Effect of Injection Parameters on Warpage and Sink Index of High-Gloss Injection Parts

High-gloss injection molding technology is also called rapid cool and heat injection technology which can be used to eliminate weldmark on the surface of plastic parts, and improve the surface glossiness. However, the warpage, sink index and volume shrinkage of the parts are considered difficult to solve by using this technology. Reasons that cause the warpage and sink index of the parts were discussed in this paper firstly. Then, by using a LCD panel produced in practical injection process as an example, through orthogonal experimental design and finite element simulation, this paper discusses the effects of the injection molding parameters such as mold temperature, melt temperature etc. on warpage and sink index of the parts. The results are of great significance to help to set practical process parameters and assure the part quality in injection process.

Miniature Joule–Thomson (JT) Cryocoolers for Propellant Management

Boil-off of cryogenic propellants is an issue of concern in any space mission. There could be boil-off of liquid propellants in the cryogenic storage tank, transfer line or in the space vehicle external tank itself due to heat leak. The current insulation technology uses a multilayered thermal protective coating of 304 Stainless Steel and Welded Invar, which allows the propellant to withstand the extreme internal and external temperature variations generated during pre-launch, launch, and flight operations, which does not provide for zero boil-off (ZBO). Usage of a cryocooler to prevent propellant boil-off would potentially reduce the launch costs. Owing to its attractive features like simplicity, compactness and rapid cool-down characteristics, an innovative concept of using Joule-Thomson (JT) cryocoolers for prechilling, densification and ZBO applications of cryogenic propellants is focused upon. The liquid oxygen propellant transfer line at NASA Kennedy Space Center is considered for demonstration of the above concept. Various thermodynamic cycle parameters are optimized for the cryocooler to make the demonstration possible. Cycle optimization is done also taking into account the feasibility to develop some crucial components for the JT cryocooler like a micro channel heat recuperator and cold heads. Current state of developments in the heat exchanger is briefly described. Some advantages of using miniaturized cryocoolers in launch vehicle operations are also discussed.

Simulations of the Pressurizer Safety Valve Stuck Open Accident for the Development of the Accident Sequences in the Low Power/Shutdown PSA

We have simulated the pressurizer safety valve (PSV) stuck open accident in a Korea Standard Nuclear power Plant (KSNP). The purpose of the simulation is 1) to investigate the mitigation function available for the important accident sequence having considerable core damage frequencies and 2) to support the determination of the accident sequences with relevant success criteria for the Low Power Shutdown (LP&S) Probabilistic Safety Assessment (PSA). The analysis showed that the PSV stuck open accident in a KSNP has both the characteristics of a small and medium LOCA in the sense that the primary system pressure decreases slowly but the break flow is sufficient enough to uncover the core in the early stages of the accident. we found that, in the accident sequence of a high pressure safety injection (HPSI) failure, core damage could occur earlier before reaching the actuation set-pressure of the safety injection tank (SIT) provided that no operator action is considered. We also performed the simulation of a rapid cool-down by a steam generator for this accident sequence to investigate the feasibility of the SIT injection before core damage occurs. From these simulations, if the operators start the rapid cool-down operation within 15 minutes, it was shown that SIT could be injected and core damage could be prevented if the subsequent Low Pressure Safety Injection (LPSI) and Shutdown Cooling System (SCS) is successfully operated.

Development and Testing of a Small-Scale Collins Type Cryocooler

Future spacecraft cooling and sensing systems will require advanced multi-stage cryocoolers capable of providing continuous cooling at multiple temperature levels ranging from 10K to 95K. A multi-stage 10K cryocooler is under development that applies modern microelectronic sophistication to achieve high efficiency in a reliable, compact design. The cryocooler is based upon a novel modification of the Collins cycle, a cycle commonly used in many high-efficiency terrestrial cryogenic machines. Innovations of the design include floating piston expanders and electromagnetic smart valves, which eliminate the need for mechanical linkages and thereby reduce the input power, size, and weight of the cryocooler in an affordable modular design. The floating piston expander and smart valves have been successfully developed in room temperature experiments using a series of proof-of-concept component prototypes. These experiments have resulted in a new warm-end configuration with improved expansion power dissipation and a new cryogenic valve design that reduces expander clearance volume and improves cold-end integration. A sophisticated LabView based control algorithm was developed over the course of the room temperature experiments that enables electronic control of the expansion cycle. Software based control will enable variable valve timing and adaptive control logic. This will result in a cryocooler with rapid cool-down and transient response capabilities as well as the ability to operate at high efficiency at arbitrary steady state load points. In parallel to this effort, a manufacturing method was developed to enable production of very long continuous lengths of small bore finned tubing. This tubing is used in the highly effective recuperative heat exchanger associated with each stage of the cryocooler. An engineering prototype has been designed that integrates the floating piston expander and recuperative heat exchanger as a functional cryocooler. The engineering prototype has been assembled and is currently undergoing development testing. This paper will present the results of the room temperature component development testing, the design of the engineering prototype, the results of initial engineering prototype development testing, and the direction of future development.

Cooling Rate Effect on Post Cure Stresses in Molded Plastic IC Packages

Residual stresses during cool down process after curing are evaluated on the basis of thermoviscoelastic finite element analyses with material properties dependent on both time and temperature. Temperature distributions in packages are predicted by solving the heat conduction equations. The effects of cool-down history on thermomechanical responses of a lead-on-chip (LOC), thin small outline package (TSOP) are investigated. Three linear cool down temperature histories are considered. Numerical results show that residual stresses in a LOC TSOP are significantly influenced by the manufacturing temperature history. Residual stresses in plastic packages are strongly time-temperature dependent due to the thermoviscoelastic behavior of molding compounds. Substantial residual stresses arise when a LOC TSOP has cooled to room temperature and rapid cool down permits small viscoelastic effects.

CLEAN AND OXYGEN-COVERED Cu3Au(110): A SURFACE STRUCTURE INVESTIGATION WITH STM AND NICISS

Cu 3 Au (110) has been investigated by scanning tunneling microscopy (STM) and 180° low energy ion scattering and detection of neutrals (NICISS). Two different terminations would be possible on the basis of a bulk-truncated surface, a gold-rich or a pure copper surface layer. From the NICISS investigation the gold-rich termination has been found. Two surface modifications could be prepared. Rapid cool-down after annealing at 800 K results in a 2×1 LEED superstructure, but careful preparation and prolonged cooling below 600 K gives a LEED 4×1 superstructure. A new pairing row model has been proposed. Upon oxygen exposure at 330 K on the quenched 2×1 surface and subsequent annealing at 800 K, a 2×1 LEED superstructure presents itself with considerably sharper half order reflexes. NICISS data propose a segregation of Cu atoms to the surface layer forming -Cu-O- rows just above the Cu rows in the Au -rich layer. The 2×1 superstructure formed is in part similar to the well-known added row structure at Cu (110)-(2×1)-O. The structure model has been verified by direct imaging of the added rows with STM.