Bag for bag filters and related manufacturing process

Abstract

The invention is a bag (100) for bag filters, comprising a tubular body or wall (200) made of a filtering material and a basket (600) reversibly inserted in said tubular wall (200). Said tubular wall (200) is completed or partially pleated, or in any case constituted by a succession of pleats (210) or curves, and comprises one or more sheets made of a filtering material that has undergone a stiffening treatment intended to give the material a certain shape memory.

Description

[0001] BAG FOR BAG FILTERS AND RELATED MANUFACTURING PROCESS DESCRIPTION

[0002] The present patent concerns the bag filters used for dust abatement in industry, and in particular it concerns a new bag for bag filters and the related manufacturing process.

[0003] Bag filters are known and are commonly used for dust abatement in gas streams of industrial processes such as, for example, grain processing plants, mechanical machining plants, etc.

[0004] Bag filters comprise a closed container in which a set of cylindrical bags are mounted vertically and side by side.

[0005] Each bag has a closed bottom end and an open end connected to an air suction system by means of which the gas stream to be purified, loaded with dust, is sucked into the container, passes through the material of which the bags are made, from the outside towards the inside, and is conveyed into an exhaust duct.

[0006] The dust carried by the current, on the other hand, comes into contact with the surface of the bags and adheres to it, forming a layer of dust that will also have a filtering function.

[0007] However, said dust layer causes a progressive increase in pressure drops, and for this reason the bags must be periodically cleaned to remove the dust deposited on their surface. For said purpose, shaking systems, generally using compressed air, are known, which cause the dust layer to come off and accumulate on the bottom of the container, from where it is removed to be subsequently disposed of.

[0008] The process of cleaning the bags by introducing air in countercurrent, that is, from the inside towards the outside of the bags, so that the air flow causes the dust to come off the bags, is also known.

[0009] The bags are usually made of non-woven fabric, polyester or polypropylene or cotton, with different possible grammage values, generally included between 300 and 600 g / m2, thickness and / or density, and consist of a sheet of said material, wrapped and sewn or glued along two opposite edges to form a cylindrical side wall.

[0010] With the known bags, filtration takes place “in depth”, that is, the entire thickness of the filtering material contributes to retaining dust.

[0011] The production process for the bags of the known type also includes the shaping of their ends and in particular requires that one end be closed by sewing or gluing a bottom made of the same material, and that the opposite end be left open, reinforced along the entire annular edge and configured to be fixed in a special housing present in a bag filter.

[0012] In fact, the open top ends of the bags are constrained in said bag filter housings, in which an annular gasket is also fitted to ensure airtightness during suction, to prevent the introduction of dust that would otherwise be sucked in together with the purified air or gas.

[0013] Inside each bag there is usually a basket, that is, a cylindrical net, usually a wire net, or in any case a net having a certain rigidity, the purpose of which is to prevent the bags from collapsing during suction.

[0014] Finally, the bags are periodically replaced. In this regard, the problem related to the need to transport and store large quantities of said bags, which are usually flattened and folded to reduce their overall dimensions, is known.

[0015] This is possible thanks to the fact that the material normally used to make the known bags does not have any shape memory.

[0016] Consequently, the bag cannot be configured in shapes other than cylindrical. The already mentioned bags are known, whose ends are pleated and sewn in such a way that curves are formed on the tubular wall and the cross section of the bag thus substantially takes the shape of a star. However, since, as mentioned, the material used has no shape memory, it is still necessary to use an inner basket having the same star-shaped cross section in order for the bag to maintain the desired shape during use. Moreover, the manufacturing process of said type of bags is rather complex and expensive.

[0017] The so-called cartridges are also known, which consist of a rigid tubular filtering body made of a very thin filtering material in a grammage included between 100 and 250 g / m2. Said material must be coupled with an inner reinforcing basket in a stable manner.

[0018] In other types of filters, filtration takes place superficially.

[0019] A drawback of the known cartridges lies in that they have a rigid tubular structure, which may have a non-circular cross section, for example starshaped, but which cannot be folded and / or flattened to reduce their overall dimensions during storage and transport.

[0020] The subject of the present patent is a new type of bag for bag filters, including among its main objects the maximization of the filtering surface, which is achieved by using the same filtering material normally used in the known bags, meaning a folding material, thus allowing the overall dimensions of the bag to be reversibly compacted during storage and transport.

[0021] Therefore, it is another object of the present invention to also reduce pressure drops and energy consumption of the filter, as well as to increase the filtration efficiency and time of use of the bag before it needs cleaning and replacing.

[0022] As a result, the frequency of cleaning operations on the bag and the frequency of replacement of the same will thus be reduced.

[0023] Furthermore, for the same filtering surface, the new bag can be shorter than the currently known bags. All this brings consequent important advantages in terms of storage space reduction and transport costs.

[0024] These and other direct and complementary objects are achieved by the new bag comprising a tubular body, wherein the side wall is made from the same filtering material normally used in the known bags after it has undergone a stiffening treatment, and is pleated or in any way constituted by a succession of pleats or curves, preferably extending in a direction parallel to the axis of the tubular body.

[0025] Given the same overall volume, the new bag thus has a larger filtering surface than a bag of the known type, which has a smooth cylindrical side wall.

[0026] In the preferred solution, said side wall is pleated, that is, formed by a succession of pleats preferably included between 8 and 30 mm in height, and wherein said pleats are preferably in a number included between 10 and 60.

[0027] The shape of said pleats, which are preferably V-shaped, also contributes substantially to stiffening the lateral surface of the bag.

[0028] Thanks to the increased filtering surface, the filtration efficiency of the new bag is increased by 20 to 250%, depending on the number, shape and size of the pleats, compared to a bag having the same volume and made of the same material.

[0029] In particular, said tubular wall is made of one or more sheets of filtering material in polyester or polypropylene, but can also alternatively be made of cotton, aramid, fiberglass, PTFE felt or Ryton, etc., meaning any material currently used to make the bags of the known type. The grammage of said material is therefore preferably included between 300 and 600 g / m2.

[0030] In a preferred solution, said at least one sheet of filtering material comprises a covering film applied to at least one face, which will preferably form the inner face of the tubular wall of the new bag. The main object of said film is to stiffen said sheet, allowing it to be folded, and to prevent or at least limit any deformation of the bag during use in a bag filter, without however modifying the filtering capacity of the bag.

[0031] Said covering film is, for example, made of polyester or acrylic or polypropylene or another suitable material and is preferably applied to said sheet of filtering material by gluing.

[0032] Said film coupled with said sheet of filtering material makes it possible to create pleats on the latter.

[0033] The combination of said pleats and said glued stiffening film also makes the bag considerably rigid during use, while still allowing it to be flattened and possibly folded during storage and transport, as the filtering material has acquired sufficient shape memory.

[0034] Thus, differently from the known bags made of the same material, which can be reversibly compacted but cannot be shaped with pleats, and differently from the known cartridges, which are instead made of a more rigid material that cannot be reversibly compacted, the new bag combines the advantages of the two previous solutions, as it can have a star-shaped cross section, that is, formed by a series of said pleats that remain undeformed even without the aid of a correspondingly configured inner basket, and furthermore can be reversibly compacted without affecting the pleated shape during subsequent use.

[0035] Said tubular wall of the new bag comprises two opposite ends, of which a first end is intended to be tightly connected to a housing in a bag filter and a second end is intended to be closed by a bottom body or connected to a second tubular wall.

[0036] According to the invention, in fact, a tubular wall can be joined to one or more further identical tubular walls in order to obtain a bag of greater modular length, for example exceeding 1.5 m. In this case, according to the invention, an annular connection body, for example made of elastomer or plastic or metal, can be inserted between two tubular walls.

[0037] A coupling flange, for example and preferably made of a flexible material, such as polyurethane, polypropylene or other rubbers, and obtained by moulding directly on said first end, or produced separately and subsequently glued to said first end, is integrally mounted on said first end of said tubular wall, in a preferably non-removable manner.

[0038] Alternatively, according to the invention, said coupling flange can instead be made of fabric, for example of the same filtering material used to make the filtering tubular wall of the bag, and sewn onto said first end of said tubular wall itself.

[0039] Alternatively, according to the invention, said coupling flange can instead be made of a metallic material and glued to said first end of the tubular wall. Said coupling flange is configured to be tightly coupled with a housing in a bag filter. According to the invention, for example, it can be shaped in such a way that it has an external shaped recess suited to accommodate an annular gasket positioned therein for airtight connection with said housing in the bag filter.

[0040] More specifically, as described and claimed below, said coupling flange can be configured according to the type of housing in which it must be installed. Said coupling flange, furthermore, is also preferably configured so that it can be coupled with a stiffening basket intended to be inserted in the tubular wall. The bag can in fact comprise a basket, for example of the known type, which in turn comprises a tubular net, preferably a wire net.

[0041] Alternatively, the bag comprises a basket in turn comprising a tubular part, preferably cylindrical, for example made from stretched or perforated or electrowelded wire net, or in any case perforated so as not to prevent filtration, possibly with a bottom, and an open top end with a flange mounted thereon, said flange being especially configured to be coupled with said coupling flange of said first end of the bag to ensure the correct assembly of the latter as well as airtightness.

[0042] Said flange of the basket is made, for example, of a preferably rigid plastic material such as polyurethane, ABS, Nylon, or metal.

[0043] The subject of the present patent also includes the process for making the new bag, wherein said tubular filtering wall is formed by folding a sheet of said filtering material with a plurality of pleats whose folding lines are preferably all parallel to one another and to a direction that constitutes the length or height of the tubular wall itself.

[0044] Said folding step is preferably carried out after a treatment step to which said sheet is subjected in order to give the material sufficient shape memory to allow said pleats to be created without seams.

[0045] For example, said treatment step involves the application of said stiffening film to the entirety or part of at least one face of said sheet, and more preferably to the face of said sheet that will constitute the inner face of the tubular body.

[0046] After or during the folding of said sheet, the same is curved to form said tubular wall.

[0047] Said sheet can be folded through mechanical processes and / or through a hot forming process.

[0048] A material that can be used to make said tubular wall can be non-woven fabric made from polymer chips, which are then extruded and spun, or from fibres that are processed chemically, by heat, or mechanically.

[0049] The material used to make said pleated tubular wall must therefore be sufficiently rigid.

[0050] Said stiffness of the material can be obtained by choosing bicomponent fibres or non-woven fabric produced from polymer chips with a high degree of hardness and stiffness such as, for example, polyester.

[0051] It is also possible to obtain a sufficiently rigid material by treating the fibrous layer with polymer solutions of various kinds, having certain stiffness characteristics once the polymer itself has been polymerized.

[0052] Alternatively, it is possible to use additives suited to make the material rigid to the desired degree and thus to allow pleats to be made on it.

[0053] If, instead, the material to be used must feature a certain degree of softness, the soft material sheet can be coupled with a rigid material, for example through a hot coupling process, with or without the addition of liquid or solid glues, or through a mechanical or electrostatic process.

[0054] A material can also be stiffened by using nets with appropriate thickness and shape and made of a metallic polymeric material or nets with glass fiber, plastic films or paper materials.

[0055] Thanks to the characteristics of the material used, said folding step intended to obtain said pleats on the tubular wall of the bag can be very conveniently performed by means of pleating machines, with consequent advantages in terms of production time and costs compared to the currently used folding processes that require complex sewing operations or the use of ultrasound.

[0056] Said coupling flange is then applied to said first end of said tubular wall, wherein said application can be carried out by directly moulding said flange on said first end, so that the moulding of the coupling flange takes place at the same time as its application to said first end.

[0057] Alternatively, according to the invention, said coupling flange can be made separately and then applied to said first end by a sewing or gluing operation. The characteristics of the new bag are better clarified in the following description, making reference to the drawings, which are attached by way of non-limiting example.

[0058] Figure 1 shows a three-dimensional view of the new bag (100), while Figure 2 shows a detail of the coupling flange (300) mounted on the top end (230) of the tubular wall (200) of the bag (100).

[0059] Figure 3 shows a three-dimensional view of a basket (600) suited to be inserted in the tubular wall (200) of the bag (100), while Figure 4 shows a detail of the flange (800) of the basket (600).

[0060] Figure 5 schematically shows how the new bag (100) can be compacted by flattening and folding it even several times in order to reduce its overall dimensions.

[0061] The new bag (100) comprises a tubular body or wall (200) made of a filtering material and pleated, or in any case consisting of a succession of pleats (210) or curves, preferably oriented parallel to the axis (X) of the tubular body (200).

[0062] In the solution shown in Figures 1 and 2, said side wall (200) is pleated, that is, formed by a succession of said substantially V-shaped pleats (210), with folding lines that are all parallel to one another and to said axis (X).

[0063] Said pleats (210), regardless of their shape, are preferably between 8 and 30 mm in height, and are preferably in a number included between 10 and 60.

[0064] Said tubular wall (200) of the new bag (100) comprises two opposite ends, of which a first end (230) is intended to be tightly connected to a housing in a bag filter and a second, opposite end (240) is intended to be closed by a bottom body (400) or connected to a second tubular wall (200’) by means of a connection body or ring (500).

[0065] In the example shown in Figure 1, said bag (100) comprises, for example, two of said tubular walls (200, 200'), which are coaxial and joined by means of said connection ring (500).

[0066] Said first end (230) of said tubular wall (200) is provided with a coupling flange (300) having an annular body (310) and a collar (320) which covers said first end (230) both internally and externally, also following its pleated outline, in order to ensure airtight connection with the tubular wall (200).

[0067] Said annular body (310) is externally shaped with an annular recess (311) intended to ensure airtight connection with the housing in the bag filter.

[0068] Internally, said annular body (310) is preferably shaped with one or more protrusions or seats for coupling with the correspondingly shaped flange (800) of a basket (600), as described below.

[0069] In the solution shown in Figure 2, said annular body (310) is, for example, internally shaped with an annular protrusion (312) matching corresponding grooves (812) on the outer surface of the flange (800) of a basket (600).

[0070] Opposite to said top end (230), the bag (100) comprises a closed bottom element (400), for example made of the same material and in the same manner as said coupling flange (300).

[0071] According to the invention, one or more containment clamps (700) can also be applied externally to said tubular wall (200) and be made, for example, of polyester fabric or of the same filtering material used to make said tubular wall (200). Said clamps (700) are, for example, glued or welded, for example through ultrasonic welding, or sewn onto said filtering tubular wall (200). The new bag (100) preferably comprises also at least one basket (600) suited to be axially inserted in said at least one tubular wall (200) in a removable manner.

[0072] Said basket (600) comprises a preferably cylindrical tubular net (610) having a first end (620), on which there is a flange (800) suited to be coupled with said coupling flange (300) of the bag (100), and a second, opposite end (630) provided with a closed bottom (640), for example made of the same material used for making said flange (800).

[0073] Said flange (800) of the basket (600) is, for example, made of a preferably rigid plastic material such as polyurethane, ABS, Nylon, or metal, and comprises an annular body (810) externally shaped for coupling with said annular body (310) of the coupling flange (300) of the bag (100).

[0074] More specifically, as can be seen in Figure 4, said annular body (810) of the basket (800) can be externally shaped with radial protrusions (811) and grooves (812) for the engagement of said annular protrusion (312) present on the inner side of the annular body (310) of the coupling flange (300) of the bag (100).

[0075] According to the invention, said flange (800) of the basket (600) can be internally provided with partitions (813) that are useful for keeping the annular body (810) against the annular body (310) of the coupling flange (300) of the bag (100).

[0076] The new bag (100) thus has a maximized filtering surface due to the presence of said pleats (210) of said tubular wall (200), which in turn are obtained thanks to the special material used. In any case, the bag (100) can be reversibly folded and compacted, for example as shown in Figure 5, and can subsequently be unfolded and opened again, returning to the pleated configuration shown in Figure 1.

[0077] Therefore, with reference to the above description and the attached drawings, the following claims are made.

Claims

CLAIMS1. Bag (100) for bag filters, comprising a tubular body or wall (200) made of a filtering material and a basket (600) reversibly inserted in said tubular wall (200), characterized in that said tubular wall (200) is completely or partially pleated or in any way constituted by a succession of pleats (210) or curves, and wherein said tubular wall (200) comprises one or more sheets made of a filtering material that has undergone a stiffening treatment intended to give the material a certain shape memory.

2. Bag (100) according to claim 1, characterized in that said tubular wall (200), once said basket (600) has been extracted, can be deformed and folded in a reversible manner.

3. Bag (100) according to claim 1, characterized in that said at least one sheet made of a filtering material comprises a stiffening film applied to the entirety or part of at least one of its faces, and more preferably at least on its face forming the inner side (220) of said tubular wall (200).

4. Bag (100) according to the preceding claim, characterized in that said covering film is preferably applied to said at least one sheet by gluing and is preferably made of one or more materials selected from: polyester, acrylic, polypropylene.

5. Bag (100) according to the preceding claim, characterized in that said tubular wall (200) comprises a plurality of pleats (210) with a folding line oriented parallel to the direction of the longitudinal axis (X) of said tubular wall (200) itself, and wherein said pleats (210) are between 8 and 30 mm in height and are in a number included between 10 and 60.

6. Bag (100) according to one of the preceding claims, characterized in that said tubular wall (200) is completely or partially made of one or more materials selected from: polyester, polypropylene, cotton, aramid, fiberglass,PTFE felt or Ryton, etc.

7. Bag (100) according to one of the preceding claims, characterized in that said tubular wall (200) comprises a first end (230) intended to be tightly connected to a housing in a bag filter, and a second opposite end (240) intended to be closed by a bottom body or connected to a second tubular wall (200), and wherein said first end (230) is provided, integrally and preferably non-removably, with a coupling flange (300) configured to be tightly connected to said housing for a bag filter.

8. Bag (100) according to the preceding claim, characterized in that said coupling flange (300) comprises an annular body (310) and a collar (320) which covers said first end (230) of the tubular wall (200) both internally and externally, following its pleated profile, and wherein said annular body (310) is: externally shaped with an annular recess (311) for airtight connection to a housing in the bag filter; internally shaped with one or more protrusions (312) or seats for coupling with the correspondingly shaped flange (800) of a basket (600).

9. Bag (100) according to one of the preceding claims, characterized in that it comprises two or more of said tubular walls (200, 200') coaxially joined to each other by means of an annular connection body (500).

10. Bag (100) according to one of the preceding claims, characterized in that said basket (600) comprises a tubular net (610) and an end (620) provided with a flange (800) configured for the airtight coupling with said coupling flange (300) of said tubular wall (200).

11. Process for making a bag (100) according to one or more of the preceding claims, characterized in that it comprises the step of folding at leastone sheet made of a filtering material intended to form said tubular wall (200), and wherein said folding step takes place downstream of a step in which said at least one sheet undergoes a treatment intended to give the material sufficient shape memory to make said pleats (210) without seams.

12. Process according to claim 11 , characterized in that said treatment step to which said sheet is subjected comprises the coupling of said stiffening film by gluing.

13. Process according to claim 11, characterized in that it comprises the step of shaping said coupling flange (300) of said tubular wall (200), which is performed according to the configuration of the bag filter housing in which said bag (100) must be installed.

14. Process according to claim 13, characterized in that said coupling flange (300) is obtained by direct moulding on said first end (230) of the tubular wall (200).

15. Process according to claim 13, characterized in that said coupling flange (300) is constrained to said first end (230) of said tubular wall (200) by gluing or sewing.

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