نشریه مهندسی مکانیک مدرس
سال دهم شماره 1 (بهار 1389)

Column flotation cells in terms of air distribution, feed and wash water systems compare to mechanical cells have better metallurgical performance. In this paper, flotation column cell scale-up has been investigated by using lab experimental results and required data for flotation column design was obtained by employing a lab scale column flotation cell with 150 cm high and 74 mm diameter in final zinc concentration cleaning stage. By using Taguchi experimental design method, four operational cell parameters were evaluated. In optimum conditions, a concentrate was produced with zinc grade, recovery and separation efficiency of 52.84%, 69.86% and 32.61% respectively.Also plant flotation mechanical cells performance in final zinc concentration cleaning stage was investigated. Results were shown that, mechanical cell concentrate could produce a concentrate with zinc grade, recovery and separation efficiency of 52.15%, 75.10% and 30.84% respectively. Mechanical cells performance was compared to column cell performance in final zinc concentration cleaning stage. Results were shown that, column cell performance was increased 0.64% zinc grade and 1.77% zinc separation efficiency. Based in obtained results, a column flotation cell was designed with 8 m high and 1.4 m diameter.

Fine-blanking is an effective and economical shearing process which offers a precise and clean cutting edge finish, eliminates unnecessary secondary operations and increases quality. Fine-blanking process utilizes triple-action tools: a punch, a stripper with an indented V-ring and a Counter punch (ejector) to generate a highly compressive stress state. The deformation is more violent and localized than that of any other metal forming operations. Therefore it is difficult to fully understand the mechanism of the process. This study investigates the effect of V-ring indenter, clearance of die, Force of holder and Counter punch, etc on state of stress, quality and accuracy of production. Some parameters have both positive and negative effect on quality of production and the life of the tool. Utilizing V-Ring indenter in Die will increase quality of production and life of the tool. Also Artificial Neural Networks was used to simulate Fine-Blanking process. It has been shown that booth of FEM and ANN is suitable for simulating and forecast of effect of the parameters on production.

Residual unbalance in hand-held power tool rotors transmits undesirable vibrations to the hand of its operator. These vibrations can be effectively suppressed using a one plane automatic dynamic balancer (ADB). This balancing device consists of several balls constrained to move inside a sealed cylindrical ball-race unit partially filled with oil. One of the hand-held power tools is an angle grinder. This study introduces the design of an ADB for eliminating vibration of a grinder based on the achieved design parameters. A physical model of the system is derived for a Jeffcott rotor with an ADB. Utilizing Lagrange's method, the nonlinear equations of motion for an autonomous system in polar coordinate system is derived. Further, the equilibrium position and the linear variational equations are obtained by the perturbation method. Moreover, the dynamic stability of the system in the neighborhood of the equilibrium positions is investigated by the Routh-Hurwitz criteria. The results of the stability analysis provide the design requirements for the ADB to achieve balancing of the system. In addition, time responses are presented by the generalized-alpha method. Employing the modal analysis method the equivalent damping and stiffness coefficients are achieved. Finally, the ADB is designed and manufactured by solving the equations of motion governed on identified unbalanced grinder. To evaluate and identify the performance of the ADB, vibration levels are measured in cases of with balancer, without balancer, and are compared with a typical commercial ADB.

An Active Magnetic Bearing (AMB) system is designed and manufactured, in which a controlled current is applied to the electromagnets of the stator by a PID controller and the generated attraction forces control the gap between rotor and stator. Effect of parameters, such as sampling frequency, excitation pattern, and the gap between rotor and stator on stability of AMB is statistically analyzed, using the experimental results. Furthermore, dynamic behavior of the system, effect of magnetic field and the resultant force, are numerically analyzed. As the system is nonlinear, experimental results are used to study the effects of nonlinearity and to control the system. In numerical analysis, the distribution and flux density of the magnetic field and the applied force on Iron shaft are calculated by Virtual Work and Maxwell Methods. In statistical analysis, the effect of frequency and gap between rotor and stator are used to determine the stable working point of the system.

This study is concerned with a correlation between the microstructure and mechanical properties of 42CrMo4 steel which was subjected quenched-tempered and step-quenching heat treatment. Quench tempering and step quenching heat treatment produced a tempered martensite and an equiaxed Ferrite-Bainite-Martensite (F-B-M) microstructure, respectively. Tensile test results indicated a yield drop effect in F-B-M microstructure with ferritic matrix. This effect was not observed on the specimens with tempered martensite and F-B-M microstructure with hard phase B-M matrix. This effect can be attributed to dislocation generation in ferrite phase during bainitic and martensitic transformations. Fractographic investigations indicated intergranular cleavage in F-B-M microstructure and micro-void coalescence in tempered martensite microstructure can be attributed to carbide formation in martensitic structure during tempering micro-void coalescence in tempered martensite microstructure

Power transition constant velocity joint is widely used in the automotive industry. Inner race is one of the power transition joint parts. Conventional method of production is time-consuming with high cost. The main objective in this paper is to investigate the material flow in precision forging of inner race and to optimize the process using a new tooling concept. In order to define and improve the process conditions, numerical simulation using MSC Super Forge software and physical modeling experiments were performed. To verify simulation results and to investigate material flow, plasticine was used for physical modeling. Results obtained from numerical simulation, are in very good agreement with experimental results

In the presented work, the lagrangian grid-free vortex element method is used for flow simulation in forced shear layer. Growth rate of instability and eddy formation is well simulated. Also, effect of eddy formation, pairing and the interaction among them are studied. In an unforced shear layer the growth rate is linear depending on the biggest instable frequency but in the forced shear layer other frequencies are taken part. The most important frequency is the forced frequency among other frequencies and the instability growth rate is no longer linear. The results show that the instability would accelerate due to increase of velocity ratio. The wavelength effect is well studied on the instability and is in good agreement with the experimental data.

The effect of aluminium content on the precipitation of in rapidly quenched Ni-Al binary alloys was investigated. Microstructural analyses of annealed and quenched samples indicate a transition from uniform to bimodal phase distribution in the composition range between 15.3 and 17.5 at.%Al. This transition is accompanied by changes in the morphology of precipitates. The microstructural observations are discussed in view of both kinetic and crystallographic considerations.