Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B5/00—Producing shaped articles from the material in moulds or on moulding surfaces, carried or formed by, in or on conveyors irrespective of the manner of shaping
  • B28B5/02—Producing shaped articles from the material in moulds or on moulding surfaces, carried or formed by, in or on conveyors irrespective of the manner of shaping on conveyors of the endless-belt or chain type
  • B28B5/026—Producing shaped articles from the material in moulds or on moulding surfaces, carried or formed by, in or on conveyors irrespective of the manner of shaping on conveyors of the endless-belt or chain type the shaped articles being of indefinite length
  • B28B5/027—Producing shaped articles from the material in moulds or on moulding surfaces, carried or formed by, in or on conveyors irrespective of the manner of shaping on conveyors of the endless-belt or chain type the shaped articles being of indefinite length the moulding surfaces being of the indefinite length type, e.g. belts, and being continuously fed
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B28—WORKING CEMENT, CLAY, OR STONE
  • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
  • B28B1/00—Producing shaped prefabricated articles from the material
  • B28B1/52—Producing shaped prefabricated articles from the material specially adapted for producing articles from mixtures containing fibres, e.g. asbestos cement
  • B28B1/526—Producing shaped prefabricated articles from the material specially adapted for producing articles from mixtures containing fibres, e.g. asbestos cement by delivering the materials on a conveyor of the endless-belt type

Definitions

• the present invention is concerned with the manufacture of building board from cementitious material.
• the invention is particularly useful in the manufacture of gypsum fibre board.
• Cementitious fibre board is made by mixing a predetermined amount of fibrous material (for example cellulose fibres or wood chippings) , water and dry cementitious material (for example dry calcined gypsum) , forming the mixture into a mat and compressing the mat and then allowing the cementitious material to set and form a board of bonded fibres and cementitious material.
• the fibrous material may be reinforcing fibres.
• Additives may be added to the mixture for acceleration of the binding process, or to improve board properties. The amount and type of additive is dependent on the desired properties of the final board.
• a three-layered cementitious fibre board comprising a mixture of fibres, water, cementitious material, lightweight aggregate such as perlite and any desired additives may be formed using the process described in International patent application No. W093/01932 of Carl Schenk for a method of production of gypsum fibre board.
• An uncompressed mat comprising a mixture of fibres, water, cementitious material and any desired additives is formed by pouring metered quantities of the mixture onto a moving conveyor belt. The mixture is spread out on the belt forming a three layer mat of significant height. The mixture making up this uncompressed mat contains about 70- 80° air by volume. This is known as the "forming stage".
• the levelled layer of mixture then passes into a continuous roller press having three main sections; a pre- compressor or pre-press (also known as a degassing press), a main press and a calibrator section.
• the moving conveyor belt carries the levelled mixture through the press sections and their associated pressing operations.
• the pre-press compresses the mat to remove air contained in the mixture, and to reduce the mat height in preparation for entering the main press.
• the pre-press is typically made up of a top belt which gradually converges with the mat carried on the moving conveyor. One or both of the belts of the pre-press are permeable so as to allow the air pressed out of the mat to escape. As the mat is moved into the pre-press, the top belt comes into contact with the top of the mat.
• the pre-press typically reduces the mat height by about 70% ( e.g. for a final board thickness of 10mm, from about 70mm to about 15-20mm) .
• the mat leaving the pre-press is about 120% - 150% of the desired thickness of the finished board.
• the main press subjects the mat to a high load and presses it to the final board thickness.
• the main press typically consists of a frame supporting two continuous belt conveyors, one running above and one below the mat. These belt conveyors are supported by closely spaced rolls which permit the conveyors to exert a significant squeezing action on the mat.
• the gypsum is partially set.
• the calibrator section is very similar to the main press and can also exert a significant load on the mat.
• the calibrator is designed to hold the mat at a set caliper until the mat cures to a solid state at the exit of the calibrator.
• the final setting of the gypsum takes place in the calibrator section or calibration press, such that the mat leaving the calibrator is a set board. In certain circumstances the board leaving the calibration press may not be finally set. Hydration of the mat may not be complete at the exit of the calibration press; a small further amount of setting may then take place after the board leaves the calibration press.
• edges of the untrimmed board leaving the calibration press will be soft due to lateral spread of the mat mixture as it is spread and pressed. These soft lateral edges of the pressed board are unsuitable for inclusion in the final manufactured board as they reduce the strength of the board and would, if left on the finished board, result in a non-uniform board. The soft edges must therefore be removed. This is done by trimming the board using a water knife. It has been found that for gypsum fibre board plant of the type described above and forming a pressed mat having a width of about 2600 mm, between 100 and 200 mm must be trimmed from each lateral edge. This means that between about 8% and 16% of the pressed material has to be either discarded or recycled; both involving considerable waste of energy. A further disadvantage of this waste is that the width of board which can be produced by a given plant must be significantly less than the width of the plant belts; in some cases the maximum possible board width is about 400mm less than the width of the plant belts.
• Gypsum fibre board may be produced in three layers; strong upper and lower surface layers and a less strong and less dense middle layer or core.
• the layered structure is advantageous as it allows one to reduce the weight of the finished board without sacrificing strength at the critical areas, that is, the surfaces.
• the less strong and less dense core layer is typically made using a gypsum mixture including a lightweight aggregate such as perlite, vermiculite or a similar filler.
• the core layer typically has a lower fibre content than the surface layers.
• the layered fibre board is made by having plant which includes means for the supply of surface and middle layer gypsum mixtures. A layer of surface mixture is spread onto the moving conveyor, a layer of the core mixture is then spread onto this first surface layer and an upper layer of surface mixture is then spread onto the core low density layer.
• the layered mat is then pressed, trimmed, cut and dried as discussed above.
• the lateral spreading of the mat as it passes through the forming stage, pre-press and main press causes a problem in addition to those discussed above; the lateral spread of the mixtures and the adhesion of the surface layers to the press belts mean that the low density, weak core layer flows to the bottom of the mat at its edges.
• This spreading effect results in a board having weak edge portions extending a significant distance into the finished board as illustrated in figures 3(a) to 3(f). Having a finished board with this low density and low strength material at the surface seriously affects the strength of the board.
• the lateral edges of the board must therefore be sufficiently trimmed that all parts of the board' s surface into which the low density mixture has been spread, and all parts of the board from which the low density mixture has been squeezed out from are discarded.
• the present invention seeks to reduce the wastage associated with cementitious fibre board plant in which an unset cementitious material is significantly compressed or compacted before it sets.
• the present invention provides process and apparatus for manufacturing building board as defined in the independent and omnibus claims to which reference should now be made. Preferred features of the invention are defined in the dependent claims.
• Preferred embodiments of the present invention allow one to significantly reduce the wastage associated with the known plant of the type described above and in International Patent Application No. WO93/01932, without reducing the strength of the finished board.
• the inventors of the present invention are the first to appreciate that a significant proportion of the lateral spread occurs in the pre-press. It has not previously been appreciated that although the mat leaving the pre-press is not set the subsequent higher pressure pressing in the main and calibrator presses does not significantly further spread the mat lateral edges .
• the present invention derives from the inventors' realisation that the critical and main source of lateral mat spread occurs during the pre-press even though the mat leaving the pre-press is not set and is yet to undergo processing steps in which significant pressures are applied to the mat before it sets .
• a significant improvement in the edge characteristics of the press and board can be achieved by providing a lateral barrier within the pre-press.
• the inventors of the present invention are the first to appreciate that the problem of soft edges can be significantly reduced by constraining lateral movement (i.e. spread) of the mat in the degassing or pre-press.
• the inventors have appreciated that very significant improvements are achieved by restraining lateral spread in the pre-press. Although not set, the mat leaving the prepress is sufficiently compacted for the lateral spread in a main press section without lateral barriers to be less significant than that in a pre-press section without lateral barriers, even though the main press exerts a greater pressure, and exerts a pressure for longer.
• Figure 1 is an illustration of a method and corresponding plant for the manufacture of layered cementitious building board
• Figure 2 is an illustration of the cross-section of a layered gypsum fibre mat on the forming belt of figure 1,
• Figures 3(a) to 3(g) are an illustration of the cross-section at different points in the manufacture of half of a layered gypsum fibre mat made according to the known method using the method and plant of Figure 1
• Figures 4(a) to 4(f) are an illustration of the cross-sections of half of a layered gypsum fibre mat made according to an embodiment of the present invention
• Figure 5 is an illustration of an embodiment of a pre-press lateral barrier
• Figure 6 illustrate a drive and/or guiding system for the barrier of figure 5;
• Figures 7 (a) to 7 (b) and Figures 8 (a) and 8 (d) are alternative pre-press lateral barrier constructions.
• Figure 9 is another alternative pre-press barrier;
• Figures 10(a) to 10(c) illustrate the compression of the barrier of figure 9 as it passes through the prepress
• Figure 11 illustrates an alternative pre-press barrier
• Figure 12 illustrates the barrier of Figure 11 as it is compressed
• Figures 13 and 14 are further alternative pre-press lateral barriers.
• Figure 15 illustrates a possible guiding mechanism for the lateral barriers of figures 8 to 11.
• layered gypsum fibre board is made by spreading three layers (1, 2, 3) through three separate mixing heads (4,5,6) onto a forming belt 7, subsequent compression to expel air from the mat (typically a reduction of about 70% in a pre-press (8) defined by a top cover belt (9) which converges towards the forming belt (7) and reduction to a final board thickness in main and calibrating presses (10, 20) defined by a press top cover belt (21) and the forming belt (7).
• the method and plant of the described embodiments are modifications to the known plant described in WO 93/01932 and reference is therefore made to this publication for details of the plant and method which are not included in the following description.
• wet recycled paper fibres for a bottom surface layer (1) are spread on a first preforming belt (not shown) , followed by a layer of hemihydrate plaster or gypsum together with additives.
• the belt carries the materials to a mixing head (4), which deposits the resulting mix on a main forming belt (7) . Water is then sprayed on the mix; this water starts hydration of the gypsum in the bottom surface layer.
• Wetted aggregate (e.g. perlite or a similar lightweight material) and fibres for the core mix are supplied to a blender from where the core mix is spread on a second pre-forming belt (not shown) , passing through a mixing head (5) to be spread on top of the bottom surface layer (1) on the main forming belt (7) .
• fibres and plaster for a top surface layer (3) are supplied to a third pre-forming belt (not shown) , are mixed in a mixing head (6) and spread on top of the core layer (2) on the main forming belt (7) .
• the layers of gypsum mixture form a mat.
• the mat (1,2, 3) passes into a pre-press or degassing press (8) which compacts the mat to a fraction of its initial height; in the particular embodiments of the invention which will be described in this document to about 30% of its initial height.
• This pre- or degassing press expels most of the excess air from the mat.
• the compacted mat is then carried by the belt through a spraying station where sufficient water for hydration of all the gypsum in the mat is sprayed onto the compacted mat and then through main (10) and calibration (20) presses successively.
• the mat has a height of about 70 mm when entering the pre-press (8), about 20 mm on leaving the pre-press and 10.2 mm on leaving the calibration press (20).
• the paper fibres reinforce the board. Fibres of alternative materials may be used to affect different board properties. For example, polymer fibres may be used to improve the impact absorbence of a finished board.
• the known gypsum fibre board plant of the type shown in Figure 1 but not including the present invention and having the successive pouring of the bottom surface, core and top surface gypsum mixtures produces an uncompacted layered mat (2) having a cross-section as shown in figures 2 and 3(c) .
• This uncompacted mat then passes into the pre-press (8).
• the pressure applied in the pre-press and the tendency for the top and bottom surfaces of the mat to adhere to the belts (7, 9) with which they are in contact both lead to further lateral or sidewise spreading of the mat (see Figures 3(d) and (e)) and of the core layer relative to the bottom and/or top surface (s) of the mat (see Figure 3(e)).
• the presence of core layer material containing aggregate such as perlite on the board surface would significantly weaken the board and it is therefore necessary to trim the edges (27) of the board as shown in Figure 3 (g) so as to produce a sufficiently strong board having a uniform structure across its width.
• the mat leaves the calibration press (20) and is trimmed to remove the non-uniform portions of the board in order to produce a uniform structure which is then dried.
• vertical edge or side belts (23) run alongside the pre-press belts and define a barrier to the lateral spread of the mat as it is compacted in the prepress.
• the vertical edge or side belts (23) move at the same speed as the conveyor or forming belt (7) and the mat (8) .
• the edge or side belts (23) are guided around rollers (24) which define a horizontal path (25) with a section (26) running parallel to the main forming belt (7) and forming a side barrier to mat spread in the pre-press or degassing press.
• the pre-press barriers of the present invention may be combined with barriers in other stages of the manufacturing process; e.g. in the forming stage, main press and/or calibration press .
• the barrier is formed by a hollow rubber tube (27) containing a fluid under pressure.
• the tube has a fabric or textile covering in a manner similar to a fire hose.
• the tube should be capable of being repeatedly compressed with little wear and return to its original state when it is no longer compressed.
• Suitable fluids include air or gas under pressure, oil or water.
• a pneumatic hollow tube (27) containing air under pressure (somewhat similar to a vehicle tyre inner tube) is believed to be particularly advantageous as it allows significant compression.
• the rubber hose-like tube 27 is guided around a horizontal path having a section running through the pre-press by guiding rollers (28) such that it passes through the pre-or degassing press (8) within the width of the press and forms a resiliently deformable barrier to spread of the mat as it is compacted in the pre-press.
• FIG. 8 (a) to 8 (d) has a circular cross-section
• other cross-sections e.g. triangular
• the inventors believe that a tube having a cross-section with a flat vertical side facing the mat and a curved side facing the guiding rollers is particularly advantageous.
• the straight face helps to keep the lateral edge of the compressed mat straight and the curved surface can more easily cooperate with the guiding rollers which would have concave surfaces for contacting the tube.
• GFB gypsum fibre board
• Figure 9 illustrates an alternative barrier construction comprising two continuous belts (30, 31) consisting of a series of elastic strips of foam forming two continuous blocks-like belts (30, 31).
• the lower and thicker block (30) of foam moves around a path similar to that described above for the edge belt of figure 6, and the upper thinner block moves around a vertical path (32) defined by rollers and having a section running through the pre-press parallel to and above the section of the belt path for the thicker lower belt (33) (see Figure 13 in which side barriers operate in forming and pre-press stages) .
• the foam belts each have co-operating and contiguous sloping faces (39,35) (30,33) which can slide across each other as shown in Figures 10(a) to 10(c) such that as the 40 mm high foam blocks enter the pre-press they overlap slightly (see Figure 10(a)) and together define a continuous barrier about 70mm high. (The height of the entry to the pre-press) . As the blocks pass through the pre-press they move relative to each other and progressively overlap more. When they overlap fully (see Figure 10(b)) they are compressed by the pre-press belts as they move further into the pre-press (8).
• the blocks may be made of a polyurethane foam having a density in the range of 50 to 400 kgm- 3 .
• a preferred range is 200 to 300 kgm "3 and a value of 300 kgm "3 is thought to be optimal.
• An advantage of this system is that it allows one to use materials which are sufficiently stiff to act as effective side barriers but which are not sufficiently elastic to be continuously compressed by about 70% as they pass through the pre-press and return to their original size as they emerge therefrom.
• the system of figures 9 and 15 allows one to overcome the conflicting requirements for a stiff side barrier which can effectively hold in the mat as it is compacted, and for an elastic barrier which can be repeatedly compressed by about 70% without degrading or losing its elasticity.
• the barrier is formed by a single foam or defendingling transilon belt 60.
• the foam belt has a sloping face when it is uncompressed; this face takes up a vertical position during compression so as to help produce a mat with straight vertical edges.
• Figure 14 shows an alternative set of foam block profiles (40, 41) which can be used in a similar manner to those of figures 9 and 10.
• the lower foam belt (40) has a rectangular cross-section about 35 mm high and can slide within an upper channel-like foam belt (41) about 40 mm high.
• twin foam belts are replaced by a single foam belt (50) which is guided around a path in a similar manner to the edge belt of figures 5 and 6.
• the foam (50) has a V-shaped profile so as to be sufficiently deformable to be able to be reversibly compacted or compressed by the requisite 70% necessary to pass repeatedly through the pre-press (8).

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Mechanical Engineering (AREA)
• Press-Shaping Or Shaping Using Conveyers (AREA)
• Laminated Bodies (AREA)
• Producing Shaped Articles From Materials (AREA)
• Conveying And Assembling Of Building Elements In Situ (AREA)

Priority Applications (5)

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Publications (1)

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Citations (4)

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• 1998
  • 1998-07-29 GB GB9816539A patent/GB2340061B/en not_active Revoked
• 1999
  • 1999-07-28 WO PCT/GB1999/002469 patent/WO2000006355A1/en active IP Right Grant
  • 1999-07-28 EP EP99936792A patent/EP1100662B1/en not_active Expired - Lifetime
  • 1999-07-28 DE DE69916618T patent/DE69916618T2/de not_active Expired - Lifetime
  • 1999-07-28 AT AT99936792T patent/ATE264735T1/de active
  • 1999-07-28 PT PT99936792T patent/PT1100662E/pt unknown
  • 1999-07-28 ES ES99936792T patent/ES2220096T3/es not_active Expired - Lifetime
  • 1999-07-28 CZ CZ20010295A patent/CZ302715B6/cs not_active IP Right Cessation
  • 1999-07-28 PL PL345669A patent/PL193129B1/pl unknown
  • 1999-07-28 DK DK99936792T patent/DK1100662T3/da active

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