Patent Description:
Thermoplastic polymers in the molten state are often filtered to remove impurities, such as solids and/or gels, before they are passed to a mold cavity or through a die plate. Examples of polymer filtering devices are shown in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

The filter portion of these devices typically includes a foraminous supporting plate and a plurality of filters resembling sticks or candles. The filters themselves are composed of tubular support structures with one or more filter media in the form of a sleeve wrapped around the tubular support structures.

Both the foraminous supporting plates and the tubular support structures available in the market today, however, suffer from a number of disadvantages. For example, the design of the tubular support structures is not very efficient for filtering or for replacement. Moreover, the foraminous supporting plates and the tubular support structures are susceptible to cracking and breakage under normal use.

Thus, there is a need in the art for improved foraminous supporting plates and tubular support structures for filtering polymer melts.

The present invention addresses this need as well as others, which will become apparent from the following description and the appended claims.

The invention is as set forth in the appended claims.

Briefly, in a first aspect, the present invention provides a polymer melt filter support. The filter support comprises:.

In a second aspect, the present invention provides a polymer melt filter. The filter comprises a filter support according to invention and one or more filter elements around the second end portion of the cylindrical body.

In a third aspect, the present invention provides a polymer melt filter plate assembly. The plate assembly comprises:.

In a fourth aspect, the present invention provides a process for filtering a polymer melt. The process comprises passing a polymer melt through the one or more filter elements around the second end portion of the cylindrical body of the polymer melt filter according to the invention, and withdrawing a filtered polymer melt from the inside of the cylindrical body.

In a first aspect, the present invention provides a polymer melt filter support. The filter support comprises:.

In another embodiment, the polymer melt filter support further comprises:
a hex fitting on the inside surface of the first end portion for receiving a hex wrench.

<FIG> shows a polymer melt filter support <NUM> according to an embodiment of the invention. The filter support <NUM> includes a hollow cylindrical body <NUM>, which resembles the shape of a tube. The body <NUM> includes or is defined by a first end <NUM>, a second end <NUM> (opposite the first end <NUM>), and a cylinder wall <NUM> (disposed between the two ends <NUM> and <NUM>). The cylinder wall <NUM> includes a first end portion <NUM> proximate or adjacent to the first end <NUM> and a second end portion <NUM> proximate or adjacent the second end <NUM>. The first end portion <NUM> includes a screw thread <NUM> on at least a portion of its outside surface. The screw thread <NUM> is adapted to engage and securely hold the filter support <NUM> in place with threaded holes in a support plate <NUM> (see <FIG>).

The second end portion <NUM> of the cylinder wall <NUM> includes a plurality of holes <NUM>. The holes <NUM> extend through the cylinder wall <NUM> so as to allow a polymer melt from outside of the body <NUM> to flow inside of the body <NUM>. Arrows F show the direction of polymer flow during normal operation. Furthermore, as will be explained in greater detail below in connection with <FIG>, the area of (or defined by) the openings <NUM> of the holes <NUM> on the outside surface of the cylinder wall <NUM> is larger than the area of (or defined by) the openings <NUM> of the corresponding holes on the inside surface of the cylinder wall <NUM>. Additionally, the shape of the openings <NUM> of the holes <NUM> on the outside surface of the cylinder wall <NUM> is non-circular. By "non-circular," it is meant any geometric shape except for a perfect circle. Examples of non-circular shapes include triangles, squares, rectangles, ovals, ellipses, quatrefoils, rhombuses, pentagons, hexagons, etc..

The number of holes in the second end portion <NUM> may be any number desired. In one embodiment, the second end portion <NUM> includes <NUM> holes arranged in <NUM> rows of <NUM> holes per row. In another embodiment, the second end portion <NUM> includes <NUM> holes arranged in <NUM> rows of <NUM> holes per row.

The cylindrical body <NUM> may be made of any material that can withstand the conditions inside of a filtering apparatus for a polymer melt over an extended period of time. Such conditions include operating temperatures of up to <NUM> and operating pressures of up to <NUM>,<NUM> psi (or approximately <NUM> MPa). Preferably, the cylindrical body <NUM> is made of <NUM>-<NUM> PH stainless steel, which has been heat treated according to Condition H <NUM> after the body <NUM> has been machined. <NUM>-<NUM> PH stainless steel is a precipitation-hardening martensitic stainless steel. It generally contains <NUM> - <NUM> wt% of chromium, <NUM> - <NUM> wt% of copper, <NUM> - <NUM> wt% of nickel, <NUM> - <NUM> wt% of niobium plus tantalum, and the balance of iron. <NUM>-<NUM> PH stainless steel may contain up to <NUM> wt% of carbon, up to <NUM> wt% of manganese, up to <NUM> wt% of phosphorus, up to <NUM> wt% of sulfur, and up to <NUM> wt% of silicon. <NUM>-<NUM> PH is commercially available. It is typically furnished in the annealed condition. This is also called the solution heat treated condition, or Condition A. According to Condition A, annealing is conducted by heat treating at approximately <NUM>°F (<NUM>) to <NUM>°F (<NUM>) and cooling to room temperature. In this condition, the material possesses a martensitic structure. To further increase its strength, the cylindrical body <NUM> is preferably precipitation hardened, after machining, by heat treatment in air at <NUM>°F +/- <NUM>°F (<NUM> +/- <NUM>) for <NUM> minutes +/- <NUM> minutes, which is known as Condition H <NUM>.

The cylindrical body <NUM> can be of any desired size. In one embodiment, the body <NUM> has a height of <NUM> inches (<NUM>). In another embodiment, the body <NUM> has a height of <NUM> inches (<NUM>). Preferably, the height of the first end portion <NUM> is the same regardless of the overall height of the body <NUM>. In one embodiment, the height of the first end portion <NUM> is <NUM> inches (<NUM>). In which case, the height of the second end portion <NUM> can be <NUM> inches (<NUM>) or <NUM> inches (<NUM>).

Preferably, the ratio of the outside diameter of the cylinder wall <NUM> to the inside diameter of the cylinder wall <NUM> ranges from <NUM> to <NUM>. In one embodiment, the cylinder wall <NUM> has an outside diameter of <NUM> inches (<NUM>). In which case, the cylinder wall <NUM> can have an inside diameter of <NUM> inch (<NUM>) to <NUM> inches (<NUM>). Preferably, the cylinder wall <NUM> has an inside diameter of <NUM> inches (<NUM>).

As seen from <FIG>, the first end <NUM> includes an opening <NUM> for the polymer melt inside of the body <NUM> to flow outside of the body <NUM>. In one embodiment, the inside surface of the first end portion <NUM> includes a hex fitting <NUM> for receiving and engaging with a hex wrench (not shown). The hex fitting <NUM>, via the use of a hex wrench, enables the filter support <NUM> to be easily attached to and removed from the support plate <NUM> (<FIG>). In the case the inside diameter of the cylinder wall <NUM> is <NUM> inches (<NUM>), the farthest distance between any two opposing points of the hex fitting <NUM> can be, for example, <NUM> inches (<NUM>).

<FIG> shows a sectional view of the filter support <NUM> and, in particular, a sectional view of the second end portion <NUM> of the cylindrical body <NUM> along line A-A in <FIG>. The cylinder wall <NUM> is represented by the solid areas. The clear areas between the solid areas represent the holes <NUM> in the cylinder wall <NUM>. From this view, it can be seen that this embodiment of the filter support <NUM> contains <NUM> holes in this row (the number of holes per row as well as the number of rows of holes can vary as desired). Moreover, it can be seen that the size or area of the openings <NUM> of the holes <NUM> on the outer surface of the cylinder wall <NUM> is larger than the size or area of the openings <NUM> of the corresponding holes <NUM> on the inner surface of the cylinder wall <NUM>. The direction of polymer melt flow through the holes <NUM> is marked by the arrow F. It has been surprisingly discovered that the larger size of the openings <NUM> on the outer wall surface increases the cross-sectional area for the polymer melt to flow and be filtered, thereby increasing the overall filtration efficiency of any filter that employs the filter support according to the invention.

<FIG> is a sectional view of the filter support <NUM> from <FIG> along line C-C. From this view, the hollowness of the cylindrical body <NUM> can be seen as well as the opening <NUM> located at the first end <NUM> and the opening <NUM> located at the second end <NUM>. The hex fitting <NUM> on the inside surface of the first end portion <NUM> of the cylindrical body <NUM> can also be seen from this view. <FIG> further shows an optional recess, indentation, or notch <NUM> along the inside surface of the cylindrical wall <NUM> at the opening <NUM>.

<FIG> is an enlarged view of the second end portion <NUM> of the cylinder wall <NUM> along circle D from <FIG>. In this view, the rows of holes <NUM> in the second end portion <NUM> of the cylinder wall <NUM> can be seen.

<FIG> is an enlarged view of the second end portion <NUM> of the cylinder wall <NUM> around area B from <FIG>. From this view, the rows of the holes <NUM> in the second end portion <NUM> of the cylinder wall <NUM> can be seen as well as the details of the holes <NUM>. As noted above, in accordance with the invention, the size or area of the openings <NUM> of the holes <NUM> on the outer surface of the cylinder wall <NUM> is larger than the size or area of the openings <NUM> of the corresponding holes <NUM> on the inner surface of the cylinder wall <NUM>. The openings <NUM> and <NUM> have a non-circular shape. The shapes of the openings may be formed by any known machining technique. Preferably, the openings <NUM> have shapes resembling an oval or an ellipse. As used herein, the terms "oval" and "ellipse" (and variations thereof) are intended to include shapes that are generally or substantially oval, and generally or substantially elliptic, respectively. When modifying geometric shapes, the terms "generally" and "substantially" mean that the actual shape resembles the named shape more than any other basic geometric shape, such as triangle, square, rectangle, circle, and oval/ellipse.

Preferably, the greatest distance between any two opposing points on the perimeter of the oval or elliptic openings <NUM> in the horizontal direction is greater than the greatest distance between any two opposing points on the perimeter of the oval or elliptic openings <NUM> in the vertical direction. In other words, the horizontal diameter (DH) of the oval or elliptic openings <NUM> is preferably greater than the vertical diameter (DV) of the openings <NUM>. The ratio of DH / DV can be at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM>, or at least <NUM>. Vertical refers the direction along (or parallel to) the axis of the cylindrical body <NUM>, and horizontal refers to the direction perpendicular to the axis of the cylindrical body <NUM>.

In one embodiment, the oval or elliptic shapes of the openings <NUM> are formed by first forming circular openings, and then taking scalloped cuts on opposing sides of the circular openings to form the oval- or elliptic-shaped openings. In the case of <FIG>, the scalloped cuts are made on the left and right sides of the originally circular openings. The scalloped cuts give the left and right sides of the openings <NUM> a generally chamfered profile.

<FIG> is an exploded view of one of the oval/elliptic openings <NUM> with markings showing DV and DH. As seen from <FIG>, the shape of the opening <NUM> is not a perfect oval or ellipse, but to the naked eye, it resembles an oval or ellipse more than other basic geometric shape. In one embodiment, DH is <NUM> inches (<NUM>) and DV is <NUM> inches (<NUM>), giving rise to an open area of <NUM> in<NUM> (<NUM><NUM>). In another embodiment, DH is <NUM> inches (<NUM>) and DV is <NUM> inches (<NUM>), giving rise to an open area of <NUM> in<NUM> (<NUM><NUM>).

Preferably, the shape of the openings <NUM> of the corresponding holes <NUM> on the inside surface of the cylinder wall <NUM> is circular. The term "circular," as used herein, is intended to include generally circular or substantially circular shapes.

The area or size of the openings (inlets) <NUM> can be, for example, at least <NUM>%, <NUM>%, or <NUM>% larger than the area or size of the openings (outlets) <NUM> of the corresponding holes <NUM>.

Also, as shown in <FIG>, to maximize the size and number of the holes <NUM>, each row of holes <NUM> can be staggered or offset from the rows immediately above and below it. For example, each row of holes <NUM> can be staggered or offset from the next row by the radius of the openings <NUM>.

<FIG> shows a cone insert <NUM> according to the invention. As seen from <FIG>, the cone insert <NUM> is adapted to fit inside of the second end opening <NUM> of the cylindrical body <NUM>, with the apex <NUM> of the cone insert <NUM> pointing towards the first end opening <NUM>. As seen from <FIG>, and <FIG>, the cone insert <NUM> includes a curved lateral surface <NUM> towards, proximate, or adjacent to its base <NUM>. The curved lateral surface <NUM> serves the function of gradually directing the inflow of polymer melt towards the center of the cylindrical body <NUM>.

The base <NUM> has a diameter that is about the same as or slightly smaller than the inside diameter of the cylindrical body <NUM>. Any gap between the diameter of the base <NUM> and the inside diameter of the cylindrical body <NUM> should be minimized so as to avoid polymer melt from collecting in or passing through the gap. The thickness of the base <NUM> should be such that the top row <NUM> of holes <NUM> directs the flow of polymer melt towards in the curved lateral surface <NUM> inside of the cylindrical body <NUM>. The curved lateral surface <NUM> together with the non-curved lateral surface <NUM> of the cone insert <NUM> gradually directs the flow of incoming polymer melt towards the direction of the first end opening <NUM> where the filtered polymer melt eventually exits the filter support <NUM>.

The cone insert <NUM> also includes a base plate <NUM> located on the other side of the base <NUM>, i.e., opposite the side with the curved lateral surface <NUM>. The base plate <NUM> preferably has a diameter that is larger than the inside diameter of the cylindrical body <NUM>, but smaller than the outside diameter of the cylindrical body <NUM>. The perimeter portion <NUM> (see <FIG>) of the base plate <NUM> is designed to abut or rest against the annular recess <NUM> in the cylinder wall <NUM> adjacent the second end opening <NUM>. Preferably, the thickness of the base plate <NUM> is such that the top surface <NUM> of the plate <NUM> is flush or level with the remaining cylinder wall <NUM> at the second end opening <NUM>.

As seen from <FIG>, the base plate <NUM> includes one or more recesses <NUM> around the perimeter of the top surface <NUM>. The recesses <NUM> form reservoirs for solder, weld metal, or some other adhesive material, to join the cone insert <NUM> with the filter support <NUM>.

As seen from <FIG>, and <FIG>, the cone insert <NUM> can also include a screw hole <NUM> for securing a cap <NUM> onto the insert <NUM>.

<FIG> show various views of a filter support cap <NUM> according to an embodiment of the invention. As seen from <FIG>, and <FIG>, the cap <NUM> is adapted to fit over the second end <NUM> of the cylindrical body <NUM> as well as the base plate <NUM> of the cone insert <NUM>. As seen from <FIG>, the cap <NUM> has a generally frustoconical shape, with a sloping side portion <NUM>, a curved side portion <NUM> below the sloping side portion <NUM>, and a vertical side portion <NUM> below the curved side portion <NUM>. The cap <NUM> includes a hole <NUM> through its central axis for passing through a screw body (shank). The screw (not shown) threads directly into the screw hole <NUM> in the cone insert <NUM> and secures the cap <NUM> to the cone insert <NUM>. When the cone insert <NUM> has been welded or otherwise secured onto the cylindrical body <NUM>, the screw would also secure the cap <NUM> to the cylindrical body <NUM>. The cap <NUM> may include a recessed area <NUM> having a generally inverted frustoconical shape in the top portion around the hole <NUM> for receiving the conical portion of a flat head or countersunk screw (not shown).

As seen from <FIG>, the bottom portion <NUM> of the cap <NUM> includes the curved side portion <NUM> and the vertical side portion <NUM>. The outside diameter of the curved side portion <NUM> and the vertical side portion <NUM> is larger than the outside diameter of the cylindrical body <NUM>. The interior of the bottom portion <NUM> includes a recess <NUM> for receiving the second end <NUM> of the cylindrical body <NUM>. The interior of the bottom portion <NUM> includes a sloping surface <NUM>, which slopes away from the outside surface of the cylinder wall <NUM>. The space created between the sloping surface <NUM> and the outside surface of the cylinder wall <NUM> allows for one or more filter elements to be held in place, around the second end portion <NUM> of the cylindrical body <NUM>.

In another embodiment of the invention, the cone insert <NUM> and the cap <NUM> include a hole through their axes for accommodating a tie rod. This embodiment is discussed in more detail below in connection with <FIG>.

In a second aspect, the present invention provides a polymer melt filter. The filter comprises the filter support according to any of the embodiments of the invention and one or more filter elements around the second end portion of the cylindrical body. There are no particular restrictions on the filter elements that may be used with the filter support of the invention, so long as they can be adapted to fit around the second end portion of the cylindrical body. Examples of filter element media include metal fiber felt, woven wire cloth, wire mesh, screen mesh, metal fiber fleeze, and a perforated metal sheet. Combinations of filter elements may be used. The filter elements may be flat or pleated. The filter elements may have any desired fineness, such as from <NUM> to <NUM>, or from <NUM> to <NUM>.

<FIG> illustrates an embodiment of the second aspect of the invention. <FIG> shows a filter element <NUM> in the form of a sleeve adapted to fit over/around the second end portion <NUM> of the filter support <NUM>. The filter element <NUM> has perforations <NUM> to let the polymer melt to pass through, but to filter out impurities in the melt, such as solids and/or gels.

The types of polymer melts that can be filtered using the filter according to the invention are not particularly limiting. Examples of suitable polymers include poly(acrylonitrile butadiene styrene), ethylene vinyl acetate copolymer, polyethylenes (including HDPE, LDPE, and LLDPE), polyamides (including PA <NUM> and PA <NUM>), polybutadiene, polyesters (including PET and PBT), polypropylene, and polystyrenes (including HIPS).

In use, a polymer melt first passes through the one or more filter elements to remove any undesired solids and/or gels in the melt. The melt then enters the inside of the hollow cylindrical body <NUM> of the filter support <NUM> via the holes <NUM> in the cylinder wall <NUM>. The polymer melt then exits the interior of the hollow cylindrical body <NUM> via the opening <NUM> in the first end <NUM> of the body <NUM>.

The support plate may have two or more threaded holes into which the filters may be screwed. The number of threaded holes can vary, for example, from <NUM> to <NUM>. In one embodiment, the support plate includes <NUM> to <NUM> holes. The threaded holes are typically oriented perpendicular to a planar surface of the support plate.

The support plate may be made of any material that can withstand the conditions inside of a polymer filtration system over an extended period of time. Such conditions include operating temperatures of up to <NUM> and operating pressures of up to <NUM>,<NUM> psi (or approximately <NUM> MPa). In one embodiment, the support plate is made of Custom <NUM>® stainless steel, which has been heat treated according to Condition H <NUM> or H <NUM>. Custom <NUM>® stainless steel generally contains <NUM> to <NUM> wt% of chromium, <NUM> to <NUM> wt% of nickel, <NUM> to <NUM> wt% of molybdenum, <NUM> to <NUM> wt% of titanium, and the balance of iron. Custom <NUM>® stainless steel may contain up to <NUM> wt% of carbon, up to <NUM> wt% of phosphorus, up to <NUM> wt% of silicon, up to <NUM> wt% of manganese, and up to <NUM> wt% of sulfur. Custom <NUM>® stainless steel is commercially available. It is typically furnished in the annealed/CT condition. This condition includes heating to <NUM>°F ± <NUM>°F (<NUM> ± <NUM>), holding at temperature for one hour, and rapidly cooling. The solution annealing is typically followed by refrigerating to -<NUM>°F (-<NUM>), holding at temperature for eight hours, then warming to room temperature (CT). The subzero cooling is usually performed within <NUM> hours of the solution annealing.

Condition H <NUM> refers to heat treatment in air at <NUM>°F +/- <NUM>°F (<NUM> +/-<NUM>) for <NUM> minutes +/- <NUM> minutes. Condition H <NUM> refers to heat treatment in air at <NUM>°F +/- <NUM>°F (<NUM> +/- <NUM>) for <NUM> hours +/- <NUM> hours.

In one embodiment, the filter plate assembly includes at least one filter that includes a cone insert and a cap having a hole through their axes for accommodating a tie rod. The tie rod has a first end extending through the hole in the cone insert and the cap, and a second end extending through the support plate of the assembly. The assembly further includes a cross bar, which is attached to the second end of the tie rod for holding the support plate inside a shaft of an apparatus for filtering a polymer melt. This embodiment of the filter plate assembly is illustrated in <FIG>, <FIG>, <FIG>, and <FIG>.

By way of background, a polymer melt filtering apparatus typically includes (a) a housing comprising an inlet channel for receiving a flow of polymer melt, a cross-bore for accommodating a movable shaft, and an outlet channel for discharging a filtered polymer melt; and (b) a movable shaft comprising a plurality of connecting channels arranged side-by-side and spanning the thickness of the shaft for connecting the inlet channel to the outlet channel. Each connecting channel includes a filter support plate assembly, which is situated across the flow direction of the polymer melt, for filtering the polymer melt. The shaft is mounted in the cross-bore of the housing and is movable in the axial direction, so that each connecting channel can be moved between a filtration position in which the inlet channel is connected to the outlet channel through the connecting channel, and a cleaning position in which the connection from the inlet channel to the outlet channel is interrupted and the plate assembly is externally accessible for cleaning.

<FIG>, <FIG>, <FIG>, and <FIG> show a movable shaft <NUM> with two connecting channels <NUM> and <NUM> arranged side-by-side and spanning the thickness of the shaft <NUM> for connecting the inlet channel to the outlet channel. Connecting channel <NUM> is provided with a filter plate assembly according to the invention. In the embodiment shown, the plate assembly includes a support plate <NUM>, two filter supports <NUM>, two tie rods <NUM>, and a cross bar <NUM>.

The support plate <NUM> has a planar supporting surface <NUM> on one side, a convex surface <NUM> on the other side, and a plurality of threaded holes <NUM>. In the embodiment shown, the filter supports <NUM> are attached to two adjacent, centrally located threaded holes <NUM>. Each of the filter supports <NUM> is provided with a cone insert <NUM> and a cap <NUM>. The cone insert <NUM> and cap <NUM> have a hole through their center for accommodating the tie rod <NUM>. The inside surface of the through-hole in the cone insert <NUM> may be tapered to help guide the tie rod <NUM> through the cone insert <NUM>. The larger end of the taper is towards the apex of the cone insert <NUM>.

The tie rod <NUM> may be threaded at both ends. One end of the tie rod <NUM> engages with a nut <NUM>. A washer <NUM> may be placed between the nut <NUM> and the cap <NUM>. The other end of the tie rod <NUM> is threaded into a threaded hole <NUM> in the cross bar <NUM>. The body of the tie rod <NUM> passes through the center of the filter support <NUM>.

The connecting channel <NUM> in the shaft <NUM> has an inlet <NUM> and an outlet <NUM>. The connecting channel <NUM> also includes a ledge or projection <NUM> running radially and protruding into the channel <NUM>, serving to support the support plate <NUM>. The cross bar <NUM> has sufficient length to span the width of the outlet <NUM>. The shaft <NUM> includes recesses <NUM> adjacent the outlet <NUM> (opening on downstream side of the connecting channel <NUM>) for accommodating the cross bar <NUM>. The tie rod <NUM>, together with the cross bar <NUM> and the nut <NUM>, surely holds the support plate <NUM> against the ledge <NUM> inside of the shaft <NUM>. This mechanism for holding the support plate <NUM> in place has a number of advantages, including minimizing or preventing the support plate from substantially moving (e.g., vibrating) during filtration, which can cause premature cracking or breakage.

<FIG> shows an exemplary shape of the cross bar <NUM> with two threaded holes <NUM> for engaging with a threaded end of the tie rod <NUM>.

Although two tie rods <NUM> are depicted in <FIG>, one or more than two may be used.

The cap <NUM>, cap insert <NUM>, tie rods <NUM>, and cross bar <NUM> may be made of any suitable material that can withstand the operating conditions. An example of such material is <NUM>-<NUM> PH stainless steel which has been heat treated according to Condition H <NUM>.

Claim 1:
A polymer melt filter support (<NUM>) comprising:
a hollow cylindrical body (<NUM>) defined by a first end (<NUM>), a second end (<NUM>), and a cylinder wall (<NUM>) having a first end portion (<NUM>) and a second end portion (<NUM>);
a screw thread (<NUM>) on the outside surface of the first end portion (<NUM>); and
a plurality of holes (<NUM>) in the cylinder wall (<NUM>) at the second end portion (<NUM>),
wherein the holes (<NUM>) allow for a polymer melt outside of the cylindrical body (<NUM>) to flow inside of the cylindrical body (<NUM>),
wherein the first end (<NUM>) comprises an opening (<NUM>) for the polymer melt inside of the cylindrical body (<NUM>) to flow outside of the cylindrical body (<NUM>),
wherein the area of the openings (<NUM>) of the holes (<NUM>) on the outside surface of the cylinder wall (<NUM>) is larger than the area of the openings (<NUM>) of the corresponding holes (<NUM>) on the inside surface of the cylinder wall (<NUM>), and
wherein the shape of the openings (<NUM>) of the holes (<NUM>) on the outside surface is non-circular, and which further comprises an opening (<NUM>) at the second end (<NUM>), a cone insert (<NUM>) adapted to fit inside of the second end opening (<NUM>), and a cap (<NUM>) for securing one or more filter elements around the second end portion (<NUM>) of the cylindrical body (<NUM>), wherein the cone insert (<NUM>) comprises a curved lateral surface (<NUM>) towards its base (<NUM>), and
wherein the cone insert (<NUM>) comprises a base plate (<NUM>),
characterised in that the perimeter of the base plate (<NUM>) comprises one or more recesses (<NUM>),
wherein the recesses (<NUM>) and an inner surface of the cylindrical body (<NUM>) define a reservoir for holding solder or weld metal for joining the cone insert (<NUM>) to the cylindrical body (<NUM>).