GB2278297A - Foraminous screen - Google Patents

Abstract

A foraminous screen, which may be of expanded metal, has a uniform array of apertures which are closed in selected areas by sections of blocking film adhered thereto. The screen may be flat or formed into a cylinder and serves as an I.C. engine exhaust silencer or as one or both supports for an annular filter element. In Fig. 3 films 2A, 2B restrict flow to the central zone of a filter element. The film may be an adhesive tape of aluminium or various plastics or an aluminium or stainless steel foil combined with filler/fibre-impregnated resins. The film may be extended over cut edges of the screen and may assist in joining two edges of the screen to form a cylinder. <IMAGE>

Description

ARTICLE WITH FORAMINOUS SCREEN The present invention relates to articles such as inlet air filters for diesel engines or automotive exhaust silencers, which comprise a foraminous screen. Such screens have been formed from sheet metal which is perforated, i.e, pierced, or expanded in specific areas to define areas through which gas can pass. In filter assemblies for diesel engines, the sheet metal is then formed into a cylindrical screen which surrounds and supports a cylindrical filter element which is made from, e.g., pleated paper, foam, or cloth, the filter element removing dust particles from the air passing through the air filter to the diesel engine air intake. In the case of exhaust silencers, the sheet metal is formed into a cylindrical screen for insertion into car exhaust systems.

Such screens have the disadvantage that perforation or expansion of the sheet metal in selected areas corresponding to the desired gas flow is inefficient in use of material and time consuming to produce and thus expensive.

According to the present invention, an article comprises a foraminous screen, having a substantially uniform array of apertures and, an imperforate blocking film adhered to the screen, and closing the apertures in selected areas of the screen.

The screen may be formed from expanded metal, which is an excellent material for forming the screen of an air filter as it is rigid enough to provide adequate support for the filter element, yet is inexpensive to manufacture, as standard expanded metal can be cut to size, and the blocking film readily adhered, especially compared to the prior art technique of perforating or expanding in selected areas an otherwise continuous piece of sheet metal.

The screen can be used in an exhaust silencer, or in conjunction with a filter element, which is supported by the screen, to form a gas filter. In the latter case, the screen and filter element may be planar, but will usually be cylindrical, with the partially closed screen inside or outside the filter element when the gas flow is radially outwardly or radially inwardly respectively. The blocking screen may also be on the inside, even when the gas flow is radially inward, this would provide additional particle removal by the exposed adhesive surface of the film.

Indeed the filter assembly may comprise two cylindrical screens of expanded metal, at least one of the screens having the closed apertures, and the filter element being supported between the two cylindrical screens.

Preferably, the blocking film is tape fixed to the face of the screen. The tape may be fixed to the screen with an adhesive. The tape/adhesive combination may be, for example, any of aluminium/acrylic, polyester/acrylic, clear polyester/XL acrylic, polyester/ silicone, or polyamide/silicone. A lacquered (epoxy) surfaced aluminium adhesive tape is particularly conducive to applications in which the article is to be spot welded, as it reduces weld explosions. The tape may have a thickness in the range 20 to 250 microns. Preferably, the tape has a thickness in the range 50 to 100 microns. The adhesive may have a thickness in the range from negligible to 250 microns, preferably in the range 20 to 60 microns. For the high temperature requirements of exhaust silencers, aluminium foil or stainless steel foil may be used in combination with a filler or fibre impregnated resin.

The blocking film may also extend around exposed edges of the expanded metal sheet in order to prevent jagged edges of the cut sheet causing damage to other components.

An example of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a plan of a screen, of a filter assembly, with attached blocking film, before shaping; Fig. 2 is a plan of a second screen, with attached blocking film, before shaping; Fig. 3 is a side view of the filter assembly; Fig. 4 is an end view of the filter assembly; Fig. 5 is a cross-sectional end view of the filter assembly; Fig. 6 is a table of suitable materials for the filter assembly; and, Fig. 7 is a table of suitable materials for an exhaust silencer.

Referring to figure 1, a sheet 1 of expanded metal is cut into a substantially rectangular shape. If the sheet were to be used for an air filter, tapes 2 are fixed to the sheet 1 by an adhesive in a desired pattern as will be described further below. If the sheet were to be used for forming a silencer, a different pattern (not shown) will be defined. Two opposing ends 3 of the sheet 1 and the central portion of the sheet 1 are left exposed, although the ends 3 may be covered by tape 2 (see Fig. 2).

The sheet 1 is then formed into a cylinder with the ends 3 defining the open ends of the cylinder. The long sides 4 of the sheet 1 are joined, e.g., by a known lockseaming process which provides strength and rigidity, or by spot welding. For exhaust silencers, the sheet 1 can be formed into a cylinder prior to application of the tape 2, which can then act as a bond to join the long sides 4 of the sheet 1.

To form an air filter, a pleated paper filter element 5 is then inserted into the cylinder and an inner cylindrical support screen 6, which may also be of expanded metal is placed inside the filter element 5. Polymer sealant and end caps 7,8 are then attached by an adhesive melt process or a cross linking curing process to the ends 3 of the cylinder to hold the outer and inner screens 1,6 and filter element 5 in position to form a rigid air filter assembly.

One of the end caps 7 has a central passage 9. When the filter assembly is in use, gas can pass through the exposed areas of the screen 1, passing through the filter element 5 and out of the filter through the passage 9 to the engine intake.

The tapes 2 are sized and positioned to optimise the performance of the filter. In particular, the lower tape 2A (Fig.3) acts as a dust trap, allowing dust to settle in the lower part of the assembly. The upper tape 2B (Fig.3) prevents flow of air from the outside through the upper region of the assembly (i.e. near the exit hole 9), which helps to keep the upper part of the filter element 5 relatively clean. These two tapes 2A, 2B may be of similar width, or one may be wider than the other.

In both the air filter and exhaust silencer examples the tape 2 and adhesive used as the blocking film must be carefully selected to meet the operating performance and production process requirements. For example in the case of an exhaust silencer the adhesive and film must be able to withstand high temperatures and corrosive conditions for sustained periods in service. In the case of the filter assembly there are often high temperatures involved during the assembly process. Further, in some cases it may be desirable to use the film as the method of joining the long sides 4 to form the cylinder in place of welding or lockseaming, in these cases the film and adhesive combination must be strong enough to maintain an effective bond across the seam. The table shown in Figs. 6 and 7 list some examples of materials which are suitable. As mentioned previously, the tape could also be placed on or wrapped around exposed edges of the sheet 1 to prevent them damaging other components or causing injury during installation.

Claims (18)

1. An article comprising a foraminous screen, having a substantially uniform array of apertures and, an imperforate blocking film adhered to the screen, and closing the apertures in selected areas of the screen.

2. An article according to claim 1, wherein the screen is formed from expanded metal.

3. An article according to claim 1 or claim 2, wherein the apertures are closed by tape fixed to the face of the screen.

4. An article according to claim 3, wherein the tape has a thickness in the range 20 to 250 microns.

5. An article according to claim 4, wherein the tape has a thickness in the range of 50 to 100 microns.

6. An article according to any of claims 3 to 5, wherein the tape is fixed to the screen with an adhesive.

7. An article according to claim 6, wherein the adhesive has a thickness in the range of up to 250 microns.

8. An article according to claim 7, wherein the adhesive has a thickness in the range of up to 40 microns.

9. An article according to claim 6, claim 7, or claim 8, wherein the tape/adhesive combination is selected from the group of aluminium/acrylic, polyester/acrylic, clear polyester/XL acrylic, polyester/silicone, or polyamide/silicone.

10. An article according to claim 3, wherein the tape is a lacquered surfaced aluminium adhesive tape.

11. An article according to claim 1 or claim 2, wherein the apertures are closed by an aluminium or stainless steel foil used in combination with a filler or fibre impregnated resin.

12. A gas filter comprising an article according to any of the preceding claims and a filter element, which is supported by the article.

13. A gas filter according to claim 12, wherein the article and filter element are planar.

14. A gas filter according to claim 12, wherein the article and filter element are cylindrical, with the partially closed screen inside or outside the filter element.

15. A gas filter assembly comprising two cylindrical articles, at least one of the articles being in accordance with any of claims 1 to 11, and a filter element supported between the two cylindrical screens.

16. An exhaust silencer comprising an article according to any of claims 1 to 11.

17. An article substantially as described with reference to figure 1 of the accompanying drawings.

18. A gas filter substantially as described with reference to figures 2 to 4 of the accompanying drawings.