CA2032785C - A press with extended press zone in a paper machine - Google Patents
A press with extended press zone in a paper machine Download PDFInfo
- Publication number
- CA2032785C CA2032785C CA002032785A CA2032785A CA2032785C CA 2032785 C CA2032785 C CA 2032785C CA 002032785 A CA002032785 A CA 002032785A CA 2032785 A CA2032785 A CA 2032785A CA 2032785 C CA2032785 C CA 2032785C
- Authority
- CA
- Canada
- Prior art keywords
- press
- shoe
- area
- roll
- 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 - Fee Related
Links
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F3/00—Press section of machines for making continuous webs of paper
- D21F3/02—Wet presses
- D21F3/0209—Wet presses with extended press nip
- D21F3/0218—Shoe presses
Abstract
A press with extended press zone in a paper machine, comprising a rotating press roll (1), a press shoe (2), and a slide band (7) sliding along the surface of the press shoe, a web (6) being passed between felts (4, 5) through the press, where it is pressed between the roll (1) and the slide band (7). The press shoe (2), designed to operate hydrodynamically, has a surface provided with a pocket area (d) formed by one or more pockets of small average thickness.
If required, pressurized lubricant can be introduced to the pocket area to achieve the desired press effect and speed.
If required, pressurized lubricant can be introduced to the pocket area to achieve the desired press effect and speed.
Description
1 ~~3~."~~~
A press with extended press zone in a paper machine This invention relates to a press with extended press zone in a paper machine for dewatering a wet fibre web, comprising - a rotating press roll and at least one press shoe extending in the axial direction of the press roll, said press shoe bearing on the press roll;
- a liquid-impermeable slide band sliding along the surface of the press shoe between the press shoe and the press roll in the direction of travel of the fibre web;
- means for introducing lubricant between the slide band and the press shoe at its entry edge; and - at least one press felt for passing the fibre web through the press between the press roll and the slide band and for receiving water from the fibre web.
In the production of paper and paper board, the flow of liquid is restricted in certain types of paper and board during the wet pressing step. In such ;
cases, the removal of water in the nip can be made more effective by increasing the length of the press zone. With roll presses, this is achieved by in- ;
creasing the diameter of the press rolls and by coat-ing the rolls with a soft material. In addition, high line loads are applied, so that the length of the press zone is increased up to 100 mm, whereby such factors as excessive masses and the durability of the , coating become restrictive. As compared with roll presses, a substantially longer press zone is achieved by so-called shoe presses in which one roll in the roll press is replaced with a stationary con cave press shoe bearing on the rotating press roll.
The felts and the fibre web are passed through the ~~03~ '~~ i nip between the roll and an elastic band sliding along the press shoe. In addition to the longer press zone, typically about 250 mm, the shoe press also causes the pressure to be distributed more evenly ,'5 over the length of the nip. As a result, considerably higher line loads than in roll presses can be applied in shoe presses without that the maximum pressure rises excessively in any point. Technically, shoe presses can be divided into two groups on the basis of the lubrication mechanism of the band sliding alo ng the shoe, viz. into hydrodynamic and hydrostatic presses.
Shoe presses based on hydrodynamic lubrication are described in US Reissue Patent 30268 and US
Patent 4,427,492, for instance. Both of these dis close a solution in which lubricant is introduced between the band and the shoe on the entry side of the band sliding along the shoe at the front edge of the shoe. The lubricant flows with the band between the band and the shoe, thus forming a wedge-shaped lubrication film on the surface of the shoe and the band. The bearing capacity of the lubrication film depends on the speed of the band with respect to the shoe, and it disappears totally when the speed approaches zero. When selecting the viscosity of the lubricant, it has to be taken into account that it might be necessary to operate the press at speeds below the design value or at load pressures exceeding the design values. In practice, this means that the viscosity is overdimensioned, as a result of which the friction losses caused by the shearing of the lubricant will be considerably greater than actually needed. For the same reasons, the shoe press based on hydrodynamic lubrication is not particularly suitable for use when a wide speed and load range is required ~~3~:'?'~
from the press.
In the hydrostatic shoe press, disclosed, e.g., in U.S. Patents 3,853,698, 4,427,492, 4,570,314 and 4,568,423, the bearing capacity is achieved mainly by ..'i introducing pressurized lubricant through the shoe between the band and the shoe, so that the lubricant presses the band against the roll and lubricates the contact surfaces between the band and shoe as it is squeezed out through the edges. With hydrostatic lubrication, the load and the bearing capacity of the shoe disappears if the flow of pressurized lubricant is interrupted for one reason or another. The lubri-cant is typically introduced into deep elongated pockets provided in the surface of the press shoe in usually the axial direction of the counter roll. In the area of the pockets the band is loaded solely hydrostatically as no hydrodynamic lubricant wedge with increasing pressure is formed therein. Accord-ingly, the pressure exerted on the band in the area of the pockets is constant, and the power required for pumping the lubricant into the pocket is substan-tially dependent on the desired thickness of the lub-rication film and the length of the entry and delivery edges acting as sealing edges in the direction of travel of the band. When low pumping losses are aimed at, the film should be thin and the sealing edges should be long. As compared with the hydrodynamic shoe, an advantage of the hydrostatic shoe is that it provides a wider range of operation as the hydrostatic pressure to be applied can be varied. On the other hand, a disadvantage is the re-sulting greater total power consumption and greater COSTS.
Distribution of pressure in the nip affects greatly the properties of the paper or board. If the ~~?3~:'~~ a compression pressure at the beginning of the press zone increases too rapidly, an excessive hydraulic pressure created in the web may cause water to flow in the direction of the web, thus impairing the strength properties of the paper as the formation of bonds between the fibres is hampered. Optimally, the compression pressure increases evenly over the length of the press zone and reaches its maximum immediately before the end of the nip. A gradually decreasing compression pressure creates an underpressure in the web, which causes part of the removed water to return to the web from the felt, thus rewetting the web.
Another essential factor affecting the prop erties of the resulting paper or board is the maximum pressure created in the nip, which must be on the right level both in view of the properties of the web and the operability of the felts to optimize the strength properties of the paper and to achieve high content of dry substance. With the roll press, the maximum pressure can be determined by calculation on the basis of the roll diameters and the compress-ibility of the coatings and the press felts. The com-pressibility of the felts, in turn, can be affected by selecting a basic fabric best suited for the press felt. Variation in the properties of the felts during operation nevertheless causes problems. When the felts wear, they get considerably thinner, which results in an increase in the maximum pressure in the nip. Impaired operating properties of the felts, in turn, make it necessary to decrease the line load of the press to keep the maximum pressure on the desired level. As a result, the dry substance content of the web decreases after the press as it is directly dependent on the pressure impulse created in the press.
~'~3.~'~~
It is typical of the pressure distribution in hydrodynamic shoe presses that the pressure increases at the beginning of the nip and the maximum value is achieved after the point of support of the shoe. The 5 pressure distribution can be affected to some extent by suitably shaping the shoe, and the position of the maximum pressure can be affected to some extent by displacing the centre of gravity of the supporting force. The pressure drop on the delivery edge of the hydrodynamic shoe is, however, relatively gradual.
The maximum pressure of hydrodynamic shoe presses can be varied only by varying the line load of the presses, as a result of which the pressure impulse changes, which, in turn, causes variation in the dry substance content of the web emerging from the press.
In the hydrostatic shoe press, the pressure in the area of the pocket is constant, and the pressure variations at the beginning of the nip and cor-respondingly in the end depend on the length of the sealing edges on the entry and delivery side. With short sealing edges, the pressure is substantially constant over the whole press zone. As a result of this, however, the pressure rises relatively abruptly on the entry side, which may cause water flows in the longitudinal direction of the web. By using several successive pockets and by dimensioning the lengths of the entry and delivery edges in different ways, the pressure distribution can be affected to some extent;
however, the pressure is still constant at each pocket and the pressure changes gradually.
The object of the present invention is to provide a compression shoe which provides a wide range of operation with respect to both the speed of the web and the load, and by means of which a desired press effect can be achieved in all operating con-ditions with the ~~mallest possible consumption of energy.
This is achieved according to the invention in such a manner that - i:n the press shoe a surface facing the slide band comprises a pocket area having at least substantially the same width as the fibre web and being narrower than the press zone in the direction of travel of the band, said pocket area comprising at least one pocket forrr~ed in the surface of the press shoe as a recess;
- t:he prE:ss comprises at lest one lubrication conduit for introducing pressurized lubricant to the pocket area; and - t:he depth of the pockets in the pocket area is such that: the press operates substantially hydrodynami~~ally above a predetermined web speed.
The b<~sic idea of the invention is that the hydrodynami~~ally operated shoe is provided with a pocket area compri;~ing o:ne or more pockets the average depth of which is about 0 t=o 0.75 mm, pressurized lubricant being introduced into the pockets. In this way the shoe operates solely hydrodynamically above a predetermined web speed a:nd the influence of the hydrostatic pressure is increased above this speed without losing the hydrodynami~~ formation of pressure and, as a consequence, the pressure increasing over the entire length of the pocket area.
In general terms, the present invention provides a press with extended press zone in a papermaking machine for dewatering a wet fiber web which comprises - a rotating press roll and at least one press shoe extending in the axia7_ direction of the press roll, said press shoe bearing on 'the press roll; - a liquid-impermeable slide band slidin<~ along the surface of the press shoe between the press ~~hoe and the press roll in the direction of travel of t:he fibre web; - means for introducing lubricant between the slide band and the press shoe; and 6a - at least one press felt for passing the fibre web through the press between the press roll and the slide band and for receiving water from the fibre web;
- a pocket area in a surface of the press shoe facing the slide band having at least substantially the same width as the fibre web and being narrower than the extended press zone in the direction of travel of the band, said pockets area comprising at least one pocket formed in t:he surface of the press shoe as a recess;
- said means for introducing lubricant including at least one :Lubrication conduit for introducing pressurized lubricant to the pocket area.
The in~rentio:n will be described in greater detail in the attache~3 drawings, where Figure 1 illustrates schematically a shoe press of the inventi~~n;
Figure 2 is a schematic cross-sectional view of the press shoe ~~f the press of Figure 1;
Figure 3 is a perspective view of the press ~~~3~:'7~
shoe of Figures 1 and 2;
Figure 4 illustrates the distribution of com-pression pressure in a hydrodynamic and a hydrostatic press; and Figure 5 illustrates the distribution of com-pression pressure in the press of the invention.
Figure 1 shows a press comprising a counter press roll 1 and a press shoe 2 which is positioned against the roll and rests on a base 3. Felts 4 and 5 extend between the roll 1 and the press shoe 2, and a web 6 to be dried is transported between the felts.
Further, a slide band 7 is provided between the lower felt 5 and the press shoe 2. The band, which is lubricated by a lubricant, slides along the surface of the press shoe 2. The lubricant is introduced to the front edge of the press shoe 2 through a conduit 8 and to the central area of the band through con-duits 9 and 10. The base 3 comprises press pistons 11 below which pressurized medium can be introduced through conduits 12 to load the press shoe 2. The structure and operation of the press are known per se, and will not be described more closely herein.
Figure 2 is a schematic cross-sectional view of the press shoe of Figure 1 on an enlarged scale. The roll-contacting surface of the press shoe 2 has a radius of curvature R, that is, the curvature of the surface is such that the press shoe 2 can operate hydrodynamically. For this purpose, a groove 13 com-municating with the lubricant introduction conduit 8 is provided in the front portion of the shoe 2. The lubrication liquid is fed into the groove, from which it is passed between the press shoe 2 and the slide band 7 by the action of the band 7 sliding along the surface of the press shoe 2, a thin lubrication film being thus formed on the band. The lubricant fed into ~EJ~~ i ~
the groove 13 through the conduit 8 has a low pressure such that it is merely able to pass the lubricant between the band 7 and the shoe so that a hydrodynamic lubrication is achieved when the band 7 moves. According to the invention, a pocket area formed by a shallow pocket is formed on the surface of the press shoe 2 over a length indicated with the letter T. The average depth of the pockets should not exceed 0.75 mm. In Figure 2, the pocket is a pocket-like recess formed in the surface of the shoe 2 with a radius of curvature R' shorter than the normal radius of curvature R of the surface. In this par-ticular case, the recess starts from the surface of the shoe 2 and ends in the surface of the shoe 2 with a clear point of discontinuity. To introduce lubrication liquid and, if required, pressurized lubrication liquid into the pocket, narrow deep grooves 14 and 15 are formed in the area of the pocket in its front and back portion, respectively.
The lubricant can be fed into the grooves at dif ferent pressures through the conduits 9 and 10.
Figure 3 is a perspective view of the press shoe of the invention. As appears from the figure, the pocket area T formed in the surface of the press shoe 2 is surrounded by an edging having the normal radius of curvature of the surface of the press shoe 2. It further appears that the lubricant introduction grooves 14 and 15 are positioned within the pocket area, and that the grooves may extend nearly over the entire pocket area or there may be several shorter grooves in succession.
The distribution of hydrodynamic compression pressure shown in Figure 4 is a pressure distribution typical of the solution disclosed in U.S. Patent 4,518,460, where the pressure increases evenly to its ;~~D3~:'~~ a maximum and decreases then gradually. The hydrostatic compression pressure distribution is typical of the solution of U.S. Patent 4,570,314, where the pressure is even within the area of the pockets.
Figure 5 illustrates the compression pressure distribution in the press with extended nip according to the invention, where the pressure is substantially on the increase throughout the press zone. As dis-tinct from the hydrodynamic solution, the pressure drop on the delivery side is substantially more abrupt.
It is possible to feed the lubricant into the grooves 14 and 15 in the front and back edges of the pocket area at different pressures. By increasing the pressure of the lubricant to be fed into the groove 15, the smoothly rising pressure pattern can be main-tained even at lower web speeds due to the hydro-dynamic effect created by the band 7 arid the pressure difference of the lubricant.
When the press shoe 2 in the press of the invention operates at its design speed, its bearing capacity consists mainly of the hydrodynamic effect, that is, the press operates at a low lubricant supply power. When the running speed is below the design speed, or a greater pressing power is required from the press, the required increase in the pressing capacity is obtained hydrostatically by feeding pressurized lubricant into the pocket area T. The lubrication film is thereby stiffer than in hydro-dynamic lubrication, and the decrease in the thick-ness of the lubrication film caused by an increase in load or a reduction in speed is smaller. By selecting the lowest possible viscosity of the lubricant on the basis of the design speed and the load, a con-siderably lower total consumption of power is ~03~ ''~~ a to achieved as compared with the shoe press solutions known from the prior art. The introduction of lubricant and the even distribution of pressure within the pocket area is based on the fact that when lubricant is fed under pressure, it spreads suf-ficiently easily over a wide area in the relatively deep grooves of the pocket area, the grooves being also relatively narrow with resgect to the width of the pocket area. Further, as the lubricant intro-duction openings are positioned on the bottoms of the grooves the formation of the hydrodynamic bearing capacity will not be disturbed notably. The depth of the lubricant introduction grooves 14 and 15 is at least five times the average depth of the pocket area, and their width is no more than one tenth of the width of the pocket area. To enable a substan-tially hydrodynamic operation of the shoe, it is very important that the depth of the pockets in the pocket area is not too great. Therefore the average depth of the pockets in the pocket area should be no more than 0.75 mm, whereby the pressure over the width of the pocket, i . e. , in the direction of travel of the web, will not be levelled out similarly as in prior art static press solutions, in which the depth of the pocket area is very great and in which the hydraulic pressure is substantially constant over the entire pocket area. As used in this text, the depth of the pocket area means the distance of its bottom from the imaginary continuous surface which the press shoe would have without the pocket recesses . In the press of the invention the hydrodynamic wedge effect is maintained in the pocket area so that the pressure rises substantially evenly, as is usual in the hydro-dynamic shoe. As compared with the hydrodynamic shoe, the pocket area provides the further advantage that ~~1~~'~~ i the maximum pressure is also shifted closer to the delivery edge of the press zone while the hydro-dynamic bearing capacity is considerably increased by suitably shaping the pocket area. By using prior art solutions to shift the centre of gravity of the sup-port forces of the shoe, the maximum pressure of the nip can be adjusted as desired, whereby it can be decreased, if necessary, without any need of de-creasing the line load of the press. One such way of shifting the centre of gravity is disclosed in FI
Patent 55103.
The invention has been described above and in the attached drawings by way of example, and it is in no way restricted to this example. Even though the shoe shown in the figures comprises a single pocket, it is possible to realize the press in such a way that the surface of the shoe comprises a pocket area formed by several pockets positioned adjacent to each other in succession in the transverse and/or longitudinal direction of the web. In all cases, it should be taken into account that the average depth of each individual pocket should not exceed 0.75 mm, as already mentioned above.
The bottom of the press shoe shown in Figures 1 to 3 is curved in shape, but it is also possible to use a rectangular shape and edges that protrude sharply from the surface, provided that the average depth does not exceed the above-mentioned value.
Further, the pocket can be sharp-angled at one edge, while the other edge defines a wide angle, as shown in Figures 1 to 3.
A press with extended press zone in a paper machine This invention relates to a press with extended press zone in a paper machine for dewatering a wet fibre web, comprising - a rotating press roll and at least one press shoe extending in the axial direction of the press roll, said press shoe bearing on the press roll;
- a liquid-impermeable slide band sliding along the surface of the press shoe between the press shoe and the press roll in the direction of travel of the fibre web;
- means for introducing lubricant between the slide band and the press shoe at its entry edge; and - at least one press felt for passing the fibre web through the press between the press roll and the slide band and for receiving water from the fibre web.
In the production of paper and paper board, the flow of liquid is restricted in certain types of paper and board during the wet pressing step. In such ;
cases, the removal of water in the nip can be made more effective by increasing the length of the press zone. With roll presses, this is achieved by in- ;
creasing the diameter of the press rolls and by coat-ing the rolls with a soft material. In addition, high line loads are applied, so that the length of the press zone is increased up to 100 mm, whereby such factors as excessive masses and the durability of the , coating become restrictive. As compared with roll presses, a substantially longer press zone is achieved by so-called shoe presses in which one roll in the roll press is replaced with a stationary con cave press shoe bearing on the rotating press roll.
The felts and the fibre web are passed through the ~~03~ '~~ i nip between the roll and an elastic band sliding along the press shoe. In addition to the longer press zone, typically about 250 mm, the shoe press also causes the pressure to be distributed more evenly ,'5 over the length of the nip. As a result, considerably higher line loads than in roll presses can be applied in shoe presses without that the maximum pressure rises excessively in any point. Technically, shoe presses can be divided into two groups on the basis of the lubrication mechanism of the band sliding alo ng the shoe, viz. into hydrodynamic and hydrostatic presses.
Shoe presses based on hydrodynamic lubrication are described in US Reissue Patent 30268 and US
Patent 4,427,492, for instance. Both of these dis close a solution in which lubricant is introduced between the band and the shoe on the entry side of the band sliding along the shoe at the front edge of the shoe. The lubricant flows with the band between the band and the shoe, thus forming a wedge-shaped lubrication film on the surface of the shoe and the band. The bearing capacity of the lubrication film depends on the speed of the band with respect to the shoe, and it disappears totally when the speed approaches zero. When selecting the viscosity of the lubricant, it has to be taken into account that it might be necessary to operate the press at speeds below the design value or at load pressures exceeding the design values. In practice, this means that the viscosity is overdimensioned, as a result of which the friction losses caused by the shearing of the lubricant will be considerably greater than actually needed. For the same reasons, the shoe press based on hydrodynamic lubrication is not particularly suitable for use when a wide speed and load range is required ~~3~:'?'~
from the press.
In the hydrostatic shoe press, disclosed, e.g., in U.S. Patents 3,853,698, 4,427,492, 4,570,314 and 4,568,423, the bearing capacity is achieved mainly by ..'i introducing pressurized lubricant through the shoe between the band and the shoe, so that the lubricant presses the band against the roll and lubricates the contact surfaces between the band and shoe as it is squeezed out through the edges. With hydrostatic lubrication, the load and the bearing capacity of the shoe disappears if the flow of pressurized lubricant is interrupted for one reason or another. The lubri-cant is typically introduced into deep elongated pockets provided in the surface of the press shoe in usually the axial direction of the counter roll. In the area of the pockets the band is loaded solely hydrostatically as no hydrodynamic lubricant wedge with increasing pressure is formed therein. Accord-ingly, the pressure exerted on the band in the area of the pockets is constant, and the power required for pumping the lubricant into the pocket is substan-tially dependent on the desired thickness of the lub-rication film and the length of the entry and delivery edges acting as sealing edges in the direction of travel of the band. When low pumping losses are aimed at, the film should be thin and the sealing edges should be long. As compared with the hydrodynamic shoe, an advantage of the hydrostatic shoe is that it provides a wider range of operation as the hydrostatic pressure to be applied can be varied. On the other hand, a disadvantage is the re-sulting greater total power consumption and greater COSTS.
Distribution of pressure in the nip affects greatly the properties of the paper or board. If the ~~?3~:'~~ a compression pressure at the beginning of the press zone increases too rapidly, an excessive hydraulic pressure created in the web may cause water to flow in the direction of the web, thus impairing the strength properties of the paper as the formation of bonds between the fibres is hampered. Optimally, the compression pressure increases evenly over the length of the press zone and reaches its maximum immediately before the end of the nip. A gradually decreasing compression pressure creates an underpressure in the web, which causes part of the removed water to return to the web from the felt, thus rewetting the web.
Another essential factor affecting the prop erties of the resulting paper or board is the maximum pressure created in the nip, which must be on the right level both in view of the properties of the web and the operability of the felts to optimize the strength properties of the paper and to achieve high content of dry substance. With the roll press, the maximum pressure can be determined by calculation on the basis of the roll diameters and the compress-ibility of the coatings and the press felts. The com-pressibility of the felts, in turn, can be affected by selecting a basic fabric best suited for the press felt. Variation in the properties of the felts during operation nevertheless causes problems. When the felts wear, they get considerably thinner, which results in an increase in the maximum pressure in the nip. Impaired operating properties of the felts, in turn, make it necessary to decrease the line load of the press to keep the maximum pressure on the desired level. As a result, the dry substance content of the web decreases after the press as it is directly dependent on the pressure impulse created in the press.
~'~3.~'~~
It is typical of the pressure distribution in hydrodynamic shoe presses that the pressure increases at the beginning of the nip and the maximum value is achieved after the point of support of the shoe. The 5 pressure distribution can be affected to some extent by suitably shaping the shoe, and the position of the maximum pressure can be affected to some extent by displacing the centre of gravity of the supporting force. The pressure drop on the delivery edge of the hydrodynamic shoe is, however, relatively gradual.
The maximum pressure of hydrodynamic shoe presses can be varied only by varying the line load of the presses, as a result of which the pressure impulse changes, which, in turn, causes variation in the dry substance content of the web emerging from the press.
In the hydrostatic shoe press, the pressure in the area of the pocket is constant, and the pressure variations at the beginning of the nip and cor-respondingly in the end depend on the length of the sealing edges on the entry and delivery side. With short sealing edges, the pressure is substantially constant over the whole press zone. As a result of this, however, the pressure rises relatively abruptly on the entry side, which may cause water flows in the longitudinal direction of the web. By using several successive pockets and by dimensioning the lengths of the entry and delivery edges in different ways, the pressure distribution can be affected to some extent;
however, the pressure is still constant at each pocket and the pressure changes gradually.
The object of the present invention is to provide a compression shoe which provides a wide range of operation with respect to both the speed of the web and the load, and by means of which a desired press effect can be achieved in all operating con-ditions with the ~~mallest possible consumption of energy.
This is achieved according to the invention in such a manner that - i:n the press shoe a surface facing the slide band comprises a pocket area having at least substantially the same width as the fibre web and being narrower than the press zone in the direction of travel of the band, said pocket area comprising at least one pocket forrr~ed in the surface of the press shoe as a recess;
- t:he prE:ss comprises at lest one lubrication conduit for introducing pressurized lubricant to the pocket area; and - t:he depth of the pockets in the pocket area is such that: the press operates substantially hydrodynami~~ally above a predetermined web speed.
The b<~sic idea of the invention is that the hydrodynami~~ally operated shoe is provided with a pocket area compri;~ing o:ne or more pockets the average depth of which is about 0 t=o 0.75 mm, pressurized lubricant being introduced into the pockets. In this way the shoe operates solely hydrodynamically above a predetermined web speed a:nd the influence of the hydrostatic pressure is increased above this speed without losing the hydrodynami~~ formation of pressure and, as a consequence, the pressure increasing over the entire length of the pocket area.
In general terms, the present invention provides a press with extended press zone in a papermaking machine for dewatering a wet fiber web which comprises - a rotating press roll and at least one press shoe extending in the axia7_ direction of the press roll, said press shoe bearing on 'the press roll; - a liquid-impermeable slide band slidin<~ along the surface of the press shoe between the press ~~hoe and the press roll in the direction of travel of t:he fibre web; - means for introducing lubricant between the slide band and the press shoe; and 6a - at least one press felt for passing the fibre web through the press between the press roll and the slide band and for receiving water from the fibre web;
- a pocket area in a surface of the press shoe facing the slide band having at least substantially the same width as the fibre web and being narrower than the extended press zone in the direction of travel of the band, said pockets area comprising at least one pocket formed in t:he surface of the press shoe as a recess;
- said means for introducing lubricant including at least one :Lubrication conduit for introducing pressurized lubricant to the pocket area.
The in~rentio:n will be described in greater detail in the attache~3 drawings, where Figure 1 illustrates schematically a shoe press of the inventi~~n;
Figure 2 is a schematic cross-sectional view of the press shoe ~~f the press of Figure 1;
Figure 3 is a perspective view of the press ~~~3~:'7~
shoe of Figures 1 and 2;
Figure 4 illustrates the distribution of com-pression pressure in a hydrodynamic and a hydrostatic press; and Figure 5 illustrates the distribution of com-pression pressure in the press of the invention.
Figure 1 shows a press comprising a counter press roll 1 and a press shoe 2 which is positioned against the roll and rests on a base 3. Felts 4 and 5 extend between the roll 1 and the press shoe 2, and a web 6 to be dried is transported between the felts.
Further, a slide band 7 is provided between the lower felt 5 and the press shoe 2. The band, which is lubricated by a lubricant, slides along the surface of the press shoe 2. The lubricant is introduced to the front edge of the press shoe 2 through a conduit 8 and to the central area of the band through con-duits 9 and 10. The base 3 comprises press pistons 11 below which pressurized medium can be introduced through conduits 12 to load the press shoe 2. The structure and operation of the press are known per se, and will not be described more closely herein.
Figure 2 is a schematic cross-sectional view of the press shoe of Figure 1 on an enlarged scale. The roll-contacting surface of the press shoe 2 has a radius of curvature R, that is, the curvature of the surface is such that the press shoe 2 can operate hydrodynamically. For this purpose, a groove 13 com-municating with the lubricant introduction conduit 8 is provided in the front portion of the shoe 2. The lubrication liquid is fed into the groove, from which it is passed between the press shoe 2 and the slide band 7 by the action of the band 7 sliding along the surface of the press shoe 2, a thin lubrication film being thus formed on the band. The lubricant fed into ~EJ~~ i ~
the groove 13 through the conduit 8 has a low pressure such that it is merely able to pass the lubricant between the band 7 and the shoe so that a hydrodynamic lubrication is achieved when the band 7 moves. According to the invention, a pocket area formed by a shallow pocket is formed on the surface of the press shoe 2 over a length indicated with the letter T. The average depth of the pockets should not exceed 0.75 mm. In Figure 2, the pocket is a pocket-like recess formed in the surface of the shoe 2 with a radius of curvature R' shorter than the normal radius of curvature R of the surface. In this par-ticular case, the recess starts from the surface of the shoe 2 and ends in the surface of the shoe 2 with a clear point of discontinuity. To introduce lubrication liquid and, if required, pressurized lubrication liquid into the pocket, narrow deep grooves 14 and 15 are formed in the area of the pocket in its front and back portion, respectively.
The lubricant can be fed into the grooves at dif ferent pressures through the conduits 9 and 10.
Figure 3 is a perspective view of the press shoe of the invention. As appears from the figure, the pocket area T formed in the surface of the press shoe 2 is surrounded by an edging having the normal radius of curvature of the surface of the press shoe 2. It further appears that the lubricant introduction grooves 14 and 15 are positioned within the pocket area, and that the grooves may extend nearly over the entire pocket area or there may be several shorter grooves in succession.
The distribution of hydrodynamic compression pressure shown in Figure 4 is a pressure distribution typical of the solution disclosed in U.S. Patent 4,518,460, where the pressure increases evenly to its ;~~D3~:'~~ a maximum and decreases then gradually. The hydrostatic compression pressure distribution is typical of the solution of U.S. Patent 4,570,314, where the pressure is even within the area of the pockets.
Figure 5 illustrates the compression pressure distribution in the press with extended nip according to the invention, where the pressure is substantially on the increase throughout the press zone. As dis-tinct from the hydrodynamic solution, the pressure drop on the delivery side is substantially more abrupt.
It is possible to feed the lubricant into the grooves 14 and 15 in the front and back edges of the pocket area at different pressures. By increasing the pressure of the lubricant to be fed into the groove 15, the smoothly rising pressure pattern can be main-tained even at lower web speeds due to the hydro-dynamic effect created by the band 7 arid the pressure difference of the lubricant.
When the press shoe 2 in the press of the invention operates at its design speed, its bearing capacity consists mainly of the hydrodynamic effect, that is, the press operates at a low lubricant supply power. When the running speed is below the design speed, or a greater pressing power is required from the press, the required increase in the pressing capacity is obtained hydrostatically by feeding pressurized lubricant into the pocket area T. The lubrication film is thereby stiffer than in hydro-dynamic lubrication, and the decrease in the thick-ness of the lubrication film caused by an increase in load or a reduction in speed is smaller. By selecting the lowest possible viscosity of the lubricant on the basis of the design speed and the load, a con-siderably lower total consumption of power is ~03~ ''~~ a to achieved as compared with the shoe press solutions known from the prior art. The introduction of lubricant and the even distribution of pressure within the pocket area is based on the fact that when lubricant is fed under pressure, it spreads suf-ficiently easily over a wide area in the relatively deep grooves of the pocket area, the grooves being also relatively narrow with resgect to the width of the pocket area. Further, as the lubricant intro-duction openings are positioned on the bottoms of the grooves the formation of the hydrodynamic bearing capacity will not be disturbed notably. The depth of the lubricant introduction grooves 14 and 15 is at least five times the average depth of the pocket area, and their width is no more than one tenth of the width of the pocket area. To enable a substan-tially hydrodynamic operation of the shoe, it is very important that the depth of the pockets in the pocket area is not too great. Therefore the average depth of the pockets in the pocket area should be no more than 0.75 mm, whereby the pressure over the width of the pocket, i . e. , in the direction of travel of the web, will not be levelled out similarly as in prior art static press solutions, in which the depth of the pocket area is very great and in which the hydraulic pressure is substantially constant over the entire pocket area. As used in this text, the depth of the pocket area means the distance of its bottom from the imaginary continuous surface which the press shoe would have without the pocket recesses . In the press of the invention the hydrodynamic wedge effect is maintained in the pocket area so that the pressure rises substantially evenly, as is usual in the hydro-dynamic shoe. As compared with the hydrodynamic shoe, the pocket area provides the further advantage that ~~1~~'~~ i the maximum pressure is also shifted closer to the delivery edge of the press zone while the hydro-dynamic bearing capacity is considerably increased by suitably shaping the pocket area. By using prior art solutions to shift the centre of gravity of the sup-port forces of the shoe, the maximum pressure of the nip can be adjusted as desired, whereby it can be decreased, if necessary, without any need of de-creasing the line load of the press. One such way of shifting the centre of gravity is disclosed in FI
Patent 55103.
The invention has been described above and in the attached drawings by way of example, and it is in no way restricted to this example. Even though the shoe shown in the figures comprises a single pocket, it is possible to realize the press in such a way that the surface of the shoe comprises a pocket area formed by several pockets positioned adjacent to each other in succession in the transverse and/or longitudinal direction of the web. In all cases, it should be taken into account that the average depth of each individual pocket should not exceed 0.75 mm, as already mentioned above.
The bottom of the press shoe shown in Figures 1 to 3 is curved in shape, but it is also possible to use a rectangular shape and edges that protrude sharply from the surface, provided that the average depth does not exceed the above-mentioned value.
Further, the pocket can be sharp-angled at one edge, while the other edge defines a wide angle, as shown in Figures 1 to 3.
Claims (10)
1. A press with extended press zone in a paper machine for dewatering a wet fibre web, comprising - a rotating press roll and at least one press shoe extending in the axial direction of the press roll, said press shoe bearing on the press roll;
- a liquid-impermeable slide band sliding along the surface of the press shoe between the press shoe and the press roll in the direction of travel of the fibre web;
- means for introducing lubricant between the slide band and the press shoe; and - at least one press felt for passing the fibre web through the press between the press roll and the slide band end for receiving water from the fibre web;
- a pocket area in a surface of the press shoe facing the slide band having at least substantially the same width as the fibre web and being narrower than the extended press zone in the direction of travel of the band, said pockets area comprising at least one pocket formed in the surface of the press shoe as a recess;
- said means for introducing lubricant including at least one lubrication conduit for introducing pressurized lubricant to the pocket area.
- a liquid-impermeable slide band sliding along the surface of the press shoe between the press shoe and the press roll in the direction of travel of the fibre web;
- means for introducing lubricant between the slide band and the press shoe; and - at least one press felt for passing the fibre web through the press between the press roll and the slide band end for receiving water from the fibre web;
- a pocket area in a surface of the press shoe facing the slide band having at least substantially the same width as the fibre web and being narrower than the extended press zone in the direction of travel of the band, said pockets area comprising at least one pocket formed in the surface of the press shoe as a recess;
- said means for introducing lubricant including at least one lubrication conduit for introducing pressurized lubricant to the pocket area.
2. A press according to claim 1, wherein the average depth of each pocket in the pocket area is no more than 0.75 mm.
3. A press according to claim 1, wherein the pocket area is formed by one pocket the length of which in the direction of travel of the fibre web is 40 to 60% of the length of the press zone.
4. A press according to claim 1, wherein the pocket area is formed by at least two pockets positioned successively in the direction of travel of the fibre.
5. A press according to claim 4, wherein the pockets are positioned substantially side by side to form a continuous pocket area.
6. A press according to claim 1, wherein the pocket area is formed by at least two pockets positioned successively in the axial direction of the press roll with their ends close to each other.
7. A press according to claim 1, comprising lubrication conduits for introducing lubricant into each pocket to the front edge of the pocket in the direction of travel of the fibre web substantially over the entire width of each pocket.
8. A press according to claim 7, comprising in each pocket a lubricant introduction area formed by at least one groove extending in the axial direction of the roll, the width of each groove being no more than one tenth of the width of the pocket area and the depth being at least five times the average depth of the pocket area.
9. A press according to claim 8, comprising lubrication conduits for introducing pressurized lubricant into at least two portions of the pocket area positioned successively in the direction of travel of the fibre web.
10. A press according to claim 1, wherein the latter edge of at least one pocket in the direction of travel of the fibre web becomes lower in a wedge-like manner in the direction of travel of the web.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FI896163A FI91789C (en) | 1989-12-21 | 1989-12-21 | Paper machine long zone press |
| FI896163 | 1989-12-21 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2032785A1 CA2032785A1 (en) | 1991-06-22 |
| CA2032785C true CA2032785C (en) | 2001-05-01 |
Family
ID=8529558
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002032785A Expired - Fee Related CA2032785C (en) | 1989-12-21 | 1990-12-20 | A press with extended press zone in a paper machine |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5110417A (en) |
| AT (1) | AT400588B (en) |
| CA (1) | CA2032785C (en) |
| DE (1) | DE4040392B4 (en) |
| FI (1) | FI91789C (en) |
| GB (1) | GB2239268B (en) |
| IT (1) | IT1244213B (en) |
| SE (1) | SE506721C2 (en) |
Families Citing this family (22)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4138788C2 (en) * | 1991-11-26 | 1995-05-18 | Escher Wyss Gmbh | Device for dewatering a fibrous web |
| FI98844C (en) * | 1991-12-23 | 1997-08-25 | Valmet Paper Machinery Inc | Press section in paper machine, especially for printing paper grades |
| SE469600B (en) * | 1991-12-23 | 1993-08-02 | Valmet Karlstad Ab | pressure shoe |
| FI94267C (en) * | 1992-12-30 | 1995-08-10 | Valmet Paper Machinery Inc | Long nip press shoe |
| DE4337583A1 (en) * | 1993-11-04 | 1995-05-11 | Voith Gmbh J M | Press device for treating a material web, in particular a paper web |
| US5441604A (en) * | 1994-02-17 | 1995-08-15 | Beloit Technologies, Inc. | Extended nip press apparatus |
| DE4410129A1 (en) * | 1994-03-24 | 1995-09-28 | Kleinewefers Gmbh | Press device for sheet material |
| DE19544978C2 (en) * | 1995-12-01 | 1998-07-30 | Voith Sulzer Papiermasch Gmbh | Press roll |
| US5951824A (en) * | 1997-06-19 | 1999-09-14 | Beloit Technologies, Inc. | Compliant hydrodynamic/hydrostatic shoe for papermaking press |
| US5897747A (en) * | 1997-08-08 | 1999-04-27 | Beloit Technologies, Inc. | Machine direction profiling of extended nip press shoe |
| SE512792C2 (en) * | 1998-09-25 | 2000-05-15 | Valmet Karlstad Ab | Arrangement and method for lubrication during pulse pressing of a fiber web |
| US6248210B1 (en) * | 1998-11-13 | 2001-06-19 | Fort James Corporation | Method for maximizing water removal in a press nip |
| FI113788B (en) | 1999-04-14 | 2004-06-15 | Metso Paper Pori Oy | Press |
| FI991154A0 (en) | 1999-05-21 | 1999-05-21 | Sunds Defibrator Pori Oy | long nip press |
| SE517618C2 (en) * | 1999-10-27 | 2002-06-25 | Stora Kopparbergs Bergslags Ab | Apparatus and method in connection with the manufacture of paper or cardboard |
| JP3875898B2 (en) * | 2002-02-06 | 2007-01-31 | イチカワ株式会社 | Shoe press device for paper machine |
| AT411908B (en) * | 2002-10-17 | 2004-07-26 | Andritz Ag Maschf | PRESS ROLLER WITH A PRESS SHOE SLIDING ON A CARRIER |
| DE10259232A1 (en) * | 2002-12-17 | 2004-07-15 | Eduard Küsters Maschinenfabrik GmbH & Co. KG | Device for forming an elongated gap |
| FI20065771A0 (en) * | 2006-12-04 | 2006-12-04 | Metso Paper Inc | Load member in a fiber machine |
| DE102009045378A1 (en) | 2009-10-06 | 2011-04-07 | Voith Patent Gmbh | Press roller for use in press device in e.g. calender for formation of press gap for dehydration of paper in machine for manufacturing and/or smoothing paper, has supporting surface comprising multiple recesses without oil supply point |
| DE102009045414A1 (en) | 2009-10-07 | 2011-04-14 | Voith Patent Gmbh | press roll |
| CN112522984B (en) * | 2020-12-17 | 2022-06-07 | 淄博泰鼎机械科技有限公司 | Shoe type presser |
Family Cites Families (18)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3853698A (en) * | 1972-04-17 | 1974-12-10 | Beloit Corp | Large roll hydraulic press with pressurized fluid supports |
| US3783097A (en) * | 1972-05-30 | 1974-01-01 | Beloit Corp | Hydrodynamically loaded web press with slipper bearing shoes |
| US4201624A (en) * | 1978-09-05 | 1980-05-06 | Beloit Corporation | Extended nip press |
| DE3102526C2 (en) * | 1981-01-27 | 1985-05-23 | J.M. Voith Gmbh, 7920 Heidenheim | Pressing device for dewatering webs, in particular paper webs |
| US4428797A (en) * | 1981-05-26 | 1984-01-31 | Beloit Corporation | Extended nip shoe for a nip in a papermaking machine |
| US4427492A (en) * | 1981-05-26 | 1984-01-24 | Beloit Corporation | Extended nip shoe for a nip in a papermaking machine |
| FI71979B (en) * | 1981-06-24 | 1986-11-28 | Escher Wyss Ag | PRESSVALS |
| DE3126492C2 (en) * | 1981-06-30 | 1983-10-20 | Escher Wyss AG, Zürich | Press roll |
| FI65103C (en) * | 1982-05-05 | 1984-03-12 | Tampella Oy Ab | LAONGZONSPRESS FOER EN PAPPERSMASKIN |
| FI70952C (en) * | 1982-10-14 | 1986-10-27 | Valmet Oy | ANORDNING MED LAONG PRESON VID PRESSBEHANDLING AV FIBERBANA |
| FI71369C (en) * | 1983-03-23 | 1986-12-19 | Valmet Oy | LAONGNYPPRESS FOER PAPER MASK |
| DE3408118A1 (en) * | 1984-02-06 | 1985-08-14 | Sulzer-Escher Wyss GmbH, 7980 Ravensburg | WET PRESS FOR DRAINING A FIBER TRAIN |
| DE3408119A1 (en) * | 1984-02-06 | 1985-08-14 | Sulzer-Escher Wyss GmbH, 7980 Ravensburg | WET PRESS FOR DRAINING A FIBER TRAIN |
| DE3607941A1 (en) * | 1985-10-30 | 1987-05-07 | Escher Wyss Gmbh | Pressing device for dewatering a web of material |
| EP0289477A3 (en) * | 1987-04-28 | 1989-03-08 | Valmet Paper Machinery Inc. | Method for hot-pressing of a paper web and a drying device for the implementation of the method |
| FI78941C (en) * | 1987-04-28 | 1989-10-10 | Valmet Paper Machinery Inc | FOERFARANDE FOER VARMPRESSNING I EN PAPPERSBANA OCH TORKNINGSANORDNING FOER TILLAEMPNING AV FOERFARANDET. |
| SE461171C (en) * | 1988-05-25 | 1992-05-15 | Valmet Paper Machinery Inc | LONG NYP PRESSES BEFORE PAPER OR CARTON MACHINERY |
| SE461154B (en) * | 1988-05-25 | 1990-01-15 | Valmet Paper Machinery Inc | LONG NYP PRESSES BEFORE PAPER OR CARTON MACHINERY |
-
1989
- 1989-12-21 FI FI896163A patent/FI91789C/en active IP Right Grant
-
1990
- 1990-12-17 US US07/628,014 patent/US5110417A/en not_active Expired - Lifetime
- 1990-12-17 DE DE4040392A patent/DE4040392B4/en not_active Expired - Fee Related
- 1990-12-18 AT AT0257290A patent/AT400588B/en not_active IP Right Cessation
- 1990-12-19 GB GB9027511A patent/GB2239268B/en not_active Expired - Lifetime
- 1990-12-20 SE SE9004071A patent/SE506721C2/en not_active IP Right Cessation
- 1990-12-20 CA CA002032785A patent/CA2032785C/en not_active Expired - Fee Related
- 1990-12-20 IT IT02245990A patent/IT1244213B/en active IP Right Grant
Also Published As
| Publication number | Publication date |
|---|---|
| AT400588B (en) | 1996-01-25 |
| IT9022459A0 (en) | 1990-12-20 |
| GB2239268A (en) | 1991-06-26 |
| SE9004071D0 (en) | 1990-12-20 |
| DE4040392A1 (en) | 1991-06-27 |
| FI896163A0 (en) | 1989-12-21 |
| GB2239268B (en) | 1994-04-06 |
| SE506721C2 (en) | 1998-02-02 |
| DE4040392B4 (en) | 2006-08-10 |
| FI896163A (en) | 1991-06-22 |
| CA2032785A1 (en) | 1991-06-22 |
| IT9022459A1 (en) | 1991-06-22 |
| ATA257290A (en) | 1995-06-15 |
| FI91789B (en) | 1994-04-29 |
| GB9027511D0 (en) | 1991-02-06 |
| FI91789C (en) | 1994-08-10 |
| US5110417A (en) | 1992-05-05 |
| IT1244213B (en) | 1994-07-08 |
| SE9004071L (en) | 1991-06-22 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA2032785C (en) | A press with extended press zone in a paper machine | |
| KR900002103B1 (en) | Enclosed shoe press | |
| US4576682A (en) | Long-nip press for a paper making machine | |
| US4482430A (en) | Extended nip press lubricating system for a paper machine | |
| EP0718434B1 (en) | Press section of paper machine, in particular for printing paper qualities | |
| US5626723A (en) | Surface contoured press jacket for a shoe press | |
| KR900002104B1 (en) | Bearing blanket for an extended nippress | |
| EP0770727B1 (en) | Method and device for dewatering of a paper web by pressing | |
| US5167768A (en) | Wide nip web press and method using a press shoe with two pivots | |
| SE461920B (en) | DEVICE WITH LONG PRESSURE ZONE FOR PRESSURE FIBER COATING | |
| EP1060307B1 (en) | An extended nip press and shoe therefor | |
| JPH01280090A (en) | Vertical groove press roll | |
| FI109302B (en) | Pressko | |
| JP2001520330A5 (en) | ||
| CA2147730A1 (en) | Roll for a papermaking machine | |
| WO1993023614A1 (en) | A shoe type press | |
| US4767501A (en) | Method for equalizing compression pressure in a press nip of a paper machine | |
| GB2187517A (en) | Pressure or glide shoes for a controlled deflection roll | |
| US6228221B1 (en) | Dewatering press and process | |
| US6387216B1 (en) | Long shoeless nip press | |
| US6936139B2 (en) | Shoe press apparatus of a papermaking machine | |
| FI80137B (en) | BELASTNINGSSKO FOER BOEJNINGSKOMPENSERAD VALS OCH EN BOEJNINGSKOMPENSERAD VALS FOERSEDD MED BELASTNINGSSKOR. | |
| CA2266934C (en) | Hydrostatic shoe for controlled crown roll |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |