GB2078669A

GB2078669A - Improvements In or Relating To a Method for Removing a Concrete Panel from a Form

Info

Publication number: GB2078669A
Application number: GB8120526A
Authority: GB
Original assignee: L & N Int As
Current assignee: L & N Int As
Priority date: 1980-07-04
Filing date: 1981-07-02
Publication date: 1982-01-13
Also published as: FI65184C; FR2486131A1; FR2486131B1; DK291280A; GB2078669B; FI812085L; DE3125492A1; DE8118905U1; FI65184B

Abstract

A method for removing a concrete panel from a form, where a lifting pressure is applied to the lower side edge of the concrete panel (1) by means of a lifting frame (7, 8) suspended in a crane hook (2). The concrete panel (1) is removed from the form (3) in a mainly vertical position by means of a cantilever foot or feet (5), and is steadied against the frame by a claw on a swivel arm (6). Since the panel is lifted from the bottom, rather than being pulled from the top, the concrete does not need a great tensile strength, and the hardening time is reduced, as the compressive strength of newly poured concrete is considerably greater than the tensile strength. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to a Method for Removing a Concrete Panel from a Form Description of Invention This invention relates to a method for removing a substantially planar concrete panel from a form and to a lifting frame for use in working the method.

In some known methods for removing concrete panels of the above-mentioned kind from forms the concrete panel has been lifted up from the form after a certain necessary period for hardening of the concrete by using draw hooks or the like that are screwed into inserts embedded in the concrete, or by using members that engage nuts threaded on bolts that are also embedded in the concrete. Furthermore, methods are known, where the concrete panel is lifted up from the form by means of suction cups mounted on the upper side of the concrete panel. These known methods have a common feature in that the tensile strength of the concrete unit must be able to resist the load exerted during lifting if the panel is not to be damaged.

As the tensile strength of newly poured concrete is minimal, it is necessary to leave the newly cast panel within the form for a relatively long hardening time when utilising the known methods, in order to avoid damaging the newly cast concrete panel, when it is removed from the form. This gives rise to relatively long operating cycles when producing concrete panels and thus leads to poor use of the form capacity. It would be desirable to use a form again as quickly as possible after a panel has been cast in the form.

Attempts have been made to accelerate the hardening of the concrete by heating the form e.g.

by leading steam under pressure over or through the form, and in this way a considerable reduction of the hardening time, and correspondingly the duration of the operational cycles, has been obtained. The addition of heat, however, is a measure demanding much energy, and thus it increases the price of the production considerably. For reasons of economy therefore this solution is not attractive.

From Swedish Published Specification No.

379,668 a method for removing substantially planar concrete panels from forms is known, where the panel is removed from the form by means of a vertical lifting pressure applied to the lower side edge of the panel. The pressure is exerted via the lower form face, which is shaped as a lifting yoke and accompanies the concrete unit to its storage place together with a vertical -supporting frame. The disadvantage of this known method is that the lifting yoke, which, as mentioned, constitutes part of the form, accompanies the concrete unit and cannot be removed until the concrete has obtained a sufficient degree of strength.

The purpose of this invention is to provide a method and a lifting frame for removing a substantially planar concrete panel from a form, by which method the hardening time prior to removal of the panel is reduced considerably in relation to the time used by hitherto known methods, and where the lifting apparatus used by this method can be used immediately for removing another concrete panel from a form.

According to one aspect of this invention there is provided a method for removing a substantially planar concrete panel from a form, said panel being cast in a substantially vertically oriented form or a form that can be brought into such a position, said method comprising the steps of removing the panel from the form by means of a vertical lifting pressure applied to the lower side edge of the panel, when the form is in a vertical position, by one or more cantilevered feet provided adjacent the bottom of a lifting frame, which is designed to co-operate with one side face of the form to support the concrete panel while it is raised, and subsequently using a holding mechanism mounted adjacent the upper part of the lifting frame to engage upper side edge of one face of the concrete panel to hold it in position when a predetermined part of the panel is free of the form.

The form may be a vertical form, or a form that can be tilted to be vertical.

By using this method, it is possible to utilise a lifting frame which is not brought into contact with the concrete panel until the panel has to be removed from the form. During the first stage of the removal of the panel it is guided by the side face of the form and the cantilevered feet at the bottom of the concrete unit. As soon as the upper edge of the panel is at an appropriate point above the upper edge of the form, the holding mechanism is activated, and then the concrete unit is held safely between the holding mechanism mounted at the top and the feet at the bottom of the lower side edge of the panel.

By applying a lifting pressure on the lower side edge of the concrete panel, the panel is only exposed to a compressive force during the removal from the form and as the compressive strength of newly poured concrete is considerably greater than the tensile strength of newly poured concrete, the desired reduction of the hardening time is obtained. Thus, it has been found in connection with the manufacture of concrete panels having 300 kg cement per m3 concrete a reduction of the hardening time of approx. 3 hours can be obtained, i.e. from 7.6 hours to approx. 4.5 hours by using a method according to the invention instead of a conventional method using lifting hooks or the like.

Preferably a plurality of cantilever feet are used, distributed transversely of the panel, said feet being able to exert pressure on parts of the lower side edge of the concrete panel, complementary shaped recesses in the lower side face of the concrete panel being desjgned releasably to receive said parts.

As a result of this the unit can be stored on beams or blocks placed side by side, as the cantilevered feet can be disengaged from the stored concrete unit by a downwards inclined movement. The lifting frame can then be used immediately for removing another concrete unit from the form.

This invention also relates to a panel whenever removed from a form by a method as described above.

The invention also relates to a lifting frame for use in working the method, said frame comprising a supporting frame with a vertical extent substantially corresponding to the extent of the concrete panel, wherein said lifting frame has one or more cantilever feet projecting laterally adjacent the bottom thereof, and adjacent the top as it has a holding mechanism projecting in the same lateral direction, which mechanism is designed as a pivotally mounted swivel arm and provided at its free end with a claw, and is designed to hold the panel against the supporting frame.

A lifting frame of this type may be built of simple mechanical elements and is therefore a sturdy and safe mechanism, which is important, when it has to be used as described here.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a sectional elevation of the concrete panel immediately before it is lifted, and Figure 2 is a corresponding view but in which the concrete panel has been partly removed from the form.

In the embodiment shown in the drawing a planar concrete panel 1 has been cast in a substantially vertical position, and is illustrated with one face leaning against a face 3 of a form.

At the bottom the panel 1 is resting on a face of a U-sectioned girder 4.

As shown in the drawings, a lifting frame comprising at least two horizontal bars 8 and at least two vertical struts 7 connected to the bars 8 has been suspended from a crane hook 2. At the bottom of said struts inwardly directed cantilevered feet 5 are provided, adapted to engage against the underside of the girder 4. In the position shown in Figures 1 and 2 the lifting frame 7, 8 also provides a lateral support for the concrete panel 1.

A lifting force is provided through the crane hook 2, and thus the lifting frame 7, 8 is moved upwardly, and consequently the concrete panel 1 slides relative to the form force 3 and 5 guided in this sliding movement by the form face 3 as the cantilevered foot 5 exerts an upwardly directed force on the concrete panel 1 through the girder 4. The upwardly directed face is a compressive force rather than a tensile or stretching force.

When the upper side edge of the concrete panel has been lifted by a sufficient distance from the form 3 (Figure 2), a swivel arm 6 pivotally mounted on the lifting frame 7, 8 can be pivoted so that a claw on the swivel arm 6 engages against the upper edge of the face of concrete panel 1 which is facing away from the lifting frame 7, 8. Thus the concrete panel 1 is held between the swivel arm 6, the lower cantilevered foot 5, and the face of the lifting frame running parallel with the concrete panel. In this position the concrete panel 1 can be carried to a storage place.

It should be noted that a method according to the invention can be performed by means of other lifting frames or other mountings, which differ from those shown in the drawing. As mentioned above, it is important that in lifting up the concrete panel away from the form a compressive load should be applied to the concrete panel which is contrary to earlier practice, when a tensile stress or stretching force has been exerted on the concrete panel during removal of the panel.

In alternative embodiments the girder 4 can be replaced, as the means supporting the lower edge of the concrete panel during the casting process, by a segment of the form face. The segment will then be fastened to the form face 3, and the means that are moved along the form face 3 during the removal of the concrete panel are then short segments aligned with the segment fastened to the form face, one opposite each strut 7. These movable means may be of trapezoidal shape and may be mounted in alignment with said segment in such a way that they can easily be released from the same.Furthermore, movable girders or girder segments 4 can be omitted completely during the lifting operation, if at the beginning of the removal procedure, parts of the segment of the form face fastened to the form face 3 are first removed, said parts of the segment being for example trapezoidal parts cut-off from the rest of the segment, and thereafter the cantilevered foot 5 is brought to engage directly against the bare parts of the lower side of the concrete panel. If this course of action is adopted the cantilevered foot 5 can be provided with a pin or the like engaging in a hole or a groove in the said lower side of the concrete panel. This contributes to a lateral support of the lower part of the concrete panel. The abovementioned omission of the girders 4 implies that the distance h between the underside of the lifting frame and the concrete unit is reduced by the height of the girders. The height of the necessary supports of the concrete panel at the storage place can then be correspondingly reduced.

Claims

1. A method for removing a substantially planar concrete panel from a form, said panel being cast in a substantially vertically oriented form or a form that can be brought into such, a position, said method comprising the steps o'f removing the panel from the form by means 3f a vertical lifting pressure applied to the lower side edge of the panel, when the form is in a vertical position, by one or more cantilevered feet provided adjacent the bottom of a lifting frame, which is designed to co-operate with one side face of the form to support the concrete panel while it is raised, and subsequently using a holding mechanism mounted adjacent the upper part of the lifting frame to engage upper side edge of one face of the concrete panel to hold it in position when a predetermined part of the panel is free of the form.

2. A method according to claim 1, wherein a plurality of cantilever feet are used, distributed transversely of the panel, said feet being able to exert pressure on parts of the lower side edge of the concrete panel, complementary shaped recesses in the lower side face of the concrete panel being designed releasably to receive said parts.

3. A lifting frame for use in working a method according to claim 1 or 2, wherein said frame comprises a supporting frame with a vertical extent substantially corresponding to the extent of the concrete panel, wherein said lifting frame has one or more cantilever feet projecting laterally adjacent the bottom thereof, and adjacent the top as it has a holding mechanism projecting in the same lateral direction, which mechanism is designed as a pivotally mounted swivel arm and provided at its free end with a claw, and designed to hold the panel against the supporting frame.

4. A method for removing a concrete panel from a form substantially as herein described with reference to the accompanying drawings.

5. A panel whenever removed from a form by a method according to claim 1, 2 or 4.

6. A lifting frame substantially as herein described with reference to and as shown in the accompanying drawings.

7. Any novel feature or combination of features disclosed herein.