Stock material or miscellaneous articles – All metal or with adjacent metals – Honeycomb – or with grain orientation or elongated elements...
Reexamination Certificate
2000-05-11
2003-03-25
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Honeycomb, or with grain orientation or elongated elements...
C428S603000, C422S180000, C502S527220
Reexamination Certificate
active
06537681
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a honeycomb, particularly a catalytic converter substrate, pursuant to the generic part of Claim
1
and a process for its manufacture.
BACKGROUND OF THE INVENTION
A honeycomb of this type is known from DE 27 33 640, which consists of an alternating arrangement of corrugated and plane foil layers. The flow ducts, which display a sinusoidal or triangular cross-section, are, however, unfavourable in terms of the catalytic function, as the gussets of the ducts are virtually ineffective, particularly in the case of laminar flow. In addition, the properties of the honeycomb under fluctuating temperature conditions are unfavourable because the large-area soldering of the plane and corrugated foils results in a very stiff honeycomb structure. As a result, however, local and temporal temperature fluctuations cannot be adequately balanced out, as a result of which the geometry of the flow ducts is subject to irreversible changes and cracks can occur in the cell walls, this being intensified by vibratory stresses on the honeycomb. The service life of honeycombs of this kind is thus in need of improvement.
In order to increase the stability of the honeycomb, it is moreover known from EP 0 245 738 that rigid bearing walls extending into the honeycomb are provided. The manufacture of honeycombs of this kind is, however, relatively complex, as the foil layers have to be cut through for this purpose. In addition, the fastening of the thin foils to the comparatively thick, rigid bearing walls presents a problem.
SUMMARY OF THE INVENTION
The object of the invention is to create a honeycomb that displays sufficient stability with high resistance to thermal shocks, that permits the most favourable possible design of the flow ducts in terms of flow and that is simple and inexpensive to manufacture.
According to the invention, this object is solved by a honeycomb with the features of Claim 1. Due to the fact that the dimensions of the stiffening elements, which run essentially parallel to the foil layers, transverse to their longitudinal direction, is small compared to the dimensions of the honeycomb structure in this direction, mass transport within the flow ducts, and thus also the effective reaction cross-section of the ducts, is virtually not reduced. Unfavourable cross-section geometries resulting from the formation of gussets thus virtually do not occur at all, or only in areas of small volume. In addition, owing to their orientation parallel to the foil layers, the stiffening elements can easily be incorporated into the honeycomb structure during its manufacture. A certain degree of stiffening is already achieved by the minimum distance between adjacent foil layers being limited in the case of structured foils, meaning that foil structures, for example, are supported by the stiffening elements. In particular, the stiffening elements can prevent elongation of the honeycomb structure in a direction perpendicular to the flow ducts or foil profiles, which would lead to the undesirable formation of spaces between foil layers of different elongation and thus to unfavourable vibratory stresses in the honeycomb structure. Moreover, as a result of the stiffening elements introduced, the honeycomb according to the invention can be made up of foils with virtually any desired structure or orientation, as it is no longer necessary to fasten the foil layers to each other.
The stiffened areas of the honeycomb structure can have punctiform or locally isolated dimensions or, in the case of stiffening elements of corresponding length, they can form stiffening zones. In all cases, the stiffening elements according to the invention locally fix the foils relative to each other more strongly, thus producing larger areas of the honeycomb structure displaying high flexibility.
In order to achieve sufficient stabilisation of the honeycomb structure, it suffices in itself for the length of the stiffening elements, regardless of the direction in which they extend, to be equal to or greater than the transverse dimension of a duct in one direction, e.g. height or width, and for them to bridge a flow duct, for example, i.e. to act on opposite walls of a duct or the housing. Also, the stiffening elements can extend only over several duct diameters transverse to the longitudinal direction of the duct, e.g. 5 to 10 duct diameters, or over the entire width of the honeycomb. In the case of non-isometric or non-isogonal ducts, the stiffening elements can also extend over only part of the duct cross-section amounting to a multiple of the duct dimension in the cross-sectional direction of smaller size, e.g. twice this dimension or more.
Advantageously, the dimension of the stiffening elements transverse to their longitudinal dimension is small compared to the dimensions of the flow ducts in this direction, e.g. in the range of {fraction (1/10)} to {fraction (1/50)} of the dimension of the flow ducts in this direction or less, without being limited to these values. The transverse dimension of the stiffening elements can be {fraction (1/100)} to
{fraction (1/1000)} or less of the duct length, for example, if these run transverse or at an angle to the ducts. Accordingly, when using the same material, the width of the stiffening elements can be just
0.5 to 10 times, preferably 1 to 5 times, the thickness of the foils making up the honeycomb structure, without being limited to these values.
If, for example, a honeycomb is available which has a flow duct length of 100 mm and a flow duct diameter of 1 mm, strip-like stiffening elements with a width of several millimeters and/or stiffening wires with a diameter of several hundredths to several tenths of a millimeter arranged transverse to the flow ducts can be provided. If the stiffening elements are arranged in the longitudinal direction of the ducts, their width can be in the range of 0.01 to 0.5 mm, preferably 0.003 to 0.2 mm. It goes without saying that, given corresponding honeycombs with larger duct diameters, which can easily also be in the region of approx. 1 cm or more for corresponding applications, the stiffening elements can display correspondingly larger diameters or widths.
It is also possible for several stiffening elements to be assigned to one foil or one pair of foils or several adjacent foils.
The stiffening elements preferably extend over the entire honeycomb structure in their longitudinal direction.
The stiffening elements are advantageously designed to be elastically deformable under operating conditions, perpendicular to their longitudinal direction, particularly in the direction of the flow ducts.
The stiffening elements can run between adjacent foil layers, although they can also pass through profiled foils or be woven into plane foils, and/or connect adjacent foils to each other.
In their longitudinal direction, the stiffening elements are advantageously connected to the foil layers and/or the housing in a manner capable of absorbing tensile forces, e.g. by means of suitable jointing techniques, such as welded connections, positive, frictional and/or material connections. However, connection of the stiffening elements to the foil layers, in particular, can also be achieved by coating with a ceramic material required to produce a catalytic coating.
In order to achieve frictional connection of the stiffening elements to the foil layers, the stiffening elements can be woven into the foil layers, particularly connecting two adjacent foil layers in the process, or be clamped in corresponding folds in the foils. Areas of the foils can be notched out to this end, or the stiffening elements can be inserted into the folds of connecting webs located at the face ends of the foils. Correspondingly, the structured areas, such as the foil corrugations, can also be provided with notched tabs or projections running in the longitudinal direction of the ducts, these being arranged one behind the other, possibly at an offset height, and forming a lead-through for wires or the like running parallel to the flow ducts.
However, an
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