IE842973L

IE842973L - Compressing of fibrous cement slabs

Info

Publication number: IE842973L
Application number: IE842973A
Authority: IE
Original assignee: Bell Masinenfabriek Ag
Priority date: 1983-12-09
Filing date: 1984-11-21
Publication date: 1985-06-09
Also published as: ES8604805A1; FI76952B; EP0144881A2; IE56098B1; DK585884D0; FI76952C; DK585884A; JPH0321323B2; CH661470A5; DE3468832D1; AU567379B2; EP0144881A3; JPS60139405A; FI844536L; BR8406032A; ATE32041T1; DK160684C; AU3643184A; DK160684B; FI844536A0

Abstract

1. Method of compacting damp, corrugated fibrous cement sheets (3) which lie on a permeable, pressure-resistant pressing base (5) and which with the latter are pressed between an upper (2) and a lower (1) matrix to compact the fibrous cement material, wherein the aqueous filtrate which is pressed out is removed via a channel system which is open to the permeable pressing base (5) and is provided on the lower matrix (1), wherein the channel system (9, 13, 14) has a current of air flowing through it from a source of positive air pressure (19) in the direction of the removal of the filtrate, to a suction point (17), which current entrains, accelerates and transports the drops of aqueous filtrate which have percolated through the pressing base (5) on compacting, and wherein the current of air is driven through the channel system (9, 13, 14) at such a velocity and in such a quantity sufficient to divide the drops of the filtrate into particles, in order to carry them, atomized, with the current of air through the channel system without wetting the walls of the channel system.

Description

H 0 9 8 The invention concerns a process for compressing damp corrugated fibrous cement boards, which are situated on an incompressible permeable pressing base and which are compressed with this latter between an upper and a lower 5 matrix to compress the fibrous cement mass, where the aqueous filtrate pressed out is taken away via a system of channels open to the permeable pressing base, provided at the lower matrix, where the system of channels can have a flow of air from a source with positive air pressure 10 in the direction of removal of the filtrate to a suction position which, during compression through the pressing base, carries over, accelerates and transport drops of the aqueous filtrate which have trickled through, A better quality of the product is achieved by compression: the values of strength are raised and the weatherproofing is improved. The preformed fibrous cement board is made 10 to 25% thinner in this way.

According to a preferred method, this is done in a press in which the pressing base is driven with the preformed, damp, corrugated fibrous cement board onto the lower matrix. The pressing base is a perforated board corrugated according to the corrugated shape 25 of the fibrous cement board, the surface of which is provided with a sieve net or strainer layer, which bridges the holes in the sheet. The surface of the lower matrix has corrugations which correspond precisely to the lower 30 side of the pressing base. The pressure surface of the upper matrix has corrugations which correspond to the upper side of the compressed fibrous cement board.

The fibrous cement board is compressed between the matrices 2 using a pressure of 50 to 200 kp/cm (5 to 20 MPa), which is reached within 2 to 10 seconds and maintained for a further 1 to 20 seconds. While the pressure is rising to a maximum, an aqueous filtrate flows out of the fibrous cement mass through the sieve net or strainer and the holes of the pressing base and is taken away through a system of channels at the lower matrix. After the compression process is completed, the matrices are moved apart and the pressing base with the compressed fibrous cement board is driven out of the press, then unloaded and a further pressing base, which has in the meantime been loaded with fibrous cement board to be compressed, is driven into the press. The unloaded pressing base returns, in order to be loaded in a subsequent cycle with a new fibrous cement board to be compressed. A number of pressing bases circulate in a circuit.

The homogeneity of the fibrous cement board, which is to be achieved by compressing, presupposes even pressure, using a high pressure and an even dewatering of the mass. The aqueous filtrate, which is to be pressed out of the mass, must be evenly and quickly removed from the mass.

This problem is not satisfactorily solved in a pressing device known from DE B1 206 776, where differing from the features of the present invention, flat plates are simultaneously corrugated and pressed between corrugated matrices, but 5 the filtrate is removed via channels in the lower matrix.

GBA-1 535 356 shows the filtrate in the manufacture of cardboard plates being sucked upwards through an upper matrix. The removal of the filtrate can be aided by 10 blowing a flow of air into the collecting spaces of the filtrate. However, this filtrate has no contents forming a crust. Great difficulties are caused by the fact that the previously provided removal paths for the filtrate lose their flow capacity after 15 a short operating period by encrustation, so that collections of filtrate are formed, which, after reduction of the pressure are sucked back into the mass. This causes uneven damping which, during binding of the fibrous cement plates, causes locally varying vibration. 20 This causes losses of strength and therefore a loss of quality of the final product. These encrustations are due to the properties of the filtrate, which, among other components, contains a considerable amount of lime. Finally, this leads to a state where production has to be 25 interrupted in order to clean or de-crust the paths.

It is not possible to make the paths greater, as the strength of the lower matrix or the pressing base would be adversely affected and they would no longer withstand the high working pressures. It may also happen that hard foreign bodies enter the mass, which could then cause damage to the weakened matrices or pressing bases.

The purpose of the invention is to find measures for 5 the process described above, which make an even, complete and trouble-free removal of the pressed-out filtrate possible, with means which do not adversely affect the strength or stability of the device concerned, particularly the lower matrix and the pressing base. It 10 should also be possible to compress fibrous cement boards of small formats with a set of tools, i.e. a lower and an upper matrix and with pressing bases of the same format.

The present invention provides a method of compacting damp, corrugated fibrous cement sheets which lie on a 15 permeable, pressure-resistant pressing base and which with the latter are pressed between an upper and a lower matrix to compact the fibrous cement material, wherein the aqueous filtrate which is pressed out is removed via a channel system which is open to the permeable pressing 20 base and is provided on the lower matrix, wherein the channel system has a current of air flowing through it from a source of positive air pressure in the direction of the removal of the filtrate, to a suction point, which current entrains, accelerates and transports the 25 drops of aqueous filtrate which have percolated through the pressing base on compacting, and wherein the current of air is driven through the channel system at such a velocity and in such a quantity sufficient to divide the drops of the filtrate into particles. In order to carry them, atomized, with the current of air through the channel system without wetting the walls of the channel system.

Advantageous versions of the process according to Claim 1 are stated in the sub-claims.

The process according to the invention and its advantages are described and explained in more detail below. The 10 description refers to the drawings, which show: Fig. 1, a view on the front of parts of an upper and lower matrix Fig. 2, an enlarged partial longitudinal section through the lower matrix along line I-I in Fig. 1. 15 Fig. 3, an enlarged section from Fig. 1, and Fig. 4, a schematic side view of a source of compressed air connected to the lower matrix.

The compression of a fibrous cement board 3 occurs in a space 4 between a lower matrix 1 and an upper matrix 2. 20 The matrices are built into a press of known design, which is not shown in the drawing, and can be moved vertically relatively to one another by means which are also not shown. A damp preshaped, i.e. corrugated fibrous cement board 3 to be compressed lies in an 25 intermediate space 4 between the two matrices 1 and 2 on a permeable, non-compressible pressing base 5.

This latter is made of a perforated sheet with holes 6. The pressing base 5 is situated on the surface having corrugations of the lower matrix 1, where the form of the corrugations of matrix 1 and the form of the 5 corrugations of the adjacent side of pressing base 5 are matched to one another, so that the pressing base 5 can be situated close to the surface of matrix 1. The surface of pressing base 5 is provided with a fine meshed sieve net or strainer 7, which bridges the holes 6 10 of pressing base 5. A separating layer 8, is provided between the fibrous cement board 3 and the form of the corrugations of the upper matrix 2, which said layer prevents adhesion of the fibrous cement plate to the upper matrix 2.

With the lowering of the upper matrix 2 to the lower matrix 1, a pressure is raised from zero to a maximum. This causes surface pressure to be applied between the matrices, which compresses the fibrous cement mass of the fibrous cement board. An aqueous filtrate is pressed 20 out of the mass and trickles downwards through the meshes of the sieve net or strainer 7 and through the holes 6 of pressing base 5 into a system of channels 9, 13, 14 at the lower matrix, which is connected to holes 6 or is open to holes 6 respectively„ In order to achieve a desired compression effect, the 2 surface pressure within the range of 50 to 200 kp/cm (5 to 20 MPa) must be produced. After the desired maximum surface pressure has been reached in a period of 2-10 seconds, for example, the respective pressure is maintained for a period of some seconds, e.g. 1 to 20 seconds. After this, the matrices 1 and 2 are moved apart and the compressed fibrous cement board with the 5 pressing base is driven out of the space between the matrices.

At the corrugated surface of the lower matrix 1, the system of channels connected to the holes 6 of pressing 10 base 5 for removing the pressed-out filtrate has channels or grooves 9 opposite to the holes 6 and open in the upward direction. The said channels or grooves run over the width of matrix 1 where a corrugation trough 10 goes to corrugation crest 11 and to the next corrugation 15 trough 10 and are arranged close to one another in the length of matrix 1, as is made clear in Fig 1 in cross section and in Fig 2 in longitudinal section.

The division or distribution of the channels 9 on matrix 20 1 and the division or distribution of the holes 6 through the pressing base 5 are selected so that there is always a sufficient number of holes above the channels 9 and only a few of these above the bars 12 between the channels. In order to remove the filtrate from channels 25 9, a vertical hole 13 is provided in each corrugation trough of each channel 9, which leads to manifolds 14, which run the length of the matrix below the corrugation troughs 10 through the matrix.

Distribution channels 15 run parallel to the manifolds 14 below the corrugation crests 11, which said distribution channels are connected to a source of compressed air.

Holes 16 lead from these channels 15 to each corrugation crest 11 and to each channel 9, through which the 5 compressed air flows on the corrugation crest 11 into the channels 9 bridged by pressing base 5 and through these to the corrugation troughs 10 and through holes 13 into manifolds 14. This flow path is shown in Fig 1 and Fig 3 by the arrows drawn there. The cross sections 10 of holes 13 and 16 and the cross section of channels 9 are approximately equal.

A sufficient air flow speed in channels 9 is in the range of 15 to 20 metres/second. This is sufficient to ensure 15 that the drops of the filtrate pressed out are carried over and accelerated by the air flow, atomized into small particles or into mist and are transported at this said speed through the channels 9 and the holes 13 into the manifolds 14, without wetting the walls of these 20 relatively narrow flow profiles.

Therefore, no encrustations and no collections of the filtrate are formed, not even in the corrugation troughs 10 of channels 9, so that when the pressure 25 is reduced, no filtrate can be sucked back into the fibrous cement mass of the compressed fibrous cement board. The maintenance of the pressure in the final phase of compression must correspond to the time which is necessary for removing the filtrate from the channels. This is completed in a few seconds.

As shown in Fig 4, all the manifolds 14 running below the corrugation troughs 10 in the longitudinal direction 5 on the front of the lower matrix 1 are connected to a suction line 17 (on the right of the picture), which leads via a separator 18, for separating the filtrate from the air to the suction side of a fan 19.

The pressure side of the fan 19 has all the air distribution 10 channels 15, which run through the matrix in the longitudinal direction under the corrugation crests 11, connected to it via a pressure line 20 (on the left of the picture). The channels 15 are covered on the opposite side of matrix 1. The channels 14 are covered 15 correspondingly on the opposite side of matrix 1 to suction line 17. The air therefore flows from a source of positive pressure, the fan 19 to the air distribution channels 15, from this latter through holes 16 to the corrugation crests 11, through the channels 9, where the 20 drops of filtrate are carried over, accelerated, turned into mist and this air/filtrate mixture flows through the holes 13 into the manifolds 14 and into separator 18. After separation of the filtrate in the separator 18, the air is again transported via the fan 19 into the air 25 distribution channels 14 and so on in the described circuit.

Because of the intensive transport effect of the powerful air flow, it is possible in this process to keep all the sections of the system of paths described above within dimensions which do not adversely affect the strength of the lower matrix, so that the matrix will 5 withstand the relatively high working pressures. The same applies to the adaptation of the pressing base 5 to matrix 1 as regards strength. It is logical that this ratio must be chosen so that at worst, e.g. if hard foreign bodies penetrate the fibrous cement 10 mass to be compressed, the pressing base 5 is the only thing damaged, but not the lower matrix 1.

For this purpose, the width of the channels 9 and the width of the bars 12 provided between the channels 9 15 must be chosen so that the material of the pressing 5 bridging the channels 9 and the bars 12 is not pressed or driven into the channels 9 at the normal high working pressure, although it must have a lower strength than the material of matrix 1. The edges of the bars 20 12 are therefore left sharp, i.e. they must not be rounded off, so that the material of pressing base 5 is not bent at the bars 12 under the pressure. The channels 9, like the bars 12, may only be a few millimetres wide and both may be roughly the same width. The holes 25 of the pressing base 5 can be chosen with the same density, where the holes 6 are at the apexes of an imaginary equilateral triangle with a side of several millimetres, if a hard foreign body occurs in the fibrous cement mass, then for a certain thickness of the foreign body in relationship to the thickness of the fibrous cement board to be compressed, the pressure may rise so much locally that the material of pressing base 5, the perforated sheet, no longer withstands it and penetrates into one or more channels locally. The 5 matrices and the channels 9 and the bars 12 remain undamaged. The pressing base damaged locally is taken out of the process and is replaced by a spare one. The damaged pressing base can easily be repaired by inserting and welding in a suitable perforated piece, ready for 10 re-use.

The cross section of the longitudinal channel 14 or 15 corresponds roughly to the sum of the cross sections of the channels 9 lying above it and connected to it 15 by holes 13 or 16 respectively, where the said channels are bridged by pressing base 5, so that they form channels in this way. Here, in the covered channels 9, there is the above-mentioned flow speed of about 15 to 20 metres/sec. The speed is double this said speed 20 in the connecting holes 13 and 16 respectively.

As an equal quantity of air is driven into the channels 9 at the corrugation crests 11 as is sucked out at the corrugation troughs 10, there is only a very small 25 pressure drop between these two points. The whole system of the air paths or air/filtrate mixture paths is a semi-closed circuit system, in which the connecting holes 13 and 16 are the positions with the greatest pressure drop. This automatically ensures that there is 30 the same speed of flow in all parts of all channels 9 from corrugation crest to corrugation trough, regardless of whether a fibrous cement board is compressed on the pressing base, which covers the whole area of the pressing base, or whether it is a smaller board. It 5 is therefore possible, using the same device, i.e. with matrices 1 and 2 and pressing board 5, which are designed for the largest format of the fibrous cement board under consideration, to process fibrous cement boards of a smaller format, e.g. shorter or narrower 10 format, as required by the market, without any additional devices or without conversion.

At the speeds of flow produced by this process, the drops of filtrate flowing through the pressing base 5 or 15 even under suction effect into the channels 9, are immediately carried over and removed. This is done by atomising the drops with a volume excess of air relative to the volume of filtrate to be removed. In this excess of air, the walls of the filtrate removal paths 20 are not wetted, so that no encrustations narrowing the paths are formed. The paths are kept dry, so that after the pressure is reduced, there is no suction back of the pressed out filtrate into the compressed fibrous cement board. Even dehumidification of the whole surface 25 of the fibrous cement board is therefore achieved.

For manufacturing reasons, the lower matrix 1 may be divided into a number of longitudinal sections. Such a dividing line is numbered 21 in Fig. 2. 13

Claims

1. Method of compacting damp, corrugated fibrous cement sheets which lie on a permeable; pressure-resistant pressing base.and which with the latter are pressed 5 between an upper and a lower matrix to compact the fibrous cement material, wherein the aqueous filtrate which is pressed out is removed via a channel system which is open to the permeable pressing base and is provided on the lower matrix, wherein the channel system has a current 10 of air flowing through it from a source of positive air pressure in the direction of the removal of the filtrate, to a suction point, which current entrains, accelerates and transports the drops of aqueous filtrate which have percolated through the pressing base on compacting, 15 and wherein the current of air is driven through the channel system at such a velocity and in such a quantity sufficient to divide the drops of the filtrate into particles, in order to carry them, atomized, with the current of air through the channel system without wetting 20 the walls of the channel system.;

2. Method according to Claim 1, wherein the drops of filtrate are entrained at a velocity of the air current of 15 to 20 m/sec with a volumetric excess of air relative to the volume of the filtrate to> be removed. 25

3. Method according to Claim 1, wherein the air for the current of air is driven through an air channel system provided in the lower matrix, which system opens into the channel system for the removal of filtrate. 14

4. Method according to Claim 1, wherein the pressing base with the compacted fibrous cement sheet, is held under pressure between the matrices until all the filtrate which is pressed out of the fibrous cement 5 material on compacting is carried away from the region beneath the pressing base.

5. Method according to Claim 1 or 4 respectively, wherein a network of grooves provided on the surface of the lower matrix is used to collect the filtrate which has 10 percolated through the pressing base, this network on the one hand being connected to the air channel system and on the other hand being connected to the channel system for the removal of filtrate, so that during operation a current of air prevails between the connection points 15 in the grooves.

6. Method according to Claim 5, wherein the collection of the filtrate is carried out by means of grooves, which run over the width of the lower matrix in each case from a wave trough over a wave crest into the 20 next wave trough and are arranged closely one behind the other over the length of the matrix, in each case the grooves being connected on the wave crest to the air channel system and on the wave trough to the channel system for the removal of filtrate, so that in the 25 groove during operation a current of air prevails from the wave crest to the wave trough.

7. Method according to Claim 6, wherein the drops of filtrate, which have percolated through into the grooves on compacting are taken up and carried away at a flow velocity of 15 to 20 m/sec in the grooves. 5

8. Method according to Claim 5, wherein a lower matrix with grooves and a sheet metal, apertured pressing base are used, in which the distribution of the grooves on the matrix and the distribution of the perforations in the pressing base are co-ordinated with each other such that 10 a) when the pressing base is in position, in each case a requisite number of perforations is situated over the grooves to remove the quantity of filtrate, b) the width, viewed in longitudinal section, of the groove and of the cross-pieces between the grooves is 15 so selected with reference to the strength of the material of the pressing base that a penetration of the material of the pressing base into the grooves under operating pressure is prevented.

9. Method according to Claim 8, wherein, viewed in 20 longitudinal section, the cross-pieces and the grooves are of approximately the same width, the cross-pieces having a plane surface and sharp edges to the grooves.

10. Method according to Claim 5, wherein a lower matrix is used, which is provided with channels 25 running in the longitudinal direction through the matrix from front face to front face, arranged under each wave crest and each wave trough, bores 16 being provided from these channels to each of the grooves running above, which in each case extend to the > wave crest area or respectively to the wave trough area, and air being blown in through the channels running under i 5 the wave crests and the air/filtrate mixture being carried away through the channels running under the wave troughs.

11. Method according to Claim 10, wherein a circulatory system is used, in which the channels 10 running under the wave troughs are connected via a separator to the suction side of a ventilator, and the channels running under the wave crests are connected to the delivery side of the ventilator.

12. Method according to Claim 10, wherein a lower 15 matrix is used, in which the connecting bores between the grooves and the channels running in the longitudinal direction through the matrix and the grooves themselves have approximately the same cross-section.

13. Method according to Claim 10, wherein the 20 cross-section of the respective channel running in the longitudinal direction through the matrix is approximately equal to the sum of the cross-sections of the grooves lying above the channel and connected therewith through bores. 25

14. Method according to Claim 10, wherein on the passage of the flow through the channels, bores, grooves, bores and channels, the bores are the points at which there is the greatest fall in pressure. MACLACHLAN & DONALDSON Applicants' Agents, > 47 Merrion Square, DUBLIN 2.