Patent Application
20070050978
1 Field of the Invention
The invention relates to a method for preparation of a sleeve tightly encompassing a core. The invention is specifically directed to production of a sleeve surrounding a catalytic filter. Such sleeve and filter are particularly useful for cleaning exhaust gas from diesel engines in vehicles and vessels.
2 Description of Related Art
Numerous methods of manufacturing pipes, tubes and sleeves are already described in the technical literature.
US Patent Application No. 2004/0155293 discloses a perforated sleeve, which is formed by winding a perforated metal strip in helical turns. This is used for filters, where the fluid flows through the perforated wall of the sleeve.
A double wall pipe is described in U.S. Pat. No. 4,823,847 and is also wound helically. To obtain a precise size of outer diameter, the pipe is mechanically expanded by inserting press shoes inside the pipe.
Another filter is made from many layers of perforated strips wound helically as described in US Patent Application No. 2004/0004110.
Prior art describes helically wound tubes, where fluids flow through the tube wall, or where the size of the outer diameter has to be precise.
It is the object of the invention to find a method for producing a sleeve, which must tightly encompass a porous core to avoid any by-pass of the core, when a gas flows through the core in the sleeve.
Pursuant to the above object, the invention provides a method for preparation of a metallic sleeve surrounding a core comprising the steps of helically winding a metallic strip and helically welding the strip forming the sleeve, inserting the core in the sleeve, coaxially encompassing the sleeve with a plurality of movable segments and exposing the sleeve to pressure force by pressing the segments against outer surface of the sleeve until a preset dimension of the sleeve is obtained.
The invention further provides a method for preparation of a metallic sleeve encompassing a core, which is a monolith surrounded by an intumescent mat.
The invention even further provides a method for preparation of a metallic sleeve, where the monolith is a catalysed filter or a catalytic converter and the mat is made from a fibrous material preferably comprising vermiculite. This is useful for installation in a pipe with exhaust from a diesel engine.
The invention even further provides a metallic sleeve with a core prepared according to the preparation method.
The sleeve of the invention makes it possible for a gas to flow through an inserted porous body without by-passing the body.
In a filter or converter comprising a monolith surrounded by a sleeve gap between the monolith and the sleeve must be avoided in order to ensure that no fluid by-passes the monolith and often the gap must be avoided in a very wide temperature range.
The sleeve typically is made from metal and the monolith from a ceramic material, which means that the thermal expansion of the sleeve is higher than the thermal expansion of the monolith.
To avoid a gap under these conditions, a mat is inserted between the sleeve and the monolith.
The material of the mat must be selected so that the mat expands again after having been considerably compressed even down to half thickness.
During preparation of the filter, the monolith surrounded by the mat is inserted in the sleeve, and then the outer surface of the sleeve is exposed to pressurizing forces.
This results in that the material of the sleeve yields axially in tension and circumferentially in compression direction.
If the properties of the sleeve such as thickness, yield strength and similar are not exactly the same along the entire sleeve, the material will during this pressurizing buckle at positions, where the properties deviate. Such deviations typically occur near a welding seam.
Usually tubes with low thickness compared to their diameter are prepared from a square plate, which is rolled and welded. Outer pressure forces as the ones mentioned above acting on such a tube are orthogonal to the welding seam, which means that the material yields in a direction along the welding seam and orthogonal to the welding seam. This creates concentrated stresses. Further, the material has a high tendency to buckle, where deviations in material properties occur; these deviations are near the welding seam.
When a sleeve is manufactured according to the invention by helically winding a long strip and then welding, the welding will have a helical shape, which has the advantage that pressurizing this tube makes the material yield in a direction at an angel with the welding seam. In this case with helical welding buckling is avoided and smooth surfaces of the tube are obtained.
A long metal strip is helically wound and welded to form a channel typically a tube. This forms a sleeve.
A core is produced and the diameter or other relevant dimensions are measured with a high accuracy. A mat is wound around the core and placed in a machine, which pushes the core and mat into the sleeve and transfers it to a pressurizing machine.
In this pressurizing machine the sleeve is surrounded by a number of pressurizing segments, which form a cylinder with narrow, axial spaces between and by a length of at least 5% longer than the sleeve and with a diameter being larger than the diameter of the sleeve.
The pressurizing segments are pushed together by a surrounding conical device. The movement of the segments are stopped when a specified diameter of the sleeve is obtained. During the pressurizing the thickness of the mat is reduced to approximately the half. The pressurizing takes place at ambient temperature.
This method enables a pressurization without creating buckles of the sleeve, which otherwise would damage the core.
In one embodiment of the invention, the core is a monolith, preferably a catalyzed, ceramic monolith and the mat is an intumescent mat, preferably containing vermiculite being particular useful as a diesel exhaust gas filter or converter, which are used at temperatures from −30° C. to 500° C. The sleeve expands more than the ceramic monolith when heated, but empty space is avoided as the intumescent mat expands widely. This ensures that all the exhaust gas passes the catalyst.
The filter has a length of 100-500 mm preferably 150-350 mm and a diameter of 100-450 mm preferably 150-350 mm. The sleeve has a wall thickness of 1.0-2.5 mm preferably 1.25-2.00 mm and the thickness of the mat in the finished filter is 3-8 mm, preferably 4-6 mm.
The pressurization is performed by 6-10, preferably 8 segments.
The invention is further illustrated in the drawings, where
Cylindrical sleeves were produced from a square piece of metal by rolling and welding forming axial welding seams.
The sleeves were produced with a length from 150 mm to 350 mm, outer diameter from 150 mm to 350 mm and a wall thickness from 1.25 mm to 2.00 mm.
A sleeve and a monolith with an 8-10 mm thick mat wound around it were placed in a machine, which pushed the monolith into the sleeve.
The mat was an intumescent mat made from a fibre material containing 30-40% vermiculite, which can be pressed to half the thickness and then expands again when heated.
The sleeves were exposed to pressure forces on the entire outer surface by eight segments forming an outer cylinder with a little space between. The segments pressed against the outer surface of the sleeve until a preset diameter of the sleeve was obtained. The mats were pressed to a thickness of 4.4 mm.
During pressurizing the length of the sleeve increased 1-1.5% and the wall thickness increased 1%.
Some of the sleeves were buckled during the pressurization. The sleeve buckled 10-20 mm in an inward direction in the entire length of the sleeve. The buckle was in the heat affected zone of the welding seam, because of the low yield strength in this zone.
Then cylindrical sleeves were produced from a long metal strip, which was helically wound to cylinders. The cylinders were welded forming sleeves with helical welding seams. Sleeves, monoliths and mats had same dimensions as the sleeves mentioned above.
Monoliths with mats were inserted in the sleeves, and the sleeves were pressurized in the same way as described above.
The pressurization force was 10 t, which pressurized the sleeves until the thickness of the mat was 4.4 mm.
The helically wound sleeve did not show buckles after pressuring.
The invention is useful for producing sleeves with circular, square, hexagonal, octagonal or other geometric cross-section, where the sleeve encompasses a core, where no slip between sleeve and core is allowed. This is especially relevant for filters and converters, where the core is a filter material, which evidently must not be by-passed. Examples of such filters and catalytic converters are filters for cleaning diesel exhaust gas. These filters will comprise catalysed ceramic monoliths able to reduce NOx to N2 and/or hold back soot particles in the exhaust gas.
These filters are suitable for installation in vans, trucks, vessels, diesel locomotives and similar.
| Number | Date | Country | Kind |
|---|---|---|---|
| PA 2005 01238 | Sep 2005 | DK | national |
