Pressing assembly and a method for forming a depression within a moving, wet gypsum board

Abstract

A pressing assembly (10) and a method for forming a depression (105) within a moving, wet gypsum board (100) is disclosed. The assembly comprises a pressing head (16) comprising a pressing surface which is arranged to contact the board, and a support member (17), the pressing head (16) being arranged to compress a portion of the board between the pressing surface and the support member (17) to form a depression (105) within the board (10). The pressing surface comprises a first and second surface portion (24, 25) separated by a relief portion (27), which is arranged to press the board (100) toward the support head (17) with less compressive force than the first and second surface portion (24, 25). The assembly further comprises drive means (18, 19, 22) for moving the pressing head and the support member in a first direction which substantially corresponds with the direction of the moving board, and a second direction which is substantially perpendicular to a plane of the board, while the speed of the pressing assembly in the first direction substantially matches the speed of the board.

Claims

1. A method for forming a depression within a moving, wet gypsum board, the method comprising the steps of: providing a pressing assembly including a tapered die attached to a pressing head, the tapered die including a recess; providing a gypsum board moving in a direction of travel at a first speed; moving the pressing head in the direction of travel of the gypsum board, such that the speed of the pressing head in the direction of travel of the gypsum board substantially matches the first speed, while simultaneously causing the pressing head to move towards the gypsum board, to bring the recess into contact with a portion of the gypsum board, and causing the tapered die to compress the gypsum board to substantially simultaneously form a depression on either side of a comparatively uncompressed gypsum board portion.

2. A method according to claim 1, wherein the step of moving the pressing assembly in the direction of travel of the board, such that the speed of the pressing assembly in the direction of travel of the board substantially matches the speed of the board, includes adjusting the speed of the pressing assembly when there is a difference between the speed of the pressing assembly and the speed of the moving board.

3. A method according to claim 2, wherein the speed of the pressing assembly in the direction of travel of the board is matched to the speed of the board using a Hoekens linkage.

4. A method according to claim 2, wherein the speed of the pressing assembly in the direction of travel of the board is matched to the speed of the board using a hypotrochoid motion.

5. A method according to claim 1, wherein the step of causing the pressing assembly to contact and compress the board is carried out when at least 10% of the gypsum hydration has occurred.

6. A method according to claim 1, wherein the step of causing the pressing assembly to contact and compress the board is carried out when at least 40% of the gypsum hydration has occurred.

7. A method according to claim 1, wherein the gypsum board comprises silicone oil.

8. A method according to claim 7 wherein the silicone oil is present in an amount of 100-1200 g/m.sup.3.

9. A method according to claim 1, wherein the step of causing the pressing assembly to contact and compress the board is carried out when at least 60% of the gypsum hydration has occurred.

10. The method as described in claim 1 wherein the recess is an aperture and the depression is formed by causing the aperture to compress against the gypsum board.

11. A method of making a gypsum board, the method comprising: (a) imparting motion to a gypsum board in such a way that that the gypsum board translates in a first direction at a first speed; (b) moving a pressing surface with a recess adjacent the gypsum board in the first direction and substantially at the first speed while performing (a) prior to contacting the gypsum board with the pressing surface; (c) contacting the gypsum board with the recess of the pressing surface while moving the pressing surface in the first direction and substantially at the first speed; and (d) compressing the gypsum board with the pressing surface while performing (c), forming a depression on either side of a comparatively uncompressed portion of the gypsum board.

12. The method of claim 11, further comprising sensing the speed of the pressing surface and subsequently performing (c) when the sensed speed of the pressing surface is the first speed.

13. The method as described in claim 11 wherein the recess is an aperture and the depression is formed by causing the recess to compress against the gypsum board.

Description

(1) The invention will now be described by way of example only with reference to the accompanying Figures, in which:

(2) FIG. 1 is a side view of a pressing assembly according to an embodiment of the present invention, disposed within a gypsum board production line;

(3) FIG. 2 is a plan view of the pressing assembly illustrated in FIG. 1;

(4) FIG. 3 is a front view of the pressing assembly illustrated in FIG. 1;

(5) FIG. 4 is a magnified view of the die disposed upon the pressing head;

(6) FIG. 5 is a perspective view of a continuous board;

(7) FIG. 6 is a magnified longitudinal sectional view taken along line A-A of FIG. 5, across a depression created by the pressing assembly according to an embodiment of the present invention;

(8) FIG. 7 is a perspective view of a board sheet; and

(9) FIG. 8 is a flow chart of the steps associated with a method of forming a depression within a moving, wet gypsum board according to an embodiment of the present invention.

(10) FIG. 9 is a sectional view of the die disposed on the pressing head, according to a second embodiment of the invention.

(11) Referring to FIGS. 1 to 4 of the drawings, there is illustrated a pressing assembly 10 according to an embodiment of the present invention for forming a depression 105 within a wet gypsum board 100 as illustrated in FIGS. 5 and 6 of the drawings, as the board 100 moves along a production line. The continuous board 100 comprises a layer of wet gypsum 101 disposed between a first and second liner material 102, 103. The liners 102, 103 are folded over each other along longitudinal side edges thereof to define longitudinal side edges 104a, 104b of the board 100 and to prevent the gypsum 101 from passing out from between the liners 102, 103. The pressing assembly 10 is disposed within the production line and the board 100 is supported upon a bed of rollers (not shown) disposed either side of the assembly 10. The board 100 is driven through the assembly 10 in a direction which is substantially parallel to the longitudinal side edges 104a, 104b of the board 100, at a substantially constant speed by a roller platform 11. The roller platform 11 comprises a substantially rectangular roller frame 12 having a plurality of rollers 13 which extend across the frame 12 between opposite longitudinal roller frame members 12a, and which is held in a substantially horizontal configuration, substantially level with the bed of rollers (not shown), by a plurality of frame legs 14.

(12) The pressing assembly 10 is arranged to form a depression 105 within the board 100 at periodic intervals along the length thereof as the board 100 passes through the pressing assembly 10. The depressions 105 are arranged to extend substantially across the board 100, in a direction which is substantially transverse to the longitudinal side edges 104 of the board 100; however, the skilled reader will recognise the depressions 105 may be formed across the board at an alternative angle to the longitudinal side edges 104. The continuous board 100 is then cut across the board 100 within the depressions 105 to form a board sheet 200 as illustrated in FIG. 7 of the drawings. The longitudinal side edges of the board sheet 200 each have a first portion 201a, 201b that is perpendicular to the faces of the board sheet, and a second portion 203a, 203b that is oriented at an oblique angle to the faces of the board sheet. Lateral side edges extend substantially transverse to the longitudinal side edges 201, 201b, and similarly have a first portion 202a, 202b that is perpendicular to the faces of the board sheet, and a second portion 106, 107 that is oriented at an oblique angle to the faces of the board sheet. Thus, the board sheet 200 has tapered edges extending around its entire perimeter.

(13) Referring to FIGS. 1 to 3 of the drawings, the assembly 10 comprises a support frame 15 for supporting a pressing head 16 and a support member 17. The support frame 15 is substantially rectangular in shape and comprises opposite longitudinal 15a and lateral side members 15b, the latter of which are arranged to extend substantially perpendicular to the roller platform 11 and thus the plane of the board 100. In contrast, longitudinal side members 15a of the support frame are arranged to extend in a plane substantially parallel to the roller platform, in a direction which is substantially transverse to the longitudinal roller frame members 12a. The pressing head 16 and support member 17 are arranged to extend across the width of the support frame 15, between lateral side members 15b, and are orientated substantially parallel to a plane of the board 100.

(14) The pressing head 16 comprises a first drive unit 18 disposed at each longitudinal end thereof, which are arranged to drive the head 16 along the lateral side members 15b within the frame 15. The support member 17 comprises a second drive unit 19 disposed at each longitudinal end thereof which are arranged to similarly drive the member 17 along the lateral side members 15b within the frame 15. The first and second drive units 18, 19 thus enable the separation of the pressing head 16 and the support member 17 and thus their separation from the board 100, which is arranged to pass therebetween, to be varied.

(15) The support frame 15 is itself held in a fixed orientation upon the roller platform 11 with respect to the board, by a drive arrangement 20 which is arranged to drive the support frame 15 along the board 100 substantially parallel to the direction of travel of the board 100. The arrangement 20 comprises two support poles 21, one of which extends through each lateral side member 15b of the support frame 15, and are separately coupled at each end thereof to a pair of frame legs 14. The arrangement 20 further comprises a third drive unit 22 disposed upon each lateral side member 15b for driving the support frame 15 back and forth along the support poles 21. In this respect, the support poles 21 enable the pressing head 16 and support member 17 to move in a first direction which is substantially along the board 100, substantially parallel to the direction of travel of the board 100, whereas the lateral side members 15b enable the pressing head 16 and support member 17 to move in a second direction which is substantially perpendicular to the plane of the board 100.

(16) The assembly 10 further comprises one or more sensors (not shown) associated therewith for sensing the speed of travel of the board 100. The sensors are arranged to output a signal which is input to the first, second and third drive units 18, 19, 22, to affect the speed at which the pressing head 16 and support member 17 become driven along the support frame 15 and the support poles 21.

(17) The pressing head 16 is illustrated in the drawings as being disposed substantially below the board 100 and thus the support member 17, however, the skilled reader will recognise that this arrangement may be reversed with the pressing head 16 disposed above the board 100 and thus the support member 17. Referring to FIG. 4 of the drawings, the side of the pressing head 16 disposed adjacent the board 100 comprises a die 23 which may be detachably coupled thereto or which may be formed integrally therewith. The die 23 extends between opposite longitudinal ends of the pressing head 16, and is arranged to extend across the width of the board 100.

(18) The die 23 comprises a first and second longitudinal side edge 24a, 24b, which are arranged to extend across the board, and from which extend a first and second substantially planar pressing surface 25, 26, respectively. The first surface 25 is inclined with respect to the direction of travel of the board 100 and the second surface 26 is declined with respect to the direction of travel of the board 100, such that the first and second pressing surfaces 25, 26 converge in a direction which is away from the pressing head 16 and the respective longitudinal side edges 24a, 24b of the die 23, toward a relief portion 27 disposed substantially centrally of the die 23. In this respect, the first and second surface portions 25, 26 are arranged to create opposed tapers 106, 107 within the gypsum board 100. The relief portion 27 is arranged to extend along the length of the die 23 and may comprise an aperture (not shown) disposed therein, or a recess 28, as illustrated in FIG. 4 of the drawings.

(19) Referring to FIG. 8 of the drawings there is illustrated a method 300 according to an embodiment of the present invention. During use, the board 100 is driven through the assembly 10 by the rollers 13 disposed upon the roller platform 11, between the pressing head 16 and the support member 17, at constant speed. The support member 17 and pressing head 16 are subsequently accelerated at step 310, from a first stationary position, along the first direction by the third drive units 22, along the support poles 21, to a speed which substantially matches the speed of the board 100 through the assembly 10. This speed is monitored by comparing the relative speed between the board 100, and the pressing head 16 and support member 17, as determined using the sensors (not shown). The pressing head 16 and support member 17 are simultaneously driven at step 310 along the lateral side members 15b of the support frame 15, by the first and second drive units 18, 19, to a position adjacent an upper and lower face of the board 100, respectively.

(20) When the speed of the pressing head 16 and support member 17 in the first direction substantially matches the speed of the board 100, namely when relative speed is within substantially 0.1% of the board speed, the first and second drive units 18, 19 are arranged to drive the support member 17 and the pressing head 16 toward each other at step 320, to compress the board 100 along the width thereof and thus form a depression 105 within the wet gypsum. The support member 17 is arranged to resist the upward force from the pressing head 16 and presents a sufficiently smooth and large surface compared with the face of the die 23, to avoid forming a depression (not shown) on the upper surface of the board 100.

(21) The first drive units 18 disposed on the pressing head 16 are arranged to control the speed at which the pressing head 16 is driven in and out of the board 100 and permit a controlled steady pressing in phase, a short constant press and a withdrawal. Moreover, the compressing of the board 100 while maintaining minimal relative speed between the board 100 and the pressing head 16 minimises the accumulation of wet gypsum either side of the depression 105, which would otherwise present an undesirable bulge or protuberance in the dried board.

(22) As the board 100 is compressed, the wet gypsum 101 disposed between the liners 102, 103 becomes compressed between the pressing surfaces of the die 23 and the support member 17. The first and second pressing surfaces 25, 26 are arranged so that the recess 28 does not exert any compressive force on the board. Thus, the resulting longitudinal sectional shape of the board 100, as illustrated in FIG. 6 of the drawings comprises first and second opposed taper regions 106, 107 which extend into the board 100, toward an uncompressed, raised support step 108. The portion of gypsum disposed within the raised step 108 is therefore less densified than the portion of the board 106a, 107a disposed either side thereof.

(23) The depth to which the die 23 is arranged to press into the board 100 may be varied by monitoring the force applied to the board 100 using a force sensor (not shown), for example, or by monitoring a fixed position upon the pressing head 16 with respect to a reference position upon the assembly 10, for example. Once the board 100 has been compressed to form the opposed tapers 106, 107 either side of the support step 108, the separation of the pressing head 16 and the support member 17 is then increased and the pressing head 16 and support member 17 are decelerated in the first direction to a second stationary position at step 330. The pressing head 16 and support member 17 are then driven in a second direction at step 340 back along the support poles 21 from the second position to the first position for subsequent pressing of the board 100. The cycling of the pressing head 16 and the support member 17 from the first position to the second position and back to the first position is controlled to ensure that the depressions 105 are formed at equally spaced positions on the board 100, namely within 2 mm. This ensures that the resulting boards 200 which are formed by cutting along the central portion of the depressions 105 comprise substantially the same length.

(24) The boards 200 are formed by cutting the board 100 with a cutting blade (not shown) along the less densified portion of the board within the depressions. The less densified portions enable the continuous board 100 to be cut more easily than if the continuous board 100 was cut along a densified portion, prolong the life of the cutting blade (not shown) and minimise an snagging of the blade (not shown) on the board 100 which may otherwise tear the liners 102, 103 of the board 100.

(25) FIG. 9 shows an alternative configuration of the die disposed on the pressing head, according to a second embodiment of the invention. In contrast to FIG. 4, the first pressing surface 25a, 25b and the second pressing surface 26a, 26b are each divided into two parts. The outer parts 25b, 26b of the first and second pressing surfaces are co-planar, while the inner parts 25a, 26a are inclined relative to each other and relative to the outer parts 25b, 26b, so that the inner parts 25a, 26a protrude from the pressing surface.

(26) In addition, FIG. 9 shows a further optional feature of the die, namely that the base 30 of the recess is located inwardly of the plane defined by the outer parts 25b, 26b of the first and second pressing surfaces.

(27) The following worked examples are presented by way of illustration only.

EXAMPLE 1

(28) Two gypsum boards were provided in which Board A contained silicone oil in an amount of 320 g/m.sup.3, while Board B contained no silicone oil.

(29) Board A and Board B were pressed according to the method set out in FIG. 8, and were both subjected to the same load during the step 320 in which the pressing head 16 and the support member 17 are driven towards each other.

(30) The maximum taper depth achieved for Board A was 1.5 mm, whereas the maximum taper depth achieved for Board B was 1.0 mm (the maximum taper depth was measured after removal of the compressive force, and after drying of the board).

EXAMPLE 2

(31) Two gypsum boards were provided in which Board C contained silicone oil in an amount of 480 g/m.sup.3, while Board D contained no silicone oil.

(32) The boards were pressed according to the method set out in FIG. 8.

(33) The Boards were visually examined to see if blistering had occurred between the liner of the board and the underlying gypsum. The results are given in Table 1 below:

(34) TABLE-US-00001 Board C Board D Pressed region No blistering observed Blistering observed Unpressed region No blistering observed No blistering observed