Method of inspecting a honeycomb structural body for purifying exhaust gases and apparatus used in the method

Abstract: A method of inspecting an alternately sealed honeycomb structuralbody (1) is provided which can quickly, efficiently and accurately inspect presence of defects of the honeycomb structural body in a simple and economical manner. The method comprises flowing particulates in axial direction of the throughholes (2) from one end surface to the other end surface of the honeycomb structuralbodyy (1), catching the particulates on a gas-permeable screen (11) intimately mounted on the other end surface to form a pattern of the particulates, and checking the figure to inspect defects at internal partition walls and sealing portions of the honeycomb structural body(1).

Description: The present invention relates to a method of inspecting a honeycomb structural body for purifying exhaust gases, particularly a Diesel particulate filter (abbreviated as DPF, hereinafter) for purifying exhaust gases from Diesel engines, and an apparatus used in the method. The aforementioned DPF is composed of a porous ceramic honeycomb structural body having partition walls defining throughholes which are alternately sealed at alternate end surfaces of the honeycomb structural body to force an exhaust gas supplied from one end surface to flow out from the other end surface through the partition walls. Thus, DPF can remove fine particulates in exhaust gases by filtration through the porous partition walls. Therefore, in the production process of DPF, the produced DPF has to be inspected to ensure that no defects at internal partition walls, i.e., cracks which are called "internal cracks" and excessively large pores of diameters larger than those required for the filtration exist, and that defects at the sealed portions, i.e., non-sealing or insufficient sealing due to gaps formed between the sealing agent and the partition walls and holes formed in the sealing agent, do not exist. As a method of inspecting the internal defects of such honeycomb structural body, the method of applicant's Japanese Patent Publication No. 62-53,767 has been known wherein the honeycomb structural body is inspected about the internal cracks by irradiation thereof from one end surface with a light to project a projection image on a screen arranged at the other end surface, and checking presence or absence of a disturbance of the light permeating through the internal cracks of the partition walls. However, the inspection method was applied to honeycomb structural bodies not having sealing portions at alternate end surfaces, such as catalyst carriers for purifying exhaust gases, so that it is hardly applicable to DPF having throughholes which are alternately sealed at alternate end surfaces of the honeycomb structural bodies, because the inspection light can not permeate through the sealing portions even if the internal cracks are existing on the partition walls. As regards the defects at the sealing portions, if the defects are small, the amount of the light permeating through the defects is small, so that the inspection of the defects by means of a screen is difficult. If the defects are not projected on the screen, the throughholes have to be inspected one by one, resulting in problems of inefficient and inaccurate inspection. US-A-2,751,779 discloses a method and device for inspecting the efficiency of gas cleaning apparatus, in which a filter disc is used to collect dust particles in a gas flow and a camera is used to record the colour change of the disc due to the deposition of the dust particles thereon, so that the system efficiency can be found out by comparing the respective darkness changes of filter discs at the system inlet and outlet. An object of the present invention is to obviate the above drawbacks and problems. Another object of the present invention is to provide a quick, simple, economical and accurate method of inspecting the defects at partition walls and sealing portions of a honeycomb structural body for purifying exhaust gases having throughholes which are alternately sealed at alternate end surfaces of the honeycomb structural body, such as DPF. A further object of the present invention is to provide an inspection apparatus used in the present method. The present invention in one aspect is a method of inspecting a honeycomb structural body as set out in claim 1. The present invention in a second aspect is an apparatus for inspecting a honeycomb structural body as set out in claim 5. For a better understanding of the present invention, reference is made to the accompanying drawings, in which: Fig. 1 is a schematic cross-sectional view of an example of the apparatus of the present invention; Fig. 2 is a plan view of an example of figure of particulates showing existence of internal defects of a honeycomb structural body; and Fig. 3 is a schematic enlarged plan view of a portion thereof. Numbering in the Drawings. 1 ... honeycomb structural body for purifying exhaust gases 2 ...throughholes 3 ...sealing agent 5 ...supporting member 6 ...gas-feeding pipe 7 ...switch valve 8 ...gas generator for producing a particulate-containing gas 9 ...gas discharge stuck 10 ...gas outlet pipe 11 ...screen 12 ...restraining screen Hereinafter, the present invention will be explained in more detail with reference to examples. Example 1 Referring to Fig. 1, a ceramic honeycomb structural body 1 to be inspected for purifying exhaust gases has throughholes 2 which are alternately sealed at alternate end surfaces of the honeycomb structural body 1 by means of a sealing agent 3, as shown in Fig. 1. The mode of sealing the throughholes 1 is not necessarily a checkered mode and can be varied in various modes. For example, the sealing can be made at alternate rows of the throughholes on alternate end surfaces of the honeycomb structural body 1. Such various modes are included in the present invention defining the throughholes which are expressed as "which are alternately sealed at alternate end surfaces of the honeycomb structural body". The honeycomb structural body 1 is gastightly supported at peripheral portion of one end surface thereof by means of a conical supporting table 5. The supporting table 5 is communicated at the lower portion with a gas-feeding pipe 6 which has a switch valve 7 at the lower end. The pipe 6 has two branch pipes at the switch valve 7, one branch pipe being communicated with a gas generator 8 which produces a particulate-containing gas, and the other branch pipe being communicated with a gas discharge duct 9. The gas generator 8 in this example is a device for generating a gas containing black soot particulates of a size range of 0.1-1.0 µ, for example. However, in the present invention, particulates other than soot can be used. For example, white particulates, such as wheat flour, can be used. The switch valve 7 is provided for exiting the particulate-containing gas produced by the gas generator 8 to the gas exhaust duct 9 at first, and is necessary when using a soot gas generator which is unstable at start time of the inspecting operation. The honeycomb structural body 1 mounted on the supporting table 5 has at its upper end surface an intimately contacted gas outlet pipe 10 via a gas-permeable screen 11. As the material of the screen 11, use is made of any gas-permeable material, such as flexible cloth or filter paper, or rigid material, such as glass or ceramic material. If a flexible screen 11 is used, a roughly meshed restraining screen 12 is preferably arranged between the gas outlet pipe 10 and the screen 11 under pressure so that the screen 11 can intimately contact with the honeycomb structural body 1. The color of the screen 11 is preferably white when the particulates are soot, and black when the particulates are white, for facilitating easy visualization of the figure of the particulates adhered on the screen 11. Example 2 In this example, the present inspection method will be explained in more detail with reference to the above exemplified apparatus. The alternately sealed honeycomb structural body 1 to be inspected for purifying exhaust gases is set on the supporting table 5, the screen 11 is mounted on the upper end surface of the honeycomb structural body 1, and the gas outlet pipe 10 is intimately contacted on the upper end surface of the honeycomb structural body 1 via the screen 11. Then, the switch valve 7 is switched to pass a particulate-containing gas produced by the gas generator 8, such as a soot-containing gas generated by insufficient combustion of a fuel, in the throughholes 2 of the honeycomb structural body 1 in the axial direction thereof from the lower end surface thereof. In this case, the minute soot particles can not pass through the sealing agent 3 at the sealing portions 3 of the throughholes 2, so far as the sealing portions have no defects. Thus, though a portion of the soot particulates is caught on the partition walls of the honeycomb structural body 1, the other portion of the soot particulates is permeated through the partition walls to flow to the upper end surface of the honeycomb structural body 1 and is caught on the gas permeable screen 11 to form a figure of soot particulates corresponding to a sealing state of the sealing portions at the upper end surface of the honeycomb structural body 1. Therefore, if the honeycomb structural body 1 is normal or has no defects at the sealing portions and the partition walls, a figure of soot particulates corresponding to the non-sealing portions or open portions of the upper end surface of the honeycomb structural body 1 can be obtained on the screen 11. However, if the honeycomb structural body 1 has internal cracks, etc., on the partition walls, the soot particulates flow through the internal cracks in the neighboring throughholes 2 in large amounts, so that the figure of soot particulates on the screen 11 assumes, for example, a linear pattern or a dotted pattern, as shown in Figs. 2 and 3, which are different from the figure of normal honeycomb structural body. Similarly, also in case when the alternately sealed honeycomb structural body 1 has defects, etc., at the sealing portions, the figure of soot particulates caught on the screen 11 is clearly different from the figure of normal honeycomb structural body. Therefore, if the screen 11 having a figure of soot particulates caught thereon is removed or taken out from the apparatus so as to be checked by a naked eye, the presence or the absence of the defects of the sealed honeycomb structural body 1 can easily be inspected. In place of the above exemplified way of checking the figure of soot particulates formed on the screen 11 by a naked eye, various another ways of inspecting the honeycomb structural body 1 can also be used. For example, brightness or darkness of the figure of soot particulates may be automatically measured to emanate a signal which reports the presence of the defects when the brightness or the darkness trespasses a certain level. The above inspection apparatus can be installed on a conveyor transporting a number of sealed honeycomb structural body so as to automatically inspect all of the honeycomb structural bodies. As explained in detail in the foregoings, the present invention passes a flow of particulates through a sealed honeycomb structural body from one end surface thereof to the other end surface, catches the particulates on a screen intimately contacted to the other end surface of the honeycomb structural body to form a figure of the particulates, and checks the figure of the caught particulates to inspect defects of the sealed honeycomb structural body. Therefore, the present invention can quite easily find out defects of the sealed honeycomb structural body as compared with the conventional method of directly inspecting the honeycomb structural body by a naked eye. Also, in comparison to the conventional method of using a light, a more accurate inspection can be performed in the present invention. Therefore, the present invention obviates the drawbacks and problems of prior art, so that it is eminently useful to development of the industry.

Claims: A method of inspecting a honeycomb structural body (1) for purifying exhaust gases having a number of throughholes (2) which are alternately sealed at alternate end surfaces of the honeycomb structural body with the internal walls separating the throughholes being porous, the method comprising causing particulate material to flow in the axial direction of the throughholes from one end surface to the other end surface of the honeycomb structural body, catching the particulate material on a gas-permeable screen (11) intimately mounted on the other end surface to obtain a pattern of the particulates, and checking the pattern to detect defects at internal partition walls and sealing portions of the honeycomb structural body. The method of claim 1, wherein the alternate sealing (3) is effected in a checkered mode. The method of claim 1, wherein the alternate sealing (3) is effected at alternate rows of the throughholes. The method of claim 1, wherein the particulate material is black soot or wheat flour. An apparatus for inspecting a honeycomb structural body (1) for purifying exhaust gases having a number of throughholes (2) which are alternately sealed at alternate end surfaces of the honeycomb structural body with the internal walls separating the throughholes being porous, comprising a supporting member (5) which gas tightly supports peripheral portion of one end surface of the honeycomb structural body, a gas generator (8) communicating with the supporting member for producing a gas containing particulate material and a gas-permeable screen (11) arranged on the other end surface of the honeycomb structural body (1) for catching the particulate material passing through the body. The apparatus of claim 5, which further comprises a roughly meshed restraining screen (12) on the downstream side of the gas permeable screen (11) for ensuring intimate contact of the gas permeable screen to the upper end surface of the honeycomb structural body (1).

Inventors: HIJIKATA TOSHIHIKO, HORIE RYOUZI, YAMADA SATORU, HIJIKATA, TOSHIHIKO, HORIE, RYOUZI, YAMADA, SATORU
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1991
Main classification: G01N15
IPC codes: F01N3, G01N33, G01N19, F01N11, G01N15, G01M19