Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY

(Vol.38 No.434 March 1997)

Effects of Rolling Conditions on Edge-drop of Cold Rolled Strips

―Development of Technology for Reducing Edge-drop of Cold Rolled Strips by Pair-cross Mill Ⅳ―

Tetsuo KAJIHARA, Shoichi HASHIMOTO, Yutaka MATSUDA, Atsushi TOMIZAWA, Ryuji HAMADA and Shunji KAMADA

(Received on February 29, 1996)

Effects of several rolling conditions on the thickness deviation of cold-rolled strips, the printing ratio of the roll crown to the strip crown and the crown transfer coefficient in cold rolling have been investigated using the 3-dimensional slab method. Strip thickness has an important effect on these characteristics, and normalized thickness deviation, which is defined as the inverse of rolling force per unit width, and the region in which edge drop occurs become large with increasing strip thickness. These findings indicate that Pair cross mill should be arranged in up-stream stands of tandem cold mills to reduce the edge drop of strips. The thickness deviation of strips predicted using the roll crown printing ratio and the crown transfer coefficient agrees with the one measured using the new commercial tandem cold mills, where Pair cross mills are introduced from the first to three stands.
Key words : cold strip rolling, edge drop, roll crown printing ratio, crown transfer coefficient, Pair cross mill.

Contraction Tube Using CNC Prototype Spinning Machine

XueJun CAI, Makoto MURATA and Keniji KAMIMURA

(Received on April 2, 1996)

The CNC spinning machine has been developed to produce flexible cross-sections for tubular parts and has been actually used to manufacture many kinds of parts. However extensive research has not been carried out and experimental analysis has not been conducted. The effects of working conditions such as working pitches and speeds on the working force, ratio of contraction and working accuracy are experimentally examined. The characteristics of the prototype CNC spinning machine developed by the authors were clarified in the report.
Key words : CNC machine, tube contraction, spinning, flexible cross section of tube.

Shock Line Formation in Drawing and Redrawing and its Relation with Steel Properties

Keiichi SHIMIZU, Fumio KUNISHIGE and Tomoyuki WADA

(Received on April 25, 1996)

During drawing and redrawing with a small shoulder radius, the surface contacting the die shoulder contains a shock line due to shock bending at the beginning of drawing and redrawing. The amount of thickness reduction at the shock line is calculated based on the difference between static and dynamic friction. The effects of steel properties (carbon contents, carbon in solution, secondary cold rolling ratio, texture and rolling direction) on the formation of a shock line are studied through the proposed simulating test. It is estimated that high cold reduction ration, high carbon content, and low value of (222) / (200) ratio make for the formation of shock line.
Key words : redrawing, shock line, formability test, material property, cold rolling

Prevention of Crossbow in Electrogalvanizing line

Toshiro FUJIWARA, Tetsu MATOBA, Matsuo ATAKA, Itaru AOKI and Takashi JIMMA

(Received on May 17, 1996)

In the electrogalvanizing line of a steel strip, the phenomenon of crossbow leads to variations in coating weight. The relationship between crossbow and the properties of the rubber pressure roll which is used to press the strip to the conductor roll was studied, experimentally and theoretically. In a horizontal cell type line, the strip has only slight contact with the metal conductor rolls. However, in this area of contact, the strip is subjected to longitudinal bending and unbending deformation, resulting in crossbow or gutter. Consequently, crossbow can be prevented by reducing the bending strain to within the range of elastic strain, for example, by ( I )keeping the strip curvature less than that of the yield curvature or by (2)keeping the bending moment to which the strip is subjected less than the yield bending moment. Our studies were primarily directed toward (2), i.e., bending moment reduction. Because the bending moment is the product of the pressing force and the length of the contact arc, controlling it is considered to be effective for reducing deformation of the rubber roll.
Key words : straightening, flatness, crossbow, electrogalvanizing, rubber roll bending.

Intrinsic Criterion of Diffuse Necking

Hitoshi MORITOKI and Eiki OKUYAMA

(Received on May 23, 1996)

Diffuse necking is defined as the plastic instability that results from the simultaneous stationarity of loads. It is termed stationarity when loads remain unaffected by strain increments. However, in practice, stationarity cannot be realized at the critical deformation obtained from this condition except at specific loading paths. It is found that the inconsistency between the assumption of simultaneous stationarity and its unreality can be attributed to the particular characteristics associated with the rate type constitutive equation. Therefore, the condition of stationarity must be replaced with a concept consistent with the critical state, which represents no difference between load rates in the respective multiple solutions. However, detailed examination reveals that these load rates must be zero when the solution becomes multiple, that is, simultaneous stationarity is realized. Consequently, the fact that not the stress or the strain but the load or the displacement is applied to the specimen must be taken into account in considering sheet formability, where the stress or the strain cannot be specified without using the constitutive relation. When the load varying according to the loading path is increased beyond the critical strength of the deforming element of the specimen, it stops increasing, even if the external load is increased further. At that point, the simultaneous stationarity of the loads can be realized, which satisfies the intrinsic criterion of diffuse necking. It is proven that the critical deformation characterized by this intrinsic criterion has a multiple strain rate which is represented in an indefinite form. Finally, critical deformation for a three-dimensional problem is discussed.
Key words : plastic instability, diffuse necking, multi-solutions.

Effect of Bending Condition on the Pipe Bending Method Using a Floating Expanding Plug

Masao NAKAMURA, Seijiro MAKI, Yasunon HARADA and Kiyotaka HAYASHI

(Received on May 31, 1996)

The Influences of operational variables such as expansion ratio, bending roll position, lubrication, material property and wall thickness upon thrust, bending moment, limit bending radius, wall thickness difference and flattening are investigated in order to determine the optimum conditions of pipe bending using a floating expanding plug. (1) An increase of the expansion ratio increases the thrust but decreases the bending moment, wall thickness difference and flattening. (2) The bending roll closest to the plug decreases the bending moment and wall thickness difference, but increases flattening. (3) Good lubrication provides a small wall thickness difference, thrust and bending radius. (4) A small wall thickness difference and bending radius are obtained for work-hardened pipes. (5) Better shape is obtained for thinner walled pipes.
Key words : tube forming, bending, expanding, new forming process, forming property