• Restorative Dentistry and Endodontics
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• v.38 no.4
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• pp.222-226
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• 2013

Objectives: The aim of this study was to assess the influence of operator experience level on the lifespan of the WaveOne Primary file (Dentsply Maillefer, Ballaigues, Switzerland) in extracted teeth. Materials and Methods: Moderately curved canals of extracted maxillary and mandibular molars were randomly distributed into 2 groups: experienced and inexperienced operators. Ten files were allocated to each group (n = 10). Each canal was prepared until the working length was reached, and the same file was used to prepare additional canals until it separated. The number of canals prepared before file separation was recorded. The fragment length of each file was measured, and the location of the fragment in the canal was determined. Data were statistically analysed using the independent 2-sample t-test. Results: The 2 operators prepared a total of 324 moderately curved canals of maxillary and mandibular molars. There was no significant intergroup difference in the mean number of canals prepared (p = 0.27). The average lifespan of the WaveOne Primary file was 17.1 and 15.3 canals, and the longest lifespan was 25 and 20 canals, when used by experienced and inexperienced operators, respectively. There were no statistically significant intergroup differences in separated fragment length and location. Conclusions: Within the limitations of this study, operator experience level appears to have no effect on the lifespan of the WaveOne Primary file in preparation of moderately curved canals. Single teeth with multiple canals can be prepared safely even by a novice operator by using a single file.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.113-120
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• 2013

Graphite is commonly used as a solid lubricant leading to low friction coefficient and abrasion. In this study, wear behavior of sealing graphite(HK-6) at elevated temperature was evaluated. Reciprocating wear test was carried out as wear occurred graphite as a seal(HK-6) is positioned between the liner and driving shaft. Variables which are temperature, sliding speed and contact load are set. This study suggest optimized environment conditions through the wear properties of graphite.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.5
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• pp.95-100
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• 2013

The important design factors for designing solid lubricating of dynamic seal are tightness, wear resistance and lubricant films. In this study, the effect factors influenced solid lubricating properties of the graphite were analyzed and wear behaviour caused for various test conditions was compared with results obtained from reciprocating wear tests. Also the optimal conditions for formation of lubricant films were investigate to evaluate wear properties of graphite materials. The repeated procedure for the formation of wear particles and lubricant films, and the dissipation of lubricant films was estimated the wear mechanisms with changes of wear depth. Therefore the lubricant film of graphite seal was generated by adhesion of wear particles on the worn surface and it was very useful in wear characteristics.

• Journal of the Korean Society for Railway
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• v.18 no.5
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• pp.410-418
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• 2015

A slider of the pantograph undergoes uneven and abnormal wear due to sliding contact with the catenary. In the case of rain, the loss of lubricant increases the frictional resistance for the reciprocating motion between the catenary and the slider, accelerating local wear. The slider in the winter should have good wear resistance, which can be achieved through alloy design. Uneven and abnormal wear were not observed in the results of a driving test using a wear resistant slider. It was found that the increased density of the slider enhanced the corrosive effects of Fe-Ti, preventing the occurrence of abnormal wear by maintaining the wear and arc resistance in the rainy season. Also, mechanical and electrical wear did not affect the composition of the slider, and this improved the wear resistance. Inaddition, the slider was applied to an entire train and was tested during driving; ananalysis of the correlation of the catenary was performed, including during the rainy season and the winter season.

• Restorative Dentistry and Endodontics
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• v.45 no.3
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• pp.33.1-33.10
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• 2020

Objectives: This study was conducted to evaluate the effects of traditional and contracted endodontic cavity (TEC and CEC) preparation with the use of Reciproc Blue (RPC B) and One Curve (OC) single-file systems on the amount of apical debris extrusion in mandibular first molar root canals. Materials and Methods: Eighty extracted mandibular first molar teeth were randomly assigned to 4 groups (n = 20) according to the endodontic access cavity shape and the single file system used for root canal preparation (reciprocating motion with the RCP B and rotary motion with the OC): TEC-RPC B, TEC-OC, CEC-RPC B, and CEC-OC. The apically extruded debris during preparation was collected in Eppendorf tubes. The amount of extruded debris was quantified by subtracting the weight of the empty tubes from the weight of the Eppendorf tubes containing the debris. Data were analyzed using 1-way analysis of variance with the Tukey post hoc test. The level of significance was set at p < 0.05. Results: The CEC-RPC B group showed more apical debris extrusion than the TEC-OC and CEC-OC groups (p < 0.05). There were no statistically significant differences in the amount of apical debris extrusion among the TEC-OC, CEC-OC, and TEC-RPC B groups. Conclusions: RPC B caused more apical debris extrusion in the CEC groups than did the OC single-file system. Therefore, it is suggested that the RPC B file should be used carefully in teeth with a CEC.

• Journal of Biosystems Engineering
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• v.34 no.2
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• pp.114-119
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• 2009

Field test was conducted to investigate primary factors reducing rapeseed harvesting using a reciprocating cutter-bar of combine. The results showed that the correlation between crop moisture content and yield loss had a U-type, which indicated that the yield reduction increased at too high and too low crop moisture contents. The proper ranges of crop moisture contents were 27${\sim}$35%, 21${\sim}$56%, and 62${\sim}$73% in case of grain, pod and stem, respectively. Crop moisture content was negatively correlated with header loss, but positively correlated with threshing loss. In contrary, stem moisture content showed positive correlations with total loss, threshing loss and separation loss. Working speed was positively correlated with header loss. Total flow rate, pod flow rate and stem flow rate were highly correlated with threshing loss and separation loss. However, grain flow rate did not show any correlation with total loss. According to the principal component analysis, two principal components were derived as components with eigenvalues greater than 1.0. The contribution rates of the first and the second components were 52.7% and 38.9%, which accounted for 91.6% of total variance. As a contributive factor influencing total loss of rapeseed mechanical harvesting, a crop moisture content factor was greater than a crop flow rate factor. The stepwise multiple regression analysis for total loss was conducted using crop moisture content factor, crop flow rate factor and coefficient. However, the model did not show any correlation among independent and dependent factors ($R^2$=0.060).

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.738-747
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• 2006

The friction behaviour of Si-wafer, diamond-like carbon (DLC) and two self-assembled monolayers (SAMs) namely dimethyldichlorosilane (DMDC) and diphenyl-dichlorosilane (DPDC) coated on Si-wafer was studied under loading conditions in milli-newton (mN) range. Experiments were performed using a ball-on-flat type reciprocating micro-tribo tester. Glass balls with various radii 0.25 mm, 0.5 mm and 1 mm were used. The applied normal load was in the range of 1.5 mN to 4.8 mN. Results showed that the friction increased with the applied normal load in the case of all the test materials. It was also observed that friction was affected by the ball size. Friction increased with the increase in the ball size in the case of Si-wafer. The SAMs also showed a similar trend, but had lower values of friction than those of Si-wafer In-terestingly, for DLC it was observed that friction decreased with the increase in the ball size. This distinct difference in the behavior of friction in DLC was attributed to the difference in the operating mechanism. It was observed that Si-wafer and DLC exhibited wear, whereas wear was absent in the SAMs. Observations showed that solid-solid adhesion was dominant in Si-wafer, while plowing in DLC. The wear in these two materials significantly Influenced their friction. In the case of SAMs their friction behaviour was largely influenced by the nature of their molecular chains.

• Tribology and Lubricants
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• v.35 no.1
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• pp.30-36
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• 2019

The tribological properties of paper-based friction materials are crucial to the performance of a wet clutch system. In this work, the friction and wear characteristics of a paper-based friction material in boundary lubrication state was experimentally investigated using a pin-on-reciprocating tribotester under various normal forces and temperatures. It was found that the wear rate of the friction material increased from $5.8{\times}10^{-6}mm^3/N/cycle$ to $5.5{\times}10^{-5}mm^3/N/cycle$ after 1,700 cycles of testing at $80^{\circ}C$ as normal force increased from 2 N to 7 N. The friction coefficient was also found to increase from 0.135 to 0.155 with increasing normal force from 2 N to 7 N. The increase in contact pressure with increasing normal force may be responsible for these results. In addition, as temperature increased from $20^{\circ}C$ to $80^{\circ}C$, the wear rate of the friction materials increased from $2.0{\times}10^{-5}mm^3/N/cycle$ to $3.6{\times}10^{-5}mm^3/N/cycle$ while the friction coefficient decreased from 0.163 to 0.146. This result may be associated with the decrease in the hardness of friction materials with increasing temperature. Furthermore, plastic deformation on the friction materials was mainly observed after the test. The outcome of this work may be useful to gain a better understanding of the tribological properties of friction materials, and therefore can contribute to the development of friction materials with enhanced performance for wet clutch systems.

• Tribology and Lubricants
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• v.35 no.3
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• pp.183-189
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• 2019

The driver seat of an automobile is in direct contact with the driver and provides the driver with a safe and comfortable ride. The seat consists of a frame, a rail, and many recliners. In recent years, strength and operating force measurement testing of the recliner have become vital for designing car seats. However, performance evaluation requires expensive testing equipment, numerous seat products, and considerable time. Therefore, the trend is to reduce experimentation through interpretation. This study examines the lubrication of solid lubricant for automotive seat recliners and confirms the friction and wear performance. In this study, the lubrication behavior of solid lubricants for car seat recliners is investigated to ascertain the friction and wear performance and to provide accurate values for the strength analysis. The friction material consists of a pin and a plate made from steel, which is widely used in recliners. The friction and wear under lubrication conditions are measured by a reciprocating friction wear tester. The friction coefficient is obtained according to the load and speed. Based on the obtained results, it is possible to achieve a reduction in the error of the test value and the analysis by providing the friction coefficient and wear of the lubricant. The results can be applied to the analysis of automobile seat design.

• Tribology and Lubricants
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• v.37 no.1
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• pp.25-30
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• 2021

The surface texture produced via surface texturing is an important approach for controlling the tribological behavior of friction behavior of mechanical devices. The purpose of this study is to investigate the effect of grooves generated via ultrasonic nanocrystal surface modification (UNSM) technology on the tribological performance of AISI 4150 steel against stainless steel 316L. In the study, tribological tests are performed under two different regimes, namely mixed and hydrodynamic lubrication, by varying the applied normal load and reciprocating speed during the tests. According to the test results, the friction coefficient decreases as static load (10 N, 30 N, and 50 N) of UNSM technology increases in the mixed lubrication regime. Conversely, the friction coefficient increases as the static load (10 N, 30 N, and 50 N) of UNSM technology increases in the hydrodynamic lubrication regime. Hence, the results indicate that micro-grooves generate hydrodynamic pressure in the outlet, which increases the oil film thickness between the two mating surfaces. This potentially leads to a reduction in friction in the mixed lubrication regime due to the prevention of contact of asperities and debris. However, the results indicate an adverse effect in the hydrodynamic lubrication regime. In this regard, additional experiments should be performed to investigate the effect of grooves generated by UNSM technology at varying conditions on the friction behavior of AISI 4150 steel, which in turn can be controlled by the generated pressure and oil film thickness at the contact interface.