Testing of substrate monoliths

Abstract

1. A method for testing a substrate monolith (1), the substrate monolith (1) comprising: i) a plurality of channels extending longitudinally along a Z-axis of the substrate monolith (1); and ii) an array of walls extending along the Z-axis and forming partitions between adjacent channels, the array of walls comprising first walls (10) oriented parallel to the first axis of the substrate monolith (1) and second walls (11) oriented parallel to the second axis of the substrate monolith (1), the first axis and the second axis both being orthogonal to the Z-axis, the method comprising: a) applying an impulse (J) to a substrate monolith (1) with an impact tool (22) to induce mechanical vibrations in the substrate monolith (1); b) sensing the mechanical vibrations of the substrate monolith (1); c) determining a fundamental frequency of the sensed mechanical vibrations; and d) comparing the fundamental frequency of the sensed mechanical vibrations with a fundamental frequency obtained from testing a second substrate monolith, wherein in step a), an impulse vector (30) of the impulse (J) has a non-zero first axial component (31) and a non-zero second axial component (32).

Description

[Technical Field]

[0001] The present disclosure relates to a method for testing substrate monoliths and a testing apparatus for carrying out the method. [Background technology]

[0002] The substrate monoliths are used to treat exhaust gases emitted from internal combustion engines, such as those of vehicles. The substrate monoliths may treat the exhaust gases, for example, by filtering the exhaust gases to remove particulate matter and / or by using catalysts to oxidize and / or reduce components of the exhaust gases, such as carbon monoxide, unburned hydrocarbons, and nitrogen oxides.

[0003] Substrate monoliths can typically be formed from sintered metals, ceramics, metal fibers, or the like. Substrate monoliths are fragile, for example, due to their material composition and / or due to the presence of thin-walled structures that define channels for gas flow within the substrate monolith. Therefore, substrate monoliths may be prone to cracking when subjected to mechanical and / or thermal shock. Fabrication of substrate monoliths necessarily involves mechanical manipulation of the substrate monolith on a production line, which can result in mechanical loads on the substrate monolith, for example, due to accidents or when transferred from one part of the production line to another. The manufacturing process also involves the application of thermal changes, for example, during firing and cooling of the pristine substrate monolith and during calcination of the substrate monolith after application of a washcoat. Therefore, it may be desirable to test the substrate monolith for cracks and / or other defects during or after fabrication before the substrate monolith is shipped to a customer.

[0004] A problem with testing substrate monoliths is that cracks or other defects can be difficult to visually identify. External cracks (i.e., cracks propagating to / from the outer surface of the substrate monolith) may be narrow, may be closed at rest, and / or may be difficult to identify under lighting conditions typically present on a production line. Internal cracks within the body of the substrate monolith cannot be easily visually inspected, especially by a human operator on a production line. Visual inspection is also generally time-consuming and therefore, in practice, can only be applied to a small sample percentage of the substrate monoliths produced.

[0005] Some human operators are known to percusse the substrate monolith with their fingers in an attempt to identify the presence of defects by listening for a "dull" response. However, this technique requires a certain level of experience on the part of the human operator, and in addition, sound perception varies from person to person. Conclusions from such "percussion" tests are therefore very difficult to interpret and difficult to report to customers in a useful manner. Furthermore, as with visual inspection, this method is time consuming and can only be applied to a small sample percentage of the substrate monoliths produced. Summary of the Invention

[0006] In a first aspect, the present invention provides a substrate monolith, the substrate monolith comprising: i) a plurality of channels extending longitudinally along the Z-axis of the substrate monolith; ii) an array of walls extending along the Z axis and forming partitions between adjacent channels; 1. A method of testing a substrate monolith, wherein the array of walls comprises a first wall oriented parallel to a first axis of the substrate monolith and a second wall oriented parallel to a second axis of the substrate monolith, the first axis and the second axis both being orthogonal to a Z axis, comprising: The method is: a) applying an impulse to the substrate monolith with an impact tool to induce mechanical vibrations in the substrate monolith; b) sensing mechanical vibrations of the substrate monolith; c) determining the fundamental frequency of the sensed mechanical vibration; d) comparing the fundamental frequency of the sensed mechanical vibration with a fundamental frequency obtained from testing a second substrate monolith; In step a), the impulse vector of the impulse has a non-zero first axis component and a non-zero second axis component.

[0007] Advantageously, the fundamental frequencies obtained from the substrate monolith being tested and the second substrate monolith are used for comparison. Using the fundamental frequency may reduce or eliminate destructive interference from other frequencies.

[0008] The method can also be performed very quickly, for example, in less than 5 seconds per substrate monolith. Advantageously, the method does not rely on the perception of a human operator, making it suitable for use in production lines. In particular, it has surprisingly been found that the method can be performed despite the presence of relatively large amounts of background noise, such as is typically present in a factory production line setting.

[0009] Advantageously, the impulse vector of the impulse has a non-zero first axial component and a non-zero second axial component. Therefore, the impulse vector is not directly aligned with either the first or second wall of the substrate monolith. This angling of the impulse vector has been found to produce a lower fundamental frequency in the sensed mechanical vibration compared to an applied impulse vector that is aligned with the first or second wall of the substrate monolith. Additionally, the angling of the impulse vector has been found to produce a stronger signal amplitude for the fundamental frequency when used with a substrate monolith that is more easily distinguishable from other resonances and background noise (including, for example, background noise from factory settings).

[0010] Additionally, a further advantage is that the stronger resonant response of the substrate monolith when the impulse vector is not directly aligned with either the first or second wall means that the magnitude of the impulse can be reduced, thereby reducing the chance of the impact tool damaging the substrate monolith when applying the impulse.

[0011] Without wishing to be bound by theory, the stronger and more distinct resonant response of the substrate monolith when the impulse vector is not directly aligned with either the first or second wall is believed to be due to the in-plane anisotropy of the substrate monolith. The first and second walls of the substrate monolith create a "honeycomb" network of cells in a plane perpendicular to the Z axis. Typically, in a substrate monolith, the thickness of the first and second walls (cell walls) is smaller than the width of the cell openings. Taking the example of a square cell, the plane of the substrate monolith perpendicular to the Z axis may resemble a checkerboard pattern with a 2D array of hollow square cells with centers aligned parallel to the first and second axes. This plane is anisotropic in terms of stiffness, with different stiffness depending on the direction of the applied force. In particular, in the square cell example (assuming a constant wall thickness for all walls), the stiffness parallel to each of the first and second walls will be the same. However, the stiffness at 45° to the first and second walls of the square channel will be lower.

[0012] In a preferred example, in step a), the impulse vector has substantially equal first and second axial components. This may be particularly appropriate, for example, when the channel has substantially the same length dimension in each of the first and second axes. One example would be a square cell. If the channel has another shape, the angulation of the impulse vector may need to be adjusted. For example, if the channel is rectangular (non-square) or rhomboidal, the impulse vector may be angled, for example, to be parallel to the longest in-plane diagonal dimension of the channel.

[0013] In some examples, in step a), the impulse is applied by striking the substrate monolith in a direction oblique to the first axis and the second axis. In some examples, the first axis and the second axis are mutually orthogonal and are the X-axis and Y-axis of the substrate monolith, respectively. In such examples, in step a), the impulse may be applied by striking the substrate monolith in a direction at 45° to the X-axis and the Y-axis.

[0014] In some examples, the plurality of channels includes quadrilateral-shaped channels, optionally square-shaped channels.

[0015] In some examples, the substrate monolith is supported on a support system to isolate the substrate monolith from external vibrations.

[0016] In some examples, the support system comprises a single support member. In some other examples, the support system comprises multiple support members. In such examples, the support members may be three, four, or more separate support members. The or each support member may comprise a flat support, a rounded support, a knife-edge support, or a point support for contacting the surface of the substrate monolith and, optionally, the base. In some examples, the or each support member may comprise a rigid member. However, in other preferred examples, the or each support member may comprise a flexible or elastic member. For example, the or each support member may be formed from a foam, such as polyurethane foam, an elastomer, or a rubber.

[0017] In some instances, the substrate monolith may be supported at one or more nodes of the substrate monolith, preferably at one or more of the cardinal nodes of the substrate monolith.

[0018] In some examples, sensing the mechanical vibrations of the substrate monolith in step b) includes sensing the mechanical vibrations in the time domain using a transducer. In some examples, the transducer may include a contact accelerometer that may be attached to the surface of the substrate monolith. However, in other preferred examples, a non-contact transducer may be used. For example, a microphone, optionally a unidirectional microphone, may be used to sense the mechanical vibrations by sensing sound waves generated by the mechanical vibrations of the substrate monolith.

[0019] In some examples, determining the fundamental frequency in step c) includes transforming the sensed mechanical vibration into the frequency domain to generate a frequency spectrum of the sensed mechanical vibration. In such examples, determining the fundamental frequency in step c) may further include applying a Power Spectral Density (PSD) analysis to the frequency spectrum.

[0020] Advantageously, converting sensed mechanical vibrations to the frequency domain can produce more reliable results for a wider range of substrate monoliths compared to time domain analysis. For example, many substrate monoliths are formed from ceramics that may be highly porous and / or contain many microcracks. This can lead to such substrate monoliths not producing a pure tone when impacted. As a result, time domain analysis of mechanical vibrations has proven difficult. This difficulty can be overcome according to the present method by converting to the frequency domain.

[0021] The transformation to the frequency domain may be, for example, by use of a Fast Fourier Transform algorithm. The use of PSD analysis may advantageously reduce or eliminate ambiguity in determining the fundamental frequency from the frequency spectrum.

[0022] In some examples, the impact tool can be configured to apply a predetermined impulse. The impact tool can be automated. For example, the impact tool can be a computer controller to improve the accuracy and repeatability of the impulse, particularly with respect to its magnitude. In some examples, the impact tool can be an automatic hammer. In some examples, the impact tool can include a metal or wooden head that contacts the substrate monolith during use. Wooden heads may be preferred where the substrate monolith is particularly fragile. Metallic heads may be preferred where it is desirable to obtain greater signal strength from the impact. As an example of a metallic head, a stainless steel head can be used. It has also been found that an alumina material is particularly effective for the head. It has been found that the head material does not change the resulting fundamental frequency, but can affect signal strength, as discussed above.

[0023] The second monolith may, for example, comprise a reference substrate monolith, or a substrate monolith from a different batch of substrate monoliths compared to the substrate monolith, or may be a substrate monolith from the same batch of substrate monoliths as the substrate monolith.

[0024] For example, the second substrate monolith may be a reference substrate monolith, and the method may further include making a determination regarding the cracking state of the substrate monolith based on a comparison of the fundamental frequencies obtained for the substrate monolith and the reference substrate monolith.

[0025] Advantageously, the reference substrate monolith may be a substrate monolith that is known to be crack-free, eg, substantially free of defects.

[0026] The comparison of fundamental frequencies may include determining whether there is a difference in fundamental frequencies. Optionally, it may include determining whether the difference exceeds a threshold amount. The threshold amount may be an absolute amount (e.g., number of Hertz) or a relative amount (e.g., percentage deviation of the frequency obtained for the substrate monolith compared to a reference substrate monolith).

[0027] Comparing the fundamental frequencies may include determining the direction of the shift in fundamental frequency, for example, whether the fundamental frequency obtained for the substrate monolith is greater than or less than the fundamental frequency obtained for the reference substrate monolith.

[0028] For example, the substrate monolith and the second substrate monolith may be from a first batch and a second batch of substrate monoliths, respectively, and the method may further include making a determination regarding a variance between the batches of substrate monoliths based on a comparison of the fundamental frequencies obtained for the substrate monolith and the second substrate monolith.

[0029] In making the determination, the fundamental frequencies obtained from one or more substrate monoliths from a first batch can be compared to the fundamental frequencies obtained from one or more substrate monoliths from a second batch, for example, each batch tested can include 3 or more, 5 or more, or 10 or more substrate monoliths tested.

[0030] Comparing the fundamental frequencies may include determining whether there is a statistically significant difference between the fundamental frequencies obtained for the first batch of substrate monoliths and the fundamental frequencies obtained for the second batch of substrate monoliths.

[0031] For example, the substrate monolith and the second substrate monolith may be from a single batch of substrate monoliths, and the method may further include making a determination regarding the variance within the batch of single substrate monoliths based on a comparison of the fundamental frequencies obtained for the substrate monolith and the second substrate monolith.

[0032] In making the determination, fundamental frequencies obtained from three or more, five or more, or ten or more substrate monoliths of a single batch may be used.

[0033] Comparing the fundamental frequencies may include determining whether there is a statistically significant variation in the fundamental frequencies obtained for a single batch of substrate monoliths.

[0034] In some examples, the method is carried out on a production line configured to process a plurality of substrate monoliths.

[0035] The substrate monolith may be formed from, for example, sintered metal, ceramic, or metal fibers, etc. For example, the substrate monolith may be formed from cordierite, various forms of silicon carbide, or aluminum titanate.

[0036] The substrate monolith may be a "pristine" substrate monolith or, alternatively, may include a composition (known as a washcoat) that coats the porous structure of the substrate monolith. The washcoat may be a catalytic washcoat to produce a catalyzed substrate monolith with catalytic functionality, such as oxidation, NOx trapping, or selective catalytic reduction activity. The catalytic washcoat may include a catalyst selected from the group consisting of a hydrocarbon trap, a three-way catalyst (TWC), a NOx absorbent, an oxidation catalyst, such as a diesel oxidation catalyst (DOC), a selective catalytic reduction (SCR) catalyst, a lean NOx catalyst, and a combination of any two or more thereof. The catalysts, such as the TWC, NOx absorbent, oxidation catalyst, hydrocarbon trap, and lean NOx catalyst, may contain one or more platinum group metals, particularly those selected from the group consisting of platinum, palladium, and rhodium.

[0037] In some instances, the substrate monolith being tested may be a calcined substrate monolith. In such instances, the substrate monolith and the reference substrate monolith are preferably subjected to substantially the same calcination conditions.

[0038] The substrate monolith can include either a flow-through substrate monolith or a filter substrate monolith. In a flow-through substrate monolith, multiple channels (also referred to as "cells") extend longitudinally along the length (Z-axis) of the substrate monolith, and the channels are open at both ends. In a filter substrate monolith (also referred to as a "wall-flow filter substrate monolith"), multiple channels ("cells") extend longitudinally along the length (Z-axis) of the substrate monolith, with channels that are open at a first end of the substrate monolith being closed at the opposite end, and channels that are open at the opposite end being closed at the first end, with every other adjacent channel having an open end (or closed end) at the first end of the filter substrate monolith and a closed end (or open end) at the opposite end, such that viewing the end of the filter substrate monolith resembles a chessboard of open and closed channels. Fluid communication between the open channels at a first end of the filter substrate monolith and the open channels at the opposite end is through the porous wall structure of the filter substrate monolith.

[0039] The outer shape and dimensions of the substrate monolith, as well as properties such as channel wall thickness and its porosity, can vary depending on the intended use of the substrate monolith. The substrate monolith can be configured for use with an internal combustion engine (ICE) to filter exhaust gases emitted by the internal combustion engine. The internal combustion engine can be a spark ignition engine, e.g., a gasoline ICE, or a compression ignition engine, e.g., a diesel ICE.

[0040] In a second aspect, the present disclosure provides a test device for carrying out the method of the first aspect, comprising: a support system for isolating the substrate monolith from external vibrations; Impact tools and a transducer for sensing mechanical vibrations of the substrate monolith; an analyzer for determining a fundamental frequency of the sensed mechanical vibration; A testing apparatus is provided in which the impact tool comprises an automatic hammer configured to apply an impulse to the substrate monolith with an impulse vector having a non-zero first axial component and a non-zero second axial component.

[0041] In some examples, the support system and the impact tool are both coupled to an alignment frame configured to ensure that the impulse vector of an impulse applied by the impact tool to a substrate monolith supported by the support system has a non-zero first axial component and a non-zero second axial component. [Brief explanation of the drawings]

[0042] Aspects and embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] FIG. 1 is a schematic diagram of a substrate monolith. [Figure 2] FIG. 1 is a schematic diagram of a test apparatus. [Figure 3] FIG. 1 is an end view of a portion of a substrate monolith. [Figure 4] FIG. 1 is a schematic end view of a substrate monolith undergoing an impulse. [Figure 5] FIG. 1 shows an end view of a portion of two substrate monoliths. [Figure 6] 1 is a graph of frequency versus amplitude showing the effect of impulse direction; [Figure 7] 1 is a graph of frequency versus amplitude illustrating exemplary test results. [Figure 8] 1 is a graph of frequency versus amplitude illustrating exemplary test results for cracked and uncracked substrate monoliths. [Figure 9] 1 is a plot of the fundamental frequencies obtained for 42 samples of substrate monoliths. [Figure 10] 1 is a plot of the fundamental frequencies obtained for two batches each containing 10 samples of substrate monolith. [Figure 11]1 is a frequency versus amplitude graph illustrating exemplary test results for substrate monoliths from four different sources. [Figure 12] 1 is a plot of the fundamental frequencies obtained for 10 samples of substrate monoliths from a single batch. DETAILED DESCRIPTION OF THE INVENTION

[0043] Those skilled in the art will recognize that one or more features of one aspect or embodiment of the present disclosure may be combined with one or more features of any other aspect or embodiment of the present disclosure, unless the immediate context teaches otherwise.

[0044] Figure 1 is a schematic diagram of a substrate monolith 1. The substrate monolith 1 comprises a plurality of channels extending longitudinally along the Z axis of the substrate monolith 1 and an array of walls 10, 11 extending along the Z axis that form partitions between adjacent channels.

[0045] The array of walls comprises a first wall 10 oriented parallel to a first axis of the substrate monolith 1 and a second wall 11 oriented parallel to a second axis of the substrate monolith 1, both of which are orthogonal to the Z axis. The first axis and the second axis may be orthogonal to each other. The first axis may be the X axis of the substrate monolith 1, and the second axis may be the Y axis of the substrate monolith 1, respectively.

[0046] The first wall 10 and the second wall 11 may define a "cell" 12 when viewed in the XY plane of the substrate monolith 1. In the illustrated example, the cell 12 is square-shaped. However, the cell 12 may take other shapes. The substrate monolith 1 may have a cylindrical outer shape, although other shapes may be provided.

[0047] According to the present disclosure, a method for testing a substrate monolith 1 comprises: a) applying an impulse J to the substrate monolith 1 with an impact tool 22 to induce mechanical vibrations in the substrate monolith 1; b) sensing mechanical vibrations of the substrate monolith 1; c) determining the fundamental frequency of the sensed mechanical vibration; d) comparing the fundamental frequency of the sensed mechanical vibration with a fundamental frequency obtained from testing a second substrate monolith; In step a), the impulse vector 30 of the impulse J has a non-zero first axial component 31 and a non-zero second axial component 32 .

[0048] 2 shows a schematic diagram of a test apparatus 20 suitable for performing tests on substrate monolith 1. Test apparatus 20 comprises a support system 21 for isolating substrate monolith 1 from external vibrations, an impact tool 22, a transducer 23 for sensing mechanical vibrations of substrate monolith 1, and an analyzer 24 for determining the fundamental frequency of the sensed mechanical vibrations.

[0049] The support system 21 and the impact tool 22 may both be coupled to a position alignment frame 25 configured to ensure that the impulse vector 30 of the impulse J applied by the impact tool 22 to the substrate monolith 1 supported by the support system 21 has a non-zero first axial component 31 and a non-zero second axial component 32.

[0050] The support system 21 may include one or more support members 26. Each support member 26 may comprise an elastomer, foam, or rubber member. In some preferred examples, three or four support members 26 may be used, positioned at one or more nodes of the substrate monolith 1, preferably at one or more of the base nodes of the substrate monolith 1. For example, the support members 26 may contact the base of the substrate monolith 1 at a point around the nodal circle of the substrate monolith 1. The nodal circle may be a circle whose diameter is about 68% of the average diameter of the substrate monolith, in the case of a cylindrical substrate monolith. In some particularly preferred examples, four support members 26 may be used, evenly spaced around the nodal circle, angularly spaced with a 90° separation between them.

[0051] The impact tool 22 may comprise, for example, an automatic hammer configured to apply an impulse J having an impulse vector 30 with a non-zero first axial component 31 and a non-zero second axial component 32 to the substrate monolith 1. The impact tool 22 may be configured to apply a predetermined impulse to the substrate monolith 1. The impact tool 22 may preferably be computer controlled. In some examples, the impact tool 22 may be an automatic hammer. The impact tool 22 may comprise a metal or wooden head 27 that contacts the substrate monolith 1 during use.

[0052] The transducer 23 may comprise a contact or non-contact transducer. For example, the transducer 23 may be an accelerometer that may be attached to the surface of the substrate monolith 1. In a preferred example, the transducer 23 may be a microphone, optionally a unidirectional microphone, that may be used to sense mechanical vibrations by sensing sound waves generated by the mechanical vibrations of the substrate monolith 1.

[0053] Analyzer 24 may include a controller 40. Controller 40 may include one or more processors 41, an impact tool controller 42, a signal input 43 connected to transducer 23, and a memory 44, e.g., for storing software and data. Optionally, analyzer 24 may further include an output, e.g., a display screen 45.

[0054] The one or more processors 41 may include analysis programming for analyzing the sensed mechanical vibrations and transforming the sensed mechanical vibrations into the frequency domain to generate a frequency spectrum of the sensed mechanical vibrations. For example, the analysis programming may perform a fast Fourier transform. The one or more processors 41 may further perform a power spectral density (PSD) analysis on the frequency spectrum.

[0055] The one or more processors 41 may be provided in a single machine housing, or in multiple housings, and / or may be provided by distributed processing means, for example cloud-based processors.

[0056] 3 is an end view of a portion of substrate monolith 1 illustrating one of the cells 12 defined in the XY plane by a first wall 10 (parallel to the X axis) and a second wall 11 (parallel to the Y axis). The stiffness of substrate monolith 1 parallel to each of the first wall 10 and second wall 11 is indicated by arrow k. x and k y For a square cell substrate monolith 1, typically, k x =k y However, the stiffness at an angle (e.g., 45°) to the first and second walls 10 and 11 of the square channel is lower, as indicated by arrow k in FIG. d This is exemplified by:

[0057] As described above, the impulse vector 30 of the impulse J has a non-zero first axial component 31 and a non-zero second axial component 32. In a preferred example, the impulse vector 30 may have substantially equal first axial component 31 and second axial component 32. This is illustrated in Figure 4, where the impulse J is applied by striking the substrate monolith 1 in a direction oblique to the first axis (X-axis) and the second axis (Y-axis). In the illustrated example, the impulse J is applied by striking the substrate monolith 1 in a direction at 45° to the X-axis and the Y-axis.

[0058] FIG. 5 illustrates the angle of the impulse vector 30 for two example substrate monoliths 1. The cells 12 in the example on the left side of FIG. 5 are uniform square cells. The cells 12 in the example on the right side of FIG. 5 are of various sizes and shapes, in a pattern referred to as an "octosquare." In particular, the first wall 10 and the second wall 11 define smaller square cells 12a and larger cells 12b. The larger cells 12b may have truncated corners to form octagonal cells. However, for purposes of this disclosure, it should be noted that for the octagonal cells 12b, the side of the cell 12b having the longest dimension is the side aligned parallel to the first and second axes. Therefore, the angle of the impulse vector 30 can be considered to extend diagonally for the octagonal cells 12b, as indicated by the arrows in FIG. 5, just as for the square cells 12a.

[0059] The second monolith may, for example, comprise a reference substrate monolith, or a substrate monolith from a different batch of substrate monoliths compared to Substrate Monolith 1, or may be a substrate monolith from the same batch of substrate monoliths as Substrate Monolith 1. [Example]

[0060] In the following examples, substrate monoliths were tested using the methods and testing equipment described above.

[0061] Example 1 The effect of impact direction was investigated using a pristine (uncoated) aluminum titanate filter substrate monolith with octosquare-shaped cells. The substrate monolith was impacted with two types of impacts by an impact tool. In the first type of impact, the impulse vector was aligned parallel to the first axis of the substrate monolith ("parallel direction"), so that it was at 0° relative to the first axial wall. In the second type of impact, the impulse vector was aligned obliquely to the first axis, so that it was at 45° relative to the first axial wall (and also the second axial wall) of the substrate monolith ("oblique direction").

[0062] Figure 6 illustrates the frequency spectra obtained from both types of impact using the test apparatus. Specifically, the mechanical vibrations sensed by the microphone during the test were converted to the frequency domain to generate a frequency spectrum of the sensed mechanical vibrations. As can be seen, for the parallel impact, the frequency spectrum does not contain a single, clearly strongest fundamental frequency. In contrast, the oblique impact produces a clearly identifiable fundamental frequency near 1000 Hz, and the fundamental frequency also has a larger amplitude compared to the parallel impact.

[0063] Example 2 7 illustrates another exemplary frequency spectrum obtained from a flow-through substrate monolith using the tests of the present disclosure. The flow-through substrate monolith was a square-cell cordierite substrate coated with a PGM / AL2O3 catalyst. In this example, an impact angled at 45° to the first axial wall was used to obtain a single clearly identifiable fundamental frequency near 1300 Hz.

[0064] Example 3 The second substrate monolith of the method may be used as a reference substrate monolith. The method may further include making a determination regarding the cracking state of the substrate monolith based on a comparison of the fundamental frequencies obtained for the substrate monolith and the reference substrate monolith.

[0065] Figure 8 illustrates three frequency spectrum results obtained by this method for three filter substrate monoliths. The filter substrate monoliths were aluminum titanate substrates with octosquare-shaped cells and coated with CuO / zeolite: an uncracked substrate monolith ("Good"), which served as the reference substrate monolith; a first cracked substrate monolith ("Cracked 1"); and a second cracked substrate monolith ("Cracked 2"). Cracked 1 and Cracked 2 comprised washcoated, calcined substrate monoliths heated to 600°C in an oven. The overdoor was then opened to allow cool air to pass over the hot surface of the substrate monoliths. Due to the resulting thermal shock, surface cracks were observed on the substrate monoliths, extending 3 to 16 cm along the Z axis and penetrating 1 to 5 cm radially.

[0066] As can be seen, the fundamental frequency obtained from the good (reference substrate monolith) was 1636 Hz compared to 1412 Hz and 1532 Hz from Cracked 1 and Cracked 2, respectively. The change in fundamental frequency (a decrease in this example) can be used to determine whether the tested substrate monolith has cracked.

[0067] Example 4 As with external cracks, the present method can be used to identify whether a substrate monolith has internal cracks, which may develop, for example, when the substrate monolith is subjected to high cooling rates after calcination.

[0068] Figure 9 illustrates the fundamental frequencies obtained from 42 samples of SCRF filter substrate monoliths. The filter substrate monoliths were aluminum titanate substrates with octosquare-shaped cells and coated with CuO / zeolite. The samples were heated to a calcination temperature of 500°C and then subjected to cooling rates varying from 3 to 9°C / min, as follows:

[0069] [Table 1]

[0070] After cooling, no visible external cracks were observable on any of the samples. However, testing according to the present disclosure was able to identify that cooling rates greater than 5°C / min resulted in discernible internal cracks from the resulting decrease in fundamental frequency. As can be seen, at 6°C / min, several samples suffered from internal cracks. A clear trend of increasing internal crack occurrence with increasing cooling rate was observed, until at a cooling rate of 9°C / min, all tested samples suffered from internal cracks.

[0071] In this example, a second substrate (reference substrate) may be selected that has been subjected to a slow cooling rate of, for example, 3°C / min or less, to obtain a "reference" fundamental frequency of about 1770 Hz.

[0072] Example 5 The substrate monolith and the second substrate monolith may be from a first and second batch of substrate monoliths, respectively, and the method may further include making a determination regarding a variance between batches of substrate monoliths based on a comparison of the fundamental frequencies obtained for the substrate monolith and the second substrate monolith.

[0073] FIG. 10 illustrates the fundamental frequencies obtained from two batches of ten flow-through substrate monoliths. Each flow-through substrate monolith was a square-cell cordierite substrate coated with a PGM / AL2O3 catalyst. Both Batch 1 and Batch 2 had identical slurry compositions, washcoat loadings, calcination temperatures, etc., but were produced at different times. As can be seen from the results, the fundamental frequencies appear to be generally consistent between batches. Furthermore, statistical testing using a t-test indicated that the variance between batches was not statistically significant for this example.

[0074] Thus, the method can be used to judge between substrate monoliths produced at different times.

[0075] Example 6 FIG. 11 illustrates the fundamental frequencies obtained from four different flow-through substrate monoliths, which are comparable in terms of end use but originate from four different manufacturers. Each substrate monolith was an uncoated cordierite substrate with square cells. In this case, the second substrate monolith could be the previously selected substrate monolith. The other substrate monoliths could be potential replacement material monoliths being compared to the previously selected substrate monolith. As can be seen, in this example, the previously selected substrate monolith produces a fundamental frequency of approximately 415 Hz. For the three potential replacements, option 1 has a similar fundamental frequency of approximately 425 Hz, while options 2 and 3 have fundamental frequencies of 485 Hz and 492 Hz, respectively.

[0076] Thus, the method can be used to discriminate between substrate monoliths obtained from different sources.

[0077] Example 7 The substrate monolith and the second substrate monolith may be from a single batch of substrate monoliths having the same configuration, and the method may further include making a determination regarding the variance within the batch of single substrate monoliths based on a comparison of the fundamental frequencies obtained for the substrate monolith and the second substrate monolith.

[0078] In Figure 12, a sample of 10 GPF filter substrate monoliths was tested. Each filter substrate monolith was an uncoated cordierite substrate with square cells. As can be seen, the resulting fundamental frequencies varied from approximately 2620 Hz to 2905 Hz.

[0079] Comparing the fundamental frequencies may include determining whether there is a statistically significant variation in the fundamental frequencies obtained for a single batch of substrate monoliths.

Claims

1. A substrate monolith, the substrate monolith comprising: i) a plurality of channels extending longitudinally along the Z-axis of the substrate monolith; ii) an array of walls extending along the Z-axis and forming partitions between adjacent channels; 1. A method of testing a substrate monolith, wherein the array of walls comprises a first wall oriented parallel to a first axis of the substrate monolith and a second wall oriented parallel to a second axis of the substrate monolith, the first axis and the second axis both being orthogonal to the Z-axis, comprising: The method comprises: a) applying an impulse to the substrate monolith with an impact tool to induce mechanical vibrations in the substrate monolith; b) sensing the mechanical vibration of the substrate monolith; c) determining the fundamental frequency of the sensed mechanical vibration; d) comparing the fundamental frequency of the sensed mechanical vibration with a fundamental frequency obtained from testing a second substrate monolith; A method wherein in step a) an impulse vector of said impulse has a non-zero first axis component and a non-zero second axis component.

2. 2. The method of claim 1, wherein in step a), the impulse vector has substantially equal first and second axial components.

3. 3. The method of claim 1 or 2, wherein in step a), the impulse is applied by striking the substrate monolith in a direction oblique to the first axis and the second axis.

4. The method of any one of claims 1 to 3, wherein the first axis and the second axis are mutually orthogonal and are the X-axis and Y-axis, respectively, of the substrate monolith.

5. 5. The method of claim 4, wherein in step a), the impulse is applied by striking the substrate monolith in a direction at 45 degrees to the X-axis and the Y-axis.

6. The method of any one of claims 1 to 5, wherein the plurality of channels comprises quadrilateral-shaped channels, optionally square-shaped channels.

7. The method of any one of claims 1 to 6, wherein the substrate monolith is supported on a support system to isolate the substrate monolith from external vibrations.

8. 8. The method of claim 1, wherein in step b) sensing the mechanical vibrations of the substrate monolith comprises sensing the mechanical vibrations in the time domain using a transducer.

9. 9. The method of claim 1, wherein in step c) determining the fundamental frequency comprises transforming the sensed mechanical vibration into the frequency domain to produce a frequency spectrum of the sensed mechanical vibration.

10. 10. The method of claim 9, wherein in step c) determining the fundamental frequency comprises applying a power spectral density (PSD) analysis to the frequency spectrum.

11. 11. The method of any one of claims 1 to 10, wherein the second substrate monolith is a reference substrate monolith, and the method further comprises making a determination regarding a cracking state of the substrate monolith based on the comparison of the fundamental frequencies obtained for the substrate monolith and the reference substrate monolith.

12. 11. The method of any one of claims 1 to 10, wherein the substrate monolith and the second substrate monolith are from a first batch and a second batch of substrate monoliths, respectively, and the method further comprises making a determination regarding a variance between batches of the substrate monoliths based on the comparison of the fundamental frequencies obtained for the substrate monolith and the second substrate monolith.

13. The method of any one of claims 1 to 12, wherein the method is carried out on a production line configured to process a plurality of substrate monoliths.

14. The method of any one of claims 1 to 13, wherein the substrate monolith comprises a flow-through substrate monolith or a filter substrate monolith.

15. A test device for carrying out the method according to any one of claims 1 to 14, comprising: a support system for isolating the substrate monolith from external vibrations; Impact tools and a transducer for sensing mechanical vibrations of the substrate monolith; an analyzer for determining a fundamental frequency of the sensed mechanical vibration; The testing apparatus, wherein the impact tool includes an automatic hammer configured to apply an impulse to the substrate monolith with an impulse vector having a non-zero first axial component and a non-zero second axial component.

16. 16. The testing apparatus of claim 15, wherein the support system and the impact tool are both coupled to an alignment frame configured to ensure that the impulse vector of the impulse applied by the impact tool to the substrate monolith supported by the support system has the non-zero first axial component and the non-zero second axial component.

Images