NZ201987A - Dewatering press having belt with a smooth surface and a further surface which contains voids for the passage of liquids - Google Patents

Description

m 2019 8 i gl Priority Date(s): 3d.. .9.3. L, Complete Specification Filed: Class: £) A J .if 3. JQ$.

Publication Date: .... fl.l .JUN.MS" P.O. Journal. No: AMENDED under Sectioa? —of tha Patents Act 1951 from// 3 - 5 - ;jRS5BTANr*COMMIS51QNER OF PATENTS NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION N.Z. No, DEWATERING PRESS We, ALBANY INTERNATIONAL CORP., a New York Corporation of 1 Sage Road, -Manand-s, New York 12201, United States of America, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- 201987 The field of the invention relates to mechanisms for extracting water from a web of material, and more particularly from a fibrous web formed in a papermaking machine.

During the papermaking process, a web is formed by depositing a fibrous slurry on a forming wire. A large amount of water is drained from the slurry during this process, after which the newly-formed web proceeds to a press section. The press section includes a series of press nips. The web finally proceeds to a drying section including heated dryer drums where the water content is reduced to a desirable level.

In view of the high cost of energy, it is desirable to remove as much water as possible from the web prior to its entering the drying section. The dryer drums in this section are often heated by steam and costs can be substantial if a large amount of water needs to be removed.

The use of extended press nips has been found to be advantageous over the use of nips formed by pairs of adjacent rollers. By extending the time the web is subjected to pressure in the nip, a greater amount of water can be removed. This fact has been recognized by those skilled in the art, and several patents have been granted in the area. These patents include -e-rS-s—Rcioouo Patent 30 >268 and U.S. Patents 4 ,201,624, 4,229,253 and 4,229,254.

In using extended press nips to dewater a fibrous web, the web has typically been sandwiched between two moisture-absorbing felts and a belt. The felts are trained 2 201987 around a cylindrical press roll with the web between them while the belt is arranged for applying pressure to the felts and roll. A pressure shoe exerts pressure on the belt in the press area.

A problem has been encountered during the dewatering of webs in extended nips. It has been found that a bulge develops in the belt ahead of the nip. This problem is recognized in U.S. Patent Nos 4,229,253 and 4,229,254, and certain belt constructions are suggested for overcoming the problem.

Broadly the invention consists of a press for dewatering a fibrous web comprising a press roll having a cylindrical exterior surface, a flexible belt comprising a base fabric partially impregnated with a polymeric material, a first side of the belt having a uniform smooth impervious impregnated surface, an extended nip provided between the press roll and the belt, papermakers felt means extending through the nip, a pressure shoe having an exterior surface engaging the first side of the belt and applying pressure to the felt means and, in use, to a fibrous web in the nip, and a second side of the belt containing voids into which liquid is transferred from the felt means which is in contact with the belt during the passage of the web and felt means through the nip. 201987 A significant advantage of this belt construction is that it can be made in any length since it does not require a mandrel during the manufacture thereof. A base fabric may be made endless using conventional fabric technology and then coated with the material.

The resulting structure is both light in weight and sufficiently stable to operate under paper machine conditions. It has sufficient abrasion resistance to resist any wear that might take place in the extended nip apparatus. Unlike materials which are built up in the manner of a rubber tire and can flow and/or delaminate, the invention provides a belt which will maintain its integrity. It also solves the problem of bulging near the press nips.

In the following more detailed description of the invention reference will be made to the accompanying drawings in which:- 201987 Figure 1 is a side elevational view of an extended press nip according to the invention, Figure 2 is a partially sectional front view of the press nip shown in Figure 1, Figure 3 is a sectional side elevational view of a belt employed in the invention, and Figure 4 is a sectional side elevation view of an alternate embodiment of belt employed in the invention.

An extended press nip is provided by the invention for dewatering a travelling web of material. The nip 10 is defined by a cylindrical press roll 12, a pressure shoe 14 having an arcuate surface facing the press roll, and a belt 16 arranged such that it bears against the surface of the press roll. The arcuate surface of the pressure shoe has about the same radius of curvature as the press roll. The distance between the press roll and the pressure shoe may be adjusted by means of conventional hydraulic or mechanical apparatus (not shown) connected to a rod 18 pivotally secured to the shoe 14. The rod may also be actuated to apply the desired pressure to the shoe. It will be appreciated that the pressure shoe and press roll described above and shown in Figures 1 and 2 are conventional and that other arrangements may be utilized in accordance with the invention.

One embodiment of the belt 16 in accordance with the invention is shown in detail in Figure 3. The belt 16 comprises a two layer woven monofilament base fabric 20 with 201987 multifilament or spun stuffer yarns 21 which is impregnated with a polymeric material. Thermosetting resins such as polyurethanes have been found to be suitable impregnating materials. Thermoplastic polymers such as polypropylene are also acceptable.

The base fabric 20 is sufficiently open to allow impregnation to eliminate the possibility of undesirable voids forming in the final fabric on the pressure shoe side. These voids are undesirable because they would allow the lubrication used between the belt and shoe to pass through the belt and contaminate the felt and fibrous web. The stuffer yarns 21 provide a barrier of sufficiently low permeability to prevent passage of the resin during the coating and impregnating process to the side with voids. It is endless in final construction and uniform in thickness. The fabric must also be made to have sufficient stability under paper machine conditions. In other words, it must have length stability, width stability, and guidability.

The thermoplastic resin or thermosetting resin used should be substantially one hundred percent solid composition to avoid the formation of bubbles during the curing process of the resin in the belt structure which could cause voids on the coated side.

Side 17 of the belt can be grounded smooth for contact with the pressure shoe 14. The opposite side contains voids, as a result of the weave and absence of impregnation, into o/ 20198 which liquid can be transferred during the passage of the web, felt and belt through the nip.

A further example of the first embodiment is shown in Figure 4. The components are similar to those in Figure 3. The components of Figure 4 are numbered as those of Figure 3 with a prime following. Belt 16"1" of Figure 4 is a multi layer structure with a barrier layer provided by stuffer yarns 21^. These stuffer yarns, 21^", can be multifilament or spun. The belt is coated and impregnated as described previously to provide a smooth impervious surface 17^ and a surface with voids 181 on the remaining side. The use of belt 16^ is the same as previously described for belt 16.

A second embodiment of this invention uses a different method of introducing the polymeric material into the belt structure. In this second method polymeric material is pressed into the surface. The depth of penetration is controlled by the pressing force used and the temperature applied. Either thermoset or thermoplastic polymers can be used. Thermoplastic polymers are especially advantageous for this method since their viscosity in melted form can be controlled by temperature. By controlling the viscosity the depth of penetration can be controlled and the necessity of a barrier in the fabric structure is eliminated for polymers of the right viscosity.

In this method the belt 16 is positioned around a pair of rollers. One of the rollers is an oil heated cylinder. 201987 Polymeric material in sheet form, of the proper caliper, is placed between the belt and the heated cylinder and allowed to rotate around the cylinder. The cylinder temperature is maintained at the level desired to melt the polymeric material to the proper viscosity. It is then forced into the belt by the tension of the belt around the cylinder and roller. An outside pressure roll can be used to create additional pressure if needed. The sheet of polymeric material is trimmed so no overlap occurs in the material pressed into the belt.

Belts manufactured in accordance with the invention have been found to have many desirable characteristics. They move easily over the pressure shoe and are capable of transmitting pressure from the shoe to the web and press roll. Sufficient flexibility is obtained, and the belts have proven to be unaffected by lubricant applied prior to entering the press nip.

In comparison with belts currently known to the art, the invention provides a belt which is relatively thin and light in weight. Thick belts have the disadvantage of tending to flow while within the nip. A 24'6" X 170" belt impregnated with a thermosetting resin in accordance with the invention weighs about two hundred pounds. A similar size belt having bulge-resistant characteristics and having a structure defined in the above mentioned patents weighs about twelve hundred pounds. Unlike the heavier belts, the invention does not require a reinforcing structure. 20198 The manufacture of the belt according to the invention may be accomplished economically and without the need for mandrels or autoclaves which limit the size of other belts. A belt of any length can accordingly be produced. A web may be needled into the woven base if desired. If the base structure has not been woven endless it is joined endless using conventional joining techniques applicable to forming fabrics in the paper industry.

A belt made in accordance with this invention may be utilized with the apparatus shown in Figure 1. The belt 16 is positioned between the pressure shoe and the pressure roller. The smooth coated side 17 of the belt is engaged by the shoe. A fibrous web 24 carried between first and second felts 26 and 27 respectively is introduced into the press nip 10. The side of the belt 17 engaging the shoe 14 is lubricated by lubricating means 28 positioned ahead of the nip.

The belt 16 is easily repaired should a hole or other surface irregularity develop therein. The damaged portion is cleaned with a solvent and a suitable amount of coating is applied with a blade. A heat gun is employed to cure the surface which can then be sanded.

Because of the excellent flexibility characteristics of the base structure and the fact that the coating layers can be kept to a minimum, the surface of the belt will have less tendency to fail due to bending fatigue. This is due to the fact that, because of the low caliper, the surface plane of the 2019 coated surface is at a minimum distance from the neutral axi of bending. This reduces the percentage of elongation and compression at the surface plane during bending.

It will be appreciated that the belt utilized in the invention may include a base fabric made from various polyme materials having the necessary properties for application in papermaking machines. Materials other than polyurethane and polypropylene may also be employed as the coating material. Also the weave of the belt may be altered although a multilayered belt is desirable for creation of the voids.

AS AMENDED 201587

Claims (7)

WHAT WE CLAIM IS:

1. A press for dewatering a fibrous web comprising a press roll having a cylindrical exterior surface, a flexible belt comprising a base fabric partially impregnated with a polymeric material, a first side of the belt having a uniform smooth impervious impregnated surface, an extended nip provided between the press roll and the belt, papermakers felt means extending through the nip, a pressure shoe having an exterior surface engaging the first side of the belt and applying pressure to the felt means and, in use, to a fibrous web in the nip, and a second side of the belt containing voids into which liquid is transferred from the felt means which is in contact with the belt during the passage of the web and felt means through the nip.

2. A press according to claim 1, wherein the polymeric material is substantially entirely solid composition.

3. A press according to claim 1 or claim 2, wherein the -face. base fabric is a multilayer fabric with a non-^uae layer of stuffer barrier yarns.

4. A press according to any one of the preceding claims, in which the polymeric material is a solid polyurethane resin composition.

5. A press according to any one of the preceding claims, in which the base fabric is woven.

6. A press according to claim 3, wherein the base fabric is of monofilaments with the exception of the stuffer yarns which are multifilament or spun. 201587

7. A press according to claim 1, substantially as described with reference to Figures 1 and 2 and Figure 3 or Figure 4 of the accompanying drawings. ALBANY INTERNATIONAL CORPORATION, By Their Attorneys HENRY HUGHES LIMITED «