AIR FILTER AND MODULE TO BE USED FOR BUILDING UP SUCH A FILTER

Abstract: An air filter of which the dimensions may be easily adapted to the shape and dimensions of air ducts, especially air ducts of air condition equipments, comprises a number of frame shaped modules (1) made of plastics material. To each module a filter bag (2) is welded. The side faces (1a, b, c, d) of each module are provided with a system of ribs (5) or embossments (6). For joining modules substantially airtightly together a system of ribs or embossments on a side face of a module is connected to a complementary shaped system of ribs or embossments on the side face of another module by sliding movement or snap action. Preference is given to an embodiment whereby inclined side boundaries of interengaging complementary systems form a dovetail connection.

Description: The invention relates to a module intended for an air filter, as disclosed in GB-A-2036591. Air filters are very widely used in air conditioning installations for the purpose of removing particles of matter from a current of air. Electrete material known under the trade name "Filtrete", in particular, leads to excellent results because both negative and positive electrical charges are permanently incorporated in the surface of the fibres. Charged and uncharged particles of matter are collected: charged particles because they are attracted by strong Coulomb forces, and uncharged particles because they are polarized by the strong field around the fibres and converted into macroscopic dipoles, so that they are attracted. Because the particles are attracted by the fibres, the structure of the filter material can be open, so that air resistance is low. In conjunction with the charges in the fibres, the open structure leads to high capacity. The material repels moisture and is resistant to long-lasting temperature loads up to 80°C and to temperature loads of short duration up to 100°C. A fastening moulding is mounted in a duct in the air circulation system and in it a main frame containing the fibrous filter material is fastened. The outside dimensions of the main frame are obviously adapted to the inside measurements of the fastening moulding. In practice there are numerous shapes and dimensions of air ducts, depending on the desired filter capacity and the type of construction. Adaptation is expensive and laborious. The modules shown in GB-A- 2 036 591 are made of thin wire; adjacent parts of the wire frames are joined together by U-shaped clamping members. This joining system is working to connect the frames in one direction only, that is to say that a filter composed of these wire frames has a variable length of the cross section and a fixed width. The adaptation of this filter construction to the dimensions of air duct is rather inadequate. Further the airtightness of this frame connection with the aid of U-shaped clamping members leaves a lot to be desired. The main object of the invention is to avoid these disadvantages and to provide a module for making an air filter of which the dimensions may be easily adapted to the shape and dimensions of air ducts. According to the invention the module is square and made of plastic materials, the side walls are provided with a system of ribs or embossments arranged according to a crenellated pattern, the system of ribs or embossments of two side faces are complementary to the system of ribs or embossments of two other side faces, the side boundaries of the ribs or embossments are inclined with respect to the plane of the side faces, and two of the side faces are provided with a resilient locking member and the other two side faces are provided with a rib or edge on or behind which a locking member of a similar module may be snapped. The locking members prevent the connected modules from moving with respect to each other. The modules can be assembled to form air filters of any desired dimensions. It is possible for an air filter composed of modules to be disposed in circular ducts provided that the relatively small segmental spaces between the outside periphery of the air filter and the inside periphery f the air ducts are masked off. The square modules for example have a side length of about 95 millimetres. The maximum possible use can also be made of a round cross-section of an air duct with the largest possible filter area. An important advantage is that the suppliers of the air filters do not need to hold stocks of a large number of filters of different dimensions. It is essential that the modules can be airtightly joined together without additional means, that is to say solely with means which are fixed components of the modules. Since the side boundaries of the systems of ribs or embossments have a crenellated shape, the air flowing into the dovetail connections will undergo twice a flowing direction change of 90°. This causes such an increased resistance that the air will follow the way of lesser resistance through the filter. The invention also relates to an air filter comprising a number of modules substantially airtightly joined together, each of the modules being provided with a filter element. The filter elements will be carried out as filter bags which can be supported internally and externally, but it is simpler and more economical for the bags to be self-supporting, that is to say able to extend straight from the module without any assistance. This self-supporting feature can be assisted if the filter bag simply have two longitudinal welt seams diagonally opposite each other. The invention will now be explained more fully with the aid of the drawing, in which one example of embodiment is illustrated. Figure 1 shows in perspective an elevation of an air filter according to the invention. Figure 2 shows in perspective an elevation of a module of the filter shown in figure 1, with the filter bag partly cut away. Figure 3 is a longitudinal section through two modules fastened to one another. The air filter shown in figure 1 comprises a number of modules 1 and filter bags 2, the number of the latter corresponding to the number of modules. Each of the modules 1 is made by injection moulding of plastics material and has the form of a square frame having a projecting edge 3, to which a filter bag 2 is fastened by welding. The material of the filter bags consists of weldable plastics fibres. The projecting edge 3 is provided with ribs 3a melting during the welding operation and penetrating through the filter material. The side faces of the modules are provided with a rib system 5 and a system of embossments 6. The embossment system 6 of the side face 1c, which is directly opposite to the side face 1a, corresponds to the embossment system of the side face 1b. The rib system of the side face 1d, which is directly opposite the side face 1b, corresponds to the rib system 5 of side face 1a. The side boundaries of the embossment system 6 of the side faces 1b and 1c as well as the side boundaries of the ribs of the rib system 5 of the side faces 1a and 1d are provided on the outer periphery with inclined bounding faces 7 resp. 8. The embossment system 6 of face 1b or 1c can be pushed into the rib system 5 of a face 1a or 1d of another module, the aforesaid inclined bounding faces interengaging after the style of a dovetail arrangement. If the systems 5, 6 are made with precision, it is possible in this way to obtain a firm practically air tight connection between the modules. The connection can be made very quickly. As the name itself suggests, the modules are of standard dimensions. The length of the side of the square is for example 9.5 centimetres, and the total height is 4.5 centimetres. The inclined bounding faces of the systems 5 and 6 have a crenellated pattern. The resulting frame can be fastened in an existing or specially installed mounting moulding in the air duct. Air filters of widely varying dimensions and shapes can be produced with the aid of the modules, but the outside dimensions must always amount to a whole number times the length dimension of the modules. A U-shaped main frame 14 can be applied around the complete filter; transverse edges 15 of frame 14 fit into notches 16 in the modules. The filter bags consist of two strips of filter material joined together along two longitudinal weld seams 9 and a single transverse weld seam 10. The longitudinal seams 9 contribute towards ensuring that the bag will be self-supporting throughout its useful like, that is to say that no additional means will be required to enable the bag to project at right angles to the frame. The initial resistance of the filter bags is relatively low and their life is long. An important advantage of the invention is that for any dimensions and shape of the duct in which an air filter has to be installed the manufacturers of the air filters need manufacture and keep in stock only modules of standard dimensions. Furthermore, the users can adapt the number of modules to the desired air flow to be filtered, taking into account the desired filter efficiency, because the modules are manufactured in such a manner that they can offer different efficiencies irrespective of the rate of flow of the air through the filter. If the duct opening is larger than desired, a part of the opening can be blanked off with dummies of the same size as the modules but having an impermeable plastics wall instead of a filter bag. A filter of the desired dimensions can quickly be assembled with the aid of modules. Polypropylene is a preferred material for the modules, but other plastics materials can also be used. The inlet rim 11 of the modules is streamlined in order to keep resistance low. The inclined bounding faces of systems 5 and 6 have a crenellated pattern. By the crenellated pattern of the dovetail connections a kind of labyrinth sealing is obtained causing such a great resistance that the air will follow the way of smaller resistance through the filter. The side faces 1b and 1d are provided with a resilient locking member 12 having a thickened portion 12a which in the locking position interlocks with rib 13 of rib system 5. By this construction two connected modules can not move with respect to each other.

Claims: Module intended for an air filter, characterized in that the module is square and made of plastic materials, the side walls (1a, 1b, 1c, 1d) are provided with a system of ribs or embossments (5, 6) arranged according to a crenellated pattern, that the system of ribs or embossments (5) of two side faces (1a, 1d) are complementary to the system of ribs or embossments (6) of two other side faces (1b, 1c), that the side boundaries of the ribs or embossments (5, 6) are inclined with respect to the plane of the side faces, and that two of the side faces (1b, 1c) are provided with a resilient locking member (12) and the other two side faces (1a, 1d) are provided with a rib or edge (13) on or behind which a locking member (12) of a similar module may be snapped. Air filter comprising a number of frames (1) substantially airtightly joined together, each of the frames being provided with a filter element (2), characterized in that the frames (1) are modules as claimed in claim 1.

Inventors: VALKENBURG, JOHANNES, VAN DER SPEK, FERDINAND PETER, VAN WEERDEN, JAN
Applicants: FILTRETE B.V.
Application year: 1987
Main classification: B01D46
IPC codes: B01D46, F24F13