CA1201883A - Manufacture of endless belts for use in extended nip press - Google Patents
Manufacture of endless belts for use in extended nip pressInfo
- Publication number
- CA1201883A CA1201883A CA000472312A CA472312A CA1201883A CA 1201883 A CA1201883 A CA 1201883A CA 000472312 A CA000472312 A CA 000472312A CA 472312 A CA472312 A CA 472312A CA 1201883 A CA1201883 A CA 1201883A
- Authority
- CA
- Canada
- Prior art keywords
- base fabric
- belt
- cylinder
- polymeric material
- fabric
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Paper (AREA)
Abstract
ABSTRACT
An endless belt for use in an extended nip press is manufactured by providing an endless base fabric, mounting the base fabric about a heated cylinder and second roller, introducing a polymeric sheet between the base fabric and the cylinder, the polymeric material having a lower melt point than the base fabric, and applying tension on the belt by means of the second roller. The cylinder is heated such that the polymeric material melts and is forced into the base fabric by the pressure generated due to the tension on the base fabric, the polymeric material forming a smooth surface on the side of the base fabric facing the cylinder, The depth of penetration of the polymeric material into the base fabric is controlled by controlling the heat and pressure used in order to provide voids on the second side of the fabric.
An endless belt for use in an extended nip press is manufactured by providing an endless base fabric, mounting the base fabric about a heated cylinder and second roller, introducing a polymeric sheet between the base fabric and the cylinder, the polymeric material having a lower melt point than the base fabric, and applying tension on the belt by means of the second roller. The cylinder is heated such that the polymeric material melts and is forced into the base fabric by the pressure generated due to the tension on the base fabric, the polymeric material forming a smooth surface on the side of the base fabric facing the cylinder, The depth of penetration of the polymeric material into the base fabric is controlled by controlling the heat and pressure used in order to provide voids on the second side of the fabric.
Description
912~
This application is a divisional application of Canadian application ~o. 412,052 filed September 23, 1982, which relates to mechanisms for extracting water from a web - of material, and more particularly from a fibrous web formed in a paper~aking machine.
During the papermaking process, a web is ~ormed 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 o~ energy, it i9 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 re~oved.
The use of extended press nips has been found to be advantageo~s over the use of nips formed by pairs of adjacent rollers. By extending the tlme the web is subjected to pressure in the nip, a greater amount o~ water can be removed.
This fact has been recognized by those skilled in the art, and several U.S. Patents have been granted n the area. These patents include Re. 30,268, 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. I'he felts are trained 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.
~2~
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,~54, and certain belt construc-tions are suggested Eor overcoming the problem.
The invention of the parent app:Lication proposed an apparatus for dewatering a fibrous web including an extended press nip provided by a roll and a specifically designed belt which is forced toward the roll by a pressure shoe for applying pressure to the felt and fibrous web in the nip. The belt comprises a base fabric which is impreg-nated with a thermoplastic or thermosetting polymeri~ mate-rial. The base fabric has a coated and impregnated side which would operate against the pressure shoe and a second side facing the felt and web. This second side contains voids into which water or other liquid could be transferred during passage of the felt and web through the nip. 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 manufa~ture thereof. A base Eabric 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 pro-blem of bulging near -the press nips.
The invention of the present divisional application is directed to a method~for manufacturing an endless belt for use in an extended nip press, which comprises providing an endless base fabric, mounting the base fabric about a heated cylinder and second roller, introducing a polymeric sheet between the base fabric and the cylinder, the polymeric material having a lower melt point than the base fabric, and applying tension on the belt by means of the second roller.
The cylinder is heated such that the polymeric material melts and is forced into the base fabric by the pressure generated due to the tension on the base fabric, the polymeric material forming a smooth sur~ace on the side of the hase fabric facing the cylinder. The depth of penetration of the polymeric material into the base fabric is controlled by controlling the heat and pressure used in order to provide volds on the second side of the fabric.
Further features and advantages of the inventions of both the parent and divisional applications will become more readily apparent from the following description of preferred embodiments, with reference to the appended drawings in which:
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 l;
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.
The extended press nip illustrated in Figs 1 and 2 is suitable for dewatering a travelling web of material. The ~r ~L2~
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 1-2 are conventional and that other arrangements may be utilized in accordance with the invention~
One embodiment of the belt 16 is shown in detail in Figure 3. The belt 16 comprises a two layer woven mono-filament base fabric 20 with multifilament or spun stuffer yarns 21 which is impregnated with a polymeric material 22.
Thermosetting resins such as polyurethanes have been ~ound 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 ~oids 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 pro-cess to the side with voids. It is endless in final construc-tion and uniform in thickness. The fabric must also be madeto have sufficient stability under paper machine conditions.
~20~
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 con-tact with the pressure shoe 14. The opposite side contains voids, as a result of the weave and absence of impregnation, into 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' of Figure 4 is a multiLayer 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 18' on the rem~;n;ny side. The use of belt 16' is the same as pre~iously described for belt 16.
~ second embodiment uses a different method of introducing the polymeric material into the belt structure.
In this second me~hod polymeric material is pressed into the surface. The depth of penetration is controlled by the pres-sing force used and the temperature applied. Either thermo-set or thermoplastic polymers can be used. Thermoplastic polymers are especially advantageous for this method since their viscosity in melted form can be controlled by tempera-ture. By controlling the viscosity the depth of penetration ~ 2~
.a 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.
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 main-tained 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 out-side pressure roll can be used to create additional pressure i~ needed. The sheet of polymeric material is trimmed so no overlap occurs in the material pressed inko 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 trans-mitting pressure ~rom the shoe to the web and press roll.
Sufficient fle~i~;lity is obtained, and the belts ha~e proven to be una~fected 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 thermose-tting 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.
The manufacture of the belt according to the inven-tion 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 end]ess 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.
~ ibrous web 2~ carried between first and second felts ~6 and 27 respectively is introduced into the press nip 1~. The side of the belt 17 engaging the shoe 14 is lubricated by lubricat-ing means 28 positioned ahead of the nip.
The belt 16 is easily xepaired should a hole or other surface irregularity develop therein. The damaged por-tion 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 coated surface is at a minimum distance from -the neutral axis 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 poly-~2~
meric materials having the necessary properties for applica-tion in papermaking machines. Materials other than poly-urethane 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.
This application is a divisional application of Canadian application ~o. 412,052 filed September 23, 1982, which relates to mechanisms for extracting water from a web - of material, and more particularly from a fibrous web formed in a paper~aking machine.
During the papermaking process, a web is ~ormed 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 o~ energy, it i9 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 re~oved.
The use of extended press nips has been found to be advantageo~s over the use of nips formed by pairs of adjacent rollers. By extending the tlme the web is subjected to pressure in the nip, a greater amount o~ water can be removed.
This fact has been recognized by those skilled in the art, and several U.S. Patents have been granted n the area. These patents include Re. 30,268, 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. I'he felts are trained 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.
~2~
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,~54, and certain belt construc-tions are suggested Eor overcoming the problem.
The invention of the parent app:Lication proposed an apparatus for dewatering a fibrous web including an extended press nip provided by a roll and a specifically designed belt which is forced toward the roll by a pressure shoe for applying pressure to the felt and fibrous web in the nip. The belt comprises a base fabric which is impreg-nated with a thermoplastic or thermosetting polymeri~ mate-rial. The base fabric has a coated and impregnated side which would operate against the pressure shoe and a second side facing the felt and web. This second side contains voids into which water or other liquid could be transferred during passage of the felt and web through the nip. 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 manufa~ture thereof. A base Eabric 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 pro-blem of bulging near -the press nips.
The invention of the present divisional application is directed to a method~for manufacturing an endless belt for use in an extended nip press, which comprises providing an endless base fabric, mounting the base fabric about a heated cylinder and second roller, introducing a polymeric sheet between the base fabric and the cylinder, the polymeric material having a lower melt point than the base fabric, and applying tension on the belt by means of the second roller.
The cylinder is heated such that the polymeric material melts and is forced into the base fabric by the pressure generated due to the tension on the base fabric, the polymeric material forming a smooth sur~ace on the side of the hase fabric facing the cylinder. The depth of penetration of the polymeric material into the base fabric is controlled by controlling the heat and pressure used in order to provide volds on the second side of the fabric.
Further features and advantages of the inventions of both the parent and divisional applications will become more readily apparent from the following description of preferred embodiments, with reference to the appended drawings in which:
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 l;
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.
The extended press nip illustrated in Figs 1 and 2 is suitable for dewatering a travelling web of material. The ~r ~L2~
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 1-2 are conventional and that other arrangements may be utilized in accordance with the invention~
One embodiment of the belt 16 is shown in detail in Figure 3. The belt 16 comprises a two layer woven mono-filament base fabric 20 with multifilament or spun stuffer yarns 21 which is impregnated with a polymeric material 22.
Thermosetting resins such as polyurethanes have been ~ound 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 ~oids 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 pro-cess to the side with voids. It is endless in final construc-tion and uniform in thickness. The fabric must also be madeto have sufficient stability under paper machine conditions.
~20~
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 con-tact with the pressure shoe 14. The opposite side contains voids, as a result of the weave and absence of impregnation, into 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' of Figure 4 is a multiLayer 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 18' on the rem~;n;ny side. The use of belt 16' is the same as pre~iously described for belt 16.
~ second embodiment uses a different method of introducing the polymeric material into the belt structure.
In this second me~hod polymeric material is pressed into the surface. The depth of penetration is controlled by the pres-sing force used and the temperature applied. Either thermo-set or thermoplastic polymers can be used. Thermoplastic polymers are especially advantageous for this method since their viscosity in melted form can be controlled by tempera-ture. By controlling the viscosity the depth of penetration ~ 2~
.a 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.
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 main-tained 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 out-side pressure roll can be used to create additional pressure i~ needed. The sheet of polymeric material is trimmed so no overlap occurs in the material pressed inko 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 trans-mitting pressure ~rom the shoe to the web and press roll.
Sufficient fle~i~;lity is obtained, and the belts ha~e proven to be una~fected 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 thermose-tting 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.
The manufacture of the belt according to the inven-tion 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 end]ess 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.
~ ibrous web 2~ carried between first and second felts ~6 and 27 respectively is introduced into the press nip 1~. The side of the belt 17 engaging the shoe 14 is lubricated by lubricat-ing means 28 positioned ahead of the nip.
The belt 16 is easily xepaired should a hole or other surface irregularity develop therein. The damaged por-tion 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 coated surface is at a minimum distance from -the neutral axis 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 poly-~2~
meric materials having the necessary properties for applica-tion in papermaking machines. Materials other than poly-urethane 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.
Claims (2)
1. A method for manufacturing an endless belt for use in an extended nip press comprising:
providing an endless base fabric;
mounting said base fabric about a heated cylinder and second roller;
introducing a polymeric sheet between said base fabric and said cylinder, said polymeric material having a lower melt point than said base fabric;
applying tension on said belt by means of the second roller;
heating said cylinder such that the polymeric material melts and is forced into the base fabric by the pressure generated due to the tension on the base fabric, said polymeric material forming a smooth surface on the side of the base fabric facing the cylinder; and controlling the depth of penetration of the polymeric material into the base fabric by controlling the heat and pressure used in order to provide voids on the second side of the fabric.
providing an endless base fabric;
mounting said base fabric about a heated cylinder and second roller;
introducing a polymeric sheet between said base fabric and said cylinder, said polymeric material having a lower melt point than said base fabric;
applying tension on said belt by means of the second roller;
heating said cylinder such that the polymeric material melts and is forced into the base fabric by the pressure generated due to the tension on the base fabric, said polymeric material forming a smooth surface on the side of the base fabric facing the cylinder; and controlling the depth of penetration of the polymeric material into the base fabric by controlling the heat and pressure used in order to provide voids on the second side of the fabric.
2. A method as claimed in claim 1, wherein pressure is applied on the base fabric and polymeric sheet while they are on the cylinder by means of a third roller outside the fabric loop.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000472312A CA1201883A (en) | 1981-09-24 | 1985-01-17 | Manufacture of endless belts for use in extended nip press |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US30514881A | 1981-09-24 | 1981-09-24 | |
| US305,148 | 1981-09-24 | ||
| CA000412052A CA1190779A (en) | 1981-09-24 | 1982-09-23 | Dewatering press |
| CA000472312A CA1201883A (en) | 1981-09-24 | 1985-01-17 | Manufacture of endless belts for use in extended nip press |
Related Parent Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000412052A Division CA1190779A (en) | 1981-09-24 | 1982-09-23 | Dewatering press |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1201883A true CA1201883A (en) | 1986-03-18 |
Family
ID=25669815
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000472312A Expired CA1201883A (en) | 1981-09-24 | 1985-01-17 | Manufacture of endless belts for use in extended nip press |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1201883A (en) |
-
1985
- 1985-01-17 CA CA000472312A patent/CA1201883A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |