FILTER BAG FOR A FILTER SECTION

Abstract: A filter bag for a filter section (1) which is one of a plurality of filter sections assembled to an annularly shaped filter disk for a rotating filter. The filter bag is shaped after the configuration of the filter section and adapted to be pulled over it and to be closed. In advance, a strip (9) is fastened to the outlet end (7) of the filter bag and is provided with at least one filtrate outlet opening (10).

Description: The present invention relates to a filter bag for a filter section, said filter section having discharge means for filtrate and being one of a plurality of filter sections assembled to an annularly shaped filter disk for a rotating filter, said filter bag comprising a filtering medium material and having an outlet and further being shaped in conformity with said filter section so as to be enabled to be pulled over and fitted onto said filter section. It is known from a.o. GB-A-028,568 to sew filter bags for filter sections, one or more sides of the bag being provided with a zip fastener for closing the bag when it has been pulled over a filter section. Subsequently, outside the bag, either at the outer or inner periphery thereof, a means closing the corresponding bag end is attached. This means may be a nozzle means. These known embodiments, thus, require mounting work after the bag has been applied onto the section. In another known embodiment, employed by the applicant, the filter bag after having been mounted onto the section is shrunk with hot steam so that it meets up tightly against the section. Thereafter, a nozzle, usually of acid-resisting material, is mounted on the section and a hole is cut in the filter cloth through the filtrate discharge opening or openings of the nozzle. This method is expensive and laborious, as well as difficult to perform for untrained personnel when exchanging the filter bag, e.g. in a paper mill. The object of the invention is to find a solution to this problem, which has been achieved in that the invention has been given the characteristic features stated in claim 1. This solution brings with it a series of advantages: no separate detail must be subsequently mounted, which, on the one hand, in the case of an expensive acid-resistant nozzle involves a significant saving in material costs, and, on the other hand, a corresponding saving in man power caused by the mounting not having to take place. Mounting and changing of filter bags in the industries is considerably simplified and made less expensive; it has already proved that the need for personnel at mounting and changing of filter bags is reduced by one man. Another advantage of the invention is that the strip can be provided with sealings or made ingegral with such sealings, as required. The characterizing features of the invention are disclosed in the following claims. The invention will now be described in the following with reference to the accompanying drawings in which figure 1 is a perspective view of a typical filter section for a rotating filter, and figures 2, 3 and 4 are sectioned perspective views to a larger scale of three different embodiments of a filter bag in accordance with the invention. The filter section 1 illustrated in figure 1 is of the known type which is intended to be mounted in a filter rotor together with a plurality of other similar sections, there to form an annular filter disk. Several such disks mounted axially one after the other are carried by the same rotor and are partially submerged in a container for the liquid to be filtered, a collection trough for particles such as cellulose fibres deposited on the filter disks, being inserted through the central opening of the disks. A filter section 1 usually comprises two more or less perforated, plate-shaped, mutually spaced elements 2 and 3, constituting the carcass of the section, and a filter means in the form of a filter cloth 4 or the like, which by e.g. ridges 5, formed in the plate-shaped elements is kept spaced from the element surfaces. Other embodiments may be used, but lack any real importance for this invention. An advantageous embodiment of the filter means is a bag of filter cloth, which is tailored for accurately fitting a given filter section. The filter bag is pulled over the filter carcass and is sewn together, or it is provided with a zip fastener 6 (fig. 1), which is closed after fitting the bag onto the carcass, subsequent which the filter bag, which is usually made from plastics material, is shrunk by steam to tightly join up with the filter carcass. In the known embodiments, a nozzle of acid-resistant material is then mounted in the outlet end 7 of the filter section. In accordance with the present invention, the filter bag is already provided during its manufacture with a means which replaces the known type of nozzle. Such a means 8 is indicated in figure 1 and is shown in more detail in three different embodiments in figures 2, 3 and 4. In accordance with the invention, a strip 9 is fastened into the nozzle or outlet end of the filter bag, this strip being provided with at least one through flow opening 10 for filtrate, where such is required for use together with a given type of filter section carcass. For keeping the filter bag together the opening or openings 10 are provided with transverse studs 11. Preferably, the strip 9 is made from a relatively rigid, but flexible plastics material, e.g. polypropylen, which is sufficiently soft to enable sewing through it. Accordingly, it is preferred that the strip 9 is sewn to the filter bag, although other attachment means can be conceived, such as glueing and heat bonding between the materials of strip and filter bag. In the embodiment according to figure 2, the filter bag 4 is located outside the strip 9 and is fastened with stitches 12 through filter cloth and strip. The filter cloth 4 serves here as a seal between the filter section and the connecting means of a filter rotor, where the filter section is to be mounted. In the embodiment according to figure 3, the strip 9' is located outside the filter cloth 4 and is fastened by stitches 12, which are placed between parallel sealing ribs 13 formed in the material of the strip 9', these ribs being arranged two on either side of the opening or openings 10. An alternative embodiment of the flat strip illustrated in figures 2 and 3 is illustrated in figure 4. Here the strip 9'' has been provided with long sides 14 and preferably also unillustrated short sides, i.e. the strip has approximately the configuration of an open box. The filter cloth is here attached to the insides of the sides, but can of course also be attached to the outsides. In stead of sealing means formed in the material of the strip, separate sealing means in the form of strips, etc. can be mounted outside the filter bag and strip, irrespective of whether the strip is inside or outside the filter bag. It is achieved by the invention that the outlet openings do not need to be made in the filter cloth after mounting the filter bag on a filter carcass, since these openings are made in the strip. At the same time a saving in filter cloth material is achieved, since only sufficient filter cloth material required by a working allowance for the stitches is required at the outlet end of the filter bag, where the strip is mounted.

Claims: A filter bag for a filter section, said filter section having discharge means for filtrate and being one of a plurality of such sections assembled to an annularly shaped filter disk for a rotating filter, said filter bag comprising a filtering medium material (4) and having an outlet and further being shaped in conformity with said filter section so as to be enabled to be pulled over and fitted onto said filter section, characterized in that said outlet comprises a strip (9) of a relatively rigid material fastened to said filter bag, said strip (9) including a generally flat portion provided with at least one opening (10) located over and communicating with said discharge means when said filter bag is fitted onto said filter section. A filter bag according to claim 1, characterized in that said generally flat portion comprises two elongated strip portions spaced by at least two spacing means (11), said elongated strip portions and said at least two spacing means defining said at least one opening (10). A filter bag according to claim 2, characterized in that said two elongated strip portions are attached to said filtering medium material (4) in overlapping relationship therewith. A filter bag according to claim 3, characterized in that said two elongated strip portions are sewn to said filtering medium material (4). A filter bag according to claim 2, characterized in that said strip (9) is located outside said filtering medium material (4). A filter bag according to claim 5, characterized in that said strip (9) is provided with integral sealing means (13). A filter bag according to claim 2, characterized in that said strip (9) is located inside said filtering medium material (4). A filter bag according to claim 2, characterized in that each of said two strip portions is provided with an integral web portion (14), said web portion being attached to said filtering medium material (4). A filter bag according to claim 1, characterized in that said strip is of plastics. A method of manufacturing a filter bag for a filter section characterized by the steps of: shaping a filtering medium material (4) to a bag having the shape of said filter section and having a first and a second open end, providing a strip of a relatively rigid material with at least one opening therein, and attaching said strip to said first open end.

Inventors: NILSSON, BJARNE
Applicants: NILSSON, BJARNE
Application year: 1988
Main classification: B01D33
IPC codes: B01D33