GB2088245A - Filter bag supports - Google Patents

Abstract

A filter element 11 of a dust extraction unit, comprises a plurality of substantially flat filter bags 17 arranged on a base member 18. In use, the open mouths 19 of the bag 17 face downwards into the air flow through the unit. The sides 21 and 23 of adjacent bags 17 are prevented from contacting by means of interposed spacers 25, which are pervious to air. Spacers are each secured to one side of one bag and are constructed as fibrous mats or metal cages. The bag interiors are empty. <IMAGE>

Description

SPECIFICATION Dust extraction The present invention relates to the extraction of dust from the atmosphere, particularly in a workshop environment.

Dust extraction units have been used for several years to remove dust and other unwanted particles, including toxic dusts, produced by a manufacturing or industrial process, at its source, thereby keeping the air within a building free of dust.

A common type of dust extraction unit comprises a fan and one or more filter elements enclosed in a suitable cabinet with air inlets and outlets. The fan sucks air laden with dust, through the filter elements, and expels the cleansed air through the air outlet into the external atmosphere or back into the building. The filter elements are pervious to air but capable of separating from the air the particles of dust, or other extraneous material. The material of the filter will depend upon the anticipated extent and type of the unwanted particles in the air, in the application to which the dust extractor unit is to be put.

With such a dust extraction system it is necessary periodically to halt the extraction process in order that the accumulated dust on the filter elements may be removed. If this is not done then air flow through the filter element will be progressively reduced as the dust builds up on the element.

A variation on the dust extraction unit described is identical except that no fan is fitted.

Instead the air prime mover is located separately and air may be either blown or sucked through the unit. This arrangement is used, without a dust collecting receptacle, for venting of storage silos, and the present invention relates equally to this application.

An important parameter for all such systems is the surface area of the filter element or elements compared to the anticipated rate of flow of air through the extractor unit. The greater the surface area of the filter element of the extractor unit, the greater will be the potential through-put of air through the device. A large surface area for the filter is also desirable to reduce the build-up of dust on the filter to a minimum and so reduce to a minimum the frequency with which the extractor must be stopped for cleaning of the filter elements.

A convenient way of presenting a large surface area of filter to an air stream of limited crosssectional area, as in a duct, or the body of a dust extraction unit, is to use filter elements so positioned as to present the filtering surfaces at an acute angle to the direction of the air flow.

A plurality of substantially flat filter bags may be arranged in a row perpendicular to the air flow, with the openings of the bags facing either into or away from the air stream and the adjacent edges of the openings of adjacent bags being joined together.

However, in order for such an arrangement to be effective, the air flow must be able to pass substantially unhindered through the side walls of the bag. However, if in order to increase the filter area for a particular dust extractor unit, the bags are fitted closer together so as to enable more bags to be placed in the filter element, the air pressure differences across the walls of the bags may be such that the side walls of the bags come into contact. This reduces the efficiency of the extractor since no filtering action takes place where the bag walls are in contact. There is accordingly a practical limitation on the number of bags which may be accommodated in an extractor of a particular size.

A common type of dust extractor overcomes this problem by arranging the flat filter bags so that they lie with the openings of the bags facing away from the air stream. A steel mesh or cage is commonly inserted into each of the pockets formed thereby so as to prevent adjacent walls of the bags coming into contact.

However, this arrangement causes difficulties in the construction of the filter housing, and it is usually considered preferable to arrange the filter bags such that the openings in the bags face into the air stream.

According to the present invention there is provided a filter element for a dust extraction unit comprising a plurality of substantially flat filter bags arranged in a row substantially perpendicularly to the direction of air flow through the dust extraction unit, there being interposed between adjacent bags a spacer, said spacer being capable of preventing contact between the side walls of adjacent bags and being pervious to air.

A filter element according to the present invention thus prevents the contact of adjacent side walls of adjacent bags, allowing the bags to be placed closer together, and so increasing the filter area, of a particular dust extractor unit.

Preferably said spacer is a sheet or mat of fibrous material or a mesh or cage of metallic material. More preferably the spacer is of nonwoven fibrous material.

Preferably said spacer is of such dimensions as to cover the greater part of the area of the adjacent side wall of the filter bag. More preferably said spacer covers substantially the whole of the area of the side wall of the adjacent filter bag.

Preferably one of said spacers is fixed, either permanently or removably, to one side of each of said filter bags. More preferably it is permanently fixed, and most preferably one spacer is sewn to one side of each of said filter bags.

The filter bags composing the filter element may be of any suitable material, said material being dependent upon the type of dust handled and the filtration efficiency required and typical materials being woven cotton, terylene (Registered Trade Mark) needle felt and epitopic needle felt.

A filter element according to the present invention may be used on dust extraction units for applications substantially identical to those for which a conventional dust extraction unit may be used.

An embodiment of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:~ Figure 1 shows a cut-away perspective view of a dust extraction unit employing a filter element in accordance with the present invention; Figure 2 shows a perspective view of the filter element of Figure 1; Figure 3 shows a side elevation of a portion of the filter element of Figure 1; and Figure 4 shows a front elevation of the filter element of Figure 1.

Referring particularly to Figure 1, a dust extraction unit indicated generally by 1 including a filter element in accordance with the present invention comprises a cabinet 2 within which is located at the top thereof a fan and fan motor 3.

The fan is so designed as to suck dust laden air into air inlet 5 at the lower side of the machine, and thence into the body 7 of the extraction unit.

The drop in air speed and the sudden change in flow direction caused by the relative crosssectional areas and orientations of the air inlet 5 and extractor body 7 cause larger particles of dust to drop directly into dust collecting bin 9 at the bottom of the extraction unit 1.

The remainder of the fine dust is carried with the air flow through filter element 1 The dust is deposited on the inside of the filter bags whilst the air passes through the side walls of the bags and thence to clean air outlet 13 at the top of the extractor unit.

The dust extractor unit illustrated also includes a motor 15 which, when the main fan motor 3 is at rest, may be used to perturb the filter element so as to dislodge the deposits of dust on the inside of the filter bags, so that the dust falls down the unit into the dust collecting bin 9. This bin 9 may then be removed from emptying and subsequently replaced.

Referring now particularly to Figures 2, 3 and 4, the filter element 1 1 of the dust extraction unit 1 comprises a plurality of substantially flat filter bags 17 arranged parallel to one another on a base member 18. In use, base member 18 holds the mouths 19 of bags 17 open and facing into the direction of the air flow into the body 7 of the dust extraction unit 1. The lower edges of the openings 19 of adjacent side walls such as 21 and 23 of bags 17 are joined together such as at 22.

The closed ends of the bags 1 7 are retained in position by means of members 20.

Interposed between adjacent sides 21 and 23 of bags 17 are spacers 25. Spacers 25 are rectangular mattresses of a resin bonded acrylic fibre. A mattress is sewn to the side 21 of the bag 17 in a substantially central position so as to cover substantially the whole area of the side wall to any one of bags 17. Only a single side of each bag is so covered. In an alternative embodiment a metallic cage or mesh is used instead of the acrylic fibre mattress.

The material and the size of bags 17 are those most suited to the conditions under which the dust extraction unit is intended for use.

A filter element in accordance with the present invention having a spacer interposed between adjacent filter bags is thus less liable to failure due to the contact of the side walls of adjacent bags caused by the pressure on the fan side of the filter element, because the spacer prevents adjacent walls of bags 17 coming into contact, thus ensuring that the maximum possible surface area of the filter element is available for the passage of air through the filter element, the spacer itself being pervious to the passage of air.

Claims (10)

1. A filter element for a dust extraction unit, said element comprising a plurality of substantially flat filter bags which, in use, are arranged in a row substantially perpendicularly to the direction of air flow through the dust extraction unit and with the mouths of the bags facing into the air flow, there being interposed between adjacent bags a spacer, said spacer being capable of preventing contact between the side walls of adjacent bags, and being pervious to air.

2. A filter element according to claim 1 wherein said spacer is a sheet or mat of fibrous material.

3. A filter element according to claim 2 wherein said spacer is of a non-woven fibrous material.

4. A filter element according to claim 1 wherein said spacer is a metallic mesh or cage.

5. A filter element according to any of the preceding claims wherein said spacer is of such dimensions as to cover the greater part of the area of the adjacent side wall of the filter bag.

6. A filter element according to claim 5 wherein said spacer covers substantially the whole of the area of the side wall of the adjacent filter bag.

7. A filter element according to any of the preceding claims wherein one of said spacers is attached to one side of each of said filter bags.

8..A filter element according to claim 7 wherein the spacer is permanently attached to said bag.

9. A filter element according to claim 8 wherein the spacer is sewn to one side of the bag.

10. A filter element according to claim 1 and substantially as herein described.

1 1. A filter element for a dust extraction unit, substantially as herein described with reference to the accompanying drawings.