MXPA95005201A - Improved formation in a two fabric paper machine - Google Patents

Abstract

A forming section for a two-fabric paper machine using formation blades having shallow cavities in their top surfaces which withdraw fluid from the stock and propel it back through the fabric so as to break up the flocculated mat without causing excessive drainage and loss of fines. The parameters required to design the blade cavity, the top surface of the blade, and the angles of wrap of the fabrics about the blades so as to obtain bestáresults are provided.

Description

TRAINING SECTION TO BE USED ON A TWO FABRIC PAPER MANUFACTURING MACHINE BACKGROUND OF THE INVENTION (A) FIELD OF THE INVENTION The present invention generally relates to a & 6'ction of formation to be used in a manufacturing machine í / e paper of two fabrics. The invention is specifically directed to improving the formation of paper made in the machine.

(B) DESCRIPTION OF THE PREVIOUS TECHNIQUE The need to shake the fluid while forming in a self-winding web on single-cloth or two-fabric paper machines is well known. In single-cloth Fo rdrinier type machines, the agitation means are mainly: 1.- The horizontal agitation mechanism, which is used in machines whose speeds are less than approximately • + 00 m / min, and 2.- The agitation caused by vertical movement of the fabric as it passes over the table rolls, sheets or suction boxes having top and regular surfaces.

These last devices replace the agitation mechanism at high speeds, thus providing the critical agitation necessary for good paper formation. The forming zones of two two-fabric papermaking machines are of two general types: hybrid formations and spacers. In the hybrid formers, the supply is partially formed on a first web initially, as in a F? L? Rdrinie-r machine of a single web, and then subjected to drainage pressure between two cells in a final stage of the training area. In the space former, the fluid supply is immediately directed into the space between two forming fabrics. There are two generic types of spacers: roll-spacers, where the drainage pressure is created by converging the cloth on a rotating roll, and blade spacers, where the pressure of the table is created by the passage of the fabrics on stationary blades at some angle of winding to induce pressure pulses between the fabrics. Both hybrid and space trainers can benefit from the present invention. The need for agitation in two-fabric paper machines is well known. Roll-space formers offer generally poorer formation than knife-space formers, but provide better fine particle retention because the crushing action of the fabric winding around the roller does not "gite the material supply . On the other hand, it is known that blade-space formers improve the good formation of the sheet, but generally a finer particle retention more deficient than the roll-space formers due to the pressure pulses induced in the supply material by the stationary blades as the fabrics move over them as they move through the forming section. The magnitude and presence of these pressure pulses are limited by the geometry of the forming section, with a large forming shoe, for example, already providing several large coiling angles, or relatively smaller coiling angles. These same pressure pulses induce shear effects on the supply material that breaks up lumps, thus improving the formation. A mathematical model of the pressure distributions? R ~ «e occur between the forming fabrics that pass over the stationary blades in the blade-space former has recently been proposed by Zhao and Kerek.es (ßOa Annual Meeting, Technical Section of the CPPA , February 1-2 1994, Montreal, Quebec, Preprints Sct. A, pp A31-A3 &), and the magnitude of the pressure pulses were initially measured by Brauns (72nd Annual Meeting, CPPA Technical Section, January 2A -29 19β6, Preprints Sect. A ,, Msntreal, Quebec, pp. A275-A2 < S2). The pressure pulses are induced in the supply material as the fabrics are wound around these blades as they move through the forming section. The blades mentioned in these references are described as scraper blades with a flat felling contact surface. Attempts to improve the agitation described by this simple type of blade action have been made by Sead (FUÁ 4, 420,370), Fbihara (FU «+, 999,087) and Bando (USA 5, &; , 392), among others. The pumping agitation devices described by Saad provide a fabric contacting surface, formed from multiple insertable cross-machine direction inserts, between which are located channels having closed flat bottoms and steeply sloping side walls. These channels, it is claimed, induce pressure pulses, and therefore agitation, in the supply material by causing the liquid to be extracted on its upstream side by a rolling action, and then it is drawn back through the the fabric towards the supply material through the wall of the upward sloping channel on its downstream side. However, the steeply sloping upstream walls of these agitator channels, which decline in the downstream direction at an angle of approximately 63 ° with respect to the contact surface of the fabric (column 5, line 51-54, and Figures 2-6), prevent a spontaneous rolling action from developing which would otherwise draw water from the supply material into the channel, and therefore are ineffective.

Practical limitations to the angular declination of the diverging surface walls upstream of the agitator channels are well known, and have been described by Wrist (USA 2.92 «4é5) and Johnson (USA 3, S74.99 &). These references teach that, in order for the agitator blades to be effective to develop a useful rolling action that will draw liquid in a continuous from the supply material suspension above, the angle of declination of the divergent surface wall upstream of a The agitation channel would not be greater than about 5o (Wrist, col 3, lines 19-24) to about 5 ° (Johnson, col 3, lines 43-45, col 6. lines 19-23) from the surface of fabric contact. In US 4,999.0A7, Ebihara describes a section of two fabric formation in which drainage devices are arranged on opposite sides of the two fabrics to press fwcia inward toward the supply material, thus making the fabrics follow a zig-like path. zag through the training area. Cavities are provided to receive the fluid expelled from between the fabrics by the pressing action of the device on the opposite side of the pair of fabrics. This fluid is forced back towards the supply material sandwiched between the fabrics by a wedge-shaped surface whose distance from the contact fabric decreases in the downstream direction. The force exerted by the pressing action of the device on the opposite side of the fabric is forced to force water into this cavity from the supply material sandwiched between the two fabrics. The wall upstream of each cavity is at right angles to the contact surfaces of the fabric and consequently a rolling action can never be developed at this point which will spontaneously pass fluid into the cavities. In US 5,245,392, Bando discloses a forming apparatus for use in a fabric forming section. The apparatus consists of two devices, located alternately on opposite sides of the fabrics, whose cloth contact surfaces are composed of several shoe blades each separated from the other by a space or cavity to which vacuum is applied for drainage. The platforms of the shoe blades have flat front portions that coincide with the travel line of one of the two fabrics, a middle portion that cf *? > it engages a wedge-shaped trough whose depth in relation to the fabrics decreases in the downstream direction, and a rear portion which may be flat or which may be sloping away from the fabrics in the downstream direction. Shoe blades are located in such a way that the fabrics advance over the previous portion without bending. Folding the fabric over the back portion of each blade generates a pressure pulse that starts on the wedge-shaped trough and extends in the downstream direction. Each trough starts suddenly at 90 °, as in Fbihara, and then inclines angularly upwards until it finds the portion of contact surface of the fabric down the blade. It is obvious from the teachings of the prior art of Wrist and Johnson that the sudden 90 ° depression angle of the upstream diverging walls of the troughs as taught by Bando would not spontaneously laminate the ag > _? a from the supply material sandwiched between the fabrics. The removal of water, therefore, from the two fabrics that are being folded as they pass through the downstream portion of each Zapata blade. This bending generates a pressure pulse in the supply material that can cause the water to enter the trough and then back through the space between the fabrics. However, this is uncertain, and possibly this pulse does not pass water to the trough. The prior art is full of descriptions of stationary knife spools that are said to develop agitation in the supply material either in single-cloth or two-cloth paper machines., in US 3,573,159 Sepall discloses a device for agitating supply material in which the liquid, drained from the supply material by rolling action, is forced back towards the fabric by means of drainage channels on the surface of the device for producing A succession of pressure pulses in the succession of the supply material. The disadvantage of the Sepall appliance is that it is &; a massive permanent part of the machine that requires considerable support structure. Sepall does not teach any of the critical parameters required for the application of the device in section > two fabric forming machines. In US 3,674,990, Johnson describes an improvement to the Sepall device where multiple replaceable blades are used to agitate the supply material in a single-cloth machine. The blade surface comprises "web contact surfaces upstream and downstream with an intermediate agitation channel between them. The wall upstream of the channel slopes downward from the upstream platform at an angle of Io to &.times, that the wall downstream of the channel diverges upstream from the platform downstream at an angle of Io. at 70 °. The channel may be straight, curved or flat, but the angles of inclination and declination of the channel walls must be between the aforementioned limits. These limits were determined experimentally and found to be similar to the optimal divergent angle for drainage sheets described by Wrist. Wrist discovered that an effective rolling action would develop on the contact surface of the fabric of a drainage sheet if the portion downstream of that surface declined away from the fabric at an angle of about 1 to approximately 5 °. The divergent surfaces of the laminating blades that are currently used in most single-cloth machines use this angular scale. As used in a single-cloth section, the rolling action developed by Johnson's blade on the declination surface t upstream of the knife channel pulls the fluid in a continuum from the supply material. This liquid is then forced back towards the underside of the fabric by the tipping surface downstream of the channel. The upward force of this liquid produces an alteration in the upper surface of the supply material, which can benefit the formation if it is small, but worsen the formation if it is excessive. It has been found in practice that, under certain conditions, the fluid forced upwards by the downstream divergent wall will lift the fabric from the rear platform portion of the blade, thus allowing white water to escape from the cavity between the fabric and the surface < ^ * »The blade along with its fine particles, thus reducing retention. Under such conditions, the blade also causes drainage to occur, which is contrary to its purpose of agitation without draining the supply material. It would be convenient if the papermaking could be more effectively controlled without the concomitant detrimental effects of the prior art, particularly the reduced retention. Therefore, the problem which this invention intends to result in is: providing means whereby a locally generated pressure pulse can be produced, which is relatively independent of the geometrical limitations of the trajectories of the fabric through the forming section , and that it does not increase local drainage and reduce retention.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides means for overcoming the aforementioned disadvantages of the prior art by providing a forming section for use in a two-fabric papermaking machine, which comprises in combination: (i) a first and second loops of forming fabric endless motion, both loops having a linear tension in the machine direction through the forming section and moving in a joint displacement from a p-Thru direction up to a downstream direction, and between said fabrics being transported a layer of supply material of known thickness; (ii) at least one forming blade extending transversely to the direction of travel of the fabric and in contact with the first fabric in such a way that under tension in the machine direction both fabrics with supply material between they are wrapped around at least one blade; (iii) the forming blade (at least one) has an upper face, a bottom and contact edges with the fabric upstream and downstream; (iv) the upper face of the blade (at least one) having substantially coplanar upstream and downstream surfaces in contact with the first web with an intermediate cavity therebetween; (v) the cavity having diverging walls upstream and downstream with an intermediate surface therebetween, the wall of the upstream cavity diverging from the contact surface of the upstream fabric at an angle of Io to fl °, the wall of the cavity downstream diverging from the contact surface of the downstream cloth at an angle of Io to ñ ° to define a cavity whose depth from the plane of the substantially coplanar contact surfaces to the intermediate surface is around from one tenth to approximately 3/4 of the thickness of the supply material that is transported between the first and second fabrics on the cavity; (vi) the first fabric being wound around the edges of the blade (at least one) to have a total roll angle that is equal to or greater than 0.5 ° while in contact with the contact surfaces upstream and downstream; (vii) the second fabric also wrapping around the edges of the blade (at least one) so that it has a total roll angle that is equal to or greater than 0.5 ° and, (viii) both the first and the second cloth coiling about the edge downstream of the contact surface downstream of the blade (at least one) with a roll angle that is equal to or greater than 0.5 °. It has been found to be particularly advantageous if, in the forming section of this invention, the bottoms of the blades are each provided with a depression in the form of = l to allow easy assembly on cooperating T-shaped mounting rails. , as described by White and others in the US 3,337,394. The oscillating movement of the blades on the mounting rail over the normal operation of the machine can therefore be restricted to no more than ± 0.25 ° by this means, and each blade can be replaced quickly and easily as required by the «/ additions of paper manufacture. The forming section of the present invention is structured and arranged in such a way that at least one removable forming blade is located so that it is in contact with a first of the two fabrics in such a way that the first fabric passes over and makes contact with both contact surfaces of the fabric upstream and downstream of the blade. The tensions of the fabric, and the angles formed by the fabrics as they wrap around the edges upstream and downstream of at least one blade, cause pulses of fluid pressure to be developed which serve to agitate the material of the fabric. sustained supply between fabrics and thus improve training. The beneficial effects of these fluid pressure pulses can be optimized if the contact surface downstream of at least one blade is sufficiently wide to oppose at least 5% of the force of the pressure pulse generated by the winding angle of the fabrics on the edge downstream of the blade. The geometry of the blade surface is such that a rolling action is developed on the blade cavity which will pull fluid from the supply material; this fluid is then forced back into the supply material by its velocity on the wall downstream of the upward slope of the cavity. This induces a turbulence in the fluid supply material that will improve the training environment. Fabric tensions, and their winding angles on the downstream portion of the blade, cooperate with the aforementioned rolling action to prevent a leakage of supply material through the first fabric at this point. The surface geometry of the blade, the position of the blade and the web tensions therefore now cooperate in a novel manner in the forming section of this invention to improve web formation in a manner that does not affect the shape of the web. damaging the retention of fine particles in the supply material, and whose effectiveness is not limited by the structure and geometry of the forming section of the papermaking machine. In a first preferred embodiment, the forming section of the present invention is composed of a plurality of contact surfaces of stationary fabrics, at least one of which is a forming blade, and is structured and arranged in such a way that only the first fabric travels in contact with all the contact surfaces of the fabric, and the path described by the two fabrics as they move over the contact surfaces of the fabric is that of a segmented curve. In a second preferred embodiment, the forming section of the present invention is composed of a plurality of contact surfaces of stationary fabrics at least one of which is a forming blade, and is structured and arranged in such a way that the stationary fabric contacting surfaces including at least one forming blade are located in alternate positions on opposite sides of the two fabrics whereby each of the first and second fabrics alternately contact the stationary fabric contacting surfaces at as they travel along a substantially zic zac course through the training section.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described with reference to the drawings in which: Figure 1 is a side elevation of a portion of a forming section of a manufacturing machine of? open surface, single-ply paper, which operates under normal operating conditions and which is equipped with a prior art agitator blade; Figure 2 is a graphic illustration of the fluid pressures in the shaker channel of the prior art agitator shown in Figure 1; Figure 3 is a graphic illustration of the mechanical pressure exerted by the forming fabric on the surfaces of the prior art stirrer blade of Figure 1; and Figure 4 is a side elevation of a portion of the forming section of a two-ply papermaking machine in accordance with the present invention, operating under normal operating conditions and being equipped with a single cutter blade. training; Figure 5 is a graphic illustration of the fluid pressures that occur between the first and second fabrics as it passes over the forming blade of Figure 4; Figure 6 is a graphic illustration of the fluid pressures that occur in the cavity of the forming blade of Figure 4 as the first and second webs pass thereover; Figure 7 is a graphic illustration of the mechanical forces exerted by the first and second fabrics on the eponstantially coplanar surfaces of the forming blade of Figure 4; Figure 8 is a side elevational view of a norition of the forming section of a two-fabric papermaking machine which is at rest and which is equipped with a single forming blade as shown in Figure 4; this figure is similar to figure 4 and is provided to more clearly show the roll angles of the fabrics as they pass over a forming blade; Figure 9 is an illustration of one embodiment of the Present invention in which a plurality of blades of for acióii as shown in Figure 4 are all located in a curve on a Jado of the formation fabrics; and Figure 10 is an illustration of a second embodiment of the present invention in which a plurality of forming blades as shown in Figure 4 are located in alternate positions on opposite sides of the forming section. . All of the pressures described in the text accompanying these figures are relative to atmospheric pressure as measured on or near the surface of the blade or supply material. As shown in the figures, all the angles have been exaggerated for clarity purposes. In all the figures, the fabric or training fabrics move from left to right.

DETAILED DESCRIPTION OF THE DRAWINGS In Figure 1 there is shown an agitator blade according to the prior art of Johnson, FU 3,674,996, and as shown in that patent. The blade is illustrated as if it were in normal operation in a single-cloth open surface papermaking machine. The blade 101 has upper, lower and upstream and downstream sides that provide an anterior edge 102, a rear tjr *, rear 103, an upstream flat contact surface 104 having a width A, a flat contact surface downstream. 105 having a width B which is coplanar with the surface 104, and a channel 106. The channel 106 is intermediate between the contact surfaces 104 and 105 and comprises three discrete planar surfaces, which form an upstream wall 107, a wall 10 floor or bottom 108, and a downstream wall 109. Wall 107 is diverted downstream of 104 at an angle A that is from Io to & Wall 109 is deflected upstream of 105 at an angle B which may be from Io to 70 °. As shown in this figure, the activity of supply material has been exaggerated for clarity purposes. Due to the negative fluid pressure developed in the upstream wall 107, as shown at 120 in Figure 2, the supply material 110 is subjected to a rolling action which pulls fluid through the bottom of the fabric 113. As this fluid progresses through the channel to the lower wall 108, the negative fluid pressure insulates to zero as in 121 and then begins to increase positively as in .1 2 as the supply material approaches the 109 downstream wall of the canal. The supply material is therefore positively forced back at this point through the fabric 113 to the supply material layer 110 above. The free surface of the supply material is separated by two actions as the fabric advances on the Johnson shaker blade. First, a small deviation of the fabric 1.13 towards the channel 106 caused by the negative fluid pressure developed in the wall 107 accelerates the supply material, producing a stroke lift lll. Second, the rising fluid from the channel 106 on the surface 109 may contribute to the alteration of the surface as in 119. A problem associated with this blade design when used in an open surface forming section is that, if the pressure positive developed by the rising fluid exceeds the weight of the supply material 110 on the forming fabric 113 above the cuvet J the 101, as shown by the curve 123 in Figure 2, the fabric 113 can be lifted from the surface 105, and the liquid, the fine particles and fibers as in 114 can be discarded between the fabric and the blade at the trailing edge 103, thus draining these components from the supply material. Neither drainage, nor the loss of fine particles nor the instability and excessive free surface are desirable in most cases. If this positive pressure does not exceed the weight of the supply material, as shown in curve 124 of Figure 2, then drainage at the trailing edge 103 of the blade will not occur. Figure 3 illustrates the mechanical pressure applied to the cloth 113 and the supply material 110 to the - * -, fabric contact profiles 104 and 105 of the blade 101 in reaction to the fluid pressure developed by the upstream wall. of the channel 106. As the fabric passes over the surface 104, this mechanical pressure rapidly increases to a maximum at the edge downstream of the surface 104, adjacent to the negative fluid pressure zone in the wall 107, and then drops at zero as the fabric passes over the channel 106. This is shown by the curve 130 in Figure 3. The mechanical pressure exerted by the fabric on the blade at the contact surfaces of the downstream cloth 105 is already it is very small or zero, as shown by curve 131, and its magnitude depends on the weight of the supply material above it and the magnitude of the positive pressure generated by the upstream supply material in the wall downstream 109. If the fabric and the inherent weight of the supply material do not exert any mechanical pressure on the downstream surface 105, then the runoff of supply material will occur on this surface as in 114. At speeds of high machine and low supply material weights, certainly the fluid supply material will drain from the trailing edge 103 of the knife 101. At lower machine speeds and higher feed material weights, the edge of the knife 103 can be sealed by the weight of the supply material, in which case the fluid pressure will remain positive up to the downstream point of the channel and the mechanical pressure on the surface 105 is finite. The effectiveness of this blade in a section of formation of the open surface is therefore limited by these conditions. In figure 4 a portion of a forming section of a two-ply paper machine according to the teachings of the present invention is shown. As shown in this diagram, the papermaking machine is in normal operation with the two fabrics moving on a forming blade 201, the first fabric 213 contacting the surface of the blade and the second fabric 214 traveling at the same speed as the first and confining between them is a supply material layer having a thickness S. The path taken by the two forming fabrics as they advance over the forming blades and through the forming section of this invention may be a zic zac or a segmented curve. The winding angle of the first fabric 213 around the upstream edge 202 of the knife 201 is; the winding angle of this same fabric at the downstream edge 203 of the blade is d. In this way, the total winding angle e of the first fabric 213 around the edges of the knife 201 is equal to the sum of c and d. The winding angle of the second fabric 214 around the upstream edge 202 of the knife 201 is f; the winding angle of this same fabric at the edge downstream of the blade is g. The total angle of winding of the fabric 214 around the edges of the knife 201 is h which is equal to the sum of f and g. The total angle of winding of the fabric around the edges of a forming blade is therefore defined as the angle that is subtended by the angles "upstream and downstream of winding the fabric around the edges of the fabric. blade, and is given by the following: total winding angle of the first fabric = e = c + d total winding angle of the second fabric ~ h = f + g Fl thickness S of the supply material 210 as it is held between the fabrics 213 and 214 decreases drainage of the liquid through the fabrics away from the blade 201 as the fabrics advance from the upstream edge to the downstream edge of the blade 201. The internal and external forces act on; fabrics, causing them to deviate from a strictly parallel course as they are wound around the blade. In this way, when the machine is in operation, the total winding angles e and h of the two fabrics will necessarily be equal, nor will the pairs of winding angles upstream and downstream, c and f, d and g, be equal. Only when the formation section is static and the fabrics are under tension, will these pairs of angles be equal to each other because it is then that the trajectories of the two fabrics around the blade are altered. Those skilled in the art will also understand that, when the training section is in operation, the. curl angles c and f, and d and g of fabrics 213 and 214 will be slightly different than if they are measured when the forming section is static. The blade 201 extends transversely to the direction of travel of the fabric and has upper, lower, and upstream and downstream sides that provide upstream edge 202, a downstream edge 203, and an upstream flat fabric contact surface. 204, a downstream flat cloth contacting surface 205, both surfaces 204 and 205 being substantially caplet-like, and a cavity 206 that is intermediate between contacting surfaces 204 and 205 and whose depth below these surfaces is. As shown in Figure 4, the cavity 206 is composed of two discrete planar surfaces, forming an upstream wall 207 and a downstream wall 209 that meet in an intermediate surface 206, forming the bottom of the cavity 206. As shown in this figure, the intermediate surface 208 forms the line of intersection of the walls 207 and 209. It is contemplated that, under certain papermaking conditions, it may be advantageous to extend the surface 208 in such a way as to have a certain width of direction of the finite machine. If this is done (see blade 301 in FIG. 9), then the surface 208 is extended in such a manner as to be parallel to the plane of the coplanar substantially upstream and upstream contact surfaces 204 and 205, or slightly inclined. with respect to this plane at an angle of about Io to about 8o. Alternatively, it can also be contemplated that the surface of the blade cavity may have a somewhat elliptical shape, rather than being made of several discrete surfaces 207, 208 and 209 as shown in Figure 4. Depending on the «Paper manufacturing issues, the curve has a tangent angle in the Jado upstream of the cavity that is around Io at 8 ° and a tangent angle on the downstream side of about Io to 8o (see blade 402). in figure 10). In both cases, the tangent is taken at the tip where the curve coincides with the upper surface of the blade. Those skilled in the art will readily realize that choices regarding the optimum size and shape of the blade cavity 206 will be determined by the papermaking conditions prevailing in the forming section at the time such selection is made. The wall 207 is deflected downstream of the surface 204 at an angle or that is around Io to 8o. Wall 209 deviates from the surface 205 at an angle p which is also around Io to 8o. As shown in this figure, the angles o and p have been exaggerated for clarity. The supply material 210, between the fabrics 213 and 214 as it passes over the knife 201, has an e S? Spesor S that decreases from the upstream edge 202 to the downstream edge 203 d? Due to the drainage of the liquid at through the fabrics. The fabrics 213 and 214, which are shown moving on the surface of the forming blade 201 at a known speed, have tensions N and M respectively, and are wound around the edges of the blade 201 to have total wrapping angles e and h. As the fabrics 213 and 214 approach the upstream edge 202 of the blade 201 at winding angles c and f respectively, both of which are greater than zero, a pressure pulse of positive fluid is induced in the material of the fluid. 210 supply as it is held between the fabrics. The shape and magnitude of this upstream pulse is somewhat similar to what is described occurring at the edge downstream of the blade in the model proposed by Zhao and Kerekes. As shown in n. 220 in FIG. 5, this positively increasing fluid pressure pulse increases in magnitude to a maximum together before the edge 202, and then decreases rapidly to zero as the fabrics advance over the fabric contacting surface. upstream 204. The magnitude and shape of this fluid pressure pulse are functions of the N and M tensions of the fabrics 213 and 214, the winding angles cyfa as the fabrics are wound on the upstream edge 202 / * >; - * the blade, speed of the fabric, resistance to drainage of the pulp, thickness of the fluid supply material, movement of the fluid supply material between the fabrics at this point, and other variables, such as stiffness of the fabric. As they move downstream on the forming blade, the fluid pressure in the supply material sandwiched between the fabrics begins to increase on the downstream contact surface 205. This fluid pressure increases to a maximum at the current edge. «Under blade 203, 201, as shown by curve 222, producing a pulse similar in shape and magnitude upon producing it at the upstream contact surface 204, which is represented by curve 220. The configuration of this second pulse downstream is described in the model proposed by Zhao and re is and is also regulated by the tensions of the fabric, its winding angles, and the other variables described above. Hereinafter, the pulse phenomena of positive fluid pressure that is induced in the supply material and regulated by the aforementioned parameters are simply referred to as pulses ZK. Two beneficial effects for the formation of paper that result from the ZK pulses are, first, drainage of liquid through the fabrics away from the blade and, second, redistribution of the fibers in the supply material held between the fabrics as advancing on the upstream edge 202 of the blade. The supply material 210 conveyed between the fabrics 213 and 214 is thus subjected to two distinct pulses ZK as it passes over the surface of the forming blade 201, whose shape and magnitude are mainly regulated by the tensions of the fabric and the wrapping angles of the fabrics around the upstream and downstream edges 202 and 203 of the blade. Both pulses ZK induce a shearing effect on the supply material, which extends upstream from the contact surfaces of the fabric upstream and downstream of the blade. As illustrated in Figure 4, the cavity 206 of the blade 201 is located proximate the upstream edge 202, and the upstream flat contact surface 204 is correspondingly short. The actual location of this cavity on the surface of the blade will include in the forming effects provided by the forming section of this invention. In this way, the optimum surface geometry of the blade will be determined by papermaking conditions and the formation section geometry. For example, if the cavity is located near the edge upstream of the blade, as illustrated in FIG. 4, then the onset of negative pressure in the cavity due to a rolling action occurring will be very close to the end of the pulse. of pressure ZK developed forward of the ^ -p of upstream of the blade, as shown in 221 in Fig. 5. If the cavity is located closer to the point of the blade, then the supply material is subjected to three phenomena of fluid pressure separated in succession, the first being the pulse ZK produced by the tension of the fabric and the winding at the edge upstream of the blade, the second being the turbulence created by the movement of fluid towards adetro and outside the cavity 206, as described below, and the third being the second pulse ZK produced at the downstream edge of the As the fabrics advance over the cavity of the blade 206 def When the walls 207 and 209 enter, and a surface 208 is present, a second phenomenon occurs which also has a beneficial effect on the formation of supply material. As the first web 213 advances on the upstream contact surface 204, it reaches the upstream diverting wall 207 of the blade cavity to form:. 206. A negative fluid pressure develops as the first fabric passes over the upstream deflection wall 207 of cavity 206 due to a rolling action, as described by Wrist in E.U.A. 2.92A, 465. As shown in Figure 6, the fluid pressure in the cavity 206 first decreases from zero to a minimum negative value as in 230 as the first fabric 213 passes the upstream diverting wall 207. The fluid pressure ^ o is increases to zero at the intermediate point 208 of the cavity, and then positively increases as well as at 231 on the upward sloping surface 209, remaining later positive at the end of the cavity, as in 232. The initial fluid pressure is Negative in the cavity 206 serves to pull liquid from the supply layer 210 sandwiched between the fabrics 213 and 214 to the wall 207, as also described by Wrist. As the fluid pressure in this cavity increases to a positive value, as in 231, the liquid is then forced back through the first leg 213 towards the supply material layer 210 by the shallow angle p of the upward sloping wall 209 while the fabric is supported on the downstream contact surface 205 by the tensions N and M of the fabrics 213 and 214 as they are wound on the downstream edge 203. Irrespective of the location of the fabric. of the cavity on the surface of the blade, it is critical that the downstream surface 205 of the blade 201 have a width in the direction of the machine sufficient such that the beneficial effects of the turbulence caused by the fluid emerging from the running wall below 209 of the cavity 206 are not inhibited by the pulse ZK created next to the downstream edge 203. In a preferred embodiment of the present invention, the co The downstream contact 205 of the blade 201 will be large enough to become at least 75% of the pulse force ZK developed at the downstream edge 203 of the blade.; The beneficial effects of both the turbulence and the ZK pulse can therefore be maximized. A further critical feature of this invention is that the depth K of the cavity 206 will be limited to a value that ensures that the cavity remains fluid-filled during normal operation of the papermaking machine. If the cavity is too deep in relation to the thickness of the upstream supply material, then the rolling action will stop and the beneficial effect of the forming blade will be lost. The fluid passing between the fabrics will then be discontinuous, producing a new uncontrolled and indeterminate entry of fluid into the supply material layer held between the forming fabrics on the downstream cavity wall. Unless a continuous fluid flow is provided by the rolling effect developed on the cavity, the formation will be adversely affected. It should be noted that in this house, and unlike the blade shown in the prior art forming section of Figure 1, the positive fluid pressure developed in the downstream wall 209 of the cavity 206 does not drop to zero on the surface of downstream contact 205. Instead of it, it remains positive until the end of cavity 206 before dropping to a bit on surface 205. Since both fabrics S * "wind around the same forming blade, the pressure of the liquid being forced through the first fabric 213 on the downstream surface 209 of the cavity is opposite and there is contraction thereon by the stresses N and M of the two fabrics. The liquid is thus forced to enter the space between the fabrics again, thus producing a fluid movement in the supply material which serves to reorient the fibers and improve the formation of the band. In Figure 7 is shown an ion repression of the mechanical pressures exerted by the fabrics and supply material on the surfaces 204 and 205 of the blade 201. These mechanical pressures are developed in reaction to the forces generated by the winding angles of the fabrics and the negative fluid pressure developed on the surface 207 of the cavity. As the fabrics pass over the upstream surface 204, they are positively held on this surface by their winding angles c and f in the upstream bar 202, if the fabrics do not approach the knife 201 tangentially. The mechanical pressures on the surface of the blade 204 in relation to the winding angles and the negative fluid pressure increase almost immediately to a maximum as shown by curve 240. This mechanical pressure rapidly decreases to zero over the cavity, and then increases again on the surface 205 as the zone of negative fluid flow in the wall 207 passes. In this way, the leading edge of the cavity is always sealed by the rolling action developed on the surface 207, and the strength of this seal can be increased by increasing the roll angle c of the fabric 213 on the upstream edge 202. Mo is mechanical pressure exerted on the surfaces 207, 208 and 209 of the blade cavity. The mechanical pressure then increases again as 241 as the fabrics and the supply material pass over the downstream surface 205 due to the pressure pulse ZK generated in the supply material, the tensioners of the fabric. N and M, and the winding angles d and g of the fabrics at the downstream edge 203. Thus, unlike the prior art of Figure 1, the surface of the upstream and downstream blade are effectively sealed avoiding so there is leakage of supply material from between the cloth and the surface of the blade that would otherwise reduce the retention, and the beneficial reorientation and effec- tive grilling caused by the geometry of the blade san contained in the material of the blade. I supply sandwich between the fabrics. If the winding angle c of the first fabric is small, then the upstream contact surface 204 should have a width in the machine direction c sufficient to ensure a firm seal between the fabric and this surface of the blade. However, if the angle c is very large, e.g., from about 0.5 ° to approximately Io, then the stray run away from the blade, caused by the ZK pulse at this point, will occur and the The upstream touch surface 204 can be made relatively small, for example from about 2 mm to 5 mm. If c is small, at the angle of about 0 ° to about 0.5 °, then the contact surface 204 should be made larger, for example from about 5 mm to about 25 mm, to ensure a reliable seal. As indicated above, the width D of the downstream contact surface 205 is also of importance. It has been found that this surface must have a width in the direction of the machine sufficient in such a way that: i) it is sufficiently large to oppose a majority of the ZK pulse force that develops as the two fabrics are wound on the downstream edge 203 of the forming blade, and ii) the beneficial effects of the ZK pulse created at the downstream edge 203 are not affected by judicially by the turbulence of emerging fluid created by the cavity 206. The precise anc uva of the contact surface downstream referred to satisfy the The aforementioned requirements, is a function of many variables, such as the speed of the fabric, the resistance to drainage of the pulp, the weight of the supply material, the tensions of the fabric and the angles of winding around the blades of training, to name a few. ? "* Has found that if the downstream contact surface 205 is sufficiently wide to oppose at least 75% of the ZK pulse developed on the current edge aha ^ o 203, then its beneficial effects will be maximized. If this is done, then the contact surface downstream will be sufficiently wide, so that the fluid emerging from the cavity does not interfere with the ZK pulse. The surface geometry of the blade is therefore a design variable specific to the application of this invention that must be controlled to optimize the formation in -re-spces to the dynamics of the papermaking machine and to the ca «? D? C? Ons of the material supply of paper? Figures 4 to 7 illustrate the invention under dynamic papermaking conditions. In practice, the winding angles are difficult to measure under these conditions, and it will be understood that for this invention, these angles must be measured for static fall when the machine is not fuzzy. say, when there is no supply material S between fabrics 213 and 214). This case is illustrated in Figure 6. The winding angle of the first 212 around the upstream edge 202 of the blade 201 is c; the angle of winding of this same fabric in the downstream stream 203 of the same blade 201 is d. In this way, the total winding angle of the fabric 213 around the knife 201 is defined for the width of the machine in which the machine is at rest as e which is equal to the sum of c and d. The angle of winding of the second fabric 214 around the bore of the top 202 of the blade 201 is f; the roll angle of this same fabric at the downstream edge 203 of the blade is g. The total angle of winding of the fabric 214 about the blade 201 is if only defined by the case where the machine is at rest as h which is equal to the sum of f and g. Regardless of whether the machine is at rest or in operation, the following relations must be fulfilled: Total wrapping angle of the first fabric = c + d = total wrapping angle of the second fabric ~ f + g = h When the machine is in reverse and there is no supply material S sandwiched between the fabrics, the fabrics 213 and 214 are parallel and e = h, c = f, and d = g. A feature of this invention is that the total winding angle, e, of the first fabric 213 around the upstream and downstream edges 202 and 203 of the forming blade 201 should be equal to or greater than 0.5 ° as measured when the paper machine is at rest. The total winding angle h of the second fabric 214 around these same edges must also be equal to or greater than 0.5 ° as measured when the machine is at rest. In addition, each of the fabrics 213 and 214 must be wound on the downstream contact surface 203 of the same forming blade 201 with winding angles d and g that are? - to one equal to or greater than 0.5 ° as measured when the machine It is at rest. In addition, the first fabric 213 must contact the upstream and downstream fabric contacting surfaces 204 and 205 of the forming blade 201. Thus, for any forming blade in a forming section d < = the present invention, the winding angles e and h of each fabric 213 and 214 around any knife 201 must simultaneously satisfy the following conditions when the papermaking machine is at rest: i. e 0.5 ° and d = 0.5 °, and 2. h 0.5 ° and g ≤ 0.5 °, and 3. a cloth dt-be making contact with the supporting surface of the forming blade. The upstream winding angle c of the first fabric 213, and the upstream winding angle f of the second fabric 214, can be equal to zero (ie: c = f = 0), in which case the first fabric it would approach the forming blade 201 tangentially but in contact. When the machine is in operation, a pressure pulse ZK would not occur between the fabrics 213 and 214 just before the upstream edge 202 of the blade. However, the fluid pressure would still develop in the cavity of the blade 206, as previously explained because the first web 213 would be sealed at the upstream edge 202 of the blade 201 due to the action of suction rolling. of the diverging surface 207. A pressure pulse ZK would occur at the contact surface downstream of the blade due to the wrapping angles of the fabrics and their stresses, as explained above. The effectiveness of this downstream ZK pulse will be regulated by the width D in the direction of the machine from the downstream contact surface 205. This surface must have a sufficient width to ensure that: i) the beneficial effects of the ZK pulse are not adversely affected by the turbulence of emergent fluid created by the cavity 206, and ii) approximately 75% Jel pulse ZK occurring close to the downstream edge 203 is opposed by this surface. In Figure 9 there is shown an embodiment of the present invention in which a plurality of the blades; 300, 301 and 302, whose cross-sectional profile is essentially as previously described, are arranged transversely to the direction of travel of the fabrics 213 and 214 on the side of the curved forming shoe in the section of formation of a papermaking machine Two fabrics. As illustrated in Figure 9, the papermaking machine is in operation and the forming blades are arranged in such a way that the fabrics that engage them form a segmented curve. The forming section is arranged in such a way that the first fabric 213 is wound to each blade with a total winding angle e that is equal to or greater than 0.5 ° as measured when the machine is at rest. The second fabric 214 is also wound around each blade with a total winding angle h that is equal to or greater than 0.5 ° when measured at rest. Both fabrics are wound to the contact surface downstream of each blade with a winding angle that is equal to or greater than 0.5 ° as measured when the machine is in stationary phase. The drainage of liquid from between the fabrics takes place due to the tensions N and M of the fabrics 213 and 214, and their winding angles on each blade, decreasing the thickness of the supply material as it proceeds downstream. As shown in this figure, the thickness of supply material is represented by the letters W, X, Y and Z. As the fabric and the supply material advances downstream, the thickening of the supply material layer it decreases from a relatively high value as in W to a relatively lower value as in Z. In this way, in this embodiment, the depth k of the cavity on each successive blade can be adjusted to maintain the continuity of fluid flow as the laminated fluid of the supply material on the surface 207 moves in and out of the knife cavities 206. The depth k of the cavity on the first blade upstream of the ion section can thus be greater than the last blade downstream. Because the depth of the cavity k is a? Ntion of the thickness of the supply material held between the fabrics above the knife, the depth k will generally decrease from the upstream end to the downstream end of the forming section of this invention. . The width of the machine direction D of the web contacting surfaces downstream of the forming blades used in the forming section of this invention may also vary according to the thickness of the supply material. In general, the width of this downstream contact surface can be decreased as the thickness of the supply material decreases from an upstream direction to a downstream direction to optimize the beneficial formation effects produced by the ZK pulse in the edges downstream of the blades. As indicated above, if the contact surface of the downstream cloth is sufficiently wide to oppose approximately 75% of the force of the ZK pulse, then the beneficial formation effects provided by the knife pocket "; combination with the curl angles downstream of the fabrics around the blades will be maximized. However, it is neither necessary nor desirable that all the blades on the curved forming shoe are forming blades in accordance with the teachings herein. It may be advantageous to intermix these forming blades with diverting blades or other types of supporting blades? ? * s fabrics as are well known in the art.The actual location of the forming blades and other blades in the forming section will vary depending on the type of paper being manufactured., the operating conditions of the machine, the desired level of agitation and other factors. In Fig. 10 a second embodiment of the present invention is shown in which a plurality of blades 401, 402 and 403, substantially as described above, are located alternately on opposite sides of the two fabrics 213 and 214 to make contact alternately with the first one 213 and the second fabric 214. The relative weight of the supply material is shown in F, G and H. The blades are located so that each fabric is rolled up and entangled in each blade with a total angle of winding that is equal to or greater than 0.5 °, and also so that the two fabrics allow a zigzag path as they advance between. training blades. In this mode, the supply material is subject to the phenomena alternately; of fluid pressure previously described from opposite sides of the fabric. The drainage therefore occurs alternately through the first and second fabrics 213 and 214 away from the blades so that the thickness of the supply material held between the fabrics decreases from a relatively high value F at the upstream end of the fabric. training section at a relatively low value H at the low running end. Similarly, shearing forces and pulsation effects caused by the forming blade cavities and the ZK pulses induced on both sides upstream and downstream of the blades as explained above, are induced from opposite sides of the blades. two fabrics, thus uniformly mixing and redispersing the fibers as the fabrics advance through the forming section. As described above, the roll angles of the fabrics around the blades must conform to the requirements of the invention. From this ./.añera, the first fabric 213 is wound on the first blade 401 with a total winding angle that is equal to or greater than 0.5 ° while in contact with its contact surfaces upstream and downstream, the second fabric 214 must also be wound to the first blade 401 with a total winding angle that is equal to or greater than 0.5 °, and the winding angle of the cloths 213 and 214 t - n the end of the contact surface downstream of the first blade 401 must be equal to or greater than 0.5 °. Although the positions of the first and second fabrics 213 and 214 are reversed in the second blade 402 so that 214 becomes the first fabric and 213 becomes the second fabric, relative to its relative positions in the blade 401, the same requirements indicated above must be met for both fabrics. That is, both fabrics 213 and 214, the second blade 402 must be wound, so that the total individual wrapping angles are each equal to or greater than 0.5 °, and the second fabric 214 contacts the contact surfaces. carriage up and downstream of the blade 402 and the winding angle of each of the fabrics of the edge downstream of the blade is equal to or greater than 0.5 °. In the third blade 403, the relative positions of the fabrics are reversed to those described in the first blade 401. Not all blades in the forming section described in this embodiment need to be forming blades. Other types of forming fabric support structures, such as those known in the art, may also be located between the forming blades, so long as the requirements of the invention are met. The actual position of the forming blades and other support structures in the forming section will depend on the type of paper you are making, the operating conditions of the forming section and other variables as indicated above. The geometry of the blade cavities of the blade used in this invention may vary, but the angle of divergence of the wall upstream of the cavity from the flat surface upstream should be within the range of Io. approximately 8o In a similar manner, the divergence angle of the wall downstream of the cavity should also be within the range of about Io to about 8 °. Surprisingly, it has been found that if the angle of divergence of this downstream wall is greater than 8o, then the beneficial agitation effects induced in the supply material by its movement through this cavity is severely diminished.Relatively, the depth k of the cavity on each successive blade , as well as the width in the machine direction of the downstream contact surface, should be related to the thickness of the supply material at that point. «T-s was described above. It may be convenient, for a better control of the level of agitation in the supply material, to design the knife cavities so as to contain a floor 208 whose width in the machine direction is greater than 0 if this is done, then the step of the cavity may be parallel to the plane intersecting the upstream and downstream edges 202 and 203 of the contact surfaces of the fabric, at angularly inclined to be at an angle with respect to this plane, as long as the angle does not exceed 8o. . Alternately, blade cavities having a somewhat elliptical shape can be provided such that an angle tangent to the upstream and downstream sides of these curved surfaces where the surfaces upstream and downstream are located should be around from Io to approximately 8 °. In addition to the limitations indicated above, the depth k of the cavity must also be limited to / íi-inserve the continuity of the fluid flow towards the cavity.

Although not all effects are known with precision, it has been found that the maximum effective cavity depth k is a function of the following: i) The ease with which the supply material can be pulled from the fluid between the fabrics; this depends on the type of supply material, the amount of fiber mat deposited on the fabric upstream of the forming blade, and the drainage of the fabric; ii) The depth of the supply material, which is between the fabrics as it passes over the point of maximum depth k of the cavity.; and iii) The magnitude and degree of the pressure pulse ZK generated at the edge downstream of the forming blade; If the puls extends upstream on the cavity, it can inhibit the upward flow of the fluid and limit the effectiveness of the blade. It has been found-in practice that the maximum depth k of the cavity must not exceed 3/4 of the thickness of supply material S which is located upstream thereof, and a cavity depth which is less than one. 1/10 of this thickness has little effect. A more preferred scale for the depth of the cavity k is about 1/2 to about 1/10 of the thickness of the supply material S which is sandwiched between the fabrics as they pass over the cavity. The location of the blade cavity on the supporting surface of the blade fabric is also critical. It has been found in practice that the beneficial agitation effects provided by the blades are mostly effective when the cavity is located close to the edge upstream of the blade whereby the cape C is relatively small. However, the beneficial effects can also be «? obtain locating the cavity a little from the midpoint of the anchor in the direction of the blade machine. If the cavity is located downstream of the point of the blade, it seems doubtful that much improvement is obtained in the formation of the band. The selection of a gea «t > The optimum blade surface ratio for use in the forming section of this invention will depend on the conditions of the supply material, the speed of the machine and other variables unique to the particular application. Preferably, the forming blades themselves are provided with a polished ceramic surface in order to preserve the geometry of the contact surfaces. the fabric The ceramic material from which these surfaces are formed can be selected from the group consisting (but not limited to) of the following: aluminum oxide, hardened alumina, zirconia, silicon nitride, silicon carbide, silicon carbide or silicon titanate. Alternatively, wear resistant inserts can be installed on one or both of the upstream and downstream contact surfaces of the blades as taught in Buchanan in E.U.A. 3,446,702 to form the contact surfaces with the fabric. Preferably, these inserts are composed of one of the above-mentioned ceramic materials, but other wear resistant materials can also be used. The blade body can be made of an easily machinable material such as a high density, high molecular weight polyethylene. It is preferred that the forming blades in the forming section of this invention, as shown in Figure 4, be mounted on T-shaped rails that engage T-shaped grooves formed in the bottom of the blade, as described. in White, US 3,337,394. It is critical in this assembly that the manufacturing talent of the T-shaped groove and the T-shaped bar minimize the oscillation of the knives. The magnitude of this blade ascillation should not exceed ± 0.25 ° and is preferably smaller. Other mounting means which minimize the oscillation of the blade to a value within the aforementioned edges can be used to place the forming blades in the forming section of this invention. Since very small angles are important in this invention, accurate maintenance of the knife orientations to maintain alignment with the fabrics is critical.

RESULTS OF THE EXPERIMENTAL TEST Testing on a space-forming "operation" at 1,027 m / min to "36 grams per square meter of directory grade paper showed significant improvements in both porosity and sheet formation when 11 of the 13 standard shoe blades were replaced by forming blades in accordance with the teachings of the present invention. The forming blades were equipped to be installed in the training shoe using T-bar supports whose center-to-center spacing was 114 mm. The total shoe roll angle was 16 °, thus providing a total roll angle per blade of 1.33 °. The 70 mm wide forming blades were provided with a shallow V-shaped cavity that had 25.4mm side walls that were symmetrically angled down to 2o from contact surfaces running up and downstream to provide a depth 0.89 mm. The blades were provided with 9.5mm contact surfaces upstream and downstream. These forming blades did not show an improvement in leaf formation index as measured by a Reed NUI training tester (t non-uniformity index) by 2.0, and reduced sheet porosity by 19% when operating on the shoe under normal vacuum conditions. Although the present invention has been described with reference to two preferred embodiments, it will be understood that it can not be limited. Various modifications can be made without departing from the spirit or scope of the invention as defined by the appended claims.

Claims (20)

NOVELTY OF THE INVENTION CLAIMS

1. - A training section for use in a two-fabric papermaking machine, comprising, in association with: (i) a first and second loops of endless motion forming fabric, both loops having a linear tension E? ? steering the machine through the forming section and moving in a joint displacement of 3 from an upstream direction to a downstream direction, and between said fabrics a layer of supply material of known thickness being transported; (ii) at least one forming blade extending transversely to the travel direction of the fabric and in contact with the first fabric in such a way that under the tension in the machine direction < * Fabric with abrasion material between them are wound around at least one blade; (iii) the forming blade (at least one) has an upper face, a bottom and edges of contact with the fabric upstream and downstream; (iv) the upper face of the blade (at least one) having two substantially coplanar upstream and downstream surfaces in contact with the first web with an intermediate cavity therebetween; (v) the cavity having diverging walls upstream and downstream with an intermediate surface therebetween, the wall of the upstream cavity diverging from the contact surface of the upstream fabric at an angle of the a & amp; The wall of the downstream cavity diverging from the contact surface of the downstream fabric at an angle of Io to 6o to define a cavity whose depth from the plane of contact surfaces substantially j-flat to the surface intermediate is about one tenth to about 3/4 the thickness of the supply material that is transported between the first and second ones over the cavity; (vi) the first fabric being wound around the edges of the blade (at least one) to have a total roll angle that is equal to or greater than 0.5 ° while in contact with the contact surfaces upstream and downstream; (vii) the second fabric also wrapping around the edges of the blade (at least one) so as to have a total angle fi & > winding which is equal to or greater than 0.5 ° and, (viii) both the first and second fabrics are wound around the edge downstream of the contact surface downstream of the blade (at least one) with a winding angle that is equal to or greater than 0.5 °.

2. A training section for use in a two-fabric papermaking machine according to claim 1, further characterized in that the bottom of the forming blades is provided with mounting means for locating the blade in the section. of formation, so that the oscillation of the blade on the mounting means is restricted to a value that is not greater than + 0.25 °.

3. - A forming section for use in a two-fabric papermaking machine according to claim 1, further characterized in that the contact face of the fabric running down the blade (at least one) is sufficiently wide to oppose at least 75% of the force of the ZK pulse generated by the curling angles of the forming webs.

4. A training section for use in a two-fabric papermaking machine according to claim 1, further characterized in that it includes a plurality of forming blades.

5. A training section for use in a two-fabric papermaking machine according to claim 4, further characterized in that the knives are formed on the same side of the two fabrics.

6. A training section for use in a two-fabric papermaking machine according to claim 4, further characterized in that the forming blades are arranged on both sides of the two cloths.

7. A training section for use in a two-fabric papermaking machine in accordance with claim 1, further characterized as a parison, a forming blade is typically assembled.

8. - A training section to be used in a two-cloth papermaking machine in compliance with "? the vindicating rei 1, further characterized in that the contact surfaces of the fabric of the forming chip (at least one) contain inserts of a wear-resistant material.

9. A training section for use in a two-fabric papermaking machine according to claim 8, further characterized in that the inserts are made of a ceramic material.

10. A training section for use in a cloth papermaking machine according to claim 1, further characterized in that the upper face of the forming blade (at least one) is a polished ceramic surface.

11. A training section for use in a two-cloth papermaking machine in accordance with claim 5, further characterized in that all the & Training blades are arranged transverse to the travel direction of the fabric along the radius of a curved forming shoe.

12. A training section for use in a two-fabric papermaking machine according to claim 6, further characterized in that the forming blades are arranged on opposite sides of the two fabrics to make the fabrics follow a path in zig .lag.

13. A training section for use in a two-fabric papermaking machine according to claim 1, characterized in that at least in one blade the depth of the cavity of the plane of the contact surfaces with the Tissue substantially planar to the intermediate surface is about 1/10 to approximately i / 2 the thickness of the supply material that is transported between the first and second fabrics over the cavity.

14. A training section for use in a two-fabric papermaking machine according to claim 2, further characterized in that it includes a plurality of forming blades.

15. A training section for use in a two-fabric papermaking machine in accordance with ,.) to claim 14, further characterized in that the forming blades are arranged on the same side of the two fabrics.

16. A forming section for use in a two-fabric papermaking machine according to claim 14, further characterized in that the forming blades are disposed on both sides of the two fabrics.

17. A training section for use in a fabric papermaking machine according to claim 2, further characterized in that at least one forming blade is detachably mounted.

18. A training section for use in a two-fabric papermaking machine according to claim 15, further characterized in that all the forming blades are arranged transverse to the direction of travel of the fabric along the radius of a curved training shoe.

19. A profile section for use in a two-cloth paper machine according to claim 16, further characterized in that the forming blades are alternately located on opposite sides of the two fabrics to make that the fabrics follow a trajectory in ig zag. 20.- A training section for use in a two-cloth papermaking machine in accordance with "? claim 2, further characterized because at least The depth of the cavity of the plane of the contact surfaces with the fabric substantially co-planar to the intermediate surface is approx. 1/10 to approximately 1/2 of the thickness of the supply material. It is transported between the first and second fabrics on the cavity. TRAINING SECTION TO BE USED IN A MANUFACTURING MACHINE! OF PAPER OF TWO FABRICS SUMMARY OF THE INVENTION A forming section for a two-fabric papermaking machine that uses forming blades having shallow cavities on its upper surfaces that have fluid from the jig material and pushes it back towards the fabric to break the flocculated mat without producing excessive drainage and loss? fine particles. The parameters required to design the blade cavity, the upper surface of the blade and the wrapping angles of the cloths around the blades are provided to obtain the best results. JJ / cgt * c rm * ieoh