• Restorative Dentistry and Endodontics
• /
• v.41 no.1
• /
• pp.63-67
• /
• 2016

During clinical endodontic treatment, we often find radiopaque filling material beyond the root apex. Accidental extrusion of calcium hydroxide could cause the injury of inferior alveolar nerve, such as paresthesia or continuous inflammatory response. This case report presents the extrusion of calcium hydroxide and treatment procedures including surgical intervention. A 48 yr old female patient experienced Calcipex II extrusion in to the inferior alveolar canal on left mandibular area during endodontic treatment. After completion of endodontic treatment on left mandibular first molar, surgical intervention was planned under general anesthesia. After cortical bone osteotomy and debridement, neuroma resection and neurorrhaphy was performed, and prognosis was observed. But no improvement in sensory nerve was seen following surgical intervention after 20 mon. A clinician should be aware of extrusion of intracanal medicaments and the possibility of damage on inferior alveolar canal. Injectable type of calcium hydroxide should be applied with care for preventing nerve injury. The alternative delivery method such as lentulo spiral was suggested on the posterior mandibular molar.

• Transactions of Materials Processing
• /
• v.24 no.5
• /
• pp.317-322
• /
• 2015

A process for the concurrent welding and extruding of pipe was designed for continuous production of fin tubes. Unlike a conventional pipe extrusion, the new process is able to extrude a pipe continuously without limit of length by using spring type wire material. The current paper provides the basic research for welding during the extrusion using a spring type wire material. The object of the current study is to investigate the possibility that the spring type wire material could be extrude into a welded pipe. The appropriate extrusion ratio was selected through investigation of loads using computer simulations. As a result, experiments showed that pipe could be welded and simultaneously extruded with spring type wire material of aluminum. The tensile strength of the welded and extruded aluminum pipe can reach 80% of tensile strength of original aluminum feedstock.

• Transactions of Materials Processing
• /
• v.31 no.6
• /
• pp.344-350
• /
• 2022

Extruded Mg-Bi binary alloys are known to have an undesirable bimodal grain structure containing a large amount of coarse unrecrystallized grains. Accordingly, to improve the microstructural homogeneity of extruded Mg-Bi alloys, it is necessary to promote the dynamic recrystallization (DRX) behavior during hot extrusion. An effective way to promote DRX is an increase in nucleation sites for DRX through a pre-deformation process before extrusion, such as cold pre-forging and hot pre-compression. However, the application of these pre-deformation processes increases the cost of final extruded Mg products because of an increase in energy consumption and decrease in productivity. Therefore, a low-cost new continuous process with high productivity is required to improve the microstructural homogeneity and mechanical properties of extruded Mg alloys without a drastic increase in the entire process cost. This study proposes a new extrusion method using an extrusion billet with a truncated cone shape (i.e., tapered billet) instead of a conventional extrusion billet with a cylindrical shape. When the hot extrusion of a Mg-5Bi alloy is conducted using the tapered billet, the DRX behavior during extrusion is considerably promoted. The DRX fraction and average grain size of the extruded alloy significantly increase and decrease from 65% to 91% and from 225 ㎛ to 49 ㎛, respectively. Consequently, the extruded Mg-5Bi alloy fabricated using the tapered billet has a finer homogeneous grain structure and higher tensile elongation than the extruded counterpart fabricated using the cylindrical billet.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.11 no.6
• /
• pp.152-157
• /
• 2012

This study investigates compressive strength of ice pellet strip which is potential medium for Natural Gas Hydrate(NGH) extruded from die holes of Twin-roll Press for Continuous Pelletizing(TPCP). Recently, the prototype of TPCP is newly developed where ice powder is continuously fed and extruded into strip-type pellet between twin rolls. The system is specifically designed for future expansion towards mass-production of ice pellet strips or solid form of natural gas hydrate. It is shown that the compressive strength of pellet strip heavily depends on factors in extrusion process such as disk size, surface smoothness, ring size, taper shape, feeding mechanism, and rotational speed. Here, the mechanism of TPCP, along with compressive strength of pellets is discussed in terms of its feasibility for producing NGH pellets in the future.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.11 no.1
• /
• pp.110-117
• /
• 1987

A new kinematically admissible velocity field for a generalized three-dimensional flow is introduced, in which the flow is bounded by an analytic die-profile function. Then, by applying the upper-bound method th the velocity field, the flow patterns as the upper-bound method are obtained. Extrusion of elliptic sections from round billets is chosen as a computational example. Computation and experiments are carried out for work-hardening material such as aluminum alloy 2024. In order to visualize the plastic flow, the grid marking technique is employed. The theoretical predictions both in extrusion load and deformed pattern are in good agreement with the experimental data.

• Proceedings of the Korean Fiber Society Conference
• /
• 1990.06b
• /
• pp.8-8
• /
• 1990

A new method for the graft polymerization of acrylonitrile onto starch is presented. Graft polymerization of acrylonitrile onto starch and the subsequent hydrolysis in sodium hydroxide solution to prepare absorbents is well known. This process has been utilized to produce the commercial product, Super Slurper. In a typical batch process, ~5% starch in water mixture is gelatinized at $95^{\circ}C$ under stirring for 1 hour then cooled to room temperature. The graft polymerization itself is carried out for approximately 2 hours at $25~30^{\circ}C$ on the gelatinized starch by eerie ion initiation. In this study, graft polymerization of acrylonitrile onto starch via a reactive extrusion process which is a continuous, efficient process is described. Initial concentration of starch in water is 35% and the reaction temperatures are between $50~80^{\circ}C$. However, the most significant difference in the reactive extrusion process is the short time in which the graft polymerization takes place. Preliminary results on the properties of graft polymerization products obtained from the reactive extrusion process are compared to those obtained from the batch process as well as the absorbency of the hydrolyzed samples. Absorbent material has also been prepared by sequential grafting and saponification in the extruder followed by a 2 hour heat treatment of the extrudate in an air circulated oven at $100^{\circ}C$.

• Elastomers and Composites
• /
• v.33 no.4
• /
• pp.255-266
• /
• 1998

One-step continuous reactive blend with EPDM is investigated using a modular intermeshing corotating twin screw extruder This was performed via anionic polymerization mechanism. Mechanical properties were characterized and compared with mechanical blends.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.325-326
• /
• 2006

Using $6wt%Y_2O_3-2wt%Al_2O_3$ as sintering additives and Si as a raw powder, the continuously porous in-situ $Si_2N_2O-Si_3N_4$ bodies were fabricated by multi-pass extrusion process and their microstructures were investigated depending on the addition of carbon (0-9wt%) in the mixture powder. The introduction of $Si_2N_2O$ fibers observed in the unidirectional continuous pores as well as in the pore-frame regions of the nitrided bodies can be an effective method in increasing the filtration efficiency. In the case of no carbon addition, the network type $Si_2N_2O$ fibers with high aspect ratio appeared in the continuous pores with diameters of 150-200 nm. However, in the case of 9wt% C addition, the fibers were found without any network type and had diameters of 200-250 nm.

• Steel and Composite Structures
• /
• v.49 no.4
• /
• pp.393-405
• /
• 2023

In this paper, the energy absorption capability of a novel cruciform composite lattice structure was evaluated through the simulation of compression tests. For this purpose, several test samples of Polylactic acid cellular reinforced with continuous glass fibers were prepared for compression testing using the additive manufacturing method of material extrusion. Using a conventional path design for material extrusion, multiple debonding is probable to be occurred at the joint regions of adjacent cells. Therefore, an innovative printing path design was proposed for the cruciform lattice structure. Afterwards, quasistatic compression tests were performed to evaluate the energy absorption behaviour of this structure. A finite element model based on local material property degradation was then developed to verify the experimental test and extend the virtual test method. Accordingly, different combinations of unit cells' dimensions using the design of the experiment were numerically proposed to obtain the optimal configuration in terms of the total absorbed energy. Having brilliant energy absorption properties, the studied cruciform lattice with its optimized unit cell dimensions can be used as an energy absorber in crashworthiness applications. Finally, a cellular structure will be suitable with optimal behavior in crush load efficiency and high energy absorption.

• Macromolecular Research
• /
• v.16 no.1
• /
• pp.6-14
• /
• 2008

Polypropylene (PP)-layered silicate nanocomposites were developed using a new processing method involving a supercritical carbon dioxide ($scCO_2$)-assisted co-rotating twin-screw extrusion process. The nanocomposites were prepared through two step extrusion processes. In the first step, the PP/clay mixture was extruded with $CO_2$ injected into the barrel of the extruder and the resulting foamed extrudate was cooled and pelletized. In the second step, the foamed extrudate was extruded with venting to produce the final PP/clay nanocomposites without $CO_2$. In this study, organophilic-clay and polypropylene matrix were used. Maleic anhydride grafted polypropylene (PP-g-MA) was used as a compatibilizer. This study focused on the effect of $scCO_2$ on the dispersion characteristics of the clays into a PP matrix and the rheological properties of the layered silicate based PP nanocomposites. The dispersion properties of clays in the nanocomposites as well as the rheological properties of the nanocomposites were examined as a function of the PP-g-MA concentration. The degree of dispersion of the clays in the nanocomposites was analyzed by X-ray diffraction and transmission electron microscope. Various rheological properties of the nanocomposites were measured using a rotational rheometer. In the experimental results, the $scCO_2$ assisted continuous manufacturing extrusion system was used to successfully produce the organophilic-clay filled PP nanocomposites. It was found that $scCO_2$ had a measurable effect on the clay dispersion in the polymer matrix and the melt intercalation of a polymer into clay layers.