GB2248578A - Casting stratified concrete roofing tiles - Google Patents

Abstract

The tiles (2) are cast by a tile making machine (4) having twin hoppers (8 and 10) located in series overlying a conveyor carrying tile pallets (P). The lower layer (48) is formed at lower pressure in the first hopper (10) with a thickness of up to three times the thickness thereof in the finished product and with an exaggerated upper profile commensurate with obtaining a stratified tile in which the upper and lower layers (50) and (48) are substantially of even thickness when a conventional mortar is compacted thereon by the second hopper (8). Concrete roofing tiles made in this way enable the economic use of more expensive materials such as cement, pigment, polymers, etc. whilst ensuring that the lower layer (48) does not break through the upper layer (50) to reduce the aesthetic appeal of the tile (2). <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO THE MANUFACTURE OF ROOF TILES This invention relates to the manufacture of roof tiles and especially it relates to improvements in a method of manufacturing stratified concrete roof tiles.

It is very well known to manufacture concrete roof tiles by feeding a concrete mortar from a hopper mounted above a continuously moving conveyor carrying a succession of tile pallets, the hopper defining with the pallets a mould having a slit-like opening through which the concrete mortar is discharged onto each pallet in turn to form a ribbon of mortar thereon, the ribbon being subsequently cut transversely to form individual tiles on associated ones of said pallets.

Such an arrangement is disclosed in the Complete Specification of Applicant's British Patent No. 1577321 in which Specification at page 3, lines 90 to 115, it is further disclosed that a second hopper disposed upstream of a first hopper may be used to produce tiles in a two-stage process, the upstream hopper producing a first bottom layer of a concrete mortar on the pallets and the downstream hopper providing a second layer of concrete mortar over the said bottom layer to provide stratified tiles; that is, composite tiles formed of more than one layer of the tile making materials used.

One of the major disadvantages of stratified tiles and especially of those tiles with contoured upper profiles, for example "Bold Roll" and/or "Roman" tiles, is the nonuniform displacement of the two mortar layers, from which the tiles are formed. Ideally, the mortars of the two layers should be displaced so that each each layer is of even thickness or substantially so throughout a lateral cross-section thereof. This has not always been the case for tiles have often been made where there is no acceptable control with respect to the displacement of the mortars of the said layers with the result that in extreme cases the lower layers of mortar extend through the upper layers to give inutile products.It is of little significance if some of the stratified tiles are of wholesome appearance with the upper layer of each tile, i.e. that layer which provides the upper surface in use, being of sufficient thickness throughout its cross-section that, despite wear over its useful life, it will always give the appearance of being a tile of solid colour throughout. This is because the manufacturer cannot identify any tiles which may not have a sufficient thickness to their upper layers that they never wear to reveal the base mortar. Thus, if the even distribution of the mortar in the lower and upper layers of the end product can be ensured within acceptable limits, the incidence of inutile products due to mortar of the lower layer extending through the upper layer will be greatly reduced if not eradicated.

Our experiences in the manufacture of stratified tiles as hereinbefore defined leads us to believe that the main factors controlling the displacement of successive layers of mortar are (a) the geometry of the tile profile; (b) the rheology of the tile mortars; (c) the differential speeds of successive sections of tile making rollers and packshafts used for making profiled roof tiles; (d) the drag effect of non-moving components found in con ventional tile making machines, e.g. the "cheek" plates which control the width of the tiles as they are pro cessed through the slit-like opening as aforesaid; and, (e) the pressure head of the materials in their associated hoppers and especially the pressure head of material in the downstream hopper.

In addition, because of the compaction techniques used for the placement of one layer upon another in a conventional tile machine, there is a risk that the two layers will not combine to give a tile which will resist delamination at the interface of the two layers throughout its useful life.

The present invention seeks to overcome these disadvantages and conveniently provides a method of making a tile as hereinbefore defined comprising the steps of (a) mixing two mortar batches; (b) feeding the two mortar batches to associated first and second hoppers of a tile making machine; (c) causing a first of said batches of mortar to be processed from said first hopper as a primary ribbon of mortar on a plurality of tile pallets fed seriatim beneath said first hopper; (d) passing the pallets with the primary ribbon of mortar formed thereon beneath said second hopper whereby a secondary ribbon of mortar is formed overlying said primary ribbon to form a stratified ribbon of mortar on said pallets; (e) cutting said ribbon of mortar at the joints between said pallets to form 11green-state" tiles on associate ones of said pallets; and, (f) causing or allowing said "green-state" tiles to be cured to provide finished products; characterised in that the first batch of mortar is caused to be processed from said first hopper to form a primary ribbon as aforesaid and having, in a direction normal to the direction of processing of said primary ribbon, an exaggerated cross- section having an upper profile which differs extensively from the desired profile of the finished product and which cross-section is determined by a combination of the desired profile requirements, the density of the primary layer and the flow characteristics of the mortar of the primary ribbon when a secondary ribbon of mortar is formed thereover in a second hopper, said flow characteristics being such that the mortars of the two ribbons are constrained by mutual interaction to form the stratified ribbon of mortar as hereinbefore described, the ribbon of mortar providing upper and lower layers of substantially even thicknesses.

Preferably in the method according to the preceding paragraph the two batches of mortar are of different moisture content compliant with the workability characteristics of the materials being used with the mortar fed to the first hopper preferably having a lower moisture content than the mortar fed to the second hopper.

Conveniently the moisture content of the mortar fed to the first hopper is 6 to 10% and the moisture content of the mortar fed to the second hopper is 7 to 11%.

In the method according to the last two preceding paragraphs the thickness in cross-section of the lower layer exceeds that of the upper layer by a ratio of up to 10:1.

In further refinements to the method as hereinbefore disclosed the primary ribbon of mortar is self-supporting and is up to three times and preferably up to one-and-a-half times the thickness of the lower layer in use of a concrete roof tile and an upper surface of the primary ribbon is profiled as it passes through an outlet aperture of the first hopper, to give the primary ribbon the exaggerated cross-section as aforesaid.

Conveniently the mortars fed to the first and second hoppers typically comprise sand, normal tile making cement and pigments with aggregates/cement ratios within the range of 3:1 to 8:1 and preferably the two mortars have different aggregate/cement ratios.

Preferably the primary ribbon of mortar is formed at less than 0.5 of the normal tile making pressures evident in conventional concrete tile making machines and the stratified ribbon of mortar is formed at normal tile making pressures.

This invention also conveniently provides a tile making machine comprising first and second hoppers, including conventional roller and/or slipper arrangements, means for feeding tile pallets seriatim beneath said hoppers, means for feeding mortars to the first and second hoppers whereby, when the machine is in use, a stratified ribbon of mortar is formed upon said pallets, and knife cutting means downstream of said hoppers whereby the ribbon of mortar may be cut to form discrete "green-state" tiles on associated pallets; characterised in that the first hopper comprises a contoured blade element for so forming the upper surface of a primary ribbon of mortar that it has an exaggerated cross-section upon entering said second hopper commensurate with ensuring that despite the desired profile of the finished products and the flow characteristics of the primary ribbon and a secondary ribbon of mortar formed thereon in said second hopper, the two ribbons of mortar conveniently combine to give a stratified ribbon of mortar wherein upper and lower layers thereof are of substantially the same thicknesses throughout the cross-section of the "green-state" tiles so formed.

In the tile-making machine according to the last preceding paragraph the element for forming the upper surface of the base layer may be disposed so that the primary ribbon of mortar has a thickness in some areas, upon entering said second hopper, of up to three times and preferably up to one-and-a-half times the thickness of a lower layer in use of a concrete roof tile with the pressure applied to the mortar in the first hopper preferably being less than 0.5 of the pressure applied to the tile making mortars in the second hopper of the said machine.

Conveniently the blade element may be provided by a conventional slipper or a shaped platen which may be adjustably mounted on a downstream end wall of the first hopper.

The invention further provides a concrete roof tile manufactured by a method or apparatus as defined herein.

By way of example, a specific method and apparatus in accordance with the invention for the manufacture of stratified concrete roof tiles will now be described with reference to the accompanying drawings in which Figure 1 is a schematic side elevation of a twin hopper tile making machine; Figure 2 is a schematic side elevation of a modified arrangement to that shown in Figure 1; Figure 3 is a perspective view of a platen illustrated in Figure 1; Figure 4 shows a modification to the platen of Figure 3; Figure 5 is a section view along the line V-V of Figure 1; and, Figure 6 is a section view along the line VI-VI of Figure 1.

In the manufacture of stratified tiles, that is tiles made from more than one layer of concrete mortar, by conventional tile processing methods, it has proven difficult if not impossible to ensure the uniform displacement of the layers of mortar throughout the cross-section of the tiles.

This is particularly so in the production of profiled tiles such as "Bold Roll" or "Roman" tiles where the effects of the differential speeds of the hopper components on the mortars in the tile hoppers of conventional tile making machines result in non-uniform displacement of the mortars giving products which are unacceptable for the intended purpose.

The present invention thus comprises a unique tile making machine 4 which enables a novel method of making stratified concrete roof tiles 2 to be effected so that the layers of mortar of the stratified tile 2 are of uniform thickness or are substantially so throughout their cross-section as herein defined.

The tile making machine 4, see Figure 1, comprises twin hoppers 8 and 10 located in series overlying a pallet conveyor 12. The conveyor 12 is of conventional design, is supported on floor mounted columns 12a and 12b and comprises support rails 12c on which pallets P are supported as they pass seriatim beneath the hoppers 8 and 10.

The hopper 8 is also of conventional design and provides support for a roller 13, a slipper 14 and a pack shaft 16.

The hopper 10 is located upstream of the hopper 8 and comprises a pack shaft 18 located towards a front wall 20 thereof. The front wall 20 provides support for an adjustably mounted contoured blade element 22, see Figures 1 and 3, the purpose of which element 22 will be made clear hereinafter.

The blade element 22 has an irregularly shaped lower profile 24 which extends across the width of the hopper 10 to provide a processing outlet together with side wall portions 26 and 28 of the hopper 10 and the upper surfaces 30 of the pallets P passing therebeneath along said conveyor 12, see Figures 1, 3 and 6.

Located above each hopper 8 and 10 are respective material feed conveyors 34 and 36 for feeding mortar to said hoppers, see Figure 1.

Downstream of the hopper 8, the tile making machine is provided with a conventional tile cutting knife 38 which is mounted for reciprocal vertical and longitudinal movement on a knife carriage 40 illustrated schematically in Figure 1.

The tile making machine also comprises a pallet spacing conveyor 43 which is arranged beneath the conveyor 12 and adjacent the knife carriage 40 for a purpose also to be made clear hereinafter.

When the machine of Figure 1 is in use in the manufacture of stratified concrete roofing tiles, two batches of mortar are fed by the conveyors 34 and 36 to the hoppers 8 and 10 respectively. At the same time pallets P are fed seriatim along the support rails 12c of the conveyor 12 so that mortar in hopper 10 is compacted by the pack shaft 18 and is therafter formed as a shaped ribbon 42 of mortar on said pallets P as it passes beneath the blade element 22.

At this stage the ribbon 42 is in some areas up to some three times the thickness of the lower layer in use of the finished tile and comprises an exaggerated upper profile 44, see Figure 5, which only approximates to that required of the finished product, the exaggerated profile 44 being provided for a purpose to be described herein.

The ribbon 42 is then carried by the pallets P beneath the hopper 8 whereat the mortar therein is compacted by the packshaft 16, to be thereafter formed, by the roller 13 and slipper 14, as a second layer overlying the ribbon 42 and to be processed as a stratified composite ribbon 46, see Figures 1 and 6.

The ribbon 46 comprises a lower layer 48 and an upper layer 50 of substantially even thicknesses through the lateral cross-section thereof, see Figure 6 in which the two layers 48 and 50 are notionally divided by the chain dotted line 49.

The ribbon 46 is thereafter cut by the knife 38 of the tile cutting arrangement whereupon trailing ends of the pallets P are engaged by drive elements 52 of the conveyor 43 whereby the "green-state" tiles 2 on their associated pallets P are conveyed to racking devices prior to transportation to curing chambers, etc.

From the foregoing it is evident that the cross-section of the ribbon 42 is crucial to the formation of the finished product which is a bold-roll tile with stratified layers of even thickness throughout the cross-section thereof. It is believed that, profiling the upper surface of the ribbon 42 to give a ribbon of exaggerated cross-section, as shown in Figure 5, negates the effects of the differential surface speeds of the various surfaces of the roller 13, the pressure head of mortar in the hopper 8 and the drag effect of the "cheek" plates 54 and 56 associated with the hopper 8 on the mortar in the hopper. This is because extra mortar is provided in required areas of the ribbon 42 to compensate for the excesses created by the differential speeds and drag effects encountered by the intermixed mortars in the hopper 8. Results achieved using the new method supports this belief; however, further important parameters which must also be observed in carrying the novel method into effect are given below.

1. The two batches of mortar in the hoppers 8 and 10 are of different moisture content with the moisture content of 6 to 10% being evident in hopper 10 and the moisture content of 7 to 11% being evident in hopper 8.

Generally, it has been determined that the moisture content of the mortar of hopper 8 should exceed that of hopper 10 for the best results to be achieved.

However, due to the rheological characteristics of the various mortars used for making concrete roofing tiles, it may transpire that the moisture contents in the hoppers 8 and 10 should be the same, or substantially so.

2. The ribbon 42 should be formed at less than 0.5 the pressure which is evident in conventional tile making machines.

3. The ribbon 42 should be up to three times and specifi cally up to one-and-a-half times the thickness of the lower layer in the finished product and, as it is formed at less than half the pressure of normal tile making machines, it is evident that the mortar ribbon 42, although being self- supporting, is considerably less dense than the ribbon 46 extruded from the hopper 8.

4. The mortar used in the hoppers 8 and 10 is a mix of sand, normal tile making cement and pigments with aggre gate/cement ratios within the range of 3:1 to 8:1, see Examples 1 and 2 hereinafter given.

5. The moisture content and composition of the mortars used should be chosen to ensure that the rheologies of the two mortars, i.e. their flow characteristics, are such that the two combine in the hopper 8 to give a homogenous end product with a cohesive infrastructure between the two mortars at the interface thereof. In experimental trials conducted to determine the veracity of the above statements the mortars used had aggregate/ cement ratios of 3.6:1 with the mortar in hopper 8 having a pigment dosage of 1% based on the weight of cement and the mortar in hopper 10 having a pigment dosage of some 40% of that in hopper 8.

In the main the moisture contents of the mortars in the hoppers 8 and 10 were within the parameters set out in paragraph No. 1 above, that is the moisture contents of the mortar in hopper 8 at 7.4 to 8.0% exceeded those moisture contents at 7.1 to 7.7% in the hopper 10.

Several experiments were conducted with the moisture contents of the two mortars being the same or substan tially so at 6.5 to 7.9% and some experiments were also effected wherein the moisture content of the mortar in hopper 8 at 7.5t was exceeded by the moisture content of the mortar in hopper 10 at 8.0%.

The best results were obtained from the experiments where the moisture contents of the two mortars were the same or where that of the mortar in hopper 8 exceeded that of hopper 10.

Example No. 1 A tile having a dry weight of 4.4 kg with upper and lower layers making up 30% and 70% of the total thickness of the tile respectively, was made from the following constituents: a) Upper layer i) Sand 0.929 kg ii) Cement 0.273 kg iii) Pigment 0.008 kg (i.e. 2.86% by wt. of cement) b) Lower layer i) Sand 2.175 kg ii) Cement 0.640 kg iii) Pigment 0.009 kg (i.e. 1.43% by wt. of cement) Both larers had an A/C ratio of 3.4 to 1 and a W/C ratio of 0.4 to 1.

The lower layer was formed in the hopper 10 at negligible pressure and the composite stratified tile 2 was formed at normal tile making pressure.

Example No.2 A tile having a dry weight of 4.4 kg with upper and lower layers of substantially half the total tile thickness was made from the following constituents: a) Upper layer i) Sand 1.545 kg ii) Cement 0.454 kg iii) Pigment 0.019 kg (i.e. 4.288 by wt. of cement) b) Lower layer i) Sand 1.551 kg ii) Cement 0.456 kg iii) Pigment 0.010 kg (i.e. 2.14% by wt. of cement) The A/C and W/C ratios were the same as for Example No. 1 as were the forming pressures for the base layer and the stratified tile.

In manufacturing a stratified tile by the method disclosed herein the thicknesses of the layers 48 and 50 of the tiles 2 can be controlled within well defined limits, that is, the respective thicknesses of the lower and upper layers 48 and 50 can be controlled with an accuracy which are not considered to be available in the prior art methods. In addition, the even distribution of the mortars in their respective layers throughout the cross-section of the finished product gives such layers the uniform thicknesses required for quality products. Also, the manner in which the two batches of mortar are treated in the hoppers 8 and 10 ensures the cohesivity of the finished product whilst ensuring that the mortar forming the lower layer 48 does not break through the upper layer 50 to appear at the upper surface thereof and to spoil the finished product.

These facts also enable the economic use of the more expensive materials such as cement, pigment, polymers, plasticisers, etc. in the manufacture of stratified concrete roof tiles.

In the tile shown schematically in Figure 6 the lower layer 48 appears to be of similar thickness to the upper layer 50 and indeed this may be the case; however, in order to conserve the more expensive materials and/or those materials in short supply, the thickness in cross-section of the lower layer 48 made of commonly available cheaper materials can exceed the thickness in cross-section of the upper layer 50 made of expensive less common materials by a ratio of up to 10:1.

While the tile 2 shown in Figure 6 comprises a layer 50 which extends wholly across the width thereof, in a modified process according to the present invention the upper layer 50 may be formed to extend only across a defined region of the tile 2, for example, the lower layer 48 may conveniently form the whole of the left hand side-lock portion of the tile shown in Figure 6 and the upper layer may extend across the remainder of the tile 2 to form said left hand side-lock to the right-hand side of the tile as shown in Figure 6.

Whereas the novel method of making the stratified concrete tile remains unaltered, the tile making machine may be modified as shown in Figure 2 in which the twin hopper arrangement is replaced by a hybrid hopper 9 having first and second sections 9a and 9b corresponding to hoppers 10 and 8 respectively of Figure 1. All other features are essentially the same as those of Figure 1 and they have, therefore, been accorded like reference characters.

In addition the blade element 22 of Figures 1, 2 and 3 may be replaced by an element 60, as shown in Figure 4, which element 60 comprises a shaped lamina 62 for engaging and forming an upper surface of the ribbon 42 as it exits from the hopper 10. For this purpose the shaped lamina 62 extends forwardly and downwardly in use at a shallow angle to the axis of flow of the pallets P therepast, which shallow angle is chosen to be commensurate with the avoidance of any build up of detritus on said slipper. To all intents and purposes the element 60 acts as a conventional slipper which is operated, however, at less than normal tile making pressures.

In a further alternative provided by the present invention, the element 22 may in fact be replaced by a conventional slipper similar to that shown in the hopper 8.

Claims (22)

1. A method of making a tile as hereinbefore defined comprising the steps of (a) mixing two mortar batches; (b) feeding the two mortar batches to associated first and second hoppers of a tile making machine; (c) causing a first of said batches of mortar to be processed from said first hopper as a primary ribbon of mortar on a plurality of tile pallets fed seriatim beneath said first hopper; (d) passing the pallets with the primary ribbon of mortar formed thereon beneath said second hopper whereby a secondary ribbon of mortar is formed overlying said primary ribbon to form a stratified ribbon of mortar on said pallets; (e) cutting said ribbon of mortar at the joints between said pallets to form "green-state" tiles on associate ones of said pallets; and, (f) causing or allowing said "green-state" tiles to be cured to provide finished products; characterised in that the first batch of mortar is caused to be processed from said first hopper to form a primary ribbon as aforesaid and having, in a direction normal to the direction of processing of said primary ribbon, an exaggerated cross- section having an upper profile which differs extensively from the desired profile of the finished product and which cross-section is determined by a combination of the desired profile requirements, the density of the primary layer and the flow characteristics of the mortar of the primary ribbon when a secondary ribbon of mortar is formed thereover in a second hopper, said flow characteristics being such that the mortars of the two ribbons are constrained by mutual interaction to form the strati fied ribbon of mortar as hereinbefore described, the ribbon of mortar providing upper and lower layers in use of a concrete roof tile of substantially even thicknesses.

2. A method according to Claim 1 wherein the two batches of mortar are of different moisture content compliant with the workability characteristics of the materials being used.

3. A method according to either one of Claims 1 and 2 wherein the mortar fed to the first hopper has a lower moisture content than the mortar fed to the second hopper.

4. A method of making a tile according to any one of Claims 1 to 3 wherein the moisture content of the mortar fed to the first hopper is 6 to 10% and the moisture content of the mortar fed to the second hopper is 7 to 11%.

5. A method according to any one of Claims 1 to 4 wherein the thickness in cross-section of the lower layer exceeds that of the upper layer.

6. A method according to Claim 5 wherein the thickness in cross-section of the lower layer exceeds that of the upper layer by a ratio of up to 10:1.

7. A method according to any one of the preceding claims wherein the primary ribbon of mortar is self-supporting and is up to three times the thickness of the lower layer in use of a concrete roof tile.

8. A method according to any one of Claims 1 to 6 wherein the primary ribbon of mortar is self-supporting and is up to one-and-a-half times the thickness of the lower layer in use of a concrete roof tile.

9. A method according to any one of Claims 1 to 8 wherein an upper surface of the primary ribbon is profiled as it passes through an outlet aperture of the first hopper, to give the primary ribbon the exaggerated cross-section as aforesaid.

10. A method according to any one of the preceding Claims wherein the mortars fed to the first and second hoppers typically comprise sand, normal tile making cement and pigments with aggregates/cement ratios within the range of 3:1 to 8:1.

11. A method according to Claim 10 wherein the two mortars have different aggregate/cement ratios.

12. A method according to any one of Claims 1 to 11 wherein the primary ribbon of mortar is formed at less than 0.5 of the normal tile making pressures evident in conven tional concrete tile making machines.

13. A method according to any one of Claims 1 to 12 wherein the stratified ribbon of mortar is formed at normal tile making pressures.

14. A tile making machine comprising first and second hoppers, including conventional roller and/or slipper arrangements, means for feeding tile pallets seriatim beneath said hoppers, means for feeding mortars to the first and second hoppers whereby, when the machine is in use, a stratified ribbon of mortar is formed upon said pallets, and knife cutting means downstream of said hoppers whereby the ribbon of mortar may be cut to form discrete "green-state" tiles on associated pallets; characterised in that the first hopper com prises a contoured blade element for so forming the upper surface of a primary ribbon of mortar that it has an exaggerated cross-section upon entering said second hopper commensurate with ensuring that despite the desired profile of the finished products and the flow characteristics of the primary ribbon and a secondary ribbon of mortar formed thereon in said second hopper, the two ribbons of mortar combine to give a stratified ribbon of mortar wherein upper and lower layers thereof are of substantially the same thicknesses throughout the cross-section of the "green-state" tiles so formed.

15. A tile making machine according to Claim 14 wherein the element for forming the upper surface of the base layer is disposed so that the primary ribbon of mortar has a thickness in some areas, upon entering said second hopper, of up to three times the thickness of a lower layer in use of a concrete roof tile.

16. A tile making machine according to Claim 15 wherein the element for forming the upper surface of the base layer is disposed so that the primary ribbon of mortar has a thickness in some areas, upon entering said second hopper, of up to one-and-a-half times the thickness of a lower layer in use of a concrete roof tile.

17. A tile-making machine according to either one of Claims 14, 15 and 16 wherein the pressure applied to the mortar in the first hopper is less than 0.5 of the pressure applied to the tile making mortars in the second hopper of the said machine.

18. A tile making machine according to any one of Claims 14, 15, 16 and 17 wherein the blade element is provided by a conventional slipper.

19. A tile making machine according to any one of Claims 14, 15, 16 and 17 wherein the blade element is provided by a shaped platen.

20. A tile making machine according to any one of Claims 14 to 19 wherein the blade element is adjustably mounted on a downstream end wall of the first hopper.

21. A method of making a tile, substantially as hereinbefore described with reference to the accompanying drawings.

22. A tile made substantially as hereinbefore described with reference to the accompanying drawings.