Bag Filter Unit

Abstract

A bag filter unit for a filter module comprising a front plate carrying a U-shaped frame which supports a bag filter element. The fabric filter element is formed with overlapped seams having rows of stitches at the edges of the overlapped fabric which are spaced to lie beyond the frame elements so as not to increase the overall thickness of the fabric which is contacted by such elements. The elements are spring pressed to hold the filter bag under tension and to relieve strains on the bag due to variations in size or shrinkage.

Description

This invention relates to bag filter elements which are adapted for use in a bag filter module and has for an object to provide a unit having novel and improved characteristics.

A more specific object is to provide a construction which is capable of reducing bag failures.

The unit in accordance with the present invention includes a front plate through which the ends of a U-shaped element extend to form a generally rectangular frame over which the fabric filter bag is placed. The open end of the bag is clamped against the front plate to form a rigid support.

Bags of this type are usually seamed and stitched around their edges which rest upon the U-shaped element. This has provided a source of bag failure due to the thickness of the seam and because of the small clearance usually provided for the insertion of the bag unit into the front wall of the module. This tends to injure the bags as they are inserted or removed.

The present invention overcomes this difficulty by overlapping the edge portions of the two fabric layers and stitching along the two overlapped edges, the amount of overlap being sufficient to cause the rows of stitches to be displaced inwardly of the frame elements. The stitches are thus prevented from being pinched between the sides of the frame elements and the edges of the slots in the front wall through which the unit is passed. Also only two thicknesses of material are present in the area of the bag which contacts the frame elements.

In order to maintain the bag under a predetermined tension and to compensate for minor variations in size due to manufacturing variations or due to shrinkage, the U-shaped element is spring biased in its supporting front plate so as to hold the bag distended against the spring pressure.

By means of the above features, weakening of the bags due to excess stress or due to contact with the front wall of the module is avoided and the useful life of the bags is substantially increased.

The nature of the invention will be better understood from the following description, taken in connection with the accompanying drawing in which a specific embodiment has been set forth for purposes of illustration.

In the drawing:

FIG. 1 is a perspective view of a bag filter unit embodying the invention;

FIG. 2 is a partial section taken along the line 2--2 of FIG. 1 showing the spring mounting for the frame;

FIG. 3 is a partial section taken on the line 3--3 of FIG. 1 showing the overlapped seam and the stitching; and

FIG. 4 is a sectional view similar to FIG. 3 illustrating a further embodiment of the invention.

Referring to the drawing more in detail, the unit is shown as embodying a front plate 10 and a U-shaped element 11 having top and bottom portions 12 and 13 respectively and an end portion 14. The ends 15 and 16 of the top and bottom portions extend through holes in the front plate 10 and are provided with internal plugs 17 into which retaining screws 18 are threaded. The screws 18 are slidable in a cupped member 19 which is secured to the front plate 10 and have heads 20 which form a stop to limit the internal movement of the screws. Springs 21 are disposed over the screws 18 between the end of the cupped member 19 and the plugs 17 to hold the frame in extended position. The exposed parts of the screws 18 and the cupped member 19 are shown as shielded from dust by caps 22 which may be composed of stretchable material and may be snapped in place over the assembly.

The front plate 10 is provided with a slot 25 which communicates with the interior of the bag to be described.

The filter bag 30 comprises a pair of panels having overlapped edges 31 which are of sufficient width to span the frame elements and are secured together by rows of stitches 32 at their respective edges. The edges of the panels and the rows of stitches are extended to lie inwardly and beyond the frame elements so that they cannot become pinched between the frame elements and the slot 34 in the front wall 35 of the module in which the units are used.

The open end of the bag 30 is formed wth a bead 36 which is clamped between the inner surface of the front plate 10 and the outer surface of the front wall 35 to seal the bag for filter purposes. The front plate 10 may be held against the front wall 35 by suitable means shown as a cross bar 37.

In order to hold the bag distended, a set of coiled springs 38 may be stretched between an upper flange 39 of the top frame element 12 and a lower flange 40 on the lower frame element 13.

In operation the unit comprising the frame with the fabric bag in place thereon is inserted through the slot 34 in the front wall 35 of the module until the front plate 10 is brought into position to clamp the bead 36 of the filter bag against the outer surface of the front wall 35. When so clamped the bag is held under a predetermined tension by the springs 21 which cause the ends 15 and 16 of the frame elements to slide in the front plate to extend the frame inwardly. The bag is thus held under a tension determined by the springs 21 regardless of variations in bag dimensions.

The edges of the panels and the rows of stitches are located within the confines of the supporting frame elements so that they cannot be squeezed between these elements and the edges of the slots 34 in the front wall 35 as the units are inserted.

An alternative arrangement of the bag stitching is shown in FIG. 4 wherein the bag panels 41 are similar to those above described but terminate within the confines of the frame elements 12 and 13. Strips 42 of a stronger material extend over the frame elements and are stitched to the edges of the bag panels.

This form may reduce the thickness of fabric over the frame elements, particularly when the bag panels are formed of felted material. The material of the strips 42 may have high strength and wear resistance and thus improve the life of the bags.

Claims

What is claimed is:

1. A bag type filter unit for a bag filter module having a front wall provided with openings to receive the filter units, comprising a front plate having an opening to communicate with the interior of the bag and a U-shaped frame element having upper and lower and end portions, the ends of the upper and lower portions being supported in said front plate to form a generally rectangular frame for a filter bag, said ends of said upper and lower portions being slidable in said front plate and spring means carried by said front plate and cooperating with said ends of said upper and lower portions to urge said U-shaped element rearwardly with respect to said front plate, wherein said spring means includes springs in pressure engagement with the end portions of the frame element and carried in cup members mounted on said front plate and enclosing said end portions of said frame element.

2. Apparatus as set forth in claim 1 including screws slidable in said cup members and secured in said end portions of said frame element, said springs being carried on said screws.

3. Apparatus as set forth in claim 2 including heads on said screws adapted to form a stop to limit the retraction of said frame element in said front plate.