Technical field The present disclosure relates to air filters for use in industrial vacuum cleaners, and specifically to a bag filter technology for use such a vacuum cleaner.

Background Industrial vacuum cleaners are commonly used to filter particles from an air stream in order to collect the particles in a receptacle. The air passing through the vacuum cleaner may pass several separation steps before being blown out of the vacuum cleaner again. An example of such a filter step is a cyclone which separates larger particles. Another separation step is usually needed to catch finer particles, if desired. Fine particles may be separated from the air stream using a suitable filter comprising a filter material chosen to only let particles smaller than a predetermined size through with the air stream, whilst larger particles than that are trapped in/on the filter media. A challenge is to allow such filters to operate for a long time before needing to be replaced. The vacuum cleaner is sometimes designed to allow the filter to be checked ‘chocked’ to loosen some of the particles and have them fall down in the receptacle 15. However, not all filter designs allow them to be chocked. Also, a challenge is to design the filter such that a high enough air flow is allowed to run through the filter whilst keeping the size of the filter small.

Summary

An object of the invention is to provide a filter which can separate small particles, such as dust from a concrete polishing/grinding process or any other type of dust normally occurring in industrial environments, from an airflow whilst allowing long lifetime of the filter before it need to be replaced. Another object of the present disclosure is to provide a filter which allows a high airflow whilst keeping the size of the filter down. Another object of the present invention is to provide a filter which allows a high airflow whilst minimizing the pressure drop of said airflow through the filter.

According to a first aspect of the present disclosure, these and other objects are achieved by a bag for a filter for filtration of particles in a gas flow according to claim 1 or any one of its dependent claims 2-6. The bag comprises: a tubular outer layer comprising a first end portion and an opposite second end portion, and a tubular inner layer configured to extend inside the tubular outer layer from an open end portion of the tubular inner layer at the second end portion of the tubular outer layer at least partly along an extent of the tubular outer layer, to a closed end portion of the tubular inner layer, wherein the tubular outer layer is connected to the open-end portion of the tubular inner layer, and wherein the tubular inner layer and the tubular outer layer are shaped and sized such that a circumferential space is formed between the tubular inner layer and the tubular outer layer.

The combination of the tubular outer layer and the tubular inner layer extending inside the tubular outer layer provides a large surface area for filtering of particles from the airflow. Air enters the filter bag through the tubular outer layer from radially outside the tubular outer layer, through the tubular outer layer and into the circumferential space. Air also enters the filter bag through the open-end portion of the tubular inner layer where it passes from radially inside the tubular inner layer and into the circumferential space. The circumferential space between the tubular outer layer and the tubular inner layer provides a passage for filtered air to flow through to exit the bag.

By providing a large surface area for filtering, the pressure drop of the airflow through the filter may be reduced. A reduced pressure drop is advantageous in that less suction force is required for sucking the airflow through the filter. A further advantage of a reduced pressure drop is the that local strain acting on the filter material is also reduced, which may prolong the lifetime of the filter. Still further, a reduced pressure drop of the airflow through the filter enables an increase of the filtering capacity as well as permitting the dimensions of the filter, e.g. diameter, length, etc., to be kept to a minimum.

The connection between the tubular outer layer and the tubular inner layer may be formed by a hollow disc-shaped connecting member attached to the tubular outer layer and to the tubular inner layer.

The hollow disc shaped member separates the tubular inner layer and the tubular outer layer at the second end portion, thereby ensuring the circumferential space is not tapering to a narrow shape at the second end portion, which in turn enables improved fluid flow at the second end portion.

The connecting member may be made from a gas permeable filter material, such as needle felt.

Needle felt is a suitable material for filtering small particles such as dust in industrial environments. Also, the needle felt material allows a dust cake formed on the cake side of the filter to separate from the filter material and fall off into a suitable receptacle for cleaning of the filter, thus prolonging the lifetime of the filter. Furthermore, needle felt material enables dust particles to penetrate and lodge themselves within the material thereby increasing the filtering capacity of the filter and reducing the filtering time.

The connecting member may be sewn to the tubular inner layer and to the tubular outer layer.

The closed end portion of the tubular inner layer is sewn closed.

The tubular outer layer may be formed from a rectangular piece, and the tubular inner layer formed from a rectangular piece of material folded such that it is closed at its closed end portion.

Forming the closed end portion of the tubular inner layer by folding is a simple yet robust way of closing the tubular inner layer.

The closed end portion of the tubular inner layer is sewn closed.

Sewing is a simple yet robust way of ensuring the closed end portion is kept closed whilst enabling high airflow.

According to a second aspect of the present disclosure, the objects are also achieved by a filter assembly comprising a bag and a cage, according to claim 8 or any one of its dependent claims. The filter assembly is for filtration of particles in a gas flow and the filter assembly comprises a bag as described above, and a cage configured to extend between the tubular outer layer and the tubular inner layer for supporting the bag such that the tubular outer layer is extended.

The cage supports the tubular outer layer from within and allows is to withstand overpressure acting on the radially outer side of the tubular outer layer such that the shape of the bag is maintained even at high pressure difference on the cake side and on the clean air side of the layers. The cage also maintains the bag in its extended state before use and in use. Yet, the bag can be replaced when it has reached its end of life and a new bag be fitted on the cage. Replacing only the bag is more environmentally friendly than replacing a whole filter assembly and spare bags can be stored flat/folded to save space. The cage may be designed such that upon the gas flow entering the filter assembly, the tubular inner layer is adapted to move freely in a radial direction to an axis longitudinally extending from the first end portion to the second end portion. In other words, the cage only restricts the radial movement of the tubular outer layer. This is advantageous in that the free radial movement of the tubular inner layer enables a better distribution of the airflow in the circumferential space, decreasing the strain concentrations on both the tubular outer layer and tubular inner layer resulting in a longer lifetime of the filter assembly. The tubular inner layer is therefore not required to be directly attached to, or constrained by, a supporting structure along its length, thereby enabling the cage to encompass a less complex structural design, i.e. a structure only providing radial support along the length of the tubular outer layer. A less complex structural design of the cage reduces the disrupting effect the cage components have on the airflow inside the filter.

This in turn results in a reduction of turbulence in the airflow thereby lowering the pressure drop through the filter. Additionally, a less complex structural design reduces the amount of material required for producing the cage, which reduces its weight as well as its cost of production. The manufacturing and the assembly process of a filter assembly are also simplified by the less complex structural design of the cage.

Further, when in use, the cage enjoys an improved stability when withstanding high-pressure generated by the incoming airflow in comparison to cages having complex structural designs, e.g. cages with restrictive structures supporting and surrounding both filter layers in a double layer filter. That is, a cage encompassing a less complex structural design may comprise a lower number of components exposed to high strain, e.g. due to leverage.

The closed end portion of the tubular inner layer may be provided with first attachment means and wherein the cage is provided with corresponding second attachment means for removably attaching the closed end portion of the tubular inner layer to the cage with the tubular inner layer extended within the cage.

The attachment means keeps the closed end portion of the filter fixed, which enables a reverse air flow through the filter, for example for cleaning/chocking purposes to remove dust cake from the layers.

The first attachment means may comprise a hole which is optionally provided with an eyelet, and the second attachment means may comprise a hook configured to fit through the hole of the first attachment means.

The hook engages the hole and thereby provide a fixed position of the closed end portion of the inner layer.

The second attachment means may be attached to cage at a top end thereof, in the longitudinal direction of the filter assembly. This is beneficial for the structural stability of the cage. It is further beneficial in that it enables the tubular inner layer to extend as far as possible, thereby maximizing the filtering surface area of the tubular inner layer.

The filter assembly may comprise a base plate to which one or more filter assemblies of the type described above are attachable with the first end portion the tubular outer layer of each respective filter assembly interfacing a respective hole of the base plate. The filter assembly is configured to seal between each tubular outer layer and the base plate.

The base plate provides an interface between the one or more filter assemblies and the dust collector/vacuum cleaner. Each filter assembly can be detached and maintained, for example by full replacement of the filter assembly or by change of bag.

The first end portion of the tubular outer layer may be provided with a resilient circumferential rim sized larger than the respective hole of the base plate, wherein the rim is provided with a circumferential recess sized to allow the edge of the respective hole of the base plate to extend into the recess for engaging the rim to the base plate.

The resiliency of the rim enables it to be manually deformed such that it is insertable through the respective hole of the base plate upon being mounted to the base plate, wherein the rim subsequently springs back out to its original shape with the base plate extending into the circumferential recess thereby removably attaching the filter assembly to the base plate.

The tubular outer layer is configured to fit with the first ring and the second ring such that the first ring and the second ring tension the bag onto the rings.

The first ring and the second ring are provided with adhesive or double-sided adhesive tape facing the tubular outer layer.

Brief description of drawings

Fig. 1 shows a bag for a filter for filtration of particles in a gas flow.

Fig. 2 shows a cage for supporting the bag shown in fig. 1.

Fig. 3 shows three filter assemblies, each comprising the bag shown in fig. 1 and the cage shown in fig. 2. One of the filter assemblies is shown without its tubular outer layer for illustrative purposes. The filter assemblies are mounted to a base plate suitable for mounting in a vacuum cleaner or dust collector.

Fig. 4 shows a schematic cross-sectional view (not drawn to scale) of an upper portion of a resilient circumferential rim sized larger than the respective hole of the base plate, wherein the rim is provided with a circumferential recess sized to allow the edge of the respective hole of the base plate to extend into the recess for engagement of the rim to the base plate. Fig. 5 shows a cross-sectional view of an industrial vacuum cleaner fitted with a filter assembly comprising three bag filters.

Detailed description A bag 1 for a filter for filtration of particles from an airflow, and a related filter assembly according to a first embodiment will hereinafter be described with reference to the appended drawings. As shown in fig. 1 , the bag 1 comprises a tubular outer layer 2 comprising a first end portion 3 and an opposite second end portion 4. The bag 1 also comprises a tubular inner layer 5 configured to extend inside the tubular outer layer 2 from an open end portion 6 of the tubular inner layer 5 at the second end portion 4 of the tubular outer layer 2 along an extent of the tubular outer layer 2, to a closed end portion 7 of the tubular inner layer 5. In other embodiments, the tubular inner layer 5 may alternatively extend only partly along the length of the tubular outer layer 2.

The tubular outer layer 2 is connected to the open end portion 6 of the tubular inner layer 5. Also, the tubular inner layer 5 and the tubular outer layer 2 are shaped and sized such that a circumferential space 8 is formed between the tubular inner layer 5 and the tubular outer layer 2. In this embodiment, the overall shape of the filter and the circumferential space is cylindrical with a hollow-circular cross section but in other embodiments the general shape of the filter could be configured in other ways, such as with a hollow-rectangular cross-section or somewhere in-between hollow-circular and hollow-rectangular, provided the cage 11 is also configured to support the tubular inner layer 5 and the tubular outer layer 2 as needed. However, a hollow-cylindrical shape is advantageous since it provides substantially circular cross-sectional shaped of the inner tubular layer, which is a shape stable to high-pressures without much support from the cage 11, which enables a less complex design of the cage 11.

The tubular outer layer 2 used to form the general cylindrical shape of the respective tubular inner layer and the tubular outer layer 2 are formed from a rectangular piece of material. Also, the tubular inner layer 5 is formed from a rectangular piece of material folded such that it is closed at its closed end portion 7.

The connection between the tubular outer layer 2 and the tubular inner layer 5 is formed by a hollow disc-shaped connecting member 9 attached to the tubular outer layer 2 and to the tubular inner layer 5. In other embodiments, the connecting member could alternatively be provided in the form of a portion of the tubular outer layer or the tubular inner layer appropriately shaped to form a connection between the tubular inner layer and the tubular outer layer.

The connecting member 9 is made from a gas permeable filter material, such as needle felt. However, the connecting member could alternatively in other embodiments be made of some other material, such as a piece of non-permeable plastic or rubber.

In this embodiment, the connecting member 9 is sewn to the tubular inner layer 5 and to the tubular outer layer 2 but could in other embodiments alternatively be attached by a suitable adhesive or, depending on the choice of material of the connecting-member, by being injection molded onto the tubular outer layer 2 and the tubular inner layer 5.

The closed end portion 7 of the tubular inner layer 5 is sewn closed but could in other embodiments be closed by using an adhesive or by fitting a piece of plastic to close the inner tubular member.

As shown in figs. 1 and 3-5, the filter assembly comprises: a bag 1 as described above, and a cage 11 configured to extend between the tubular outer layer 2 and the tubular inner layer 5 for supporting the bag 1 such that the tubular outer layer 2 is extended.

The closed end portion 7 of the tubular inner layer 5 is provided with first attachment means 12 and the cage 11 is provided with corresponding second attachment means 13 for removably attaching the closed end portion 7 of the tubular inner layer 5 to the cage 11 with the tubular inner layer 5 extended within the cage 11.

The first attachment means 12 comprises a hole, and the second attachment means 13 comprises a hook 16 configured to fit through the hole 14 of the first attachment means 12. The material around the hole could optionally be reinforced by provision of an eyelet in the hole.

With reference to fig. 2, an embodiment of the cage 11 is shown in which the cage 11 is configured to extend between the tubular outer layer 2 and the tubular inner layer 5 for supporting the bag such that the tubular outer layer 2 is extended. In this embodiment, the cage 11 comprises a plurality of longitudinal ribs 27, and a plurality of annular ribs 28, wherein the plurality of annular ribs 28 extends in a transverse direction to a longitudinal extension of the plurality of the longitudinal ribs 27. The plurality of the longitudinal ribs 27 and the plurality of the annular ribs 28 are connected such that the cage 11 has a substantially cylindrical shape. The cage 11 may be positioned such that it supports the tubular outer layer 2 and maintains it in its extended state before use and in use. As shown in fig. 2, the plurality of the longitudinal ribs 27 are connected to the plurality of the annular ribs 28 such that a space is created in the center of the cage 11 enabling the tubular inner layer 5 to move freely in a radial direction to an axis longitudinally extending from the first end portion to the second end portion.

Referring again to figs. 1 and 3-5, the filter assembly 10 comprises a base plate 17 one or more cages 11 and associated bags 1 are attachable with the first end portion 3 the tubular outer layer 2 of each respective bag 1 interfacing a respective hole 18 of the base plate 17. The filter assembly 10 is configured to seal between each tubular outer layer 2 and the base plate 17.

To achieve a sealing connection between each bag 1 and the base plate, the first end portion 3 of the tubular outer layer 2 is provided with a resilient circumferential rim 19 sized larger than the respective hole 18 of the base plate 17. The resiliency of the rim 19 allows it to be temporarily deformed to fit in the hole 18 of the base plate 17 at installation. The rim 19 is provided with a circumferential recess 22 sized to allow the edge of the respective hole 18 of the base plate 17 to extend into the circumferential recess 22 of the base plate 17 for engagement between the rim 19 and the base plate 17.

The rim 19 comprises a resilient first ring 20, and a resilient second ring 21, wherein the first and second rings 20, 21 are shaped such that the circumferential recess 22 is formed between the first ring 20 and the second ring 21. Each ring is formed by a piece of string/rope but could in other embodiments alternatively be made of any other suitable material. In this embodiment, the first and second rings 20, 21 are not able to spring back on their own and are thus complimented by a flexible steel ring 26 provided radially inside of the first and second rings 20, 21. The first and second rings 20, 21 are attached to the steel ring 26 by adhesive/adhesive tape 23, but in other embodiments, any other suitable means for enabling alignment/positioning of the first and second rings 20, 21 on the steel ring are possible. Once mounted to the base plate 17, the steel ring 26 of the rim 19 presses the bag 1 against the edge of the hole 18 in the base plate 17 to seal between the bag 1 and the base plate 17.

In other embodiments, the rim 19 could have any other suitable design allowing it to be releasable attached to the base plate 17, such as a rim design with rigid members movably connected using hinge means or a rim made by injection molding of a suitable flexible thermoplastic material.

The tubular outer layer 2 is configured to fit with the first ring 20 and the second ring 21 such that the first ring 20 and the second ring 21 tension the bag 1 onto the rings 20, 21. In other embodiments, any other suitable fit between the bag 1 and the rim may be provided.

The filter assembly 10 is for example used in an industrial vacuum cleaner 24 such as the one shown in cross-section in fig. 5 with three bags 1 and cages 11 mounted to a base plate 17. In use, air passes from the inlet hose through the inlet of the vacuum cleaner 24 and there distributes in a distribution chamber 14 over the cake sides of the bags 1. As filter cake deposit builds up on the bags 1 in use, the filter cake can be shocked or otherwise forced off the bags 1 such that at least a portion of the cake falls into the lower receptacle 15, thereby prolonging the lifetime of the bags 1. From the distribution chamber 14 the air flows into the open end portion 6 of the tubular inner layer 5 and from there through the tubular inner layer 5 and into the circumferential space 8. Also, air flows from the distribution chamber 25 to through the tubular outer layer 2 and into the circumferential space 8. The present bag design provides a large filtering surface area in a small footprint yet allowing use of highly efficient and long-life filtering materials such as needle felt. Needle felt has little rigidity on its own but can be used with the current design of the filter since the tubular outer layer 2 is supported on the cage 11 from its inside thereby preventing implosion of the tubular outer layer 2, and since the tubular inner layer 5 is stably inflated by the incoming air.

After the air has passed through the bag(s) 1 it is routed to a HE PA filter for additional filtering and then released to surrounding air.

The present filter design is especially advantageous for use in collecting fine heavy dust.

The filter technology can be equally well used with other type of devices in which a flow of gas needs filtering of particles, such as other type of dust collectors.