Patent Publication Number: US-8968623-B2

Title: Process and apparatus for demolding and palletizing cast concrete blocks

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Applicants claim priority to U.S. Provisional Patent Application Ser. No. 61/370,078 filed Aug. 2, 2010. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     TECHNICAL FIELD 
     The invention relates to casting concrete blocks, and more particularly to a process and apparatus for demolding and palletizing cast concrete blocks. 
     BACKGROUND OF THE INVENTION 
     It is known that concrete blocks may be cast in cavities in, for example, a resilient polyurethane mold. For blocks having straight sides, the mold may be inverted and the blocks release onto a support or collection surface. However, when the blocks have intricate surfaces, it can be difficult to separate or demold the blocks from the mold. Manthei et al. U.S. Pat. No. 7,618,578 shows a process for demolding large cast concrete blocks from a resilient mold where the blocks have, for example, exterior surfaces shaped to simulate weathered natural stone blocks. These blocks may have sufficiently deep surface grooves, recesses and projections which make it difficult to demold. According to that patent, the resilient mold in which the blocks are cast is supported in a rigid frame during the casting and curing steps. Corners of the mold are tethered to the support frame to allow the mold to drop a limited distance from the frame when the frame and mold are inverted. In operation, a concrete block is cast in the mold. After the block has cured, a forklift or other apparatus is used to pick up the frame, mold and block. While being held together, the frame, mold and block are then inverted. While supporting the block, the frame and mold are lifted, allowing the resilient mold to be suspended from the frame by the tethers. The weight of the block causes the resilient mold to bend and stretch sufficiently to release the block. The block is then set on a pallet or other support surface, and the frame and mold are turned upright so that they are ready for use in casting another block. This process for demolding blocks relies on the weight of the block to cause the mold to bend. It is more difficult for demolding smaller, lighter weight blocks with irregular surface shapes which may retain the blocks in the mold. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention relates to demolding concrete blocks from a resilient mold in which they were cast. During casting and curing, the resilient mold is supported in a rigid frame. The blocks may be cast by either conventional wet casting or dry casting processes. After the blocks have cured, the frame is picked up, for example, with a forklift. The forklift positions a rigid, flat support against the top of the mold, and inverts the mold, frame and blocks together. The frame is then separated from the mold by the forklift and the mold is moved into a demolding machine where it is positioned above a support surface, such as a pallet or a conveyor. The mold is generally rectangular and includes two opposing edges. The demolding machine clamps onto the opposing edges of the inverted mold and then the support is withdrawn. The weight of the blocks causes the mold to sag and at least some of the blocks may fall from the mold onto the support surface. If blocks are still retained in the mold, a plunger mechanism is moved to press against the upper surface of the inverted mold to push from the mold any blocks which have not released. After all of the blocks have dropped onto the support surface, the plunger mechanism is retracted. If the support or collection surface is a pallet, guide mechanisms may be provided to help guide the blocks as they fall onto the pallet and/or may be moved against the sides of the blocks on the pallet for arranging the blocks on the pallet. The pallet may be supported on an adjustable height mechanism and may be lowered after each layer of blocks is deposited on the pallet in order to deposit an additional layer of blocks on the pallet. The process is then repeated until a desired number of layers of blocks are stacked on the pallet. 
     Preferably, the mechanisms which clamps onto the opposing edges of the inverted mold are mounted to freely pivot when the support is withdrawn from under the mold to allow the mold to sag. By allowing the clamping mechanisms to pivot, stresses on the mold will be reduced to extend the useful life of the mold. 
     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 perspective view of an exemplary mold and support frame for casting concrete blocks; 
         FIG. 2  is a fragmentary cross sectional view through an exemplary mold for casting concrete blocks according to the invention; 
         FIG. 3  is a perspective view of apparatus according to the invention for demolding and palletizing cast concrete blocks; 
         FIG. 4  is a fragmentary perspective view of the front end of a forklift supporting a frame separated from an inverted mold and ready for positioning the inverted mold in the apparatus of  FIG. 3  for demolding blocks; 
         FIG. 5  is a fragmentary side elevational view showing details of a mold gripping mechanism which has a fixed location; and 
         FIG. 6  is a fragmentary side elevational view showing details of a mold gripping mechanism which is mounted to rotate to reduce stress in the mold. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is directed for a process and apparatus for demolding and palletizing concrete blocks. The process and apparatus are particularly useful for demolding concrete blocks which have exterior configurations that make it difficult to remove the cured blocks from a resilient mold in which the blocks are cast. The blocks may have, for example, exterior surfaces with undercuts, grooves, rounded edges, recesses, projections, etc. which must be separated from the molds in which the blocks are cast without damage to the blocks and the mold. The molds may be designed for casting a single block or for simultaneously casting a plurality of blocks which may be the same or may be of different shapes, sizes and surface designs. 
     A process for demolding a single large block from a mold is disclosed in Manthei et al. U.S. Pat. No. 7,618,578, the disclosure of which is incorporated herein. 
       FIG. 1  shows an exemplary rigid frame  20  which supports a resilient mold  21  in which concrete blocks (not shown) are cast. The frame  20  may be made from steel, for example, and the mold  21  is formed from a resilient, tough, abrasion resistant resilient material, such as polyurethane. The exemplary mold  21  is shown in  FIG. 1  as having eight cavities  22  for simultaneously casting eight concrete blocks. It will be appreciated that the mold  21  may be designed for casting only a single block or for simultaneously casting a desired number of blocks. The number of blocks will be limited by the size of the mold  21 , the size and shapes of the blocks, the size of the pallet or other support surface where the blocks are deposited, and the size of the demolding apparatus. The frame  20  provides support for the mold  21  while blocks are cast in the cavities  22  and while the cast blocks cure. The blocks may be cast using known wet casting or dry casting processes. Preferably, the frame  20  includes corner supports  23  which allow the frames and molds to be stacked when not in use and while the newly cast blocks cure. The frame  20  also includes two spaced slots  24  and  25  for receiving forklift tines to allow lifting and moving the frame  20  together with the mold  21  and blocks cast in the cavities  22 . 
       FIG. 2  is a fragmentary cross sectional view through the exemplary mold  21  which is designed for simultaneously casting a plurality of blocks. The cross section extends through two cavities  22   a  and  22   b  in which different size and shaped blocks are cast. Exterior sides  26  and  27  and a bottom  28  of the mold  21  are supported by the rigid frame  20  ( FIG. 1 ) during casting blocks and curing of blocks cast in the cavities  22 . The sides  26  and  27  are angled other than 90° from the bottom  18  to allow the mold  21  to be easily separated from the support frame during the demolding process. The mold  21  has a flat top  29  which is generally rectangular in shape. Raised edges  30  and  31  extend above at least a portion of the two opposite sides  26  and  27  and the top  29 . The raised edges  30  and  31  are used to hold the mold while demolding the cast blocks, as discussed below. 
     The invention is directed to a process and apparatus for demolding concrete blocks from the resilient mold  21  in which they are cast. The process is particularly useful for blocks having textured and shaped surfaces which may not easily release from the mold  21 , for example, due to the block design and/or relatively low weight. In a first embodiment of the invention, the frame  20  and the mold  21  which has cured blocks are picked up, for example, with a forklift or with an automated transfer machine. A rigid plate is positioned against the open top of the mold and the mold, the frame and the plate are inverted so that the mold and the blocks are supported on the plate. The form  20  is raised above the inverted mold  21  and the plate, mold, and blocks are moved into the demolding apparatus where opposing edges on the mold are engaged by the demolding apparatus. At this point, the support plate, mold and blocks are positioned a short distance above a pallet or other collection surface where the demolded blocks are to be stacked. The forklift then withdraws the frame  20  and plate from the demolding apparatus. As the plate and the frame are withdrawn from the demolding apparatus, the weight of the blocks causes the resilient mold to stretch and sag as it is supported only by the demolding apparatus gripping the opposing edges of the mold. Some or all of the blocks may release from the sagging mold and drop onto the pallet. If any blocks are still retained in the mold, a plunger mechanism is moved downwardly to press against the inverted mold to help release the blocks from the stretched mold so that they fall onto the pallet. Optionally, the plunger mechanism may be vibrated as it presses on the mold to help release the blocks. 
     The apparatus may include movable side members to help align and position the demolded blocks on the pallet or on a layer of previously demolded blocks stacked on the pallet. The side members may be operated to guide the blocks as they fall onto the pallet, or may be operated to push the blocks together after they have fallen onto the pallet. Where a pallet is to hold several layers of cast blocks, the pallet may be supported on an adjustable height table. After each layer of blocks is deposited on the pallet, the table is lowered by the height of the blocks to provide space for the next layer of blocks to be stacked on the pallet. After the pallet is filled with blocks, it may be moved to a storage area, for example, either via a forklift or via a conveyor system. In a modification of this process, the rectangular mold may be provided with raised edges on at least a portion of all four sides. The demolding apparatus may then engage all four edges and pull apart each opposing pair of edges to stretch the mold in two directions. In either embodiment, the mold is stretched to the point necessary to release the blocks or to make the blocks easy to push from the mold, and not to the point of damaging the resilient mold. 
     Preferably, the demolding apparatus is hydraulically operated. Hydraulic cylinders can be provided for controlling movement of all movable parts in the demolding apparatus. 
       FIG. 3  shows one embodiment of apparatus  35  for demolding cured concrete blocks from a resilient mold  36 . The apparatus includes a rigid support frame  37  having a left side  38  and a right side  39 . The resilient mold  36  is illustrated being gripped on a left edge  40  by a mechanism  41  mounted on the left support frame side  38  and being gripped on a right edge  42  by a mechanism  43  mounted on the right support frame side  39 . A pallet  44  is shown supported on an adjustable height table  45 . A plunger mechanism  46  is located adjacent a top  47  of the support frame  37 . The plunger mechanism  46  can be lowered to press against the sagging mold  36  to help release any cast blocks which do not fall from the mold  36  when it is stretched. 
       FIG. 3  is shows the demolding apparatus  35  without any blocks. For demolding, the blocks and inverted mold  36  are initially supported on a plate (not shown) which is positioned by the forklift where the gripping mechanisms  41  and  43  can engage the edges  40  and  42  of the mold  36 . When the forklift is moved to withdraw the plate away from the apparatus  35 , the mold  36  will sag and stretch under the weight of the blocks. Some blocks may fall onto the pallet  44  while other blocks may not release from the mold  36 . If blocks remain in the mold  36 , the plunger mechanism  46  is lowered to push the blocks from the mold  36 . Preferably, the plunger mechanism  46  includes multiple sections (two sections  46   a  and  46   b  are illustrated) which are mounted to pivot into contact with the curvature of the sagging mold  36 . If desired, the plunger mechanism  46  may be vibrated to help release the blocks. 
     Since the mold  36  sags and stretches as the blocks are released, the blocks may not be arranged on the pallet  44 . Left and right guide mechanisms  48  and  49  may be positioned to help guide the falling blocks onto the pallet and may be rotated to push the blocks together on the pallet. The left and right guide mechanisms  48  and  49  may be rotated either at the same time or alternately, or only one may be individually rotated if the blocks on only one side of the pallet need compacting. As additional layers of blocks are stacked on the pallet  44 , the guide mechanisms  48  and  49  keep the blocks properly stacked for stability on the pallet  44 . For illustration purposes, the left guide mechanism  48  is shown in a retracted position where it will not interfere with upward movement of the pallet  58 , and the right guide mechanism  49  is shown in a lowered, rotated position where it can guide falling blocks onto the pallet  44 . Preferably, the various movable components of the apparatus  35  are moved through the use of conventional hydraulic cylinders. 
     Various attachments are commercially available for use with forklifts to meet needs for different applications.  FIG. 4  is a fragmentary perspective view of the front portion of a forklift  54  which adapted for use with the invention. The forklift  54  is provided with a substantially vertical mast assembly  55  on which a carriage  56  is mounted for up and down movement. The carriage assembly  56  includes a two forks or tines  57  (only one shown in broken lines). The tines  57  can be raised and lowered and moved towards and away from each other on the carriage assembly  56 . In the illustration, the tines  57  are positioned in the two spaced slots  24  and  25  in the frame  20 , and therefore not visible. The carriage assembly  56  also mounts a plate  58 , which is shown supporting the mold  21 . The plate  58  can be moved on the carriage assembly  56  towards and away from the tines  57  independently from the movement of the tines  57 . Further, the carriage assembly  56  is mounted on the mast so that it can be rotated through at least 180° for inverting the mold  21 . 
     Initially, the frame  20  supports the mold  21  in the arrangement shown in  FIG. 1 , with the mold  21  supported by the frame  20 . The mold cavities are filled with concrete and then moved to a curing station while the concrete blocks cure. For demolding, the forklift  54  engages the frame  20  by inserting the tines  57  into the frame slots  24  and  25  for lifting and moving the mold to the demolding apparatus  35 . Prior to inserting the mold  21  into the demolding apparatus, the plate  58  is moved into contact with the top of the mold  21 . Preferably, the plate  58  is pressed against the mold  21  to clamp the mold  21  in the frame  20 . Optionally, the plate  58  may be spring mounted on the forklift carriage assembly  56  to maintain some pressure on the mold  21  to firmly hold the mold  21  in the frame  20 . After the frame  20  and mold  21  are raised sufficiently to clear any obstacles such as the ground, the carriage assembly  56  is then rotated 180° to invert the frame and the mold. After they are inverted, the frame  20  is raised to a position above the mold  21 , for example, to the position shown in  FIG. 4 . The height of the carriage assembly  56  is adjusted, as necessary, so that the mold edges  30  and  31  will align with the gripping mechanisms ( 41  and  43  in  FIG. 3 ) and the mold  21  is moved by the forklift  54  into the demolding apparatus  35 . The gripping mechanisms  41  and  43  are then hydraulically activated to clamp onto the mold edges  30  and  31 . The forklift  54  is backed away from the demolding apparatus  35 , moving both the plate  58  and the frame  20  away from the apparatus  35 . 
     As the plate  58  is pulled away from the apparatus  35 , the weight of the cast blocks and the flexibility of the mold  21  will cause the center area of the mold  21  to sag and stretch. Some or all of the cast blocks may fall onto the pallet  44  or on top of a layer of blocks already stacked on the pallet  44 . During this time, the guide mechanisms  48  and  49  may be positioned so that their lower edges are next to the pallet  44  to help guide the falling blocks onto the pallet  44 , as shown in  FIG. 5 . If any of the blocks have not fully released from the mold  21 , the plunger mechanism  46  is lowered until the pivotable sections  46   a  and  46   b  press against the mold  21 . The plunger mechanism  46  may be vibrated or reciprocated up and down, as necessary, to release from the mold  21  any remaining blocks. After all of the blocks are released, the plunger mechanism  46  is retracted. The two guide mechanisms  48  and  49  then may be moved, as necessary, for pushing the blocks together on the pallet  44  so that additional layers of blocks can be stacked on the pallet  44 . 
       FIG. 5  shows a fragmentary portion of a mold gripping mechanism  60  gripping an edge  61  of a mold  62 . The gripping mechanism  60  is mounted on a bracket  63  which is stationary on the demolding apparatus. The illustrated gripping mechanism  60  has a fixed clamping member  64  which is secured to the bracket  63  and a rotatable clamping member  65 . The rotatable clamping member  65  is mounted on the clamping member  64  or may be mounted on a bracket (not shown) secured to the bracket  63  to rotate on a bolt  66 . When the mold  62  is positioned in the demolding apparatus, a lip  67  on an edge  68  of the mold  62  is hooked over an edge  69  of the first clamping member  64 . A hydraulic cylinder  73  is then operated to rotate the second clamping member  65  so that the lip  67  is clamped between the clamping members  64  and  65 . 
       FIG. 5  illustrates the effect of rigidly clamping the mold edge  68  and allowing the mold to sag. The illustrated fragmentary portion of the mold shows in dashed lined the bending effect on a block cavity  70  adjacent the gripping mechanism  60  and on a block cavity  71  spaced further from the gripping mechanism  60 . The cavities  70  and  71  open at a mold surface  72 . When the mold edge  68  is rigidly held to extend in a horizontal direction, unnecessary stresses are induced in the sagging mold  62 . As illustrated, the sides of the cavity  70  adjacent the surface  72  are forced together in the directions of the arrows adjacent the cavity  70 . This tends to hold a cast block in the cavity  70 , requiring unnecessary force to push the block from the cavity  70  and reducing the useful life of the mold  62 . However, the sides of the cavity  71  adjacent the mold surface  72  will be spread apart to facilitate release of a block from the cavity  71 . 
       FIG. 6  shows a slight modification to the mold gripping mechanism  60  in which the bracket  63  is suspended from a pivot point  74 . A hydraulic cylinder  75  is provided for positioning the first and second clamping members  64  and  65  while the mold  62  is moved into the demolding apparatus and the opposing edges of the mold are clamped. After the edges of the mold are clamped and before withdrawing the support from under the mold, hydraulic pressure on the cylinder  75  is released so that the mold gripping mechanism  60  is free to pivot. When the support is withdrawn from under the mold  62 , the mold  62  free to sag into a more uniform curve with reduced stresses on the mold. As shown in the illustration, the sides of both cavities  70  and  71  will diverge at the mold surface  72 , thus helping the release of blocks from both cavities. 
     It will be appreciated that various constructions may be used for engaging opposing edged or rims of the mold to facilitate stretching the mold to release the cured concrete blocks. It also will be appreciated that the apparatus may be modified for engaging and stretching the mold in a forward and back direction in addition to stretching in a left and right direction if needed for releasing a specific block. This may be useful for block designs where the block is strongly held in the mold due to the block surface configuration.