Method and apparatus for testing end-closed pipe

Abstract: A mechanical strength-inspecting apparatus for end-closed hollow pipes, e.g. of ceramics, is disclosed. This apparatus includes an air chuck (2) for holding an outer peripheral surface of the pipe (W), and a pressing means (5) coaxially provided with the air chuck. The pressing means has an elastomeric pressing element (8) adapted to contact and conform to the end closure surface (9) of the pipe (W), and press that surface with a predetermined force, measured by a load cell (10).

Description: The present invention relates to an apparatus for inspecting mechanical strength of end portions of end -closed hollow pipes. For example, it may be usable to inspect mechanical strength of bottom portions of bottom-closed hollow pipes made of zirconia and having one end closed off by the same material. Although the above ceramic bottom-closed hollow pipe is used, for example, as a constituent member for cells, no bottom portion strength-inspecting apparatuses have been formerly known, which could accurately inspect strength of the bottom portion of the bottom-closed hollow pipe of this type. Under the circumstances, examination has been made to inspect strength of the bottom portion of the bottom-closed hollow pipe in the state that pressure is applied inside the hollow pipe. However, it is difficult to inspect the strength of the bottom portion, because when high pressure is applied to the interior of the slender bottom-closed hollow pipe, a side wall is first broken. Accordingly, when such slender bottom-closed hollow pipes are used as constituent parts for fuel cells, they are often broken due to lack in strength at their bottom portions to pose a practical problem. The problem addressed herein is to provide apparatus for inspecting mechanical strength of bottom portions of bottom-closed hollow pipes, which enables ready and accurate inspection of the mechanical strength of the bottom portions of e.g. slender bottom-closed hollow pipes. The term "mechanical strength" used in the specification and claims is intended to mean the following. The mechanical strength involves both mechanical strength of a bottom portion and bonding strength between a peripheral wall portion and the bottom portion in the case of a one end-closed pipe. If the bonding strength is smaller than the mechanical strength, the former is measured. On the other hand, if the bonding strength is greater than the mechanical strength, the latter is measured. In Figs. 1A through 1E, specific forms of the bottom-closed hollow pipes are shown by way of example. In these figures, A and B denote a peripheral wall portion and a bottom portion of the bottom-closed hollow pipe, respectively. In Figs. 1A through 1D, the bottom portion is bonded to an end portion of the peripheral wall portion with an appropriate bonding agent. The present invention is applicable not only to the bonded type bottom-closed hollow pipes as shown in Figs. 1A through 1D but also to an integral type as shown in Fig. 1E. In the hollow pipe shown in Fig. 1E, a bottom portion B is not bonded to a peripheral wall portion A, but the former is simultaneously and integrally formed with the formation of the peripheral wall portion, for example, by a casting process. The mechanical strength of the bottom portion B of a bottom-closed hollow pipe as shown in Fig. 1E may also be measured in embodiments of the invention. A first aspect of the present invention is characterized in that apparatus has an air- or other fluid-operated chuck for holding the outer peripheral surface of the bottom-closed hollow pipe sealed at the bottom portion, and a pressing means operable coaxially with the air chuck, wherein the pressing means has a relatively deformable pressing element which is to contact the outer surface of the bottom portion of the bottom-closed hollow pipe from an outer side thereof and to axially press the outer surface of the bottom portion. In a second aspect, testing apparatus is provided with a fluid-operated (particularly, air-operated) chuck for holding the outer peripheral surface of the bottom-closed hollow pipe sealed at the bottom portion, and a pressing means provided coaxially with the air chuck, wherein the pressing means is provided with a pressing rod for passing the interior of the bottom-closed hollow pipe, and reaching and pressing the bottom surface of the hollow pipe through an elastic pressing element attached to the tip of the pressing rod. We have found that by using apparatus with these features, whether adhesion strength of the bottom portion of the bottom-closed slender hollow pipe is acceptable or not can be accurately inspected by applying given forces to the bottom portion of the hollow pipe held by the air chuck by means of the elastic pressing element from the inner surface or the outer surface of the bottom portion in the axial direction of the hollow pipe. Various preferred objects, features and advantages of the invention will be appreciated upon reading of the following description of embodiments when taken in conjunction with the attached drawings, with the understanding that some modifications, variations and changes of the same could be made by the skilled person in the art to which the invention pertains. Reference is made to the attached drawings, wherein: Figs. 1A through 1E are partially sectional views of bottom-closed hollow pipes of which mechanical strength may be measured by the apparatus embodying the invention; Fig. 2 is a partially sectional view of an embodiment according to the first aspect of the present invention; Figs. 3 and 4 are a side view and an enlarged sectional view of a principal portion of Fig. 2, respectively; Fig. 5 is a partially sectional view of another embodiment according to the first aspect of the present invention; and Fig. 6 is a partially sectional view of an embodiment according to the second aspect of the present invention. The present invention will be explained in more detail with reference to the embodiments shown in the attached drawings. In Figs. 2 and 3, a reference numeral 1 is a base, and an air chuck 2 is vertically arranged in a central hole of the base, for supporting the outer peripheral surface of a bottom-closed straight pipe W. The pipe may be of ceramics, e.g. zirconia. The air chuck includes guide members 3, 3 at upper and lower portions, and a ring-shaped elastic member 4 is arranged in the central portion of a frame of the air chuck. After the hollow pipe is passed through a central hole of the elastic member 4, the elastic member is radially inwardly expanded by air pressure to hold the outer peripheral surface of the bottom-closed hollow cylinder W. Thus, the air chuck can assuredly hold the bottom-closed hollow pipe W in that state that the pipe W is well aligned with the air chuck. If the holding forces are insufficient, as shown in Figs. 2 and 3 by imaginary lines, another air chuck 2 may be provided above the air chuck 2, through supporting poles and a base at upper ends of the poles. A reference numeral 5 is a pressing means coaxially arranged under the air chuck 2. In this embodiment, the pressing means 5 includes an air cylinder 6 arranged vertically under the base 1, a pressing rod 7, and an elastic pressing element 8, made of such as hard rubber, attached to the upper tip of the pressing rod 7. That is, rods X and Y are extended downwardly from the base 1, while upper ends of the rods are fixed to the base by bolts. The rods X and Y penetrate bases 1A and 1B under the base 1. The bases 1A and 1B are slidably held through the rods X and Y by means of bolts. The air cylinder 6 is fixed to the under face of the base 1B, and a plunger of the air cylinder 6 is passed through a central hole of the base 1B, and butted or fixed to the under face of a load cell 10 positioned above the base 1B. The lower end of the pressing rod 7 is placed or fixed onto the upper portion of the load cell 10, and the rod 7 passes a central hole provided in the base 1A. A bearing 11 is located on the base 1A. The pressing rod 7 is aligned with the bottom-closed hollow pipe held by the air chuck by means of the upper end of the bearing 11 and the load cell 10. As shown in Fig. 4, the elastic pressing element 8 is adapted to contact and press only a sealed bottom surface 9 of the bottom-closed hollow pipe W from the exterior side. The pressing element 8 has an upper surface curved to conform with the outer profile of the bottom-closed hollow pipe W. By so constructing, local concentration of loads upon the bottom surface 9 can be prevented, and alignment between the bottom-closed hollow pipe and the pressing element can be readily effected. Further, a load cell 10 is interposed between the air cylinder 6 and the pressing rod 7, so that the inspecting means can accurately detect pressing forces at every moment. The bearing 11 vertically movably supports the pressing rod 7, and receives the pressing rod 7 at an upper end only. Thereby, the bearing 11 prevents slanting of the bottom-closed hollow pipe W in cooperation with the load cell. Fig. 5 illustrates a second embodiment in which an elastic pressing element 8 has such a structure that the pressing element 8 is expanded with fluid pressure to be deformed to conform with the configuration of the bottom surface 9 of the bottom-closed hollow pipe W. That is, the elastic pressing element 8 is an elastic rubber member 12 attached to an interior end of a cylindrical guide 7′ made of stainless steel or the like and attached to or extended from the upper end of the pressing rod 7. When fluid pressure such as oil pressure, hydraulic pressure, pneumatic pressure or the like is applied to the cylindrical guide 7′ through the pressing rod 7, the elastic rubber 12 expands so that the elastic pressing element may closely adhere to the bottom surface 9 of the bottom-closed hollow pipe W. In this embodiment, the other constituent parts are the same (the base 1A and the bearing 11 are not shown, although they may be omitted), and therefore explanation thereof is omitted. In order to inspect mechanical strength of the bottom-closed hollow pipe W having the bottom portion sealed by means of the bottom strength-inspecting apparatus embodying the first aspect of the present invention, the bottom-closed hollow pipe W is downwardly inserted through the air chuck 2 in an opened state as shown, and the bottom face 9 is placed on the elastic pressing element 8 of the pressing means 5. At that time, the bottom-closed hollow pipe W is aligned with the pressing element 8 by means of the upper and lower guide portions 3, 3 of the air chuck 2 and the elastic pressing element 8. Then, pneumatic pressure is applied to the air chuck 2, and the outer peripheral surface of the bottom-closed hollow pipe W is firmly chucked. By actuating the air cylinder 6, only the bottom surface 9 of the bottom-closed hollow pipe W is pressed. At that time, the pressing forces can be accurately detected by means of the load cell 10. Bottom-closed hollow pipes, which are not broken at the bottom face 9 under application of given forces, are judged acceptable. On the other hand, if bottom-closed hollow pipes W have weak mechanical strength for some reasons, their bottom faces 9 will be broken. As explained above, according to the first aspect of the inspecting apparatus of the present invention, the mechanical strength of the bottom portion of the bottom-closed hollow pipe W can be readily and accurately inspected. Also, since relatively soft conforming pressing element 8 is used, local concentration of load upon the bottom surface 9 can be prevented, and the mechanical strength can be measured, while breakage of the material itself constituting the bottom-closed hollow pipe W can be avoided. Fig. 6 illustrates an embodiment according to the second aspect of the present invention in which a pressing means 13 is provided above an air chuck 2 arranged in a central hole of a base 1. This pressing means 13 is supported at another base fixed to upper ends of supporting poles to which the base 1 is also fixed. An air cylinder 6 is provided above the pressing means 13 through a load cell. The pressing means 13 is provided with a pressing rod 14 which can reach the inner bottom face 9 of the bottom-closed hollow pipe W. The pressing rod 14 is provided with an elastic pressing element 15 at its tip, and the elastic pressing element 15 pushes the bottom surface of the hollow pipe W from the inside. The construction of the pressing element is the same or similar to that in the first aspect of the present invention. In the embodiment of Fig. 6, hard rubber is used as the elastic pressing element 15, but a material, which is deformed by expansion with fluid pressure, may be used. In order that the mechanical strength of the bottom portion of the bottom-closed hollow pipe W having the bottom sealed may be inspected by means of the bottom strength-inspecting apparatus for the bottom-closed hollow pipe embodying the second aspect of the present invention, the bottom-closed hollow pipe W is first held by the air chuck 2, the pressing rod 14 is inserted into the interior of the hollow pipe, and the elastic pressing element 15 at its lower end is contacted with the bottom surface 9 of the pipe. The pressing rod 14 is lowered by the air cylinder 6 to press the bottom surface 9 of the pipe from the inside. As a result, if the bottom-closed hollow pipe W has low mechanical strength, the bottom face 9 is broken. As in the same with first aspect of the present invention, bottom-closed hollow pipes, which are not broken under application of given forces, are judged acceptable. As mentioned above, by means of the apparatus described, the mechanical strength of the bottom portion of the slender bottom-closed hollow pipe having the bottom portion formed by sealing the end portion can be readily and accurately inspected from the outside or the inside of the pipe by means of the elastic pressing element. Further, by means of the apparatus described, since the elastic pressing element easy to conform with the configuration of the bottom portion of the bottom-closed hollow pipe is used, the mechanical strength can be accurately inspected, while breakage of the material itself due to local concentration of stresses can be avoided. Therefore, the present invention can greatly contribute to the industrial development as the bottom strength-inspecting apparatus for the bottom-closed hollow pipes.

Claims: Apparatus for testing the strength at the end closure (9) of an end-closed pipe (W), comprising an air-operated chuck (2) for gripping the outer surface of a pipe (W) to be tested so as to hold the pipe (W) in a test position, and pressing means (5,13) operable axially relative to the chuck (2), the pressing means (5,13) comprising a relatively deformable element (8,15) for contacting the end surface of the end-closure of a closed end of a pipe (W) so held in the test position and pressing against it with a predetermined force. Apparatus according to claim 1, comprising a load cell (10) for determining the force with which the pressing element (8) presses against the pipe end closure surface. Apparatus according to claim 1 or claim 2 in which the pressing means (5,13) comprise a fluid-operated cylinder (6), a press rod (7,14) connected at one end to the cylinder so as to be movably by actuation thereof, and connected at the other end to the pressing element (8,15) to press it with said predetermined force. Apparatus according to any one of claims 1 to 3 in which the pressing element (8,15) has a three-dimensionally formed face for conforming contact with the end surface of the pipe in use. Apparatus according to any one of the preceding claims in which the deformable pressing element comprises an elastomeric element, to conform on contact with the end surface of the pipe. Apparatus according to any one of the preceding claims in which the pressing element comprises a rubber member (12) attached at the end of a guide cylinder (7½) on a pressing rod (7) of the pressing means (5), and fluid pressure can be applied behind the rubber member (12), through the pressing rod (7), to help achieve conforming contact. Apparatus according to any one of the preceding claims in which the pressing element (15) is adapted to press on the end surface of the pipe from the interior of the pipe. A method of testing the mechanical strength at the end closure (9) of an end-closed pipe (W), comprising gripping the pipe (W) in a chuck (2) defining an axial direction; pressing axially with a predetermined force on the surface of the end closure (9) of the pipe with a relatively deformable pressing element (8,15) which makes substantially conforming contact with the surface of the end closure (9). A method according to claim 8 in which the pipe (W) is a ceramics pipe. A method according to claim 8 or claim 9 in which the pressing element (8) presses on the pipe end closure (9) from outside the pipe (W). A method according to any one of claims 8 to 10 in which the pipe end closure (9) has a curved surface to which the pressing element (8) conforms.

Inventors: TANAKA KOJI, YAMADA SATORU, TANAKA, KOJI, YAMADA, SATORU
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1991
Main classification: G01N3
IPC codes: G01N3, G01N33