GB2278567A - Method of forming a pressed product with uneven edges - Google Patents

Abstract

A method of forming a pressed product such as a paving slab (7) with partially uneven edges (7B) in which the product is formed in a press having a cavity (2) in which material is compressed by a movable pressing head (4). The partially uneven edge (7B) is formed by a removable plastics insert (8) placed in the cavity (2) or placed between the material to be pressed and the pressing head (4), the insert (8) extending across one face of the cavity (2) and having uneven edges extending part way up the sides of the cavity (2) to form the partially uneven edges (7B). <IMAGE>

Description

A METHOD OF FORMING A PRESSED PRODUCT This invention relates to a method of forming a pressed product, such as a paving slab, with a partially uneven edge.

Products such as paving slabs, bricks, building blocks etc are usually made either by a semi-dry pressing process or by a wet casting process. In the pressing process, a semi-dry material, such as concrete, is placed within a press cavity and then compressed therein bv means of a movable pressing head. The material is thus compressed and adopts the shape defined by the cavity and the pressing head.

The pressing head is then withdrawn, and the product removed from the cavity and left to dry.

Conventional paving slabs are formed in a square cavity having flat sides and by a pressing head with a flat surface which forms one of the major faces of the slab. It is known that a pattern or texture can be formed on one of the major faces of the slab by using a pressing head with the required pattern or texture formed therein. This method of forming a pattern in the pressed product is restricted to the pattern being formed in the face formed by the pressing head and due to problems in cleaning the pattern on the head between each pressing, is restricted to relatively shallow patterns or textures.

With a wet casting process a wet material such as flowable concrete is poured into a mould and allowed to set within the mould so the product is formed to the shape of the mould. Such a casting process allows a wide variety of shapes, patterns etc to be formed in the product by the use of an appropriately shaped mould and/or inserts but suffers from the disadvantage that the process is relatively slow, especially compared with the semi-dry pressing process referred to above.

Paving slabs formed by the wet casting process also usually have inclined edges to assist in removing them from the mould. The edges of adjacent paving slabs cannot therefore be butted up closely with each other.

The present invention aims to provide a way of forming a product with a partially uneven edge by means of a pressing process.

Thus, according to a first aspect of the invention, there is provided a method of forming a pressed product with a partially uneven edge in which the product is formed in a press having a cavity in which material is compressed by means of a movable pressing head, the partially uneven edge being formed by a removable insert placed in the cavity or placed between the material therein and the pressing head.

According to a second aspect of the invention, there is provided a pressed product formed by the method as detailed above.

According to another aspect of the invention, there is provided an insert for use in a method of forming a pressed product as detailed above.

Other features of the invention will become apparent from the following description and from the subsidiary claims of the specification.

The invention will now be further described, merely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a conventional semi-dry pressing apparatus for forming products such as paving slabs; Figure 2 is an enlarged view of part of a paving slab showing an insert used in a method according to one form of the invention attached thereto; Figure 3 is a perspective view of a paving slab with the insert still attached thereto; Figure 4 illustrates removal of the insert from the paving slab to leave a slab with uneven edges according to the method described herein and Figure 5 is a view of two paving slabs formed by this method showing how they can be formed wiht uneven edges yet be butted up closely to each other.

The conventional pressing apparatus shown in Figure 1 will first be briefly described. This comprises a rotating table 1, four cavities 2 formed therein, a hopper 3 for feeding semi-dry concrete into the cavity 2 at position A, a pressing head 4 for compressing the concrete within the cavity 2 at position B, and a pusher bar 5 for pushing a slab ejected from a cavity at position C onto a conveyor belt 6. The apparatus has two further arms (not shown) between which the paving slab is gripped as it is pushed onto the conveyor 6. These arms rotate the paving slab so that it is standing on edge on the conveyor 6. Figure 1 shcws a plurality of paving slabs 7 standing on end which have been loaded onto the conveyor.The semi-dry concrete used in such a process would typically comprise around 10 gallons (45.5 litres) of water per 600-700kg of stone aggregate and around 70kg of cement (which is just enough water to hydrate the cement).

The apparatus operates automatically and carries out the following cycle: concrete is fed into the cavity at position A. The means for doing this are well known in the art so will not be described further.

The table 1 rotates so that the filled cavity is moved to position B.

Pressing head 4 is lowered to compress the semi-dry concrete in the cavity 2 and then raised again. The table 2 rotates so that the cavity 2 is moved to position C. The base of the cavity is then moved upwards to eject the paving slab thus formed therein from the cavity.

The pusher bar 5 then moves to push the ejected paving slab onto the conveyor. During this process, the paving slab is gripped between the two further arms (not shown) which rotate the paving slab so that it is stood on one edge. The paving slabs 7 thus formed are thereby lined up in a row on the conveyor belt 6 which moves them to a drying station (not shown) where they are left to dry for 12 to 24 hours. The table 1 rotates further to move the cavity 2 to position D whilst the base of the cavity is lowered. The cavity is then moved to position A again to begin the next cycle.

This process is well known and such apparatus is capable of forming around 2000 paving slabs in an eight hour shift.

As well as paving slabs with flat faces and edges, there is a demand for paving slabs which look more like slabs made from natural rock, so they have a more rustic appearance. To achieve this appearance, it is desirable to form a pattern in at least one of the major faces of the slab which imitates the form of face produced by splitting natural rock.

More importantly, it is desirable to provide the slab with uneven edges, i.e. instead of having a sharp 900 angle between the major face and the surrounding edges it is desirable that this angle vary along the length of the edges, e.g. by being more rounded in some areas than others. This means that at least part of each edge of the paving slab is uneven rather than being flat.

Although it has been possible to form slabs with uneven edges by the wet casting method, it has up until now not been possible to form such a slab using the semi-dry pressing method described above. It is possible to form a pattern in either the base of the cavity 2 or in the face of the pressing head 4 which is pressed into the cavity. However, such patterns have to be cleaned frequently, sometimes between every pressing operation, to remove concrete which has remained within the recesses of the pattern after forming a paving slab. Such cleaning can be carried out using rotary bushes passing across the patterned part of the cavity or pressing head. However, unless the pattern is relatively smooth the brushes would be rapidly worn out or torn to pieces. This method is not. therefore, suitable for forming paving slabs with uneven edges as this would require a pattern having 1-2cm projections to extend down the edges of the slab.

The process described herein thus uses an insert 8 such as that iilustrated in Figure 4 to form the uneven edges. The insert 8 is preferably in the form of a sheet of plastics material, e.g. ABS, with turned over edges. The insert 8 is of approximately the same dimensions as the major face of the paving slab to be formed so that it fits snugly into the bottom of a cavity 2 of the pressing apparatus.

The turned over edges of the insert 8, however, extend at least partway up each of the sides of the cavity 2. As shown in Figures 3 and 4, the turned over edges are uneven in that they project to different height up the sides of the cavity 2 at different positions along the edges. The thickness of the turned over edges also varies along the lengths of each side of the insert.

To form a paving slab with an uneven edge, the insert 8 is first placed in the bottom of a cavity 2 when in position D so that the major face of the insert lies on the base of the cavity and the turned over edges of the insert extend part-way up the side walls of the cavity 2.

Concrete is then loaded into the cavity 2 at position A and is compressed by the pressing head at position B as described above. At position C, the paving slab 7 together with the insert 8 is ejected from the cavity 2. The insert 8 remains attached to a major face of the paving slab so the slabs 7 are stood on edge with the insert 8 still attached thereto as shown in Figure 2. Indeed, when the slabs 7 are stood on edge they partially stand on the turned over edges of the inserts so the insert 8 is effectively held in contact with the slab 7.

The insert 8 therefore remains in contact with the slab 7 whilst the slab is drying. If the insert 8 were removed before the slab 7 had dried there would be a danger that its removal would damage or break away the edges of the paving slab. As Figure 2 illustrates, the edge of the paving slab 7 with the insert attached thereto is essentially flat.

The slab 7 with insert 8 attached thereto can therefore be stably stood on its edge as in the conventional process described above. If the insert 8 was removed, the slab 9 would be much less stable because the slab 7 has been formed with an uneven edge.

Once the slab has dried (after 12 to 24 hours) the insert 8 is removed as illustrated in Figure 4. The paving slab 7 is thus formed with an uneven edge which corresponds to the uneven shape of the turned over edges of the insert 8. However, this uneven edge only extends part-way across the edges of the slab 7. So the lower parts of the edges (in the orientation shown in Figure 4) is still flat as in a conventional paving slab. This means that the upper portion of the edges of the paving slab is uneven to simulate the appearance of a slab formed from natural rock whilst the lower portion is flat and square so the paving slabs can still be butted up accurately to each other.

Figure 5 shows two paving slabs 7 laid adjacent to each other. It will be seen that the lower portions 7A of the edges of the slabs can be butted up against each other whilst the upper portions 7B of the edges are uneven so that an uneven gap 10 is left between the upper surfaces of the slabs.

The form of the overturned edge of the insert 8 may vary as required.

However, it preferably covers between 30 and 40% of the area of the edge of the slab so leaving 60-70% of the edge with a flat, square surface.

As well a forming the uneven edges as described above, the major surface of the insert may also carry a pattern 9 to form a corresponding pattern on a major face of the paving slab 7. This may be a pattern to imitate natural rock or any other decorative finish.

Once the inserts 8 have been removed from the slabs 7, they can be re-used again in forming further paving slabs. They may require cleaning to remove any deposits or build up of concrete which remains adhered thereto. Cleaning may be carried out using brushes or immersion in liquid or by any other suitable process. As the inserts 8 are relatively inexpensive compared to the components of the pressing apparatus itself they can also be disposed of. In some circumstances, it may also be desirable to leave the inserts 8 attached to the paving slabs so that the inserts provide additional protection for the slab 7 and prevent adjacent slabs scraping against each other during shipping or stacking. The inserts 8 may then be removed at the point of sale or by the end user before the paving slab is laid.

As the inserts 8 are left in contact with the slab 7 until the slab is dry, this method also tends to provide a better finish on the surface of the slab than previous methods when a pattern is imprinted on the slab by part of the press cavity. This enables more intricate and/or deeper patterns to be formed. As the inserts 8 are relatively inexpensive, removable items, they can also be easily changed or re-designed when it is desired to form a different pattern on the paving slabs.

Although the method described above involves placing the insert in the bottom of the cavity 2, it would also be possible to position the insert 8 between the concrete in the cavity and the pressing head 4 either by laying the insert on top of the concrete in the cavity 2 or attaching the insert 8 to the pressing head 4.

The inserts 8 may be put in position by hand or the pressing machine could be modified to position them automatically. Similarly, although it would usually be desirable to leave the inserts attached to the slabs 7 while the slabs 7 are drying, they could be detached from the slabs once the slabs have been ejected from the cavity 2 and the pressing apparatus could, again, be modified to carry this out automatically.

The uneven edge formed by the insert may be different on each of the four edges of the paving slabs or may be similar. In some circumstances, it may be desirable for the edges to match each other to improve the appearance of the uneven space left between the upper surfaces of slabs laid next to each other.

Although the above example relates to paving slabs made from concrete.

it will be appreciated that an uneven edge may be formed in a similar manner on any product which can be made by the type of pressing operation described and from any material suitable for use in such a pressing operation.

Claims (18)

1. A method of forming a pressed product with a partially uneven edge in which the product is formed in a press having a cavity in which material is compressed by means of a movable pressing head, the partially uneven edge being formed by a removable insert placed in the cavity or placed between the material therein and the pressing head.

2. A method as claimed in claim 1 in which the insert extends across one face of the cavity and extend at least part way across one or more side faces thereof, which side faces form the edges of the product.

3. A method as claimed in claim 1 or 2 in which, once compressed, the product is ejected from the cavity with the insert attached thereto.

4. - A method as claimed in claim 3 in which the product with the insert attached thereto has a substantially flat edge.

5. A method as claimed in claim 4 in which the product is stood on the said substantially flat edge.

6. A method as claimed in claim 3, 4 or 5 in which the insert is left attached to the slab whilst the slab is drying.

7. A method as claimed in claim 6 in which the insert is left attached to the slab during storage and/or shipping.

8. A method as claimed in any preceding claim in which the edges of the insert which form the partially uneven edges of the product have different heights and/or thicknesses along their length.

9. A method as claimed in any preceding claim in which the edges of the insert which form the partially uneven edges of the product cover between 30 and 40% of the area of the respective sides of the cavity.

10. A method as claimed in claim 9 in which the remaining 60 to 70% of the area of the respective sides of the cavity are substantially flat and perpendicular to the face of the pressing head whereby 60-70 h of the edges of the product are formed substantially flat and square to the major faces thereof whereby adjacent products can be accurately butted up to each other whilst leaving a gap between the uneven portions of their edges.

11. A method as claimed in any preceding claim in which a pattern is formed on a face of the insert whereby a corresponding pattern is formed on a face of a product formed thereby.

12. A method as claimed in any preceding claim in which the product formed is a paving slab.

13. A method as claimed in any preceding claim in which the product is formed from semi-dry concrete.

14. A method of forming a pressed product substantially as herein before described.

15. A pressed product formed by a method as claimed in any preceding claim.

16. A pressed product having a partially uneven edge substantially as hereinbefore described.

17. An insert for use in a method of forming a pressed product with a partially uneven edge as claimed in any of claims 1 to 14.

18. An insert substantially as hereinbefore described for use in a method of forming a pressed product as claimed in any of claims 1 to 14.