for dry casting the block of  FIG. 1  in a dry cast block machine; 
         FIG. 3  is a side elevational view of a wall block having a highly textured face and steps on the top and on the bottom of the block to the rear of the face according to a third embodiment of the invention; 
         FIG. 4  is a cross sectional view through a form and a resilient member for dry casting the block of  FIG. 3  in a dry casting machine; 
         FIG. 5  is a side elevational view of a wall block having a highly textured face and a lip projecting from the lower rear edge of the block across the width of the block according to a fourth embodiment of the invention; 
         FIG. 6  is a cross sectional view through a form for dry casting the block of  FIG. 5 ; and 
         FIG. 7  is a cross sectional view through a form for dry casting a wall block having a highly textured face. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a conventional dry casting block machine, a form for shaping sides of the block is lowered onto a pallet or other rigid support surface. The form has an open top and an open bottom and may have a single cavity for casting a single block or may have a plurality of cavities for simultaneously casting a number of concrete blocks. Each cavity is then filled with a dry casting concrete mixture. One or more shoes or plungers are mounted on the machine to be positioned above each cavity. The shoes have the same shape and size as the adjacent form cavities. The plungers are then lowered into the top of the form cavities and a high pressure is applied to each plunger for pressing and compacting the dry cast concrete in the cavity. The applied pressure may be, for example, in the range of 2,000 to 10,000 pounds, or more. It should be appreciated that higher pressures may be required when larger blocks are formed. After the block or blocks are formed, the pressure on the shoes is reduced to a level for holding the blocks on the pallet while the shoes are lifted from the blocks, and the shoes are then retracted. The blocks are then transferred to a curing area. 
     It is known, for example, in U.S. published patent application No. 2008/0174041, the disclosure of which is incorporated herein, that a textured mold for forming the face of a concrete block can be positioned on a support surface in a dry cast block machine and that a form can be positioned over the mold for defining a cavity in which a block is cast. The cavity is filled with the dry cast concrete mix and a shoe is lowered into the cavity to compress the concrete mix. The form is then raised, leaving the block supported on the mold. The block is then moved to a curing station before separating the block from the mold. This process has been used in the past only for forming blocks having straight sides and a face which does not extend past any of the sides, top and bottom of the block body. 
       FIGS. 1 and 2  illustrate a one embodiment of a method for dry casting concrete blocks in a conventional dry cast block casting machine.  FIG. 1  shows a side elevational view of a block  10  cast according to the method. The block  10  has a textured face  11  which may simulate weathered natural stone with deep erosion grooves and irregularities. Behind the face  11 , a step  12  is formed so that a top  13  of the block  10  is lower than an upper edge  14  of the face  11 . A step  15  extends below a lower edge  16  of the face  11  to a bottom  17  of the block  10 . When one block  10  is stacked on another, lower block  10  to form a wall (not shown), the step  15  abuts the step  12  to position the face of the upper block slightly to the rear of the face of the lower block so that the wall will have an incline and improved stability. 
       FIG. 2  is a cross sectional view of a form  18  and a urethane mold  19  for casting the block  10 . The mold  19  has a cavity  20  for forming the shaped face  11  of the block  10  and a portion of the bottom  17  of the block up to a point  21  on the bottom  17  opposite the step  12 . The form  18  has a vertical central opening or cavity  22  which forms the portion of the block  10  to the rear of the upper step  12  and the point  21 . A side  23  of the form  18  overlaps a portion of a top of the mold cavity  20  for forming the step  12  on the top of the block  10 . As with the first embodiment of the invention, after the block  10  is cast, the form  18  is pulled away from the block  10  while the block  10  remains supported on the mold  19 . The block  30  and the mold  19  are then moved to a curing area. After the block  10  has cured, the mold  19  is stripped from the block and is returned to the area of the block machine for use in casting another block. 
     It should be noted that the mold cavity  20  may be shaped so that the step  15  is either straight or curved across the width of the block  10 . Providing a curved or arcuate shape to the step  15  across the width of the block  10  can facilitate arranging stacked blocks in a wall to form a curved wall. It also should be noted that the step  15  is formed by the shape of the mold cavity  20 . The mold cavity  20  may be modified to move the step  15  from the forward position on the face shown in  FIGS. 1 and 2  to any desired location back towards the point  21  by simply modifying the design of the mold cavity  20 . 
       FIGS. 3 and 4  illustrate a third embodiment of a method for dry casting concrete blocks in a conventional dry cast block casting machine.  FIG. 3  shows a side elevational view of a block  25  cast according to the method. The block  25  has a textured face  26  which may simulate weathered natural stone with deep irregular erosion grooves and irregularities. Behind the face  26 , a step  27  is formed so that a top  28  of the block  25  is lower than an upper edge  29  of the face  26 . A step  30  extends below a lower edge  31  of the face  26  to a bottom  32  of the block  25 . The steps  27  and  30  are vertically aligned. When one block  25  is stacked on a lower block  25  to form a wall (not shown), the steps  27  and  30  abut to position the face  26  of the upper block  25  directly above the face  26  of the lower block so that the wall will be vertical. 
       FIG. 4  is a cross sectional view of a form  33  and a resilient mold  34  for casting the block  25 . The mold  34  has a cavity  35  which is shaped to define the face  26  of the block  25  and the form  33  has a vertical opening or cavity  36  with sides  37  and  38  spaced for forming the top  28  and the bottom  32 , respectively, of the block  25 . As shown, the form  33  is offset relative to the mold cavity  35  for forming the steps  27  and  30  on the block  25 . The size of the steps  27  and  20  will be determined by the amount of offset between the form  33  and the mold cavity  35 . If no steps are needed, then the form opening  36  is aligned with the mold cavity  35  while the block is formed. Further, if opposing steps are desired on the side of the cast block, it is only necessary to offset the form  33  relative to the mold cavity  35  is a direction perpendicular to the  FIG. 4  view. 
       FIG. 5  is a side view of two stacked blocks  40 , each of which has a lower lip  41  which extends below a bottom surface  42  of the block along a back  43  of the block  40 . Each block  40  has a shaped face  44 . The block faces  44  may simulate, for example, natural stone blocks. The lip  41  on each block  40  aligns the block with a lower block in the stack so that the face of the upper block is positioned slightly behind the face of an adjacent lower block in the stack. 
       FIG. 6  shows a form  45  and a resilient mold  46  for casting the block  40  in a conventional dry cast block machine according to a fourth embodiment of the invention. The mold  46  has a shaped cavity  47  for forming the face  44  of the block  40 . The form  45  has a width the same as the height of the block  40  plus the lip  41 . A side  48  of the form  45  is aligned with an edge  49  of the cavity  47  for forming a top  50  of the block  40  which is flush with the upper edge of the block face  44 . A core  51  is positioned in the form  45  for forming the bottom  42  of the block  40 . The core  51  may be molded longitudinally into an opening (not shown) in the form  45  and held there while a block  40  is cast, and then withdrawn from the form before withdrawing the form from the cast block  40 . After casting, the block  40  and the mold  46  are moved to a curing area. Alternately, the core  51  may be positioned in the form  45  prior to casting a block. The core  51  may either pulled from the block  40  or may remain with the block  40  during the cure time after the form is separated from the block  40 . The core  51  may be disposable, such as made from a foam plastic material, or it may be more permanent, such as made from polyurethane or another durable plastic material or from metal. 
       FIG. 7  is a cross sectional view through a rigid form  55 , a resilient mold  56  which is preferably made from urethane, and a rigid support plate or pallet  57  for manufacturing a dry cast block  58  according to a fifth embodiment of the invention. The interior  59  of the form  55  and a shaped recess  60  in the mold  56  form a cavity in which the block  58  is dry cast in a conventional dry cast block machine. The form  55  includes a lower skirt  61  which rests on the pallet  57  and presses against the perimeter of the mold  56  for providing support to the mold  56  when the dry concrete mix is compacted to form the block  58 . 
     The various methods described above for dry casting concrete blocks all work with many existing dry cast concrete block machines. It will be appreciated that various modifications and changes may be made to the above described preferred embodiment of a method for dry casting concrete blocks without departing from the scope of the following claims