AIR FILTRATION UNIT

Abstract: An air filtration unit comprises a box having a frame (F) defining two open panels, a filter element (E) being mounted within the frame and held therein by strip members (4A, 4B, 4C, 4D) extending across at least one of the open panels.

Description: AIR FILTRATION UNIT The invention relates to an air filtration unit and a method for producing such a unit. A known air filtration unit comprises a fibrous filter element housed within a box frame, see GB-A-2346819. It is known to make a frame is made from a cardboard blank which is folded to form two parallel panel walls and an intermediate side web. Holes are punched out of the panels to form a framework to allow air to pass through the filter element and keep the element with the box. Typically the cardboard frame is made by die-cutting a cardboard blank. The cardboard cut away is wasted and is costly to dispose of. It is one object of the invention to provide an air filtration unit of box form. It is another object to provide a method of producing the frame of the box which has the potential to reduce cardboard wastage and costs. According to the invention in one aspect there is provided an air filtration unit comprising a box frame containing a filter element, the box comprising a frame and having two opposite open panels, the air filtration element being present in the thickness of the frame between the two open panels, at least one open panel having strip members which extend across that panel characterised in that the ends of the strip members and/or the margins of the frame defining the panel opening are shaped so that the sides of the frame bordering the panel are at a substantially uniform level. The ends of the strip members may be connected to the outer surface of the margins of the frame; preferably they are set into the thickness of the margins. For this purpose indentations are preferably formed in the margins of the frame defining the panel opening to receive the end portions of the strip members so as to minimise and ideally eliminate any increase in the overall thickness of the margin. The strip members may take any convenient form. Typically they will be long strips and arranged to cross to form a network. Preferably the box frame is made as one unit and the strip members are added. The end portions of the strip members are preferably secured to the margins of the frame by a pressure-sensitive adhesive. The frame members and strip members are preferably made from cardboard, but could be of any other suitable material such as a light-weight plastic. In another aspect the invention provides a method of making a box having a frame and to contain a filter element, the method comprising: • cutting a blank of cardboard or the like to form an elongate wide length; • making two generally parallel longitudinal fold lines along the blank; • folding the blank along the lines to form a side comprising two margins and an intermediate web; • arranging four such sides to form a rectangle and securing the ends together to define a box frame having two opposite open panels; • shaping the ends of the strip members and/ or the margins of the frame of one panel so that when assembled thereto the frame will have a substantially uniform level, and • securing the strip end portions to the margins of the frame which define that panel. Preferably the method includes the step of shaping the blank to form all four sides of a rectangular box frame i.e. four side lengths are made from one blank and the free ends are secured together. Preferably the method includes the step of forming indentations in the margins of the blank to receive an overlap joint at a corner so to avoid any increase in the thickness of one of the sides having an open panel. Preferably the method includes the step of securing the ends of the strip members to the margins of the frame using a pressure-sensitive adhesive. The filter member is constructed from any fibrous material suitable for air filtration purposes. The material is generally folded concertina style to increase the surface area over which filtration is possible. The filter member may be inserted into the box (or a precursor of the box) at any convenient step. In order that the invention be well understood it will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a front elevation of one air filtration unit of the invention; Figure 2 is a partial cross sectional view taken along the line A-A on Figure 1; and Figure 3 is a partial sectional view taken along the line B-B on Figure 1. The filter comprises a box defined by a frame F having four side lengths F1,F2,F3,F4 each having two parallel margins 2,3 separated by an integral web 1 (see Figure 3). The side lengths are joined together at their corners to form airtight seals. The margins define two opposite open panels, top and bottom of the box. The box frame houses a folded air filter element E such that air can flow across the element via the open panels, as shown by the arrow A. Because of the frame structure the panels are open and define windows through which air may flow through the filter element E. The element E is dimensioned so that the edges thereof contact the inner surfaces of the intermediate web 1 on all sides. Strip members 4A,4B,4C,4D bridge different margins of one or both panels in a criss-cross fashion. The cross strips 4A,4B,4C,4D hold the filter element E in place without significantly reducing the air flow. The strips are separate elements which have been applied to the margin after the frame has been formed. The strips are longer than the distance between the margins of the opposite sides, and the strip ends 5 are set into indentations 6 formed in the margins bounding the panel to avoid any increase in the margin thickness. The cross-strips are fixed in place using a pressure-sensitive adhesive. As shown in Figure 2, indentations 6 are formed in the margin of the frame and also in the strips 4A,4B,4C,4D where one crosses over another, as at X. The box frame F is made by cutting a blank from a length of cardboard equal to the box perimeter and scoring two spaced fold lines generally parallel to its major axis to define the margins 2,3 and the intermediate web 1. The length may be provided as a roll of card material. Scoring the intermediate web 1 at right angles to the margins 2 and 3 at positions equal to the frame side length produces the corner fold in three places, then the blank is joined to itself by an internal overlap at the fourth corner to form the box. The area where the margins 2 and 3 overlap when folded at the corner is indented to avoid an increase in margin thickness. The element E is inserted into the open box and margins 2 and 3 folded down onto it, and pressure-sensitive adhesive is used to create a bond. The ends 5 of the strips 4A,4B,4C,4D are set into the pre-formed indentations 6 and secured by adhesive. There is little wastage of cardboard, and the technique is simple. The invention is not limited to the embodiment shown. As illustrated, the strips are made flush with the surface of the filter box by virtue of indentations. As shown the indentations are in the margins of the box frame, but of course they could also be at the end of the strips. Where two frame lengths are abutted together to form a corner there will be an increase in thickness. It is much preferred to avoid that so that the box frame face has a smooth flush external appearance throughout. Therefore, an indentation is formed at one end of a frame side portion and the overlapping portion is received in the indentation to maintain a flush surface. In this example the strip members are arranged diagonal to the outer frame structure F, an arrangement of the strip members parallel to the frame 1 would be equally as effective. The number of cross-strip members is dependant upon the overall dimensions of the filter. The strips can be made integral with the margins and joined at their longitudinal centres. The outer frame structure F is generally made from one blank of cardboard, however two or four blanks joined together would be equally effective

Claims: CLAIMS 1. An air filtration unit comprising a box frame (F) containing a filter element (E), the box comprising a frame (F) and having two opposite open panels, the air filtration element (E) being present in the thickness of the frame (F) between the two open panels, at least one open panel having strip members [4A,4B,4C,4D] which extend across that panel, characterised in that the ends (5) of the strip members (4A,4B,4C,4D) and/or the margins (2,3) defining the panel opening of the frame (F) are shaped so that the sides of the frame (F) bordering the panels are at a substantially uniform level. 2. A unit according to Claim 1, wherein the margins (2,3), of the frame (F) bordering the open panels have indentations (6) by which ends (5) of the strip members (4A,4B,4C,4D) are set into the thickness of the margin (2,3) of the frame (F). 3. A unit according to Claim 1 or 2, wherein the overlapping corner joints of the frame (F) bordering the open panels are set into the thickness of the respective margins (2,3). 4. A unit according to Claim 1,2 or 3, wherein the frame (F) comprises side lengths (F1 ,F2,F3,F4) and the side lengths (F1,F2,F3,F4) and strip members (4A,4B,4C,4D) are formed of cardboard. 5. A unit according to any preceding Claim, in which the end portions (5) of the strip members (4A,4B,4C,4D) are secured to the margins (2,3) of the frame (F) by a pressure-sensitive adhesive. 6. A method of making a frame (F) to contain an air filter element [E], the method comprising: • cutting a blank of cardboard or the like to form an elongate wide length; • making two generally parallel longitudinal fold lines along the blank; • folding the blank along the lines to form a side length (F1,F2,F3,F4) comprising two margins (2,3) and an intermediate web (1); • arranging four sides (F1 ,F2,F3,F4) to form a rectangle and securing the ends together to define a box frame (F) having two opposite open panels; • shaping the ends (5) of the strip members (4A,4B,4C,4D) and/or the margins (2,3) of the frame (F) so that when assembled thereto the frame (F) will have a substantially uniform level; and • securing the strip ends (5) to the margins (2,3) of the frame (F). 7. A method according to Claim 6, including the step of forming indentations (6) in the margins (2,3) of the frame (F) and locating the end (5) of the strip members (4A,4B,4C,4D) in the indentations (6). 8. A method according to Claim 6 or 7, including the step of shaping one blank to form all four sides (F1 ,F2,F3,F4) of the rectangle. 9. A method according to Claim 7 or 8, including the step of forming indentations (6) in the margins of the blank to receive an overlap joint at a corner so to avoid any increase in the thickness of a side (2,3) of the frame (F) bordering the open panel. 10. A method according to Claim 6, 7, 8 or 9, wherein the strip members [4A,4B,4C,4D] are secured to the edges of the margin (2,3) of the frame (F) by a pressure sensitive adhesive.

Inventors: ADDINGTON RICHARD HAROLD, ADDINGTON, RICHARD, HAROLD
Applicants: ADDINGTON RICHARD HAROLD, INTERFILTA UK LTD, ADDINGTON, RICHARD, HAROLD, INTERFILTA (UK) LIMITED
Application year: 2000
Main classification: B01D46
IPC codes: B01D46