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손동휘(Dong-Hwi Son),서영수(Young-Soo Seo),박근(Keun Park) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
Weldlines are generated during the injection molding process when two or more melt flows are brought into contact. At the welded contact region, a ‘V’-shaped notch is formed on the surface of the molded part. This ‘V’-notch deteriorates not only surface appearance but also mechanical strength of the molded part. To eliminate or reduce weldlines so as to improve the weldline strength, the mold temperature at the corresponding weld locations should be maintained higher than the glass transition temperature of the resin material. The present study implements high-frequency induction heating in order to rapidly raise mold surface temperature without a significant increase in cycle time. This induction heating enables to local mold heating so as to eliminate or reduce weldlines in an injection-molded plastic part. The effect of induction heating conditions on the weldline strength and surface appearance of an injection-molded part is investigated.
서영수(Young-Soo Seo),손동휘(Dong-Hwi Son),박근(Keun Park) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
High-frequency induction is an efficient way to heat mold surface by electromagnetic induction in a non-contact manner. Thanks to its capability of rapid heating and cooling of mold surface, it has been recently applied to the injection molding. The present study applies the high-frequency induction heating for elimination of weldlines in an injection-molded plastic part. To eliminate weldlines, the mold temperature of the corresponding weld locations should be maintained higher than the glass transition temperature of the resin material. Through experiments, the maximum temperature of 143℃ is obtained on the mold surface around the elliptic coil, while the temperature of the mold plate is lower than 60℃. An injection molding experiment is then performed with the aid of induction heating, and the effect of induction heating conditions on the surface appearance of the weldline is investigated.
도수 촉진과 막대를 이용한 몸통의 전방 굴곡 운동에 따른 요추와 고관절 굴곡 각도의 변화
정성대 ( Sung Dae Choung ),박규남 ( Kyue Nam Park ),홍지아 ( Ji A Hong ),조민수 ( Min Sue Cho ),손동휘 ( Dong Hwi Son ),신헌석 ( Heon Seock Cynn ) 한국전문물리치료학회 2011 한국전문물리치료학회지 Vol.18 No.1
The purpose of this study was to identify the effects of manual facilitation and a stick on lumbar and hip joint flexion angles in subject with lumbar flexion syndrome during forward bending from a sitting position. Fifteen subjects with lumbar flexion syndrome were recruited for this study. As a pretest, all subjects performed three repetitions of bending the trunk forward until the tips of their fingers touched the target bar. After this pretest, the subjects practiced the forward bending of the trunk 10 times, using either manual facilitation or a stick. Then, as a posttest, all subjects repeated the pretest procedure. The flexion angles of lumbar spine and hip joint during forward bending in a sitting position were measured using a three-dimensional motion analysis system. A paired t-test was used to determine the statistical differences between pre-test and post-test flexion angles and pre- and post-test flexion angle differences between forward bending with manual facilitation and forward bending with a stick. The level of statistical significance was set at p=.05. The results of the study showed that the angle of the lumbar flexion decreased significantly and the bilateral hip flexion angle increased significantly when performing forward bending with stick and manual facilitation. Furthermore, the angle of lumbar flexion decreased significantly and the angle of bilateral hip flexion increased significantly in forward bending with a stick compared to forward bending with manual facilitation. The findings of this study indicate that both forward bending with manual facilitation and sticks could be used to prevent excessive lumbar flexion and increase hip flexion, and that forward bending with a stick is more effective than forward bending with manual facilitation for inducing lumbar spine and hip joint angle changes.