FILTER OF DEPTH LAYER TYPE

Abstract: A filter of depth layer type comprises a generally cyl­ indrical filter body (2) formed by laminating filter elements (10) each in the form of a thin sheet of filtering material having a central hole (10), and these central holes (10) pro­ vide a conduit (4) extending in the axial direction through the filter body (2). The filter body (2) has a density dis­ tribution in which the density is lowest at the outer peri­ pheral area which serves as an inlet for the fluid to be filtered, and becomes progressively higher toward the conduit (4), which serves as an outlet for the filtered fluid.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a filter of depth layer type which can remove impurities from a fluid with very high reliability in spite of a simple structure. Description of the prior Art A filter body of a filter of depth layer type has such a density distribution that the density is lowest in an area of its inlet side where a fluid such as oil to be filtered flows into the filter, and the density is progressively increased toward an area of its outlet side where the oil flows out from the filter. Because of such a density distribution, the filter of depth layer type can arrest a large amount of large and small impurities at a low pressure with least possibility of clogging. A filter of so-called roll paper type is known as an example of prior art filters of this kind. In the filter of roll paper type, a filtering material is wound into the form of a roll, and one of the axial ends of the roll is radially most compressed to have a highest density so as to provide a density distribution in which the density progressively decreases from that end toward the other end of the roll. A fluid such as oil is supplied from the large-diameter side toward the small-diameter side of the roll, that is, from the low-density inlet side toward the high-density outlet side of the roll to remove impurities from the oil. A filter of herringbone twill type for filtering a fluid such as oil is also known as another example of prior art filters of this kind. The filter of twill type includes a filter body made by winding a braid-like filtering material in a twill pattern around a hollow cylindrical core member. The manner of winding is such that the filtering material is initially closely wound under a strong tension on the outer peripheral surfare of the core member and is then progressively coarsely wound under a progressively lower tension. That is, the filter body of the filter of twill type has a density distribution in which the density becomes progressively higher radially inward. However, in the filter of roll paper type described above, creases tend to be produced on the surface of the filter body during compression of the filtering material in the radial direction, and, when these surface creases are produced as a result of strong compression, undesirable paths of oil are formed in the filter body through which oil flows directly without being filtered. Therefore, the filter of roll paper type has had the problem that the desired delicate density distribution cannot be provided in the filter body due to the impossibility of strong compression of the filtering material, and the impurity arresting capability cannot be improved. Also, in the case of the filter of herring bone twill type, the total length of the filtering material wound in the twill pattern around the core member is large, and, in addition, the filtering material must be wound while changing the tension and direction of winding to provide the radial density distribution described above. Therefore, the filter of twill type has had the problem that the requirement of a great deal of labor and time results in a high cost, and uniformity of the properties of products is difficult to attain. DE-B-1 109 648 discloses a filter with the features set forth in the first part of claim 1. The individual filter elements, which are laminated upon each other to form the filter body, each consist of a thin sheet of filter material and has a shape that is formed by four sectorial recesses, between which a pair of radially opposite narrow lobes and a pair of opposite wide lobes with straight outer edges are situated. Adjacent sheets are rotated by 60% so that a filter body having a shape of a somewhat hexagonal prism with rounded edges is produced. The complicated shape of the individual filter sheets entails comparatively high manufacturing costs and large amounts of waste. SUMMARY OF THE INVENTION It is an object of the present invention to provide a filter of the depth layer type capable of efficiently removing impurities from a fluid such as oil inspite of an uncomplicated structure. The invention meets this object by the filter characterised in claim 1, a preferred development of the invention being set forth in claim 2. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of an embodiment of the filter of depth layer type according to the present invention. Fig. 2 is front elevation view of the filter shown in Fig. 1. Fig. 3 is a graph showing the relation between the degree of pressurization and the degree of compression in the filter shown in Fig. 1. An embodiment of the filter of the depth layer type according to the present invention will be described with reference to Figs. 1 to 3. Referring to Fig. 1, the filter includes a filter body 42 which is in the form of a hexagonal prism in its overall shape and has a central through-hole or conduit 44. This filter body 42 is formed by alternately laminating many filter elements 46 in three different directions, that is, at an angle of 120° therebetween to constitute the shape of the hexagonal prism. Each of the filter elements 46 is in the form of a rectangular sheet of a filtering material such as paper or nonwoven cloth and has a central circular hole 48. The ratio between the short and long sides of the rectangular sheet is preferably 1: √ 3 . These filter elements 46 are laminated so as to form a hexagonal external shape as described above and so that their circular holes 48 are continuously aligned to define the conduit 44 extending through the center of the filter body 42. In the filter body 42 constituted in the manner described above, all the filter elements 46 are superposed in an area C around the conduit 44, 2/3 of the filter elements 46 are superposed in areas B, and 1/3 of the filter elements 46 are superposed in areas A,as shown in Fig. 2. Therefore, this filter body 42 has the function of depth layer filtration in that the filter density is low in its outer peripheral portion and progressively increases toward the center of the filter body 42. Thus, when a flow such as oil to be filtered flows into the filter body 42 from the outer peripheral surface of the filter body 42 and flows out from the central conduit 44 of the filter body 42, relatively large impurities are arrested in the outer peripheral filter-body portion, and relatively small impurities are arrested in the central filter-body portion. Therefore, impurities including those of very small sizes can be efficiently arrested. This filter body 42 may be suitably compressed in the direction of lamination. When the filter body 42 is thus compressed in the direction of lamination, the superposed states of the portions of the filter elements 46 in the areas A, B and C are changed to change the distances between the portions of the filter elements 46 in the individual areas. Suppose that the filter body 42 a has a total length L₁ before pressurization, and this total length L₁ is reduced to a length L₂ after pressurization. In this case, the degree of pressurization is expressed as and the relation between the degree of pressurization and the degree of compression is as shown in Fig. 3. It will be seen in Fig. 3 that the filter element portions in the area C are compressed in proportion to the degree of pressurization of all the filter elements 46 as shown by a curve t C . It will also be seen that the filter element portions in the areas B start to be compressed after the degree of pressurization of all the filter elements 46 exceeds about 30% as shown by a curve t B ,.and the filter element portions in the areas A start to be compressed after the degree of pressurisation of all the filter elements 46 exceeds about 60% as shown by a curve t A . Thus, the states of compression of the portions of the filter elements 46 in the areas A, B and C can be suitably changed. In this case, holding plates are disposed at both ends respectively of the filter body 42, and, after the step of predetermined pressurization as described above, the holding plates are fixed in position by suitable fixing means. The aforementioned embodiment has referred to employment of filter body in the form of a hexagonal prism. However, it is apparent that the present invention is in no way limited to a filter body of such a specific shape, and the ratio between the long and short side of the filter elements and the directions of lamination of the filter elements 46 may be suitably modified to provide filter bodies of any other shapes including an octagonal prism.

Claims: A filter of the depth layer type comprising a generally prismatic filter body (42) formed of a plurality of laminated filter elements (46) each in the form of a thin sheet of filtering material having a central hole (48), the holes (48) providing a continuous inner conduit (44) axially extending through said filter body (42), adjacent filter elements (46) being rotated with respect to each other by a predetermined angle about the axis so that central portions of the laminated filter elements (46) result in a central area of the filter body (42) having the highest density, with the density becoming progressively lower towards outer peripheral portions of the filter elements (46), characterised in that all said filter elements (46) are in the form of rectangular sheets. The filter of claim 1, wherein each rectangular sheet has a ratio of 1:√ 3 between its short and long sides, and said predetermined angle is 120°.

Inventors: NAKAJIMA, YOSHIAKI, SUZUKI, TADASHI, WADA, YONEJI
Applicants: TAKANO CORPORATION
Application year: 1988
Main classification: B01D29
IPC codes: B01D27, B01D39, B01D29