Papers by Keyword: Remanence

Abstract: NdFeB magnets were first developed in 1984 and are the most powerful permanent magnets that may possess energy products up to 60 MGOe. However, their working temperature and corrosion resistance are lower as compared to that of Alnico and SmCo magnets. Demand of NdFeB magnets recently has increased due to rapid growth of electrical vehicles. In this research work, NdFeB magnets developed through powder metallurgical technique are investigated for thermal effect on magnetic characteristics. The effect of increase in temperature on remanence, coercivity and energy product were measured using pulsed field magnetizer. Samples for testing were prepared from sintered bricks using wire cut machine. Demagnetization curves for the samples were measured at temperatures in the range of 20-110°C, and the results were analyzed. Decline in magnetic characteristics with temperatures is noted. Performance of the magnets with increase in temperature is essential to be analyzed specially for their use in high-speed motors.

Abstract: Permanent Magnets made in the form of hybrid bonded BaFe₁₂O₁₉ / NdFeB and with binder of Poli Vynil Alcohol (PVA) as much as 3% of the total mass in each sample. The weight ratio hybride system BaFe₁₂O₁₉ : NdFeB is 0 % BaFe₁₂O₁₉ : 100 % NdFeB ; 50% BaFe₁₂O₁₉ : 50 % NdFeB and 70% BaFe₁₂O₁₉ : 30 % NdFeB. The material preparation process was begun from mixing of raw materials using HEM for 15 minutes, then added 3% wt. of PVA. The mixed powder was formed a pellet using a hydraulic press with a force of 4 tons for 1 minute, then heated with an vacuum oven at a temperature of 110 ° C for 1 hour and the last step was magnetization using impulse magnetizer. The characterization of pellet sample was done namely measurement of bulk density, flux magnetic and hysteresis loop using VSM and then measurement of corrosion resistance of hybride bonded magnet. The characterization results show that bulk density value of sample hybride 50% BaFe₁₂O₁₉ – 50 % NdFeB is more larger than sample hybride 70% BaFe₁₂O₁₉ – 30 % NdFeB , and The highest coercivity and remanence values ​​of 3900 Oe and 2500 Gauss respectively were achieved in samples with a composition of 50% Ba-ferrite - 50% NdFeB. The hybride bonded magnet Ba-ferrite/NdFeB has more corrosion resistance than bonded magnet 100 % NdFeB.

Abstract: A bonded permanent magnet of Barium hexa Ferrite has been made using powder BaFe₁₂O₁₉ (commercial ferrite) and a polymer of bakelite powder as binder. The composition of bakelite was varried 5% wt. The preparation of sample was begun with mass weighing for each material, then mixed together using ball mill for 1, 6 and 12 hours and using aquades as milling media. The mixed powder is dried in an oven at 110 °C for 4 hours, then the particle size distribution was measured. After that, the dried sample powder was pressed to form a pellet at pressure 40 MPa and temperature about 160 °C for 20 minutes. The characterization of sample pellet was done such as measurement of bulk density, hardness , magnetic properties using VSM and anylisis of microstructure using SEM. The results of the characterization show that the density and magnetic properties tend to increase with increasing of milling time, where the highest density, hardness and highest magnetic properties are achieved at sample with milling time for 12 hours. The value of magnetic properties at this condition are flux magnetic of 530 Gauss, remenance of 3100 Gauss, coercivity of 1,10 kOe.

Abstract: Aiming at the evaluation of creep damage at elevated temperature of ferromagnetic materials in engineering application, the hysteresis loop measurement technology was adopted to study the creep damage behaviour of 1Cr5Mo steel. The creep testing at 600°C/90MPa of 1Cr5Mo steel were carried out to prepare specimens with various degrees of creep damage. The variation of magnetic parameter including coercivity (H_C) and remanence (Br) with creep damage was analyzed. The microstructure evolution of 1Cr5Mo steel with different degrees of creep damage was observed by optical microscope. The results show that the coercivity and remanence show certain regularity with creep damage at elevated temperature. Moreover, the regularity is repeatable which indicates that the measurement technology based on magnetic parameters can be used for the evaluation of high temperature creep damage.

Abstract: The existence of exchange coupling or magnetostatic coupling between two phases, one magnetically hard and other magnetically soft is a way for obtaining higher maximum energy product (BH_max). In this study, it is discussed the microstructures for obtaining either exchange coupling or magnetostatic coupling in real materials. One relevant condition is that the assumptions of the Stoner-Wohlfarth model should be obeyed, with both phases, hard and soft, with dimensions less than single domain particle size. A real possibility is enveloping a spherical grain of hard phase with a first shell of soft phase, and another second shell or layer of a paramagnetic phase. The paramagnetic phase may play relevant role promoting magnetically decoupling between the grains.

Abstract: Hybrid bonded magnet Ba-Ferrite/NdFeB with 5% wt Epoxy Resin (ER) as polymer binder hsa been developed with variations in BaFe₁₂O₁₉ to NdFeB weight ratio. The variation of the BaO6Fe₂O₃ : Nd-Fe-B weight ratio are 90%:10%; 80%:20%; 70%:30% and 60%:40%. The magnetic particle consist of Ba-Ferrite and NdFeB were mixed until homogenize and compacted by using hydraulic press machine with 8 Tonf force to form a disc shape sample. The disc sample was dried using vacuum dryer with 10 mm bar pressure at 80°C for one hour before being magnetized using impulse magnetizer. The best %wt composition ratio of Ba-Ferrite/NdFeB is 70%/30% and 60%/40%. The hybrid bonded magnetic properties at the best %wt composition ratio are: bulk density = 4.28-4.43 g/cm³, FM = 1057-1121 Gauss, Br = 3.46-3.70 kG, Hc = 3.25-3.70 kOe, and BHmax = 1.60-1.70 MGOe.

Abstract: The martensitic transformations (MT) in austenite stainless steel (SUS316) were observed by using a sensitive Flux-Gate (FG) sensor just after the magnetizations by the permanent magnet in the terrestrial field. MT in the small deformation range less than 5% elongation, was visualized by the 2-dimensional profile at each position together with the profile of the thickness deformations with an accuracy of several microns. We found the local MT enhancements up to 400[nT] at the positions along the changes of the thickness. In this experiment, the observations of MT were able to avoid the effects of the external fields or of the ac fields which was generated by the gating function in the FG sensor.

Abstract: Electromagnetic Current Transformer (CT) is one of the main equipment in power system, and the remanence in the measuring or protective windings of CT will influence the stability of the power system. Measuring CT is mainly used for the electric energy measurement in normal working condition, focusing on the steady operation state; while protective CT is usually used in fault or short-circuit condition, and the transient transfer characteristic is of significant important. Considering high remanence operation environment in the power system, the numeric analytical model of CT, which is working in the saturation condition, is depicted in this paper. With analyzing the amount of exciting current caused by remanence and deducing the transfer characteristic of CT, the influence of the remanence on the relay protection and the corresponding precautions are proposed, providing accurate and reliable theoretical basis for the protective CT’s correct action and safety operation after system failure. Finally, the electromagnetic transient model of protective CT (TPY) is built in PSCAD, the simulation result of which shows the validity and practicability of the proposed model.

Abstract: The Henkel plot and the Δm plot of a longitudinal barium ferrite hard disk and γ-Fe2O3 flexible disk were simulated by the improved Preisach-DOK model.The study results show that the barium ferrite exhibit large positive interactions, as shown by large positive in the Δm plot, and tend to resist demagnetization, leading the oriented barium ferrite possess the unusual remanence characteristic.

Abstract: The topics chosen Fe3O4 and r-Fe2O3 nano-magnetic particle, respectively, with polyurethane and polyacrylate mixed ,mixed evenly coated on the surface of the fabric, then on before and after coating fabric tensile properties, tear resistance mechanical properties tested and compared. Experimental results show that: the choice of Fe3O4 better than r-Fe2O3 remanence effects, selection polyacrylate better softness than the selection of polyurethane, the latitude and longitude to the breaking strength was increased in the magnetic coating of the fabric, while the tear strength and abrasion resistance were reduced .