Abstract:
A filter device includes a filter housing ( 10 ), a filter inlet ( 12 ), a filter outlet ( 14 ), and a filter element ( 16 ). The filter element divides a filter area ( 18 ) into two partial areas ( 20, 22 ). One partial filter areas is conical in form with the cross-section of that partial area ( 20 ) being tapered from the filter inlet ( 12 ) to the filter outlet ( 14 ). The partial areas are separated from each other by the filter element. This arrangement results in an optimum residence time distribution inside the filter device at a uniform flow rate, which is particularly useful for highly viscous fluids such as polymer melts or similar.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a filter device with a filter housing having an inlet, an outlet and a conical filter element subdividing the filter space into two subspaces. 
   BACKGROUND OF THE INVENTION 
   Filter devices, such as those disclosed in U.S. Pat. Nos. 4,964,984, 4,169,795, 4,052,315, 4,043,918, and in GB 2 075 364), are readily obtainable on the market in a multiplicity of embodiments. The structure of the filter elements, which filter impurities out of a fluid, is determined by the manufacturer. Filter elements of higher quality have a multilayer meshed structure which may rest at least on one supporting fabric to enable the structure to resist higher pressure or pressure peaks. 
   In principle, it is desirable to arrive at uniform flow behavior inside the filter space during the filtration process, while avoiding dead spaces. The requirements set for the desired behavior increase as the viscosity of the fluid increases, especially if liquefied polymer materials or polymer solutions are to be filtered. 
   U.S. Pat. No. 3,817,377 discloses a generic filter device, in particular one for separation of impurities from hot thermoplastic polymer material. In one embodiment of the conventional filter device shown in  FIGS. 4 and 5  of that patent, a conical filter element subdivides a conical filter space into two conical subspaces. The conicities of the two subspaces extend constantly in opposite directions but to different extents, that is, with different cross-sections relative to one point of reference. The diameter of the filter element is measured from the filter outlet in the direction of the filter inlet more or less constantly. The resulting conicity of the filter element is referred to the longitudinal direction of the filter outlet. The bounding walls following the subspaces as housing elements have a conical orientation comparable to that of the filter element, so that the conventional solution applied for this purpose is complex in structure. Control of flow, which is unfavorable from the viewpoint of energy, is obtained because of the different cross-sectional patterns referred to one point of comparison, especially in the case of high-viscosity fluids. 
   SUMMARY OF THE INVENTION 
   Objects of the present invention are to provide filter devices with improved filter operation from the viewpoint of energy consumption. 
   According to the present invention, narrowing of the cross-section of one of the two subspaces occurs to the same extent as does widening of the cross-section of the other subspace. One of the subspaces extends outward toward the exterior. The other subspace extends inward toward the center of the filter device. Each subspace is bounded by a cylindrical wall. The filter element narrows conically in the direction from the filter outlet to the filter inlet. Because of the equally varying cross-sections and volumes of the two subspaces, an optimal dwell time distribution is achieved, along with uniform rate of flow of fluid of especially high viscosity, such as one in the form of liquefied polymer material or a polymer solution. Also, in filtering operation, dead spaces inside the filter housing may be prevented and uniform distribution of the mass to be filtered is provided. This arrangement results in filtration operation with acceptable energy costs and in cost reduction. In addition, the fluid to be filtered expands from a narrow cross-section toward a wide cross-section and, conversely, from a wide subspace into a subspace with correspondingly narrowed cross-section. 
   To obtain conical subspaces, the filter element itself is conical in form and tapers from the filter outlet in the direction of the filter inlet. Accordingly, as viewed in the fluid or filter direction, the subspace with the cross-section tapering toward the filter outlet is mounted upstream from the filter element. The other subspace with the widening cross-section is downstream of the filter element. Preferably, the filter element has a supporting tube. The filter material is mounted on the supporting tube so as to be replaceable. The support tube ensures that the filter element is able to perform its function when subjected to high pressures. The replaceability allows the filter element material, once depleted, to be replaced with new material without making complete replacement of the filter element plus supporting tube necessary. The filter housing is preferably cylindrical in form, at least in the area of the filter element. 
   In an especially preferred embodiment of the filter device of the present invention, the filter inlet and outlet have cross-sections open in the direction of the filter space so that uniform distribution of the fluid to be filtered is also ensured in these locations. The filter housing, the filter inlet and outlet, and the filter element with supporting tube and filter material are preferably formed of special steel materials. 
   Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
       FIG. 1  is an elevational side view, partly in section, of a filter device according to an embodiment of the present invention; 
       FIG. 2  is a side elevational view, partly in section of the filter element illustrated in  FIG. 1 ; and 
       FIG. 3  is an enlarged partial side elevational view, partly in section, of the lower connection area of the filter device of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The filter device, essentially cylindrical as a whole, has a filter housing  10  and filter inlet  12  and filter outlet  14 . A filter element  16  as a whole is mounted inside the filter housing  10 . This element subdivides a filter space  18  into a first subspace  20  and a second subspace  22 . The first subspace  20  tapers, as is shown in  FIG. 1  in particular, from the filter inlet  12  to the filter outlet  14  in free cross-section. The second subspace  22  on the other hand, widens from the filter inlet  12  to the filter outlet  14  in cross-section. The tapering of one subspace  20  in cross-section proceeds to the same extent and steadily as does widening of the other subspace  22  in cross-section. Hence, the two subspaces  20  and  22  are juxtaposed so as to be conical in form. In addition, the subspaces  20  and  22  form closed ring-shaped chamber structures inside the filter device. 
   The filter element  16 , which itself is conical in shape and tapers conically from filter outlet  14  to filter inlet  12 , is used to create the conicity in the subspaces  20  and  22 . 
   The filter element  16  has meshed filter material  24 , the inner circumference of which rests against a supporting tube  26  with fluid passages. The filter material  24  surrounds the outer circumference of the supporting tube  26 , and is applied around the supporting tube  26  as a filter mesh. The filter housing  10 , on the other hand, is cylindrical in shape in the area into which the filter element  16  is introduced. As seen in  FIGS. 1 and 3  for the lower area, the filter inlet  12  and the filter outlet  14  have opening cross-sections to the filter space  18  which are free so that a uniform distribution of the rate of movement of the fluid to be filtered, especially fluid in high-viscosity form such as liquefied polymer material or a polymer solution, is ensured. In the last-named case, the filter housing  10 , the filter inlet  12 , and the filter outlet  14 , as well as the filter element  16  with supporting tube  26  and filter material  24 , are made of special steel material. 
   As the illustration in  FIG. 2  shows, the filter element  16  may also be constructed without a supporting tube  26 , and the filter material  24  in the form of a special steel mesh is introduced so as to be self-supporting between end caps  28  and  30 . As viewed in the figures, in the area of the upper end cap  28  the free end of the hollow cylindrical filter material  24  is bent inward to form a point of application  32  on the upper end cap  28 . The end caps  28  and  30  are rigidly connected to the filter material  24  and may be pulled away with it, to the extent it is present, from the supporting tube  26  and disposed of separately, if the degree of fouling makes this necessary. New, unused filter material  24  with corresponding end caps  28 , is then forced onto the supporting tube  26  or is inserted together with it into the filter device as a component. 
   As  FIG. 1  also shows, the filter element  16  is fixed in place between an upper receptacle element  34  and a lower receptacle element  36 . On its free end, the upper receptacle element  34  has a conical guide cone which, together with the upper cover element  38  of the filter housing  10 , delimits a fluid channel  40 . Channel  40  forms a circulating ring channel and is configured in its cross-sectional form, as illustrated, to provide a uniform inflow of the high-viscosity into the first subspace  20 . For this purpose, the fluid channel  40  narrows toward its free frontal end where it discharges into the first subspace  20 , opposite the entry point extending in the same form at the fluid inlet  12 . The direction of delivery of the fluid is indicated by an arrow in  FIG. 1 . The direction of drainage at the filter outlet  14  is also indicated by an arrow. 
   The fluid flowing through the filter device in the direction of the arrow, which is charged with fouling on the filter inlet  12  side, passes through the fluid channel  40  into the first conical subspace  20  and fills this subspace so that there is no dead space. In the event of a uniform dwell time in the first subspace  20 , the fouled fluid passes evenly and constantly through the filter material  24  and is there suitably filtered clean. The cleaned fluid then passes through the free passage points of the supporting tube  26  into the second subspace  22  and the other fluid channel  42  on the filter outlet  14  from the filter device, now cleaned. As regards the double conicity of the two subspaces  20 ,  22  mounted so as to extend in opposite directions, it is characterized by uniform rate of flow, so that optimal dwell time distribution over the filter element is ensured. 
   Inside the filter device upper receptacle element  34  rests on a rod-shaped filter element  44 , which preferably is also is made of special steel material. The filter element  44  may also be guided or extended inside the filter device by the receptacle element  34 , and fixed in position inside the filter device. The filter housing  10  has a cylindrical central housing section  46  rigidly connected to the upper cover element  38  and the lower cover element  50  by weld joints  48  on the edge. The lower cover element  50  holds the lower receptacle element  36  on the filter housing  10  in place by screw connection  52 , thereby immobilizing the filter element  16  inside the filter space  18  as a whole. The upper cover element  38 , as viewed in the direction of  FIG. 1 , narrows in diameter upward and forms a connection point for a swivel nut  54  by which a feed connection piece  56  for delivery of liquefied polymer material may be connected. On the opposite end of the filter device, a corresponding swivel nut  58  is provided by which a drain connection piece  60  for discharge of the filtered fluid in the form of purified liquefied polymer material is connected to the filter device. A corresponding threaded section (not shown) facilitates the pertinent fastening. 
   Loosening of the screw connection  52 , which comprises several fastening screws mounted radially over the circumference of the filter device, permits detachment of the lower receptacle element  36  and removal of the filter material  24  with and without supporting tube  26 . Filter element replacement can thus be carried out quickly. The filter element  16  and the filter material  24 , as well as the two subspaces  20 ,  22  as thus conditioned, exhibit only slight conicity, for example, in the form of inclination relative to the horizontal and/or in the transverse direction of the filter device of the order of magnitude of 1° to 5°. 
   While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.