Abstract:
A compression shoe for use on a concrete products forming machine comprises a main body and a plated layer overlaid on the main body. The main body is configured to be slidingly received within a mold cavity of a concrete products mold. The plated layer overlaid on the main body of the compression shoe comprises a uniform electroless nickel (Ni), phosphorus (P), and polytetrafluoroethylene (PTFE) nano dispersion coating to effect enhanced material release characteristics by preventing the build-up of material on the compression shoes and enhancing their wear characteristics.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0001]    This invention relates generally to concrete products forming machines (CPMs) and more particularly to compression shoes used in such machines that form molded products. 
       2. Description of the Prior Art 
       [0002]    Prior art machines for forming concrete products within a mold box include a product forming section comprising a stationary frame, an upper compression beam and a lower stripper beam. The mold assembly includes a head assembly that is mounted on the compression beam, and a mold box that is mounted on the frame and receives concrete material from a feed drawer. An example of such a system is shown in U.S. Pat. No. 5,807,591 which describes an improved concrete products forming machine (CPM) assigned in common to the assignee of the present application and herein incorporated by reference for all purposes. 
         [0003]    Current production process consists of a mold containing forming cavities in which concrete material is filled. During each machine cycle, a pallet is brought in contact with the bottom surface of the mold, closing the bottom side of the cavities. Concrete material is deposited into the top of each cavity and then vibrated to concentrate the material. During this cycle a compression shoe is inserted into the top surface of the cavities which then compresses further and forms the top of the concrete material to a specific surface configuration. 
         [0004]    Conventional compression shoes are comprised of case hardened steel that is machined precisely to fit the cavity opening and to create a specific shape characteristic into the top formed surface of the concrete material. The compression shoe when contacting the top surface of the concrete material causes concrete material to adhere to the contact surface. This adherence can build up during the multiple cycle process causing the original surface to be altered and the concrete product being formed to have inferior appearance. 
         [0005]    A known method for addressing the build-up of concrete on the compression shoe during multiple cycles is to apply heat to the compression shoe to elevate the temperature adequately to hydrate the surface tension between the compression shoe and the concrete material during the forming process. This method, however, is highly energy inefficient since heating energy must be constant applied to the compression shoes, thus elevating the temperature of the work environment as well as possibly degrading the lifetime of the shoe. 
         [0006]    Accordingly, there is need for alternate methods for preventing the build-up of material on the compression shoes and enhancing their wear characteristics. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention comprises utilizing a plated layer overlaid on the main body of the compression shoe. This plated layer is comprised of an electroless nickel, phosphorus, polytetrafluoroethylene (Ni—P-PTFE) Nano dispersion coating. Electroless nickel&#39;s ability to plate uniformly makes this coating ideal for surfaces that have texture that are not compromised by the additional coating layer. The release characteristic is further improved with the introduction of PTFE. During the co-deposit process, Teflon particles are actually plated along with the electroless nickel and become part of the plated coating itself. This provides for greatly enhanced lubricity throughout the life of the coating. As the coating wears, new PTFE particles are continuously exposed. This process provides release enhancement of the forming surface no longer requiring heat to maintain the surface quality of the compression shoe. 
         [0008]    Another characteristic of the Ni—P-PTFE plated surface is through heat treatment (approx. 400 C.) of the plated surface, after the plating process, to achieve a higher surface hardness for improved wear ability against the abrasiveness of the concrete mixture, therefore an improved compression shoe wear life. 
         [0009]    Another aspect of the invention includes a method for making a molded concrete product within a mold box of a type having an array of cavities. The method comprises first lifting a pallet against an underside of the mold box so that it seals bottom openings of the mold box cavities. The array of cavities within a mold box are then filled with concrete material. Once the cavities are filled with concrete compression shoes are then lowered into top openings of the mold box cavities so that bottom surfaces of the compression shoes rest against and compress the top surface of the concrete material within the array of cavities. The bottom surfaces of the compression shoes are formed with a plating layer in contact with the concrete product formed of electroless nickel (Ni), phosphorus (P), and polytetrafluoroethylene (PTFE). The compression shoes are then lowered together with the pallet so that the concrete material is pressed in molded fashion out the bottom openings of the mold box cavities. The compression shoes are then lifted back out through the top openings of the mold box cavities once the molded concrete products are completely moved out from the cavities and onto the pallet. The process can then start again to produce additional sets of molded concrete products. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of a head assembly of a concrete products forming machine that includes compression shoes implemented according to embodiments of the invention positioned over the filled cavities of a mold assembly. 
           [0011]      FIG. 2  is a side elevation sectional view taken along line  2 - 2  of  FIG. 1  in a subsequent production process with the compression shoes partially inserted into the mold cavities and pushing the molded concrete products out the bottom end of the cavities. 
           [0012]      FIG. 3  is a sectioned side elevation view of a compression shoe constructed according to teachings of the invention. 
           [0013]      FIG. 4  is a magnified view of a portion of  FIG. 3  showing a sectioned side elevation of the compression shoe side constructed according to teachings of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  illustrates a mold assembly  10 , including a mold box portion  12  and a head assembly portion  14  that are mounted together in alignment with one another onto a concrete products forming machine (CPM)—not shown—as described further below. Whereas the mold box  12  is mounted within a lower part of the concrete products machine, as by spanning across a pair of vibrationally enabled mounting shelves, the head assembly is coupled to a vertically moveable compression beam  15 . 
         [0015]    Mold box  12  is arranged with a particular configuration that dictates what type, size, and shape of molded product it is to produce. As such, mold box includes a body with a front wall  16  and a back wall (not shown) joined together with side walls  20 ,  22  and having an array of openings formed therein, e.g. cavity  24  ( FIG. 2 ), for receiving and molding concrete material  100  into concrete products  200 . The side walls  20 ,  22  each have a side face  26  that spans between a bottom facing surface  28  of the side face and a top facing surface  30  to form the dimensions of the cavities  24 . These dimensions ultimately determine a size and shape of the molded concrete product  200  formed using the mold box  12 , subject to a top surface profile or pattern imparted to the top of the concrete material  100  by a compression shoe  32  as described below. 
         [0016]    The head assembly  14  includes multiple compression shoes  32 , coupled vertically with respective head legs  34 , that are shaped for slidingly inserting through a top side  30  of the mold assembly  12  and into the mold cavities  24 . A top-mounted connector plate  36  couples head legs  34  and the shoes  32  together in registry with the cavities  24  of the mold assembly  12 . The shoes  32  compress the concrete material  100  into a molding condition and push the molded concrete products  200  completely out a bottom side  28  of the mold box. The shoes  32  are then collectively raised and slidingly removed out the top side  30  of the mold box  12  so as to again expose the open tops of the cavities  24  and to allow the mold box to receive and mold additional concrete products. In this fashion, mold box  12  and head assembly  14  are constructed to form molded concrete products  200  having a certain size and configuration, whereas different mold boxes can have differently configured assemblies resulting in different products. 
         [0017]    In use, the head assembly  14  is raised via the compression beam  15  of the CPM so as to expose the cavities  24 . A feed drawer moves concrete material over the top of the mold box  12  and dispenses the material  100  into the contoured cavities  24  of the mold box. The preferred materials  100  used to form the concrete products  200  produced by methods of the present invention include zero slump concrete with a cement content of between about 14%-16% by weight. A pallet  38  is maintained against the underside of the mold cavities  24  during this filling step to prevent material from spilling out the bottom end of the mold box  12 . The feed drawer typically includes an agitator assembly (not shown) within the drawer that operates to break up the concrete and improve its consistency prior to dropping it into the mold. As the concrete material is dispensed, a vibration system shakes the mold box to spread the concrete material evenly within the mold box cavities in order to produce a more homogeneous concrete product. A wiper assembly, mounted to the front of the feed drawer, then moves against the bottom surface of the compression shoes  32  to scrape excess concrete from the compression shoes  32  when the feed drawer is moved to an operative position above the mold box. 
         [0018]    After the concrete  100  is dispensed into the mold cavities  24 , the feed drawer retracts from over the top of the mold box. A spreader, bolted separately to the front of the feed drawer, scrapes off excess concrete from the top facing surface  30  of the mold box  12  when the feed drawer is retracted after filling the mold cavities  24 . The result is that the cavities  24  of the mold box are completely filled with concrete  100  or some other moldable material as shown in  FIG. 1 . 
         [0019]    After the cavities  24  are filled with concrete  100 , the vertically moveable compression beam  15  and coupled head assembly  14  are lowered to an intermediate position so that the compression shoes  32  are pushed into the tops of corresponding cavities  24  in the mold box and against the top surface of the concrete material  100 . The shoes compress the concrete material  100  during the vibration process and ensure that the top surface of a resulting concrete product  200  retains a top surface profile imparted by a bottom surface profile of the compression shoe as described further below. 
         [0020]    With the shoes  32  at the top  30  of the mold box cavities  24  and against the top of the concrete  100 , and with the pallet  38  held against the bottom of the concrete within the cavities, the mold is vibrated by the CPM to remove air pockets from within the molded product and to ensure that the concrete fills the entirety of the mold cavity, thus resulting in more uniform molded concrete products  200 . 
         [0021]    After compression is complete, the pallet  38  is lowered via a stripper beam (not shown) as the head assembly  14  pushes further into the cavities  24  against the now-molded material  200  as shown in  FIG. 2 . The shoes  32  thus continue to compress the concrete products into a molding condition and push the molded concrete products  200  out a bottom side  28  of the mold assembly until the molded concrete products are fully removed from the cavities and sitting upon the pallet  38 . The pallet is then removed and a new pallet moved into position, the shoes  32  slidingly removable back out the top side of the mold cavities  24 , and the production cycle continued to allow the mold box to receive and mold additional concrete products. 
         [0022]    The mold box and head assembly are matched together and configured to form concrete products in a specific shape, size, and number. Each product configuration requires a different mold. When the operator desires the CPM to produce products in different configurations, the mold assembly must be detached from mounts on the CPM and removed along with the assembly. A different mold box and head assembly must then be moved into place and mounted within the CPM. 
         [0023]    As shown best in  FIG. 2 , and due to the nature of the molding process and the concrete materials used, the compression shoes  32  must be closely fitted within the cavity  24  dimensions. As the shoes  32  press against the top of the molded product  200  so as to force the product out the bottomside of the mold as shown in  FIG. 2 , the top surface of product can adhere to the shoe  32  as the shoe is retracted back up through the cavity  24  for the next production step. This results in a molded product having a defective top surface profile, which must therefore be rejected. 
         [0024]    The present invention utilizes a plating layer atop the steel body of the compression shoes that reduces the adhesion with the molded material so as to prevent tear-away, as well as improves the durability of the shoes in an abrasive environment such as with molding concrete products. 
         [0025]      FIGS. 3 and 4  illustrate a compression shoe  32  of a type used in the present invention. Compression shoe  32  includes a main body  40  formed of a hard, durable, and relatively inexpensive material such as steel, e.g. carburizing steel with a carbon content of approximately 18%-20% that has been carburized and case hardened. A plated layer  42  is overlaid overtop the main body  60  of the compression shoe. Plated layer  42  is formed at least overtop a bottom  44  of the compression shoe  32  main body  40 , as this is the surface that contacts the concrete material  100  during the molding process. However, the plated later  42  can also be formed overtop the side surfaces  50 ,  52  of the compression shoe main body  40  as well as overtop the top surface  54 . 
         [0026]    The bottom surface  44  of the compression shoe  32  can be imparted with a particular negative profile that is intended to be transferred to the molded concrete product  200 . One example of this profile is shown in  FIGS. 3 and 4 , where upwardly angled peripheral surfaces  46 ,  48  formed in the bottom surface of compression shoe  32  form chamfered edge around the top peripheral surface of the molded concrete product  200 . 
         [0027]    This plated layer is preferably comprised of an electroless nickel, phosphorus, polytetrafluoroethylene (Ni—P-PTFE) nano dispersion coating. The rate of deposit of the plating later is constant and includes a plating thickness of between about 0.0022 to 0.006 inches. It has been discovered that electroless nickel&#39;s ability to plate uniformly makes this coating ideal for surfaces that have texture or a distinctive profile that are not compromised by the additional coating layer. 
         [0028]    The release characteristic is further improved with the introduction of polytetrafluoroethylene (PTFE) also commonly known as Teflon. During the co-deposit process, Teflon particles are actually plated along with the electroless nickel and become part of the plated coating itself. This provides for greatly enhanced lubricity throughout the life of the coating. As the coating wears, new PTFE particles are continuously exposed. In a preferred embodiment, phosphorus is co-deposited with this Ni and PTFE materials at between a 2%-13% proportion, and preferably between about 10% infusion rate. This process provides release enhancement of the forming surface and no longer requires the continuous application of heat to maintain the surface quality of the compression shoe. 
         [0029]    Another characteristic of the Ni—P-PTFE plated surface is through heat treatment (approx. 400 C.) of the plated surface, after the plating process, to achieve a higher surface hardness for improved wear ability against the abrasiveness of the concrete mixture, therefore an improved compression shoe wear life. 
         [0030]    Having described and illustrated the principles of the invention in a preferred embodiment thereof, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. Other materials and processes may be used, such as EN-P infusion alone and not heat treated, EN-P-PTFE not heat treated, and various surface conditions before the coating process. We claim all modifications and variation coming within the spirit and scope of the following claims.