Continuous controlled drainage
AssigneeJWI Ltd.
InventorVictor E. Hansen
Life of this patent
Estimating the term…
Abstract
A process and apparatus for improving stock formation on an open surface paper making machine is described. By the use of both a path for the forming fabric which introduces a controlled level of agitation into the stock, and a low level of vacuum in a suction box extending continuously for at least the major proportion of the forming section, improvements both in paper quality, such as improved wire mark, and in machine operation, such as an improved first pass retention, are obtained.
Claims13
In a paper making machine having an open surface forming section, including at least a travelling continuous forming fabric, which passes over a breast roll adjacent a head box having a head box slice through which aqueous stock is deposited onto the forming fabric, in which forming section the solids content rises from an initial low value as deposited from the head box through the head box slice onto the forming fabric to a value of from about 2% to about 4%, an apparatus for improving paper formation consisting essentially of in combination:
- (a) a suction means located beneath the forming fabric and extending from a point adjacent the head box slice to the end of the forming section;
- (b) a foraminous support surface for the forming fabric on the suction means;
- and
- (c) a vacuum pump means including vacuum control means, whereby the level of vacuum in the suction means is controlled;
- wherein:
- (i) the suction means comprises either a single suction box divided into a plurality of separate chambers by a plurality of vacuum tight divisions extending across the width of the suction box, and each chamber is provided with both a separate vacuum control means and a separate drainage means, or a plurality of contiguously adjacent suction boxes each of which is provided separately with both a vacuum control means and a drainage means;
- (ii) the foraminous support comprises a series of spaced apart forming fabric supporting blades having a generally planar top surface transverse to the direction of travel of the forming fabric in a common essentially horizontal plane providing therebetween suction accessible gaps in which the forming fabric is substantially unsupported and is drawn downward to form stock agitating undulations in the gaps, the surface including water seal forming blades disposed intermediately in the gaps between the fabric supporting blades, and having a top surface transverse to the direction of travel of the forming fabric at a lower level than the top surface of the forming fabric supporting blades and at least forming water seals at the downward undulations in the forming fabric, together with sealing strips interposed between the ends of the blades adjacent the lateral edges of the forming fabric;
- (iii) the fabric supporting blades in the foraminous support surface are regularly spaced to generate a continuous controlled level of agitation at a pulse frequency of at least 40 Hz in the stock on the forming fabric, and wherein the blades are provided with mounting means, the mounting means being structured and arranged to provide for a pulse frequency of up to at least 120 Hz, so that the blades can be spaced to provide a pulse frequency of from at least 40 Hz to up to at least 120 Hz. and
- (iv) a forming fabric supporting blade in the foraminous support surface is located substantially above both either a transverse vacuum tight division, or a pair of contiguous transverse walls in the suction means, and each of the first and the last, walls in the suction means in the forming section, thereby providing a vacuum tight seal across the width of the forming fabric between the evacuated parts of the suction means in the forming section.
In a paper making machine having an open surface forming section including at least a continuous travelling forming fabric, which passes over a breast roll adjacent a head box having a head box slice through which aqueous stock is deposited onto the forming fabric, in which forming section the solids content of the stock rises from an initial low value as deposited from the head box through the head box slice, to a value of from about 2% to about 4%, an apparatus for improving paper formation consisting essentially of in combination:
- (a) a relatively short foraminous dewatering device adjacent the head box slice which includes a plurality of stationary stock drainage elements disposed in supporting relationship substantially of the forming fabric, and which includes at least one drainage chamber;
- (b) a suction means located beneath the forming fabric and extending from a point adjacent the end of the short foraminous dewatering device to the end of the forming section;
- (c) a foraminous support surface for the forming fabric on the suction means;
- and
- (d) a vacuum pump means including vacuum control means, whereby the level of vacuum in the suction means is controlled;
- wherein:
- (i) the suction means comprises either a single suction box divided into a plurality of separate chambers by a plurality of vacuum tight divisions extending across the width of the suction box, and each chamber is provided with both a separate vacuum control means and a separate drainage means, or a plurality of contiguously adjacent suction boxes each of which is provided separately with both a vacuum control means and a drainage means;
- (ii) the foraminous support surface comprises a series of spaced apart forming fabric supporting blades having a generally planar top surface transverse to the direction of travel of the forming fabric in a common essentially horizontal plane providing therebetween suction accessible gaps in which the forming fabric is substantially unsupported and is drawn downward to form stock agitating undulations in the gaps, the surface including water seal forming blades disposed intermediately in the gaps between the fabric supporting blades, and having a top surface transverse to the direction of travel of the forming fabric at a lower level than the top surface of the forming fabric supporting blades and at least forming water seals at the downward undulations in the forming fabric, together with sealing strips interposed between the ends of the blades adjacent the lateral edges of the forming fabric;
- (iii) the fabric supporting blades in the foraminous support surface are regularly spaced to generate a continuous controlled level of agitation at a pulse frequency of at least 40 Hz in the stock on the forming fabric, and wherein the blades are provided with mounting means, the mounting means being structured and arranged to provide for a pulse frequency of up to at least 120 Hz, so that the blades can be spaced to provide a pulse frequency of from at least 40 Hz to up to at least 120 Hz;
- and
- (iv) a forming fabric supporting blade in the foraminous support surface is located substantially above both either a transverse vacuum tight division, or a pair of contiguous transverse walls in the suction means, and each of the first and the last walls of the suction means in the forming section, thereby providing a vacuum tight seal across the width of the forming fabric between the evacuated parts of the suction means in the forming section.
Dependencies are inferred from the claim text.