Abstract:
Methods and apparatus for testing the strength of ceramic honeycomb structures are described. The apparatus includes a chamber that utilizes a flexible, generally cylindrical member including integral flanges to apply compressive force to the periphery of the honeycomb structure. According to some embodiments, a portable apparatus with an open chamber is provided to allow for rapid testing of multiple honeycomb structures.

Description:
FIELD OF THE INVENTION 
     This invention relates to strength testing of ceramic honeycomb structures. More particularly, the invention relates to apparatus and methods for testing the compressive strength of such structures. 
     BACKGROUND OF THE INVENTION 
     Compressive strength is an important feature of thin-walled ceramic honeycomb structures, which are used in the manufacture catalyst supports. Honeycomb structures have a webbed cellular or channeled core structure surrounded in most cases by a smooth integral outer skin layer. The manufacture of structures by extrusion to form cellular ceramic honeycombs of cordierite composition and very low thermal expansion from plasticized mixtures of ceramic batch materials is described in U.S. Pat. Nos. 3,790,654 and 3,885,977. Such honeycombs remain in widespread commercial use as catalyst supports for emissions control applications such as automotive exhaust treatment systems. 
     One way of improving the exhaust conversion efficiency of catalyst supports is to produce honeycomb products with thinner webs. Currently, the assignee of the present patent application manufactures catalyst supports having web thicknesses in the range of two mils. Thinner webbed structures result in parts that have reduced compressive strength. In the manufacture of exhaust system components, catalyst supports are typically surrounded with a housing comprised of a metal layer. The process for surrounding the parts with a metal layer is known in the art as “canning”. The canning process used to place a metal housing around ceramic catalyst supports exerts compressive stresses on the catalyst support. Manufacturers of catalyst supports must be able to provide products that are able to withstand compressive forces encountered during canning processes. 
     Various apparatus exist for testing compressive strength of ceramic honeycomb structures. One type of apparatus involves enveloping a sample in a rubber boot, immersing the enveloped sample in hydraulic oil and applying isostatic pressure to the sample from all directions. One drawback of this apparatus is that it does not simulate the true compressive forces encountered by catalyst supports during the canning operation. Furthermore, this type of apparatus is relatively large and stationary. In addition, the envelopment, loading and removal of the sample is time consuming, inconvenient for the operator and unclean because the enveloped sample is loaded directly into the hydraulic oil. Since the apparatus is too large to transport, samples must carried to and from the machine. Various apparatus exist for testing tubular products, however, these apparatus do not permit rapid loading, testing and unloading of the product. New methods of testing ceramic honeycomb structures, particularly in a production environment, are needed. 
     SUMMARY OF THE INVENTION 
     The invention relates to apparatus and methods for testing the compressive strength of ceramic honeycomb structures. In certain embodiments, a portable compressive strength testing apparatus is provided. According to other embodiments, samples can be easily and rapidly loaded, tested and unloaded from the apparatus. In some embodiments, the portability of the apparatus and the ease and speed of loading, testing and unloading samples facilitates the testing of large quantities of ceramic honeycomb structures. In other embodiments, a failure detector is provided to determine when a part has experienced failure that cannot be detected by visual inspection. 
     Advantages of the invention will be apparent from the following detailed description. It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of a main housing and loading and unloading portion of the strength testing apparatus according to one embodiment of the invention; 
     FIG. 2 is an exploded perspective view of a main housing and a flexible member in a honeycomb structure compressive strength testing apparatus according to one embodiment of the invention; 
     FIG. 3 is an assembled cross-sectional view of a main housing used in a strength testing apparatus according to one embodiment of the invention; and 
     FIG. 4 is a perspective view of a strength testing apparatus on a cart according to one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Before describing several exemplary embodiments of the invention, it is to be understood that the invention is not limited to the details of construction or process steps set forth in the following description. The invention is capable of other embodiments and of being practiced or carried out in various ways. 
     The invention provides apparatus and methods for testing the compressive strength of a ceramic honeycomb samples. Referring to FIGS. 1-4, an exemplary embodiment of an apparatus  10  for testing the compressive strength of ceramic honeycombs is shown. The apparatus  10  includes a main housing  12  having a generally cylindrical chamber  14  and a generally cylindrical, flexible member  16  disposed within the main housing  12 . The flexible member  16  defines a sample  17  loading and testing area  18  and a gap  20  between the flexible member and the main housing  12 . The gap  20  provides a fluid holding area  22 . A fluid inlet  24  and fluid outlet  26  are in fluid communication with a pressure generator  21  for supplying fluid under pressure to the fluid holding area  22  and to expand the flexible member  14  inwardly to provide uniform compressive force on the periphery of the sample  17 . A top plug  28  and a bottom plug  30  seal the chamber  14  during testing of the sample  17 . The apparatus  10  also includes a mechanism for automatically moving samples  17  in and out the sample loading and testing area. Preferably, the mechanism for moving the sample  17  in and out of the sample loading and testing area includes a retractable plunger  32  that is adapted to move the bottom plug  30  upwardly and downwardly. A top pad  34  is associated with the top plug  28 , and a bottom pad  38  is associated with the bottom plug  30 . The top pad  34  and bottom pad  38  are in contact with the sample  17  during testing, and should be made from a material that will not chip a ceramic part. The bottom pad  38  also provides lower support for the sample  17  during testing. Preferably, the plunger  32  is hydraulically or pneumatically activated. However, other mechanisms can be used to move sample in and out of the sample loading and testing area. For example, the sample  17  could be moved by a plate supporting the sample  17  attached to a movable screw type mechanism, or the sample could be raised by a support driven by a chain, pulley, belt or other suitable mechanism for raising or lower the sample  17  into the sample test area  18 . 
     As shown in FIG. 2, the flexible member  16  comprises a generally cylindrical main body  19 , a top flange  21  and a bottom flange  23  integrally formed with the main body  19 . The flanges  21 ,  23  extend radially from the top and bottom of the main body. The flanges  21 ,  23  also include integral gaskets  25 ,  27  for sealing with the main housing  12 . The housing may further include a top recess  40  and a bottom recess (not shown) around the periphery of top and bottom surfaces of the main housing  12 . In certain embodiments, the gaskets  25 ,  27  have a cross-sectional diameter large enough so that the gaskets  25 ,  27  extend beyond the top and bottom recesses (see FIG.  1 ). A top sealing cap  42  and a bottom sealing cap  44  are secured to the main housing  12  such that the sealing caps  42  and  44  compress the gaskets  25 ,  27  to form a fluid tight seal. As shown in the Figures, the sealing caps  42 ,  44  are secured to the main housing  12  with a plurality of retaining members such as bolts  50 . However, the sealing caps  42 ,  44  can be secured to the main housing  12  by other means such as by clamps. 
     The main housing  12 , the plugs  28 ,  30  and the sealing rings  42 ,  44  are preferably made from a metal capable of sustaining the forces generated by the pressure generator and required for compressive strength testing ceramic honeycomb samples. Typically, the chamber is pressurized to pressures between about 50 pounds per square inch and 250 pounds per square inch. The pads  34 ,  38  are preferably made from a soft material such a polymer or polyurethane. The flexible member  14  is preferably made from polyurethane. 
     Referring to FIG. 1, preferably the top plug  28 , bottom plug  30  and the plunger  42  are retractable such that they can move towards and away from the sample testing area  18  to open and seal the testing area  18 . The top plug  28  can be retracted by a pneumatically or hydraulically controlled top plug actuator  52  or other suitable mechanism for moving the plug. The bottom plug  30  can be retracted by pneumatically controlled bottom plug actuator  54  or other suitable mechanism for moving the plug. In preferred embodiments, the bottom pad  38  for supporting the sample  17  can be moved in and out of sample chamber  18  by a pneumatically controlled bottom pad actuator  56 . 
     Referring to FIG. 4, preferably, the entire apparatus  10  is sized to fit on a portable cart  60  to facilitate use of the compressive strength testing apparatus  10  in various locations of manufacturing plant. Other optional features of the strength testing apparatus include an operator control panel  62 , and an enclosure  64  for housing electrical, pneumatic and hydraulic controls (not shown). The main housing  12 , the top plug  28  and the bottom plug  30  and their associated actuators are preferably housed in an enclosure  66 . The main housing  12  can be secured to a mounting bracket  68  associated with the cart  60 . The top plug  28  and actuator can be mounted on a movable stage  70  capable of moving in the direction of arrow  71 . Movable stage can be moved with a pneumatic or hydraulic control system. The inlet  24  and outlet  26  are in fluid communication with a pressure generator, preferably a pressure generator able to produce hydraulic pressure. Preferably, the inlet  24  and outlet  26  are connected to the pressure generator by high pressure hoses and quick connect/disconnect fittings (not shown). 
     According to certain embodiments, a sensor (not shown) is included and is connected to the testing area and the hydraulic and pneumatic controls for determining failure of the sample during testing. It will be understood that complete or catastrophic failure of the part can be determined by visual inspection of the sample or by detection of an audible crack. However, in certain instances, the part may not catastrophically fail, and a sensor can be included to detect failure of the part. Such sensors may include a pressure sensor connected to the hydraulics of the apparatus to monitor sudden and rapid changes in pressure indicative of a part failure. Upon detection of a sudden pressure change, the apparatus  10  can be equipped with an alarm to alert the operator, or the apparatus can be configured to shut off upon activation of an alarm. Another type of sensor that can be operably connected to the test area of the apparatus is an acoustic sensor capable of detecting cracking in the sample that is not audibly detectable by a human. The acoustic sensor can be connect to an audible and/or visual alarm to alert an operator, or the machine can be configured to shut down upon detection of a crack in a sample. 
     In use, the apparatus  10  is located in a convenient location for testing honeycomb samples in a manufacturing facility. The stage  70  supporting the top plug  28  and actuator is moved away from the main housing  12  so that sample testing area  18  can be loaded with a sample. The bottom plug  30  is moved upwardly into a closed position by engaging the bottom plug actuator  54 , and then the bottom pad  38  is raised to the top of the sample loading area  18  by engaging the bottom pad actuator  57 . A sample  17  is loaded on the bottom pad  38 , and the bottom pad actuator is engaged to lower the sample  17  into the sample testing area  18 . The stage  70  supporting the top plug  28  is moved so that the top plug is located above the sample testing area  18 . The top plug actuator is engaged to close the top plug over the sample testing area  18 . The pressure generator then supplies fluid pressure through the inlet  24  to the desired testing pressure for the sample  17 . Fluid fills the fluid holding area  22 , and pressure from the fluid causes the flexible member  16  to exert a compressive force on the periphery of the sample  17 . After the sample has been tested to the desired pressure, a signal is sent to the pressure generator, and the fluid exits the fluid holding area  22  through outlet  26 . The top plug  28  is then moved upwardly away from the sample testing area, and the stage  70  supporting the top plug is moved away from the sample testing area  18  so that the sample  17  can be unloaded. The bottom pad actuator  56  engages to raise the sample out of the sample testing area  18  so that an operator can remove the sample and load another sample. It will be understood that most of the steps described above, with the exception of the operator loading and unloading the sample on and off the bottom pad are preferably automated and controlled by a control system. In preferred embodiments, the apparatus  10  is adapted to load, test, and unload a sample in less than about 30 seconds, and more preferably, in less than about 15 seconds. Samples can be loaded and unloaded by an operator quickly and easily, without having to reach into the sample testing area. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.