Mould filling method

Abstract

A method of filling a mold with a settable material, such as a cementitious mixture, is disclosed. The mold includes a plurality of cavities that open to a top face of the mold, and is suitable for forming building elements, such as pavers, for covering surfaces. The method includes providing an additional volume per unit area of settable material to at least part of selected ones of the cavities, and compacting the settable material in at least part of all of the cavities, including the additional volume per unit area of settable material provided to the selected ones of the cavities, to substantially the same thickness. A mold and a scraper suitable for use in the method are also disclosed.

Claims

1. A method of filling a mould with a settable material using an apparatus that includes the mould comprising at least a first cavity and a second cavity, each cavity being open to a top face of the mould, a scraper comprising at least a plurality of displaceable segments, and a mechanism that produces selective upward displacement of at least one segment of the scraper while simultaneously not displacing other segments of the scraper, the method comprising: over filling the first cavity and the second cavity with the settable material, the first cavity being smaller than the second cavity; moving the scraper across the top face of the mould; upwardly displacing at least one first segment as the first segment passes over the first cavity while simultaneously not upwardly displacing at least one second segment as the second segment passes over the second cavity so that a height of a bottom edge of the first segment is above a height of a bottom edge of the second segment; and achieving a desired material density and thickness of the settable material in the first cavity and the second cavity by a selective use of vibration or tamping or both.

2. The method of claim 1, wherein the mechanism comprises at least one rail arranged on the top face of the mould adjacent an edge of the first cavity.

3. The method of claim 2, wherein the first segment deforms as the first segment passes over the at least one rail.

4. The method of claim 2, wherein the first segment is pivotally mounted to a support rod of the scraper so that the first segment pivots upward as the first segment passes over the at least one rail.

5. The method of claim 2, wherein the settable material in the first cavity is leveled to a first height, and the settable material in the second cavity is leveled to a second height, wherein the first height is greater than the second height, wherein the second height is substantially aligned with the top face of the mould.

6. The method of claim 5, wherein the first height is substantially aligned with a top surface of the at least one rail.

7. The method of claim 1, the mould further comprising at least a third cavity, the method further comprising: over filling the third cavity with the settable material; upwardly displacing at least one third segment as the third segment passes over the third cavity so that a height of a bottom edge of the third segment is below the height of the bottom edge of the first segment and above a height of the bottom edge of the second segment; achieving a desired material density and thickness of the settable material in the third cavity by a selective use of vibration or tamping or both.

8. The method of claim 7, wherein the first cavity is smaller than the third cavity, and the third cavity is smaller than the second cavity.

9. The method of claim 1, wherein the mechanism comprises one or more actuators.

10. The method of claim 9, wherein the one or more actuators are electronically controlled.

11. The method of claim 9, wherein the one or more actuators are hydraulic or pneumatic.

12. A method of filling a mould with a settable material using an apparatus that includes the mould comprising at least a first cavity and a second cavity, each cavity being open to a top face of the mould, a scraper comprising at least a plurality of displaceable segments, and a mechanism that produces selective upward displacement of at least one segment of the scraper while simultaneously not displacing other segments of the scraper, the mechanism comprising at least one rail arranged on the top face of the mould adjacent an edge of the first cavity; the method comprising: over filling the first cavity and the second cavity with the settable material; moving the scraper across the top face of the mould; upwardly displacing at least one first segment as the first segment passes over the first cavity while simultaneously not upwardly displacing at least one second segment as the second segment passes over the second cavity so that a height of a bottom edge of the first segment is above a height of a bottom edge of the second segment, the first segment deforming as the first segment passes over the at least one rail; and achieving a desired material density and thickness of the settable material in the first cavity and the second cavity by a selective use of vibration or tamping or both.

13. The method of claim 12 wherein the step of over filling includes overfilling the first cavity and the second cavity with the settable material, in which the first cavity is smaller than the second cavity.

Description

(1) Reference has already been made to FIGS. 1 to 3 of the accompanying drawings, in which:

(2) FIG. 1 is a perspective view of a set of pavers having different sizes and arranged in a pattern suitable for installation;

(3) FIG. 2 is a top view of the set of pavers of FIG. 1; and

(4) FIG. 3 shows, schematically, a sequence of steps in a known manufacturing process suitable for manufacturing a set of pavers such as that shown in FIGS. 1 and 2.

(5) The present invention will now be described, by way of example only, with reference to the remaining accompanying drawings, in which like reference numerals are used for like features, and in which:

(6) FIG. 4 is a perspective view of a mould according to an embodiment of the invention;

(7) FIG. 5 is a perspective view of a first intermediate step in a method according to the invention, using the mould of FIG. 4 and a scraper according to another embodiment of the invention;

(8) FIGS. 6(a) and 6(b) are perspective views of a subsequent intermediate step in the method illustrated in FIG. 5, from two different angles;

(9) FIG. 7 is a perspective view of a further subsequent intermediate step in the method illustrated in FIG. 5;

(10) FIG. 8 is a perspective view of a yet further subsequent intermediate step in the method illustrated in FIG. 5;

(11) FIGS. 9(a) to 9(d) are side sectional views of parts of moulds according to further embodiments of the invention;

(12) FIG. 10 is a perspective view of a mould according to another embodiment of the invention;

(13) FIG. 11 is a perspective view of a mould according to a further embodiment of the invention;

(14) FIGS. 12(a), 12(b) and 12(c) are enlarged views of the areas marked A, B and C respectively in FIG. 11;

(15) FIG. 13 is a side sectional view of part of a scraper according to another embodiment of the invention; and

(16) FIG. 14 is a side sectional view of a part of a scraper according to still another embodiment of the invention.

(17) A mould according to the present invention is shown in FIG. 4. The mould 208 includes a plurality of cavities 210 for receiving a cementitious casting mix. For clarity, only four cavities 210 are shown in FIG. 4, but in reality a greater number of cavities 210 would be provided in an arrangement suitable for casting a set of block-like pavers such as that shown in FIGS. 1 and 2 and described above.

(18) The plurality of cavities 210 includes cavities of several different sizes. In FIG. 4, two large cavities (labelled “L”), one medium-sized cavity (labelled “M”) and one small cavity (labelled “S”) are shown.

(19) The top face 212 of the mould is generally planar, except for a region surrounding the small cavity S, which is provided with lifting means in the form of a raised frame 230. The frame 230 includes two spacer bars or rails 232 arranged on opposite sides of the cavity S and orientated parallel to a filling direction (indicated by the arrow F in FIG. 4). The frame 230 is completed by two lift bars 234, extending between the rails 232 in a direction perpendicular to the filling direction F. The lift bars 234 are arranged on opposite sides of the cavity S.

(20) The cavities 210 also open to the bottom surface of the mould (not shown in FIG. 4). In use, the bottom surface of the mould rests on a pallet or similar device (not shown), so that the bottom of each cavity 210 is closed. In this way, each cavity 210 can receive and retain a quantity of cementitious casting mix.

(21) The mould 208 is filled using a process as described with reference to FIG. 3, using a feed drawer that receives the casting mix from a hopper. According to the invention, however, the feed drawer is equipped with a scraper having a modified form, as will now be described.

(22) One scraper 220 according to the invention is shown in FIG. 5. For clarity, the feed drawer is not shown in FIG. 5, but it will be understood that a scraper 220 of the type shown in FIG. 5 is mounted to the front edge of the feed drawer.

(23) The scraper 220 according to the invention includes a plurality of sections or segments 222 arranged in a common plane. Each segment 222 is made from a relatively flexible rubber material, such as natural rubber, and is mounted to the feed drawer by suitable fastening means that pass through mounting holes 224 in each segment.

(24) As explained with reference to FIG. 3, the feed drawer is moveable back and forth with respect to the mould 208 in a filling direction F. When the feed drawer is positioned above the mould 208, the casting mix 216 is transferred to the cavities 210 and to the top surface 212 of the mould 208.

(25) FIG. 5 shows an intermediate stage in the manufacturing process, in which the feed drawer (not shown) is positioned above the mould 208 and in which mix 216 fills the cavities 210. Additionally, excess mix is present on the top surface 212 of the mould 208, both directly on top of, and on the top surface 212 between, the cavities 210. The excess mix is not shown in FIG. 5 for clarity. A retaining scraper (not shown) is attached to the rear edge of the feed drawer so that the mix is retained between the scraper 220 and the retaining scraper. The retaining scraper can be of conventional form.

(26) The scraper 220 is positioned so that the bottom edge 226 of each segment 222 is in contact with the top surface 212 of the mould 208. When the feed drawer moves in the filling direction, the scraper 220 slides across the top surface 212 to remove at least a portion of the excess mix from the mould 208, and to level the mix 216 in the cavities.

(27) The segments 222 of the scraper 220 are dimensioned to match the spacing between the rails 232 of the frame 230 around the small cavity S. As shown in FIGS. 6(a) and 6(b), when the scraper 220 reaches the first lift bar 234 of the frame 230, one of the segments 222a is caused to deform by bending so that the segment 222a can pass over the lift bar 234. In this way, the bottom edge 226a of the segment 222a is lifted above the surface of the mould 208. Said another way, the bottom edge of the scraper 220, formed by the bottom edges 226 of the adjacent segments 222, changes shape to accommodate the lift bar 234.

(28) As the scraper 220 continues to travel across the mould 208, the peripheral regions of the bottom edge 226a of the deformed segment 222a ride along the rails 232 of the frame 230. In this way, the bottom edge 226a of the deformed segment 222a remains above the level of the surface of the mould 208. As a result, the mix 216 in the small cavity S is leveled to a height corresponding to the height of the mould 208 plus the height of the frame 230.

(29) Once the scraper 220 passes the second lift bar 234, adjacent the far edge of the small cavity S, the deformed segment 222a is able to return to its original shape, in line with the adjacent segments 222. This is shown in FIG. 7. The bottom edge 226 of the scraper 220 thus returns to a straight configuration, and the scraper 220 continues to level the mix 216 in the remaining cavities 110 to the height of the top surface 212 of the mould 208.

(30) Movement of the feed drawer continues until the scraper 220 reaches the edge of the mould 208, as shown in FIG. 8.

(31) During the filling process, the mix 216 settles in the cavities. The mould 208 may also be vibrated to help packing and compaction of the mix 216. As the mix 216 settles, the level of the mix may drop from the top surface 212 of the mould 208 or, in the case of the small cavity S, from the top surface of the frame 230. If necessary, the feed drawer can be passed back over the mould 208 so as to top up the level of the mix 216 in the cavities 210. It will be appreciated that the respective segment 222a of the scraper 220 will lift as the scraper 220 passes in either direction over the frame 230.

(32) After filling in this way, the small cavity S contains a greater volume, or additional volume, of mix 216 per unit area than the larger cavities L, M. In other words, by virtue of the frame 230, the depth of the mix 216 in the small cavity S is greater than the depth of the mix 216 in the larger cavities L, M. The lifting means or frame therefore acts as a depth-increasing means for the small cavities. The frame causes a smaller portion of the excess volume of the mix 216 to be removed from the small cavity S by the scraper than from the larger cavities L, M.

(33) The mix 216 in each of the filled cavities 210 is tamped by a suitable tamping device (not shown). The tamping device includes a plurality of tamping shoes corresponding to each cavity 210 that compact and compress the mix 216 so that the height of the mix 216 in each cavity 210 becomes substantially the same. While the tamping shoes are still in place atop the mix 216 in each cavity, the mould 208 is lifted upwards from the pallet. The tamping shoes are then lifted to leave the self-supporting, compacted blocks of mix 216 on the pallet. The blocks are then cured to form the finished pavers.

(34) As noted above, the mix 216 tends to fill to a lower density in the small cavities S than in the larger cavities M, L. By virtue of the invention, however, the small cavities S contain an additional volume of material per unit area to compensate for this lower filling tendency. As a result, after tamping and compaction, the density of the mix 216 in the small cavities S is comparable to the density of the mix 216 in the larger cavities M, L. Consequently, the mechanical performance of the small pavers is consistent with the mechanical performance of the larger pavers produced in the same process. In particular, the small pavers are less prone to damage at their edges and corners, since the presence of the additional volume of material forces the material to pack densely into the corners and edges of the respective cavities.

(35) It may be desirable to influence the distribution of the additional volume of material within a single cavity 210. It will be appreciated that the distribution of the additional volume of material is influenced by the position of the top surface of the respective rail 232 relative to the top face of the mould.

(36) In some circumstances, it is preferred that the additional volume of material is applied uniformly across the area of the cavity 210. This can be achieved by providing rails 232 having a uniform thickness, as shown in cross-section in FIG. 9(a). As can also be seen in FIG. 9(a), the rails 232 may include ramp portions 232a at each end, in order to help the segments 222 of the scraper 220 ride up onto the rails 232. The ramp portions 232a may instead be part of the lift bars 234.

(37) FIG. 9(b) shows an alternative arrangement, in which the rails 232 are generally wedge-shaped. In this case, more additional volume of material would be deposited towards the end of the cavity 210 closest to the thick end of the wedge shape than towards the end of the cavity 210 closest to the thin end. Such an arrangement may be useful in ensuring that the resulting paver has a uniform density in situations where, for processing reasons not associated with the lifting means, the material tends to settle or compact more densely at one end of the cavities 210 than at the other end.

(38) FIG. 9(c) shows another alternative arrangement, in which each rail 232 increases in thickness moving from the ends of the rail towards its centre. In this case, the additional material is distributed preferentially towards the middle of the cavity 210. In this example, ramp portions are not required.

(39) FIG. 9(d) shows yet another alternative arrangement, in which each rail 232 decreases in thickness moving from the ends of the rail 232 towards its centre. In this case, the additional material is distributed preferentially towards the ends of the cavity 210.

(40) It will be appreciated that, by the provision of suitably shaped rails 232, other distributions of the additional material within a cavity 210 could be achieved. Furthermore, it may be desirable to provide additional material to selected parts of every cavity in the mould using shaped rails 232 such as those shown in FIGS. 9(b), 9(c) and 9(d).

(41) A set of pavers such as that shown in FIGS. 1 and 2 can be produced using the above-described method and apparatus, using a suitably-shaped mould. FIG. 10 is a perspective view of part of such a mould 308, which is similar to the mould 208 described above with reference to FIG. 4.

(42) The mould 308 comprises several cavities 310 of each of small (S), medium (M) and large (L) sizes. A frame 330, consisting of rails 332 and lift bars 334, is provided on the top surface 312 of the mould 308 around each small cavity S. Recesses 336 are provided in the walls of the cavities 110, to form the spacers 104 on the walls of the pavers 100.

(43) The mould 308 can be manufactured by fixing rails 332 and lift bars 334 to the top surface 312 of a conventional mould in the appropriate locations, for example by welding. The rails 332 and/or the lift bars 334 could instead be formed integrally with the rest of the mould 308 during its fabrication.

(44) A set 102 of pavers 100 as shown in FIGS. 1 and 2 can be produced using the mould 308 and a suitable scraper 220 as previously described.

(45) It will be appreciated from FIG. 10 that two adjacent segments 222 of the scraper 220 will be lifted when the scraper 220 encounters a small cavity S that is oriented with its longest edge parallel to the scraper 220. One such cavity is labelled 310a in FIG. 10. In this case, each segment rides along only one rail 322. The material of the segments 222 is stiff enough so that the bottom edge of each lifted segment does not droop downwards towards the cavity 310a.

(46) For comparison, a set 102 of pavers 100 was manufactured using a mould with the same arrangement of cavities as the mould 308 shown in FIG. 10, but with lifting means provided for only some of the small cavities S. The wet density (i.e. the mass of the compacted blocks of mix after removal from the mould divided by the volume of the compacted mix) of the pavers 100 was measured.

(47) The wet density of the pavers cast in the small cavities S without lifting means was approximately 94% of the wet density of the pavers cast in the medium-sized cavities M, and approximately 93% of the wet density of the pavers cast in the large-sized cavities L.

(48) In contrast, the wet density of the pavers cast in the small cavities S with lifting means, in accordance with the invention, was approximately 103% of the wet density of the pavers cast in the medium-sized cavities M, and approximately 102% of the wet density of the pavers cast in the large-sized cavities L. Use of the present invention therefore significantly increases the packing of material in the small cavities S compared to the larger cavities M, L, resulting in improved mechanical properties of small pavers 100 produced in accordance with the invention compared to small pavers produced by conventional means.

(49) In the embodiments described above, only the small cavities S of the moulds are provided with lifting means. It will be appreciated, however, that the casting mix will also tend to pack to a lower density in the medium-sized cavities M than in the large cavities L, albeit that the phenomenon will occur to a lesser degree than in the small cavities S.

(50) Accordingly, in a further embodiment of the invention, lifting means may also be provided around the medium-sized cavities M, so as to ensure that the density of the resulting medium pavers is consistent with the density of the large pavers. A suitable mould 408 is shown in FIG. 11 and in FIGS. 12(a) to (c).

(51) In this embodiment, the mould 408 includes a plurality of cavities 410 of small (S), medium (M) and large (L) sizes, arranged in the configuration required to cast a set 102 of pavers 100 as shown in FIGS. 1 and 2. The mould 408 is suitable for use in a manufacturing process as described above, using a scraper of the type shown in FIG. 5. The mould is shown in FIGS. 11 to 12(d) in an intermediate stage of a manufacturing process in which the cavities 410 of the mould have been filed with a casting mix of cementitious material, and in which the mixture has been leveled by the action of the scraper.

(52) As shown most clearly in FIG. 12(a), which is an enlarged view of the area marked ‘A’ in FIG. 11, lifting means in the form of frames 430a are provided on the top face 412 of the mould 408 around each of the small cavities S. As in previous embodiments, each frame 430a includes two rails 432a on opposite sides of the cavity S, extending in a direction parallel to the direction F in which the feed drawer moves, and two lift bars 434a, also on opposite sides of the cavity S but extending in a direction perpendicular to the direction F (that is, parallel to the plane of the scraper in use).

(53) In use of the mould 408, the frames 430a cause displacement of segments of the scraper as they pass over the small cavities S, so that the bottom edges of the segments are lifted to a height H.sub.S above the top face 412 of the mould 408.

(54) As shown in FIG. 12(b), which is an enlarged view of the area marked ‘B’ in FIG. 11, lifting means in the form of frames 430b are also provided around each of the medium-sized cavities M. Like the frames 430a around the small cavities S, the frames 430b around the medium-sized cavities M are made up of rails 432b and lift bars 434b.

(55) In use, the frames 430b cause displacement of the segments of the scraper as they pass over the medium-sized cavities M so that the bottom edges of the segments are lifted to a height H.sub.M above the top face 412 of the mould 408. The height H.sub.M is less than the height H.sub.S to which the bottom edges of the scraper segments are lifted as they pass over the small cavities S.

(56) As shown in FIG. 12(c), which is an enlarged view of the area marked ‘C’ in FIG. 11, there are no frames around the large cavities L. Therefore, as the segments of the scraper pass over the large cavities, the bottom edges of the segments slide along the top face 412 of the mould.

(57) Because of the difference in the heights of the frames 430a, 430b, the additional volume of material per unit area provided to the small cavities S of the mould 408 is larger than the additional volume of material per unit area that is provided to the medium-sized cavities M. In this way, the tendency for the mix to compact to a lower density as the size of the cavities 410 decreases can be accurately compensated for, and the density of the pavers produced from the mould 408 is effectively independent of the size of the pavers.

(58) In the above-described embodiments of the invention, the application of an additional volume per unit area of material to selected cavities is achieved by cooperation of flexible segments of a scraper bar with lifting means provided on the top surface of the mould. It will be understood, however, that the effect of the invention could be achieved using different apparatus.

(59) For example, it is conceivable that the method of the present invention could utilise a conventional mould, with no lifting means. In such a case, the scraper may incorporate actuating means to lift or displace the segments according to the pattern of cavities in the mould, to fill the mould with additional material where desired. When actuating means are provided, the segments of the scraper may have dimensions substantially less than the width of the cavities of the mould.

(60) The actuating means could be one or more electronically controlled actuators such as motors or solenoids, or one or more hydraulic or pneumatic actuators, for example. One or more actuators could be associated with each segment of the scraper. The layout of the mould could be pre-programmed into a controller of the actuators, and the controller could be arranged to displace the necessary segments at the appropriate time as the scraper passes over the mould.

(61) In one alternative, for example, the scraper comprises a plurality of rigid plates that are pivotally mounted on a support rod or bar. The plates are arranged so that individual plates can ride up on the rails of the lifting means, and then drop down again to contact the top face of the mould when the plate moves away from the lifting means. The plates may be biased to return to their original position, for example by being spring loaded or suitably weighted.

(62) By way of illustration, FIG. 13 shows a scraper 520 of an alternative embodiment of the invention in side view. The scraper 520 includes a plurality of segments 522, one of which is shown in FIG. 13. Each segment 522 includes a rigid plate 523 mounted to a corresponding lever 525. Each lever 525 has a lower arm 525a, to which the plate 523 is mounted, an upper arm 525b, and a pivot mounting 525c. Each lever 525 is pivotally mounted to a support rod 527, by way of the pivot mounting 525c, so that each lever 525 can turn about the support rod 527 in the direction indicated by arrow V.

(63) The support rod 527 is mounted to a scraper support 529. The scraper support 529 may optionally be attached to a feed drawer (not shown).

(64) An upstanding bracket 531 is provided on the scraper support 529 so that a face of the bracket 531 opposes a face of the upper arm 525b of the lever 525. A compression spring 533 is provided between the bracket 531 and the upper arm 525b so as to bias the upper arm 525b away from the bracket 531. A guide pin 535 extends from the bracket 531 through a vertically-extending slot (not shown) in the upper arm 525b. The arrangement of the guide pin 535 and the slot is such that turning movement of the lever 525 about the slot is possible, but side-to-side movement of the lever 525 is prevented. The guide pin 535 retains the spring 533.

(65) The scraper support 529 is positioned such that, in use of the scraper, a bottom edge 526 of each plate 523 is biased against the top face 512 of the mould 508 due to the action of the spring 533. In this way, the plates 523 act to scrape excess material from the top face 512 of the mould, as previously described.

(66) The bottom edge 526 of each plate 523 can be lifted above the top face 512 of the mould 508 in order to leave additional material in a selected cavity by using lifting means (not shown) on the top face 512 of, or otherwise associated with, the mould 508 as previously described. When a plate 523 reaches the lifting means, the lever 525 turns in a clockwise direction to lift the bottom edge 526 of the plate 523. When the plate 523 leaves the lifting means, the lever 525 is caused to turn in an anticlockwise direction by the action of the spring 533 to lower the bottom edge 526 of the plate 523.

(67) In a variation of the scraper shown in FIG. 13, an actuator is provided between each bracket 531 and each corresponding upper arm 525b. Each actuator controls the position of the bottom edge 526 of the corresponding plate 523.

(68) In another alternative, the scraper comprises a plurality of segments that are arranged to reciprocate in a vertical direction. Upward movement of a plate is caused by the bottom edge of the plate rides up onto the rails of the lifting means.

(69) Again, the scraper could instead include actuators for effecting upward movement of the plates without the use of lifting means. FIG. 14 is a side view of one segment 622 of such a scraper 620. The segment 622 includes a vertical plate 623 mounted for reciprocal vertical movement with respect to a scraper support 629. A linear motion actuator 637 is attached to the scraper support 529. The actuator 637 is connected to the plate 623 by way of a linkage 639. The actuator 637 is operable to lift and lower the plate 623 relative to the scraper support 629. In this way, by operation of the actuators 623, the bottom edges 626 of the plates 623 can be raised and lowered with respect to the top face 612 of a mould 608 in use of the scraper, so as to provide an additional amount of material to the mould 608 where desired.

(70) In the above-described embodiments, the feed drawer moves relative to the mould. However, it is also conceivable that the mould could move relative to the feed drawer. A scraper according to the invention could be provided on each side of the feed drawer, so that the feed drawer could move back and forth across the mould between respective starting positions on each side of the mould.

(71) It may be desirable that a scraper according to the invention is placed in contact with the mould only at certain stages of the filling process. For example, it may be desirable to ensure that the scraper moves only in one direction with respect to the mould. In other words, it may be desirable to lift the scraper during a pass of the feed drawer across the mould in a first direction, and to lower the scraper onto the top face of the mould during a pass of the feed drawer in a second, opposite direction. In another example, when the feed drawer makes more than one pass over the mould, it may be desirable that the scraper according to the invention is only placed in contact with the mould for the final pass.

(72) To this end, a scraper according to the invention may be operable to move the scraper into and out of contact with the top face of the mould. For example, the scraper may be mounted to a support assembly that can raise the scraper so that its bottom edge clears the top face of the mould, and lower the scraper back on to the mould when required so that scraping occurs. Such a system could be used in combination with a conventional scraper, so that the mould is scraped by a conventional scraper during some stages of the mould-filing operation and by a scraper according to the invention during other stages.

(73) Instead of a feed drawer as described above, the cementitious material could be provided to the cavities by other filling means, such as by feed tubes or by manual means. In such a case, a scraper according to the invention could be mounted to a suitable scraper holder that moves relative to the mould, or that is fixed relative to a moveable mould.

(74) Whilst the examples given above relate to compensating for filling density variations due to size differences between building elements in a set, filling density variations can also occur for other reasons. For example, when cavities of the same size but with different orientations relative to the filling direction are included in a mould, cavities of a particular orientation may tend to fill to a lower density than those of another orientation. Filling density variations may also arise due to the shape of the cavities, the arrangement of the cavities in the mould, the presence and arrangement of spacer-forming recesses in the mould, the spacing between the cavities, the position of the cavities relative to the edges of the mould, the flow behaviour of the settable material in the feed drawer and around the mould, localised differences in the agitation and vibration behaviour of the mould-filling apparatus, uneven charging of the feed drawer, and so on.

(75) As will be appreciated, the present invention may be used to compensate for filling density variations in these cases also, by providing additional material to appropriate selected cavities and/or to appropriate parts of selected cavities.

(76) Furthermore, it will be understood that the scraper of the present invention is not limited to use in a method to compensate for filling density variations. By adjusting the shape of the bottom edge of the scraper as the scraper passes over the mould, for example by lifting or otherwise displacing segments of the scraper, additional material can be provided to selected parts of some or all of the cavities so as to define recesses, bars and other such features. As will be appreciated, in such cases, the tamping device used to compact the material after filling is suitably shaped to preserve the features.

(77) Although the present invention has been described with reference to cementitious material, it is equally applicable to other settable, compactable materials, particularly those having a relatively high viscosity and relatively large aggregate or particle sizes.

(78) The present invention is not limited to the manufacture of building elements for surface coverings. The invention can be used to manufacture building elements such as blocks, slabs and tiles for use in many other applications, such as for cladding, retaining walls, architectural masonry, decorative masonry, roofing, and so on.

(79) The present invention is not limited to the manufacture of building elements having uniform thickness across the whole area of the element. For example, building elements for retaining walls may include a region of increased thickness in the form of a bar extending across the width of the element on its undersurface. This feature is known in the art as a rear lip or back lip. When laid in a retaining wall, the back lip of an element engages with the back upper corner of an element in the adjacent row below, thereby providing a mechanical engagement to increase the retention capability of the wall.

(80) The present invention can be adapted to produce such elements, for example by providing a tamping shoe that is profiled to mould the back lip during compaction of the material. In this method, an additional volume per unit area of settable material would be provided to part of selected ones of the mould cavities, and then the settable material in part of all of the cavities, including the additional volume per unit area of settable material provided to the selected ones of the cavities, would be compacted to substantially the same thickness.

(81) Said another way, parts of each of the cavities corresponding to the parts of the elements that are to have the same thickness after manufacturing would be compacted to substantially the same thickness during the compaction stage. Additional settable material would be provided beforehand to the parts of the selected cavities where required, to compensate for packing density variations between the cavities before compaction.

(82) Other features that give rise to non-uniform thickness dimensions within an element, such as protrusions, cavities, recesses, weather bars, spacers and so on, can also be accommodated in the context of the invention. In general, when the resulting element does not have uniform thickness across its whole area, the invention can still be applied to a part of the area of each cavity.

(83) The present invention is applicable to several types of casting process, and is not limited to use in the manufacture of building elements. For example, as well as the process described above, in which the blocks of compacted cementitious material are removed from the mould after compaction, the invention would also offer a benefit in a process in which the blocks of compacted cementitious material remain in the mould as they harden or cure.

(84) It will be appreciated that many other variations and modifications not explicitly described above are also possible without departing from the scope of the invention as set forth in the appended claims.