Paper making and fiber liberation – Apparatus – Running or indefinite length product forming and/or treating...
Reexamination Certificate
2001-01-22
2002-03-26
Hastings, Karen M. (Department: 1731)
Paper making and fiber liberation
Apparatus
Running or indefinite length product forming and/or treating...
C162S352000
Reexamination Certificate
active
06361657
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a mounting assembly for use with resiliently mounted blades located opposite to a forming shoe in the forming section of a twin fabric papermaking machine. In such a machine, since the blades are located on each side of the two fabrics, each blade contacts only the machine side of the nearer fabric. This invention is particularly concerned with a flexible mounting which allows the blades mounted thereon to conform locally to Z-direction variations in the path of the forming fabrics across the width of the moving forming fabrics. The flexible mounting allows the blade to move so that the angle of wrap of the forming fabrics as they pass in sliding contact over the fabric contacting surface of the blade is maximized at one of the blade edges and minimized at the other as the blade is displaced further towards the fabrics.
BACKGROUND OF THE INVENTION
Many structures have been proposed for mounting static forming fabric supporting elements, such as blades, which are used in the forming section of a two, or twin, fabric paper making machine, in which the aqueous stock is injected or conveyed into the space between two opposed forming fabrics. In the forming section, blades in contact with the machine side of each forming fabric are used to improve formation and to assist in the removal of fluid so that an incipient paper web is formed. In certain forming sections of this type, the two forming fabrics moving as a pair are caused to wrap about blades located on both sides of the two forming fabrics and thus follow a somewhat zigzag path through the forming section.
In twin fabric forming sections equipped with opposed blades, a first set of flexibly mounted blades is located on one side of the fabrics, and a second set of more or less rigidly mounted blades is located on the other side of the fabrics. Suitable machine structures are provided to support both sets of blades, which are collectively referred to as forming shoes. The flexible mountings often utilize arrangements of pressurized hoses or springs to urge the blades into contact with the adjacent one of the two forming fabrics. This invention is concerned with an improved means for flexibly mounting these blades, in which the mounting is flexible in essentially two ways. First, the mounting means of this invention permits the blade to be forced into uniform intimate contact with the machine side of the nearer forming fabric across the width of the forming section. Second, the mounting allows parts of the blade to deflect in the Z-direction locally across the width of the forming fabric in response to localized variations that may occur, and still maintain the blade in intimate contact with the face of the forming fabric.
In the context of this invention, the following terms have the meanings given:
“machine direction” means a direction substantially parallel to, or coincident with, the overall direction of travel of the pair of forming fabrics through the forming section;
“cross machine direction” means a direction essentially within the plane of the forming fabrics and perpendicular to-the machine direction;
“Z-direction” means a direction essentially perpendicular to both the machine and cross machine directions, and
“blade” means any stationary fabric contact element used in the forming section of a twin fabric paper making machine.
Many arrangements have been proposed in the prior art for resiliently mounting the fabric contacting elements used in a twin fabric forming section. These known mountings locate the blades in the cross machine direction, and provide for movement of the blades in more or less the ““Z-direction”. However, in these mountings, Z-direction movement of the blades often involves frictional sliding between fixed and moveable parts of the mounting, which is frequently hampered by clogging of the mechanism by fibers and other matter. Further, in the known prior art arrangements the sliding movement components are generally stiff and inflexible, and thus do not allow for any localized flexing of the blade in the Z-direction in response to localized changes in conditions. Consequently, when localized misalignment of the blade with the forming fabric occurs, areas of poor formation and uneven drainage occur across the incipient paper web.
Many of the prior art mounting means cause the blade to move towards the fabrics in the Z-direction, and maintain the fabric contacting surface of the blade generally perpendicular to that direction. Further Z-direction movement causes the fabrics to wrap over the blades more or less symmetrically, which increases frictional contact between both the leading and trailing edges of the blade and the machine side of the forming fabric. This contact is known to accelerate the rate of fabric wear. To reduce the rate of fabric abrasive wear due to the wrap angle at the sharp leading edge, the radius of curvature of the blade leading edge is often increased. This has been found to create new problems, because any fluid that was adhering to the machine side surface of the forming fabric will be propelled back into the stock by the rounder edge as the fabrics pass over the fabric contacting surface of the blade. This phenomenon has been found to impair paper formation.
Kade et al, in U.S. Pat. No. 4,865,692, disclose a support structure for a blade, for use in a conventional single fabric open surface forming section. In this structure, two C-section beams extending across the width of the machine are interlocked to provide an essentially S-shaped structure. The upper C-beam carries the blade, and the lower C-beam is mounted onto the drainage box. The two C-beams are joined together by a flexible spring steel strip, and are urged apart by a clamping element so that the two C-beams engage to form the S-shape. The clamping element is typically an inflatable hose. An adjusting beam is also located between the two C-beams, which also carry stop surfaces. By moving the adjusting beam, different stop surfaces are engaged by pressurizing the clamping means, thus altering the angle of inclination of the fabric contacting surface relative to the machine direction of movement of the fabric. However, this structure only allows a small angular change, the axis about which the angle changes is not defined with any precision, and interlocking of the two C-beams into an S-shaped structure precludes any movement in the Z-direction. Further, although movement of the upper C-beam does not involve any sliding contact, that movement is controlled by the sliding adjusting beam.
BRIEF DESCRIPTION OF THE INVENTION
The present invention seeks to provide a mounting for a blade in the forming section of a two fabric paper making machine which allows for movement of the complete blade in the Z-direction, localized flexibility of the blade across the width of the forming section in the Z-direction, and some freedom to alter the angle of inclination of the contacting surface in relation to the undeflected path of the forming fabrics. The mounting allows the fabric contacting surface of the blade to be urged into contact with one of the pair of forming fabrics so that it is initially oriented substantially parallel to the contacted surface of the undeflected forming fabric. The blade mounting provides the option of allowing the blade to engage the fabrics so that their angle of wrap about the blade is minimized at the leading edge, and maximized at the trailing edge. This is because the mounting allows the blade to rotate over an arc as it is displaced towards the fabrics. This arrangement reduces the angle of wrap of the forming fabrics about the leading edge of the blade, and permits the use of a relatively sharp doctoring leading edge on the blade. Alternatively, the mounting allows the blade to be engaged with the fabrics so that the wrap angle is maximized at the leading edge, and minimized at the trailing edge. If this arrangement is used, then it is recommended that the radius of curvature of the doctoring leading edge of the blade be increased to r
Baker Harold C.
Hastings Karen M.
Hendry Robert G.
Wilkes Robert A.
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