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1

Role of filling material on defects of thin-walled tube bending process

Sedighi M., Kahnamouei J. T.

Journal of Theoretical and Applied Mechanics

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2014

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Vol. 52 nr 1

227--233

EN

This paper investigates approaches to avoid common defects such as the wrinkling, cross section distortion and changing in wall thickness in the bending process of a thin-walled tube. A series of experimental tests has been carried out by filling the tube with melted lead and different types of rubbers. Firstly, tubes were filled by several kinds of rubbers and bended, but the wrinkling was observed at the inner side of the tubes. Also the cross section distortions happened to be above the acceptable range. Therefore, rubbers could not be a suitable filling material for steel tubes. As the second case, lead was used as the filling material to avoid the defects. For this purpose, the tubes were filled by liquid lead and it was solidified to form a leady core to support the inner part of the tube bend. After the bending process, lead is melted and removed. This removable leady core was called the ‘Leady Lost Core’. To study the process numerically, a 3D finite element model of the horizontal bending process has been built using a commercial code. Experimental tests have been carried out to verify the simulation results and developed to provide additional insight. To consider the friction coefficient, in this work, “The Barrel Compression Test” method has been used. Comparisons between the experimental and finite element results have shown remarkable agreement. They show that wrinkle initiation and cross section distortion can be avoided with a lost core of low temperature melting metal like lead or tin.

2

Numerical and experimental study on aluminium pipe bending process

Domanowski P., Nowak B.

Journal of Polish CIMAC

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2011

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Vol. 6, no 3

33-42

EN

In this paper the analysis of cold working bending process of the aluminum pipe was presented based on both numerical simulations and experimental tests. The parameters such as wall thickness above and below bending axis were compared and discussed for both numerical simulations and experimental tests. The numerical simulations were performed in Abaqus 6.9/CAE computational environment on the basis of finite element method while the bending machine was designed and constructed for the purpose of tests. The usefulness of numerical simulations was also discussed.

3

Analiza przyczyn pękania rur ze stali X20CrMoV121 w procesie gięcia

Niewielski G., Lalik S., Szala J.

Hutnik, Wiadomości Hutnicze

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2004

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Vol. 71, nr 4

182-187

PL

W pracy przedstawiono wyniki badań pękniętych rur z wysokostopowej martenzytycznej stali X20CrMoV121 (wg DIN 17175) stosowanej między innymi do produkcji rur na przegrzewacze pary w urządzeniach energetycznych. Stosowanie obróbki cieplnej (normalizowania) z temperatury końca walcowania oraz błedy technologiczne, mogące powstać w trakcie procesu wytwarzania rur, prowadzą czasami do ich pękania w trakcie kształtowania. Stwierdzono, że zasadniczą przyczyną pękania rur w procesie gięcia na zimno jest obecność wad pochodzenia metalurgicznego oraz częściowe podhartowanie powierzchni wewnętrznej rury w procesie normalizowania. Podhartowanie to spowodowane zostało wzbogaceniem stali w procesie ciągnienia w węgiel pochodzący ze smarów zawierających grafit. Wytwarzanie w wysokich temperaturach austenityzowania doprowadziło do dyfuzji węgla w głąb materiału od powierzchni wewnętrznej rur.

EN

In the work are presented test results of cracked pipes of the highly alloyed martensitic X20CrMoV21 steel (to DIN 17175) used, among others for production of pipes for steam superheaters in power industry equipment. Application of heat treatment (normalizing) from the final rolling temperature as well as engineering errors liable to occur during manufacturing process of pipes are sometime causing their cracking during plastic forming operations. It was discovered that the main cause of pipe cracking in cold bending process is the presence of defects having metallurgical origin as well as local prehardening of internal pipe surface during the normalizing process. This prehardening was caused by carbon enrichment of steel during drawing process from lubricants containing graphite. Holding in high austenitizing temperatures caused a diffusion of carbon deep into material from the pipe internal surface.

4

Amodel of deformation geometry in pipe bending processes

Śloderbach Z.

Engineering Transactions

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1999

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Vol. 47, iss. 1

3-20

EN

The paper presents a complete set of geometric relationship for logarithmic measures of longitudinal, circumferential and radial strains arising in bending of thin- and thick-walled pipes. The strain can be determined at each plane parallel to the principal plane of bending and at each plane perpendicular to them, so that each point of the bending zone is accounted for. The relationships have a direct reference to engineering practice since they express strains as functions of pipe geometry and bending process variables. The calculation results were compared with experimental data for the bend angle equal to 18O and the bending zone range index equal to 1 and 3. Suitable plots are incorporated.