US 4,024,015 AGranted

Web-forming method and apparatus

AssigneeValmet Corporation

InventorMatti Kankaanpaa

Life of this patent

Estimating the term…

Loading patent…

Abstract

A web-forming method and apparatus particularly suited for cellulose pulp. The web is initially formed on a rotary wire cylinder which has a horizontal axis and a crest situated at the highest part of the cylinder over the horizontal axis, the cylinder during rotation thus having an upwardly travelling side which turns upwardly toward the crest and a downwardly travelling side which turns downwardly from the crest. At the upwardly travelling side of the cylinder is a headbox having its slice situated adjacent the crest for projecting onto the rotating cylinder a pulp slurry jet at a speed greater than the peripheral speed of the cylinder, so that the deposited pulp slurry will start to form a web while turning with the cylinder up to and then downwardly from the crest thereof. An outer wire has a portion wrapped partially around the cylinder, through an angle of at least 180.degree., and the web which initially forms freely on the cylinder is compressed between the outer wire and the cylinder with the outer wire travelling with the cylinder, so that in this way dewatering is accelerated. The outer endless wire is guided around a pickup roll to travel onto the latter from the cylinder while continuing to carry the web, so that in this way the web is detached from the cylinder and is carried away from the latter with the outer wire before the latter returns to the cylinder.

Claims20

Dependent claims

In a cellulose web-forming method, the steps of directing only a single pulp slurry jet containing unbeaten cellulose fibers onto a rotating wire cylinder, which has a diameter on the order of 2.5-5 meters a horizontal axis and a crest situated over said axis, substantially tangentially with respect to the cylinder in the direction of rotation thereof at a velocity substantially greater than the peripheral velocity of the wire cylinder and at a location adjacent but situated in advance of said crest, considered in the direction of rotation of the cylinder, by an angle at least great enough to provide for the pulp jet after initially engaging the wire cylinder an appreciable extent of travel with the cylinder upwardly in opposition to gravititational resistance while turning through several degrees around said axis to said crest and then beyond the crest downwardly from the latter, then compressing the deposited pulp between the wire cylinder and an outer wire which is wrapped partially around the wire cylinder through an angle of at least 180.degree. but substantially less than 360.degree., after the deposited pulp has traveled beyond said crest through a given angle prior to being compressed, said compression of the pulp and the travel thereof around said axis producing a dewatering of the pulp in a direction outwardly away from said axis, dewatering the pulp in a direction inwardly toward said axis simultaneously with the outward dewatering thereof, then guiding the outer wire with the compressed pulp thereon, before reaching the location where the pulp slurry jet is directed onto the wire cylinder, around a pickup roll situated adjacent the wire cylinder, returning the outer wire from said pickup roll back to the rotating cylinder, with the latter being the only wire cylinder with which said outer wire cooperates, while simultaneously directing the cellulose web from said outer wire to a press section, while subjecting the pulp jet from the time that it initially engages the wire cylinder until it enters between the wire cylinder and the outer wire only to suction, forming in this way an initial free-forming phase where the web has an opportunity and time to acquire a structure and strength enabling it to for the initially freee forming web prior to compression thereof withstand the subsequent phases of treatment, while providing for the initially free forming web prior to compression thereof on the wire cylinder an angular range of 45.degree.-150.degree. and directing the pulp slurry jet onto the rotating wire cylinder at a location within a range from said several degrees up to 60.degree. in advance of said crest.

In a web-forming apparatus, particularly adapted to form a cellulose web from a pulp slurry jet containing unbeaten cellulose fibers, rotary wire cylinder means for participating in the formation of a web at its exterior surface, said cylinder means having a diameter on the order of 2.5-5 meters a horizontal axis and over its axis at its uppermost part a crest situtated between opposed sides of said cylinder means which respectively travel upwardly toward and downwardly away from said crest while said cylinder means rotates around said axis in a given direction, headbox means having a slice situated at the upwardly traveling side of said cylinder means adjacent but spaced at least at a substantial angle in advance of said crest thereof for directing a pulp slurry jet onto said cylinder means at a velocity substantially greater than the peripheral velocity of said cylinder means to be carried thereby from said slice upwardly through and beyond said crest and then downwardly beyond the latter at the downwardly traveling side of said cylinder means, said headbox means being the only headbox means which cooperates with said wire cylinder means, endless outer wire means wrapped partially around said wire cylinder means through an angle of at least 180.degree. but substantially less than 360.degree. with respect to said axis for compressing the web on said cylinder means between the latter and said outer wire means during rotation of said cylinder means, said outer wire means traveling together with said cylinder means at the portion of said outer wire means which is wrapped partially around said cylinder means to consitute a twin-wire former with said cylinder means, rotary pickup roll means situated beside said cylinder means at the upwardly traveling side thereof at a greater distance from said crest than said headbox means so that the latter is situated between said pickup roll means and said crest, said outer wire means extending from its portion which is wrapped partially around said cylinder means partially around said pickup roll means to be partially guided thereby while supporting the web upon separation from said cylinder means, means returning said outer wire means from said pickup roll means back to said cylinder means, said cylinder means being the only cylinder means which cooperates with said outer wire means, the compression of the web between said cylinder means and said endless outer wire means and the travel of the web around said axis both acting to provide a dewatering of the web directed outwardly away from said axis, suction means acting on said web situtated between said cylinder means and endless outer wire means for providing an inwardly directed dewatering of the web simultaneously with said outwardly directed dewatering thereof, means separating the web from said outer wire means at the region of said pickup roll means and for directing the web toward a press section, an initial forming angle being defined between said slice of said headbox means and the location where the outer wire means first engages the web on said cylinder means, said initial forming angle having a size around said axis of between 45.degree. and 150.degree., means for subjecting the web at said initial forming angle only to suction, said initial forming angle being sufficiently great to provide the web with an opportunity and time to acquire a structure and strength which will enable the web to withstand subsequent phases of treatment thereof, said slice of said headbox means being situated from said crest at an angle from said substantial angle up to 60.degree. with respect to said axis.

Dependencies are inferred from the claim text.