A corrugated metal plate is frequently used as a heat insulation cover (also referred to as a heat insulator, including one having a vibration-damping function and/or sound absorption function) that is arranged close to an exhaust manifold or exhaust pipe (muffler) as an automobile's heat generating section. A typical corrugated metal plate is proposed in Patent Publication 1.
The corrugated metal plate disclosed in Patent Publication 1 is one which is prepared by using a thin metal plate of aluminum or the like as a flat plate material and in which both of cross-sectional shapes respectively along two directions, that is, one particular direction (X-direction) and a direction (Y-direction) perpendicular thereto are formed into a wave shape by a repetition of an alternate arrangement of a projection portion and a recess portion.
One described in Patent Publication 1 has one characteristic that is high in elastic property by having in a particular cross-section a so-called bag-shape recess portions 23 (see FIG. 5 of Patent Publication 1) in which a bottom side of an inner portion has a width wider than that of an open side (mouth side).
As to the recess portion in which a bottom side of an inner portion has a width wider than that of an open side (mouth side) in a particular cross-section, from the viewpoint of press working property, it is nothing else but a condition in which the shape of the recess portion turns into a hooking relation by an undercut or inverse relation relative to a direction of withdrawal of a press tool (mold) that makes the recess portions.
In the corrugated metal plate described in Patent Publication 1, however, the wave shape by a roughness repetition to include the recess portions has a special shape. Therefore, it is necessary to conduct the press operation or bending operation several times by using a special pressing facility. Thus, it is forced to have an increased cost by an increase of the number of working operations. In addition, there exists a part where a bending operation has been conducted such that the plate members are locally overlapped in connection with an inverse shape of the recess portion. Therefore, in this part, stress concentration tends to occur, for example, in the case of receiving the vibration force repeatedly.
Furthermore, in the corrugated metal plate described in Patent Publication 1, since both of the cross-sectional shapes in the two directions are corrugated, it is possible to expect the surface rigidity improvement effect. However, the difference of rigidity against bending between X-direction and Y-direction tends to result in a significant strength difference. Furthermore, the shape is significantly different between the front side and the back side. Therefore, for example, in the case of forming into a predetermined three-dimensional shape as a heat insulation cover that is a product, the corrugated metal plate turns into a shape having directional property including a front-and-back relation. As a result, the corrugated metal plate is not superior in usability.
Furthermore, in case that, for example, the corrugated metal plate described in Patent Publication 1 is used as a base plate and then this is formed into a predetermined three-dimensional shape (product shape), for example, as a heat insulation cover that is arranged close to an exhaust manifold that is an automobile's heat generating section, by conducting a bending operation to have a pan shape (shallow pan shape or deep pan shape) or cup shape, the recess portion, in which bottom side of an inner portion has a width wider than that of an open side (mouth side) as mentioned above, may unexpectedly function as a liquid pool.