US3730657A - Mold assembly for pressing concrete - Google Patents

Abstract

A mould assembly for use in a concrete pressing process includes edge formers presenting mould surfaces to the concrete filling and slidable in the direction of pressing. Friction pads, permanent magnets or non-permanent magnets, are used firstly to hold the edge formers in place whilst the concrete is being introduced into the mould and secondly to control the downward movement of the edge formers when they are engaged by the moving platen of the press. During the latter part of the pressing process the friction pads or magnets are withdrawn or deenergised (as the case may be) so that the edge formers are free to move simultaneously with the adjacent edge surfaces of the concrete filling which expands slightly after withdrawal of the press platen. The friction pads or magnets are brought into operation again for the withdrawal of wall members of which the edge formers form a part. In some embodiments of the invention the presence of a plunger which is engaged by the moving platen of the press during the latter part of the pressing process allows the friction pads or magnets to be automatically controlled.

Description

United States Patent Malet et al.

[ MOLD ASSEMBLY FOR PRESSING CONCRETE Inventors: Michael Anley Malet; David Leslie Hills, both of St. Albans, England [73] Assignee: National Research Development Corporation, London, England [22] Filed: May 28, 1971 211 App]. No.: 148,099

Related US. Application Data Primary Examiner-J. Spencer Overholser Assistant Examiner-B. D. Tobor Attorney-Cushman, Darby & Cushman 5 7 ABSTRACT A mould assembly for use in a concrete pressing process includes edge formers presenting mould surfaces to the concrete filling and slidable in the direction of pressing. Friction pads, permanent magnets or non-permanent magnets, are used firstly to hold the edge formers in place whilst the concrete is being introduced into the mould and secondly to control the downward movement of the edge formers when they are engaged by the moving platen of the press. During the latter part of the pressing process the friction pads or magnets are withdrawn or de-energised (as the case may be) so that the edge formers are free to move simultaneously with the adjacent edge surfaces of the concrete filling which expands slightly after withdrawal of the press platen. The friction pads or magnets are brought into operation again for the withdrawal of wall members of which the edge formers form a part. in some embodiments of the invention the presence of a plunger which is engaged by the moving platen of the press during the latter part of the pressing process allows the friction pads or magnets to be automatically controlled.

13 Claims, 7 Drawing Figures nun! Patented May 1, 1973 4 Shoots-Shut 1 505 03 \WS/O Patented, May 1, 1973 4 Sheets-Shoot 2 Patented May 1, 1973 3,730,657

4 Shoots-Shoot 5 MOLD ASSEMBLY FOR PRESSING CONCRETE This application is a continuation in part of our copending application Ser. No. 879,879 filed Nov. 25, 1969 US. Pat. No. 3,667,880 and entitled Pressing of Articles.

This invention relates to pressing processes, and in particular to the pressing of concrete articles such as panels of concrete, reinforced or otherwise, for build ing or engineering purposes.

A process for pressing concrete articles is already known in which a wet concrete mix is fed to a mould, levelled if necessary, for example, by vibratory means, and the mould placed between the platens of a press which applies pressure to force water out of the mix. So that the same press can be used for the production of different sizes of panel, the mould area is delimited by wall members located between the platens and reducible in the direction of pressing.

Unexpected damage to the wall faces of the pressed article can occur however during the pressing process, particularly where the article is formed with a profiled edge e.g. to accommodate a waterproof bond between adjacent panels.

According to one aspect of the present invention, there is a reducible non-resilient wall member arranged to collapse during pressing of the concrete filling and to expand simultaneously with the concrete filling after release of pressure thereby to discourage significant relative movement between the operative face(s) of the wall member and the associated face(s) of the pressing.

In one embodiment of the invention the wall member includes a movable edge former arranged to be held in place during at least the initial part of the pressing process by motion-restraining means. The motionrestraining means conveniently comprises one or more friction pad units. Each friction pad unit may, for example, comprise a friction pad, a back-up plate, spring means acting between the friction pad and the back-up plate, the assembly then including also a cam shaft arrangement engaging the free surface of the back-up plate. I

In another embodiment, in which the edge former must include magnetisable material eg ferrous material, the motion-restraining means comprises one or more magnets. The magnets may be permanent magnets (e.g. pot magnets or bar magnets), or electromagnets (e.g. switchable semi-permanent electromagnets or conventional electromagnets). Alternatively switchable magnetic chucks may be used e.g. permanent magnets which can be switched on or off at will. Where permanent magnets are used, then each magnet is conveniently movable between a first position in which it is adapted to engage with the edge former and other positions in which it is spaced from the edge former. Thus in one example the permanent magnet is connected with a back-up plate and the assembly includes spring means acting on one face of the back-up plate and a cam shaft arrangement engaging the other face of the back-up plate.

In some embodiments of the invention, the assembly I is automatically actuated during the pressing process to render the motion-restraining means inoperative over the latter part of the pressing process.

Where the assembly includes a cam-shaft arrangement to operate the friction pad units or the magnets as the case may be, the assembly conveniently includes also a plunger arranged to be actuated during the latter part of the pressing process, actuation of the plunger causing a corresponding rotation of the cam-shaft arrangement to move the back-up plate away from the edge former and thereby render the motion-restraining means inoperative.

According to another aspect of the invention there is provided a method of pressing concrete comprising the steps of providing a mould assembly reducible in the direction of pressing, filling the mould with a wet concrete mix, exerting pressure on said mix to expel excess water from the mix, removing said pressure on the mix, and thereafter expanding the mould assembly in the direction of pressing simultaneously and contiguously with the expansion of the filling in said direction.

In order that the invention may be more fully understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, of which:

FIG. 1 shows a vertical section through a first mould assembly using friction pads as the motion restraining means as it would appear immediately prior to the introduction of the material into the mould;

FIG. 2 shows a plan view ofa friction pad unit used in the embodiment of FIG. 1;

FIG. 3 shows a detail taken on the line FIG. 4 shows a vertical section through a second mould assembly using pot magnets as the motion restrainingmeans as it would appear immediately prior to the introduction of material into the mould;

, FIG. 5 shows a somewhat'diagrammatic plan view of a third mould assembly;

FIG. 6 shows a somewhat diagrammatic plan view of a fourth mould assembly; and

FIG. 7 shows a somewhat diagrammatic plan view of a fifth mould assembly.

Thus referring first to FIGS. 1 to 3, a mould assembly in accordance with the present invention comprises a reducible non-resilient wall member 12 having a fixed profile former 14 connected with a mould back 16 by a toe plate 18. The fixed former 14 has a rectangular step portion 20 arranged to receive the lower part of a movable profile former 22 which is in sliding engagement with an upper section 24 of mould back 16. In the illustrated embodiment, items14l, 16, 18 and 22 are made of iron and the weight of movable former 22 is then typically 3 lbs per foot run.

The movable former 22 is shown held in a raised position against the vertical faces of stepportion 20 and back section 24 by a plurality ofspring-loaded friction pads, such as pad 25, each forming part of a respective unit 26. In the illustrated embodiment the pads are spaced six inches apart along the length of the movable former and the biasing springs (29) are chosen so that the pads in operation exert a holding force on the movable former of, say, not less than 6 lbs per foot run of the movable former.

FIG. 2 shows a friction pad unit in more detail. As will be seen from that figure, the unit comprises a pad of friction material, a back-up plate 102 and springs 29 acting between pad 100 and plate 102. The effective rating of the springs can be varied by means of a shim 106 of appropriate thickness.- The unit is of III-III of FIG.

rectangular cross section when viewed from the front and the dimensions of pad 100 are typically two inches high by four inches long. Pad 100 may, for example, be a Ferodo friction pad or alternatively, it might, for example, be made from Fibrax brake-lining material.

A vertical plunger 30 for the assembly is provided with a vertical slot 32 (FIG. 3) carrying a roller contact 34. This contact engages with a spur 107 on a shaft 28 which extends within mould back 16. In addition, shaft 28 carries a series of cams, such as cam 36, engaging with the back-up plates of respective friction pad units 26. As already indicated FIGS. 1 and 3 show the assembly as it would appear immediately prior to the introduction of material into the mould. In this state of affairs, the plunger 30 extends proud of the upper sur face of the mould back 16 but to a lesser height than the upper edge of the movable former 22.

In operation, four mould assemblies such as that above described are located on a perforated plate 40 with filter paper 502 above the bottom platen of the press to provide the initial mould volume. Struts 41 are used to engage the outer walls of the mould backs 16 to hold them in place during pressing. Further details of the struts and perforated plate etc may be had by reference to co-pending British Patent Application No. 56110/68 or our previously referenced patent application Ser. No. 879,879 filed Nov. 25, 1969 US. Pat. No. 3,667,880.

The mould surfaces are coated with a suitable release agent, e.g. an oil such as Noxcrete or Cormix and then the mould volume is filled, levelled, etc., in the usual way whereafter the top platen of the press is brought into engagement with the upper edge of formers 22. The depth of the concrete filling at this stage is typically 220 mm. A typical mix for the filling would be in the proportions (by weight) of 14 percent Portland Cement, 13 percent Fly Ash, 40 percent of 3/16 inch sand, 33 percent of )4 inch aggregate and an initial water/cement ratio (by weight) of about 1.

Further movement of the top platen compresses the mix and displaces formers 22 further into the stepped portions of fixed formers 14. The pressing motion is completed before the lower edges of formers 22 engage with the horizontal surfaces of step portions 20. In the present example the depth of the filling at this stage would be about 200 mm., say, and the final water/cement ratio about 0.65.

During the pressing operation, the top platen engages plungers 30 when about 75 to 100 percent of the final compaction has been carried out i.e. when the depth of the filling is between 205 mm. and 200 mm. in the present instance. Downward movement of the top platen, after engagement with the plungers, depresses the plungers to rotate shafts 28 and cams 36 so as to release the holding pressure exerted by friction pads 24 on formers 22. Thus during the last part of the pressing process, the movable edge formers are held in place by the frictional forces exerted on them where they engage with mould backs 16 and fixed formers 14. Although these latter forces are sufficient to prevent the formers 22 sliding under the force of gravity over the external surfaces of the pressed article, they will allow the formers 22 to follow the slight expansion of the article (l-2 mm. in the example cited) which has been found to occur when pressure is first released on withdrawing the top platen from engagement with the mix and edge formers 22. This facility has been found to result in an improved finish to the edge faces of the pressed article and to prevent any trapped portions of the profiled article (eg at 42, 43 in FIG. 1) from breaking off (on withdrawal of the associated edge former assembly) as a result of a hitherto unpermitted expansion of the trapped portion relative to the remainder of the pressed article.

Prior to withdrawal of the mould assemblies and removal of the pressed article, the shaft 28 is turned to bring the friction pads once more into gripping relationship with formers 22. A detachable handle 108 can be attached at one end of the shaft 28 for this purpose. Alternatively a pneumatic wrench (not shown) could be used. The mould assemblies are then withdrawn perpendicularly and the pressed article can be removed from the mould floor in the usual way with a vacuum pad see, for example, co-pending British Pat. application No. 56l l0/68. To restore the mould assemblies to their illustrated positions in readiness for the next pressing operation, the shaft 28 is rotated to release the friction pads, the former 22 is raised manually and the shafts are further rotated to hold the movable formers once again in their raised positions. Alternatively a small hydraulic jack or lever can be used to raise formers 22 without withdrawing the friction pads first. Rotation of the shaft to bring the friction pads into their operative positions causes plunger 30 to be moved to its raised position in readiness for the next pressing operation.

FIG. 4 shows an alternative arrangement in which a movable edge former is initially held in place magnetically.

In more detail, the mould assembly includes a plurality of pot magnets arranged in vertically staggered fashion along the length ofa beam 10 at about every six inches of the beam length. Using the same type of movable formers 22 as in the embodiment of FIGS. 1 to 3, the pot magnets can be three-inch diameter Eclipse" magnets such as the Magnetic Holdfast (Model 94]) currently available. Each magnet comprises a powerful permanent magnet 44 housed in a cylindrical mild steel shell 45. The shell 45 is apertured to enable the magnet 44 to engage directly with the edge former 22 when the magnet is in the operative position illustrated. At its other end the shell 45 is centrally apertured to accommodate an actuating rod 46 carrying a stop nut 48 which is urged against stop girders 52 by disc springs 54. Stop girders 52 are connected together by actuating plates or back-up plates 50 engaged by the cams, such as cam 60, of a cam shaft 62 passing down the length of the beam 10. The back plate of the beam is apertured at 56 to allow axial movement of the rods 46 against the action of the disc springs 54. The plunger assembly is similar to that already described and illustrated in FIG. 3 of the accompanying drawings and hence a parallel description is not included here. The perforated plate assembly is illustrated in more detail however and shows, in addition to plate 40 and paper 502, a solid mould base 503 on the bottom platen 510 of the press, a 182 inch grillage 505, a coarse perforated plate 507 (6 inch holes in 3/16 inch plate) and a fine perforated top plate 509 (l/l6 inch holes in l/16 inch plate).

Prior to commencement of the pressing operation proper, the beams are adjusted to provide an appropriate mould for the article to be pressed and the mould is prepared and filled as before.

The pressing operation is similar to that above described for the first embodiment with the difference that the movable edge formers are initially held not by friction pads but by magnets 44. The plunger 30 is similarly connected with the cam shaft (62) by a rollerspur assembly of the type already described in relation to the first embodiment of the invention so that depression of plunger 30 moves the spur downwardly to rotate the cam shaft in an anti-clockwise sense (as viewed in FIG. 4). This rotation of shaft 62 causes the cams 60 to urge the respective back-up plates 50 away from the mould volume thereby to withdraw the magnets into their inoperative positions. As before, the shafts may be manually rotated by fitting end handles (such as detachable handle 108) or by means of a pneumatic wrench (not shown) to bring the magnets into and out of holding engagement with formers 22 as required.

Another embodiment of the invention is shown in FIG. 5. In this embodiment, the pot magnets of the second embodiment are replaced by suitable semi-permanent electro-magnets, i.e. by electromagnets which remain in an energised or de-energised state, as the case may be, without the need for an external electrical supply, but which can only be switched from one condition to the other by an externally supplied electric pulse. Thus referring now to FIG. 5, a mould assembly comprises wall members 12 each comprising items 14, 16, 18 and 22 described in relation to FIG. 1. For clarity, these individual items have not been shown in FIG. 5. Each wall member incorporates a number of switchable semi-permanent magnets 120 connected with a respective common electric plug terminal 122. Terminals 122 are associated with corresponding socket members 123 connected with a common supply through a single switch 131.

At the beginning of the pressing operation, the magnets 120 are in their energised condition and hold the moving formers 22 in their uppermost positions (as shown in FIGS. 1 and 2 for example). Concrete mix is then introduced into the 'mould and levelled etc. and the top platen of the press is brought down to depress formers 22 and compact the material in the mould. At between 75 and 100 percent of full compaction of the filling, switch 131 is operated to de-energise the magnets so that the edge formers are free to follow the slight reeirpansion of the filling that will occur after compaction has been completed and the top platen withdrawn. After re-expansion of the filling, switch 131 is operated manually to re-energise the magnets so that the wall members are again held in place by the mag nets. This enables the wall members to be withdrawn without fear of the edge formers 22 dragging downwardly on the edge faces of the pressing. If desired, terminals 122 can be unplugged from their sockets 123 during the actual withdrawal operation and need be replugged again only when it is desired to raise A controlled by a respective plunger switch 133. This is operated by the top platen during the latter part of the compaction stage of the process to de-energise the associated magnets 120. The plunger switch is manually reset to energise the electromagnets prior to withdrawal of the wall members.

Another alternative embodiment of the invention is shown in FIG. 6. In this embodiment, the switchable semi-permanent electro-magnets of the previous embodiment are replaced by conventional electro-magnets 200 which can be energised from a common source 202. The magnets associated with any one wall member are controlled by an appropriate switch 204 or by a master switch 206. The sequence of energisation and de-energisation of the magnets is carried out as described in the previous embodiment, but of course the connection with the electrical supply must be maintained whilst the magnets remain energised.

FIG. 7 shows another embodiment of the invention in which the magnetic units of the previous embodiments are replaced by switchable magnetic chucks 600 e.g. an Eclipse No. AX 510. Chucks of this type comprise permanent magnets which can be switched on or off manually by respective key mechanisms 602 at the outer faces of the units. In a modification (shown in broken lines), these key mechanisms are controlled by mechanical linkages 604'with four plungers 606 which are actuated during the latter part of the pressing step by the descending platen to switch the magnets off. The remainder of the operation is analogous to that of the earlier embodiments and will not be further described here therefore.

It will be understood that the mould assemblies described in the above examples are by way of example only and alternative designs of fixed and movable edge formers may equally well be used with the assemblies of the present invention. Examples of such designs will be apparent from a study ofU.S. Pat. No. 3,591,228 and United Kingdom Pat. No. 1,236,927.

We claim:

1. For use in a concrete pressing process, a-mould assembly comprising a wall member reducible in the direction of pressing, an edge former included in said member and which is moveable in the direction of pressing, motion-restraining means for exerting a holding force on said edge former, control means operative to bring said motion-restraining means into and out of operation, and actuator means for actuating the control means to render the motion-restraining means inoperative during the latter part of the pressing operation, whereby the reducible wall member is free to expand simultaneously with the concrete filling after release of compaction pressure on the filling thereby to discourage significant relative movement between the operative face of the wall member and the associated face of the filling.

2. An assembly as claimed in claim 1 in which the motion-restraining means comprise at least one friction pad unit.

3. An assembly as claimed in claim 2 in which the friction pad unit comprises a friction pad, a back-up plate, spring means acting between the friction pad and the back-up plate, and the assembly including a cam shaft arrangement engaging the free surface of the back-up plate.

4. An assembly-as claimed in claim 1 in which the edge former is of magnetisable material and the modon-restraining means comprises at least one magnet.

5. An assembly as claimed in claim 4 in which the magnet is a permanent magnet.

6. An assembly as claimed in claim 5 in which the permanent magnet, which has a magnetic field, is movable between a first position in which the magnetic field is adapted to engage with the edge former and other positions in which it is spaced from the edge former.

7. An assembly as claimed in claim 6 in which the permanent magnet is connected with a back-up plate and including spring means acting on one face of the back-up plate and a cam shaft arrangement engaging the other face of the back-up plate.

8. An assembly as claimed in claim 4 in which the magnet comprises a switchable magnetic chuck.

9. An assembly as claimed in claim 4 in which the electromagnets are switchable semi-permanent electromagnets.

10. An assembly as claimed in claim 1 wherein the actuator means includes means for automatically operating it during the pressing process to thereby render the motion-restraining means inoperative over the latter part of the pressing process.

11. An assembly as claimed in claim 10 in which the actuator means comprises a plunger arranged for engagement by the moving platen of the press during the latter part of the pressing process, further motion of said platen in the direction of pressing automatically operating said plunger.

12. An assembly as claimed in claim 11 in which the control means includes a cam shaft, and including means coupling the plunger with the cam shaft.

13. An assembly as claimed in claim 11 in which the motion-restraining means comprises a switchable magnet, the plunger comprises part of a plunger switch, and the control means includes an electric connection with said magnet, said plunger switch being connected positioned in said electric connection.

Claims (13)

1. For use in a concrete pressing process, a mould assembly comprising a wall member reducible in the direction of pressing, an edge former included in said member and which is moveable in the direction of pressing, motion-restraining means for exerting a holding force on said edge former, control means operative to bring said motion-restraining means into and out of operation, and actuator means for actuating the control means to render the motion-restraining means inoperative during the latter part of the pressing operation, whereby the reducible wall member is free to expand simultaneously with the concrete filling after release of compaction pressure on the filling thereby to discourage significant relative movement between the operative face of the wall member and the associated face of the filling.

2. An assembly as claimed in claim 1 in which the motion-restraining means comprise at least one friction pad unit.

3. An assembly as claimed in claim 2 in which the friction pad unit comprises a friction pad, a back-up plate, spring means acting between the friction pad and the back-up plate, and the assembly including a cam shaft arrangement engaging the free surface of the back-up plate.

4. An assembly as claimed in claim 1 in which the edge former is of magnetisable material and the motion-restraining means comprises at least one magnet.

5. An assembly as claimed in claim 4 in which the magnet is a permanent magnet.

6. An assembly as claimed in claim 5 in which the permanent magnet, which has a magnetic field, is movable between a first position in which the magnetic field is adapted to engage with the edge former and other positions in which it is spaced from the edge former.

7. An assembly as claimed in claim 6 in which the permanent magnet is connected with a back-up plate and including spring means acting on one face of the back-up plate and a cam shaft arrangement engaging the other face of the back-up plate.

8. An assembly as claimed in claim 4 in which the magnet comprises a switchable magnetic chuck.

9. An assembly as claimed in claim 4 in which the electromagnets are switchable semi-permanent electromagnets.

10. An assembly as claimed in claim 1 wherein the actuator means includes means for automatically operating it during the pressing process to thereby render the motion-restraining means inoperative over the latter part of the pressing process.

11. An assembly as claimed in claim 10 in which the actuator means comprises a plunger arranged for engagement by the moving platen of the press during the latter part of the pressing process, further motion of said platen in the direction of pressing automatically operating said plunger.

12. An assembly as claimed in claim 11 in which the control means includes a cam shaft, and including means coupling the plunger with the cam shaft.

13. An assembly as claimed in claim 11 in which the motion-restraining means comprises a switchable magnet, the plunger comprises part of a plunger switch, and the control means includes an electric connection with said magnet, said plunger switch being connected positioned in said electric connection.

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