• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.14 no.2
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• pp.79-87
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• 1978

This is an experimental study on friction welding and heat treatment of engine exhaust valve materials whose welding combination is SCr4 as stem to 21-4N as head and SUH3 to 21-4N. In this study, not only the experiments of friction welding under the selected optimum welding condition and the examination of the mechanical properties were carried out, but also the heat treatment of friction welded specimens under the two selected conditions was taken to obtain the better welding character, eliminating the latent stress and the hardness peak which appeared at the welded zones of heat resisting steel(21-4N, SUH3) and low alloyed steel ($SCr_4$) friction weldments. The results obtained by the experiments and consideration in this study are as follows: I) It was experimentally proved quite reasonable that 'speed=3,OOO rpm, heating pressure Pl=8 kg/ mm2, upsetting pressure p, = 20 kg/mm', heating time $t_1$ = 3 see, upsetting time TEX>$t_2$ = 2.5 sec' was selected as the optimum welding condition for friction-welding the engine exhaust valve materials $SCr_4$ to 21-4 Nand SUH 3 to 21-4 N. 2) The results of the previous study and this one on friction welding of such dissimilar materials as SUH 3-SUH 31, SCr 4-SUH 31, SCr 4-SUH 3, SUH 3-CRK 22, SCr4-21-4 Nand SUH3-21-4 N agreed with each other substantially in the friction welding characteristics at welded interface zones. 3) It was also certified quite satisfactory that '600\ulcornerCX30 min. Xroom air cooling' as an optimum heat treatment condition of the friction welded materials SCr 4-21-4 Nand SUH 3-21-4 N was experimentally determined to eliminate the latent stress and the hardness peak at welded zones. 4) About 20% of the tensile strength before heat treatment of friction welded specimens was decreased after heat treatment 600\ulcornerCX30 min. Xair cooling, but the location of fracture was moved from heat affected zone to parent $SCr_4$ & SUH3. 5) Microscopic examination of the weld joints friction-welded and heat-treated under the above mentioned conditions revealed that the weld zone is very narrow and has a fine grained intermixed structure without any welding defects. 6) The above mentioned conditions can be also utilized as friction welding parameters of the other dissimiar materials for engine valve production.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.86-92
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• 2016

A high-capacity battery installed in a hybrid vehicle or electric vehicle is used to power, or as a power supply for, electric sub-assemblies. In order to use a high-capacity battery as a power supply for electric sub-assemblies, such as an electronic control unit or for lighting, radio, and navigation, there is a need for a DC converter that changes a high voltage of 240-400V to a low voltage of 12-14V, which is done with a low-voltage DC-DC converter (LDC). An LDC undergoes long-term aging so as to reduce latent defects in the production process. With regard to the usual aging method, an LDC is a DC-DC converter. So, a DC power supply is connected and used as input, and a programmable DC electronic load is the output. For stable operation, a product having a larger capacity by 10% (compared to an LDC) is used, and has a structure where electric power is dissipated into 100% heat. So, there is a problem with volume, based on the use of two pieces of equipment to test the LDC, and another problem based on the generation of heat in the programmable DC electronic load. Hence, this paper suggests a load test method as a way of recycling, where a significant portion of the electricity dissipated as heat in a load tester is returned as input. The method realizes savings of 80% or more in the electricity dissipated as heat through improvement in the efficiency of the recycling load tester.