Papers by Author: Yasushi Takase

Abstract: Cast iron and steel rolls used in the continuous pickling line must be changed frequently because the continuous acid wash equipment induces wear on the roll surface in a short period. The damage portions are usually repaired by using the flame spray coating. Recently, ceramics materials are planed to be introduced to prevent the damage because of their high abrasion and corrosion resistances. In this study new roll structure is considered where a ceramics sleeve is connected with steel shafts at both ends by shrink fitting. Here, the ceramics sleeve may provide a longer lifetime and reduces the cost for the maintenance. However, attention should be paid to the maximum tensile stresses appearing between the ceramics sleeve, spacer rings and steel shafts because the fracture toughness, plasticity and fatigue strengths of ceramics are extremely lower than the values of steel. In this study, finite element method analysis is applied to the new structure, and the maximum tensile stress and stress amplitude have been investigated with varying the dimensions of the structure. Fatigue strengths of ceramics are also considered under several geometrical conditions.

Abstract: Steel conveying rollers used in hot rolling mills must be exchanged very frequently at great cost because hot conveyed strips induce wear on the surface of roller in short periods. In this study, new roller structure is considered which has a ceramics sleeve connected with two short steel shafts at both ends by shrink fitting. Here, the ceramics sleeve may provide longer life and reduces the cost for the maintenance. However, sometimes the steel shaft has to be pulled out for exchange. Simply, heating outside surface and cooling inside surface of the shaft are necessary for separation. However, attention should be paid to the maximum thermal stress of the ceramics sleeve in the process of separation. In this paper, finite element method analysis is applied to the structure and thermal stress has been calculated with the varying dimensions of the structure. Also several effects on thermal stress have been investigated, such as the effect of shrink fitting ratio, outside diameter, the fitted length, thickness of shaft, materials an so on. Finally the most appropriate thermal conditions to reduce maximum stress and make separation easy have been discussed, which is very useful for designing of new rollers.

Abstract: Recently, permanent magnet motors are widely used in wide industrial fields because they are suitable for compact mechanical system. The motor core is usually manufactured from magnetic steel sheet with press machine. However, usually most parts of the plate are scalped, and only small percent of the sheet is used for the core. The spiral accumulating core system is suitable for manufacturing the core more ecologically because in this system more than 50% of the magnet steel sheet can be used. In this study, therefore, the effective Young’s modulus of the spiral accumulating core is considered in order to find out a good method to fix the core. In this analysis, effective Young’s modulus of spiral accumulating core used for permanent magnet motor is considered by the application of the finite element method to 3D models, whose layers and slits are periodically arranged. Then, effects of slits, layers and embossing interlockings on effective Young’s modulus are analyzed. Finally, a convenient method of calculation based on rule of mixture is newly proposed for estimating the effective Young’s modulus of the real spiral accumulating core.

Abstract: The low pressure die casting machine has been used in industries because of its low-cost and high efficiency precision forming technique. In the low pressure die casting process is that the permanent die and filling systems are placed over the furnace containing the molten alloy. The filling of the cavity is obtained by forcing the molten metal, by means of a pressurized gas, to rise into a ceramic tube, which connects the die to the furnace. The ceramics tube, called stalk, has high temperature resistance and high corrosion resistance. However, attention should be paid to the thermal stress when the ceramics tube is dipped into the molten metal. It is important to reduce the risk of fracture that may happen due to the thermal stresses. To calculate the thermal stress, it is necessary to know the surface heat transfer coefficient when the ceramics tube dips into the molten metal. In this paper, therefore, the three-dimensional thermo-fluid analysis is performed to calculate surface heat transfer coefficient correctly. The finite element method is applied to calculate the thermal stresses when the tube is dipped into the crucible with varying dipping speeds and dipping directions. It is found that the thermal stress can be reduced by dipping slowly when the tube is dipped into the molten metal.

Abstract: Cast iron and steel conveying rollers used in hot rolling mills must be changed very frequently because conveyed strips with high temperature induces wear on the roller surface in short periods. This failure automatically stops the production line for repair and maintenance of conveying rollers. In this study a new type of roller is considered where a ceramics sleeve is connected with two short shafts at both ends by shrink fitting. Here, a ceramics sleeve provides longer life and therefore reduces the cost for the maintenance. However, for the hollow ceramics rollers, care should be taken for maximum tensile stresses appearing at both edges of the sleeve. In particular, because fracture toughness is extremely smaller compared with the value of steel, stress analysis for the roller is necessary for ceramics sleeve. In this study FEM analysis is applied to the structure, and the maximum stress has been investigated with varying the dimensions of the structure. It is found that the maximum tensile stress appearing at the end of sleeves takes a minimum value at a certain amount of shrink fitting ratio.

Abstract: In this study, singular stress fields at the ends of fibers are discussed by the use of models of rectangular and cylindrical inclusions in a semi-infinite body under pull-out force．The body force method is used to formulate those problems as a system of singular integral equations where the unknown functions are densities of the body forces distributed in a semi-infinite body having the same elastic constants as those of the matrix and inclusions.Then generalized stress intensity factors at the corner of rectangular and cylindrical inclusions are systematically calculated with varying the elastic ratio, length, and spacing of the location from edge to inner of the body. The effects of elastic modulus ratio and aspect ratio of inclusion upon the stress intensity factors are discussed.