| 摘要 |
PURPOSE:To prevent the decrease and flattening of the sectional area in a pipe and to maintain the smoothness on the inside circumferential surface by forming the top part to the arc surface of the same radius as the radius of the arc surface of a sacrificial plate and coupling integrally plural pieces of intermediate core segments from the part near the root toward the arc surface. CONSTITUTION:Plural pieces of the intermediate core segments 2 are positioned to the point where a straight pipe material A is bent and formed to an elbow part B in continuation with the end face in the fitting part of a core 1 in one straight part. The section thereof forms wedge-shaped slopes 2h', 2h' of the width decreasing toward the arc surface 2c with the front and rear faces connected to parallel surfaces 2h, 2h. The angle alpha between both slopes 2h' and 2h' is determined by the magnitude of the bending radius R of the elbow part B. The sacrifitial plate 4 consisting of a low melting material is provided with a fitting groove to accept the fitting pieces of the cores 1, 3 in both straight parts and the fitting pieces of the segments 2.
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