Papers by Keyword: Mechanical Grinding

Abstract: Nanocrystalline materials have different properties compared to materials with microcrystalline grains. Nanocomposites, as a subdivision of nanomaterials, have different magnetic properties for each individual constituent. In the paper, a series of nanocomposite materials from the sphere of W ferrites are developed by mechanical grinding. Mixtures of commercial BaO and α-Fe₂O₃ powders, in the micron range, were used. The commercial powders were mechanically ground in order to reach the nanometric range. The use of suitable grinding parameters for ceramic powders led to the discovery of the nanometric range in a not very long time. An important parameter, which was used in the current research, was wet grinding which is a more suitable method for obtaining finer powders than dry grinding. Dividing the materials as finely as possible ensures a better reactivity due to the free valences of the ions on the surface of the granules and due to the fact that the number of contact points and the contact surface are much larger than in coarse-grained materials. The powders were unilaterally compacted, using a cylindrical die with an inner diameter of 15 mm. A resistive heating device was designed and built in order to assure the sintering process of the samples. Before resistive sintering, a thermal simulation of the heating process was carried out to see the distribution of the thermal field in the samples at different temperatures. According to the simulation, the optimal heating temperature was chosen. The sintered samples were analyzed from the point of view of the magnetic properties and it was found that the samples with the granulation in the nanometric range have higher magnetic characteristics than those in the micron range.

Abstract: Electrochemical polishing (ECP) is a promising approach to finishing surface to achieve high quality of surface. However, it cannot satisfy requirements of mirror finishing yet. In this paper, a mirror finishing method for cold rolling rollers is proposed. The whole process of the surface finishing can be divided into two phases: electrochemical polishing and mechanical grinding. An anodic film is formed exception for anodic dissolution during ECP. A small amount of the anodic film and metal material are removed by abrasive paper in mechanical grinding. Activated metal surface is exposed again and dissolved in electrochemical reaction after mechanical grinding. Residual of anodic film protects rollers. It is a cyclic process of mirror finishing. Experimental results showed that a mirror finishing surface of up to Ra0.02-0.05μm can be obtained by using this method and that it is effective and efficient.

Abstract: Engineering ceramics have been widely employed in the aerospace, automotive and tool field. However, they are difficult to machine due to their high hardness and brittleness. Circumferential electric discharge milling and mechanical grinding compound machining method is employed in this paper. The temperature distribution model for the compound machining of SiC ceramic is established, and the temperature distribution is calculated at different machining conditions. The results show that with the compound machining method, the higher material removal rate can be obtained at rough machining condition, and the better machined surface quality can be obtained at finish machining condition.

Abstract: Advanced engineering ceramics have been widely used in modern industry due to their excellent physical and chemical properties. However, they are difficult to machine due to their high hardness and brittleness. End electrical discharge milling and mechanical grinding compound machining method is employed to machine SiC ceramic in this paper. The process is able to effectively machine a large surface area on SiC ceramic. Furthermore, the tool for the compound machining of SiC ceramic is designed based on the goal of the higher material removal rate, the lower tool wear, and the better machined surface quality. The results show that with the designed tool for the compound machining, the higher material removal rate, the lower tool wear, and the better machined surface quality can be obtained.

Abstract: Cobalt ferrites were prepared by citrate sol-gel method, chemical co-precipitation, mechanical grinding, respectively. The grain size, morphology, and the size of crystal particles were studied by x-ray diffraction (XRD) and scanning electron microscope (SEM). Cobalt ferrite showed different morphologys when prepared by different methods, It was tapered corners which prepared by sol-gel method; It was tetrahedral which prepared by mechanical grinding method; It was sphere which prepared by chemical co-precipitation method. The average grain size of cobalt ferrite was less than 100nm, while particles prepared by chemical precipitation method were the smallest. The size of Cobalt ferrite prepared by sol-gel method was decreased with the cobalt content increased.

Abstract: The multi-facet drill shows good performance during materials are difficultly machined. However, for a new type of the drilling point, the grinding has been the main problem that restricts its application. To properly grinding the drill point confirms the design parameters, the relationship between design parameters and grinding parameters must be resolved. The mathematical model is the key to solve this problem. In this paper, according to the design of the high manganese steel drilling tool, a mathematical model has been established by the plane grinding method to solve grinding parameters, and to achieve improved mechanical grinding of drill point.

Abstract: Composite photocatalysts, prepared by mechanical grinding TiO₂ with bentonite/ organobentonite, were applied in the dynamic photodegradation of gaseous toluene. A substrate enriched environment surround the loaded TiO₂ was formed by the adsorption of the added sorbents, leading to an increase in the degradation rate. The performance of composite catalysts was quite different in the initial and the long-term period of photocatalysis. The differences could be attributed to the adsorption properties of added sorbents related to adsorbility, hydrophilicity and diffusion feasibility, etc. The longer alkyl-chain of organobentonite formed a better partition phase resulting in an ideal adsorption capacity. However, as the alkyl-chain length increased, the diffusion path was segmentally clogged which seriously hindered the photocatalysis in the initial period. Although the adsorption capacity of original bentonite was quite small, the facility of diffusion changed it into the best performer in the initial period. Organobentonite with relatively short alkyl-chain conceived a little smaller adsorption capacity than the longer one. Moreover, the former one showed much more trending to diffuse the adsorbed toluene to catalyst. The long-term period of photocatalysis was also affected by the hydrophilicity of catalyst. Hence, the performance of organobentonites added composite catalyst mended a lot in the final degradation rate. Thus, organobentonite as 20DTAB with the advantage of large adsorption capacity and good diffusion feasibility is believed to be a promising carrier of photocatalys.

Abstract: With four-probe and laser light scattering techniques, we have studied the dependencies of the conductivity and the particle sizes of p-toluene sulfonic acid doped polypyrrole on the mechanical grinding time. As the chemically synthesized polypyrrole was mechanically grounded in a mortar from 0 to 8 hours, its conductivity decreased from 607 to 10 S/m while and its particle size decreased from 27 to 4 m. If the mechanical grinding continued, the conductivity of the polymer was found to be up to 1680 S/m. Our results have demonstrated that mechanical grinding is an effective method to control the conductivity of the p-toluene sulfonic acid doped polypyrrole.

Abstract: Mg2Ni powder was heated up to 880°C which is higher than the melting point of Mg2Ni alloys (760°C) for 30 minutes and immediately cooled into water (14°C). And then, mechanical ball milling was conducted for 1,4,8,10,12,24 hours respectively. As milling time increased discharge capacity was increased to maximum of 700mAh/g at 12hours then decreased with increasing milling time. The best high rate dischargeability (HRD) characteristic also obtain at the 12 hours ball milling time. Therefore, the ball milling time could be shorten to 12 hours by heat treatment and rapid cooling. Praseodymium (0,0.2,0.5,0.7,1.0%Pr) was added to Mg2Ni alloys. These alloys were ground for 12 hours to investigate the improvement of cycle life. The cycle life was remarkably improved with increasing the amount of Pr. The best amount of Pr was 0.7 wt%.