FR2541438A1 - POSITIVE IMPULSE BLADE FOR PRE-CONDITIONING A WET WEB OF MATERIAL CARRIED BY A CANVAS IN A DEHYDRATION MACHINE - Google Patents

Abstract

POSITIVE PULSE BLADE 22 FOR PRE-CONDITIONING A BAND OF WET MATERIAL 28 CARRIED ON A CANVAS 32. THE BLADE 22 IS REMOVABLY MOUNTED IN A FIXED POSITION UNDER THE WET BAND 28 AND THE CANVAS 32 WHICH PASS ON THIS BLADE. THE BLADE HAS A SURFACE OF UPPER WEAR 52 INTENDED TO COME IN CONTACT WITH THE CLOTH. A FORCE (GRAVITY, LOWER PRESSURE OR HIGH PRESSURE) IS APPLIED SO THAT THE WATER FROM THE BAND 28 IS DRAWN UP BY THE LOWER FACE OF THE CANVAS AND REMAINS ADHESIVE TO THIS LOWER FACE. BLADE 22 HAS A FRONT EDGE WHOSE CONFIGURATION TENDS TO PUSH UP, THROUGH CANVAS 32 AND INTO THE GROUND OF BAND 28, WATER DRAWN AGAINST THE LOWER FACE OF THE CANVAS WHEN IT REACHES BLADE 22.

Description

The present invention relates to a positive-impulse blade during the

pre-conditioning of a

  strip of wet material carried by a canvas.

  In dehydration machines, in particular

  culier in the paper industry, in which it

  is usual to carry out dehydrating operations

  tion at the wet end of a tree machine, we

  continually pursues research aimed at obtaining

  nin a more efficient dehydration process.

  We can cite as an example of a type of machi-

  to which this research applies the Fourdrinier or flat table paper machine which uses a

  suction or dewatering box to which

  plique a depression to extract water from an assembly consisting of a wire cloth and a sheet of material forming a wet band A difficulty which manifests itself in a process of this type consists in that the material to be dehydrated accumulates under the shape of a mud (wet strip) on the metallic canvas and that, as the whole composed of the canvas and the sheet of wet material progresses along the

  machine, it tends to compress or compact itself

  burr or entangle This compaction effect makes water extraction more difficult This drawback

  is further accentuated when we consider that depression

  is applied at several points different from the length of the paper machine, in particular at the

  part forming the wet end The application con-

  aunt of a depression results in a constant negative impulse applied to the wet band, which tends even more to compact the mud on the wire mesh The result is a progressive reduction

  the yield that accompanies the progression of treatment.

  Various attempts have already been made to increase the court

  ter the yield of dehydration For example, we have

  used an increase in depression, either app-

  pleating a stronger constant suction force,

  either by applying a progressive suction force-

  increasing as compaction increases during the dehydration process We have already imagined a great variety of different types

  of blades, sheets, hydrodynamic and deflected nlans

  ters, with a wide variety of configurations,

  to strengthen the dehydration process by de-

  negative pressure and pulse For example, we imagined

  born to reverse the traditional blade shapes and

  to use stepped blades with different pro-

son.

  We have explored to some degree the pos-

  sensitivities of the principle of positive impulses, in part

  particular with regard to chainlines This con-

  consists in putting the metallic fabric which carries the wet strip in contact with chainlines which push the band upwardly through the canvas and

  possibly apply a positive impulse Tou-

  However, this action is impossible to control and is limited to a direct relationship between the speed and the diameter of the rollers. It cannot be adjusted with a

  appropriately to ensure increased return

  dehydration process, especially in combination with blades and a vacuum It is clear that there is room for an improved device

  drying or dehydration which takes advantage of the advantages

  blade profile stages to generate a negative impulse and extract water from the wet strip through

  the canvas and also to apply a Dosi-

  tive to the strip through the canvas so as to loosen

  the band compacted and nour strengthen dehydration.

  Naturally, the device should be adaptable for

  allow the application of negative and positive impulses

  tives ap Appropriées spread over the length of the ma-

  china, especially if it is the wet end

  of a paper machine Naturally, it is desired-

  ble to have a simple and low-cost construction

  teuse, for example of an improved configuration

  with a single blade which can be disassembled

  ble in a fixed position in an existing machine

  such as a Fourdrinier type machine.

  Attempts to combine the positive impulse with another treatment activity have posed

  problems with the success of dehydrating-

  final tion of the strip For example, devices that dehydrate and then retain water in a base tank of another structure until

  the water level in the tank determines an im-

  impulse to push the felted band upwards, are undesirable for various reasons In some of these devices, there is no convenient means of adjusting the positive impulse action In addition, in some, a weight considerably

  increased for the whole Other devices do not

  do not allow the water in the mud to drain through the wire mesh and return to the mud at

  through this canvas In all these devices, we

  holds an accumulation of foreign bodies and a colma-

  installation, and the water trapped in the tank impedes the consistency of the water

  entrained under the inner face of the canvas The pre-

  sence of water entrained under the underside of the fabric is desirable to increase the efficiency of the impulse action, in that the layer of water entrained in motion can be controlled and directed

  or projected across the strip with the possibility of ob-

  hold an extremely positive impulse.

  The combination of a positive impulse action and a simultaneous dehydration action does not allow

  not achieve the desired result The dehydra-

  tation is less effective in that only one

  tie water from the mud is returned to the tablecloth through the canvas and that, therefore, the agi-

less pronounced.

  Another attempt regarding dehydrata-

  tion consists in separating the water extracted from the strip so that more of the water is discharged

  in a drainage groove and that a smaller part

  tie is directed in the form of a film on the

  wear surface of the hydrodynamic plane or of the blade.

  This is intended to produce a lubricated surface giving

  nant anpui to the fabric when the latter passes over the fixed blade In this type of device, one obtains only a minimal or zero effect on the state of the fibers of the strip This device is not designed to agitate the fluid nor to pass it from bottom to top through the canvas and return it to the strip The only effect consists in the formation of a thin effect film

lubrication.

  It is therefore obvious that there is no principle

  cipe to separate dehydration and 'pre-

  conditioning of the strip in such a way that the

  strip fibers can be worked before the

  dehydration depression, so as to ensure optimal and efficient evacuation of the liquid

or water from this strip.

  In view of the above, the main

  objects of the invention consist in making a blade adapted

  tee to be mounted on a dewatering machine such as a paper machine The blade is designed with a superior wear surface over which passes a

  mobile canvas which carries a strip of wet material.

  By contact with a predetermined configuration of the

  front edge of the blade, roughly the whole of about forty

  predetermined amount of liquid entrained below the surface

  interior of the fabric is directed upwards, through

  towards the canvas, to precondition the strip for its subsequent dehydration. The subsequent dehydration of the band moves

  then occur with or without the assistance of the rear edge

  first slide, * or by introduction to subsequent dewatering blades At this time, a negative pulse produced by vacuum can be applied to

  the wet band to assist the dewatering operations

  dratation. An object of the invention is to produce a blade of the above type which is of a unitary construction

  and adapted to be mounted on a standard type of machine

  well known sic such as a Fourdrinier type machine.

  The blade is suitable to be mounted for several ex-

  please to form a row of blades which have aligned wear surfaces, over which pass a metallic cloth and a sheet superimposed on this cloth constituting a wet strip. The blade is adapted

  to be mounted in such a way that a force

  required, for example depression or severity, entral-

  do a predetermined proportion of the water carried on the underside of the canvas and that, when the canvas is moving towards the blade, the water is pushed upward through the canvas and introduced into the wet strip to precondition this strip for dehydration

  Dreconditioning occurs in practice

  without drainage, drainage or other drainage

  what about the whole formed by the strip and the canvas.

  An object of the invention is to provide a blade provided with a front edge martie having a configuration which comprises a point which is spaced from the interior surface of the fabric by an equal or greater distance.

  the thickness of the liquid entrained under the underside

  of the canvas when it goes towards the blade In this way, the entrained liquid passes between the canvas and the point of the blade and is thus directed upwards by the blade, towards the canvas and through the canvas or penetrate the wet strip The result is a positive impulse action which has only

  for the purpose of deconditioning the strip.

  According to the invention, the part of the blade comprises

  taken between the joint and the upper wear surface may form any acute or obtuse angle or a

  any combination of acute or obtuse angles, or

  core it can include curved parts, provided that the blade directs the entrained liquid upwards, making it pass through the fabric and making it penetrate into the strip. An example of an effective angle is an angle between 0 and 100 An example of an effective distance for the spacing between the tip of the front edge and the underside of the fabric, relative to the entrained amount of liquid present under the face

  lower of the canvas would be 6 mm, when the thick-

  sor of the liquid is equal to or less than 6 mm and the point is spaced from the underside of the fabric by a distance equal or greater than 6 mm In this way, the entrained water is almost completely directed upwards through the canvas, and introduced into the

  strip and practically no amount of water is drained

born of the whole.

  Another object of the invention is to produce a variant shape for the blade according to the invention

  in which this blade has in the region adjja-

  centered or consecutive to the upper wear surface, a configuration designed to facilitate the application of a negative impulse In one embodiment, this would include the use of a step to form a hollow adjacent or consecutive to the surface d wear, and a drainage slot and means to

  deviation in front of the blade in the direction of travel

  canvas instead of reintroducing entrained water

  born, you can use a following blade designed for dehydration. An object of the present invention is to produce a blade which is designed to precondition a wet strip by constituting the first blade of a series of blades provided at the wet end of a machine such as a paper machine In this way , the strip is preconditioned before being subjected to the action of a series of dehydration blades. As a variant, the positive impulse blade intended to precondition the band can be one of a series of such blades and she

  can also be one of a series of blades that al-

  tarnish with a corresponding series of dewatering blades

  dratation so that the wet strip is Precondi-

  operated with a positive impulse by a front blade

  to be brought to the dehydration blade in this way

  lesson, dehydration is facilitated by a precondition-

  continuous movement of the strip preceding dehydration.

  The blades would then be spaced apart so as to provide suitable drainage slots therebetween in a way

classic.

  An object of the present invention is to produce a blade with positive preconditioning pulse which tends to loosen the felted band first, the water of which can then be again entrained under the underside of the fabric by the same blade, or evacuated when subjected to the action of means of dehydration

placed downstream.

  An object of the invention is to use the positive pulse blade according to the invention in combination with a source of vacuum, in such a way that a set vacuum value is applied to the strip to drive a predetermined quantity of liquid. under the lower surface of the fabric to be brought to the front edge configuration of the blades, so that the liquid is discharged upward through the fabric and introduced into the strip of material,

  to achieve a preconditioning effect.

  Another object of the invention is to realize

  a blade structure which induces positive impulses

  tives in locations comprising the first blade of a Fourdrinier machine-comprising a series of blades in which the following blades are blades of

  dehydration, or that constitutes a blade of an arrangement-

  alternating re-conditioning blades and blades

  dehydration The pre-conditioning blade with im-

  positive drive according to the invention is intended to be

  used with training boards, hu-

  mides, hydrodynamic planes assisted by depression

  twin canvases, and in combination with

  In addition, the principle

  of the blade according to the invention can be extended ma-

  to include the front edge of a stationary device

  any official placed below the means of training

  tion such as hydrodynamic planes and / or de-

flectors.

  The action of the blade according to the invention can be reinforced by the use of a vacuum upstream of the front edge and in the region adjacent to this front edge; this depression which drives the liquid under the underside of the fabric also serves to keep the strip applied while the liquid is pushed upwards in the strip through the fabric, this in order to reinforce the preconditioning action, and it has also has the effect of closing the device so as to allow precise control

  the preconditioning effect to obtain a dehydra-

effective later.

  An object of the invention is to entrain and retain a predetermined amount of water under the underside of a moving fabric which is

  back up through the belt, to condi-

  tion the strip for its subsequent dehydration The liquid is almost completely reintroduced into the strip through the cloth and it is not produced by

  drainage or dehydration during the action of con-

  The result is an improvement in the formation of mud on the canvas and a reduction in the filtration resistance of the strip during the subsequent dewatering action.

  of the band is favored by the separation and re-

  fiber distribution in a more efficient arrangement -

  In addition, the liquid or water can thus be distributed, thanks to the additional time which the strip has to normalize. This characteristic is ensured by the fact that no dehydration occurs during

  the preconditioning action, but that this dehydra-

  tation does not happen until later A goal of the invention

  tion is to ensure a tight control of the action of Dronditioning since the value of the vacuum applied with respect to the speed of movement of the fabric and the strip will allow precise adjustment of the quantity of liquid entrained under the underside of the canvas to come into contact with the blade, and the return of all the liquid upwards, in the strip The fact of using the water contained in the strip and of neither collecting nor retaining the water pulled

  tape in a tank, reduces the risk of accu-

  mulation of dirt in the installation and also reduces

  the weight load exerted on the machinery.

  In addition, there is no interaction with the liquid

  entrained, so that this liquid can move li-

  brement and that it is controlled so as to move jointly with the cloth to come directly into contact with the blade and to be driven directly upwards, in the band, through the cloth, to allow to obtain the most effective and

  most positive in the preconditioning action.

  In summary, the subject of the invention is a provision

  sitive to precondition a wet strip of material

  intended to be dehydrated later The device

  tif includes a positive impulse blade which is suitable

  tee to be removably mounted in a fixed position with respect to a fabric which carries the wet strip of material intended to be driven above this blade The blade has an upper wear surface intended to come into contact with the fabric which carries the band wet material The blade has a front edge of a suitable configuration to direct towards

  the top just about all of the liquid that's

  dragged under the underside of the fabric by a downward force, and to push this liquid through the fabric when it came into contact with the front edge, in order to apply a positive impulse to the

  wet strip and precondition the strip for faci-

  liter the subsequent dehydration of this strip.

  As a variant, it goes without saying that the device according to the invention can be oriented in another

  arrangement that the horizontal arrangement describes and re-

  presented For example Dle, the device can be used in a vertical or inverted arrangement However, the

  driving force cannot be derived from the

  in positions other than those described.

  Other features and benefits of

  the invention will appear during the description which

  will follow In the accompanying drawings, given solely by way of example of embodiment of the invention: FIG. 1 is a partial view from above

  the wet end of a paper machine, on the

  which are mounted a succession of blades; FIG. 2 is a partial view, in elevation and section, of this wet end, taken along the plane of line 2-2 of FIG. 1; and

  Figure 3 is a partial view in elé ya-

  tion and section, on a larger scale, of this end

wet.

  The upper surface of a nartie from the extreme

  wet moth of a papermaking machine 20 of the Fourdrinier type is shown in FIG. 1 FIG. 2 is a side elevation view of a part of the machine 20 which includes a series of spaced and aligned blades, which

  are mounted on this machine by demon connections

  tables, in a classic way One of the blades illus-

  blade 22, is a positive impulse preconditioning blade produced in accordance with the invention and is placed between two dehydration blades

  conventional 24 and 25 A slot 26 is provided in each

  that the gap between two blades 24 and 22 and a slot 27 is made between the blades 22 and 25 Forces

  descendants, which may consist of a

  pressure supplied by a conventional vacuum source, are applied separately to slots 26 and 27 and, from

  this way at the top surface of the machine 20.

  Appropriate end caps 62 are provided for hermetically sealing the ends, so that

  that the slots 26 and 27 are in the central part

  machine trale 20 The wet strip of material 28

  is in the form of a strip of fibers 30

  placed on the canvas 32 The sheet is initially in the form of a mud which densifies during its course when it is subjected to the normal forces of gravity and to an additional depression force when this force is applied during the treatment. purpose of the machinery is to carry out the final elimination of the water or the dehydration or the final drying of the wet strip 28. Anpproriated commands can be issued

  a standard vacuum source to regulate individual

  due Ilement the depression applied to the slot 26 and that applied to the slot 27 Normally, these two depressions are of different values The gravitational force or the vacuum force applied to the slot 26 is not intended to ensure dehydration but to entrain the liquid against the underside of the cloth 32 and also to keep the cloth in contact with the upper wear surface 52 of the blade 22 On the other hand, the vacuum applied to

  through slot 27 is designed to assist dehydration

  band 28, to collect water and to

evacuate it from machinery.

  With regard to the slot 27, the vacuum is applied to the entrained water coming from the wet strip which must then be dehydrated by the front edge of the blade 25 On the contrary, the water which is extracted from the strip 28 is entrained under the underside of the

  canvas 32 and flows with the canvas 42 towards the blade 22.

  However, no part of this entrained water is eliminated, it is retained with the moving canvas.

and with the band.

  The blade 24 is a conventional blade of the shoulder type, which comprises a front horizontal wear surface part 34 which ends in a shoulder 36 communicating with a recessed surface 38 The vertical space between the surfaces 34 and 38 forms a

  region intended to generate a negative impulse applied

  quée to the wet band by communication with the slot 26 A predetermined vacuum value is applied

  to the strip through the slot 26 to drive a quan-

  tity of liquid 40 against the inner face of the cloth 32, of a predetermined thickness "t" Gravity and this negative impulse action tend to compact and felt the mud of the strip on the cloth, making

  thus more difficult the elimination of the liquid from the ban-

  of Blade 22 is used to remove the felted strip

  to make it more likely to undergo deliquefaction ef-

  usually effective, the liquid it is

  The strip is water and, in the rest of the description

  description of the embodiment shown, water will be identified as the liquid to be removed from the

  strip This water removal is a habitual operation

  tuelle in the papermaking machinery.

  The blade 22 includes a protuberance 42 which projects downwards under its lower surface 44

  to lock with receiving surfaces

  ted by a conventional paper machine The 22 mu- blade

  end of its protuberance 42 is adapted to be mounted in any one of a certain number of positions on the paper machine It can be the first of a row of blades, the blade 22 being a conditioning blade and the blades following are dehydration blades such as blade 25, or else

  there may be a combination of the two types of blades.

  It is possible to alternate pre-

  addition such as blade 22 and dewatering blades such as blade 25 so

* that the strip is preconditioned, so as to reinforce

  cer dehydration action before it is

  introduced up to the dehydration blade.

  The value of the downward force used at the level of the slot 26 is sufficient to entrain the water located on the underside of the fabric. As a variant, compared to the use of a blade such

  that the blade 24, at the entrance to the machine, it is possible

  ble to use an ordinary support or roller or another conventional support means The blade which comes into contact with the fabric before any dehydration at

  the interior of this installation would be blade 22.

  The blade 22 includes a front edge 44 intended

  to establish the initial contact with the moving canvas 32

  ment and with the water entrained with this fabric The inner part 46 of the front edge can be bevelled downwards and towards the rear end 45 of the blade 22 The upper part 48 of the front edge 44 is bevelled upwards and towards the rear end of blade 22 La

  lower part 46 and upper part 48

  join a vertex or a point 50 The other end

  from the bottom 46 ends at an inner edge

  laughing 44 of the blade 22 and the other end of the part

  upper 48 ends with a superior wear surface

  lower 52 of the blade which comes into contact with the cloth 32 passing over this blade, and it is closed in this mutual contact arrangement when it is subjected to the vacuum acting through the slot 26 The part

  upper 48 therefore forms a pinch slot in com-

  hoeing with the underside of the fabric 32 The tip 50 is spaced by a predetermined distance "d"

  below the inner surface of the fabric 32.

  This distance is determined so as to be equal to or greater than the thickness "t" of the entrained water 40

  which covers the inner surface of the fabric 32 when

  that a vacuum is applied to the slot 26 In this way, all of the entrained water 40 passes between the tip 50 and the underside of the fabric 32 and it is discharged upwards and through the fabric 32 forming a positive impulse No amount of water is evacuated through the slit 26 The upward flow of water through the strip loosens the felted mud deposited on the canvas, so that water can be extracted from the wet band in an easier and more effective way in the following This action is called the application of a positive impulse In addition

  of improved mud formation, the creation

  tion of a positive pulse in this way also reduces the filtration resistance of the strip and ensures an improvement in the redistribution of water and fibers throughout the mass of the strip before actual dehydration occurs at a moment

later and downstream.

  The tape then passes beyond the surface

  of wear 52 of blade 22 and, at this time, it is exposed

  seée to depression with dehydration effect in the

  slot 27 The preconditioned strip is then dehydrated.

  tee and water is collected through slot 27 to

  to be evacuated As indicated above, the name

  bre of preconditioning blades 22 and dehydration blades 25 can be chosen at will, as well as their order of succession Several preconditioning blades can be placed in a succession followed by several dehydration blades or the blades

  repackaging and dehydration can al-

dull between them.

  Each of the blades is provided with a notch 54 in its rear edge, to facilitate the mounting of the

  end sealing members for sealing the ex-

  hoppers in a conventional manner, so that the vacuum is concentrated in the

central part of the slots.

  The blades are interchangeable and removable,

  so that they can be replaced and interchan-

  at any time desired In addition, they can be made of conventional plastic

  or nylon, in a well known conventional manner.

  In paper machines, it has proved effective for dehydration to form a thickness "t" up to 6 mm, at most, for the entrained water, and a distance "d" between the tip 50 and the fabric. 32 at least equal to or greater than 6 mm In this way, all of the entrained water is pumped upward through the fabric 32 Dar the front edge portion 48 of the blade, to ensure the packaging In the embodiment described, there is shown an acute angle between the upper Dartie 48 of the front edge 44 and the

  canvas 32 The value of this angle can be chosen arbi-

  trire and this angle can be acute, for example up

  as 10 as shown, either a right angle or an obtuse angle at the point of introduction of the fabric, or else a series of segments can be provided

  staggered with different slope angles or

  core one or more curved surfaces The only condition

  tion required is that the water entrained against the surfa-

  this inner of the canvas be pushed upward at

  across the strip to perform conditioning.

  In operation, and as shown,

  the canvas 32 scrolls from left to right, entrained

  born by suitable means of conventional type carried by the machine It passes over the wear surface 34 of the blade 24, after which it is exposed to the action of the slot 26, where a predetermined depression applied to this slot will have for effect that a thickness of water

  predetermined will be driven against the lower surface

  re of the fabric 32 during the movement of this fabric.

  No part of this water is entrained through the

  slot 18 The belt and the entrained water are then directed

  to the front edge 44 All of the water will come into contact with the front edge 44, above the tip 50, and will be pumped upward through the strip by contact with the upper surface 48 of an edge before 44 This creates a positive impulse

  on the tape and conditions the tape for dehydration

  Subsequent tation The unconditioned strip is then introduced into the depression in the slot 27, where the water is drawn against the underside of the fabric, to then be eliminated by the front edge of the blade before being evacuated. canvas

  32 promotes dehydration To facilitate the gathering

  bleed water, the front edge 56 of the blade 25 is bi-

  sided down and backwards, towards the rear edge

  blade 25, to help steer the mete

  lange of air and water for drainage through the slot 27. The strip 28 is then conveyed to other

  conditioning and / or dehydrating blades and slots

  tion to continue to be treated the same.

  The dehydration effect can occur after a negative pulse applied to the tape as opposed

  to a positive impulse which is applied during ac-

conditioning.

  To create the force that passes water through the canvas so that it is drawn against the

  surface of this canvas, we can use either the depres-

  either gravity, pressure, or com-

  combination of these various actions The construction of the

  device will be determined, among other things, by the orienta-

tion of the strip and the canvas.

Claims (23)

REVEN TDICATIONS   1 Positive impulse blade intended for use in the preconditioning of a wet strip of material transported by a canvas, characterized in that it comprises means making it possible to mount the blade (22) in a fixed position relative to the canvas   (32) and to the strip of wet material (28) which passes over   below, means intended to entrain water from the wet bank (28) against the underside of the fabric (3-2), an upper wear surface (52) provided on the blade (22) to enter into contact with the fabric (32) which carries the strip of wet material (28), a front edge (25) of the blade (22) having a configuration which tends to direct upwards, through the fabric (32), little nearly all of the liquid which is entrained against the underside of this fabric, when this liquid approaches the blade (22), to apply in this way a positive impulse to the wet strip (28) and   to pre-condition the tape to facilitate dehy-   subsequent dratation of this band.   2 Positive impulse blade according to resale   dication 1, characterized in that the means serving   entrain water from the wet strip (28)   be the underside of the fabric (32) include at   minus one of the following: application of a   pressure, gravity and application of pressure on the band (28) and the canvas (32).   3 Positive impulse blade according to resale   dication 1, characterized in that the front edge of the   blade (22) has a point (50) spaced at a distance   tance 9 redetermined (d) below the underside of the fabric (32) which carries the strip (28), this predetermined distance (d) being greater than the thickness (t)   liquid against the underside of the fabric (32).   4 Positive impulse blade according to resale   dication 2, characterized in that the part (48) of the front edge of the blade (22) which is between the point (50) and the underside of the fabric (32) forms an acute angle (d) of predetermined value , with the underside of the fabric to facilitate the projection of the entrained liquid against the underside of the fabric from bottom to top through the fabric (32) and in the strip (28).   Positive-impulse blade according to claim 1, characterized in that the blade (22) comprises a rear part which follows the upper wear surface (52) and which is adapted to be placed upstream of a space drainage (27), this part having a configuration which tends to entrain the liquid against the lower surface of the fabric and to apply a   negative impulse to facilitate liquid elimination   of the strip (28) so that the liquid is col-   read through the flow space (27) when the strip has previously been subjected to a positive pulse pre-conditioning.   6 Positive impulse blade according to resale   dication 5, characterized in that the negative pulse applied to the flow space (27) is obtained by at least one of the following means: application of a depression, severity and pressure.   7 Positive impulse blade according to resale   dication 5, characterized in that said rear part   is adjacent to the drainage space (27).   8 Positive impulse blade according to resale   dication 1, characterized in that the blade (22) is mounted   on the wet end of a paper machine to   pre-conditioning a wet strip (28) for its removal consecutive hydration.   9 Nositive impulse blade according to the resale   dication 1, characterized in that the blade (22) is mounted in court constituting one of the blades of a series of   blades (22, 24, 25) which succeed one another in the direction of the   placing the wet strip (28) so that the blade   (22) generates a positive impulse court pre-condition-   the wet strip (28) and at least one of the others   blades (24, 25) generates a negative impulse, the alter-   impulse applied to the wet band provided   effective dehydration of this strip.   Positive impulse blade according to resale   dication 3, characterized in that the point (50) of the front edge of the blade is spaced from the fabric (32) by   distance (d) equal to or greater than 6 mm.   11 Positive impulse blade according to resale   dication 1, characterized in that 100% of the liquid (40) entrained against the underside of the fabric (32) is pushed upward through the fabric (32) by the lime (22).   12 Positive impulse blade according to resale   dication 1, characterized in that the liquid (40) en-   dragged against the underside of the canvas is routed   born with the blade (22) without being supported from below and without means of restraint until it is attacked by the front edge of the blade.   13 Positive impulse blade according to resale   dication 1, characterized in that a dehydra-   tation (25) is placed to come into contact with the   cloth (32) and to dehydrate the pre-conditioned strip (28) and the canvas (32).   14 Method for preconditioning a wet strip of material transported on a canvas, characterized in that a positive impulse blade (22) and the strip of wet material (28) on the canvas (32) are provided in position so that the canvas carrying the wet band (28)   comes into contact with the blade (22) and passes over an   upper wear face (52) of this blade, the strip of wet material (28) and the fabric (32) are subjected to a predetermined force before they reach the blade in the direction of movement, so as to oblige water   from the strip to be driven against the underside   of the fabric and to be brought into contact with the blade, and a front edge is provided on the blade having a configuration which tends to project almost all of the water entrained from bottom to top through the fabric and into the strip, to apply a positive impulse to   the wet strip and precondition the strip to facilitate   ter the subsequent dehydration of the strip.   Process according to claim 14, charac-   in that the means used to entrain water   coming from the wet strip (28) against the underside -   of the fabric (32) comprise at least one of the following means: application of a vacuum, gravity and pressure exerted on the entire strip (28) of the canvas (32).   16 Method according to claim 14, charac-   terized in that the front edge of the blade has a point (50) spaced a predetermined distance (d) below the underside of the fabric (32) which   carries the strip (28), and in that the predetermined distance   mined (d) is greater than the thickness (t) of the liquid   (40) driven against the underside of the fabric.   17 The method of claim 16, charac-   terized in that the part of the front edge of the blade (22)   which is between the tip (50) and the underside   of the fabric forms a predetermined acute angle (d) with the underside of the fabric (32) to facilitate projection from bottom to top, through the fabric (32) and into the strip (28 Y, of the liquid (40 ) trained against underside of the canvas.   18 The method of claim 14, charac-   characterized in that the blade (22) comprises a rear part which follows the upper wear surface (52) and is adapted to be placed upstream of a drainage space (27), this part having a configuration which tends to entrain the liquid against the underside of the fabric and to apply a negative impulse, to facilitate the evacuation of the liquid from the strip and the passage of this liquid through the drainage space (27) when the strip (28 ) has been previously submitted   to a positive preconditioning impulse.   19 The method of claim 18, charac-   terrified in that the negative impulse applied to the es   drainage space (27) is generated by at least one of the following means: application of a vacuum, gravity and pressure.   20 The method of claim 18, charac-   terized in that the rear part is adjacent to the es drainage space (27).   21 The method of claim 14, charac-   terized in that the blade (22) is mounted on the wet end of a paper machine to pre-condition a   wet strip (28) for subsequent dehydration.   22 The method of claim 14, charac-   terized in that the blade (22) is mounted to constitute one of the blades of a series of blades (22, 24, 25) which follow one another in the direction of movement of the wet strip   (28), so that the blade generates a po-   sitive to pre-condition the wet strip and that at least one of the other blades generates a negative pulse, the alternation of the pulses applied to the wet strip (28) ensuring effective dehydration of this band.   23 The method of claim 16, charac-   terized in that the point (50) of the front edge of the blade is encased in the underside of the fabric (32)   distance (d) equal to or greater than 6 mm.   24 The method of claim 14, charac-   terized in that 100% of the liquid (40) entrained against the underside of the fabric (32) is pushed towards the   high through the canvas by the blade (22).   25 Method according to claim 14, characterized in that the liquid (40) entrained under the underside of the fabric (32) is conveyed to the blade (22)   without being supported from below and without means of content   tion until it is contacted with the front edge of the blade.   26 Positive impulse blade according to resale   dication 1, characterized in that a dehydra-   tation (25) is positioned to come into contact with the fabric (22) and to dehydrate the entire strip   pre-conditioned (28) and canvas (22).