A study of the mechanism of crack initiation on a mandrel bar for mandrel mill rolling in a seamless tube

Abstract

An investigation was carried out on the mechanism of crack initiation on a mandrel bar used for the mandrel mill operation in seamless tube manufacturing. Close observations of the mandrel bar surface suggested that crack initiation may be induced by a thermal shock. In order to check the validity of this hypothesis, laboratory tests mainly based on cyclic temperature treatment were then carried out in a laboratory and a method was proposed to improve the mandrel bar life. After the estimation of the temperature on the mandrel bar surface both by numerical analysis during rolling and stripping and by an experimental approach during the stripping operation, an acceleration test using a corrugated mandrel bar was carried out on the mandrel mill to verify the validity of the proposed method (to improve the mandrel bar life).

A study of the reinforcement technology used to improve the life of mandrel bars used in seamless tube manufacturing by mandrel mill rolling

“…In previous papers [5,6] the present authors have studied crack initiation on a mandrel bar and been able to show that the major cause of the initiation of microcracks on a mandrel bar is a sharp increase in the surface temperature followed by a sharp cooling. The authors' conclusion was that both maintaining good lubrication and eliminating unusual rolling may suppress crack initiation.…”

“…There are numerous research studies on the rolling load and relevant matters [1][2][3], but very few investigations have been carried out on the influence of contact pressure on the damage to the tools [4]. In previous papers [5,6] the present authors have studied crack initiation on a mandrel bar and been able to show that the major cause of the initiation of microcracks on a mandrel bar is a sharp increase in the surface temperature followed by a sharp cooling. The authors' conclusion was that both maintaining good lubrication and eliminating unusual rolling may suppress crack initiation.…”

Hot Tube-Forming

“…Up to now, great efforts have been conducted to provide insights into the skew-roll piercing process via experimental, analytical, and numerical methods (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23). Pater et al (11) presented a 3D thermomechanical modeling and simulation of the whole piercing process of thick-walled tubes in two rolls skew rolling mill.…”

“…Komori (18) numerically obtained the effects of the piercing rolling conditions (the feed angle, the minimum roll gap, the maximum plug diameter, the plug advance, and the guide shoe diameter) on various rolling properties such as the outer diameter, the inner diameter, the roll force, the mandrel force, the equivalent strain distribution, and the equivalent strain rate distribution. Akiyama et al (19) carried out the study on the mechanism of crack initiation on a mandrel bar used for mandrel mill operation in seamless tube manufacturing, and they thought that the crack initiation might be induced by a thermal shock by both laboratory tests and numerical analysis.…”

Thermomechanical analysis of a piercing mandrel for the production of seamless steel tubes

“…In reference [2] the effects of abnormal formation of ferrite on austenite grains during the rolling of hot tubes are analysed. In references [3] and [4] the beginning of fracture on the mandrel tip during the manufacture of seamless tubes is studied. Here, laboratory tests and a numerical analysis suggest that fracture is induced by thermal shock.…”