MXPA99005715A - Using centrifugal pumps in the foam process of producing non-woven webs - Google Patents

Abstract

A non-woven web of fibrous material is produced using a moving foraminous element in the practice of the foam process. A first foam slurry of air, water, fibers and a surfactant is generated and centrifugally pumped into contact with the moving foraminous element. Substantially fiber-free foam is withdrawn from the foraminous element while forming a non-woven web of fibrous material on the foraminous element, and at least a part of the substantially fiber-free foam is used in the generation of the first foam slurry. Recycling is also typically practiced using a centrifugal pump, and the centrifugal pumps are preferably degassing pumps which remove some of the gas from the foam. By practicing the invention it is possible to produce fibrous webs using the foam process that are more than two meters wide, and at a forming speed of more than about 100 m/min (e.g. about 200-500 m/min).

Description

Use of Centrifugal Pumps in Process Based on Foam Production of Non Woven Meshes BACKGROUND AND SUMMARY OF THE INVENTION The foam-based process for the formation of fibrous non-woven meshes is basically described in US Pat. 3,716,449, 3,871,952 and 3,938,782 (incorporated herein by reference). The foam-based process has a number of advantages compared to the water-based process, which is more conventionally used in the manufacture of synthetic fiber or cellulose meshes. The invention relates to a method and apparatus for implementing the foam-based process and improving the aspects thereof. Although the process with foam has a number of advantages compared to the process with water in the production of fibrous non-woven meshes, one of the practical disadvantages thereof that has limited its commercialization for particular types of foams is the relatively narrow width of the foam. the meshes that have been produced previously from the process with foam (for example, on a scale of 1-1.5 meters) compared to the width of the mesh in typical paper machines that use the process with water, which can be up to more than ten meters. Similarly, the production rate of the foam process has typically been significantly below 100 meters per minute. The main limitation in the width of the mesh and the speed of operation of the systems of the prior art, which carry out the process with foam, have been the pumps used to carry out the process. The pumps are positive displacement pumps, such as screw pumps, propeller pumps, double helix pumps, double rotor pumps or similar, which have limited pumping capacity. Some of these positive displacement pumps are relatively insensitive to the material being pumped and, therefore, operate well in the production of fluids containing fiber and gas which are, of course, characteristics of the foam process, and that is why they use. However, some of these pumps are very outdated, expensive and easily damaged. Consequently, if the production is going to increase (for example, increasing the mesh size produced by increasing the width of the cable or other foraminous element to more than 1.5 meters), several pumps must be used in parallel. This dramatically increases the cost of assembly, and there is also the risk that one of the pumps will be damaged and therefore the entire process will be stopped to repair or replace the damaged pump.

O-A-9602702 discloses a method and adaptation for producing a paper or fiber mesh formed with foam. Said WO document discloses the pumping of foam with included fibers, and suggests several different types of pumps that are suitable for pumping the foam. The pumps mentioned are: conventional piston pumps, water ring type vacuum pumps, and so-called Discflo pumps. As common characteristics of these pumps, the following can be mentioned: they can pump media with a high gas content, their efficiency is remarkably low, and they do not separate the gas from the media that is pumping. Even in situations where the prior art recognizes, during the practice of the foam process, the desirability of removing the gas, a separate type of degassing structure is provided, and the pumping is given using a conventional positive displacement pump. For example, in Figure 3 of the US Patent no. 4,944,843 degassing is obtained by means of a centrifugal separator, but the foam that passes through the foraminous element and is removed through a conduit is pumped using a positive displacement pump. In accordance with the present invention, the disadvantages that are set forth above in a conventional foam process are overcome in a simple and effective manner.

Using centrifugal pumps to treat foam grouts (whether or not containing fibers), it is possible to increase the width of the cable (or other foraminous element) to more than two meters, and increase the formation speed to more than 100 meters per minute (for example, approximately 200-500 meters per minute). However, most centrifugal pumps are not suitable for pumping the type of slurry that is handled in the foam process according to the invention. However, the invention uses centrifugal degassing pumps which, according to the invention, are effective in carrying out the process with foam. Although centrifugal degassing pumps have been used, such as those in US Pat. Nos. 4,435,193 and 4,476,886 and Canadian patent no. 1,128,368, during many years in the pumping of liquid fibrous slurries of medium consistency (eg, approximately 6 to 18% solids) during the production of paper pulp and the like, its use in the pumping of the type of slurries that is used to carry out the process with foam until now has not been recognized as practical or as a solution to the long-time problems that have been encountered in carrying out processes with foam, as indicated above.

According to one aspect of the present invention, there is provided a method for producing a nonwoven web of fibrous material using a mobile foraminous element (such as a single cable, double cable or any other conventional foraminous element). The method comprises the following steps: (a) generating a first slurry in air foam, water, fibers and a surfactant, (b) centrifugally pumping the first slurry in foam to bring it into contact with the mobile foraminous element, (c) removing the substantially fiber-free foam from the foraminous element, while forming a non-woven web of fibrous material on the foraminous element, and (d) recycling at least part of the substantially fiber-free foam, from step (c), to its use in the practice of stage (a). The stage (d) preferably is practiced partly by centrifugally pumping the foam. Preferably, steps (b) and (d) are practiced by partially degassing the foam during centrifugal pumping thereof (e.g., using a centrifugal degassing pump as described in U.S. Patent Nos. 4,435,193 and 4,476,886 and the patent. Canadian No. 1,128,368). Steps (a) to (d) are preferably practiced using a movable foraminous element more than two meters wide (eg, 2.1 to 10 meters wide) to produce, in the manner of the nonwoven fibrous mesh, a mesh more than two meters wide. Likewise, steps (a) to (d) are preferably carried out to produce the non-woven mesh at a forming velocity of more than about 100 meters per minute (eg, at more than about 200 meters per minute, such as approximately 200 to 500 meters per minute). Preferably, centrifugal pumps are the only pumps used to pump both fibrous foam and slurries into fiber-free foam, in the practice of steps (a) to (d). In accordance with another aspect of the present invention, a process assembly with foam is also provided to produce a fibrous non-woven mesh. The assembly comprises the following components: a movable foraminous element in which a non-woven mesh can be formed; a source of a first, slurry in air foam, water, fibers and a surfactant agent; a first centrifugal pump for pumping the first foam slurry and bringing it into contact with the movable foraminous element, to form a non-woven mesh of fibrous material, while passing through the foraminous element a substantially fiber-free foam; and a recycling system that returns at least part of the foam substantially free of foam passing through the foraminous element to the source of the first foam slurry. The mobile foraminous element can be any conventional foraminous element, such as a single or double cable. The source of the first foam slurry can comprise any conventional source, such as a mixer / mill and / or a cable pit, and the foam injectors are typically used to facilitate the generation of foam after pumping and before the foam comes in contact with the foraminous element. The recycling system typically includes the pit with cables, several conduits and a second centrifugal pump (preferably, a degassing pump as described above), and the first centrifugal pump is preferably also a degassing pump. However, the recycling system can comprise any conventional component. The recycling system typically includes the pit with cables, and the second centrifugal pump foams substantially no fiber from the pit with cables to the mixer / mill. The foraminous element is preferably more than two meters wide, so as to produce a nonwoven mesh more than two meters wide. According to another aspect of the present invention, there is provided a method for using a degassing centrifugal pump The method comprises the following steps: pumping a slurry in foam that includes at least gas, water and surfactant towards the degassing centrifugal pump, while some gas is simultaneously removed from the slurry, during the production of a non-woven fibrous web by means of the foam process of the mesh production.This step is typically carried out by pumping a slurry in foam which also includes approximately 0.2 to 2.5% by weight, of fibers, and also pumping a substantially fiber-free foam, A main objective of the present invention is simply to effectively improve the performance of the process with foam to produce non-woven meshes, as well as to increase the practical width of the mesh and / or speed of formation.This and other objects of the invention will be apparent from of an examination of the detailed description of the invention, and of the claims.

Brief description of the drawings. Figure 1 is a general schematic illustration of a process system with foam, wherein the method of the invention can be carried out and the apparatus of the invention used; Figure 2 is a schematic view in detail, partially transverse and partially in elevation, showing the supply of a fiber / foam slurry from the mixer to the pump feeding the collector and main case of the system of Figure 1; and Figure 3 is a side view, almost transverse, but partially in elevation, of an exemplary degassing centrifugal pump, which is used in the practice of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS In figure 1 schematically shown with (10), an exemplary system of the process with foam to practice a process based on foam, with which it is convenient to use the invention. The system includes a mixing tank or mill (11) having an inlet (12) for fiber, an inlet (13) for surfactant and an inlet (14) for other additives such as pH adjusting chemicals, such as carbonate calcium or acids, stabilizers, etc. The particular nature of the fibers (whether glass, synthetic and / or cellulose or natural), surfactant and additives is not critical, and can vary greatly depending on the exact details of the product being produced (including its basis weight) . It is convenient to use a surfactant that can be easily rinsed, since a surfactant reduces the surface tension of the final mesh if it is still present, and it is a feature not suitable for some products. The exact amount of the surfactant used, of the thousands that are commercially available, such as those described in US Pat. Nos. 3,716,449, 3,871,952 and 4,856,456, which are not part of the present invention. The tank (11) is, merely, completely conventional, and is the same type of tank that is used as a mill in conventional papermaking systems that use the process with water. The only differences are that the side walls of the mixer / mill (11) extend upwards about three times the height than in the process with water, since the foam has a density of about one third compared to that of water. The configuration of the blade and the rpm of the conventional mechanical mixer in the tank (11), vary depending on the particular properties of the product to be produced, but is not particularly important, and a large variety of different and variable components can be employed. Also, the walls may be provided with brakes. There is a vortex at the bottom of the tank (11) from which the foam drains, but the whirlwind can not be seen once it starts working because the tank (11) is filled with foam and fiber. The tank (11) preferably also includes a large number of pH meters (15) at a number of different points. The pH affects the surface tension, and therefore it is convenient to determine it with precision. The pH meters are calibrated daily. At the moment of beginning, the water is added with the fiber from the line (12), the surfactant agent from the line (13) and other additives in the line (14); however, once the operation begins, no additional water is necessary and only the foam in the tank (11) is maintained, but there is no generation of it. The foam leaves the bottom of the tank (11), in a whirlpool, towards the line (16) driven by means of the pump (17). According to the invention, the pump (17), like all other pumps in the system (10), is preferably a degassing centrifugal pump. The foam discharged from the pump (7) passes in line (18) to other components. Figure 1 shows an optional reservoir tank (19) in dotted lines. The reservoir tank (19) is not necessary but may be convenient to ensure a relatively even distribution of the fiber in the foam, in case there was some variation that was adopted in the mixer (11). That is, the reservoir tank (19) (which is small, typically in the order of only five cubic meters) acts more or less as an "over-tank" to level the distribution of the fiber. Because the total time of the mixer (11) to the main box (30) is typically only about 45 seconds in the practice of the process, the tank (19) of deposit, if used, provides time to level the variations. When the reservoir tank (19) is being used, foam is supplied from the pump (17) in the line (20) to the top of the tank (19), and out the bottom of the tank in the line (21) driven by the centrifugal pump (22), then driven to the line (18). That is, when the reservoir tank (19) is used, the pump (17) is not connected directly to the line (18), but only through the tank (19). The line (18) extends towards the moat with cables (23). The cable trench (23) is merely a conventional tank, again the same as in the conventional water-based paper process system, but with higher sidewalls. It is important that in the cable pit (23) there are no dead corners and therefore the tank (23) is not very long. The conventional structure (24) that allows the mixture of fiber and foam in the line (18) to be introduced in the centrifugal degassing pump (25) (which is operatively connected adjacent to the bottom of the pit with cables (23)) will be described more in detail with respect to the figure 2. In any case, the pump (25) pumps the foam / fiber mixture in line (18), introduced by a mechanism (24), and additional foam from the moat with cables (23), inside the line (26). Because a relatively large amount of foam is introduced into the pump (25) from the cable pit (23), typically the consistency in the line (26) is significantly less than in the line (18) The consistency in line (18) is typically between 2 to 5% solids (fibers), while in line (26) it is between approximately 0.2 to 2.5 (for example, approximately 0. 5 to 5%), although the consistency in each case can be as high as approximately 12%. In the cable pit (23) there is no significant separation of the foam in layers of different density.

Although there is a minimum increase towards the bottom, the degree of increase is small and does not affect the operation of the system. From the line (26) the foam / fiber passes to the collector (27) having injectors (28) foam generators associated thereto. Preferably the injectors (28), which are conventional foam generating injectors (which stir the foam very well) as used in the patents? 449,? 952 and 782 incorporated herein by reference, are mounted on the manifold (27), and a large number of injectors (28) is mounted on the manifold (27). From each injector (28), a conduit (29) extends leading to the main box (30), through which one or more conventional cables pass to make paper, or any other suitable foraminous element. The main box (30) has a plurality of suction boxes (31) (typically three to five), which remove the foam from the opposite side of the cable (foraminous element) caused by the introduction of the foam / fiber mixture, and a final separation box (32) is located at the discharge end of the formed mesh (33) of the main box (30). The number of suction boxes (31) provided on the suction table to control drainage is increased for denser products or for higher speed operation. The formed mesh (33), which typically has a consistency of solids of about 40 to 60% (eg 50%), is preferably subjected to a washing action, as schematically indicated by means of the step (34) Washing in Figure 1. The high consistency of the mesh (33) means that a minimum amount of drying equipment needs to be used.

The mesh (33) passes from the washing device (34), with one or more optional covers (35), to the conventional drying station (36). When the synthetic roof / core fibers (such as Cellbond) are part of the mesh (33), in the conventional drying station (36) the drying device (34) is operated in a manner that elevates the mesh to the melting point of the cover material (typically polypropylene) while the core material (typically PET) does not melt. For example, where a Cellbond fiber is used in the mesh (33), the temperature in the drying device is usually about 130 ° C. or a little more, which is at the melting temperature of the cover fiber or slightly above, but well below the melting temperature of approximately 250 ° C. of the core fiber. In this way, the cover material provides a bonding action, but the integrity of the product (provided by the core fiber) is not compromised. Although not necessary, the process also contemplates the possibility of adding pure foam to the main box (30), or immediately adjacent to it, with a number of advantages. As seen in figure 1, the centrifugal pump (41) supplies foam from the cable pit (23) into the line (40). The foam in the line (40) is pumped to a head (42) which then distributes the foam to a large number of different ducts (43), towards the main box (30). The foam can be introduced, as indicated by line 44, directly below the roof of the main box (30) (where it is a main box for inclined cables) and / or by means of conduits (45) towards the lines (29) (or injectors 28) for introducing the foam / fiber mixture into the main box (30). The suction boxes (31) discharge the foam that was removed from the main box (30) in the lines (46) inside the cable trench (23). Typically, pumps are not needed or used for that purpose. A significant amount of the foam in the cable pit (23) is recalculated for the mill (11). The foam is removed in the line (47) by means of the centrifugal pump (48), and then passes in the duct (47) through the conventional in line density measuring device (49) to be introduced back into the tank (11), as indicated schematically in number (50). In addition to providing the density measurement of the foam in line (47) in (49), as schematically shown in Figure 1, one or more density measuring units (49A) (such as density meters) can be mounted. directly in the tank (11).

In addition to the recycling of the foam, there is also the recycling of water. The foam removed from the last suction box (32) passes through line (51) to a conventional separator (53), such as a cyclone separator. The separator (53), for example by whirling action, separates air and water from the foam introduced in the separator (53) to produce water containing very little air. The separated water passes in line (54) from the bottom of the separator (53) to the water tank (55). The air separated by the separator (53) passes in the line (56), with the help of a fan (57), from the top of the separator (53) and is discharged into the atmosphere or used in a combustion process or in some other way treated. A level (58) of liquid is established in the water tank (55), where some of the liquid is poured for drainage or treatment, as indicated schematically in (60) of Figure 1. The water is also take below the level (58) in the tank (55) through the line (61), and driven by the centrifugal pump (62) is pumped into the line (61) through a conventional flow measurement device (63) ( which controls the pump 62). Finally, the recycled water is introduced in the upper part of the mixer (11), as indicated schematically in (64) of figure i.

The typical flow rates are 4000 liters per minute of foam / fiber in the line (18), 40,000 liters per minute of foam / fiber in the line (26), of 3500 liters per minute of foam in the line ( 47), and 500 liters per minute of foam on the line (51). The system (10) also includes a number of control components. A preferred example of several alternatives for controlling the operation of the system comprises a first curled controller (71) that controls the level of foam in the tank (11). A second curled controller (72) that controls the addition of surfactant on line (13). A third curled controller (73) that controls the mesh formation in the area of the main box (30). A fourth curled controller (74) is used with the washing device (34). A fifth curled controller (75) controls the pH meters (15), and possibly controls the addition of other additives in the line (14) to the mixer (11). The curled control is also used for the surfactant agent and training control. A multivariable control system and a Neuronet control system are also provided preferably covering the other controls. Multivariable control is also used to control the flow rate in the formation of the mesh. The variables can be changed depending on their effect on the desired regulation of the process and the final result. To facilitate control of the various components, a balance (76) is typically associated with the fiber introduction (12) to determine exactly how much fiber is being added, per unit time. A valve (77) can be provided on the line (13) to control the introduction of the surfactant, as well as a balance (78). A valve (79) may also be provided in the line (14). In the system (10) there are essentially no valves provided to intentionally contact the foam at any point during its operation, with the possible exception of level control valves provided in the lines (46). Also, throughout the process practice of the system of Figure 1, the foam is maintained under relatively high cutting conditions. Due to the fact that the higher the cutting, the lower the viscosity, it is convenient to keep the foam under high cutting conditions. The foam / fiber mixture acts in the manner of a pseudo plastic, not exhibiting the Newtonian behavior. The use of the process with foam has a number of advantages compared to the process with water, particularly for highly absorbent products. In addition to the reduced drying capacity, due to the high consistency of the mesh (33), the foam process allows a uniform distribution of virtually any type of fiber or particle (without the excessive "stagnation" of the high density particles while the low density particles become " they stagnate "relatively - they do not completely stagnate in the water -) in the slurry (and finally the mesh), as long as the fibers or particles have a specific gravity of approximately 15 to 13. The process with foam also allows the production of a wide variety of meshes with basis weight, a product with increased uniformity and higher mass, compared to the products of the process with water, and a very high level of uniformity. A plurality of main boxes can be provided in sequence or two (or more) layers can be made at the same time within a main box with a double cable, etc., and / or the single layers (35) can be used to provide additional layers with great simplicity (like the coating). Figure 2 shows the introduction of the foam / fiber and foam mixture to the centrifugal degassing pump (25) associated with the pit (23) with the cables. The structure (24) is known from the Wiggins Teape process, as disclosed in the patents incorporated herein by reference, and the foam / fiber passing on the line (18) is caused to be re-directed, as shown, by means of the curved duct (83) so that through the open end (84) thereof the foam / fiber mixture is discharged directly into the inlet (85) of the pump (25). The foam coming from the pit (23) with cables also flows into the inlet (85), as shown by the arrows (86). The operation of the pump (48), given under the curled control, controls the level in the pit (23) with cables.

When the fibers to be used for making the foam are particularly long, that is, in the order of several centimeters, instead of directing the line (18) to the suction inlet (85) of the pump (25) ( as seen in figure 2), line 18 ends in line (26) downstream of pump (25). In this case, the pump (17) must of course provide a higher pressure than it otherwise would have, that is, sufficient pressure so that the flow of the (18) is in the line (26) despite the the pressure in the line (26) of the pump (25). A typical degassing pump that can be used in the manner of any of the pumps (17), (25), (41), (48), (62), in accordance with the present invention, is generally shown with the reference number (110) in Figure 3, and is basically the same as a conventional MC® pump sold by Ahlstrom Machinery Inc. and Ahlstrom Machinery Oy , and shown in US Pat. Nos. 4,435,193 and 4,476,886, and Canadian patent no. 1,128,368. The pump (100) typically comprises a conventional helical sleeve (102) with an axial input channel (104), and preferably a tangential discharge channel (106) with a pressure opening (108). In addition, the sheath comprises a sheath cover (110) and has a rotating or central axis (112). Within the helical cover (102) an impeller (114) is mounted on the shaft (112). The impeller (114) may comprise a substantially radial disc (116), on the front surface thereof (on the side of the entrance channel) there are working blades (118). Rear pallets (120) are also provided on the rear side of the propeller (114). An opening or several openings (122) extend through the disc (116), preferably close to the axis (112). The gas accumulated in the front part of the propeller (114) flows through the opening (s) (122) to the volume (1210 behind the impeller (114), ie to the volume (121) between the disc (116) and cover (110) of the pump sheath (100) The shaft (112) is rotated by any suitable source of energy, such as the electric motor shown schematically in (123) of Figure 3. The cover (110) of the cover is also provided with an annular gas outlet channel (124) around the shaft (112) or special openings (not shown) in the cover (110) of the sleeve to remove the gas separated from the volume (121) behind the propeller (114). The gas outlet channel (124) (or openings) is connected to a suction device (shown only schematically at (125) of Figure 3) which is used to create a necessary underpressure for gas removal. The suction device (125) is usually a liquid ring pump, that is, a Nash pump (so called by the traditional manufacturer of these pumps). The suction device (125) can be mounted on the same shaft (112) as the propeller (114) or provided as a separate operation device apart from the centrifugal pump (100). In Figure 3, the suction device (125) is positioned separately from the pump (100), and therefore the gas removal system of the pump (100) includes a channel (126) which is used to remove the gas or foam generated in the pump (100) towards the suction device (125). Figure 3 also shows how in cases where a large amount of fibers is conducted to the gas separation system, the separating wheel (128) can be mounted in the gas separation system, said separating wheel (128) pumps the fibers in the gas flow, due to the operation of the rear vanes (120), away from the pump (100) in the duct (130) so that the fibers do not enter the suction device (125). Wheel (128) or the like is usually not necessary particularly in short circulation applications since almost no fiber is trapped in the gas flow eliminated, and therefore its damaging effect on the suction device (125) is almost non-existent . The pump (100) described above operates so that the material in the suction channel (104) of the pump (100) starts to rotate due to the effect of the propeller (114), so that the gas in the material is collected in the front part of the propeller (114) in the manner of a gas bubble. When the effect of the suction device (125) described above is directed through the gas outlet channel (124), or openings in the cover (110) of the sheath, towards the volume (121), behind the impeller (114). ), on the front side of the propeller (114), the gas in the bubble starts to flow in the direction of the suction device (125). Suction in some exceptional cases can also start to conduct liquid and even fibers within the volume (121). In such a case, the rear vanes (120) of the propeller (114) are used to separate the liquid and / or fibers from the gas to form a separate flow which is then returned through the outer edge of the disk (116) to the main flow, and be removed from the pump (100) through the pressure outlet (108). Thus, it will be seen that, as described above, a process assembly with foam is provided to produce a fibrous non-woven mesh. The process assembly with foam includes a conventional movable foraminous element in the main box (30) on which a non-woven mesh can be formed, and a source of a first foamed slurry of air, water, fibers, and a surfactant. The source may comprise a mixer / mill (11) and / or the pit (23) with cables. A first centrifugal pump (17 or 25) pumps the first foam slurry into contact with the movable foraminous element in the main box (30) to form a non-woven mesh, while a substantially fiber-free foam passes through of the foraminous element. A recycling system, which may include the suction boxes (31), the pit (23) with cables, the conduit (47) and a second centrifugal degassing pump (48), returns at least part of the foam substantially without fiber that it passes through the foraminous element towards the source. For example, where the conduit (47) or pump (48) are used, they return part of the foam that passes through the lines (46) into the pit (23) with cables to the mixer / mill (11) . The pump (25) typically pumps the foamed slurry including fibers through the nozzles (28) that generate foam to bring it into contact with the foraminous element in the main case (30), and needs to be the only pump to do so. Because centrifugal pumps have a much larger capacity than positive displacement pumps, the foraminous element can be more than two meters wide (for example, from 2.1 to approximately ten meters wide) and still only one single pump (25). Also, the use of a centrifugal pump, such as the pumps (25) and (48), allows the formation speed to increase significantly, compared with known process systems with foam, to more than about 100 meters per minute, and made more than about 200 meters per minute (for example, approximately 200 to 500 meters per minute). In the practice of the method and use of the system, according to the present invention the typical parameters of the process with foam that can be used are established in the following table (although the index of the parameters can be much broader if the index of the product Is wider) : PARAMETER VALUE pH (substantially all the system) approx. 6.5 Temperature approx. 20-40 ° C. Collector pressure 1-1.8 bars Consistency in the mixer 2.5% Consistency in the main box .2-2.5% Consistency of the SAP additive approx. 5-20% Consisting of the mesh formed approx. 40-60% Variations of the base weight of the mesh less than% Density of the foam (with or without fibers) 250-450 grams per liter at 1 bar. Bubble bubble size average diameter of .3 - .5mm. (Gaussian distribution) Air content in the foam 25-75% (eg approximately 60%, pressure changes in the process). Viscosity there is no "target" viscosity but typically the foam has a viscosity in the order of 2-5 centipois under high cutting conditions, and from 200k - 300k centipois in low cutting conditions, said indexes may be wider depending on the way to determine the viscosity. Mesh formation speed approx. 200 to 500 meters per minute. Specific gravity of the fibers or additives, any in the index of .15-13. Concentration of the surfactant depends on many factors, such as water hardness, pH, type of fibers etc. Normally, between 0.1-0.3% of water in circulation Tension of the forming cable between 2-10 N / cm. exemplary flow rate - - mixer to the pit with cables approx. 4000 liters per minute - pit with cables to the main box approx. 40,000 liters per minute - foam recycle pipe approx. 3,500 liters per minute • - removal of the suction in approx. 500 liters recycled water per minute A main objective of the present invention is to provide very advantageous modifications of the foam-based process. Although the invention herein has been shown and described in what is now conceived to be the most practical and preferred embodiment thereof, it will be apparent to those skilled in the art that many modifications may be made thereto within the scope of the invention , said scope being the broadest interpretation of the claims below to encompass all equivalent methods and assemblies.

Claims (17)

Claims

1. A method for producing a nonwoven web of fibrous material using a movable foraminous element, said method includes the following steps: (a) generating a first slurry in air foam, water, fibers and a surfactant; (b) centrifugally pumping the first foam slurry, in contact with the movable foraminous element; (c) removing the foam substantially without fiber from the foraminous element, while forming a non-woven web of fibrous material on the foraminous element; and (d) recycling at least part of the substantially fiberless foam of step (c) for use in the practice of step (a), characterized in that, in step (b), the foam is partially degassed during the centrifugal pumping of it.

2. A method according to claim 1, characterized in that step (b) is carried out partly by centrifugally pumping the foam.

3. A method according to claim 2, characterized in that the step (d) is carried out by partially degassing the foam during the centrifugal pumping thereof.

4. A method according to claim 1 or 3, characterized in that steps (a) to (d) are carried out using a movable foraminous element more than two meters wide to produce, in the manner of the nonwoven fibrous mesh , a mesh more than two meters wide.

5. A method according to claim 4, characterized in that steps (a) to (d) are carried out to produce the nonwoven web at a forming velocity of more than about 100 m / min.

6. A method according to claim 4, characterized in that steps (a) to (d) are carried out to produce the non-woven mesh at a rate of formation of more than about 200m / min.

7. A method according to claim 1, characterized in that the only pumps used for pumping, either in the fibrous foam slurry, or in the foam slurry substantially without fiber, in the practice of steps (a) to (d) ), are centrifugal pumps.

8. A process assembly based on foam to produce a non-woven mesh of fibrous material, said process assembly having: a movable foraminous element on which the non-woven mesh can be formed; a source of a first foamed slurry of air, water, fibers and a surfactant; a first pump for pumping the first foamy slurry and bringing it into contact with the movable foraminous element, to form a non-woven mesh of fibrous material therein; and a recycling system that returns at least part of the substantially fiberless foam passing through the foraminous element to the source of the first foam slurry, characterized in that said first pump is a degassing centrifugal pump.

9. A process assembly based on foam, according to claim 8, characterized in that said recycling system includes a second centrifugal degassing pump.

10. A process assembly based on foam, according to claim 8, characterized in that said recycling system includes a second centrifugal pump.

11. A process assembly based on foam, according to claim 8, characterized in that said foraminous element is more than two meters wide to produce a non-woven mesh of more than two meters in width.

12. A process assembly based on foam, according to claim 11, characterized by foam generating injectors located between said first centrifugal pump and said foraminous element, and wherein said first centrifugal pump pumps the first foam slurry through said injectors foam generators, and is the only pump that pumps the first foam slurry through said foam generating injectors.

13. A process assembly based on foam, according to claim 8, characterized in that said source comprises a mixer / mill and a pit with cables.

14. A process assembly based on foam, according to claim 13, characterized in that said recycling system includes said pit with cables, and a second centrifugal pump for pumping foam substantially without fiber from said pit with cables to said mixer / mill.

15. The use of a degassing centrifugal pump, for pumping a slurry in foam that includes at least gas, water and a surfactant, while simultaneously removing some gas from the slurry, during the production of a fibrous nonwoven web by means of the process with foam of the production of the mesh.

16. The use according to claim 15, characterized in that said foam slurry also includes from about 0.2 to 2.5% by weight of fibers.

17. The use according to claim 15, characterized in that said foam slurry is a foam substantially free of fiber.