CA1058928A

CA1058928A - Wet press felt

Info

Publication number: CA1058928A
Application number: CA268,395A
Authority: CA
Inventors: Eric R. Romanski
Original assignee: Albany International Corp
Current assignee: Albany International Corp
Priority date: 1976-01-02
Filing date: 1976-12-21
Publication date: 1979-07-24
Also published as: BR7608808A; MX146053A; JPS52103505A; JPS5629037B2; AU499028B2; FR2330802A1; AT361288B; ATA1177A; US4300982A; DE2700054C2; DE2700054A1; NZ183005A; AU2092876A; GB1514120A; FR2330802B1; ZA767701B

Abstract

Abstract of the Disclosure A papermakers press felt having a raised pattern of substantially incompressible islands which provide void area on the back of the felt for the free passage of water which has been squeezed from the felt by press rolls, allowing lateral as well as longitudinal flow and providing a degree of pumping action.

Description

Background of the Invention In the papermaking process water is frequently effectively removed from the paper sheet by press removal as the sheet and felt upon which it is being transported are ; ;~
squeezed between rolls in the press section. In this procedure the water has been moved out of the felt throu~Jgh the felt and in ~ ;
some designs through holes in rolls of the press nip or through grooves formed in the rolls. A recent technique is shown in United States Patent ~o. 3,613,258, issued October 19, 1971, .. . ..
wherein a plurality of monofilaments are adhered to the back~
side of the press fabric to provide a plurality of water convey-ing channels into which water expressed from a paper sheet located on the face of the fabric is directed for removal. An improvement on that technique has been made in which a press fabric is coated and/or treated on the backside thereof and grooves formed therein to provide the generally parallel flow channels.
Summary of the Invention : . ~
A press fabric for use in a papermaking machine for transporting paper sheet for pressing in the nip of press rolls comprising a fabric which is needled, woven or nonwoven or a combination thereof to provide a water permeable structure having on the backside thereof a plurality of discrete spaced .
raised relatively incompressible islands which provide ~ ~ ~

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:~S8~3Z~3 intersecting channels which allow lateral and longitudinal flow of water expressed from a paper sheet located on the upper sur-face of the press fabric upon pressing in the nip.
Description of the Drawinqs Fig. 1 is a perspective view of a papermakers felt constructed in accordance with the teachings of this invention, -Fig. 2 is an enlarged segmentary view o~ the portion ;~
of the backside of the felt shown in Fig. 1 indicated by the letter A in Fig. 1 illustrating one pattern as applied thereto; ` ' Fig. 3 is a partially diagrammatic view illustrating a preferred method of applying the pattern shown in Fig. 2 to the backside of the felt shown in Fig. 1, Fig. 4 is an enlarged segmentary view similar to that of Fig. 2 illustrating an alternate pattern as applied to the backside of the felt; and ~-~
Fig. 5 is an enlarged se~mentary~-view similar to those of Figs. 2 and 4 illuskrating still another alternate pattern ;
as applied to the backside of the felt. `
Description of the Preferred Embodiment In the drawing in FigsO 1 and 2, an embodiment of the ~, invention is shown in which the numeral 10 designates a press j fabric constructed in accordance with the present invention ~ and the numeral 12 designates individual, discrete, relatively ;
3 incompressible raised dots on the back of the felt. The spacing or area between the dots as seen in Fig. 2 is indicated general~
ly by the numeral 14 and provides a matrix of intersecting channels for the free passage of water which has been squeezed from the felt by press rolls, allowing lateral as well as ~1 ~! longitudinal flow and providing a degree of pumping action. i^
The fabric can be woven, a woven substrate with needled web or totally needled. In the embodiment herein by way of example only the fabric comprises a woven substrate and ~, ' IS~39~8 needled web. Where a woven substrate is utilized, any suitable weave can be employedO
The fabric is selected in order to provide the usual desired characteristics in a press felt and the construction and materials, including the type of yarns utilized when a -woven substrate is present are so selected. Thus in selecting ~ ~ -felt construction and materials for use in this invention, the usual major desirable properties of a press felt must be con~
sidered. The felt must be selected insofar as it is possible `
to provide uniform pressure distributlon in the nip, low fluid flow resistance in the nip and minimum rewetting of the paper web from the felt.
In the preferred embodiment of the invention the ~-pattern is applied by rotary screen stencil. The stenciled pattern can be o~ many variations such as ~ots, as shown in ~-Fig. 2, ovalesque slots as shown in Fig. 4, straight or staggered chevrons as shown in Fig. 5 or any other suitable pattern of discrete, spaced raised re:latively incompressible islands which provide intersecting channels which allow lateral and longitudinal ~low of water expressed from a paper sheet located on the upper surface of the press fabric upon pressing in the nip. The pattern material can be composed of a variety ;
of materials such as PVC, urethanes, foams or latexes. The preferred material is PVC. The deposit of the material can be from .005" to .060" thick but a thickness of o020ll is preferred.
The closeness and thickness of the pattern deposit dictates the degree of bridge support and void volume on the back of the felt.
The pattern is applied using a conventional rotary screen stencil as known in the industry. Referring to Fig. 3 ~-the pattern to be deposited on the backside of felt 10 is engraved on the rotary stencil screen 16 in the conventional _ 4 _ ,, ~

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way. The rotary stencil screen is positioned on the surface of the felt to be printed. Inside the rotary screen is a pond ;
of pattern material 18 such as PVC which i9 deposited behind wiper blade (squeegee) 20 and as the Eelt passes undsr the stencil screen, the screen rotates under the influence of drive roll 22. The printing material fills the pattern voids, and as the pattern void passes under the squeegee, excess pattern material is wiped away. As the falt material leaves the stencil ~;
screen, the pattern material is deposited on the felt surface.
Depending on the type of pattern material used a period of time ;
is required for the pattern material to harden. This can be accelerated via heat, catalysts or chemical additives depending ;
on the type of printing material used An alternate pattern is shown in Fig. 4 in which side ;
staggered slots are provided by side staggered raised dash members 24. In Fig. 4 the void area between dashes is desig-nated by the numeral 14'.
A further alternate pattern is shown in Fig. 5 in - which chevron members 26 separated by spacing 14" provide the ' 20 pattern. The direction of felt travel is upwardly in Fig. 5.
The chevrons 26 trap water and carry the water in the direction of felt travel to create a pumping action.
, Thus it is seen that a press felt is provided in which lateral as well as longitudinal flow can be achieved as well as the creation of a pumping action.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A press fabric for use in a papermaking machine for transporting paper sheet for pressing in the nip of press rolls comprising a water permeable endless base fabric, an upper surface thereof for receiving in contact therewith the paper sheet to be transported, a backside thereof, a plurality of discrete spaced raised relatively incompressible island members in firm engagement with said backside, a plurality of inter-secting channels provided by said island members which allow lateral and longitudinal flow of water expressed from paper sheet located on said upper surface upon pressing in said nip.

2. A press fabric in accordance with claim 1, in which the island members are in the form of a stencilled pattern of dots.

3. A press fabric in accordance with claim 1, in which the island members are in the form of a stencilled pattern of ovalesque slots.

4. A press fabric in accordance with claim 1, in which the island members are in the form of a stencilled pattern of chevrons opening in the direction of felt travel.

5. The method of producing a press fabric for use in a papermaking machine for transporting paper sheet for pressing in the nip of press rolls including the steps of selecting a fabric which is highly water permeable, engraving a pattern of spaced members on a stencil screen, providing pattern material which upon setting will be relatively incompressible, printing the pattern on the backside of the fabric, and allowing the pattern material to harden.