• Tribology and Lubricants
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• v.29 no.4
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• pp.218-222
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• 2013

Water-lubricated ball bearings consist of rolling elements, an inner raceway, an outer raceway, a retainer, and an operating lubricant. In the water environment, ball bearings are required to sustain high loads at high speeds under poorly lubricated conditions. For the analysis of bearing behavior, friction torque is considered as the main factor at various flow rates, rotating speeds, and roughnesses between the rolling element and raceways. When the bearing operates at high rotating speeds, the friction torque between the raceway and rolling elements increases considerably. This frictional torque is an important factor affecting bearing reliability and life cycle duration. For understanding the flow conditions in the inner part of the bearing, this study focuses on the flow around the rotating and revolving rolling elements. A simple model of fluid flow inside the ball bearing is designed using the commercial CFD program ANSYS.

• Journal of Powder Materials
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• v.8 no.1
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• pp.42-49
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• 2001

Ti-50Ni(at%) and Ti-40Ni-10Cu(at%) alloy powders have been fabricated by ball milling method, and their microstructure and phase transformation behavior were investigated by means of scanning electron microscopy/energy dispersive spectrometry, differential scanning calorimetry (DSC), X-ray diffractions and transmission electron microscopy. In order to investigate the effect of ball milling conditions on transformation behavior, ball milling speed and time were varied. Ti-50Ni alloy powders fabricated with the milling speed more than 250 rpm were amorphous, while those done with the milling speed of 100rpm were crystalline. In contrast to Ti-50Ni alloy powders, Ti-40Ni-10Cu alloy powders were crystalline, irrespective of ball milling conditions. DSC peaks corresponding to martensitic transformation were almost discernable in alloy powders fabricated with the milling speed more than 250 rpm, while those were seen clearly in alloy powders fabricated with the milling speed of 100 rpm. This was attributed to the fact that a strain energy introduced during ball milling suppressed martensitic transformation.

• Journal of the Korean Society of Industry Convergence
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• v.22 no.4
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• pp.435-445
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• 2019

Ball screw drives are widely used in industry, and many studies have been devoted on precise, fast and robust control of ball screw drives. In this study, a novel position control algorithm for ball screw drives is proposed, which consist of a PD controller, a friction feedforward and a disturbance observer. The dynamics and the position error of such controller are analyzed to establish an error model, which can be used to predict the resulting position error of the given desired trajectory. Using the proposed error model, the desired trajectory can be modified so that the predicted position error can be compensated in a feedforward manner. The proposed algorithm does not require the model of the system for the error prediction, and thus can be easily applied to conventional control systems. The performance of the system is verified through simulations and experiments.

• Journal of The Korean Society of Integrative Medicine
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• v.11 no.1
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• pp.149-157
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• 2023

Purpose : Genu varum is a condition characterized by a wider than normal gap between. This may be due to muscle weakness caused by poor posture, lifestyle, or lack of exercise. This study aimed to compare the effects of ball-based squats and narrow squats on muscle thickness, Q-angle, and the gap between the knees, in order to assess the potential for improving this condition. Methods : Twenty six adult participants with genu varum were randomly assigned to either a ball-based squat group (n=13) or a narrow squats group (n=13). Both groups performed their respective exercises three times weekly for 4 weeks. The data was analyzed using paired t-tests to compare pre- and post- intervention measurements within each group, and independent t-test was used to compare the two groups. Results : Both groups showed significant improvement in the thickness of the vastus lateralis and medialis, and rectus femoris muscles, as well as a significant decrease in the gap between the knees (p<.05). However, there was no significant difference in Q-angle variation between the two group. Furthermore, there was no significant differences in the Q-angle, gap between the knees, and muscle thickness variation between both groups. Conclusion : The results suggest that both ball-based squats and narrow squats are effective in improving muscle thickness and reducing the gap between the knees in adults with genu varum. However, there was no significant difference between the two types of squats in terms of their effects on the Q-angle. These findings highlight the potential for exercise interventions to address this common postural issue.

• International Journal of Reliability and Applications
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• v.17 no.1
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• pp.51-63
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• 2016

Stress function of ball bearing is function of multiple stochastic factors and this system is so complex that analytical expression for reliability is difficult to obtain. To address this pressing problem, in this article, we have made an attempt to approximate system reliability of this important item based on reliability bounds under the stress strength setup. This article also provides level of error of this item. Numerical analysis has been adopted to show the closeness between the upper and lower bounds of this item.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.6
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• pp.753-760
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• 2007

For protection of the cylinder wall of the ball mill for grinding raw ore. the inner side of the cylinder is covered with rubber liner. The rubber is easily worn down because the rubber relatively soft compared with raw ore. So the rubber liner in the ball mill cylinder must be replaced almost every year and the cost for replacing rubber liner formidable. In this paper, for reducing or excluding the cost of replacing rubber liner the basalt liner is designed. The basalt materials are generally harder than raw ore and the basalt liner in the ball mill does not wear down and so it can be used almost permanently. The concave surfaces are made on the liner of the ball mill and the liner in the cylinder wall plays also the role of raising the steel balls mixed in the raw ore. The section profiles of the concave surface have an important effect on the performance of the ball mill. The deep concave grooves raise the steel balls to high levels and give the large potential energy to the steel balls impacting to the raw ore. But if the concave grooves are too deep. the steel balls raised too high by the concave grooves fly along the parabolic path and reach to the other side of cylinder wall and so the steel balls do not play the roles of grinding the raw ore. The forces acting to a steel ball in a concave groove of the cylinder liner are also analyzed in this paper. The formulas calculating the height and the impact point of the steel ball are introduced and presented. Based to these formulas, the optimum section profiles of the basalt liner are presented.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.9
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• pp.63-69
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• 2021

This study aims to determine the flow characteristics of a one-inch small ball valve and glove valve used in industrial plants. The flow was changed through an experimental equipment, and the internal flow characteristics of the valves were compared. Considering the pressure drop, the decrease in the slope of the ball valve based on the degree of the valve opening was relatively greater than that of the glove valve; further, the slope of the glove valve was gentle while the pressure drop was high. The flow velocity of the ball valve remains consistent after the valve was opened by 70%, whereas the flow velocity of the glove valve constantly increased. The valve loss factor of the ball valve was relatively low compared with that of the glove valve. When the valve was opened by 20%, which is the beginning stage of the valve opening, the valve loss factor of the ball valve was high and gradually became low. This is a structural problem of the ball valve, and the loss factor is significant because the flow path installed at the ball valve has a considerably small area. However, the overall loss factor of glove valve is high because it has a complicated structure of flow path.

• PNF and Movement
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• v.18 no.3
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• pp.343-350
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• 2020

Purpose: The purpose of this study was to determine how a shoulder complex stabilization exercise affects ball control and ball speed in elementary school baseball players with an instable scapula. Methods: The subjects of the study were 16 baseball players attending S elementary school in Kwangju Metropolitan City. A shoulder complex stabilization exercise was conducted three times per week for one hour for four weeks. Then, the participants were divided into a scapular instability group or stability group based on their lateral scapular slide test scores. The measurement tool was measured using the target, the ball speed tester (PR1000-BC). All inspections were measured before and after the mediation period to examine the change in the subjects according to the mediation period. Results: As a result of measuring ball control, there was a statistically significant difference in the variation over time (p < 0.05), and there was no statistically significant difference in the interaction between time and group (p > 0.05). As a result of the test of effectiveness between subjects, there was no statistically significant difference found among the groups (p > 0.05). In terms of ball speed, there was no statistically significant difference found in the variation over time (p > 0.05) as well as in the interaction between time and group (p > 0.05). In terms of the effectiveness between subjects, there was no statistically significant difference found among the groups (p > 0.05). Conclusion: It was found that the shoulder complex stabilization exercise could improve ball control for elementary school baseball players. It is believed that this will help prevent and solve possible sport damages experienced during training or competitions, thereby helping athletes use training methods to improve their exercise capacity and continue their careers.

• The Journal of the Korea Contents Association
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• v.22 no.10
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• pp.47-58
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• 2022

This research presented development contents for application of realistic content approach study that can experience T-ball sports used in regular physical education classes at indoor space with screen. The scope of application can be used for ball sports training in virtual reality sports room of elementary and junior high schools. The approach process presents an appropriate approach system for sustainable training education which is to improve T-ball sports training to target users through consultation-based collaboration with sports experts and T-ball leaders, focusing on basic training content of T-ball textbooks. In other words, the training mode was designed to induce immersion in T-ball sports classes and provide natural basic training for students at elementary schools rather than simply experience-based realistic content. The developed training content provided basic attack training according to weekly differentiated curriculum, and the approach process of training mode by difficulty level was presented to allow the user to improve the training by the degree of difficulty. In addition, the match mode approach process that reflects the game rules of T-ball sports was presented. This study can be presented as a reference production case that can be used to improve basic training and physical exercise of ball sports for industries related to development of realistic content.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1664-1667
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• 2005

The main function of Ball-Stop part is to operate power shift for vehicle with more than 5 ton when a driver changes gear using suitable force. This paper presents the implementation of a DFSS(Design For Six Sigma) for robust design of Ball-Stop part of power shift. The factors influencing Ball-Stop part performance is derived to find control factor. Based on this factor, contact force between head and detent pin analysis is performed to get optimal factor is analyzed and compared with contact force test result to verify reliability of design. This makes clear the reason why the proposed one is necessary and the role of DFSS.