EP0115958A1

EP0115958A1 - Apparatus for manufacture of cementitious building products

Info

Publication number: EP0115958A1
Application number: EP84300609A
Authority: EP
Inventors: Howard Anthony Barker; Alan William Rawe
Original assignee: Redland Technology Ltd; Redland Technologies Ltd
Current assignee: Redland Technology Ltd; Monier Braas Research and Development Ltd
Priority date: 1983-01-31
Filing date: 1984-01-31
Publication date: 1984-08-15
Also published as: GB8302585D0

Abstract

Apparatus for manufacturing a cementitious building product includes at least one twin-roll mill comprising a pair of contra-rotating rolls defining a nip therebetween, for effecting high-shear mixing of a cementitious composition. At least one transfer blade means is arranged adjacent to the rolls and at an angle to the axes thereof for effecting transfer of the cementitious composition from an upstream end of the rolls to a downstream end thereof during mixing. A band of cementitious material is thereby formed on one of the rolls and take-off means are provided at the downstream end of the rolls adjacent said one of the rolls for removing said band of cementitious material from said roll. Forming means for forming said band into blanks are also provided, said baink being cured to form a building product.

Description

The invention is concerned with improvements in apparatus adapted for use in the manufacture of cementitious products. The invention is particularly concerned with high shear mixing apparatus and processing plant including such apparatus for the manufacture of cementitious building products.
The term cementitious products, where used herein, is meant to include roofing slates, tiles, panels or the like of relatively thin cross-section and high flexural strength.
One of the major drawbacks of cementitious materials, which prevents their use for thin cross-section products, is the inherent lack of flexural strength in the finished products. Obviously, one may add reinforcing materials to improve the flexural strength of such products; however, the addition of reinforcing materials to cementitious products escalates their cost and, in the case of asbestos fibres or other fibres of a carcinogenic nature, they increase the health risk of those operatives involved in the manufacture and use of products made therefrom. In addition, it is difficult to process cementitious compositions of lcw water cement ratios, e.g. approximately 0.15 and with economically acceptable amounts of polymer additives at high production rates.
The invention provides apparatus for manufacturing a cementitious building product comprising at least one twin-roll mill comprising a pair of contra-rotating rolls defining a nip therebetween, for effecting high-shear mixing of a cementitious composition, at least one transfer blade means arranged adjacent to the rolls and at an angle to the axes thereof for effecting transfer of the cementitious composition from an upstream end of the rolls to a downstream end thereof during mixing, thereby to form a band of cementitious material on one of the rolls; take-off means at the downstream end of the rolls adjacent said one of the rolls for removing said band of cementitious material from said roll, and forming means for forming said band into blanks, said blanks being cured to form a building product.
Means are preferably provided for rotating the rolls of the mill at unequal speeds, for example, in the ratio 10:11.
There are preferably first and second twin-roll mills arranged in series, the cementitious material being fed from the downstream end of the first mill to the upstream end of the second mill.
There may be two first mills arranged in parallel, material from the downstream ends of both first mills being fed to the upstream end of the second mill.
Each twin-roll mill and transfer blade assembly comprises one high-shear mixing apparatus.
Mixing means may be provided for mixing together cement, water and a processing aid to form the cementitious composition. Conveyors are preferably provided for transferring the material from the mixing means to the first mills, from the first mills to the second mill and from the second mill to forming,pressing and curing stations.
The present invention also provides a processing plant adapted for use in producing cementitious products and comprising:

i) a batch or continuous mixer capable of intimately blending the components of a cementitious composition;
ii) two first high shear mixing apparatuses as hereinbefore defined;
iii) first conveyor means which, when the plant is in use, is arranged to feed material from the batch mixer to the primary apparatuses..
iv) a second high shear mixing apparatus as hereinbefore defined.
v) second conveyor means which, when the plant is in use, is arranged to feed material from the downstream ends of the first apparatuses to an upstream end of the second apparatus;
vi) third conveyor means which, when the plant is in use, is arranged to feed the continuous band of cementitious material to cutting means located thereover; and,
vii) transfer means which, when the plant is in use, is effective to transfer green state blanks, cut from said band of cementitious material, to a stack of such blanks;
viii) press means which, when the plant is in use is effective to press the stacks of green state blanks to compact the blanks; and,
ix) a curing chamber which, when the plant is in use, accommodates the stacks of blanks to effect curing thereof.

Conveniently the press may exert a pressure of up to 6Mpa in the blanks and the curing chamber operates at 100% RH while subjecting the tiles to a temperature of 40° to 90° for up to 8 hours.
The present invention may also provides an improved method of manufacturing cementitious products using the apparatus described above, the method comprising the , steps of processing a cementitious composition comprising a mixture of cement, water and a processing aid in a twin-roll mill thereby to subject the composition to high-shear mixing, transferring the composition from an upstream end of the mill to a downstream end during mixing, thereby to cause the composition to pass through sideways adjacent portions of the nip of the rolls of the mill; removing a band of cementitious material from the downstream end of the mill; and forming said band into blanks of building products, the blanks thereafter being cured.
The invention further provides cementitious building products manufactured by the apparatus and method described above. The products are preferably roofing tiles.
There now follows by way of example of the invention a detailed description of a high shear mixing apparatus, a processing plant utilising such apparatuses for the production of roofing slates and a method of operating the plant. The description is to be read with reference to the accompanying drawings in which:-

Figure 1 is a schematic side elevation of a processing plant incorporating two primary high shear mixing apparatuses and one secondary high shear mixing apparatus; and
Figure 2 is a schmematic plan view taken on the line II-II of Figure 1.

Artificial roofing slates have in the past been produced from reinforced cementitious materials and, apart from the well known disadvantages of utilising reinforcing materials of a carcinogenic nature, there are many other reasons why cementitious materials cannot easily be utilised in thin-sections.
For example; low flexural strength due to inadquate properties of fibres substituted for asbestos and excessive porosity in the finished product leads to excessive water absorption and poor durability in adverse conditions.
The apparatus described below overcomes or mitigates these drawbacks by providing a processing plant and apparatus whereby cementitious products of acceptable flexural strength and durability can be readily produced.
The processing plant, see Figures 1 and 2, comprises a batch mixer 10, two primary high shear mixing apparatuses 12 and 14, first conveyor means 16a and 16b between the batch mixer 10 and the apparatuses 12 and 14 respectively, one secondary high shear mixing apparatus 17, second conveyor means 18a and 18b between the primary and secondary apparatuses, third conveyor means 20 between the secondary apparatus and a stacking device 22, and pressing and curing stations not shown in the drawings.
The mixer 10 is of conventional design and is utilised, when the plant is in use, to form batches of a homogenous cementitious composition and feed the mixed composition to one or other of two conveyors 16a and 16b in turn through a discharge opening 24 in the underside of the mixer 10.
Associated with upper runs 26a and 26b of the conveyor means 16a and 16b respectively are metering gates 28 and 30 respectively. The gates 28 and 30 may be set to control, when the plant is in use, the feed rate of mixed cementitious material passing to the primary high shear mixing apparatus 12 and 14. The conveyors 16a and 16b are arranged to deliver the mixed composition to one end of their respective apparatus 12, 14.
As shown in Figure 1, the conveyor means 16a and 16b are located back to back with upstream ends 32 and 34 located underneath the mixture 10 and downstream ends 36 and 38 located overlying the apparatus 12 and 14 respectively. For convenience the conveyor means 16a and 16b in an industrial plant may be located on a floor F above the room or space where the apparatus 12, 14 and 17 are located.
The primary high-shear mixing apparatus 12 and 14 each comprise a twin-roll mill having a pair of contra-rotating rolls 40 and 42 located in side-by-side relationship with an adjustable nip defined therebetween. The rolls 40 and 42 are journalled in bearing housings 44 and 46 of conventional design and are connected to drive motors, not shown, such that the relative speed of rotation of the rolls 40 to 42 is in the ratio of 10:11. The rolls 40 and 42 are of equal diameter and arranged with their axes parallel, and horizontal.
Associated with the rolls 40 and 42 of each apparatus 12 and 14 are transfer blades 48,there being three such blades arranged overlying each roll. The blades 48 are each arranged at an acute angle to the axes of the rolls 40 and 42 with one blade 48 being parallel with each of the other blades 48 to define a part-spiral path across the upper part of the rolls 40 and 42 adjacent the nips therebetween for a purpose to be described hereinafter. In one example, the angle between the blades and the axes of the rollers was 70 .
The blades 48 are shaped to provide portions following the contours of, and adjacent to, the upper surface portions of the rolls 40 and 42. These "roll engaging portions", when the plant is in use, transfer cementitious material which is fed to upstream ends 50 of the rolls 40 and 42 and adheres to the surfaces of the faster moving rolls 40, sideways so that the blades 48 feed the material to downstream ends 52 of the rolls 40 and 42 as the rolls 40 and 42 are rotated.
The apparatuses 12 and 14 each comprise, see Figure 1, material take-off means 54 arranged at said downstream ends 52 of the rolls 40 and 42.
The take-off means 54 each comprise a doctor blade, not shown, and a roll element 56 which, when the plant is in use, separates the band of material from the rolls 40 and feeds it to the conveyor means 18.
The conveyor means 18 each comprise a belt conveyor which extends from the downstream ends 52 of the rolls 40 and 42 to overlie the apparatus 17.
The secondary high-shear mixing apparatus 17 is similar in construction and operation to the apparatus 12 and 14. Thus, the apparatus 17 comprises a pair of contra-rotating rolls 60 and 62 located in side-by-side relationship with a nip defined therebetween. The rolls 60 and 62 are journalled in bearing housings 62 and 66 of conventional design and are connected to drive motors via appropriate gearing, not shown, such that the relative speed of rotation of the rolls 60 and 62 is in the ratio 10:11. The axes of the rolls are parallel and horizontal.
Associated with the rolls 60 and 62 are transfer blades 68, there being three such blades arranged overlying the rolls. The blades 48 are each arranged at an acute angle of approximately 70° to the axes of the rolls 60 and 62 with one blade 68 being parallel with each of the other two blades 68 to define a part-spiral path across the upper reach of the rolls 60 and 62 adjacent the nip therebetween for a purpose to be described hereinafter.
The blades each have roll engaging portions similar to those described above whereby, when the plant is in use, cementitious material, fed to an upstream end 70 of the rolls 60 and 62, adheres to the surface of the faster moving roll 60 and is fed sideways by the blades 68 to a downstream end 72 of the rolls 60 and 62 as the rolls are rotated.
The apparatus 17 comprises a take-off means 74 arranged at said downstream end 72 of the rolls 60 and 62, see Figure 1.
The take-off means 74 comprises a shear blade and rotating edge cutting blades, not shown, and a roll element 76 which, when the plant is in use, separates the continuous band of cementitious material from the roll 60 and feeds it to the conveyor means 20.
The plant comprises a cutting press 80 located at an intermediate position along the run of the conveyor means 20, the press 80 having a reciprocating cutter blade generally designated 82 in Figure 1, which blade, when the plant is in use,is effective to cut the band of material into discrete blanks 83.
At a downstream end of the conveyor means 20, the plant comprises a transfer device 84 of known configuration which device, when the plant is in use, transfers the green state blanks, cut from the band by the blade 82, to the stacking device 22.
The stacking device 22 is of conventional design and is arranged when the plant is in use, to place steel pallets 86 between each layer of green state blanks 83.
The pressing station is of convention design and, when the plant is in use, it is effective to subject the stacks of blanks 83 to a pressure of 6Mpa to further compact the blanks.
The curing station of the novel plant is also of conventional design, and, when the plant is in use, stacks of blanks 83 positioned therein are subjected to a temperature of between 40° and 90°C at 100% RH for up to 8 hours.
In carrying out the method of manufacture of artificial roofing slates on the plant described above, the following procedure is used. The constituents of the cementitious composition are fed on a continuous basis to the mixer 10, i.e. as one batch of mixed materials is depleted a further batch is prepared.
The cementitious composition is one of a low water/cement ratio and contains a processing aid. Examples of such compositions are described in European Patent Application 81305630.6 (Publication No.0055035). The composition is mixed until a high degree of homogeneity is achieved. The outlet 24 of the mixer 10 is then opened and the composition, which has a crumbly consistency, is deposited on the upper run 26a or 26b of the conveyor means 16a and 16b.
The cementitious composition is carried by the conveyor means 16a and 16b under the gates 28 and 30, which gates meter the flow thereof, to fall from the downstream ends 36 and 38 of the conveyor means 16a and 16b into the nips of the rolls 40 and 52 at the upstream ends 50 thereof. For continuous processing, the spacing of the rolls (the nip) is preset at a fixed gap, for example 4nm.
The cementitious composition is subjected to high shear mixing as it passes through the nips of the rolls 40 and 42 and eventually it adheres to the surfaces of the faster moving rolls 40. It will be obvious, from a study of Figure 2, that the material adhering to the rolls 40 in the lee of the blades 48, adjacent to the nip of the rolls, will be carried into engagement with an opposite side of the blades 48 after one revolution of the rolls 40. Thus, the cementitious composition is constrained to follow part spiral paths to be carried from the upstream ends 50 of the rolls 40 and 42 towards the downstream ends 52 of said rolls.
At the downstream ends 52 of the rolls 40 and 42 the cementitious material is removed from the rolls 40 by the take-off means 54 and fed by the conveyor means 18a and 18b to the nip of the rolls 60 and 62 at the upstream end 70 thereof.
The cementitious composition is once more subjected to high shear mixing as it passes through the nip of the rolls 60 and 62 and advantageously it adheres to the surface of the faster moving roll 60. As with the apparatuses 12 and 14 the cementitious composition in the lee of the blades 68, adjacent the nip of the rolls, will be carried into engagement with an opposite side of the blades 68 after one revolution of the roll 60. Thus, the cementitious composition is constrained to follow a part spiral path and is carried from the upstream end 70 of the rolls 60 and 62 towards the downstream end 72 thereof.
At the downstream end 72 of the rolls 60 and 62 the cementitious material is in a highly plastic putty-like state and a continuous band is separated from the roll 60 by the take-off means 74 and fed onto the conveyor means 20.
At a mid-point of the conveyor means 20 the continuous band of material is cut into blanks 83 by the blade 82 and at the downstream end of the conveyor means 20 the green state blanks 83 are transferred onto a pallet 86 in a stacking device. The blanks may, for example, be roofing tiles or slates.
The stacks of blanks82 are thereafter pressed in the press for 2 hours at a pressure of 6Pa to further compact the blanks 83 and reduce-the porosity of the final products.
After pressing the stacks of blanks 83 are conveyed to the curing chamber where they are subjected to a temperature of 60° at 100% RH for 8 hours.
The cured slates are thereafter packaged and despatched. In a modified plant provision may be made for applying an organic polymer or other suitable coating material to at least one surface of the cementitious products prior to or after the curing operation.
It will be appreciated that reinforcement material, for example glass fibres, may also be added to the composition.
Cementitious products of the kind described above manufactured in a plant utilising high shear mixing apparatuses as herein before disclosed have been found to have an enhanced flexural strength and modulus of elasticity when compared to presently available commercial products.
It is believed that the intimate mixing imparted by the mixer 10 followed by the high shear mixing of the apparatuses 12, 14 and 17 together with the low pressure pressing by the press creates a material of low porosity and high density which is not readily achieved by conventional processing techniques when water cement ratios in the order of 0.15 are used.
The invention is not limited to the preferred embodiment described above and various modifications may be used. For example the arrangement of transfer blades above the rolls of the mills may be varied, according to the size of the mills and the throughput of cementitious material.
There may be more than three blades (for example, five or six) and the angle between the blades and the axes of the rolls may vary from about 60° to 80°. Guide plates perpendicular to the axes of the rolls may be provided at each end of the rolls to assist in proper transfer of the cementitious material.
The spacing and angles of the blades may vary from one end of the rolls to the other, provided the spacing between the last pair of blades is at least the width of the strip of material to be removed from the mill.
Each blade may only overlie the surface of the faster moving roll when the rolls are rotated at unequal speeds, a small part of the blade extending into the nip of the rolls, to avoid sideways travel of cementitious material which is still crumbly. Further one of the blanks may be "arrow-head" shaped with one side of the arrow-head parallel to the other blades.
This arrangement may help to prevent build up of the crumbly material on the slower moving roll.
The operation of the mills may also be varied. For example, the size of the nip may be varied by moving the slower moving roll towards and away from the faster moving roll. The rolls may be of unequal size and their speeds of rotation may be varied. One or other of the rolls may be heated or cooled to assist in plasticising the cementitious composition.

Claims

1. Apparatus for manufacturing a cementitious building product characterized by the combination of at least one twin-roll mill

comprising a pair of contra-rotating rolls defining a nip therebetween, for effecting high-shear mixing of a cementitious compostion, at least one transfer blade means arranged adjacent to the rolls and at an angle to the axes thereof for effecting transfer of the cementitious composition from an upstream end of the rolls to a downstream end thereof during mixing, thereby to form a band of cementitious material on one of the rolls; take-off means at the downstream end of the rolls adjacent said one of the rolls for removing said band of cementitious material from said roll, and forming means for forming said band into blanks, said blank being cured to form a building product.

2. Apparatus as claimed in claim 1 characterized in that means are provided for rotating the rolls of the mill at unequal speeds.

3. Apparatus as claimed in claim 1 or claim 2 characterized by first and second twin-roll mills arranged in series, the cementitious material being fed from the downstream end of the first mill to the upstream end of the second mill.

4. Apparatus as claimed in claim 3 characterized in that there are two first mills arranged in parallel, material from the downstream ends of both first mills being fed to the upstream end of the second mill.

5. Apparatus as claimed in any one of the preceding claims further characterized by mixing means for mixing together cement, water and a processing aid to form the cementitious composition.

6. Apparatus as claimed in claim 5 further characterized by first conveyor means for transferring the cementitious composition from the mixing means to the or each first mill.

7. Apparatus as claimed in claim 6 further characterized by second conveyor means for transferring material from the or each first mill to the second mill.

8. Apparatus as claimed in claim 7 further characterized by third conveyor means for transferring material from said second mill to said forming means.

9. Apparatus as claimed in any one of the preceding claims further characterized by pressing means for pressing the blanks and curing means for curing the blanks.

10. Apparatus as claimed in any one of the preceding claims characterized in that there is a plurality of parallel transfer blades associated with the or each mill.

11. Apparatus as claimed in any one of the preceding claims characterized in that the or each mill is arranged with the axes of the rolls parallel and horizontal and the or each transfer blade means is shaped to be adjacent to an upper part of the surface of at least one roll.

12. A method of manufacturing a cementitious building product in app^paratus as claimed in any preceding claim and comprising the steps of processing a cementitious composition comprising a mixture of cement, water and a processing aid in a twin-roll mill thereby to subject the composition to high-shear mixing, transferring the composition from an upstream end of the mill to a downstrean end during mixing, thereby to cause the composition to pass through sideways adjacent portions of the nip of the rolls of the mill; removing a band of cementitious material from the downstrean and of the mill; and forming said band into blanks of building products, the blanks thereafter being cured.

13. A method as claimed in claim 12 in which the rolls of the twin-roll mill are rotated at unequal speeds.

14. A method as claimed in claim 13 in which the speeds of rotation of the rolls are in the ratio 10:11.

15. A cementitious building product manufactured by apparatus as claimed in any one of claims 1 to 11.

16. A cementitious building product manufactured by a method as claimed in any one of claims 12 to 14.

17. A cementitious building product as claimed in claim 15 or claim 16 characterized in that it is a roofing tile.