• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.14 no.1
• /
• pp.51-56
• /
• 2015

This paper presents an investigation of abnormal wear of a contact jig between a nail and a nail fixture in electric resistance welding. To perform an analysis on the abnormal wear phenomenon, several methods are provided. Based on the theory of electric resistance welding, are analyzed. Using microscopic analysis, surface craters are observed. In the measurement of the electric current flow in the nail fixture, the current flow distribution is measured. From several analyses, the cause of abnormal wear in the contact jig is measured using the electric discharge of high current density at the inflow point of the electric supply to the nail fixture. An alternative shape for normal wear is proposed.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 1999.02a
• /
• pp.10-13
• /
• 1999

For large scale applications of high temperature superconductor(HTS) such as transmission cables, motors and generators, long length of flexible HTS conductors is required. Currently, HTS tape that is capable of being fabricated in long length by industrial processes is the Bi-2223 HTS tape. In this study, we fabricated 19 filamentary Bi-2223($Bi_{1.8}$$Pb_{0.4}$$Sr_{2}$$Ca_{2}$$Cu_{3}$$O_{10+X}$) HTS tape with 100m length by PIT(Powder In Tube) process. Critical current(Ic) of this long length tape was measured 18.5 A at 77 K, self field and short sample Ic is 32.5 A at the same condition. Critical current of 100m length tape was decreased by about 1/3 compared to that of short tape. This was mainly resulted from the increase of non homogeneity in oxide layer.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2001.02a
• /
• pp.104-107
• /
• 2001

Racetrack coils are used in many areas of superconductivity applications such as generators, motors, maglev, wiggler magnets and so on. Especially now a days a few advanced nations including U.S., Japan are developing high temperature superconducting(HTS) wire which has better performance than low temperature superconducting(LTS) wire. Most of HTS wires such as BSCCO-2223 are manufactured with PIT(Power In Tube) process, so the shape of the wire looks like tape different from LTS wire with round cross-sectional appearance like normal conductors. Generally HTS racetrack coils are composed of a few partial double-pancake colis and then the double-pancakes are jointed each other according to their applications.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2001.02a
• /
• pp.159-162
• /
• 2001

A Stirling cryocooler is relatively compact, reliable, commercially available, and uses helium as a working fluid. The FPFD stirling cryocooler consists of two compressor pistons driven by linear motors which makes pressure waves and a pneumatically driven displacer piston with regenerator. It is the most suitable design for a mechanical cryocooler utilized in night vision environment. In order to get optimum operating frequency, natural frequency of piston and displacer, optimum phase angle between piston and displacer, cooling capacity, performance tests of the Stirling cryocooler by the frequency characteristics were performed.

• Progress in Superconductivity and Cryogenics
• /
• v.3 no.2
• /
• pp.55-61
• /
• 2001

A free piston and free displacer (FPFD) Stirling cryocooler for cooling infrared and cryo-sensor is currently under development at korea Institute of Machinery & Materials. The FPFD Stirling cryocooler consists of two compressor pistons driven by linear motors which make pressure waves and a pneumatically driven displacer piston with regenerator. It is the most suitable design for a mechanical cryocooler utilized in night vision environment In this study, performance test of the Stirling cryocooler with different length of the split tube and operating frequency were performed to get characteristics of the cryocooler.

• Progress in Superconductivity and Cryogenics
• /
• v.3 no.2
• /
• pp.62-68
• /
• 2001

This paper presents manufacturing process and test results in the optimum pressure and operating frequency for the free piston free displacer(FPFD) Stirling cryocooler designed and manufactured by Korea Institute of Machinery &Materials (KIMM). FPFD Stirling cryocooler is currently under development uses opposed linear motors to drive opposed pistons . The performance of FPFD Stirling cryocooler is evaluated as a function fo charging pressure and operating frequency. In general as the operating frequency of the compressor is increaed but natural frequency of the displacer is almost constant. The prototype has achieved no load temperature of 49K and cooling capacity of 0.5W at 7.2K.

• Progress in Superconductivity and Cryogenics
• /
• v.3 no.2
• /
• pp.21-26
• /
• 2001

Superconducting synchronous generators and motors are designed based on 2 dimensional electro-magnetic approach. In the case of generator, if the machine output rating and terminal voltage are decided the armature rating current will be decided automatically according to its power factor. However, in the case of motor, if the output rating is given with [hp] or [kw] units, the armature terminal voltage and current are not decided directly because the machines armature input power and mechanical output are different by way of losses. So in order to calculate the armature current more accurately. the machine losses must be included in the design procedure. In this paper the machine loss of superconducting motor are analyzed and used for decision of the armature input power and current. Moreover, the differences of voltage equations between superconducting synchronous generator and motor are considered.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2001.02a
• /
• pp.33-36
• /
• 2001

A free piston and free displacer(FPFD) Stirling cryocooler for cooling infrared and cryo-sensors is currently under development at KIMM(Korea Institute of Machinery & Materials). The FPFD Stirling cryocooler employs 1) the Stirling cycle for refrigeration, 2) linear motors for driving the cryocooler, 3) spring and gas support systems, and 4) fine gap for clearance seals. It is the most suitable design for a mechanical cryocooler utilized in night vision environment. The experimental results show KIMM-E1 Stirling cryocooler (with expander manufactured by KIMM) has the higher cooling power and faster response time at optimum charging pressure.

• Progress in Superconductivity and Cryogenics
• /
• v.1 no.2
• /
• pp.15-19
• /
• 1999

For large scale applications of high temperature superconductor (HTS) such as transmission cables, motors and generators, long length of flexible HTS conductor is required. Currently, Bi-2223 HTS tape is capable of being fabricated in longer than 100 m length by industrial processes. In this study, we fabricated 100 m 19 filamentary Bi-2223 ($Bi_{1.8}Pb_{0.4}Sr_2Ca_2O_{10+x}$) HTS tape by PIT (Power in Tube) process. Critical current(IC) of this long length tape was measured 18.5 A at 77K, self field. Critical current of 100 m length tape was mainly resulted from the increase of inhomogeneity in oxide from the increase of inhomogeneity in oxide layer. Engineering critical current (Je=Ic/total tape cross-section area) that is important factor for practical applications and fabrication cost was measured 2.2 kA/cm2.

• Publications of The Korean Astronomical Society
• /
• v.13 no.1 s.14
• /
• pp.85-98
• /
• 1998

In this paper we describe MS-TCS, the telescope control system which was developed in Korea Astronomy Observatory. MS-TCS can control an equatorial type telescope equipped with stepping motors and incremental type optical encoders. MS-TCS consists of (1) POINT_TEL which is the program roning in a PC and (2) TCS-196 which is the electroics board to control the telescope. The communication between the PC and TCS-l96 is done through RS-232 or RS-422 serial line. MS-TCS can control the secondary mirror and dome. It also provide network function using TCP/IP for remote control of the telescope. MS-TCS is suitable for controlling medium to small size telescope for research and education.