GB2147516A - Edge filter - Google Patents

Abstract

A fluid filter comprises one continuous strip of resilient plastic material formed into the shape of a helix of n turns with a rectangular cross-section of width W and thickness t in a direction perpendicular to the strip length. At least one of the surfaces of the strip is embossed to form grooves. The helix is compressed so that adjacent turns abut one another with the grooves providing flow paths. The strip may be embossed and curved in one operation by feeding it between knurled frusto-conical rollers. <IMAGE>

Description

SPECIFICATION A fluid filter, element and method of manufacturing it The present invention generally relates to filtering devices and more paricularly to a novel fluid filter and method of manufacturing it.

In a fluid filter device, e.g. a device used to filter water to remove contaminants therein, the water is made to pass through a filter element, hereafter simply referred to as the filter. In many devices the filter is in the shape of a cylinder of selected outer diameter (OD) with an axial opening of a selected inner diameter (ID). The thickness of the filter wall is half the difference between the OD and the ID. Typically, the filter is designed so that water can flow from its inner axial opening to the outside or vice versa through its wall which is honeycombed. Filtering takes place by contaminants getting trapped in the filter wall as the water flows through the particular wall weave pattern.

Presently, many filters are made of plastic material. Typically, thin annular discs, having fine grooves on both surfaces, are stacked onto a suitable backbone, and pressed together. The grooves are made so as to form a cross shaped pattern at the mating surfaces of the discs. Water, passing from the outside to the inside of the disc stake or vice-versa, is filtered, the particles in the water being held back in the fine grooves. The discs are usually made by injection molding from thermoplastic materials such as polyethylene or polypropylene. To provide a filter of reasonable height a large number of discs have to be stacked upon one another and thereafter secured together to form the final filter of the desired height.

Although a filter formed of a large number of such discs or rings functions reasonably satisfactorily, its cost is quite high. This is due to the need to carefully stack many rings and secure them together, thus increasing production cost. Clearly the cost increases as the desired height of the filter increases. Also, the flow pattern in a filter made up of a large number of rings is quite limited. Thus, the filtering properties of the final filter are necessarily limited.

A need therefore exists for a new filter and/or a method of forming a filter less expensively than those herebefore described.

These and other objects are achieved by providing a filter comprising: a single continuous elongated strip of elastic matter in the shape of a continuous spiral of n turns, the cross-section in a direction perpendicular to its length being substantially rectangular with a width and thickness definable as W and t, respectively, said spirally shaped matter being sufficiently elastic to compress the spiral turns to abut one another, so as to form a hollow cylindrical body of a height H substantially corresponding to nt, where n > > 1, with fluid flow paths between the adjacent surfaces of adjacent turns.

The novel filter is produceable by first providing an elongated continuous strip of elastic matter with a cross-section perpendicular to its length which is other than rectangular.

This strip, as it passes through embossing rollers is compressed to have a rectangular cross-section while at the same time is permanently shaped into one long spirally shaped strip of matter. Also, the roller emboss the strip's opposite surfaces as it passes between them to form water flow paths of a selected pattern between adjacent turns of the strip as these turns are made to abut one another.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawings.

Figures la and 1b are simple diagrams useful in explaining the prior art; Figure 2 is an isometric view of a strip of matter from which the novel filter is formed; and Figure 3 is an isometric diagram useful in explaining the novel method of manufacturing the novel filter.

In order to highlight the advantages and novelty of the present invention, the disadvantages of the prior art will first be summarized in connection with Figs. la and ib. Typically, herebefore to produce a filter 10 of a height H with an OD of LO and an ID of L1, a large number of flat discs or rings 12 are used. The rings are identical, one of which is shown in Fig. 1 b. Each ring has an OD of LO and ID of L1, with a wall width W, where W = +(L0 - L1). The ring thickness t is very small compared to the desired filter height H.

Each ring is formed so that at least one of its surfaces is embossed to form grooves through which water can flow. The grooves are represented in Fig. 1 a by 15. To form filter 10 a large number of rings 12 are first stacked on one another, and then pressed and secured to each other to form an integral body of the filter. The filter is actually a hollow cylinder with OD and ID of LO and L1, respectively, and with a wall of thickness W, through which water to be filtered can flow between grooves 15. Typically, the rings 12 are formed of plastic matter, e.g. polyethylene or polypropylene. The disadvantages of such a filter have been discussed hereabove.

Unlike the prior art, in accordance with the present invention the novel filter is formed from one continuous elongated strip of matter, e.g. plastic, designated in Fig. 2 by 20.

The continuous strip is spirally shaped to form a plurality of convolutions or turns, each of which is effectively like a ring of an OD of LO and ID of L,. Viewed in a direction perpendi cular to its length the cross-section of the strip 20 is rectangular, having a width W and a thickness t, where, W/t is up to 30:1. At least one side or surface of the strip 20 is embossed as designated in Fig. 2 by 22.

To form a filter from strip 20, the latter is simply compressed, in the manner of compressing a coil spring until adjacent turns are pressed or ablit one another. Once compressed, the turns are secured together, e.g.

by glueing or other means. Thus the spirally shaped strip, once compressed, becomes a filter in the shape of a hollow cylinder. As to filter height, it is easily controllable by simply using strip 20 of a length with a sufficient number of turns, generally designated as n, each of thickness t so that when they are pressed together nt = H, H being the desired height of the filter. Forming a filter made up of one long spirally shaped strip is clearly much easier and cheaper than having to stack a large number of separate rings. As to the flow paths through the filter they are present through the embossed surfaces of adjacent turns of the strip. By embossing both surface of the strip embossed surfaces of adjacent turns abut one another, to produce a crisscross pattern of grooves which serve as the flow paths.This is highly desirable since it increases the flow path length and the number of possible paths, thereby increasing filter efficiency and prevents clogging. Thus, with the present invention an improved filter can be formed at less cost then herebefore attainable.

Attention is now directed to Fig. 3 in connection with which a novel method of producing the continuously long, spirally-shaped strip 20, shown in Fig. 2, will be described.

The strip is assumed to be made of plastic material. Let it be assumed that it is desired to form strip 20 of a width W, thickness t, with an OD = 2R and ID = 2r. To this end, a continuously long piece or strip 20a of plastic is first extruded, in a straight line from a thermoplastic material through a suitable extruding die (not shown). As shown in Fig. 3, viewing the cross-section of the strip 20a perpendicular to its length, it is essentially trapezoidal. The trapezoid height is W and the dimensions of its two parallel sides are t and t', where t' = t(R/r).The extruded strip 20a before it totally hardens, is made to pass through two truncated cone-shaped embossing rollers 30 and 31, of a conical shape of a selected included angle, e.g. 60 and whose axes, about which they are made to rotate by any appropriate means (not shown), are designated by 30x and 31x. Ignoring for a moment the embossing protrusions or projections 30z and 31z on the two rollers, the rollers are spaced apart so that their most adjacent surfaces are parallel and essentially form a gap on the order of t. Consequently as the trapezoidally shaped strip 20a passes through these rollers, the irapezoidally shaped strip 20a is squeezed into the rectangularly shaped, yet spirally shaped strip 20.The rollers are shaped so that the wider end of the strip 20a of thickness t' passes between the rollers whereat their circumferences C are equal to 7rR, while the narrower end of strip 20a passes where the circumference of each roller equals srr. The rollers are internally cooled to solidify strip 20a into 20, while at the same time embossing takes place.

In the absence of embossing protrusions 30z and 31z on the outer surfaces of the two rollers, the continuously long spirally shaped strip 20 would have flat top and bottom surfaces and would not have the flow path therethrough. However, by providing the protrusions 30z and 31z, which act as embossing surfaces. as the strip 20a passes through the rollers, in addition to being squeezed to assume the spiral shape, the grooves 22 are formed to serve as flow paths on both sides of strip 20. That is, the embossing projections on the rollers are spaced and directed at such an angle as to produce parallel grooves. oblique to the edge of the strip, and with opposite angular direction on the two sides Consequently when adjacent turns of the strip 20 are squeezed against one another to form essentially a hollow cylinder of wall thickness W, flow paths are formed to enable water or other fluid to flow either from inside the cylinder to the outside or vice versa.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

Claims (10)

1. A fluid filter comprising: a continuous elongated strip of elastic matter formed in the shape of a spiral of n turns with a cross-section in a direction perpendicular to its length being essentially rectangular with a width definable as W and a thickness definable as t, with at least one of the surfaces of the strip being embossed, said matter being sufficiently elastic to be compressed so that surfaces of adjacent turns abut one another to form a substantially hollow cylinder of height H which is substantially equal to n.t, with fluid being adapted to flow through the embossed surfaces of the strip.

2. A filter as recited in Claim 1 wherein said matter is plastic.

3. A filter as recited in either of Claims 1 or 2 wherein said strip is embossed on both sides thereof, whereby when said strip is compressed, embossed surfaces of adjacent turns abut one another.

4. A method of forming a fluid filter in the shape of a hollow cylinder, the steps compris ing: forming an elongated strip of compressible elastic matter with a preselected cross-section along its length; passing said strip through embossing means to convert said strip into an elongated spirally shaped strip of a plurality of turns each turn being effectively in the shape of a flat ring-shaped disc of a selected outer diameter (OD) and with a central opening of a diameter definable as the inner diameter (ID) with a wall width definable as W, wherein 2W = OD-ID and of a thickness t, the spirally shaped strip being embossed on at least one side thereof; compressing a preselected number of turns definable as n so that the surfaces of adjacent turns abut one another; and retaining the turns compressed against one another.

5. A method as recited in Claim 4 wherein the width of the elongated strip is substantially equal to W.

6. A method as recited in either Claim 4 or Claim 5 wherein the elongated strip is initially formed with an essentially trapezoidal cross-section of height W and the two parallel sides being essentially equal to t and t', wherein t equals the thickness of each turn and t' is a function oft and the OD and ID of each turn.

7 A method as recited in Claim 6 wherein t' = t(R/r) where R = i(OD) and r = +(ID).

8. A method as recited in Claim 7 wherein the elongated strip is passed through embossing means which comprise a pair of rotatable conically shaped rollers spaced apart a distance not greater than t, through which the elongated strip passes, to be spirally shaped with at least one side thereof being embossed.

9. A fluid filter substantially as described in conjunction with the Figures.

10. A method of forming a fluid filter substantially as described in conjunction with the Figures.