Mold for making a masonry block

Molds and processes that permit high-speed, mass production of retaining wall blocks having patterned or other processed front faces, as well as retaining wall blocks formed by such processes. The invention permits the front face of the block to be impressed with a pattern or otherwise directly processed, to allow the formation of pre-determined block front faces, while at the same time facilitating high-speed, high-volume production of blocks. Pre-determined front faces can include front faces having pre-determined patterns and textures, front faces having predetermined shapes, front faces made from different material(s) than the remainder of the block, and combinations thereof.

FIELD OF THE INVENTION

The invention relates generally to concrete masonry blocks and the manufacture thereof. More specifically, the invention relates to concrete masonry blocks suitable for use in landscaping applications, such as retaining walls, and manufacturing processes useful in the production of such blocks.

BACKGROUND OF THE INVENTION

Modern, high speed, automated concrete block plants and concrete paver plants make use of molds that are open at the top and bottom. These molds are mounted in machines which cyclically station a pallet below the mold to close the bottom of the mold, deliver dry cast concrete into the mold through the open top of the mold, densify and compact the concrete by a combination of vibration and pressure, and strip the mold by a relative vertical movement of the mold and the pallet.

Due to the nature of such plants and the equipment used to perform this process, it is difficult to impart a natural appearance to the face of a concrete block, particularly if the block needs to include other features, such as converging side walls, and an integral locator/shear flange(s) formed on the top and/or bottom face of the block. U.S. Pat. No. 5,827,015, which is incorporated herein by reference, discloses such a concrete masonry block suitable for use as a retaining wall block, and the common method for producing such a unit in a high speed, automated concrete block plant.

There is demand for a preformed concrete masonry unit, particularly a retaining wall block with converging side walls and/or an integral locator/shear flange formed on the top and/or bottom face, and having a more natural appearing face than is achievable by the splitting process described in U.S. Pat. No. 5,827,015, or by the splitting process described in U.S. Pat. No. 6,321,740, which is also incorporated herein by reference. In particular, there is a demand for processes and tooling that will create such blocks with such faces in high-speed, automated fashion on the type of equipment commonly available in a concrete block or concrete paver plant.

SUMMARY OF THE INVENTION

The invention relates to molds and processes that permit high speed, mass production of concrete masonry units, and, in particular, retaining wall blocks. These molds and processes can be used to create relatively simple decorative front faces on such blocks, similar to the split faces described in U.S. Pat. No. 5,827,015. These molds and processes can also be used to create more complex front faces on such blocks, similar to the split and distressed faces produced by conventional tumbling or hammermill processing, or by the process described in U.S. Pat. No. 6,321,740. These molds and processes can also be used to create unique blocks that have heretofore not been available: retaining wall blocks with converging side walls and/or integral locator/shear flanges and with front faces with significantly more complex faces, including faces with significant detail and relief not heretofore available in dry cast concrete block technology.

In a preferred embodiment, the resulting blocks have patterned front faces that simulate natural stone, as well as upper and lower faces, a rear face, opposed converging side faces, and a flange extending below the lower face. Blocks having this construction, when stacked in multiple courses with other similarly constructed retaining wall blocks, permits construction of serpentine or curved retaining walls that appear to have been constructed with naturally-occurring, rather than man-made, materials.

One aspect of this invention is that a mold made in accordance with the invention is arranged so that the portion of the block that will be the front face when the block is laid is facing the open top of the mold cavity during the molding process. This orientation permits the front face of the block to be formed by the action of a patterned pressure plate (“stripper shoe”) in a high-speed, masonry block or paver plant. The stripper shoe can be provided with a very simple pattern, a moderately complex pattern, or a highly detailed, three-dimensional pattern with significant relief, simulating naturally occurring stone. Molding the block in this orientation also makes the block face readily accessible for other processing to affect the appearance of the face, including the application of specially-selected aggregate and/or color pigments to the face.

Another aspect of this invention is that a side wall of the mold has an undercut portion adjacent the open bottom of the mold cavity. This undercut portion cooperates with the pallet that is positioned under the mold to form a subcavity of the mold. In a preferred embodiment, this subcavity forms the locator/shear flange on the surface of the block that will be the bottom of the block as laid.

Another aspect of this invention is that at least one of the side walls of the mold is angled from vertical, to form a side wall of the block as laid that includes a portion that converges toward the opposite side wall as it gets closer to the rear face of the block. This angled mold side wall is moveable, so that it moves into a first position to permit the mold to be filled with dry cast concrete and the concrete to be compacted and densified, and moves into a second position to permit the densified concrete to be stripped from the mold without interference from this mold side wall. In a preferred embodiment, the opposed mold side wall is similarly moveable, so that at least portions of the opposed side walls of the resulting block converge towards each other as they approach the rear of the block.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Overview

The present invention provides a process for producing a concrete masonry block, as well as a block resulting from the process, and a mold and mold components used to implement the process, in which a pre-determined three-dimensional pattern is impressed into the face of the block, and the front face of the block can be otherwise directly processed or worked so that a pre-determined block front face can be produced in a standard dry cast concrete block or paver machine. Direct processing or working of the front face includes molding, shaping, patterning, impressing, material layering, combinations thereof, and other processes in which the texture, shape, color, appearance, or physical properties of the front face can be directly affected. Further, the process can be implemented using multiple-cavity molds to permit high-speed, high-volume production of the masonry blocks on standard dry cast concrete block or paver equipment. Moreover, use of the inventive process and equipment eliminates the need for a splitting station, and/or a hammermill station, and/or a tumbling station, and the additional equipment and processing costs associated with such additional processing stations.

The blocks produced by the process of the present invention can have a configuration that allows construction of walls, including serpentine or curved retaining walls, by stacking a plurality of blocks, having the same or different pre-determined front faces, in multiple courses, with an automatic set-back and shear resistance between courses.

The preferred embodiment will be described in relation to the impressing of a pre-determined, three-dimensional, rock-like pattern into the front face of a retaining wall block. As a result, the block, and a wall that is constructed from a plurality of the blocks when stacked into courses, appears to have been constructed with “natural” materials. The process described herein could also be used to construct masonry blocks that are used in the construction of building walls, as well as for concrete bricks, slabs and pavers.

Masonry Block

A masonry block10according to the present invention is illustrated inFIGS. 1-3. The block10comprises a block body having a front face12, a rear face14, an upper face16, a lower face18, and opposed side faces20,22. The block10is formed from a cured, dry cast, no slump masonry concrete. Dry cast, no slump masonry concrete is well known in the art of retaining wall blocks.

The front face12, as shown inFIGS. 1-3, is provided with a pre-determined three-dimensional pattern. The pattern on the front face12is preferably imparted to the front face during molding of the block10by the action of a moveable stripper shoe (to be later described) having a pattern that is the mirror image of the front face of the block.FIGS. 12A-Care photos of blocks according to the present invention having patterned front faces.

The pattern that is imparted to the front face12can vary depending upon the desired appearance of the front face. Preferably, the pattern simulates natural stone so that the front face12appears to be a natural material, rather than a man-made material. The particular stone pattern that is used will be selected based on what is thought to be visually pleasing to users of the blocks. By way of example, the face of the block can be impressed with a pattern that appears to be a single stone, such a river rock. Or the block can be impressed with a pattern that appears to be multiple river rocks in a mortared together pattern. Or the block can be impressed with a pattern that simulates a single piece of quarry rubble, or multiple pieces of field stone, stacked in layers. Endless possibilities are available. By providing stripper shoes with a variety of different patterns, the resulting patterns on the blocks can be varied by changing stripper shoes.

The resulting detail and relief that can be provided on the front face is greater than that which can be provided on a front face of a block that results from conventional splitting techniques, and the tumbling, hammermilling and other distressing techniques previously described. The relief on the patterned front face12, measured from the lowest point to the highest point, is preferably at least 0.5 inches, and more preferably at least 1.0 inches.

In the preferred embodiment, the front face12lies generally in approximately a single plane between the side faces20,22, as opposed to the common, three-faceted and curved faces that are frequently seen in split-face retaining wall blocks, although such multi-faceted and curved faces can be easily produced with the present invention. As shown inFIG. 3, the front face12is provided with a slight rearward slant, i.e. inclined at an angle a from the bottom lower face18to the upper face16. Preferably, α is about 10 degrees. As a result, front and rear faces12,14are separated by a distance d1adjacent the lower face18and by a distance d2adjacent the upper face16, with d1being larger than d2. In the preferred embodiment, d1is about 7.625 inches and d2is about 6.875 inches. The width d3is preferably about 12.0 inches. It is also contemplated that the front face12between the side faces20,22can be faceted, curved, or combinations thereof. In these embodiments, the front face would also have a slight rearward slant.

Typically, when retaining wall blocks are stacked into set-back courses to form a wall, a portion of the upper face of each block in the lower course is visible between the front face of each block in the lower course and the front face of each block in the adjacent upper course. The visible portions of the upper faces creates the appearance of a ledge. And, in the case of dry cast masonry blocks, this ledge typically has an artificial appearance. By providing a rearward incline angle to the front face12of the block10, the appearance of the ledge can be reduced or eliminated, thus enhancing the “natural” appearance of the resulting wall.

The front face12also includes radiused edges24a,26bat its junctures with the side faces. The radiused edges24a,26bare formed by arcuate flanges provided on the stripper shoe. The radius of the edges24a,26bis preferably about 0.25 inches. The radiused edges24a,26bshift the contact points between the sides of the block10with adjacent blocks in the same course, when a plurality of blocks are laid side-by-side, away from the front face12, and result in better contact between the blocks to prevent soil “leakage” between adjacent blocks. If desired, the top and bottom edges at the junctures between the front face12and the upper and lower faces16,18could also be radiused, similar to the radiused edges24a,24b, by the provision of arcuate flanges on the stripper shoe.

With reference toFIGS. 1-3, the rear face14of the block10is illustrated as being generally planar between the side faces20,22and generally perpendicular to the upper and lower faces16,18. However, it is contemplated that the rear face14could deviate from planar, such as by being provided with one or more notches or provided with one or more concavities, while still being within the scope of the invention. The width d4of the rear face14is preferably about 8.202 inches.

Further, the upper face16is illustrated inFIGS. 1-3as being generally planar, and free of cores intersecting the upper face16. When a plurality of blocks10are stacked into courses to form a wall structure, the upper face16of each block is in a generally parallel relationship to the upper faces16of the other blocks.

The lower face18of the block10is formed so as to be suitable for engaging the upper face16of the block(s) in the course below to maintain the generally parallel relationship between the upper faces of the blocks10when the blocks are stacked into courses. In the preferred embodiment, as illustrated inFIGS. 1-3, the lower face18is generally planar and horizontal so that it is generally parallel to the upper face16. However, other lower faces can be used, including a lower face that includes one or more concave portions or one or more channels over portions of the lower face18. The distance d6between the upper face16and the lower face18is preferably about 4.0 inches.

In the preferred block10, the side faces20,22are generally vertical and join the upper and lower faces16,18and join the front and rear faces12,14, as seen inFIGS. 1-3. At least a portion of each side face20,22converges toward the opposite side face as the side faces extend toward the rear face14. Preferably the entire length of each side face20,22converges starting from adjacent the front face18, with the side faces20,22being generally planar between the front and rear faces12,14. However, it is possible that the side faces20,22could start converging from a location spaced from the front face12, in which case the side faces20,22would comprise a combination of straight, non-converging sections extending from the front face and converging sections leading from the straight sections to the rear face14. The converging portion of each side face20,22preferably converges at an angle β of about 14.5 degrees.

Alternatively, the block10can be provided with only one converging side face or side face portion, with the other side face being substantially perpendicular to the front and rear faces12,14. A block with at least one converging side face permits serpentine retaining walls to be constructed.

The block10also preferably includes a flange26that extends below the lower face18of the block, as seen inFIGS. 1-3. The flange26is designed to abut against the rear face of a block in the course below the block10to provide a pre-determined set-back from the course below and provide course-to-course shear strength.

With reference toFIG. 3A, it is seen that the flange26includes a front surface28that engages the rear face of the block(s) in the course below. The flange26also includes a bottom surface30, a front, bottom edge32between the front surface28and the bottom surface30that is arcuate, and a rear surface34that is extension of, and forms a portion of, the rear face14of the block. The front surface28is preferably angled at an angle γ of about 18 degrees. The angled front surface28and the arcuate edge32result from corresponding shaped portions of the mold, which construction facilitates filling of the mold with dry cast masonry concrete and release of the flange26from the mold.

As shown inFIGS. 1 and 2, the flange26extends the entire distance between the side faces20,22. However, the flange need not extend the entire distance. For example, the flange could extend only a portion of the distance between the side faces, and be spaced from the side faces. Alternatively, two or more flange portions separated from each other by a gap could be used.

With reference toFIG. 3A, the depth d7of the flange26is preferably about 0.750 inches. This depth defines the resulting set-back of the block relative to the course below. Other flange dimensions could be used, depending upon the amount of desired set-back. The rear surface34preferably has a height d8of about 0.375 inches.

The concepts described can also be applied to masonry blocks that are used in the construction of building walls, as well as to concrete bricks, slabs and pavers. In these cases, it is contemplated and within the scope of the invention that neither side face of the block or brick would converge, and that the flange would not be present. However, the patterned front face would provide the block or brick a decorative appearance.

Block Structures

The masonry block10of the present invention may be used to build any number of landscape structures. An example of a structure that may be constructed with blocks according to the invention is illustrated in FIG.4. As illustrated, a retaining wall40composed of individual courses42a-cof blocks can be constructed. The blocks used in constructing the wall40can comprise blocks having identically patterned front faces, or a mixture of blocks with different, but compatibly-patterned faces. The height of the wall40will depend upon the number of courses that are used. The construction of retaining walls is well known in the art. A description of a suitable process for constructing the wall40is disclosed in U.S. Pat. No. 5,827,015.

As discussed above, the flange26on the block10provides set-back of the block from the course below. As a result, the course42bis set-back from the course42a, and the course42cis set-back from the course42b. Further, as discussed above, the rearward incline of the front face12reduces the ledge that is formed between each adjacent course, by reducing the amount of the upper face portion of each block in the lower course that is visible between the front face of each block in the lower course and the front face of each block in the adjacent upper course.

The retaining wall40illustrated inFIG. 4is straight. However, the preferred block10construction with the angled side faces20,22permits the construction of serpentine or curved retaining walls, such as that disclosed in U.S. Pat. No. 5,827,015.

Block Forming Process

An additional aspect of the invention concerns the process for forming the block10. With reference toFIG. 5, an outline of the process is shown. Generally, the process is initiated by mixing the dry cast masonry concrete that will form the block10. Dry cast, no slump masonry concrete is well known in the art of retaining wall blocks. The concrete will be chosen so as to satisfy pre-determined strength, water absorption, density, shrinkage, and related criteria for the block so that the block will perform adequately for its intended use. A person having ordinary skill in the art would be able to readily select a material constituency that satisfies the desired block criteria. Further, the procedures and equipment for mixing the constituents of the dry cast masonry concrete are well known in the art.

Once the concrete is mixed, it is transported to a hopper, which holds the concrete near the mold. As discussed below, the mold assembly50includes at least one block-forming cavity56suitable for forming the preferred block. The cavity56is open at its top and bottom. When it is desired to form a block, a pallet is positioned beneath the mold so as to close the bottom of the cavity56. The appropriate amount of dry cast concrete from the hopper is then loaded, via one or more feed drawers, into the block-forming cavity through the open top of the cavity56. The process and equipment for transporting dry cast masonry concrete and loading a block-forming cavity are well known in the art.

The dry cast masonry concrete in the cavity56must next be compacted to densify it. This is accomplished primarily through vibration of the dry cast masonry concrete, in combination with the application of pressure exerted on the mass of dry cast masonry concrete from above. The vibration can be exerted by vibration of the pallet underlying the mold (table vibration), or by vibration of the mold box (mold vibration), or by a combination of both actions. The pressure is exerted by a compression head, discussed below, that carries one or more stripper shoes that contact the mass of dry cast masonry concrete from above. The timing and sequencing of the vibration and compression is variable, and depends upon the characteristics of the dry cast masonry concrete used and the desired results. The selection and application of the appropriate sequencing, timing, and types of vibrational forces, is within the ordinary skill in the art. Generally, these forces contribute to fully filling the cavity56, so that there are not undesired voids in the finished block, and to densifying the dry cast masonry concrete so that the finished block will have the desired weight, density, and performance characteristics.

Pressure is exerted by a stripper shoe94that is brought down into contact with the top of the dry cast masonry concrete in the cavity56to compact the concrete. The stripper shoe94acts with the vibration to compact the concrete within the cavity56to form a solid, contiguous, pre-cured block. In the preferred embodiment, the stripper shoe also includes a three-dimensional pattern96on its face for producing a corresponding pattern on the resulting pre-cured block as the stripper shoe compacts the concrete. Preferably, the portion of the pre-cured block contacted by the patterned shoe face comprises the front face of the block.

After densification, the pre-cured block is discharged from the cavity. Preferably, discharge occurs by lowering the pallet82relative to the mold assembly, while further lowering the stripper shoe94through the mold cavity to assist in stripping the pre-cured block from the cavity. The stripper shoe is then raised upwardly out of the mold cavity and the mold is ready to repeat this production cycle.

If the block is to have one or more converging side walls, then corresponding mold side walls, as described in detail below, must be provided in the mold. Such mold side walls must be adapted to move into a first position to permit filling of the mold, and compaction and densification of the dry cast masonry concrete, and must be adapted to move into a second position to permit stripping of the mold without damage to the pre-cured block.

Once the pre-cured block has been completely removed from the cavity, it can be transported away from the mold assembly for subsequent curing. The block may be cured through any means known to those of skill in the art. Examples of curing processes that are suitable for practicing the invention include air curing, autoclaving, and steam curing. Any of these processes for curing the block may be implemented by those of skill in the art.

Once cured, the blocks can be packaged for storage and subsequent shipment to a jobsite, and can then be used with other cured blocks in forming a structure, such as the retaining wall40in FIG.5.

Mold Assembly

The mold assembly50according to the present invention that is used to practice the invention is illustrated inFIGS. 6-10. The mold assembly50is made from materials that are able to withstand the pressure that is applied during formation of the pre-cured block, as well as provide sufficient wear life.

The mold assembly50is constructed so that the pre-cured block is formed with its front face facing upward, and with its rear face supported on the pallet82positioned underneath the mold assembly50. This permits pattern impressing or other direct processing to occur on the front face12of the block, to allow the formation of pre-determined block front faces. Pre-determined front faces can include front faces having pre-determined patterns and textures, front faces having pre-determined shapes, front faces made from different material(s) than the remainder of the block, and combinations thereof.

Further, the mold assembly50is designed so that a pre-cured block, including a block with a lower lip or flange and/or one or more converging side faces, can be discharged through the bottom of the mold assembly.

Referring toFIG. 6, the mold assembly50comprises a mold52and a compression head assembly54that interacts with the mold52as described below. The mold52comprises at least one block-forming cavity56defined therein. In one preferred embodiment, the mold52is sized for use in a standard, “three-at-a-time” American block machine, having a standard pallet size of approximately 18.5 inches by 26.0 inches, which is sized for making three blocks with their upper faces on the pallet. The mold52comprises a plurality of generally identical block-forming cavities56.FIG. 7illustrates five block-forming cavities56arranged side-by-side, which is possible when making the preferred size blocks on a standard “three-at-a-time” pallet. Of course, larger machines that use larger pallets are in use, and this technology can be used in both larger and smaller machines. The number of possible mold cavities in a single mold depends upon size of the machine and the size of the pallet. A plurality of block-forming cavities56allows increased production of blocks from the single mold52.

With reference toFIG. 7, the cavities56are formed by division plates58, including a pair of outside division plates, a plurality of inside division plates, and a pair of end liners60that are common to each cavity56. The use of outside and inside division plates and end liners to form a block-forming cavity in a mold is known to those of skill in the art. The division plates and end liners form the boundaries of the block cavities and provide the surfaces that are in contact with the pre-cured blocks during block formation, and are thus susceptible to wear. Thus, the division plates and end liners are typically removably mounted within the mold52so that they can be replaced as they wear or if they become damaged. The techniques for mounting division plates and end liners in a mold to form block cavities, and to permit removal of the division plates and end liners, are known to those of skill in the art.

In the preferred embodiment, the division plates58form the upper and lower faces16,18of the blocks10, while the end liners60form the side faces20,22. For convenience, the division plates and end liners will hereinafter (including in the claims) be referred to collectively as the side walls of the cavities. Thus, side walls refers to division plates and end liners, as well as to any other similar structure that is used to define the boundaries of a block-forming cavity.

Referring now toFIG. 8, a portion of a single block-forming cavity56is illustrated. The cavity56defined by the side walls58,60has an open top64and an open bottom66. As shown, the top ends of the side walls60(e.g. the end liners) are connected by pivots62to suitable surrounding structure of the mold52to allow the side walls60to pivot between the closed position shown inFIG. 8, where the side walls60converge toward each other, to a retracted position where the side walls60are generally vertical and parallel to each other (not shown). In the retracted position, the bottom of the cavity56is at least as wide as the top of the mold cavity, which allows the pre-cured block to be discharged through the open bottom. When only a portion of either side face20,22of the block converges, only a corresponding portion of the side walls60will be pivoted. The side wall58that forms the lower face of the block10is also illustrated inFIG. 8, while the other side wall58that forms the upper face of the block is not shown.

Pivoting of the side walls60is required in order to form the preferred block10. As discussed above, the block10is formed “face-up” in the mold52with its converging side faces formed by the side walls60. Thus, the converging side walls60, when they are angled as illustrated inFIG. 8, shape the converging side faces20,22of the pre-cured block. However, the front portion of the pre-cured block is wider than the rear portion of the block. In order to be able to discharge the pre-cured block through the open bottom66, the side walls60must pivot outward to enable downward movement of the pre-cured block through the open bottom.

Biasing mechanisms68are provided to maintain the side walls60at the converging position during introduction of the concrete and subsequent compacting of the dry cast masonry concrete, and which allow the side walls60to pivot to a vertical position during discharge of the pre-cured block. Preferably, a single biasing mechanism68is connected to each side wall60that is common to all cavities56, so that the movement of each side wall60is controlled via a common mechanism (see FIG.7). The biasing mechanisms68are illustrated as comprising air bags, which will be controlled through the use of air or similar gas. Suitable inlet and outlet ports for the air will be provided, as will a source of high pressure air. The use of biasing mechanisms other than air bags is also possible. For example, hydraulic or pneumatic cylinders could be used.

When pressurized with air, the air bags will force the side walls60to the position shown in FIG.8. When it comes time to discharge the pre-cured block(s), the pressurized air is vented from the air bags, which allows the side walls60to pivot outward under force of the pre-cured block as the pre-cured block is discharged through the open bottom when the pallet is lowered. During block discharge, the side walls60remain in contact with the side faces of the pre-cured block. Alternatively, biasing mechanisms, such as coil springs, can be connected to the side walls60to force the side walls to the retracted position when the air bags are vented. In this case, as the pallet82starts to lower to begin block discharging, the side walls60will be forced to the retracted position, and the side walls60will not contact the side faces of the block during discharge. After discharge, the side walls60are returned to the closed, angled position by re-pressurizing the air bags.

Rather than pivoting the side walls60, it is possible to use other mechanisms to permit movement of the side walls60to allow discharge of the pre-cured block. For example, the side walls60could be mounted so as to slide inwards to the position shown in FIG.8and outwards to a position where the bottom of the cavity56is at least as wide as the top of the mold cavity. The sliding movements could be implemented using a track system in which the side walls are mounted.

As shown inFIG. 8, each side wall60includes a shaping surface76that faces the cavity56. The shaping surfaces76are substantially planar. The result is the formation of substantially planar side faces20,22of the block10.

Referring now toFIG. 9, the side walls58that form the upper and lower faces16,18of the block10are illustrated. The side walls58, which are fixed and not moveable during the molding process, are substantially vertical.

The side wall58that forms the upper face16(the left side wall58inFIG. 9) includes a shaping surface78that faces the cavity56. The surface78is substantially planar, which results in the formation of a substantially planar upper face16.

The side wall58that forms the lower face18(the right side wall58inFIG. 9) includes an undercut, or “instep”, portion80at the bottom edge thereof adjacent the open bottom66. The undercut portion80, in combination with the pallet82that is introduced under the mold52to temporarily close the open mold bottom66during the molding process, defines a flange-forming subcavity of the cavity56. The flange-forming subcavity has a shape that results in the formation of the flange26on the block10.

In particular, the undercut portion80includes a shaping surface84that forms the front surface28of the flange26, a shaping surface86that forms the bottom surface30of the flange, and a shaping surface88that forms the edge32of the flange26. The portion of the flange26that is an extension of the rear face14is formed by and on the pallet82, along with the remainder of the rear face14. The shape of the surfaces84and86facilitate filling of the undercut portion80with the concrete during introduction and subsequent compacting of the concrete so that the flange26is completely formed, as well as aid in release of the flange26from the surfaces84,86during block discharge.

In the case of a block having a flange on the lower face and no converging side faces, the side walls60would be oriented vertically instead of being converging. Further, in the case of a block without a flange on the lower face and with converging side faces, the undercut80would not be present. In the case of a block without a flange on the lower face and without converging side faces, the undercut80would not be present and the side walls60would be oriented vertically.

Returning toFIGS. 6 and 8, the head assembly54is seen to include a compression head90in the form of a plate. The head90is actuated by an actuating mechanism in a manner known in the art so that the head90is moveable vertically up and down to bring about compaction of the dry cast masonry concrete in the mold cavities56and to assist in stripping the pre-cured blocks from the mold52.

Connected to and extending from the bottom of the head90are a plurality of stand-offs92, one stand-off for each block-forming cavity56as shown in FIG.6. The stand-offs92are spaced from each other, with the longitudinal axis of each stand-off oriented perpendicular to the plane of the head90and extending generally centrally through the block-forming cavity56.

A stripper shoe94, illustrated inFIGS. 6,8,9and10, is connected to the end of each stand-off92. The stripper shoe94is rectangular in shape and is dimensioned so that it may enter the respective cavity56through the open top to contact the concrete to compact the concrete, and to travel through the cavity during discharge of the pre-cured block. The dimensions of the stripper shoe94are only slightly less than the dimensions of the open top64of the cavity56, so that the shoe94fits into the cavity56with little or no spacing between the sides of the shoe94and the side walls58,60defining the cavity. This minimizes escape of concrete between the sides of the shoe94and the side walls58,60during compression, and maximizes the front face area of the block that is contacted by the shoe94.

Flanges98a,98bare formed on opposite ends of the face of the stripper shoe94, as best seen in FIG.10. The flanges98a,98bare arcuate to produce the rounded edges24a,26bon front face12of the block. If desired, arcuate flanges can be provided on the two remaining ends of the stripper shoe94, in order to produce upper and lower rounded edges on the front face12.

As discussed above, a face of the shoe94is preferably provided with a pre-determined pattern96so that, as the shoe94compacts the concrete, the pattern is imparted to the front face of the block. The pattern96preferably simulates natural stone, so that the front face of the resulting block simulates natural stone thereby making the block appear more natural and “rock-like”. A variety of different patterns96can be provided on the shoe94, depending upon the appearance of the front face that one wishes to achieve. In addition to, or separate from, the pattern96, the face of the shoe94can be shaped to achieve a faceted or curved block front face. Indeed, the face of the shoe94can be patterned and/or shaped in any manner which one desires in order to achieve a desired appearance of the block front face.

FIG. 10provides an example of a pre-determined pattern96that can be provided on the shoe94. The pattern96simulates natural stone. The pattern96is preferably machined into the shoe face based upon a pre-determined three-dimensional pattern. An exemplary process for creating the pre-determined pattern96on the shoe face is as follows.

Initially, one or more natural rocks having surfaces which one considers to be visually pleasing are selected. One or more of the rock surfaces are then scanned using a digital scanning machine. An example of a suitable scanning machine for practicing the invention is the Laser Design Surveyor 1200 having an RPS 150 head, available from Laser Design Incorporated of Minneapolis, Minn. The Laser Design Surveyor 1200 has a linear accuracy of 0.0005″ in the XYZ coordinates, and a resolution of 0.0001″. The scan data for the rock surfaces is collected and manipulated to blend the scan data for each scanned surface together to create a seamless data blend of the various rock surfaces. The software for collecting and manipulating the scan data is known in the art, for example, DataSculpt available from Laser Design Incorporated of Minneapolis, Minn.

The data blend is then scaled and/or trimmed to the dimension of the block front face. The scaled data blend represents a single rock surface blended from the individually scanned rock surfaces. The scaled blend data is then output to a three or four axis, numerically controlled milling machine for milling of the stripper shoe94. A suitable milling machine for practicing the invention is the Mikron VCP600 available from Mikron AG Nidau of Nidau, Switzerland. The milling machine mills a mirror image of the rock surface, represented by the scaled data blend, into the face of the stripper shoe94, which is suitably mounted in the milling machine in known fashion. The result is a predetermined pattern milled into the face of the shoe94, which, in turn, results in a pre-determined pattern impressed into the front face of the block when the shoe94compacts the concrete.

This process can be repeated to produce additional shoes having the same or different face patterns. This is advantageous because the patterned face of each shoe is subject to wear, and the shoe will need to be replaced when the pattern becomes excessively worn. Further, by forming a variety of different pre-determined shoe patterns, a variety of different block front face appearances can be achieved. Other shoe patterns can be formed by combining the scanned surfaces of a plurality of different rocks.

As discussed above, the resulting detail and relief that is provided on the block front face can be significantly greater than the detail and relief that is provided on the front face of a block that results from conventional splitting techniques, and the other front face distressing techniques discussed above. If desired, the scan data can be manipulated in order to increase or decrease the relief that is milled into the shoe face, which will alter the relief that is ultimately provided on the block front face.

It is known in the art that dry cast masonry concrete may have a tendency to stick to mold surfaces, such as the patterned surface of the stripper shoe94. Various techniques to enhance the release of the stripper shoe94from the dry cast concrete are known, and one or more of them may need to be employed in the practice of this invention. For example, the pattern formed on the stripper shoe has to be designed to enhance, rather than inhibit, release. In this regard, appropriate draft angles have to be employed in the pattern. The pattern-forming techniques described above permit manipulation of the scanned images to create appropriate draft angles. Release agents, such as a fine mist of oil, can be sprayed onto the stripper shoe between machine cycles. Head vibration can be employed to enhance release. And heat can be applied to the stripper shoe to enhance release. Heating mold components to prevent sticking of dry cast masonry concrete is known in the art. In the present invention, due to the detailed pattern that is to be imparted to the block front face, it is even more important to prevent sticking. In particular, it is important to be able to control the temperature of the shoe so that the temperature can be maintained at selected levels.

Preferably, as shown diagrammatically inFIG. 11, a heater100is connected to the shoe94for heating the shoe. The heater100is controlled by a temperature control unit102. A thermocouple104mounted on the shoe94senses the temperature of the shoe, and relays that information to a power control unit106that provides electrical power to the control unit102and the heater100. The system is designed such that, when the temperature of the shoe94falls below a pre-determined level as sensed by the thermocouple104, power is provided to the heater100to increase the shoe temperature. When the shoe temperature reaches a predetermined level, as sensed by the thermocouple, the heater100is shut off. Thus, the shoe temperature can be maintained as selected levels. Preferably, the control unit102is designed to allow selection of the minimum and maximum temperature levels, based on the dry cast masonry concrete that is being used. In the preferred embodiment, the surface temperature of the stripper shoe94is maintained between 120° F. and 130° F.