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  Materials Science and Technology   Comparison of thermo-mechanical stresses produced in work rolls during hot and coldrolling of Cartridge Brass 1101 --Manuscript Draft--  Manuscript Number: MST11289R2 Full Title: Comparison of thermo-mechanical stresses produced in work rolls during hot and coldrolling of Cartridge Brass 1101 Article Type: Research Paper  Keywords: Hot Rolling; Numerical Simulation; Thermo-Mechanical Hoop Stress; Shear Stress;Cold Rolling; Compression Testing Corresponding Author: Faisal Qayyum, M.S.University of Engineering and Technology, TaxilaJauharabad, Punjab PAKISTAN Corresponding Author SecondaryInformation:Corresponding Author s Institution: University of Engineering and Technology, Taxila Corresponding Author s SecondaryInstitution:First Author: Faisal Qayyum, M.S. First Author Secondary Information:Order of Authors: Faisal Qayyum, M.S.Masood Shah, PhDS. Manzoor, PhDMohsin Abbas, M.S. Order of Authors Secondary Information:Abstract: Thermo-mechanical stresses play an important role in defining the life of the work rollused in hot rolling process. In this research temperature dependent mechanicalproperties of cartridge brass are determined experimentally using high temperaturecompression tests at different temperatures and strain rates. Real life measurementsare made from a brass rolling mill as input data for the simulation boundary conditions.Hot rolls are made of AISI H11 hot work tool steel. Temperature dependent mechanicalproperties of AISI H11 steel are used. Thermal and mechanical stresses produced inthe work rolls during hot rolling process are predicted using a thermoplastic finiteelement approach in the ABAQUS StandardTM software. Hot rolling is compared withcold rolling to determine the effects produced on the work rolls. A criterion is introducedto compare the severity of stresses produced on the rolling surfaces in case of hotrolling and cold rolling based on the yield stress of the roller material for differenttemperatures. A method for separating thermal and mechanical stresses in thesimulation is also described. Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation    1 Comparison of thermo-mechanical stresses produced in work rolls during hot and cold rolling of Cartridge Brass 1101 Faisal Qayyum*; Masood Shah*; S. Manzoor*; Mohsin Abbas* *Mechanical Engineering Department, University of Engineering and Technology, Taxila, Pakistan Abstract:   Thermo-mechanical stresses play an important role in defining the life of the work roll used in hot rolling process. In this research temperature dependent mechanical properties of cartridge brass are determined experimentally using high temperature compression tests at different temperatures and strain rates. Real life measurements are made from a brass rolling mill as input data for the simulation boundary conditions. Hot rolls are made of AISI H11 hot work tool steel. Temperature dependent mechanical properties of AISI H11 steel are used. Thermal and mechanical stresses produced in the work rolls during hot rolling process are predicted using a thermoplastic finite element approach in the ABAQUS Standard TM  software. Hot rolling is compared with cold rolling to determine the effects produced on the work rolls. A criterion is introduced to compare the severity of stresses produced on the rolling surfaces in case of hot rolling and cold rolling based on the yield stress of the roller material for different temperatures. A method for separating thermal and mechanical stresses in the simulation is also described. Keywords:   Hot Rolling; Numerical Simulation; Thermo-Mechanical Hoop Stress; Shear Stress; Cold Rolling; Compression Testing.  NOTATIONS c r   Work-roll specific heat c  s  Strip specific heat k  r   Work-roll thermal conductivity k   s  Strip thermal conductivity q  Rate of heat of deformation r   Radial direction T   Temperature t   Time  x  Rolling direction  y  Thickness direction θ   Peripheral direction  ρ r   Work-roll density  ρ  s  Strip density σ  Th-Mec   Thermo-mechanical hoop stresses σ   Mec   Pure Mechanical hoop stresses σ  Th   Pure thermal hoop stresses    Percent ratio of hoop stress to yield stress in work rolls    Hoop stress    Yield stress    Yield strength of H11 Tool Steel at 25 o  centigrade Manuscript (NOT PDF FILE AT REVISE STAGE) Click here to download Manuscript (NOT PDF FILE AT REVISE STAGE): Simulation of Hot Rolling of Brass V17.docx    2 m H11  Slope indicating reduction in yield strength of H11 with an increase in temperature. I. INTRODUCTION Materials used in the work roll for hot rolling process undergo severe thermo-mechanical loading during the process cycle. In the past most of the work has been done to determine the formability of the work piece, rather than the effect of thermo-mechanical loading on the rolls. A brief summary of the work already done on the rolling process is discussed. Zone-Ching and Chang-Cheng 1  developed a three-dimensional, control-volume based finite-difference model for predicting the temperature distribution and the thermal expansion in a rotating cylindrical work roll. They took into account all boundary conditions that might be encountered during the actual hot rolling process i.e. heat convection to surrounding air and cooling water, boiling phenomenon of the cooling water and radiation losses, etc. Results obtained from their mathematical model were found close to experimental results. They found out that greatest amount of thermal expansion of the work roll along the radial direction in the middle steady stage of rolling is located at a central position closer to the exit in the contact region. CG Sun, et.al. 2   presented an integrated finite element  –   based model for the prediction of the steady-state thermo-mechanical behavior of the roll-strip system and of roll life in hot strip rolling. The model comprised of basic finite-element models, which are incorporated into an iterative-solution procedure to deal with the interdependence between the thermo-mechanical behavior of the strip and that of the work roll, which arises from roll-strip contact, as well as with the interdependence between the thermal and mechanical  behavior. Results showed that the model was effective for the prediction of the detailed aspects of the effect of the process parameters and, consequently, for the successful exploration of the process conditions that can enhance the roll performance. L. M. Galantucci and L. Tricarico 3  used commercial FEM software ANSYS 5.0 to simulate the hot rolling  process to estimate temperature distribution and stress strain fields in roller and plate during hot rolling process. Main variables and characteristics of rolling process were expressed in  parametric form. The results of simulation were verified using already published data. Martha P. Guerrero, et.al. 4  developed three models (two using the finite-difference method and one integrating the heat flow to the roll) to calculate the transient heat flow into the work rolls, and a fourth model was developed to compute the temperature distribution in the work roll at steady-state condition. It was concluded that each model has its own value, and that all of them should be used when a comprehensive analysis of the rolling conditions is required. Kazutake Komor i 5  developed a numerical model to analyze material deformation and temperature distribution in rolling of round bars. They investigated equivalent strain and temperature distribution in three-roll and two-roll rolling processes, and difference between them was clarified. M. Raudensky, et.al. 6  developed a full scale model to carry out experiments and also numerically simulated the problem to get deeper insight of the problem. They used the system to give general recommendation for cooling of work-rolls during hot rolling. They concluded that cooling increases with increasing number of nozzles, and that distant sprays help cool rolls more efficiently. A. Pérez, et.al. 7   predicted the thermal response of a work roll in a continuous hot strip mill, under typical working conditions. Their mathematical model considered length of the strip, temperature variation along the length of the strip, and temperature variation from the beginning to the end of the process. They superimposed the three different levels of this phenomenon (i) the independent cycle of the    3 roll, (ii) rolling of a strip-rest, and (iii) a whole campaign. They concluded that the surface of rollers reaches steady state condition after 10 cycles, and that whole roller reaches steady state condition when effective time of laminating is greater than 1300s. Cheng Gang Sun 8  gave a finite element (FE)-based analysis of the interfacial thermo-mechanical behavior of the roll and strip in tandem mill during hot rolling. They investigated the validity of the proposed model by comparing with experimental measurements. Then, using that model, they studied the effect of various process parameters on interfacial thermo-mechanical behavior of the roll and strip. C. Fedorciuc, et.al. 9  worked on thermal fatigue crack propagation in work-rolls during hot rolling. They developed 2D implicit FEM models considering complex thermo-mechanical interactions and cooling cycles. From that they investigated how stress state inside the roll contributes in a different manner to energy release at the crack tip, depending on initial crack length. A stress intensity factor (SIF) approach was used to derive the crack growth rate. They found out that with increasing crack length there is increase in mechanical stresses and decrease in thermal stresses at crack tip. L. Khalili 10  developed a mathematical model to assess thermo-mechanical behavior of work rolls during hot rolling processes. He worked on AA2024. Thermal and mechanical responses at steady-state conditions were investigated during the study using roll pressure and temperature field as governing boundary conditions. They concluded that both thermal and mechanical aspects are important in thermo-mechanical stresses developed within the work rolls, and that cooling design of rolls can significantly alter both the magnitude and the distribution of thermo-mechanical stresses. Ignoring heat conduction along roll axis i.e. z-direction, the basic heat transfer equation in cylindrical coordinates for a work roll can be written as Eq. 1 11    (    )    (  )     Eq. 1 It should be noted that there is a strong thermal relationship between work-roll and strip, therefore it is necessary to calculate the temperature distribution of the strip at the same time 12 . The governing heat conduction equation can be employed as Eq. 2.  (  )  (  )    ` Eq. 2 Materials used in the work roll for hot rolling process undergo severe thermo-mechanical loading during the process cycle. This imposes restrictions on the amount of deformation that can be achieved in each pass. In this work coupled thermo-mechanical FE model is used. Right boundary conditions,  process parameters and temperature dependent material data is needed to accurately simulate this problem. Temperature and strain dependent mechanical data for brass was measured in this study. The boundary conditions and other parameters were determined from the actual  process of 2 high brass rolling mill. Analysis has been carried out for the first pass and the final pass. It is believed that the thermal stresses are highest in the first pass when the billet is hottest and the bite angle is maximum. In the last pass it is believed that the thermal stresses would be lower due to cooling of billet, however mechanical stresses might show higher values due to hardening of billet material. For comparison purposes the analysis is also carried out for cold rolling in the first pass as well as for the last pass, where highest rolling stresses are expected. The model has been used to determine the hoop and shear stresses  produced in the work- rolls during hot and cold rolling. The sequence of these stresses is

Jurnal THT

Jul 23, 2017
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