Testing of substrate monoliths

Abstract

A method of 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; wherein the array of walls comprises first walls (10) orientated parallel to a first-axis of the substrate monolith (1) and second walls (11) orientated parallel to a second-axis of the substrate monolith (1), the first-axis and the second-axis both being orthogonal to the Z-axis; the method comprising the steps of: 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 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 to a fundamental frequency obtained from testing of a second substrate monolith; wherein in step a) an impulse vector (30) of the impulse (J) has a non-zero first-axis component (31) and a non-zero second-axis component (32).

Claims

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

2. The method of claim 1, wherein in step a) the impulse is applied by striking the substrate monolith in a diagonal direction with respect to the first-axis and the second-axis.

3. The method of claim 1, wherein the first-axis and the second-axis are orthogonal to one another, being an X-axis and a Y-axis respectively of the substrate monolith.

4. The method of claim 3, wherein in step a) the impulse is applied by striking the substrate monolith in a direction at 45 to the X-axis and the Y-axis.

5. The method of claim 1, wherein the plurality of channels comprise quadrilateral-shaped channels, optionally square-shaped channels.

6. The method of claim 1, wherein the substrate monolith is supported on a support system to isolate the substrate monolith from extraneous vibrations.

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

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

9. The method of claim 8, wherein in step c) determining the fundamental frequency comprises applying a Power Spectral Density (PSD) analysis to the frequency spectrum.

10. The method of claim 1, wherein the second substrate monolith is a reference substrate monolith and the method further comprises the step of making a judgement regarding a crack status of the substrate monolith based on the comparison of the fundamental frequencies obtained for the substrate monolith and the reference substrate monolith.

11. The method of claim 1, wherein the substrate monolith and the second substrate monolith are from respective first and second batches of substrate monoliths and the method further comprises the step of making a judgement regarding a variance between the batches of substrate monoliths based on the comparison of the fundamental frequencies obtained for the substrate monolith and the second substrate monolith.

12. The method of claim 1, wherein the method is performed on a production line configured to process a plurality of substrate monoliths.

13. The method of claim 1, wherein the substrate monolith comprises a flow-through substrate monolith or a filter substrate monolith.

14. A test apparatus for performing the method of any preceding claim, comprising: a support system for isolating the substrate monolith from extraneous vibrations; an impact tool; a transducer for sensing mechanical vibrations of the substrate monolith; and an analyser for determining the fundamental frequency of the sensed mechanical vibrations; wherein the impact tool comprises an automated hammer configured to apply the impulse to the substrate monolith with an impulse vector having substantially equal non-zero first-axis and second-axis components.

15. The test apparatus of claim 14, 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-axis component and the non-zero second-axis component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Aspects and embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic view of a substrate monolith;

(3) FIG. 2 is a schematic drawing of a test apparatus;

(4) FIG. 3 is an end view of a portion of a substrate monolith;

(5) FIG. 4 is a schematic end view of a substrate monolith being subjected to an impulse;

(6) FIG. 5 shows end views of portions of two substrate monoliths;

(7) FIG. 6 is a graph of frequency vs. amplitude illustrating the effect of impulse direction;

(8) FIG. 7 is a graph of frequency vs. amplitude illustrating an example test result;

(9) FIG. 8 is a graph of frequency vs. amplitude illustrating example test results for cracked and un-cracked substrate monoliths;

(10) FIG. 9 is a plot of fundamental frequencies obtained for 42 samples of substrate monolith;

(11) FIG. 10 is a plot of fundamental frequencies obtained for two batches, each containing 10 samples of substrate monolith;

(12) FIG. 11 is graph of frequency vs. amplitude illustrating example test results for substrate monoliths from four different sources; and

(13) FIG. 12 is a plot of fundamental frequencies obtained for 10 samples of substrate monolith from a single batch.

DETAILED DESCRIPTION

(14) The skilled reader will recognise 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.

(15) FIG. 1 is a schematic view of a substrate monolith 1. The substrate monolith 1 comprises a plurality of channels extending longitudinally along a 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.

(16) The array of walls comprises first walls 10 orientated parallel to a first-axis of the substrate monolith 1 and second walls 11 orientated parallel to a second-axis of the substrate monolith 1, the first-axis and the second-axis both being orthogonal to the Z-axis. The first-axis and the second-axis may be orthogonal to one another. The first-axis may be an X-axis and the second-axis may be a Y-axis respectively of the substrate monolith 1.

(17) The first walls 10 and the second walls may 11 define cells 12 when viewed in the X-Y plane of the substrate monolith 1. In the illustrated example the cells 12 are square-shaped. However, the cells 12 may take other shapes. The substrate monolith 1 may have a cylindrical external shape, although other shapes can be provided.

(18) According to the present disclosure the method of testing the substrate monolith 1 comprises the steps of: 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 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 to a fundamental frequency obtained from testing of a second substrate monolith; wherein in step a) an impulse vector 30 of the impulse J has a non-zero first-axis component 31 and a non-zero second-axis component 32.

(19) FIG. 2 shows a schematic drawing of a test apparatus 20 that is suitable for performing the test on the substrate monolith 1. The test apparatus 20 comprises a support system 21 for isolating the substrate monolith 1 from extraneous vibrations, the impact tool 22, a transducer 23 for sensing mechanical vibrations of the substrate monolith 1, and an analyser 24 for determining the fundamental frequency of the sensed mechanical vibrations.

(20) The support system 21 and the impact tool 22 may both be coupled to an 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 the non-zero first-axis component 31 and the non-zero second-axis component 32.

(21) The support system 21 may comprise one or more support members 26. Each support member 26 may comprise an elastomer, foam or rubber member. In some preferred examples 3 or 4 support members 26 may be used that are positioned at one or more nodal points of the substrate monolith 1, preferably at one or more of the fundamental nodal points of the substrate monolith 1. For example, the support members 26 may contact a base of the substrate monolith 1 at points around a nodal circle of the substrate monolith 1. The nodal circle may be a circle whose diameter is approximately 68% of the substrate monolith's mean diameter in the case of cylindrical substrate monoliths. In some particularly preferred examples, 4 support members 26 may be used that are equi-spaced around the nodal circle, that is being angularly arranged with 90 separations there between.

(22) The impact tool 22 may comprise, for example, an automated hammer configured to apply the impulse J to the substrate monolith 1 with the impulse vector 30 having the non-zero first-axis component 31 and the non-zero second-axis component 32. The impact tool 22 may be configured to apply a pre-determined 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 automated hammer. The impact tool 22 may comprise a metal or wooden head 27 that contacts the substrate monolith 1 in use.

(23) The transducer 23 may comprise a contact or non-contact transducer. For example the transducer 23 may be an accelerometer that may be applied to a surface of the substrate monolith 1. In preferred examples, the transducer 23 may be a microphone, optionally a unidirectional microphone, may be used to sense the mechanical vibrations by sensing the sound waves produced by the mechanical vibrations of the substrate monolith 1.

(24) The analyser 24 may comprise controller 40. The controller 40 may comprise one or more processors 41, an impact tool controller 42, a signal input 43 connected to the transducer 23, and a memory 44 for storage of, for example, software and data. Optionally the analyser 24 may further comprise an output, for example a display screen 45.

(25) The one or more processors 41 may comprise analysis programming for analysing the sensed mechanical vibrations and converting the sensed mechanical vibrations into a frequency domain to produce a frequency spectrum of the sensed mechanical vibrations. For example the analysis programming may perform a Fast Fourier Transformation. The one or more processors 41 may further perform a Power Spectral Density (PSD) analysis on the frequency spectrum.

(26) The one or more processors 41 may be provided in a single machine housing, or in a plurality of housings, and/or may be provided by distributed processing means, for example cloud-based processors.

(27) FIG. 3 is an end view of a portion of the substrate monolith 1 illustrating one of the cells 12 defined in the X-Y plane by the first walls 10 (parallel to the X-axis) and the second walls 11 (parallel to the Y-axis). The stiffness of the substrate monolith 1 parallel to each of the first walls 10 and the second walls 11 is illustrated by the arrows k.sub.x and k.sub.y. For a square-celled substrate monolith 1 typically k.sub.x=k.sub.y. However, the stiffness diagonally with respect to the first walls 10 and the second walls 11 (for example at 45) of the square channels will be lower and is illustrated in FIG. 3 by arrow k.sub.d.

(28) As noted above, the impulse vector 30 of the impulse J has a non-zero first-axis component 31 and a non-zero second-axis component 32. In preferred examples, the impulse vector 30 may have substantially equal first-axis and second-axis components 31, 32. This is illustrated in FIG. 4 where the impulse J is applied by striking the substrate monolith 1 in a diagonal direction with respect to the first-axis (the X-axis) and the second-axis (the 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.

(29) FIG. 5 illustrates the angle of the impulse vector 30 for two examples of substrate monolith 1. The cells 12 of the left-hand example of FIG. 5 are uniform square-shaped cells. The cells 12 of the right-hand example of FIG. 5 are of varying size and shape, in a pattern referred to as octo-square. In particular, the first walls 10 and the second walls 11 define smaller, square-shaped cells 12a and larger cells 12b. The larger cells 12b may have truncated corners forming octagon-shaped cells. However, for the purposes of the present disclosure it will be noted that in the case of the octagon-shaped cells 12b the sides of the cell 12b with the longest dimensions are those aligned parallel to the first-axis and the second-axis. Thus, the angle of the impulse vector 30 may be considered to extend diagonally relative to the octagon-shaped cells 12b as shown by the arrow in FIG. 5, in the same way as for the square-shaped cells 12a.

(30) The second monolith may comprise, for example, a reference substrate monolith, or a substrate monolith from a different batch of substrate monoliths compared to the substrate monolith 1, or may be a substrate monolith from the same batch of substrate monoliths as the substrate monolith 1.

EXAMPLES

(31) In the following examples substrate monoliths were tested using the method and testing apparatus as described above.

Example 1

(32) A bare (uncoated) aluminium titanate filter substrate monolith having octo-square-shaped cells was used to study the effect of impact direction. The substrate monolith was impacted by the impact tool with two types of impact. In a first type of impact the impulse vector was aligned parallel to the first-axis so that it was at 0 to the first-axis walls of the substrate monolith (the Parallel direction). In a second type of impact the impulse vector was aligned diagonally to the first-axis so that it was at 45 to the first-axis walls (and also the second-axis walls) of the substrate monolith (the Diagonal direction).

(33) FIG. 6 illustrates the frequency spectrums obtained from both types of impact using the test apparatus. In particular, during the test the mechanical vibrations sensed by the microphone were converted into the frequency domain to produce the frequency spectrum of the sensed mechanical vibrations. As can be seen, for the Parallel direction impacts the frequency spectrum does not comprise any single clear strongest fundamental frequency. By contrast, the Diagonal direction impacts produce a clearly discriminable fundamental frequency at around 1000 Hz that also has a greater amplitude compared to the Parallel direction impacts.

Example 2

(34) FIG. 7 illustrates another example frequency spectrum obtained from a flow-through substrate monolith using the test of the present disclosure. The flow-through substrate monolith was a cordierite substrate having square-shaped cells and was coated with a PGM/AL.sub.2O.sub.3 catalyst. In this example a single clearly discriminable fundamental frequency at around 1300 Hz was obtained using an impact angled at 45 to the first-axis walls.

Example 3

(35) The second substrate monolith of the method may be used as a reference substrate monolith. The method may further comprise the step of making a judgement regarding a crack status of the substrate monolith based on the comparison of the fundamental frequencies obtained for the substrate monolith and the reference substrate monolith.

(36) FIG. 8 illustrates results of three frequency spectrums obtained by the present method for three filter substrate monoliths. The filter substrate monoliths were aluminium titanate substrates having octo-square-shaped cells and being coated with CuO/zeolitean un-cracked substrate monolith (Good part) acting as the reference substrate monolith, a first cracked substrate monolith (Cracked part 1) and a second cracked substrate monolith (Cracked part 2). Cracked part 1 and Cracked part 2 comprised washcoated and calcined substrate monoliths that were heated in an oven to 600 C. The over door was then opened to allow cold air to pass over the hot surfaces of the substrate monoliths. Due to the resulting thermal shock, surface cracking of the substrate monoliths was observed with cracks extending from 3 cm to 16 cm along the Z-axis and penetrating 1 to 5 cm in the radial direction.

(37) As can be seen, the fundamental frequency obtained from the Good part (the reference substrate monolith) was 1636 Hz, compared to 1412 Hz and 1532 Hz respectively from the Cracked part 1 and Cracked part 2. The change in fundamental frequency (in this example a reduction) may be used to judge whether the tested substrate monolith has been cracked.

Example 4

(38) As well as external cracks, the method may be used to discern whether a substrate monolith has internal cracks. Such internal cracks may develop, for example, when a substrate monolith is subjected to high cooling rates following calcination.

(39) FIG. 9 illustrates the fundamental frequencies obtained from 42 samples of an SCRF filter substrate monolith. The filter substrate monoliths were aluminium titanate substrates having octo-square-shaped cells and being coated with CuO/zeolite. The samples were heated to a calcination temperature of 500 C. and then subjected to cooling rates varying between 3 and 9 C./min, as follows:

(40) TABLE-US-00001 Sample No. Cooling rate ( C./min) 1 to 4 3 5 to 8 4 9 to 12 5 13 to 20 6 21 to 28 7 29 to 36 8 37 to 42 9

(41) There were no visible external cracks observable on any of the sample after cooling. However, testing according to the present disclosure was able to discern that cooling rates of greater than 5 C./min resulted in internal crackingrecognisable from the decrease in fundamental frequency obtained. As can be seen, at 6 C./min some samples suffered internal cracking. A clear trend of increasing occurrence of internal cracking with increasing cooling rate was observed until at a cooling rate of 9 C./min all samples tested had suffered internal cracking.

(42) In this example the second substrate (reference substrate) may, for example, be chosen to be one that has been subjected to a slow cooling rate of less than or equal to 3 C./min such that a reference fundamental frequency of approximately 1770 Hz is obtained.

Example 5

(43) The substrate monolith and the second substrate monolith may be from respective first and second batches of substrate monoliths. The method may further comprise the step of making a judgement regarding a variance between the batches of substrate monoliths based on the comparison of the fundamental frequencies obtained for the substrate monolith and the second substrate monolith.

(44) FIG. 10 illustrates fundamental frequencies obtained from two batches of ten flow-through substrate monoliths. Each flow-through substrate monolith was a cordierite substrate having square-shaped cells and was coated with a PGM/AL.sub.2O.sub.3 catalyst. Both Batch 1 and Batch 2 had identical slurry compositions, washcoat loading, calcination temperature, etc. but were produced at different times. As can be seen from the results the fundamental frequencies appear generally consistent between batches. Further, statistical testing using a T test indicated that, for this example, the variance between the batches was not statistically significant.

(45) Thus, the method may be used to make judgements between substrate monoliths manufactured at different times.

Example 6

(46) FIG. 11 illustrates fundamental frequencies obtained from 4 different flow-through substrate monoliths that are comparable to each other in terms of their end use but are from 4 different manufacturers. Each substrate monolith was an uncoated cordierite substrate having square-shaped cells. In this case the second substrate monolith may be a previously selected substrate monolith. The other substrate monoliths may be potential replacement substrate monoliths that are being compared against the previously selected substrate monolith. As can be seen, in this example the previously selected substrate monolith produces a fundamental frequency of about 415 Hz. If the three potential replacements Option 1 has a similar fundamental frequency of about 425 Hz whereas Option 2 and Option 3 have fundamental frequencies of 485 and 492 Hz respectively.

(47) Thus, the method may be used to make judgements between substrate monoliths obtained from different sources.

Example 7

(48) The substrate monolith and the second substrate monolith may be from a single batch of substrate monoliths having the same configuration. The method may further comprise the step of making a judgement regarding a variance within the single batch of substrate monoliths based on the comparison of the fundamental frequencies obtained for the substrate monolith and the second substrate monolith.

(49) In FIG. 12 a sample of 10 GPF filter substrate monoliths was tested. Each filter substrate monolith was an uncoated cordierite substrate having square-shaped cells. As can be seen the fundamental frequencies obtained varied from about 2620 Hz to 2905 Hz.

(50) The comparison of the fundamental frequencies may comprise determining if there is a statistically significant variation in the fundamental frequencies obtained for the substrate monoliths of the single batch.