• Proceedings of the KSR Conference
• /
• 2009.05b
• /
• pp.585-592
• /
• 2009

The performance of screw compressor depends on lots of design parameters of rotor profile, such as length of seal line, wrap angle, blow hole, suction and discharge port size, number of rotor lobe, etc. The optimum rotor profile makes it possible to increase the compression efficiency with low energy consumption, and to minimize the loss of power. In this research, a new rotor profile design and performance analysis are done by computer simulation. It is expected that the volumetric efficiency is improved because the internal leakage is reduced due to the minimization of blow hole and clearance, and the stiffness of rotors is increased due to the reduction of length to diameter ratio. Also, the specific power consumption will be secured for use ranging from low to high operation speed.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.10 no.1
• /
• pp.80-86
• /
• 2011

This study compared and analyzed manual tapping and automatic tapping regarding tapping process characteristics of titanium hard-to-cut-material. Tapping process characteristics of titanium hard-to-cut-material are evaluated as the quality of a screw, wear of a tap, economic analysis, and cycle time etc. The type of screw threads after manual tapping is formed as an irregular type of screw threads, and perfect screw threads are created after automatic tapping. In addition, the chip type after manual tapping process is formed as the discontinuous chip due to work hardening, and the powder type of chip after automatic tapping process is created. In terms of cycle time, an automatic tapping process is shortened by 70% compared to manual tapping process. Insert tip wear of an automatic tapping shown in the process of 5-hole tapping is not found, but hand tap wear for finish cutting is most severe.

• Journal of Power System Engineering
• /
• v.15 no.4
• /
• pp.37-41
• /
• 2011

This paper introduces the special eddy current sensor and its characteristic for bolt hole defect evaluation in gas turbine rotor. In the past, Fluorescent penetration inspection method was used for qualitative defect evaluation in gas turbine rotor bolt hole. This method can defect the bolt hole defect but can not evaluate the defect size. Nowadays, eddy current method is used quantitative defect evaluation due to advanced sensor design technology. And eddy current method is more time and cost saving than the old method. We developed bolt shape eddy current sensor for the rotor bolt hole defect detection and evaluation. The eddy current sensor moves to the bolt hole guided by screw nut and detects the defect on the bolt hole. The bolt hole mock-up and artificial defects were made and used for the signal detection & resolution analysis of eddy current sensor. The results show that signal detection capability is enough to detect 0.2 mm depth defect. And the resolution capability is enough to differentiate 02, 0.5, 1.0 and 2.0 mm depth defect.

• Journal of the Korean Society for Precision Engineering
• /
• v.30 no.3
• /
• pp.254-259
• /
• 2013

Ball screw system is widely used as a precision mechanical linear actuator that translates rotational motion to linear motion for its high efficiency, great stiffness and long life. Recently, according to the requirements of high accuracy and stiffness, the pre-load on the ball screw which means of remove the backlash in the ball screw is usually used. Because of the preload which means the frictional resistance between the screw and nut, becomes a dominating heat source and it generates thermal deformation of ball screw which is the reason for low accuracy of the positioning decision. There are several methods to solve the problem that includes temperature control, thermal stable design and error compensation. In the past years, researchers focused on the error compensation technique for its ability to correct ball screw error effectively rather than the capabilities of careful machine design and manufacturing. Significant amounts of researches have been done to real-time error compensation. But in this paper, we developed a series of cooling methods to get thermal equilibrium in the ball screw system. So we find the optimum cooling type for improving positioning error which caused by thermal deformation in the ball screw system.

• Korean Journal of Agricultural Science
• /
• v.5 no.1
• /
• pp.29-34
• /
• 1978

In order to improve atomization of droplet of sprayers, gun-type nozzle equipped with swirl screw which could increase tangential velocity had been used in this study. The results obtained were as follow: The larger diameter of atomized droplet was, the longer it reached. Tile atomizing phenomenon while using swirl screw in the nozzle was more efficient. There was little difference of travelling distance in the both nozzles when the small diameter of disk hole was used, but thetravlling distance of the nozzle with swirl screw was evidently getting shorter with the increase of the hole diameter compared to that of the nozzle without swirl sorew. The size of sprayed particles was getting smaller owing to the phenomenon of air movement the one to two meters travelling distance of droplet from maximum travelling point.

• Journal of Korean Neurosurgical Society
• /
• v.49 no.6
• /
• pp.351-354
• /
• 2011

Objective : This investigation was conducted to evaluate a new, safe entry point for the C2 pedicle screw, determined using the anatomical landmarks of the C2 lateral mass, the lamina, and the isthmus of the pars interarticularis. Methods : Fifteen patients underwent bilateral C1 lateral mass-C2 pedicle screw fixation, combined with posterior wiring. The C2 pedicle screw was inserted at the entry point determined using the following method : 4 mm lateral to and 4 mm inferior to the transitional point (from the superior end line of the lamina to the isthmus of the pars interarticularis). After a small hole was made with a high-speed drill, the taper was inserted with a 30 degree convergence in the cephalad direction. Other surgical procedures were performed according to Harm's description. Preoperatively, careful evaluation was performed with a cervical X-ray for C1-C2 alignment, magnetic resonance imaging for spinal cord and ligamentous structures, and a contrast-enhanced 3-dimensional computed tomogram (3-D CT) for bony anatomy and the course of the vertebral artery. A 3-D CT was checked postoperatively to evaluate screw placement Results : Bone fusion was achieved in all 15 patients (100%) without screw violation into the spinal canal, vertebral artery injury, or hardware failure. Occipital neuralgia developed in one patient, but this subsided after a C2 ganglion block. Conclusion : C2 transpedicular screw fixation can be easily and safely performed using the entry point of the present study. However, careful preoperative radiographic evaluation, regardless of methods, is mandatory.

• Journal of the Korean Society for Precision Engineering
• /
• v.33 no.8
• /
• pp.669-681
• /
• 2016

Mechanical designers often make mistakes that result in unwanted over-constraints, causing difficulty in assembly operations and residual stress due to interference among parts. This study is concerned with detection and elimination of over-constraints. Screw theory is a general method that is used for constraint analysis of an assembly and motion analysis of a mechanism. Mechanical assemblies with plane-plane, pin-hole, and pin-slot constraint pairs are analyzed using screw theory to illustrate its utility. As a real-world problem, a ball valve design is analyzed using the same method, and several unwanted over-constraints are detected. Elimination measures are proposed. Nominal dimensions of some parts are adjusted, and dimensions and tolerances of the pins and holes are modified using the virtual condition boundary concept. The revised design is free of over-constraints. General procedure for applying screw theory to constraint analysis is established and demonstrated; it will contribute to improving quality of assembly designs.

• The Journal of Korean Academy of Prosthodontics
• /
• v.50 no.4
• /
• pp.318-323
• /
• 2012

Implant prostheses were classified into screw-retained prosthesis and cement-retained prosthesis by their method of retaining, and there is screw and cement retained implant prosthesis (SCRP) which has been made reflecting the strengths of these two. The advantages of the SCRP technique are easy retrievability and passive fit of implant prostheses. However, the occlusal screw holes of implant prostheses can be thought as a disadvantage with respect to esthetics and occlusion. Inappropriately positioned implants also limited the use of the SCRP technique. The present study is reporting about the case where nine implants (US II, OSSTEM, Seoul, Korea) were placed in maxilla and eight in mandible respectively in fully edentulous patients. Then, the cement-retained prosthesis was applied for the part in which the screw hole positioned improperly, and screw-retained prosthesis for properly positioned implants so that the combined screw-cement prosthesis has been produced where the satisfying result has shown in both function and esthetics. Three-year follow-up has been done for the patient.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.16 no.3
• /
• pp.38-44
• /
• 2017

The technology of electrical discharge tap machining may be appropriate for making thread out of highly brittle material. Especially, it is very difficult to machine tap with the traditional method if the brittle material has been hardened by quenching. In this study, the shape of electrical discharge blind hole tap machining was analyzed by discharge time, discharge current, and the flushing hole condition after quenched the tool steel of STD11 has discharged the tap shape with a screw-shaped copper(Cu) electrode. An experimental design was planned and analyzed by Taguchi robust experimental design. The result showed that the shape of the blind hole discharge tap was influenced by the flushing hole, discharge time, and discharge current. The most important factor of the processing conditions was found to be the discharge current. When blind hole EDM with a copper electrode with a flushing hole was conducted, the discharged shape was found to be smooth and the angle of the discharged tapped thread was also found to be close to the thread angle of $60^{\circ}$. As the values of discharge time and discharge current increased, the EDMed surface coarsened due to the increase of the single discharge energy and the shape of the thread collapsing.

• Journal of the Korean Arthroscopy Society
• /
• v.6 no.1
• /
• pp.60-63
• /
• 2002

Purpose : The purpose of this study was to introduce new femoral fixation technique using a cross-pin and a bioabsorbable interference screw in hamstring ACL reconstruction. Method : Semitendinosus and gracilis were harvested for quadrapled graft. After tibial tunnel had been made, femoral tunnel was made 35 mm in depth. Then the graft passed through the tunnels. Cross-pin was fixed through the drill hole which had been made through upper sleeve of the Rigidfix system. While pulling the graft, bioabsorbable interference screw was fixed through the anteromedial portal. Conclusion : We introduced the new femoral fixation technique using a cross-pin and a bioabsorbable interference screw as a good method with high fixation strength and tight graft-bone contact.