Effect of specific pressure on fabrication of 2D-C_f/Al composite by vacuum and pressure infiltration

Carbon fiber reinforced aluminum matrix （Cf/Al） composite has many excellent properties, and it has received more and more attention. Two-dimensional （2D） Cf/Al composites were fabricated by vacuum and pressure infiltration, which was an integrated technique and could provide high vacuum and high infiltration pressure. The effect of specific pressure on the infiltration quality of the obtained composites was comparatively evaluated through microstructure observation. The experimental results show that satisfied Cf/Al composites could be fabricated at the specific pressure of 75 MPa. In this case, the preform was infiltrated much more completely by aluminum alloy liquid, and the residual porosity was seldom found. It is found that the ultimate tensile strength of the obtained Cf/Al composite reached maximum at the specific pressure of 75 MPa, which was improved by 138.9% compared with that of matrix alloy.

Effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting aluminum alloy

The effect of synergistic action of ultrasonic vibration and solidification pressure on tensile properties of vacuum counter-pressure casting ZL114 A alloys was studied systemically through testing and analyzing the tensile strength and elongation subjected to different ultrasonic powers and solidification pressures. The results indicate that the synergistic action of ultrasonic vibration and solidification pressure can result in the refinement of grains and improvement of tensile properties. Both the highest tensile strength and elongation of aluminum alloy were obtained under synergistic action of 600 W ultrasonic power and 350 kPa solidification pressure. Moreover, the tensile fracture morphology shows obvious ductile fracture characteristics. When the solidification pressure is lower than 300 kPa, the effect of ultrasonic power on tensile strength and elongation is more obvious, but when the solidification pressure is higher than 300 kPa, the effect of solidification pressure on tensile strength and elongation is greater. Meanwhile, the size and morphology of the eutectic silicon were improved significantly by the ultrasonic vibration and pressurized solidification. The strip and massive eutectic silicon phase are completely converted into small short rod-like and evenly distributed Si phases at the grain boundary of primary α-Al.

Newly developed vacuum differential pressure casting of thin-walled complicated Al-alloy castings

The newly designed vacuum differential pressure casting (VDPC) unit was introduced, by which the capabilityof the VDPC process to produce thin-walled complicated Al-alloy castings, that are free from oxides, gas pore andshrinkage cavity and thus enhance overall part quality, was studied. Experimental results were compared with those oftraditional gravity pouring and vacuum suction casting. The first series of experiments were focused on investigating thecastability of thin section Al-alloy casting. In the second series of experiments the metallographic evidence, castingstrength and soundness were examined. Finally, case studies of very interesting thin walled complicated casting applicationswere described. The advantages of the described technique have made possible to produce thin walled complicatedAl-alloy casting (up to a section thickness of 1 mm), which is not practical for gravity pouring and vacuum suction casting.

Characterization of A390 aluminum alloy produced at different slow shot speeds using vacuum assisted high pressure die casting

The effects of vacuum assistance on the microstructure and mechanical properties of high pressure die cast A390alloy at different slow shot speeds were evaluated.Plate-shaped specimens of hypereutectic A390aluminum alloy were produced on a TOYO BD?350V5cold chamber die casting machine incorporated with a self-improved TOYO vacuum system.According to the results,the vacuum pressure inside the die cavity increased linearly with the increasing slow shot speed at the beginning of mold filling.Meanwhile,tensile properties of vacuum die castings were deteriorated by the porosity content.In addition,the average primary silicon size decreased from23to14μm when the slow shot speed increased from0.05to0.2m/s,which has a binary functional relationship with the slow shot speed.After heat treatment,microstructural morphologies revealed that needle-shaped and thin-flaked eutectic silicon particles became rounded while Al2Cu dissolved intoα(Al)matrix.Furthermore,the fractography revealed that the fracture mechanism has evolved from brittle transgranular fracture to a fracture mode with many dimples after heat treatment.

EFFECT OF RESTRAINT STRENGTHENING OF VACUUM-PRESSURED BRAZED JOINT

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Microstructure,mechanical properties and wear resistance of SiC_(p)/AZ91 composite prepared by vacuum pressure infiltration

SiC_(p)/AZ91 composites were prepared by vacuum pressure infiltration.The microstructure,mechanical properties and wear resistance of composite were studied.Results indicated that SiC particles were uniformly distributed in the metal matrix and had a good interface bonding with the metal matrix.Mg_(17)Al_(12) preferably precipitated near the SiC particles,and high-density dislocations were induced by the mismatch of the coefficient of thermal expansion(CTE)between the SiC particle and the AZ91 matrix,thereby accelerating the aging precipitation of the matrix.Compared with AZ91 alloy,the addition of SiC particles improves the hardness and compressive strength of the composite,which is mainly due to the load transfer strengthening and grain refinement strengthening mechanisms.Furthermore,a stable support surface-protecting matrix formed during the wear process because of the excellent wear resistance of SiC.

Effect of vacuum on porosity and mechanical properties of high-pressure die-cast pure copper

Pure copper tensile bars were produced by conventional die casting(HPDC) and vacuum-assist die casting(VADC) processes. Porosity and mechanical properties were investigated by using optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray computed tomography(XCT) and tensile tester. Results show that porosities including gas porosity and shrinkage porosity could be observed in copper castings. Since the application of vacuum could reduce filling related gas entrapment and facilitate solidification due to the increased heat transfer between metal and die, both number and size of the entrapped gases, as well as shrinkage porosities were significantly reduced in vacuum-assist die castings of pure copper. The porosity fraction decreased from 2.243% to 0.875% compared with that of the conventional die casting. Besides, mechanical properties were improved significantly, i.e., by 15% for ultimate tensile strength and three times for elongation.

THEORETICAL AND EXPERIMENTAL STUDY ON THE PRESSURE AND VACUUM CONTINUOUS CONTROL SYSTEM BASED ON HYBRID PUMP

A novel pressure and vacuum continuous control system, which adopts a hybrid pump as pressure and vacuum source, is presented. The mathematical model of the system is developed. The theoretical simulation and analysis on the system are implemented in order to study the relationships among the characteristics, parameters and working points of the system. The experimental investigations on the system characteristics are presented with the adoption ofa fuzzy-PID controller. The simulation and experimental results indicate that the pressure and vacuum continuous control system based on hybrid pump has good dynamic and static performance, strong robustness and satisfactory adaptability to various system parameters. According to the results, system can successfully gain high accuracy and fast response signal. Also, the mathematical model of system is also testified by the experimental results.

Integrated vacuum pressure swing adsorption and Rectisol process for CO_(2) capture from underground coal gasification syngas

An integrated vacuum pressure swing adsorption(VPSA) and Rectisol process is proposed for CO_(2) capture from underground coal gasification(UCG) syngas. A ten-bed VPSA process with silica gel adsorbent is firstly designed to pre-separate and capture 74.57% CO_(2) with a CO_(2) purity of 98.35% from UCG syngas(CH_(4)/CO/CO_(2)/H_(2)/N_(2)= 30.77%/6.15%/44.10%/18.46%/0.52%, mole fraction, from Shaar Lake Mine Field,Xinjiang Province, China) with a feed pressure of 3.5 MPa. Subsequently, the Rectisol process is constructed to furtherly remove and capture the residual CO_(2)remained in light product gas from the VPSA process using cryogenic methanol(233.15 K, 100%(mass)) as absorbent. A final purified gas with CO_(2) concentration lower than 3% and a regenerated CO_(2) product with CO_(2) purity higher than 95% were achieved by using the Rectisol process. Comparisons indicate that the energy consumption is deceased from 2.143 MJ·kg^(-1) of the single Rectisol process to 1.008 MJ·kg^(-1) of the integrated VPSA & Rectisol process, which demonstrated that the deployed VPSA was an energy conservation process for CO_(2) capture from UCG syngas. Additionally, the high-value gas(e.g., CH_(4)) loss can be decreased and the effects of key operating parameters on the process performances were detailed.

Microstructure and properties of vacuum counter-pressure cast aluminum alloy

The microstructure and properties of vacuum counter-pressure cast aluminum alloy were studied. Results indicated that under the condition of vacuum counter-pressure, liquid melts fill mould cavity under the vacuum and crystallize under high pressure which have very good effect on nucleation and solidification feeding. Compared with gravity casting, the microstructure of vacuum counter-pressure cast aluminum alloy is much finer and more uniformly distributed. Mechanical properties of vacuum counter-pressure cast aluminum alloy are improved significantly.

Flexible Furnace Concepts for Vacuum Heat Treatment Combined with High-pressure Gas Quenching

IN the past five years the process combination of vacuum hardening, respectively vacuum carburizing with high-pressure gas quenching was successfully introduced to the market, especially in the manufacture of gears. In the meantime furnace concepts for various applications are available to the industry. In the following report three plant varieties are introduced, which differ in process flexibility and throughput. This report also explains criteria for the selection of a furnace in view of the existing application requirements. Besides this a short introduction is given into the vacuum carburizing process and the high-pressure gas quenching technology.

Simulation of fuzzy control systems for nonferrous alloy vacuum counter-pressure casting

Through simulation analyses of vacuum counter-pressure casting fuzzy control systems based on MATLAB, fuzzy control systems designed by simulation can track technical route established well. When transmission functions of vacuum counter-pressure casting controlled objects are changed in operation, fuzzy control systems can carry on self-regulation and stabilize quickly, and embody the advantages of fleet response velocity and little adjusting quantity. The design of vacuum counter-pressure casting fuzzy control systems is accelerated and improved greatly by simulation based on MATLAB. Meanwhile, their design is accurate and reliable. Moreover, microstructure and properties of thin-wall aluminum alloy castings are improved effectively by using fuzzy control systems.

Vacuum-sealed casting process under pressure

A new casting method, the vacuum-sealed mold casting under pressure, has been developed, and thin wall iron castings with high precision and smooth surface have been produced successfully with this casting method. The experimental results show that the liquid iron has a very excellent filling ability because a high negative pressure is formed in the mold cavity during filling process. The vacuum-sealed mold under pressure has very high compressive strength greater than 650 kPa, which is 3-4 times as high as that of the molds produced by high-pressure molding process or vacuum-sealed molding process.

Rotary bending fatigue behavior of A356 –T6 aluminum alloys by vacuum pressurizing casting

Vacuum pressurizing casting technique, providing better mould filling and inter-dendritic feeding, can reduce the porosity greatly in cast aluminum alloys, and improve the fatigue properties. The rotary bending fatigue properties of A356-T6 alloys prepared by vacuum pressurizing casting were investigated. The S-N curve and limit strength 90 MPa under fatigue life of 107 cycles were obtained. The analyses on the fatigue fractography and microstructure of specimens showed that the fatigue fracture mainly occurs at the positions with casting defects in the subsurface, especially at porosities regions, which attributed to the crack propagation during the fatigue fracture process. Using the empirical crack propagation law of Pairs-Erdogon, the quantitative relationship among the initial crack size, fatigue life and applied stress was established. The fatigue life decreases with an increase in initial crack size. Two constants in the Pairs-Erdogon equation of aluminum alloy A356-T6 were calculated using the experimental data.

Evidence based review of negative pressure wound therapy

Vacuum-assisted closure, sometimes referred to as microdeformational wound therapy or most commonly negative pressure wound therapy(NPWT), has significantly improved wound care over the past two decades. NPWT is known to affect wound healing through four primary mechanisms(macrodeformation, microdeformation, fluid removal, and alteration of the wound environment) and various secondary mechanisms(including neurogenesis, angiogenesis, modulation of inflammation, and alterations in bioburden) which are described in this review. In addition, the technique has many established uses, for example in wound healing of diabetic and pressure ulcers, as well as burn and blast wounds. This therapy also has many uses whose efficacy has yet to be confirmed, for example the use in digestive surgery. Modifications of the traditional NPWT have also been established and are described in detail. This therapy has various considerations and contraindications which are summarized in this review. Finally, future perspectives, such as the optimal cycling of the treatment and the most appropriate interface material, are touched upon in the final segment. Overall, despite the fact that questions remain to be answered about NPWT, this technology is a major breakthrough in wound healing with significant potential use both in the hospital but also in the community.

Effect of Ilizarov external fixation combined with negative pressure sealing drainage and antibiotics in the treatment of infective tibial nonunion

Objective:Observation on the effect of Ilizarov external fixation combined with vacuum pressure sealing drainage and antibiotics in the treatment of infective tibial nonunion.Methods:79 patients with tibial infective nonunion who were treated in our hospital from August 2016 to August 2018 were divided into two groups according to random number table,with 39 patients in the control group treated with Ilizarov external fixation technology and 40 patients in the study group treated with vacuum pressure sealing drainage and antibiotics on the basis of the control group.Bone healing time and daily walking were recorded.Rasmussen score,serum intercellular adhesion molecule-1(ICAM-1)and IL-6 levels,lower limb Fugl-Meyer motor function score and lower limb BI index score were compared at different time.Results:The daily walking condition of the study group was significantly better than that of the control group(P<0.05),and the healing time of bone was significantly shorter than that of the control group(P<0.05);the Rasmussen score of the study group was higher than that of the control group at 1 month,6 months and 12 months after treatment(P<0.05);the levels of serum ICAM-1 and IL-6 in the two groups after treatment were lower than those before treatment(P<0.05),and the levels of serum ICAM-1 and IL-6 in the study group were lower than those in the control group after treatment(P<0.05).The lower limb Fugl-Meyer motor function score and lower limb BI index score of the two groups after treatment were higher than those before treatment(P<0.05),and the lower limb Fugl-Meyer motor function score and lower limb BI index score of the study group after treatment were higher than those of the control group(P<0.05).Conclusions:Ilizarov external fixation combined with vacuum pressure sealing drainage and antibiotics can promote the bone healing of patients with infective tibial nonunion,significantly improving their daily walking condition,alleviating inflammation,and recovering the knee joint function and lower limb function well.

Principles and practice of low pressure-expendable pattern casting process for magnesium alloys

A newly developed low-pressure expendable pattern casting (LP-EPC) process was introduced and its basic principles or effect factors were further analyzed. According to theoretical calculation and experimental results, the major casting parameters that are of great and critical importance on the process include pressure and flux of filling gas, decomposition characteristic and density of foam pattern, thickness and permeability of coating, pouring temperature, vacuum degree and their combination. Most of casting defects can be effectively avoided by choosing the suitable parameters. The success achieved in pouring motor housing and exhaust manifold castings demonstrates the advantages of LP-EPC process in the production of high-complicated castings with high dimension accuracy.

NOVEL “CATHODE-ON-MEMBRANE” VME PRESSURE SENSOR

This article proposes a novel "cathode-on-membrane" vacuum microelectronic (VME)pressure sensor. Compared with conventional VME pressure sensors, the package process of the new structured sensor is easier to control, and therefore it enable greater potential of nass production and high productivity. The properties of the new sensor have been theoretically investigated by computer simulations; the practical structure has been designed and fabricated; and the package technique has been studied.

Tumor Recurrence after Negative Pressure Wound Therapy: An Alert Call

In this report, we present a 22-year-old patient with soft tissue sarcoma of the lower extremity that developed wound dehiscence after surgery. Biopsy demonstrated negative margins for cancer. He was treated with negative pressure wound therapy for 6 weeks and started to present increased wound exudates, local pain and proliferating tissue that was positive for tumor recurrence. Consequently he underwent lower extremity amputation with hip disarticulation by the orthopedic team. Although we cannot determine with certainty a full causative relationship, it seems prudent to advise cautious use of negative pressure wound therapy in oncologic related wound beds.

COUNTERACTING HIGH WINDS WITH LOW PRESSURE:DEVELOPMENT AND TESTING OF A NEW ROOF VENT SYSTEM

Roof system failures are common during high wind events.In locations subject to high wind conditions,membrane roofing systems must typically be either physically attached or fully adhered to the substrate or ballast may be added to weigh down the membrane.An alternative to these installation approaches could be to use aerodynamics principles such as the Bernoulli and Venturi effects to create a low-pressure region beneath the membrane roof that is lower than the ambient pressure and thus counteracts the uplifting force.A new omnidirectional vent has been designed and tested that takes advantage of these aerodynamics principles to induce low pressure under the membrane layer.This new vent operates with no moving parts and was tested in the high-speed stability wind tunnel at Virginia Tech to wind speeds up to 233 km/h.The results demonstrate that this new vent generates pressures lower than the ambient when subjected to high wind conditions.This paper presents the design principles and performance test results for this new roof vent system and other applications for roof vent technologies.