IES20070398A2 - A bond breaking device - Google Patents

Abstract

The present invention is concerned with a bond breaking device for use in breaking the bond formed between a moulded product such as a thin walled concrete tank and the mould used to form the product, the device preferably being incorporated into the mould about a base rim thereof and comprising an annular band about the rim and displaceable relative thereto by means of a number of hydraulic rams in order to separate the moulded product from the mould. <Figure 2>

Description

stems η asq m ? Bond Breaking Deviefe j· ef Ά The present invention relates to a bonT Bre'a'krng device and, in particular, to a device for breaking the bond formed between a moulded structure, such as a concrete wall tank, and a mould during the manufacturing process .

Steel fibre reinforcement, wherein the steel fibre is added to the concrete at the mixing stage, has enabled the production of concrete tanks which are extremely lightweight for any given volume and which are of minimum wall thickness. However, the preferred known production process gives rise to manufacturing difficulties which are not experienced in the manufacture of thicker walled tanks.

In general, established manufacturing methods for thicker walled tanks involve casting the tank in the upright position, floor first, followed by the wall, after initial set of the floor. A number of such systems are known where the tank is manufactured in the inverted position in a single pour. Although these attributes are preferable for quality and productivity, such tanks are traditionally reinforced or are of sufficient wall thickness not to require any reinforcement. The tanks are fundamentally heavy and their manufacturing systems cannot be adapted to the manufacture of thin walled tanks. In particular, the known methods are only applicable to products with a low volume to weight ratio. For example, such known methods may be used to produce a tank of 150mm wall Jl 0 7 0 3®® thickness whereas a thin walled tank would typically have a similar volume with only 80mm or even 60mm wall thickness .

The present invention has been made from a consideration of the unsuitability of such known methods for thin walled concrete tank production and in order to provide an improved manufacturing system designed for the in-service condition and adapted for production of thin walled tanks. The benefits of reducing weight in handling, transport and placing in position are considerable.

In the development of a production process for the manufacture of lightweight or thin walled concrete tanks, great difficulty has been experienced in the demoulding operation. Overcoming adhesion, friction and vacuum effects between the newly formed product and the mould often results in destruction or damage to the product. Recognising that the greatest rate of strength gain in concrete is in the compressive sense, the bond breaking device of the invention has been designed to stress the product primarily in compression during extraction from the moulds.

According to the invention there is provided a bond breaking device incorporated into a mould for breaking the bond formed between a moulded structure and a mould during the manufacturing process, the mould comprising a base rim and a mould wall extending upwardly from the base rim to define the mould shape for the structure and the bond breaking device comprising a band extending around the mould wall and overlying the rim and a plurality of rams located at intervals around the mould and extending transversely to the rim to abut the underside of the band such that actuation of the rams causes the band to move relative to the rim.

Preferably, the rams comprise hydraulic rams. Preferably, the bond breaking device is incorporated into a mould comprising a base support, an annular base rim supported thereon, a circular mould wall extending upwardly from the base rim and a floor spanning the upper edge of the wall to define the mould shape for the structure.

Preferably, the band is a circular band or annulus. Preferably, the band is substantially parallel to the rim. Preferably, the width of the band is greater than its depth.

Preferably, the band overlies substantially half the width of the rim so that a portion of the rim extends beyond the outer edge of the band. Preferably, the band comprises a thin strip of material, such as a steel plate .

Preferably, each ram passes through a corresponding aperture provided in the rim. Preferably, the rams are located at regular intervals around the mould.

Preferably, the rams are located centrally between the outer edge of the rim and the mould wall. Preferably, the rams project from the underside of the rim. ΙΕΟ7 Οϊ·· The invention will now be described further, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a mould assembly incorporating a bond breaking device of the invention; Fig. 2 is a perspective view of the bond breaking device of the invention incorporated on an inner mould; Fig. 3 is a perspective view of the bond breaking device and inner mould of figure 2 with attached moulded product in the relaxed configuration; Fig. 4 is a perspective view of the bond breaking device and inner mould of figure 2 with attached moulded product in the actuated configuration; and Fig. 5 is a perspective view showing removal of the bond breaking device and inner mould of figure 2 from the moulded product.

Referring to figure 1, a mould assembly for manufacturing a moulded concrete product, such as a thin walled concrete tank, comprises an inner mould 2 and an outer mould 4 which locates over the inner mould. In use, concrete is poured into the mould assembly and allowed to cure. The bond between the outer mould 4 and the moulded product is broken by means of a bond breaking device 6 as described in our co-pending application, which is incorporated herein by reference. The outer mould 4 and bond breaking device 6 ggo 7 o s #β are then removed from the inner mould 2 and attached moulded product.

A bond breaking device 1 of the invention, which is incorporated into the inner mould 2, is then used to break the bond formed between the inner mould 2 and the moulded product so that the inner mould 2 may be removed from the moulded product.

Referring to figure 2, an inner mould 2 comprises a base support in the form of legs 8 in a cruciform configuration which support an annular base rim iO. A circular mould wall 12 extends upwardly from the base rim 10 and a floor 14 spans the upper edge of the wall 12 to define the inner mould shape for the product, which in the specific example is substantially cylindrical.

A bond breaking device 1 of the invention is incorporated into the mould 2 and comprises a band, which in the specific embodiment is a circular band or annulus 16, and a plurality of hydraulic rams 18. The band 16 extends around the mould wall 12 and overlies the base rim 10.

The band is substantially parallel to the rim. The width of the band is greater than its depth and the typically the band overlies substantially half the width of the rim so that a portion of the rim extends beyond the outer edge of the band. Typically, the band comprises a thin strip of material, such as a steel plate. 1107 0 3 98 The hydraulic rams 18 are located at intervals around the base rim 10, typically at regular intervals, and typically substantially centrally on the rim, between the outer edge of the rim and the mould wall. The rams 18 extend transversely to the rim 10 and pass through corresponding apertures provided in the rim so that one end 2 0 thereof may abut the underside of the band 16 and the other end 22 thereof projects from the underside of the rim.

In use, the device is initially in a relaxed configuration wherein the ends 20 of the rams 18 are retracted so that the band 16 lies on the upper surface of the rim 10. The moulded product is formed such that its wall lies partially on the band. When the hydraulic rams are actuated, the ends 20 extend and push the band 16 away from the rim 10, thereby transferring force from the mould to the product and breaking the bond formed between the mould and the product.

It will be appreciated that the device specifically described is a preferred embodiment of the invention only. In particular, the device may be designed to be incorporated into any suitable mould and may include any desired number of points of application or rams. Thus, for example, the device may comprise a band of any suitable shape, such as a circular band as described, or a rectangular or asymmetrical band for incorporation into a correspondingly shaped circular, rectangular or asymmetrical mould.

Referring to figures 3 to 5, the manufacturing process which uses the bond breaking device of the invention to )10 7 03 98 produce a thin walled concrete tank includes several stages. Initially, the inner mould 2, with the incorporated bond breaking device 1 of the invention, rests on the factory floor and the outer mould 4 is lowered over it. The mould assembly is then filled with concrete and allowed to cure for approximately sixteen hours. When the concrete has cured, the bond between the outer mould 4 and the moulded product is broken by suitable means 6, as described in our co-pending application, and the outer mould 4 is removed leaving the moulded product standing on the inner mould in the inverted position.

The inner mould 2 with the moulded product 24 still attached is then lifted using a gantry crane or other suitable lifting device and vertically rotated through 180° using a suitable rotating device to the normal position with the moulded product or tank 24 in the upright configuration, as shown in figure 3. Typically, the product and mould assembly is placed on timber skids on the factory floor.

At this stage, the steel plate annulus 16 of the inner mould bond breaking device 1 is in the relaxed configuration, with the ends 20 of the rams 18 retracted so that the band 16 lies on the upper surface of the rim 10. A valve is opened in the base of the inner mould to avoid the formation of a vacuum during the extraction. Without such a valve, the force required to remove the product would be significantly increased and could damage the product floor.

Referring to figure 4, the inner mould bond breaking J10 7 05 9· device 1 is then actuated so that force is applied through the annulus 16 by the series of hydraulic rams 18, effectively lifting the inner mould 2 out of the product 24 by a short distance. The product 24 is thereby forced away from the inner mould 2 and the bond is broken. Typically, the travel required by the rams 18 is approximately 100mm, indicated by the spacing 26 between the annulus 16 and rim 10 in figure 4, is required to overcome all resistances.

Referring to figure 5, with the bond broken, the inner mould 2 is then lifted clear of the finished product 24 for cleaning, oiling and storage. The product 24 may be removed to a curing location by forklift or other suitable lifting device.

In practice, the bond breaking device of the invention forms an integral part of the mould and may be adapted for use on any suitable mould. Depending on the size of the product, eight, twelve or sixteen rams are typically used. It is advantageous to use as many rams as possible. The primary function of the band or ring is to distribute the bond breaking forces uniformly and at low stress levels, thus maintaining compression in the concrete and avoiding local crushing.

The removal of concrete tanks from the inner moulds by the application of air pressure in the space between the floor and the mould, according to established methods for conventional tanks, is not appropriate to thin walled tanks, because the floor area is large relative to the area of the wall. The thin walls are unable to resist the tensile stresses developed by the «070399 large floor area under pressure and chronic breakage occurs .

Thus, it has been found that direct tension applied to the wall section in this process is unsuited to deep, thin walled structures due to the large tensile stresses developed. The level of stress developed in the extraction of such a product using the known air pressure method is about ten times greater than in conventional products.

Accordingly, the bond breaking device of the invention allows the convenient and effective manufacture of deep, thin walled structures without the above disadvantages.

With the device of the invention, thin walled tanks can be manufactured in the inverted position in a single pour. The mould and its components are mobile so that they can be operated and lifted by forklift, mobile crane or gantry crane.

A source of hydraulic power is required to actuate the device and is typically available from the lifting device or a hydraulic power pack. The manufacturing process using the device of the invention is suitable for factory or off-site manufacturing.

The device allows the use of mould walls which are nonopening and have no moving parts. Vibrators are bolted on for compaction of the concrete, although poker vibrators can be used. A slight taper in the mould walls facilitates demoulding after overcoming initial ICO7 Οϊ ·· resistances .

The products are wet-cast, that is, a high slump mix is used and left in the mould until a hardened state is reached. The alternatives, dry-casting or cassettecasting are where pressure and vibration are applied to a relatively dry concrete mix such that the product has sufficient stiffness to support its own weight on immediate demoulding. This would be typical of concrete pipe manufacture for example, and is suited to high rates of output. The key to such methods is that the concrete has a gel like quality allowing flexibility in the demoulding process. However, since thin walled concrete tanks are rigid at demoulding, small amounts of flexure would probably result in breakage. Although slower, the process using the bond breaking device of the invention minimises the product weight which is invaluable at the lifting stage on site where truck mounted cranes are used.

One of the difficulties in demoulding a newly hardened concrete product is its tendency to adhere to the mould as a result of adhesion, friction, shrinkage and the vacuum effect. In cooler conditions, these problems are exacerbated by a slower strength gain and products were often broken at the extraction stage. Being thinner and larger than conventional products, thin walled products are particularly vulnerable. Risk of breakage is much greater with non-opening moulds as significant forces must be applied to overcome both bond and friction to release the product.

Nevertheless, the benefits of using non-opening moulds 1107 0 3 99 remain. Such benefits include the avoidance of wearing parts, the elimination of grout loss, simpler cleaning, simpler preparation and resistance to deformation which could result in non-uniform wall thickness of the product. For these reasons, the bond breaking device of the invention, which allows the use of non-opening moulds with no moving parts, is particularly advantageous .

The most rapid gain in concrete strength is in the compressive sense. Concrete has very little strength in bending or shear at the time of extraction. Consequently, the extraction system using a bond breaking device of the invention aims to stress the concrete primarily in compression during the bond breaking process.

The device is suitable for use on asymmetrical, rectangular or circular moulds. The device is mobile and adaptable for use on a variety of moulds. The device allows the production of large, single component, thin walled concrete tanks.

It will be appreciated that the present invention is not intended to be restricted to the details of the above embodiment, which is described by way of example only.

Claims (5)

Claims

1. A bond breaking device incorporated into a mould for breaking the bond formed between a moulded structure and a mould during the manufacturing process, the mould comprising a base rim and a mould wall extending upwardly from the base rim to define the mould shape for the structure and the bond breaking device comprising a band extending around the mould wall and overlying the rim and a plurality of rams located at intervals around the mould and extending transversely to the rim to abut the underside of the band such that actuation of the rams causes the band to move relative to the rim.

2. A bond breaking device according to claim 1 in which the bond breaking device is incorporated into a mould comprising a base support, an annular base rim supported thereon, a circular mould wall extending upwardly from the base rim and a floor spanning the upper edge of the wall to define the mould shape for the structure.

3. A bond breaking device according claim 1 or 2 in which the band is a circular band or annulus and is substantially parallel to the rim.

4. A bond breaking device according to any preceding claim in which the band overlies substantially half the width of the rim so that a portion of the rim extends beyond the outer edge of the band. f|07 03 9·

5. A bond breaking device according to any preceding claim in which the rams are located centrally between the outer edge of the rim and the mould wall and project from the underside of the rim.