• 대한치과보철학회지
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• 제45권3호
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• pp.345-353
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• 2007

Statement of problem. Implant abutment screw joints tend to loosen under clinical conditions. Abutment screw loosening results in loss of preload in function. Purpose. Anti-rotational inner post screw (ARIPS) systems were compared with conventional abutment screws to reduce screw loosening. Reverse torque values were evaluated. Material and methods. 32 implant assemblies (Warentec, Co, Ltd, Seoul, Korea) were organized as the 30-Ncm-torque conventional groups and 30-Ncm-torque ARIPS groups in external and internal system. The specimens were tested to 106 cycles at a load of 200N. Preload reverse torque, postload reverse torque, and the ratio of postload reverse torque to preload reverse torque were evaluated. The data were analyzed with unpaired t-test in external and internal systems. Results. In the ratio of postload reverse torque to preload reverse torque, the ARIPS groups showed significant differences than the conventional screw group in both external and internal system. Conclusion. Within the limitations of this study, abutment screw loosening was effectively reduced using ARIPS system.

• 한국공작기계학회논문집
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• 제11권5호
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• pp.30-37
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• 2002

Single flighted screw injection technology is the most cost effective method for the production of film, sheet, pipe and the fundamental step in other processes including blow molding and injection molding. The temperature of polymer melts and injection pressure play a very important role in the injection molding machine. Thermal distortion and displacement of a screw by temperature difference and injection pressure difference ratio cause a friction and thermoelastic wear by metal-to-metal contact between the screw and the cylinder. In this paper we analyzed thermal distortions of a screw as functions of temperature distribution and pressure profiles by finite element analysis.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.212-220
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• 2000

Single flighted screw extrusion is the most cost effective method for the production of film, sheet, pipe and the fundamental step in other processes including blow molding and injection molding. The temperature of polymer melts and injection pressure play a very important role in the injection molding machine. Thermal distortion and displacement of screw by temperature difference and injection pressure difference cause adhesive wear by metal-to-metal contact. In this paper we analyze thermal distortion and stress of screw includes pressure and temperature distributions by finite element analysis to understand dynamic characteristics of screw.

• The Journal of Advanced Prosthodontics
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• 제7권6호
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• pp.423-430
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• 2015

PURPOSE. To evaluate the cumulative survival rate (CSR) and mechanical complications of single-tooth $Ankylos^{(R)}$ implants. MATERIALS AND METHODS. This was a retrospective clinical study that analyzed 450 single $Ankylos^{(R)}$ implants installed in 275 patients between December 2005 and December 2012. The main outcomes were survival results CSR and implant failure) and mechanical complications (screw loosening, fracture, and cumulative fracture rate [CFR]). The main outcomes were analyzed according to age, sex, implant length or diameter, bone graft, arch, and position. RESULTS. The 8-year CSR was 96.9%. Thirteen (2.9%) implants failed because of early osseointegration failure in 3, marginal bone loss in 6, and abutment fracture in 4. Screw loosening occurred in 10 implants (2.2%), and 10 abutment fractures occurred. All abutment fractures were located in the neck, and concurrent screw fractures were observed. The CSR and rate of screw loosening did not differ significantly according to factors. The CFR was higher in middle-aged patients (5.3% vs 0.0% in younger and older patients); for teeth in a molar position (5.8% vs 0.0% for premolar or 1.1% for anterior position); and for larger-diameter implants (4.5% for 4.5 mm and 6.7% for 5.5 mm diameter vs 0.5% for 3.5 mm diameter) (all P<.05). CONCLUSION. The $Ankylos^{(R)}$ implant is suitable for single-tooth restoration in Koreans. However, relatively frequent abutment fractures (2.2%) were observed and some fractures resulted in implant failures. Middle-aged patients, the molar position, and a large implant diameter were associated with a high incidence of abutment fracture.

• 대한조선학회논문집
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• 제54권2호
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• pp.161-169
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• 2017

Recently, ship owners have been requiring the assessment of the maneuverability of twin-screw ships under mechanical failures. Because this kind of assessment has not yet been conducted, it is necessary to study the types of machinery failures that can significantly affect the maneuverability of a ship, and to construct a procedure to simulate the maneuvering behavior under such failures. In this paper, the sole focus is the steering system failure from among the variety of failure types, and the maneuvering behavior of the ship under the single rudder failure is simulated for an investigation of the unique characteristics. First, the mathematical model for the twin-screw container ship is verified by comparing the simulated results for the $35^{\circ}$ turning test, $10^{\circ}/10^{\circ}$ zigzag test, and $20^{\circ}/20^{\circ}$ zigzag test under the normal operating condition with those obtained from free running model tests. After the IMO maneuvering tests are additionally simulated under the single rudder failure, the results are reviewed to investigate the maneuvering characteristics that are due to the failure. Further, the $35^{\circ}/35^{\circ}$ zigzag test and the $35^{\circ}$ turning test are simulated to additionally investigate the effects of the single rudder failure on the steering and turning abilities.

• 대한치과보철학회지
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• 제45권2호
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• pp.240-249
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• 2007

Statement of problem: A phenomenon of screw-loosening in implant abutment is frequently occurred in a single and multiple implant restoration. Purpose: This study was performed to evaluate an effect of abutment material on screw-loosening before and after a cyclic loading. In a single-tooth implant, different materials of abutment, Type III Gold alloy and Zirconium composite$(ZrO_2/Al_2O_3)$ were used. Material and method: The Gold alloy(Type III) and Zirconium composite$(ZrO_2/Al_2O_3)$ were used to make a superstructure of implant, the one of types of UCLA, Each group was constituted of 5 sample with a 30-degree offset angulated loading platform. The external hexagonal fixture was rigidly hel d in a special holding zig to ensure solid fixation without rotation during the tightening and a cyclic loading. A Titanium-alloy screw was used to connect and controlled to be tighten in 20Ncm torque by a digital torque gauge. A 20 times of consecutive closing/opening cycle were performed to evaluate the immediate torque loss. In 5 sample of each material group, an initial opening torque was recorded during 3 closing/opening cycle, then 2Hz, 200N, 1,000,000 cyclic loadings were performed, then a opening torque was evaluated. Result & Conclusion: 1. In this limited study, titanium alloy screw tightened in 20Ncm, a cold-welding phenomen on was not observed during the 20 times of closing/opening cycle(p=0.11, p=0.18). 2. In titanium alloy abutment screw, repeated opening and closing of the screw caused to progressive decrease of opening torque(p=0.014). 3. The difference in preload of screw between gold alloy abutment and ceramic$(ZrO_2/Al_2O_3)$ abutment was not significant(p=0.78). 4. The difference in torque loss of screw between gold alloy abutment and ceramic$(ZrO_2/Al_2O_3)$ abutment was not significant after 2Hz,200N, 1,000,000 cyclic loading(p=0.92). 5. In titanium alloy abutment screw tightened by 20Ncm, the screw loosening was not significant on each group after 2Hz, 200Ncm, 1,000,000 cyclic loading(p=0.59).

• 한국식품영양학회지
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• 제7권2호
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• pp.137-143
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• 1994

To optimize extrusion cooking condition of single screw extuder for production of puffed rice extrudate using response surface methodology (RSM), moisture content, barrel temperature and screw speed were determined from contour maps, showing relationship between dependent (hardness, expansion ratio, water absorption index, water solubility Index, degree of gelatinization) and independent variables. Optimum operational conditions for production of puffed rice extrudate with suitable quality properties were moisture content 17%, barrel temperature 1$25^{\circ}C$ and screw speed 210 rpm, respectively.

• 한국유체기계학회 논문집
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• 제2권3호
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• pp.37-44
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• 1999

In a screw-type centrifugal pump, the pump head deteriorates from single-phase flow to the choke due to an increased air entrainment at a wide tip clearance compared to that of a narrow tip clearance. Moreover, at a narrow tip clearance, the pump head became partially higher in a two-phase flow than that of a single-phase flow near the best efficiency point in low void fraction region. Therefore, we observed the internal flow pattern by using a stroboscope and we measured the mean size of bubbles from the images obtained with a high speed camera. Then, we investigated the influences of the mean size of bubbles, tip clearances and flow patterns on pump performance.

• 한국유체기계학회 논문집
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• 제4권3호
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• pp.39-45
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• 2001

It is reported recently that the pump head deterioration near the best efficiency point, from single-phase flow to the choke due to air entrainment became less in a screw-type centrifugal pump than in a general centrifugal pump. Moreover, at a narrow tip clearance, the pump head became partially higher in two-phase flow than that in single-phase flow. However, the internal pressure fluctuations on this pump due to air entrainment have not been studied yet. For that reason, we have examined the influences of void fraction, flow coefficient and impeller tip clearance on pressure fluctuations in the casing. The void fraction became larger, the influence of tip clearance on pressure distribution became less.

• 반도체디스플레이기술학회지
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• 제6권1호
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• pp.31-36
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• 2007

Effect of coulomb friction and backlash on the single loop position control has been studied for the precision position control. We have showed the limit cycle on the single loop system which used a ball screw that had the backlash. Also, we have made an inner loop with a classical velocity and torque controller which was forcing the current of d axis to be zero by using a permanent-magnet synchronous motor and composed the outer loop with linear encoder for sensing a position of the loader. Also, we have used least squares fit(LSF) observer for reducing noise when we got velocity from position outputs. We have shown a good result by using the dual loop through simulation and experiment.