Collapse Strength Formula for Commercial Casing under Work-Hardening due to Excessive Tensile Load

December 6,1995

Toshitaro MIMAKI, Susumu MIZUNUMA, Toshitaka TAMANO and Samon YANAGIMOTO

In a steam injection well, for example, which is a promising method for enhanced oil recovery, the well casing is subjected to excessive tensile load during the production. The collapse strength of commercial casings under extremely high axial stress close to the yield strength of the casing material has rarely been evaluated. We conducted collapse tests under excessive axial stress, which caused work-hardening of the material, and established an empirical formula by regression analysis for estimating the yield strength after work-hardening at which collapse takes place. It was found that work-hardening has a great influence on the collapse strength and that the collapse strength under work-hardening due to excessive tensile load can be estimated accurately using the proposed empirical formula, since collapse strengths thus calculated agree well with those determined exper i mental I y .

Keywords:experimental analysis external pressure, axial load, , deformation-load property, collapse strength, combined loading, work-hardening effect

Fracture during Hot Working and Improvement of Workability in Pb-Added a Brass

December 7,1995

Ryuuta ONODERA, Masanao HAMASAKI, Tatsuo YOKOTE Masatoshi ARAMAKI and Kenji HIGASHIDA

It is well known that (x brass, especially in the case that Pb Is added to improve machinability, tends to undergo edge cracking during hot working. In this work, the fracture mechanism of Pb-added (x brass specimen~ has been studied in a hot compression test (700'C, strain rate>0.1/s), in relation to the effect of grain size. Although it was impossible to compress coarse-grained specimens by 50% in height without macroscopic fracture, fine-grained specimens could be compressed by 70%. Microscopic observation showed that the surface fracture (edge cracking) is attributable to the grain boundary sliding of surface grains. These results suggest that the hot workability of the brass may be improved if the grain boundary sliding can be restrained by surface coating. Based on this idea, coarse-grained specimens were plated with zinc and held for 10 minutes at 700"C to form a P phase layer 200-300 µm thick on the surface, and then compressed. These specimens could be compressed by 80% without cracking, which shows that this method based on the above-mentioned idea is reasonable.

Keywords:forging, nonferrous metal (Cu-Zn), forming limit, Pb addition, hot working, surface fracture, grain boundary sliding, Zn plating, P phase.

Cold Continuous Rolling Behaviour of Small Steel Tubes

December 13,1995

Kazuo WATANABE and Ichiro MASUDA

The cold continuous rolling of small steel tubes to achieve larger elongation in using fewer stands is discussed. Oval-oval passes are better than oval-round passes in terms of rolling stability and accuracy of external profile. Using the former passes utilizing 6 stands, rolling with total reduction of 50 % in outer diameter is possible without causing external defects. Tension caused intentional ly by roll speed imbalance of each stand can decrease the wall thickness and polygonization, although the effect is smaller than that of hot continuous rolling. These characteristics can be explained using the conventional stretch reducer theory with the friction coefficient between rolls and tube ƒÊ = O. 1.

Keywords:tube rolling,cold rolling, tube, stretch reducer,wall thickness, tension, continuous rolling

Simulation of Strip Crown Generation by Considering Deformation in Front of Roll Bite Analysis of Strip Crown by Rigid-Plastic FEM in Cold Rolling I

December 28,1995

Hideaki FURUMOTO, Kazuo MORIMOTO, Kanji HAYASIII and Kozo OSAKADA

A method for analyzing edge thinning of sheet metal (strip crown) in cold rolling based on the finite-element method is proposed. Because the phenomenon is sensitively related to the distribution of rolling force near the edges, an appropriate model that provides a realistic rolling force distribution is necessary. The region of elastic deformation in front of the roll bite is modeled using the elastic finite-element method and is connected with the plastically deformed region modeled using the rigid-plastic finite element method. It is found that the existence of the elastic region has little effect on the rolling force distribution, but the small plastic deformation in front of the roll bite has a significant effect. Since the longitudinal length of the plastic region in the model is found to be the critical factor for representing the actual rolling force distribution, a method for determining the length in terms of the distribution of equivalent strain rate is proposed. The analytical results for the strip crown agree well with the experimental ones.

Keywords:rolling, numerical analysis, FEM, strip crown

Damage Behavior of Hard Coatings under Reciprocating Impact

January 29, 1996

Yoshinari TSUCHIYA, Tohru ARAI and Susumu SIIIMA

Damage of some hard coatings under reciprocating impact is investigated in order to evaluate the adhesive properties of coatings. Change in shape of indentations caused by impacts and the number of impacts necessary for the occurrence of damage are compared among specimens. Observed modes of damage are obtained as follows: VC coating; generation of surface crack - partial deformation - wear, Cr plating; simultaneous occurrence of crack, partial deformation and wear, TiN coating by ion plating; flattening ~ partial deformation - flaking. The indentation caused by reciprocating impact is larger in diameter and smaller In depth than that estimated by the theory. The deviation differs from one coating to another; it is largest for VC coating. VC coating requires the largest number of impacts for film damage, and TiN coating the smallest. This order corresponds to the adhesive or cohesive properties of the coating. Depth of indentation is affected by the hardness of the base metal, but is independent of the kind of coating and film thickness.

Keywords:material testing, reciprocating impact test, Iife test, material property, hard thin coatings, wear, flaking, surface damage, adhesive property, metal forming die.

Vibration Analysis of Press in Blanking

January 29, 1996

Bin GUO, Hiroshi OGIHARA and Kazuhiko NAKAMURA

In this paper, we discuss the vibration of presses, which is the origin of the noise generated in blanking. The elastic deformations, rigidities and damping ratios of the press components, the clearances between the connected parts of each component and friction between the connected parts were considered in the vibration model used in this analysis. The blanking process was represented by a load-stroke curve approximated by five straight lines. The analytical results revealed the relationship between the vibration of each component and the load-stroke curve, and it was also clarified that the occurrence of break-through greatly affects the vibration. Regarding the structural parameters of the press, the rigidity greatly affects the vibration amplitude, and the damping ratio and the clearance between connected parts affect the time required to control the vibration. The results also indicated that if the rigidity of, the press is greater than the unloading gradient at break-through, then the vibration can be effectively controlled.

Keywords:press machine, blanking, vibration, numerical analysis, break-through.

Continuous Extrusion=Drawing of Steel Wire with Rotating Wheel

February 9, 1996

Takeshi MIKI, Michiaki TATEYAMA, Samon YANAGIMOTO and Yoshitaka KAWAKAMI

Reduction of cross-sectional area by wire drawing is limited to within 40%. The CONFORM process is based on continuous extrusion and is applied to high reduction working of soft metals. In this process, dead metal accumulates vithin the die. Therefore, if this method is applied to high-strength steel wire, the die cannot tolerate the high temperature due to the heat released by working. A new process which combines extrusion and drawing is proposed. The extrusion limit is at the buckl ing point of the wire, and the drawing Iimit is at its breaking point. It is necessary that the drawing and extrusion are controlled simultaneously. The extrusion force is caused by the frictional forÏ between the rotating wheel and the wire. The necessary coefficient of friction is about O. 3 under a nominal pressure of 20 MPa. This method can be used to achieve a high reduction in cross-sectional area of up to 70 % without the formation of dead metal. The combination of drawing force and extrusion force agrees with the result according to the upper bound method presented by B. Avitzur.

Keywords:drawing, conform extrusion, upper bound method, high strength wire, drawing machine.

Evaluation of Performance of Cold Forging Oils Using Backward Can Extrusion Test

February 13, 1996

Kazuhiko KITAMURA, Toshihide OHMORI, Atsushi DANNO and Masuhiko KAWAMURA

A Iaboratory-made oil containing phosphorus type E.P. additives and typical commercial oils for cold forging of low carbon steel are evaluated using a backward can extrusion test under a 50 % reduction in cross-sectional area. The punch nose radii rp were I and 4 mm for a punch diameter of 21.2 mm. The lubricity of oils was clearly evaluated in terms of the maximum cup depth maxDP without galling, and the punch pulling force. The use of flat top end billet and 4 mm rp Punch proved to represent severe conditions for oils. maxDP of the laboratory-made oil was the greatest for all tested oils, but was only half the value obtained using the soap-phosphate coating. When billets with a conical recess in the top were used for trapping lubricant, the laboratory-made oil and one commercial forging oil showed high performance almost equivalent to that of the soap-phosphate coating for rp = I and 4 mm. A Iarge amount of effective reaction film for lubrication was detected on the extruded can surface. Thus a combination of the laboratory-made oil and the lubricant trapping method was found to be effective under the severe frictional conditions in backward can extrusion.

Keywords:tribology, Iubrication, Iubricants, cold forging, backward extrusion

A Calculation of Stress and Strain Distribution by Grid Method Containing Appreciable Measurement Error

February 21, 1996

Yukio KOJIMA, Masakazu NOGUCHI aud Tuyoshi NARITA

The region bounded by grid lines is assumed to be a 4-node isoparametric element. Nodal velocities calculated from the coordinates are smoothed in order to satisfy the incompressibility condition and the boundary condition. The smoothed velocity constitutes a kinematically admissible field, and is used to calculate the strain rate. The hydrostatic stress distribution is determined so that the equilibrium of the nodal force is satisfied approximately, The contact pressure and the frictional stress are calculated based on the nodal force at the tool-material interface. The method is applied to plane strain compression and plane strain forward extrusion of a Plasticine block. Although the measured coordinates showed appreciable error, the distributions of strain rate, hydrostatic stress and contact pressure were reasonable. The validity of the method was confirmed.

Keywords:material testing, measurement, experimental analysis, grid method, visioplasticity, Plasticine, plane strain compression, forward extrusion.

Manufacture of Large-Diameter Precision Aluminum Alloy Thin Tubes by the ED Method

March 1, 1996

Masahiko JIN, Nobuhiro KOGA, Masao MURAKAWA and Tai KUMAGAI

We aim to manufacture precision plain aluminum thin tubes, for use as photosensitive drums by only the ED process without the conventionally required turning finishing process. Although this ED method has proved to be the most efficient one for obtaining tubes with small tube diameters, it presents difficulties in obtaining large diameter tubes with the required precision, particularly of such parameters as surface finish over the outer portions and cylindricity. To overcome such problems we first modified the drawing bench, and determined the most suitable lubricant so as to provide optimal drawing lubrication conditions to obtain low surface roughness. Next we used a radially ultrasonic-vibrated plug and/or a DLC-coated plug during drawing of the extruded pipe in order to reduce internal scratching thereby improving the cylindricity of the drawn tubes. Thus, we obtained precision plain aluminum thin tubes which satisfied the relevant precision standards.

Keywords:Drawing, Tube drawing, ED method, Photosensitive drum, Radially ultrasonic-vibrated plug, DLC- coated plug .

Effect of Additives on Extrusion Characteristics of Powder-Binder Compounds

March 22, 1996

Zhongchun CIIEN, Keisuke IKEDA and Tadasu MURAKAMI

The effects of additives on the extrusion load, the appearance of extrudates and the flow behavior of Zr02 and stainless steel (SUS304L) powders containing a water-soluble binder, HPMC (hydroxypropyl methylcellulose). are investigated. With the addition of additives. the extrusion loads are reduced and the serration in the load vs. stroke curves is greatly weakened, depending on the type and content of the additives as well as the properties of the powders. If a plasticizer such as glycerol is added, the binder content necessary to obtain sound extrudates is reduced, When the lubricants used in this experiment are added to powder-binder compounds, no sound extrudates can necessarily be obtained although the extrusion loads are reduced. It is shown that the distortion near the die exit is decreased and the range of the dead zone is narrow when glycerol and/or stearic acid are used as additives. In addition, the extrusion loads increase with increasing length of the die land (/d) if /d is more than 10mm. However, the rate of extrusion load increase is reduced by the addition of glycerol.

Keywords: extrusion, forming, Zr02, stainless steel, powder, binder, additive, rheology.