• Elastomers and Composites
• /
• 제38권4호
• /
• pp.295-302
• /
• 2003

사출성형에서 성형품의 수축현상은 사출온도, 사출압력, 금형온도와 같은 성형공정에 따라 다르게 나타나며 게이트의 크기 등과 같은 금형설계에 따라서도 다르게 나타난다. 또한 수지의 결정화 유무에 따라 다르게 나타나고 있다. 본 연구에서는 여러가지 공정변수와 수지 특성에 따른 성형 수축률을 결정성수지인 poly(butylene terephthalate) (PBT)와 비결정성 수지인 polycarbonate (PC), poly(methyl methacrylate) (PMMA)를 사용하여 연구하였다. 결정성 수지가 비결정성 수지에 비해 약 3배 정도의 큰 수축률을 보였다. 사출 성형품의 성형 수축은 사출온도와 금형온도가 높을수록 그리고 사출압력이 작을수록 수축률은 커지는 경향을 보였다. 게이트의 크기가 커질수록 캐비티내의 압력전달이 원활하여 성형수축률은 작아 졌다. 또한 수지의 흐름방향과 흐름직각방향의 수축률 실험에서는 흐름방향의 수축이 더 작은 경향을 보였다. 게이트와의 거리에 따른 성형수축률은 게이트에서 가까운쪽의 수축이 먼쪽보다 더 큰 수축을 보였는데 이 현상은 잔류응력의 차이로 인하여 나타난 현상으로 해석된다.

• 한국자동차공학회논문집
• /
• 제15권1호
• /
• pp.193-200
• /
• 2007

Natural gas is one of the most promising alternatives to gasoline and diesel fuels because of its lower harmful emissions, including $CO_2$, and high thermal efficiency. In particular, natural gas is seen as an alternative fuel for heavy-duty Diesel Engines because of the lower resulting emissions of PM, $CO_2$ and $NO_x$. Almost all CNG vehicles use the PFI-type Engine. However, PFI-type CNG Engines have a lower brake horse power, because of reduced volumetric efficiency and lower burning speed. This is a result of gaseous charge and the time losses increase as compared with the DI-type. This study was conducted to investigate the effect of injection conditions (early injection mode, late injection mode) on the combustion phenomena and performances in the or CNG Engine. A DI Diesel Engine with the same specifications used in a previous study was modified to a DI CNG Engine, and injection pressure was constantly kept at 60bar by a two-stage pressure-reducing type regulator. In this study, excess air ratios were varied from 1.0 to the lean limit, at the load conditions 50% throttle open rate and 1700rpm. The combustion characteristics of the or CNG Engine - such as in-cylinder pressure, indicated thermal efficiency, cycle-by-cycle variation, combustion duration and emissions - were investigated. Through this method, it was possible to verify that the combustion duration, the lean limit and the emissions were improved by control of injection timing and the stratified mixture conditions. And combustion duration is affected by not only excess air ratio, injection timing and position of piston but gas flow condition.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제16권3호
• /
• pp.77-82
• /
• 2008

For heat pumps used in a cold region, it is very important to obtain appropriate heating capacity. Several studies using a variable speed compressor and an additional heater have been performed to enhance heating capacity at low ambient temperatures. However, for outdoor temperature conditions below $-15^{\circ}C$, it is still difficult to obtain enough heating capacity above the rated value. In recent studies, the application of gas injection technique into a two-stage heat pump yielded noticeable heating performance improvement at low temperature conditions. In this study, the heating performance of a two-stage gas injection heat pump with a rated capacity of 3.5 kW was measured and analyzed by varying refrigerant charge amount and EEV opening at the standard heating condition. The heating performance of the two-stage gas injection heat pump was compared with that of a two-stage non-injection heat pump. The heating capacity and COP of the two-stage gas injection heat pump were improved by 2-10% at the optimal charging condition over those of the two-stage non-injection heat pump.

• Elastomers and Composites
• /
• 제52권4호
• /
• pp.309-316
• /
• 2017

In injection molding, the quality of an injection molded product varies greatly depending on the molding conditions. Many researche studies have been conducted on the quality analysis of molded parts according to the molding conditions such as injection pressure, injection temperature, and packing pressure. However, there have not been many studies on the V/P switchover timing. It is known that when a large pressure is applied to a cavity in the packing phase, the cavity pressure is most affected by the packing pressure. In addition, depending on the position (timing) of the packing pressure, it can have a direct influence on quality based on the shrinkage and dimensions of the molded parts. In this study, the change in pressure profile in the cavity according to the V/P switchover position is confirmed. A CAE analysis program (Moldflow) was used to simulate and analyze two models using the PC and PBT materials. In order to compare these results with the actual injection molding results, injection molding was performed for each V/P switchover position, and the correlation between simulation and experiment, especially for the shrinkage of molded parts, was evaluated.

• 동력기계공학회지
• /
• 제17권6호
• /
• pp.18-24
• /
• 2013

An experimental study was performed to investigate the characteristics of combustion pressure and exhaust emissions when the pilot injection timing and EGR rate were changed in a CRDI 4-cylinder diesel engine. The pilot injection timing and EGR rate have a significant impact on the combustion and emission characteristics of diesel engine. In this study, the pilot injection timing and EGR rate variation were conducted to 2000rpm of engine speed with torque 50Nm. Combustion pressure and heat release rate were decreased under high EGR rate conditions but increased under the pilot injection timing $20^{\circ}$(BTDC). IMEP and the maximum pressure in cylinder(Pmax) were decreased under the same injection timing with the increase of EGR rate. The NOx emission was decreased with increasing the EGR rate. On the other hand, in the same injection timing conditions, CO, HC, $CO_2$ emissions were increased with increasing the EGR rate.

• 한국분무공학회지
• /
• 제14권2호
• /
• pp.71-76
• /
• 2009

The aim of this investigation is to study the effect of the high injection pressure on the dimethyl ether (DME) spray characteristics injected through a common-rail diesel injector under various ambient pressures. In order to investigate the effect of the injection pressure and ambient condition, the common-rail injection system with two high pressure pumps and high pressure chamber pressurized up to 40 bar were used, respectively. Spray images of DME fuel obtained from a visualization system composed of high speed camera and two metal halide lamps as the light source. From the obtained images, the spray behaviors such as a spray development process, spray tip penetration, spray width, and spray cone angle were measured for analyzing the DME spray characteristics under various experimental conditions. It was found that the spray development slowed as the ambient pressure increased and spray tip penetration at injection pressure of 90 MPa is longer than that at 50 MPa. In addition, the spray width at the end stage of injection decreased under the atmospheric conditions due to the evaporation property of DME fuel, and DME spray shows narrow spray cone angle according to the injection pressure increased.

• 한국산학기술학회논문지
• /
• 제14권11호
• /
• pp.5352-5356
• /
• 2013

최근 플라스틱 성형품은 기능적인 측면뿐만 아니라 디자인 및 광택과 같이 시각적으로 즉각 식별이 가능한 부분에 까지 많은 관심과 주의를 기울이고 있다. 이와 관련하여 성형품 광택의 제어를 위하여 성형조건이 광택에 미치는 영향에 대한 연구가 필요하지만 관련 연구는 아직 충분히 이루어지지 않고 있다. 따라서 본 연구는 플라스틱 성형품의 외관에 주로 사용되는 ABS (Acrylonitrile-Butadiene-Styrene) 플라스틱 성형품에 대하여 사출압력, 사출속도, 보압력, 수지온도, 금형온도 등의 사출조건의 변화가 성형품의 외관 광택에 미치는 영향에 대하여 사출실험을 통하여 연구하였다. 연구 결과에서 보압력이 가장 큰 영향을 미침을 알 수 있었다. 특히, 보압력 55 - 75MPa 범위에서는 광택도가 증가하지만 그 이상 증가하면 광택이 감소하는데, 그 원인은 SEM(Scanning Electron Microscope)을 통하여 수지 내부의 고무 입자의 변형에 기인한다고 유추할 수 있었다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2009년도 춘계학술대회 논문집
• /
• pp.176-179
• /
• 2009

Injection molding is one of the most general manufacturing processes of polymers. The deformation of final molded parts occurs because of the change of temperature and pressure during injection molding process. The deformation of injection molded parts depends on many operational conditions, such as, melt temperature, injection speed, mold temperature, packing pressure, and the structure of mold. In the present paper, injection molding experiments were performed to find the process conditions to affect the average shrinkage in thickness direction and the replication ratio of fine patterns on the surface for the final injection-molded LGP samples. As a results, in the cases of PC(Polycarbonate), when the melt temperature was under $285^{\circ}C$, both average shrinkage and replication ratios were mainly influenced by packing pressure. However, the replication ratio was more influenced by melt temperature than packing pressure for the cases of higher melt temperature.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2007년도 추계학술대회 논문집
• /
• pp.266-270
• /
• 2007

Small injection molded articles such as lens and mobile product's parts are usually molded in multi-cavity mold. The problems occurred in multi-cavity molding are flow imbalance among the cavities. The flow imbalance affects on the dimensions and physical properties of molded articles. First of all, the origin of flow imbalance is geometrical imbalance of delivery system. However, even the geometry of delivery system is balanced well the cavity imbalance is being developed. This comes from the unsuitable operational conditions of injection molding. Among the operational conditions, injection speed is the most significant process variable affecting the filling imbalances in multi-cavity injection molding. In this study, experimental study of flow imbalance has been conducted for various injection speeds and materials. Also, the filling Imbalances were compared with CAE results. The dimensions and physical state of multi-cavity molded parts were examined. The results showed that the filling imbalances vary according to the injection speed and flow property of resins. Subsequently, the imbalanced filling and pressure distribution in the multi-cavity affect on the dimensions and physical states of molded parts.

• 동력기계공학회지
• /
• 제2권1호
• /
• pp.80-85
• /
• 1998

Engineering plastics have been magnified its usability due to its outstanding mechanic al, electrical and chemical properties, for example, in the area of computer, electricity, electronics, automobile, camera industry. In recent, automobile speedometer system is changing from manual operation to motor operation. All plastic gears inserted by metal shaft are used In motor operated speedometer system. Therefore, in this research, experimental investigation of the shrinkage phenomenon was executed according to various inserted depth and injection conditions. In experiments, the inserted depth was controlled as 30% and 90% of the total thickness of the plastic gear. The main parameters of injection process were selected as injection pressure, holding pressure, melt temperature, injection rate. As main results, free shrinkage rate of the test part is increased about 4 times to restricted shrinkage rate and shrinkage phenomenon against all injection conditions have a trivial effect on the test parts as conventional parts.