WO2009022015A2

WO2009022015A2 - A method of encasing a filter element, an encased filter element and an apparatus for processing a sintered filter element

Info

Publication number: WO2009022015A2
Application number: PCT/EP2008/060775
Authority: WO
Inventors: Lars Tinggaard Johannesen; Carsten Abel; Peter Lundorf
Original assignee: Notox A/S
Priority date: 2007-08-16
Filing date: 2008-08-15
Publication date: 2009-02-19
Also published as: WO2009022015A3

Abstract

A sintered filter deviates from its desired shape due to the sintering normally deforming the element. The filter is provided with an outer layer adapting the outer dimensions to those of a container in which the filter is to be placed. A cushioning mat be be provided between the filter and can. The filter may be provided as a number of sub-elements fixed to each other, where the sub-elements have been provided and sintered in the desired shape so that machining is not required prior to the providing of the outer layer.

Description

A METHOD OF ENCASING A FILTER ELEMENT, AN ENCASED FILTER ELEMENT AND AN APPARATUS FOR PROCESSING A SINTERED FILTER ELEMENT

The present invention relates to how to encase sintered filter elements, and in particular how to adapt the outer dimensions of filter elements provided by a method which is not able to guarantee the outer dimensions to a sufficient degree.

Normally, when a filter element has been sintered, a suitable thickness of a cushioning material is selected for each individual element and the cushioning material to fit inside a predetermined can. This, naturally, prevents full scale automation of the production process.

Prior art of this type may be seen in EP 1741479, 1685926, 1382374, 0795075, 1839725, 1884275, 0639701, 1375852, 1375853, 1726800 and 0579956 as well as WO08/025600, DE102006000004 and CN201027558.

A first aspect of the invention relates to a method of encasing a filter element, the method comprising :

providing a sintered filter element, providing a casing for the filter element, the casing having predetermined inner dimensions, the filter element having outer dimensions smaller than the inner dimensions of the casing, - providing an outer layer of a heat resistant material on the filter element, the layer having outer dimensions corresponding to the inner dimensions of the casing, and providing the filter element with the outer layer in the casing.

In the present context, a sintered material is a material which has been provided by heating particles or powder which is thereby interconnected to form a porous material. Naturally, the filter element may, prior to sintering, have been prepared/shaped in any suitable manner, such as molding or extrusion.

Presently, the inner and outer dimensions are defined at least in a predetermined plane, such as along a cross section of the filter perpendicular to a longitudinal axis thereof. Often, filters have two opposed surfaces having entrances and outputs of filtering channels, which surfaces normally are not desired closed by an outer layer.

Naturally, the dimensions of the filter, the layer and the casing may have any geometrical shape desired, such as circular, oval, oblong, square, triangle, quadratic, star-shaped, pie-shaped, or the like. Normally, the filter has the same cross sectional shape along its length, but this is not a requirement.

Preferably, the outer layer is fixed to the filter element and extends from the surface of the filter element outwardly.

In the present context, the filter element is heat resistant, if it is able to withstand the temperatures which the filter element material will reach during normal operation. Normal operation for e.g. a flue gas filter is the temperature reached during soot collection as well as the temperatures reached during regeneration.

Naturally, the providing of the material to form the outer layer may be performed in any desired manner. Normally, the material will be provided in the form of a gas/fluid/liquid/powder/slurry/paste with a high or higher viscosity (in order to be easily dispensed and provided on the filter) and subsequently solidified/hardened or at least given a lower viscosity. This last step may be performed during heating, cooling, simply waiting (such as for the material to settle, harden, cure and/or solidify), providing radiation thereto, and/or having a chemical reaction take place, such as by introducing another substance with which the gas/fluid/liquid/powder/slurry/paste reacts and solidifies/hardens. As will be described further below, the dimensions may "correspond" in other manners than being identical. Actually, it is preferred that there is room between the outer layer and the container for an additional material.

In one situation, the outer dimensions of the outer layer correspond to the inner dimensions of the casing by, at all peripheral positions of an outer periphery of the outer layer in a predetermined cross section through the filter and casing, a predetermined distance existing between the outer layer and an inner periphery of the casing, the method then further comprising providing a sheet of at least substantially constant thickness and of a heat resistant material between the outer layer and the casing, the thickness of the sheet corresponding to the predetermined distance.

Thus, a constant distance exists in this cross section between the outer layer and the container so that the sheet will fit in the gap between the outer layer and the container.

Naturally, identical dimensions are usually impossible to obtain, but a precision within e.g. ±2 mm, such as ±1 mm may be obtainable and acceptable.

This is especially interesting in that it facilitates mass production of the filters. Thus, an embodiment relates to a method further comprising :

- providing a plurality of sintered filter elements,

providing each filter element with an outer layer with the same outer dimensions,

providing a plurality of containers with the same inner dimensions,

providing a plurality of sheets of the heat resistant materials, all sheets having the same thickness, and providing a filter element in each container, a sheet of the heat resistant material being provided between the filter element and the pertaining container.

Consequently, the presence of the outer layer automatically makes it possible to use only a single thickness of the sheet.

In this situation, the step of providing the plurality of sintered filter elements may comprise providing the elements with at least substantially identical outer dimensions prior to sintering, where the sintering may affect the outer dimensions of the filter elements differently. Thus, all filter elements may have been e.g. extruded using the same or at least substantially identical extrusion dies and subsequently sintered.

In another embodiment, the step of providing the sintered filter element comprises providing the sintered filter element as a plurality of sub-elements, having a desired shape and having been sintered in the desired shape, and fixed in relation to each other, the elements being fixed in relation to each other prior to or simultaneously to the providing of the outer layer.

This is advantageous when the individual sub-elements are preferably manufactured with a certain maximum size, volume or the like, and where the final filter is desired of a larger size/volume. An especially desired type of filter is one having a number of pie-shaped elements possibly surrounding a central circular element, whereby the spaces between the pie-shaped elements are radially positioned.

In this embodiment, the sub-elements are provided and sintered in the shape desired instead of machining these subsequently to sintering. This machining has a tendency of opening channels in the element and thereby reducing the filtering efficiency and capability of the filter. This machining will remove highly processed material, which is a waste.

Another interesting embodiment is one, wherein : the step of providing the filter element comprises providing a filter element comprising a plurality of filtering channels each having an opening at one of at least two predetermined surface parts of the filter element,

the step of providing the outer layer comprises:

- providing the filter element in an enclosure having inner dimensions corresponding to the outer dimensions of the outer layer, surface parts of the filter element, other than the predetermined surface parts, defining with the enclosure an at least substantially closed space,

providing a hardenable/curable/solidifiable material into the closed space and onto the outer surface of the filter element,

removing the filter element and the outer layer from the enclosure.

Thus, the enclosure will define the outer dimensions of the layer. In addition, as the material is introduced into the closed space, which is not defined by the predetermined surface parts, the material is not introduced into the channels. One manner of obtaining this is to cover/seal the channels and provide the whole filter inside a container defining the enclosure. Alternatively, the filter may be introduced into an enclosure with the predetermined surface parts not facing part of the enclosure, and where a sealing is provided between the enclosure and the filter so that the predetermined surface parts are not provided inside the enclosure.

Naturally, the method may comprise subsequently having the material harden/cure/solidify, such as by providing additional material or heat/radiation or the like, if required.

This method may also be used for providing the above filter provided from sub- elements in that, preferably: the step of providing the filter element in the enclosure comprises providing, in the enclosure, a plurality of sintered sub-elements each having filtering channels having openings at two or more predetermined surface parts, the sub-elements being positioned at predetermined positions in the enclosure so that the predetermined surface parts do not form part of the closed space,

the step of providing the material comprises also providing the material between sub-elements in order to fix these to each other.

Naturally, the above filters may be made of any desired material, taking into account the fluid/liquid/gas to be filtered. Thus, Cordierite or SiC (or any suitable technical ceramic or sinter metal or compounds of such materials) may be used for filtering water, flue gas, or the like, and the same or other materials may be used for filtering other media.

A second aspect relates to a filter with an outer layer for use in the above method. This filter has the advantage of known and/or predetermined outer dimensions.

A third aspect relates to a plurality of filter elements with an outer layer and having the same outer dimensions for use in the above method relating to the canning of multiple filters. This multiplicity of filters with the same outer dimensions is particularly interesting in mass production of filters.

In a fourth aspect, the invention relates to an encased filter element comprising :

a casing having predetermined inner dimensions, a sintered filter element positioned in the casing, the sintered filter element having an outer layer of a heat resistant material thereon, the layer having outer dimensions corresponding to the inner dimensions of the casing.

Thus, the filter element of the first aspect may be encased in a casing. As is mentioned above, the "corresponding to" may be any correspondence. In one situation, the outer dimensions of the outer layer correspond to the inner dimensions of the casing by, at all peripheral positions of an outer periphery of the outer layer in a predetermined cross section through the filter and casing, a predetermined distance existing between the outer layer and an inner periphery of the casing, the filter element then further comprising a sheet of at least constant thickness and of a heat resistant material between the outer layer and the casing, the thickness of the sheet corresponding to the predetermined distance.

As mentioned above, a preferred filter element comprises a plurality of sub- elements, having a desired shape and having been sintered in the desired shape, fixed in relation to each other. Also, the sub-elements are preferably fixed to each other with the same material as a material of the outer layer.

In a fifth aspect, the invention relates to an apparatus for processing a sintered filter element, the apparatus comprising :

an enclosure having predefined inner dimensions,

means for holding, in the enclosure, a filter element comprising a plurality of filtering channels each having an opening at one of at least two predetermined surface parts of the filter element, surface parts of the filter element, other than the predetermined surface parts, and the enclosure defining an at least substantially closed space,

means for providing a hardenable/curable/solidifiable material into the closed space and onto the outer surface of the filter element so as to fill a space between the filter element and the enclosure.

Naturally, the enclosure may have any desired dimensions, and the providing means may be nozzles adapted to provide the material at one or more predetermined positions. Naturally, means may be provided for ensuring that the material is provided to all desired locations inside the closed space, such as vibrating means, vacuum providing means or the like. Naturally, in order to provide the filter comprising plural sub-elements, preferably:

the holding means are adapted to hold, in the enclosure, a plurality of sintered sub-elements each having filtering channels having openings at two or more predetermined surface parts, the holding means being adapted to hold the sub-elements at predetermined positions in the enclosure so that the predetermined surface parts do not form part of the closed space,

material providing means are adapted to also provide the material between sub-elements in order to fix these to each other.

In the following, a preferred embodiment will be described with reference to the drawing, wherein :

figure 1 illustrates a first embodiment of a canned filter element, figure 2 illustrates another embodiment of a canned filter element, and figure 3 illustrates providing of paste around and between sub- elements.

In figure 1, a cross section is illustrated of a canned filter element 10 comprising a sintered filter element 12, such as a filter element made of SiC powder/grains or Cordierite. The filter element 12 may be made by extruding a paste into a honeycomb shape, which is subsequently sintered in order to obtain the final filter element 12. A filter element suitable for this use may be seen in EP-A-O 336 883 and EP-A-I 094 879.

The filter element 12 preferably comprises a number of longitudinal channels 14 extending in the direction of the filter element 12 and/or the direction of extrusion of the filter element 12.

Around the filter element 12, in the cross section of figure 1, an outer layer 16 is provided which has multiple functions, one being to provide well-defined outer dimensions which fit inside a container 18 into which the filter element 12 with the layer 16 is to be held.

As the present filters are often used on vehicles, which may move and bump during use, a heat resistant layer or mat 20 is provided between the layer 16 and the container 18 in order to absorb shock between the container 18 and the layer 16. This prolongs the life time of the filter element 12 which might otherwise break due to the shocks. In addition, this layer 16 may be used for preventing bypass of gas inside the container 18 but outside the filter element 12.

The providing of the well-defined outer dimensions of the layer 16 makes it possible to use only a single thickness of the mat 20, as a variation in the millimetre scale may require the use of a different thickness of mat 20. During sintering of filter elements 12 with identical outer dimensions of 286 mm, the outer diameter of the sintered elements may vary as much as ±3 mm, whereas a precision on the order of ±1 mm is required in order to use the same thickness of the mat 20.

Thus, using the present outer layer 16 makes serial production easy in that now the outer dimensions of the filter element 12 need no longer be determined, as these are defined by the layer 16. Then, the same mat thickness 20 may be used uncritically and without the need to verify this.

A particularly interesting type of filter element 12 is seen in figure 2 in which it is formed from a number of sub-elements 12' each having a plurality of filtering channels 14 and all coextending in the direction of the channels 14 so as to form two end surfaces having entrances/outputs of the channels 14.

In this situation, it is desired that the sub-elements 12' are interconnected in a manner so that no gas may flow there between (and avoid filtering) and so as to form a single unit which is more easily handled. Normally, this interconnection is performed by providing a paste between the individual sub-elements 12'. Normally, this is obtained by providing the elements 12' as pie-shaped elements and providing a paste, glue or the like 23 there between in order to provide a single element. Preferably, the filter has a central, circular element and a number of pie-shaped elements (now typically with the tips removed) surrounding this element. In this manner, a larger filter may be made out of filter elements 12' still having a manageable cross-sectional area.

An alternative embodiment is one in which the central element is left out and only pie-shaped elements are used.

The advantage of the pie shaped elements is that the spaces there between (the direction of the glue layers 23) is in the direction of the heat gradient, which is an advantage especially if the heat guiding capability of the glue 23 is lower than that of the filter elements 12'.

The process of combining the elements 12' may be combined with the providing of the outer layer 16 in that the sub-elements 12' may be provided in the container 18 and fixed in the desired positions in relation to each other, as is illustrated in figure 3. The providing of a paste 23 inside a container 22 will then provide the paste both between the sub-elements 12', whereby these are fixed in relation to each other, and outside these, in order to form the outer layer 16. The inner dimensions of the container 22 correspond to the desired outer dimensions of the layer 16.

In order to not force paste 23 into the channels 14 (see figure T), the surface parts of the sub-elements 12' having the openings into the channels 14, may be covered, such as by two elements 24 and 26 which may form part of the container 22, or the paste may in other manners be prevented from entering the channels 14, so that the filtering efficiency of the filter is retained.

It is noted that the actual manner of providing the sub-elements 12' preferably is by extrusion of the elements 12' in the desired shapes. It is, naturally, possible to provide more general shapes of the elements 12' and subsequently machine these (remove undesired parts) in order to obtain the desired shape. As it is desired to maintain the layers 23 as thin as possible and at the same time to have all layers 23 of a filter to have as similar a thickness as possible, preferably 2-3 mm, it is desired to precisely position the individual elements 12' in relation to each other before introducing the paste forming the layers 23 and 16.

It is seen that the use of the radial directions of the layers 23 (the use of the pie shapes) facilitates easy introduction of the paste between the elements 12' in order to prevent interstices through which the liquid or gas to be filtered may flow.

In general, the paste may be replaced by a powder/fluid/liquid/slurry, if the method is then supplemented with the step of increasing the viscosity thereof, such as solidifying/hardening/ the powder/fluid/liquid/slurry. For some materials, the viscosity is increased by drying, heating, providing radiation, or a chemical reaction, such as with other substances (liquid, powder, air, gas) which is also added.

In particular for filters adapted to filter flue gasses, it is desired that the final material (when provided, reacted, dried, sintered or the like) provided in the layer 16 and optionally also between elements 12' has a heat expansion coefficient identical to or similar to that of the filter 12 or elements 12', in that this reduces thermal stress in the filter during use or regeneration (when collected soot is burned off). Thus, it may be desired to select, for the material of the outer layer 16, the material of the filter element 12.

In addition, other properties may be desired for this material, such as watertightness, in that this may facilitate a more controllable flow of liquids through the filter during e.g. coating of the filter before use.

Naturally, the filter element 12 or sub-elements 12' may be made of any material and may actually be provided in any manner, even though sintered filter elements are of a type which poses the largest dimensional problems due to the sintering.

Claims

1. A method of encasing a filter element, the method comprising :

providing a sintered filter element, providing a casing for the filter element, the casing having predetermined inner dimensions, the filter element having outer dimensions smaller than the inner dimensions of the casing, providing an outer layer of a heat resistant material on the filter element, the layer having outer dimensions corresponding to the inner dimensions of the casing, and - providing the filter element with the outer layer in the casing.

2. A method according to claim 1, wherein the outer dimensions of the outer layer correspond to the inner dimensions of the casing by, at all peripheral positions of an outer periphery of the outer layer in a predetermined cross section through the filter and casing, a predetermined distance existing between the outer layer and an inner periphery of the casing, the method further comprising providing a sheet of at least substantially constant thickness and of a heat resistant material between the outer layer and the casing, the thickness of the sheet corresponding to the predetermined distance.

3. A method according to claim 2, the method comprising :

providing a plurality of sintered filter elements,

providing a plurality of containers with the same inner dimensions,

- providing a plurality of sheets of the heat resistant materials, all sheets having the same thickness, and providing a filter element in each container, a sheet of the heat resistant material being provided between the filter element and the pertaining container.

4. A method according to any of claims 1-3, wherein the step of providing the sintered filter element comprises providing the sintered filter element as a plurality of sub-elements, having a desired shape and having been sintered in the desired shape, and fixed in relation to each other, the elements being fixed in relation to each other prior to or simultaneously to the providing of the outer layer.

5. A method according to any of the preceding claims, wherein :

the step of providing the filter element comprises providing a filter element comprising a plurality of filtering channels each having an opening at one of at least two predetermined surface parts of the filter element,

the step of providing the outer layer comprises:

removing the filter element and the outer layer from the enclosure.

6. A method according to claim 5, wherein :

the step of providing the filter element in the enclosure comprises providing, in the enclosure, a plurality of sintered sub-elements each having filtering channels having openings at two or more predetermined surface parts, the sub-elements being positioned at predetermined positions in the enclosure so that the predetermined surface parts do not form part of the closed space,

7. A filter with an outer layer for use in the method according to any of claims 1- 6.

8. A plurality of filter elements with an outer layer and having the same outer dimensions for use in the method according to claim 3.

9. An encased filter element comprising :

10. An encased filter element according to claim 9, wherein the outer dimensions of the outer layer correspond to the inner dimensions of the casing by, at all peripheral positions of an outer periphery of the outer layer in a predetermined cross section through the filter and casing, a predetermined distance existing between the outer layer and an inner periphery of the casing, the filter element further comprising a sheet of at least constant thickness and of a heat resistant material between the outer layer and the casing, the thickness of the sheet corresponding to the predetermined distance.

11. An encased filter element according to claim 9 or 10, wherein the filter element comprises a plurality of sub-elements, having a desired shape and having been sintered in the desired shape, fixed in relation to each other.

12. An encased filter element according to claim 11, wherein the sub-elements are fixed to each other with the same material as a material of the outer layer.

13. An apparatus for processing a sintered filter element, the apparatus comprising :

- an enclosure having predefined inner dimensions,

14. An apparatus according to claim 13, wherein :

- the holding means are adapted to hold, in the enclosure, a plurality of sintered sub-elements each having filtering channels having openings at two or more predetermined surface parts, the holding means being adapted to hold the sub-elements at predetermined positions in the enclosure so that the predetermined surface parts do not form part of the closed space,

- material providing means are adapted to also provide the material between sub-elements in order to fix these to each other.