Gating system optimization of low pressure casting A356 aluminum alloy intake manifold based on numerical simulation

To eliminate the shrinkage porosity in low pressure casting of an A356 aluminum alloy intake manifold casting, numerical simulation on fi lling and solidifi cation processes of the casting was carried out using the ProCAST software. The gating system of the casting is optimized according to the simulation results. Results show that when the gating system consists of only one sprue, the fi lling of the molten metal is not stable; and the casting does not follow the sequence solidifi cation, and many shrinkage porosities are observed through the casting. After the gating system is improved by adding one runner and two in-gates, the fi lling time is prolonged from 4.0 s to 4.5 s, the fi lling of molten metal becomes stable, but this casting does not follow the sequence solidifi cation either. Some shrinkage porosity is also observed in the hot spots of the casting. When the gating system was further improved by adding risers and chill to the hot spots of the casting, the shrinkage porosity defects were eliminated completely. Finally, by using the optimized gating system the A356 aluminum alloy intake manifold casting with integrated shape and smooth surface as well as dense microstructure was successfully produced.

Drift characteristics and the multi-field coupling stress mechanism of the pantograph-catenary arc under low air pressure

The fault caused by a pantograph-catenary arc is the main factor that threatens the stability of high-speed railway energy transmission.Pantograph-catenary arc vertical drift is more severe than the case under normal pressure,as it is easy to develop the rigid busbar,which may lead to the flashover occurring around the support insulators.We establish a pantograph-catenary arc experiment and diagnosis platform to simulate low pressure and strong airflow environment.Meanwhile,the variation law of arc drift height with time under different air pressures and airflow velocities is analyzed.Moreover,arc drift characteristics and influencing factors are explored.The physical process of the arc column drifting to the rigid busbar with the jumping mechanism of the arc root on the rigid busbar is summarized.In order to further explore the mechanism of the above physical process,a multi-field stress coupling model is built,as the multi-stress variation law of arc is quantitatively evaluated.The dynamic action mechanism of multi-field stress on arc drifting characteristics is explored,as the physical mechanism of arc drifting under low pressure is theoretically explained.The research results provide theoretical support for arc suppression in high-altitude areas.

Pressurization control system for low pressure crucible casting

A new compact pressurization control system of the low pressure casting machine for crucible pressure casting has been developed. It is especially designed for the production of high-quality aluminum or magnesium alloy parts with low input cost. This machine with such a system has the virtue of economical and compact, and combines the Fuzzy-PID technology and achieves accuracies of ±2.5 mbar. At present, this machine has been adopted by several users in China for the production of aluminum alloy castings with high property requirements. Furthermore, for magnesium alloy castings, this machine can be used with the gas protect unit.

Oxidation of Fe-Cr-Ni Alloys in a Low Oxygen Partial Pressure Atmosphere to Mitigate Coke Formation

Anti-coking oxide films were prepared on a 25Cr35Ni and 35Cr45Ni alloy surface under the low oxygen partialpressure atmosphere of a H2-H2O mixture. The composition and phase structure of the oxide films were analyzed by energydispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The anti-cokingperformance of a mini tube made of a HP40 (25Cr35Ni) alloy was evaluated on a bench scale pyrolysis and coking test unit.The results showed that the surface Fe and Ni content decreased after the oxidation of the two alloys in a low oxygen partialpressure atmosphere. The oxide films were mainly composed of MnCr_(2)O_(4) and Cr_(2)O_(3). The average mass of coke in the minitube with oxide film decreased by 87% relative to that of a tube without an oxide film when the cracking temperature was 900℃. The ethylene, propylene, and butadiene yields in the pyrolysis tests were almost the same for the mini tubes withand without an oxide film. The oxide film on the alloy surface effectively inhibited catalytic filamentous coke formation.An industrial test showed that the run length of the cracking furnace with the in-situ coating technology was significantlyextended.

Cure Reaction Kinetics of Low Pressure Sheet Molding Compound System Thickened by Crystalline Polymer

Several kinetic models for unsaturated polyester cure reaction and some existing parameter estimation techniques of these models were introduced. Correlated kinetic parameters and kinetic equations of the autocatalytic empirical kinetic model of LPSMC system were determined by using isothermal DSC to scan the system which was thickened by crystalline polymer （PEG-MAH）. Through using a serial curing degree of the system to validate the model, the experimental results were basically identical with the predictions of the autocatalytic empirical kinetic model. This model could provide a theoretical reference to the determination of molding techniques of low pressure SMC.

Controlled low central venous pressure reduces blood loss and transfusion requirements in hepatectomy

AIM: To evaluate the effect of low central venous pressure (LCVP) on blood loss and blood transfusion in patients undergoing hepatectomy.

Numerical simulation of low pressure die-casting aluminum wheel

The FDM numerical simulation software,ViewCast system,was employed to simulate the low pressure die casting(LPDC)of an aluminum wheel.By analyzing the mold-filling and solidification stage of the LPDC process,the distribution of liquid fraction,temperature field and solidification pattern of castings were studied.The potential shrinkage defects were predicted to be formed at the rim/spoke junctions,which is in consistence with the X-ray detection result.The distribution pattern of the defects has also been studied.A solution towards reducing such defects has been presented.The cooling capacity of the mold was improved by installing water pipes both in the side mold and the top mold.Analysis on the shrinkage defects under forced cooling mode proved that adding the cooling system in the mold is an effective method for reduction of shrinkage defects.

Mechanism of burst feeding in ZL205A casting under mechanical vibration and low pressure

The burst feeding behavior of ZL205 A casting under mechanical vibration and low pressure was investigated by casting experiment and physical model. Experimental results indicated that the burst feeding appeared repeatedly during solidification and left a shrinkage cavity with layered structure under mechanical vibration. The castings with less shrinkage and higher density could be achieved through the vibration. The calculation results of physical model showed that the burst feeding could perform spontaneously under vibration while difficultly without vibration in low-pressure die casting. The obstruction of a casting could be broken and the grains could be rearranged by the vibration. And the obstruction could be carried away due to the inner and outer pressure difference, causing a burst feeding.

Effect of pressurizing speed on filling behavior of gradual expansion structure in low pressure casting of ZL205A alloy

The mold filling behavior of gradual expansion structure in low pressure casting was studied by two phase flow model using the Volume of Fluid method, and was verified by water simulation with a Plexiglas mold. To get smooth mold filling process and provide a guide for the pressurizing speed design in the producing practice, the mathematical model with the pressurizing speed, expansion angle and height of the gradual expansion structure was established. For validation experiments, ZL205 A alloy castings were produced under two different pressurizing speeds. Weibull probability plots were used to assess the fracture mechanisms under different pressurizing speeds. Mechanical properties of ZL205 A alloy were applied to assess the entrainment of oxide film. The results show that the filling process of a gradual expansion structure in a low pressure casting can be divided into the spreading stage and filling stage by gate velocity. The gate velocity continues to increase in the gradual expansion structure, and increases with the increase of pressurizing speed or expansion angle. Under the effect of the falling fluid raised by the jet flow along the sidewall, the fluid velocity decreases in the jet zone from ingate to free surface. As such, oxide film entrainment does not occur when the gate velocity is greater than the critical velocity, andthe gate velocity no longer reflects the real state of the free surface. The scatter of the mechanical properties is strongly affected by the entrainment of oxide films.

Effects of Tightening Torque on Dynamic Characteristics of Low Pressure Rotors Connected by a Spline Coupling

A rotor dynamic model is built up for investigating the effects of tightening torque on dynamic characteristics of low pressure rotors connected by a spline coupling.The experimental rotor system is established using a fluted disk and a speed sensor which is applied in an actual aero engine for speed measurement.Through simulating calculation and experiments,the effects of tightening torque on the dynamic characteristics of the rotor system connected by a spline coupling including critical speeds,vibration modes and unbalance responses are analyzed.The results show that when increasing the tightening torque,the first two critical speeds and the amplitudes of unbalance response gradually increase in varying degrees while the vibration modes are essentially unchanged.In addition,changing axial and circumferential positions of the mass unbalance can lead to various amplitudes of unbalance response and even the rates of change.

Study of vortex in flow fields induced by surface dielectric barrier discharge actuator at low pressure based on Q criterion

Flow fields induced by a surface dielectric barrier discharge actuator at low pressure of 7 kPa are measured by particle image velocimetry. The distribution of local vortices in the flow field is revealed by the Q criterion. The reason for the generation of vortices is analyzed and the influence of pulse frequency and duty cycle on vortices is studied. The results show that the Q criterion can reveal the small-scale vortices, which cannot be indicated by the streamline. The direction transition zone where the induced jet moves from the vertical to the tangential and the shear layer between the jet and stationary air are prone to the generation of strong vortices. The influence of pulse frequency on vortices is not obvious, but the variation of duty cycle can significantly affect the strength and distribution of vortices.

Effect of controlled low central venous pressure on renal function in major liver resection

Objective： To investigate the effects of low central venous pressure （LVCP） on blood loss and evaluate its influence on renal function in patients undergoing hepatectomy. Methods： Forty-six patients, ASA classification Ⅰ-Ⅲ, undergoing liver resection were randomized into LCVP group （n = 23） and control group （n = 23）. In LCVP group, CVP was maintained at 2-4 mmHg and MBP above 60 mmHg during hepatectomy, while in control group hepatectomy was performed routinely without lowering CVP. Volume of blood loss during hepatectomy, volume of blood transfusion, and changes of renal functions were compared between the two groups. Results： There were no significant differences in demographics, ASA score, type of hepatectomy, duration of inflow occlusion, operation time, weight of resected liver tissues, and renal functions between the two groups. LCVP group had a significantly lower volume of total intraoperative blood loss （P 〈 0.01） and RBC transfusion （P 〈 0.05）. Conclusion： Lowering the CVP to less than 5 mmHg is a simple and effective technique to reduce blood loss and blood infusion during liver resection, and has no detrimental effects on renal functions.

THE PRODUCTION OF FOAM ALUMINIUM ALLOY BY LOW-PRESSURE INFILTRATION METHOD

The influence of technical parameters on the infiltrating height of the moltenmetal in the process of Producing aluminium alloy foam by low-pressure infiltration method were investigated.Experiments indicated that the height increases with the preheating temperature of granules,theexternal pressureand the pouring temperature of molten alloy,among which the action of pre heating temperature of granules is more effective.There exists a critical pre heating temperature for different size of granules.

A two-dimensional air streamer discharge modified model based on artificial stability term under non-uniform electric field at low temperature and sub-atmospheric pressure

In this paper, an improved air discharge fluid model under non-uniform electric field is constructed based on the plasma module COMSOL Multiphysics with artificial stability term, and the boundary conditions developed in the previous paper are applied to the calculation of photoionization rate. Based on the modified model, the characteristics of low temperature subatmospheric air discharge under 13 kV direct current voltage are discussed, including needle-plate and needle-needle electrode structures. Firstly, in order to verify the reliability of the model, a numerical example and an experimental verification were carried out for the modified model respectively. Both verification results show that the model can ensure the accuracy and repeatability of the calculation. Secondly, according to the calculation results of the modified model, under the same voltage and spacing, the reduced electric field under low temperature subatmosphere pressure is larger than that under normal temperature and atmospheric pressure. The high electric field leads to the air discharge at low temperature and sub atmospheric pressure entering the streamer initiation stage earlier, and has a faster propagation speed in the streamer development stage, which shortens the overall discharge time. Finally, the discharge characteristics of the two electrode structures are compared, and it is found that the biggest difference between them is that there is a pre-ionization region near the cathode in the needle-needle electrode structure. When the pre-ionization level reaches 1013 cm-3, the propagation speed of the positive streamer remains unchanged throughout the discharge process, and is no longer affected by the negative streamer. The peak value of electric field decreases with the increase of pre-ionization level, and tends to be constant during streamer propagation. Based on the previous paper, this paper constructs the air discharge model under non-uniform electric field, complements with the previous paper, and forms a relatively complete set of air discharge simulation system under low temperature and sub atmospheric pressure, which provides a certain reference for future research.

Characteristics of long-gap AC streamer discharges under low pressure conditions

The generation and propagation of a streamer is a significant physical process of air gap discharge. Research on the mechanism of streamers under low-pressure conditions is helpful for understanding the process of long-gap discharge in a high-altitude area. This paper describes laboratory investigations of streamer discharge under alternating current（AC） voltage in a low pressure test platform for a 60 cm rod–plane gap at 30 kPa, and analyzes the characteristics of streamer generation and propagation. The results show that the partial streamer and breakdown streamer all occur in the positive half-cycle of AC voltage near the peak voltage at 30 kPa. The partial streamer could cause the distortion of current and voltage waveform, and it appears as the branching characteristic at the initial stage. With the extension of the streamer, the branching and tortuosity phenomena become gradually obvious, but the branching is suppressed when the streamer crosses the gap. The low-pressure condition has little influence on the tortuosity length and the tortuosity number of the streamer, but affect the diameter of streamer obviously.

Utilization of deep neuromuscular blockade combined with reduced abdominal pressure in laparoscopic radical gastrectomy for gastric cancer:An academic perspective

BACKGROUND Few studies have examined the specific efficacy of deep neuromuscular blockade(NMB)combined with pneumoperitoneal pressure reduction in laparoscopic radical gastrectomy(LRG)in the elderly.AIM To investigate the application effect of deep neuromuscular blockade(NMB)combined with reduced pneumoperitoneum pressure in LRG for gastric cancer(GC)in elderly patients and its influence on inflammation.METHODS Totally 103 elderly patients with GC treated in our hospital between January 2020 and January 2022 were retrospectively analyzed.Among them,45 patients treated with surgery based on deep NMB and conventional pneumoperitoneum pressure were assigned to the control group,while the rest of the 58 patients who underwent surgery based on deep NMB and reduced pneumoperitoneum pressure were assigned to the observation group.The two groups were compared in the changes of the Leiden-surgical rating scale score,serum tumor necrosis fact-α(TNF-α)and interleukin 6(IL-6)before and after therapy.The visual analogue scale(VAS)was adopted for evaluating the shoulder pain of patients at 8 h,24 h and 48 h after the operation.The driving pressure of the two groups at different time points was also compared.Additionally,the operation time,pneumoperitoneum time,infusion volume,blood loss,extubation time after surgery,residence time in the resuscitation room,TOF%=90%time and post-anesthetic recovery room(PACU)stay time were all recorded,and adverse PACU-associated respiratory events were also recorded.The postoperative hospitalization time and postoperative expenses of the two groups were counted and compared.RESULTS No significant difference was found between the two groups at the time of skin incision,60 minutes since the operation and abdominal closure after surgery(P>0.05).The observation group exhibited significantly lower VAS scores than the control group at 24 and 48h after surgery(P<0.05).Additionally,the observation group had significantly lower driving pressure than the control group at 5 min and 60 min after the establishment of pneumoperitoneum(P<0.05).Additionally,the two groups were similar in terms of the operation time,pneumoperitoneum time,infusion volume,blood loss,extubation time after surgery,residence time in the resuscitation room and TOF%=90%time(P>0.05),and the observation group showed significantly lower TNF-αand IL-6 Levels than the control group at 24 h after therapy(P<0.05).Moreover,the incidence of adverse events was not significantly different between the two groups(P>0.05),and the observation group experienced significantly less hospitalization time and postoperative expenses than the control group(P<0.05).CONCLUSION Deep NMB combined with reduced pneumoperitoneum pressure can decrease the VAS score of shoulder pain and inflammatory reaction,without hindering the surgical vision and increasing adverse PACU-associated respiratory events,and can thus shorten the hospitalization time and treatment cost for patient.

Thickening and Rheological Properties of Crystalline Polyester Used in Low Pressure Sheet Molding Compounds

Low pressure sheet molding compound （LPMC,1.0-3.0 MPa,95-103 ℃） is a new kind of thermosetting material with crystalline polyester as a physical thickenner.LPMC is different from conventional SMC using an earth oxide thickening agent （e.g.MgO） as chemical thickenner,it relies on the physical thickening of crystalline polyester.Crystalline polyester resin is the key material to mold LPMC parts.Currently there was no report about the thickening mechanism of crystalline polyester in LPMC.In this article,crystalline polyester resins,whose melting points were between 45 ℃ and 89 ℃,were synthesized by a two-step esterification.The melt points of crystalline polyesters are controlled by regulating the mol ratio of the two glycols and the two acids.And by means of varying the content of crystalline polyester resin,the thickening effect on resin paste is investigated.In addition,the thickening mechanism of crystalline polyester in LPMC was investigated by FTIR and DSC analysis.The effects of the diameters and viscosity of crystalline polyester on the rheological property and fiber distribution of LPMC sheets were studied,too.Results show that the thickening effect is excellent when the weight content of crystalline polyester resin is 3%.And there exists three kinds of functions acting in the process of thickening：swelling,hydrogen bonds and induction crystallization.During the preparing process of resin paste in LPMC,the temperature of resin paste must be kept at 90 ℃.In addition,crystalline polyester make LPMC have a perfect fluid property.When the viscosity of LPMC sheet is beyond 1 kPa s,the fiber orientation is not obvious.But when the viscosity of LPMC sheet is about 500 Pa s,the fiber shows a certain degree of orientation.Moreover the study of physical and chemical thickening mechanism of crystalline polyester and the rheological discipline of LPMC sheets in the hot mould will provide the researchers and enterprises with theory guidance.

Characterization of Femtosecond Laser-Induced Plasma under Low Pressure in Argon

An experiment of femtosecond laser-induced breakdown in argon with a pressure below normal atmospheric pressure is performed. The breakdown spectrum is mainly due to the electronic relaxation of excited Ar atoms and Ar ions. The lifetimes and characteristics of the Ar plasma are extensively studied by the time-integrated and time-resolved optical emission spectroscopy technique, which is also discussed. Under the assumption of local thermodynamic equilibrium （LTE）, the plasma temperature is calculated. Moreover, the electron density is accessed from the Stark broadening of the ionized argon lines. Finally, the validity of applications of LTE is also discussed.

Silicon Epitaxial Wafer for X Band Double Read-type DDR IMPATT Diodes by Atmosphere / Low Pressure Growth Technique

The silicon epitaxial wafter for X band double Read-type DDR IMPATT diodes has been fabricatedby normal-low pressure growth technique. The hyperabrupt impurity profile and very thin p-layer, n-layerwere achieved.

Monte Carlo Simulation of Laser-Ablated Particle Splitting Dynamic in a Low Pressure Inert Gas

A Monte Carlo simulation method with an instantaneous density dependent meanfree-path of the ablated particles and the Ar gas is developed for investigating the transport dynamics of the laser-ablated particles in a low pressure inert gas.The ablated-particle density and velocity distributions are analyzed.The force distributions acting on the ablated particles are investigated.The influence of the substrate on the ablated-particle velocity distribution and the force distribution acting on the ablated particles are discussed.The Monte Carlo simulation results approximately agree with the experimental data at the pressure of 8 Pa to 17 Pa.This is helpful to investigate the gas phase nucleation and growth mechanism of nanoparticles.