Browsing by Author "Talib, Nayyef Ahmed"

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Application of giesekus model for capillary extrusion of rubber compound
(The Society of Chemical Engineers, 2019-02) Talib, Nayyef Ahmed; Ertunç, Özgür; Mechanical Engineering; ERTUNÇ, Özgür; Talib, Nayyef Ahmed
Extrudate swell is an important phenomenon occurring when high viscoelastic materials, such as rubber and rubber compounds, are extruded. In this work, the effects of relaxation time and relaxation mode on swell predictions using a nonlinear differential viscoelastic model, that is, the Giesekus model, are studied systematically for rubber extrusion in a capillary die. The corresponding 3D, steady-state finite element simulation for predictions of swelling is presented and compared with experimental data for validation. Velocity distribution, pressure drop and circulation flow in the die are analyzed and discussed through the simulation. The results of swell prediction reveal that three-relaxation mode of the Giesekus model with a wide range of relaxation times reproduce experimental data. In addition, the number of relaxation mode and relaxation time have remarkable effects on circulation flow at the die corner and some effect on other field variables.
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Experimental and numerical investigation of rubber whether strip extrusion
(2019-01-03) Talib, Nayyef Ahmed; Ertunç, Özgür; Ertunç, Özgür; Bundur, Zeynep Başaran; Başol, Altuğ Melik; Kırkköprü, K.; Uluer, Onuralp; Department of Mechanical Engineering; Talib, Nayyef Ahmed
Extrusion is the main method used to produce rubber weather strips in automotive industries. The product quality is dependent on many factors, which include the design parameters of the die, the processing variables, and the rheological behaviour of the used material. On the other hand, the flow of the rubber compound is complex due to both the shear thinning behaviour and the high viscoelastic character of this material. Therefore, the inclusion of many factors, which have an influence on product quality during the extrusion process, cause the relationship between the die design and the flow field to be not-intuitive. The current conventional die design employs trial-error process during which the manufactured die is reworked in several trials to guarantee the required product quality. Therefore, converting the running-in experiment into a virtual one by adopting numerical modelling is a powerful method leading to a reduction in waste material and time. In addition, it can also be used for the in-depth analysis of the rheological material variables in combination with the die design parameters to evaluate their effect on product quality. In extrusion process of high reactive material such as rubber, it is important to find less reactive conditions. This because of the time course of heating is very important factor in controlling the peroxide’ degradation or scorching inside the die. Therefore, estimation of the residence time and temperature of the material for a specific die design play an important role for products quality control. In the first part of the investigations, a special extrusion die instrumented with a special sensor was designed in an industrial scale size. Extrusion experiments were conducted in an extrusion line and flow rate, temperature and pressures were measured for extruder speeds. The rheological properties of the filled rubber compound were characterized using a capillary rheometer (Rosand) at different temperatures to evaluate the required material parameters for the numerical simulation. The curing characteristics were investigated using a rubber process analyser (RPA-2000) to construct a curing curve at different temperatures. A three-dimensional model was established for modelling the non-isothermal viscous flow of the ethylene propylene diene monomer (EPDM) rubber melts. A purely inelastic model was assumed through a power law model and a mixed finite element method to solve the complex flow in the extrusion die domain. The pressure-stabilized Petrov–Galerkin (PSPG) method and streamline upwind/Petrov–Galerkin numerical scheme were employed to solve the flow equations and increase numerical stability. The results confirmed that for the EPDM rubber compound, the screw speed exerted a remarkable effect on the temperature rise and pressure drop in the extrusion die. The impact of the viscous dissipation on the thermal behaviour and pressure drop prediction was also discussed. The obtained scorch time was compared with the estimated residence time in the flow domain to elucidate the influence of the extruder speed on the curing characteristic. The results suggested that there is neither premature vulcanisation nor the start of the scorching inside the flow domain within the studied extruder speed range. The velocity uniformity index and streamline were evaluated at the die exit and the entire flow domain, respectively. The analyses of the results obtained confirmed the ability of the proposed die design to produce a defect free product without the risk of the circulation or appearance of a large distortion. The validity of the model prediction was verified by the comparison between the simulation and the experimental results. The second part of the investigations was devoted to studying the swelling phenomenon which occurred during the extrusion of the rubber. Extrudate swell is an important phenomenon occurring when high viscoelastic materials, such as rubber and rubber compounds, are extruded. In this work, the effects of the relaxation time and the relaxation mode on the swell predictions using a nonlinear differential viscoelastic model, that is, the Giesekus model, were studied systematically for the Styrene-Butadiene rubber (SBR) extrusion in the capillary die. The corresponding 3D, steady-state finite element simulation for the predictions of the swelling was presented and compared with the experimental data for the validation. The velocity distribution, pressure drop and circulation flow in the die were analysed and discussed through the simulation. The results of the swell prediction revealed that the three-relaxation mode of the Giesekus model with a wide range of relaxation time reproduced the experimental data. In addition, the number of relaxation mode and range of relaxation time had a remarkable effect on the circulation flow at the die corner and some effect on the other field variables. After the validation of the proposed model, the same model was implemented on the capillary extrusion of the EPDM rubber, which is mainly used in the weather strip in automotive industries. The swelling of the EPDM rubber was compared with the swelling of the SBR. The results obtained showed that the swell ratio of the EPDM was less than the swell ratio of the SBR for all the studied parameters. This finding approved the ability of the invoke purely inelastic model in modelling this kind of material when a viscous effect is predominant. The influence of the die design parameter such as the die length and slippage at die wall on the swell was also discussed and analysed. Finally, viscoelastic simulation based Giesekus viscoelastic model was applied for modelling of extrudate swelling in an industrial scale extrusion die. The predicted extrudate profile was compared with basic profile at die exit. The results obtained show very slight deviation in extrudate profile from basic geometry at die exit which validate the proposed die design to produce the precise extrudate dimension without necessary to make die correction. The three dimensional stress field at die exit were discussed and analysed to evaluate their effect on the evolution of some defects such as melt fracture or surface defects.
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Experimental and numerical study of rubber flow in the extrusion die of a weather strip
(Society of Chemical Engineers, 2019) Talib, Nayyef Ahmed; Ertunç, Özgür; Türkistanli, T.; Aydın, E.; Mechanical Engineering; ERTUNÇ, Özgür; Talib, Nayyef Ahmed
Extrusion is the main method used to produce rubber weather strips in automotive industries, and the quality of the final product largely depends on the thermal properties of the process output. Therefore, precise thermal control of the process is the key to product quality control. This study establishes a three-dimensional model of the nonisothermal viscous flow of ethylene propylene diene monomer (EPDM) rubber melts through a power law rheological model and a mixed finite element method. The rheological properties of the filled rubber compound were characterized using a capillary rheometer (Rosand) at different temperatures to evaluate the required material parameters for numerical simulation. Curing characteristics were investigated using a rubber process analyzer (RPA-2000) to construct a curing curve at different temperatures. The pressure-stabilized Petrov-Galerkin (PSPG) method and streamline upwind/ Petrov-Galerkin numerical scheme were employed to solve the flow equations and increase numerical stability. The power law rheological model was combined with field equations such as continuity, momentum, and energy equations to determine the complex flow behavior in an extrusion die of real geometry. Extrusion experiments were performed in an industrial extrusion line, and temperature and pressure were measured at different extruder speeds by using special sensors mounted on the extrusion die. The results confirmed that for EPDM rubber compound, the extruder speed exerted a remarkable effect on the temperature rise and pressure drop in the extrusion die. The impact of viscous dissipation on the thermal behavior and pressure drop prediction of the rubber compound flow is also discussed. The obtained scorch time was compared with the estimated residence time in the flow domain to elucidate the influence of extruder speed on the processing characteristic. The results suggested the lack of premature vulcanization or the start of scorching inside the flow domain within the studied extruder speed range. The validity of model prediction was verified by comparison between simulation and experimental results. The predicted results of the model showed good agreement with the experimental data.
Open Access
Investigation of corrosion behavior of carbon steel for petroleum pipeline applications under turbulent flow conditions
(Institute of Information Science, 2020) Ahmed, Mohammed Salih; Talib, Nayyef Ahmed; Al-Gebory, Layth Wadhah Ismael; Ahmed, Mohammed Salih; Talib, Nayyef Ahmed; Al-Gebory, Layth Wadhah Ismael
This study investigates the corrosion of steel samples immersed in water with a dynamic corrosion setup at different pH values for three different velocities and three different exposure time. The characteristics of material surface were observed by utilizing Atomic Force Micrographs (AFM). Under the dynamic and static conditions, the rate of corrosion of the steel samples in deionized water (DIW) was calculated through the weight loss measurements. It has been found that the corrosion rate of steel samples under static conditions was higher with the lower pH values. It was observed that the corrosion rate was maximum at pH = 4 and the minimum at pH = 6. The static corrosion tests suggest that the corrosion rate was high in the first two days then decreased with the increasing of time of tests. The effect of wall shear stress and time of immersion was evaluated under the dynamic corrosion tests. The results suggest that increased wall shear stress lead to an increase the corrosion rate specially at pH = 4.