Military missions in hostile environments are often costly and unpredictable,with squadrons sometimes facing isolation and resource scarcity.In such scenarios,critical components in vehicles,drones,and energy generato...Military missions in hostile environments are often costly and unpredictable,with squadrons sometimes facing isolation and resource scarcity.In such scenarios,critical components in vehicles,drones,and energy generators may require structural reinforcement or repair due to damage.This paper proposes a portable,on-site production method for molds under challenging conditions,where material supply is limited.The method utilizes large format additive manufacturing(LFAM)with recycled composite materials,sourced from end-of-life components and waste,as feedstock.The study investigates the microstructural effects of recycling through shredding techniques,using microscopic imaging.Three potential defense-sector applications are explored,specifically in the aerospace,automotive,and energy industries.Additionally,the influence of key printing parameters,particularly nonparallel plane deposition at a 45-degree angle,on the mechanical behavior of ABS reinforced with 20%glass fiber(GF)is examined.The results demonstrate the feasibility of this manufacturing approach,highlighting reductions in waste material and production times compared to traditional methods.Shorter layer times were found to reduce thermal gradients between layers,thereby improving layer adhesion.While 45-degree deposition enhanced Young's modulus,it slightly reduced interlayer adhesion quality.Furthermore,recycling-induced fiber length reduction led to material degradation,aligning with findings from previous studies.Challenges encountered during implementation included weak part adherence to the print bed and local excess material deposition.Overall,the proposed methodology offers a cost-effective alternative to traditional CNC machining for mold production,demonstrating its potential for on-demand manufacturing in resource-constrained environments.展开更多
Sorghum is an important cereal crop for smallholder farmers’ food security in many countries in West Africa. However, its production has stagnated due to several factors, such as anthracnose and grain molds. Thus, a ...Sorghum is an important cereal crop for smallholder farmers’ food security in many countries in West Africa. However, its production has stagnated due to several factors, such as anthracnose and grain molds. Thus, a study was conducted to identify local germplasms that combine high grain yield and resistance to anthracnose and grain molds under Senegalese environments. A set of 256 genotypes was assessed at Sefa, Sinthiou and Kolda research stations using an incomplete blocks design with two replications. Agro-morphological and phytopathological data were collected. The results revealed a huge phenotypic variation between the genotypes for all traits. The flowering time varied from 43 to 126 days after sowing, while the panicle length varied from 10 to 60 cm. The genotypes were generally more productive at Sinthiou (1653 Kg ha−1) compared to Kolda (164 kg ha−1) research stations. The disease parameters were significantly and positively associated, while the flowering time was strongly and positively associated to grain mold score. The genotypes were classified into three groups with plant height, panicle diameter and length, flowering time and grain mold score as the most discriminating parameters. The genotypes belonging to cluster 3, in addition of being more productive and more resistant to grain mold and anthracnose, have longer panicles. These genotypes present promising prospects for inclusion in breeding programs focused on advancing sorghum yield and disease resistance in Senegal.展开更多
The Resin Infusion or the VARTM (Vacuum Assisted Resin Transfer Molding) process has significant potential to be used to manufacture curved composites. Another way to produce curved or complex geometry is to use 3D pr...The Resin Infusion or the VARTM (Vacuum Assisted Resin Transfer Molding) process has significant potential to be used to manufacture curved composites. Another way to produce curved or complex geometry is to use 3D printers. 3D or FDM (Fused Deposition Modelling) printers are now being used to produce relatively cheaper curved parts using thermoplastics such as PLA. However, the strength and mechanical performance of these parts is limited and can be enhanced if the polymer is reinforced with a type of fiber for instance. Research is being carried out to produce fiber rein-forced thermoplastic composites but that process is expected to be more expensive than the alternative methods such as injection or compression molding. Furthermore, to understand the manufacture of a hybrid composite using thermoplastics, fibers and epoxy resin, research and investigation need to be carried out. In this research</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">, there are</span></span></span></span></span><span><span><span><span><span style="font-family:""><span style="font-family:Verdana;"> single-sided, double-sided, reusable, disposable and consumable molds. Most of the molds were created either using an FDM printer or manually. These molds were then used to manufacture flat and curved composite structures via the resin injection process, </span><i><span style="font-family:Verdana;">i.e.</span></i><span style="font-family:Verdana;"> VARTM with epoxy resin system and glass/carbon/flax fiber reinforcement. By replacing the costly metallic molds by significantly cheaper molds, the cost of production was expected to further reduce. Furthermore, using double-sided PLA molds was not expected to be a threat to the overall cost of the composite part in question compared to double-sided matched molds used in compression molding. Shear strength, tensile strength and charpy impact strength of most of the manufactured composite parts were also investigated. The strengths were compared based on the method of mold usage. The results showed that this method is effective for a cheaper production of curved epoxy resin composites. However, the strength of the part will decrease as the curved profile gets more complicated unless the basic resin infusion process is altered.展开更多
Owing to its exceptional casting performance,substantial utilization of recycled sand,and environmen-tally sustainable characteristics,frozen sand mold casting technology has found extensive application across diverse...Owing to its exceptional casting performance,substantial utilization of recycled sand,and environmen-tally sustainable characteristics,frozen sand mold casting technology has found extensive application across diverse sectors,including aerospace,power machinery,and the automotive industry.The focus of the present study was on the development of frozen sand mold formulations tailored for efficient machin-ing,guided by the performance and cutting fracture mechanism of frozen sand molds.A regional tem-perature control device was developed for the purpose of conducting cryogenic cutting experiments on frozen sand molds with varying geometrical characteristics and molding materials.The impact of milling process parameters on the dimension accuracy of both sand molds and castings,as well as castings’surface roughness,were systematically investigated by a whole-process error flow control method.The findings indicate that precise and efficient processing of complicated sand molds was achievable by using sand particles with sizes ranging from 106 to 212μm,and water content between 4 and 5 wt.%,freezing temperature below-25℃,and cutting temperature within the range of-5 to 0℃.Through the frozen-casting of representative components,it was validated that the machining error of the frozen sand mold was within±0.25 mm.Additionally,the dimensional accuracy of the flywheel shell casting conformed to the CT8 specifications.This study provides theoretical guidance for the selection of frozen-casting sand formulations and close-loop control of process size chains for complex metal parts,as well as an overall solution for the realization of sustainable development of green casting.展开更多
The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects...The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects are prone to occur.This leads to an increase in the scrap rate of casings,causing significant resource wastage.Additionally,the presence of cracks poses a significant safety hazard after the casings are put into service.The generation of different types of crack defects in stainless steel casings is closely related to casting stress and the high-temperature concession of the sand mold.Therefore,the types and causes of cracks in stainless steel casing products,based on their structural characteristics,were systematically analyzed.Various sand molds with different internal topology designs were printed using the 3DP technology to investigate the impact of sand mold structures on high-temperature concession.The optimal sand mold structure was used to cast casings,and the crack suppression effect was verified by analyzing its eddy current testing results.The experimental results indicate that the skeleton structure has an excellent effect on suppressing cracks in the casing.This research holds important theoretical and engineering significance in improving the quality of casing castings and reducing production costs.展开更多
The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inocula...The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus, mold type (green or dry) and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroids graphite cast iron castings were discussed. Finally, two regression equations relating these variables to the formation of shrinkage porosity were derived based upon the orthogonal experiments conducted.展开更多
Twenty-eight molds were isolated from clinical blood cultures and were unidentifiable by cellular morphology using conventional microscopy. Using the utility of amplification and direct sequencing of internal transcri...Twenty-eight molds were isolated from clinical blood cultures and were unidentifiable by cellular morphology using conventional microscopy. Using the utility of amplification and direct sequencing of internal transcribed spacer region of ribosomal RNA gene, 93% of these fungi were identified. Seventy-one percents of the molds were found to be associated with plants or soil with no or few published cases of human disease. These include species of basidiomycetes and ascomycetes such as Botryosphaeria dothidea, Phomopsis flavodonflavus, Inonotus pachyphloeus, Earlilella scabrosa, Calocybe indica, Athelia pellicularis, Tinctoporellus epimiltinus, Trametes lactinea, Coprinellus aureogranulat and Xylaria feejeensis. Some of the nonsporulating molds were identified as pathogen or potential pathogens in immunocompetent or immunocompromised hosts. These include Schizophylum commune and hyphomycetes such as Cladosporium cladosporoides, Aspergillus niger and Fusarium equiseti. Basidiomycetes and hyphomycetes identified in the current study are ubiquitous in the environment and are almost similar to the species of molds reported from cutaneous and respiratory samples suggesting that the fungi may represent contaminants rather than true fangaemia. Results of this study emphasize the need of an effort to minimise blood culture contamination and support the recommendation to incorporate clinical, radiologic findings and positive blood culture for molds in the diagnosis and management of invasive mycosis.展开更多
Microbial attacks during storage are one of the primary causes of product deterioration, and can limit the process of prolonging the shelf-life of harvested food. In this study, sweet potatoes were stored at temperatu...Microbial attacks during storage are one of the primary causes of product deterioration, and can limit the process of prolonging the shelf-life of harvested food. In this study, sweet potatoes were stored at temperatures of 13, 21, and 29 ℃ for 4 weeks. Samples were collected during storage and plated on potato dextrose agar, from which axenic mold cultures were obtained and identified using 26S rRNA gene sequences. Physiological changes of potato tubers were assessed with respect to pathogenicity, enzyme activity, and atmospheric storage conditions. Six fungal species were identified, namely Penicillium chrysogenum （P. rubens）, P. brevicompactum, Mucor circinelloides, C/adosporium cladosporiodes, P. expansum, and P. crustosum. The following fungal isolates, namely P. expansum, P. brevicompactum, and Rhizopus oryzae, were recovered from the re-infected samples and selected according to their levels of enzyme activity. This study revealed high levels of activity for cellulase and pectinase, which were most notable during the initial three days of testing, and were followed by a steady decrease （P〈0.05）. Polygalacturonase activity was prominent with values ranging from 12.64 to 56.79 U/mg （P. expansum） and 18.36 to 79.01 U/mg （P. brevicompactum）. Spoilage was obvious in the control group, which had a 100% decay at the end of the experimental period compared with samples treated with iprodione and sodium hypochlorite, in which the decay rates were 5% and 55%, respectively. The data for the iprodione- and sodium hypochlorite-treated samples at the end of the 3-month storage period showed that they were significantly different （P=0.041）, with the sodium hypochlorite-treated samples producing twice the rate of infection compared to the iprodione-treated samples. The comparative rate of the pro- gression of decay in the treated samples can be expressed as iprodione〈sodium hypochlorite〈control. This study demonstrates that sweet potato tissue damage is due to the activities of microbial enzymes and, in particular, the pectinases of the organisms isolated from the infected potato tissues, and suggests the advantages of utilizing iprodione as a curing agent for potato tubers before storage.展开更多
Two types of diacetatozirconic acid-yttria molds which were labeled as ZYW mold(diacetatozirconic acidyttria mold with traces of ammoium metatungstate in the slurry) and ZY mold(diacetatozirconic acid-yttria mold with...Two types of diacetatozirconic acid-yttria molds which were labeled as ZYW mold(diacetatozirconic acidyttria mold with traces of ammoium metatungstate in the slurry) and ZY mold(diacetatozirconic acid-yttria mold without ammonium metatungstate) were prepared by traditional investment casting.The ZYW and ZY molds were sintered in a carbon-reducing atmosphere and in air,respectively,at 1550℃ for 4 h.Interactions between Ti-47Al-2Cr-2Nb(at%) alloys and the molds at 1650℃ for 30 min were studied.The microstructures of the metalmold interfaces and the presence of inclusions and oxygen contamination in the TiAl bulk alloy were analyzed,and the influences of ammonium metatungstate were discussed.The results indicate that WO_(3)releases O into the TiAl melt,introducing tungsten metal into the alloy matrix.The TiAl alloy ingots cast in the ZY molds had the fewest inclusions and the lowest oxygen contamination.展开更多
Sacrificial multi-piece molds can be used for producing complex parts. To obtain the optimal design of molds automatically, a multi-objective optimal approach is proposed. Mold pieces number, material utilization and ...Sacrificial multi-piece molds can be used for producing complex parts. To obtain the optimal design of molds automatically, a multi-objective optimal approach is proposed. Mold pieces number, material utilization and partitioning area are taken as the objective functions, and the machinability of each mold piece is taken as constraint condition. Genetic algorithm (GA) is adopted to realize global optimization of partitioning process. Each mold piece in optimal scheme can be manufactured by milling and drilling operations, which reduce the tooling cost and shorten product cycle obviously. Using the proposed approach, mold design can be significantly automated for making complex parts.展开更多
Rotation sintering, also known as slush molding, is used to manufacture molded skins, such as dashboards or door interior panels for cars. At present, approximately 80% of such molded skins are manufactured using elec...Rotation sintering, also known as slush molding, is used to manufacture molded skins, such as dashboards or door interior panels for cars. At present, approximately 80% of such molded skins are manufactured using electroforms to achieve the complex free-form surfaces, and surface structures, such as leather graining that the industry demands. The manufacture of these electroforms is, however, time-consuming and expensive. This project aims to replace conventional electroforms with laser-drilled molds. Holes in tool molds should be drilled by using laser radiation as part of an automated process. The system consists of a robot with a fiber-laser beam source. A CAx （computer-aided x） process chain has been developed for this purpose in which the CAD （computer-aided design） data of the tool molds are processed, drill hole fields generated, and a machine-specific RC （robot control） program created. Process-specific fundamentals, such as suitable process windows and process control, have been devised to manufacture holes using fiber laser radiation The advantages of the new laser-drilled tool molds may result in substituting them for conventional electroforms, allowing old markets to be re-entered or additional markets to be created and targeted through new molds or lower costs.展开更多
In order to improve and evaluate the proficiency testing of cosmetic microorganism detection laboratory,strengthen the control of cosmetic microbial detection quality.In 2019 and 2020,the laboratory of the author’s u...In order to improve and evaluate the proficiency testing of cosmetic microorganism detection laboratory,strengthen the control of cosmetic microbial detection quality.In 2019 and 2020,the laboratory of the author’s unit participated in the proficiency testing(NIFDC-PT-242)and measurement audit(NIFDC-MA-2020-148)for molds and yeasts in cosmetics organized by the National Institutes for Food and Drug Control,respectively.According to the operation instruction for counting molds and yeasts in cosmetics and the Safety and Technical Standards for Cosmetics,the results of the sample for proficiency testing numbered NIFDC-PT-242 were unsatisfactory,and the results of the sample for measurement audit numbered NIFDC-MA-2020-148 were satisfactory.In view of the unsatisfactory results,the laboratory analyzed and summarized from the aspects of“human,machine,material,method and environment”,providing reference for the laboratories participating in proficiency testing and measurement audit..展开更多
The aim of this paper was to study the reaction between a Ti-6Al-4V alloy and boron nitride based investment shell molds used for investment casting titanium. In BN based investment shell molds, the face coatings are ...The aim of this paper was to study the reaction between a Ti-6Al-4V alloy and boron nitride based investment shell molds used for investment casting titanium. In BN based investment shell molds, the face coatings are made of pretreated hexagonal boron nitride （hBN） with a few yttria （Y2O3） and colloidal yttria as binder. The Ti-6Al-4V alloy was melted in a controlled atmosphere induction furnace with a segment water-cooled copper crucible. The cross-section of reaction interface between Ti alloys and shell mold was investigated by electron probe micro-analyzer （EPMA） and microhardness tester. The results show that the reaction is not serious, the thickness of the reacting layer is about 30-50 μm, and the thickness of α-case is about 180-200 pro. Moreover the α-case formation mechanism was also discussed.展开更多
At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce ma...At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed.展开更多
The correlation between the impact toughness and microstructural characteristics of a large bainitic steel bloom has been investigated. The study focuses on microcrack nucleation and propagation in the basic cleavage ...The correlation between the impact toughness and microstructural characteristics of a large bainitic steel bloom has been investigated. The study focuses on microcrack nucleation and propagation in the basic cleavage plane. To analyze the phase transformation during the wind-cooling process, the temperature field of the bloom was acquired by computer simulation, and a continuous cooling transformation experiment was conducted. The results show that compared with the surface of the bloom, the toughness of the bloom’s core is decreased by the increase in proeutectoid ferrite and the coarsening of tempered martensite–austenite constituents. The proeutectoid ferrite decreases the toughness via its effects on carbide precipitation, the formation of martensite–austenite constituents, and the bainite transformation. The relatively large tempered martensite–austenite constituents are conducive to microcrack nucleation and propagation.展开更多
The influence of submerged entry nozzle clogging on the behavior of molten steel in continuously cast slab molds was studied using commercial code CFX4.3. The results indicate that clogging at the top part of the nozz...The influence of submerged entry nozzle clogging on the behavior of molten steel in continuously cast slab molds was studied using commercial code CFX4.3. The results indicate that clogging at the top part of the nozzle port not only increases the velocity of molten steel, but also enhances the wall shear stress, F number and heat flux. This clogging has the greatest effect on the behavior of molten steel. However, clogging at the top 1/3 of the nozzle only increases the velocity of molten steel and has little influence. Clogging at the bottom of the nozzle almost has no influence.展开更多
The permeability of a new investment casting mold system prepared by adding needle cokes has been investigated in this work.The permeability tests of the molds were carried out at the temperature of 25—1200℃The resu...The permeability of a new investment casting mold system prepared by adding needle cokes has been investigated in this work.The permeability tests of the molds were carried out at the temperature of 25—1200℃The results showed that the addition of needle cork could significally increase the permeability of the molds by a factor of about 4 because the burning of needle cokes increased the porosities of the molds.Meanwhile,the needle coke modified molds exhibited higher green strength and greater thickness both on flat section and at sharp edges compared with the full fused silica mold.Taking account of the mold thickness,the needle coke modified molds had increased adjusted fracture load(AFL)by a factor of about 2 at the test temperature of 25—1200℃.The addition of needle coke significally improved the permeability of the molds during both autoclaving and casting,and optimized the correlation between the permeability and green strength of the molds.展开更多
In order to improve the performance of plaster molds for investment casting,a diverse content of glass fiber and polypropylene(PP)fiber was incorporated into the slurry for the preparation of a fiber-reinforced mold.T...In order to improve the performance of plaster molds for investment casting,a diverse content of glass fiber and polypropylene(PP)fiber was incorporated into the slurry for the preparation of a fiber-reinforced mold.The green and fired bending strengths,thermal expansion properties,permeability,and thermal shock resistance of the mold were examined,and the scanning electron microscope(SEM)with energy dispersive spectrometer(EDS)was applied for the observation of fracture morphology.With appropriate content,the introduction of glass fiber was proved to increase the green bending strength and fired bending strength,restrain the thermal expansion and improve the thermal shock resistance of the mold,while the polypropylene fiber added was able to raise the green bending strength and the permeability,reduce the thermal expansion and heighten the thermal shock resistance as well,though the fired bending strength would be weakened slightly.Evenly distributed fibers were capable of enhancing the mechanical properties of the matrix,but agglomerations and bundles of fibers resulting from excessive addition had a negative impact.Meanwhile,it was also manifested that micropores left by ablative polypropylene fibers could improve the permeability and reduce the thermal expansion of the mold,and the fired bending strength would be decreased slightly by the deterioration of continuous structure.Three different ratios of hybrid fiber were employed in plaster molds,which can meet altered requirement of castings.The samples modified with hybrid fiber possessed lower thermal deformation,higher air permeability,and better resistance of thermal shock,while the mechanical strength was equal to the fiber free sample or slightly increased.展开更多
In order to develop super-board and super-thick slabs, the flow and temperatur fields were studied in slab continuous casting molds under different practical conditions, such as slab dimensions, with-drawing slab spee...In order to develop super-board and super-thick slabs, the flow and temperatur fields were studied in slab continuous casting molds under different practical conditions, such as slab dimensions, with-drawing slab speed, design of nozzles, and superheat tempera-ture. The results showed that it is preferred to incline nozzle bores downwards and the submerged depth of the nozzles is best kept be-tween 250-300 mm. In addition, the solidified shell is thicker at the wide face than that at the narrow face, while the thin points alongthe wide face ekist both in the center and in the some area toward each respective end.展开更多
基金Generalitat Valenciana(GVA)and Spanish Ministry of Science and Innovation(Grant Nos.TED2021-130879 B-C21,CIACIF/2021/286,PID2023-151110OB-I00,and CIPROM/2022/3)to provide funds for conducting experiments and software licensessupported by the National Research Foundation,Prime Minister's Office,Singapore under its Campus for Research Excellence and Technological Enterprise(CREATE)programme。
文摘Military missions in hostile environments are often costly and unpredictable,with squadrons sometimes facing isolation and resource scarcity.In such scenarios,critical components in vehicles,drones,and energy generators may require structural reinforcement or repair due to damage.This paper proposes a portable,on-site production method for molds under challenging conditions,where material supply is limited.The method utilizes large format additive manufacturing(LFAM)with recycled composite materials,sourced from end-of-life components and waste,as feedstock.The study investigates the microstructural effects of recycling through shredding techniques,using microscopic imaging.Three potential defense-sector applications are explored,specifically in the aerospace,automotive,and energy industries.Additionally,the influence of key printing parameters,particularly nonparallel plane deposition at a 45-degree angle,on the mechanical behavior of ABS reinforced with 20%glass fiber(GF)is examined.The results demonstrate the feasibility of this manufacturing approach,highlighting reductions in waste material and production times compared to traditional methods.Shorter layer times were found to reduce thermal gradients between layers,thereby improving layer adhesion.While 45-degree deposition enhanced Young's modulus,it slightly reduced interlayer adhesion quality.Furthermore,recycling-induced fiber length reduction led to material degradation,aligning with findings from previous studies.Challenges encountered during implementation included weak part adherence to the print bed and local excess material deposition.Overall,the proposed methodology offers a cost-effective alternative to traditional CNC machining for mold production,demonstrating its potential for on-demand manufacturing in resource-constrained environments.
文摘Sorghum is an important cereal crop for smallholder farmers’ food security in many countries in West Africa. However, its production has stagnated due to several factors, such as anthracnose and grain molds. Thus, a study was conducted to identify local germplasms that combine high grain yield and resistance to anthracnose and grain molds under Senegalese environments. A set of 256 genotypes was assessed at Sefa, Sinthiou and Kolda research stations using an incomplete blocks design with two replications. Agro-morphological and phytopathological data were collected. The results revealed a huge phenotypic variation between the genotypes for all traits. The flowering time varied from 43 to 126 days after sowing, while the panicle length varied from 10 to 60 cm. The genotypes were generally more productive at Sinthiou (1653 Kg ha−1) compared to Kolda (164 kg ha−1) research stations. The disease parameters were significantly and positively associated, while the flowering time was strongly and positively associated to grain mold score. The genotypes were classified into three groups with plant height, panicle diameter and length, flowering time and grain mold score as the most discriminating parameters. The genotypes belonging to cluster 3, in addition of being more productive and more resistant to grain mold and anthracnose, have longer panicles. These genotypes present promising prospects for inclusion in breeding programs focused on advancing sorghum yield and disease resistance in Senegal.
文摘The Resin Infusion or the VARTM (Vacuum Assisted Resin Transfer Molding) process has significant potential to be used to manufacture curved composites. Another way to produce curved or complex geometry is to use 3D printers. 3D or FDM (Fused Deposition Modelling) printers are now being used to produce relatively cheaper curved parts using thermoplastics such as PLA. However, the strength and mechanical performance of these parts is limited and can be enhanced if the polymer is reinforced with a type of fiber for instance. Research is being carried out to produce fiber rein-forced thermoplastic composites but that process is expected to be more expensive than the alternative methods such as injection or compression molding. Furthermore, to understand the manufacture of a hybrid composite using thermoplastics, fibers and epoxy resin, research and investigation need to be carried out. In this research</span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">, there are</span></span></span></span></span><span><span><span><span><span style="font-family:""><span style="font-family:Verdana;"> single-sided, double-sided, reusable, disposable and consumable molds. Most of the molds were created either using an FDM printer or manually. These molds were then used to manufacture flat and curved composite structures via the resin injection process, </span><i><span style="font-family:Verdana;">i.e.</span></i><span style="font-family:Verdana;"> VARTM with epoxy resin system and glass/carbon/flax fiber reinforcement. By replacing the costly metallic molds by significantly cheaper molds, the cost of production was expected to further reduce. Furthermore, using double-sided PLA molds was not expected to be a threat to the overall cost of the composite part in question compared to double-sided matched molds used in compression molding. Shear strength, tensile strength and charpy impact strength of most of the manufactured composite parts were also investigated. The strengths were compared based on the method of mold usage. The results showed that this method is effective for a cheaper production of curved epoxy resin composites. However, the strength of the part will decrease as the curved profile gets more complicated unless the basic resin infusion process is altered.
基金supported by the National Key R&D Program of China(grant No.2021YFB3401200)the Jiangsu Provincial Basic Research Program(Natural Science Foundation)Youth Fund(grant No.BK20230885)the Special Technical Project for Equipment Pre-research(grantNo.30104040302).
文摘Owing to its exceptional casting performance,substantial utilization of recycled sand,and environmen-tally sustainable characteristics,frozen sand mold casting technology has found extensive application across diverse sectors,including aerospace,power machinery,and the automotive industry.The focus of the present study was on the development of frozen sand mold formulations tailored for efficient machin-ing,guided by the performance and cutting fracture mechanism of frozen sand molds.A regional tem-perature control device was developed for the purpose of conducting cryogenic cutting experiments on frozen sand molds with varying geometrical characteristics and molding materials.The impact of milling process parameters on the dimension accuracy of both sand molds and castings,as well as castings’surface roughness,were systematically investigated by a whole-process error flow control method.The findings indicate that precise and efficient processing of complicated sand molds was achievable by using sand particles with sizes ranging from 106 to 212μm,and water content between 4 and 5 wt.%,freezing temperature below-25℃,and cutting temperature within the range of-5 to 0℃.Through the frozen-casting of representative components,it was validated that the machining error of the frozen sand mold was within±0.25 mm.Additionally,the dimensional accuracy of the flywheel shell casting conformed to the CT8 specifications.This study provides theoretical guidance for the selection of frozen-casting sand formulations and close-loop control of process size chains for complex metal parts,as well as an overall solution for the realization of sustainable development of green casting.
基金financially supported by the National Natural Science Foundation of China(No.52175352)the Xing Liao Ying Cai Project of Liaoning Province(No.XLYC2008036)the Shenyang Youth Innovation Talent Support Program(No.RC220429)。
文摘The important supporting component in a gas turbine is the casing,which has the characteristics of large size,complex structure,and thin wall.In the context of existing 3DP sand casting processes,casting crack defects are prone to occur.This leads to an increase in the scrap rate of casings,causing significant resource wastage.Additionally,the presence of cracks poses a significant safety hazard after the casings are put into service.The generation of different types of crack defects in stainless steel casings is closely related to casting stress and the high-temperature concession of the sand mold.Therefore,the types and causes of cracks in stainless steel casing products,based on their structural characteristics,were systematically analyzed.Various sand molds with different internal topology designs were printed using the 3DP technology to investigate the impact of sand mold structures on high-temperature concession.The optimal sand mold structure was used to cast casings,and the crack suppression effect was verified by analyzing its eddy current testing results.The experimental results indicate that the skeleton structure has an excellent effect on suppressing cracks in the casing.This research holds important theoretical and engineering significance in improving the quality of casing castings and reducing production costs.
基金The paper was financially supported by the National Natural Science Foundation of China(Grant No.59235102).
文摘The effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroidal graphite cast iron have been studied, considering the parameters of carbon equivalent, inoculation, casting modulus, mold type (green or dry) and pouring temperature within specific ranges of these variables. Based on the orthogonal experiments, the metallurgical and processing parameters of the minimum casting shrinkage and the maximum casting shrinkage were obtained, and the effects of metallurgical and processing parameters on the formation of shrinkage cavities and porosities in spheroids graphite cast iron castings were discussed. Finally, two regression equations relating these variables to the formation of shrinkage porosity were derived based upon the orthogonal experiments conducted.
文摘Twenty-eight molds were isolated from clinical blood cultures and were unidentifiable by cellular morphology using conventional microscopy. Using the utility of amplification and direct sequencing of internal transcribed spacer region of ribosomal RNA gene, 93% of these fungi were identified. Seventy-one percents of the molds were found to be associated with plants or soil with no or few published cases of human disease. These include species of basidiomycetes and ascomycetes such as Botryosphaeria dothidea, Phomopsis flavodonflavus, Inonotus pachyphloeus, Earlilella scabrosa, Calocybe indica, Athelia pellicularis, Tinctoporellus epimiltinus, Trametes lactinea, Coprinellus aureogranulat and Xylaria feejeensis. Some of the nonsporulating molds were identified as pathogen or potential pathogens in immunocompetent or immunocompromised hosts. These include Schizophylum commune and hyphomycetes such as Cladosporium cladosporoides, Aspergillus niger and Fusarium equiseti. Basidiomycetes and hyphomycetes identified in the current study are ubiquitous in the environment and are almost similar to the species of molds reported from cutaneous and respiratory samples suggesting that the fungi may represent contaminants rather than true fangaemia. Results of this study emphasize the need of an effort to minimise blood culture contamination and support the recommendation to incorporate clinical, radiologic findings and positive blood culture for molds in the diagnosis and management of invasive mycosis.
文摘Microbial attacks during storage are one of the primary causes of product deterioration, and can limit the process of prolonging the shelf-life of harvested food. In this study, sweet potatoes were stored at temperatures of 13, 21, and 29 ℃ for 4 weeks. Samples were collected during storage and plated on potato dextrose agar, from which axenic mold cultures were obtained and identified using 26S rRNA gene sequences. Physiological changes of potato tubers were assessed with respect to pathogenicity, enzyme activity, and atmospheric storage conditions. Six fungal species were identified, namely Penicillium chrysogenum （P. rubens）, P. brevicompactum, Mucor circinelloides, C/adosporium cladosporiodes, P. expansum, and P. crustosum. The following fungal isolates, namely P. expansum, P. brevicompactum, and Rhizopus oryzae, were recovered from the re-infected samples and selected according to their levels of enzyme activity. This study revealed high levels of activity for cellulase and pectinase, which were most notable during the initial three days of testing, and were followed by a steady decrease （P〈0.05）. Polygalacturonase activity was prominent with values ranging from 12.64 to 56.79 U/mg （P. expansum） and 18.36 to 79.01 U/mg （P. brevicompactum）. Spoilage was obvious in the control group, which had a 100% decay at the end of the experimental period compared with samples treated with iprodione and sodium hypochlorite, in which the decay rates were 5% and 55%, respectively. The data for the iprodione- and sodium hypochlorite-treated samples at the end of the 3-month storage period showed that they were significantly different （P=0.041）, with the sodium hypochlorite-treated samples producing twice the rate of infection compared to the iprodione-treated samples. The comparative rate of the pro- gression of decay in the treated samples can be expressed as iprodione〈sodium hypochlorite〈control. This study demonstrates that sweet potato tissue damage is due to the activities of microbial enzymes and, in particular, the pectinases of the organisms isolated from the infected potato tissues, and suggests the advantages of utilizing iprodione as a curing agent for potato tubers before storage.
基金financially supported by the Beijing Natural Science Foundation (No.2164054)the National Natural Science Foundation of China (No.51301005)。
文摘Two types of diacetatozirconic acid-yttria molds which were labeled as ZYW mold(diacetatozirconic acidyttria mold with traces of ammoium metatungstate in the slurry) and ZY mold(diacetatozirconic acid-yttria mold without ammonium metatungstate) were prepared by traditional investment casting.The ZYW and ZY molds were sintered in a carbon-reducing atmosphere and in air,respectively,at 1550℃ for 4 h.Interactions between Ti-47Al-2Cr-2Nb(at%) alloys and the molds at 1650℃ for 30 min were studied.The microstructures of the metalmold interfaces and the presence of inclusions and oxygen contamination in the TiAl bulk alloy were analyzed,and the influences of ammonium metatungstate were discussed.The results indicate that WO_(3)releases O into the TiAl melt,introducing tungsten metal into the alloy matrix.The TiAl alloy ingots cast in the ZY molds had the fewest inclusions and the lowest oxygen contamination.
文摘Sacrificial multi-piece molds can be used for producing complex parts. To obtain the optimal design of molds automatically, a multi-objective optimal approach is proposed. Mold pieces number, material utilization and partitioning area are taken as the objective functions, and the machinability of each mold piece is taken as constraint condition. Genetic algorithm (GA) is adopted to realize global optimization of partitioning process. Each mold piece in optimal scheme can be manufactured by milling and drilling operations, which reduce the tooling cost and shorten product cycle obviously. Using the proposed approach, mold design can be significantly automated for making complex parts.
文摘Rotation sintering, also known as slush molding, is used to manufacture molded skins, such as dashboards or door interior panels for cars. At present, approximately 80% of such molded skins are manufactured using electroforms to achieve the complex free-form surfaces, and surface structures, such as leather graining that the industry demands. The manufacture of these electroforms is, however, time-consuming and expensive. This project aims to replace conventional electroforms with laser-drilled molds. Holes in tool molds should be drilled by using laser radiation as part of an automated process. The system consists of a robot with a fiber-laser beam source. A CAx （computer-aided x） process chain has been developed for this purpose in which the CAD （computer-aided design） data of the tool molds are processed, drill hole fields generated, and a machine-specific RC （robot control） program created. Process-specific fundamentals, such as suitable process windows and process control, have been devised to manufacture holes using fiber laser radiation The advantages of the new laser-drilled tool molds may result in substituting them for conventional electroforms, allowing old markets to be re-entered or additional markets to be created and targeted through new molds or lower costs.
文摘In order to improve and evaluate the proficiency testing of cosmetic microorganism detection laboratory,strengthen the control of cosmetic microbial detection quality.In 2019 and 2020,the laboratory of the author’s unit participated in the proficiency testing(NIFDC-PT-242)and measurement audit(NIFDC-MA-2020-148)for molds and yeasts in cosmetics organized by the National Institutes for Food and Drug Control,respectively.According to the operation instruction for counting molds and yeasts in cosmetics and the Safety and Technical Standards for Cosmetics,the results of the sample for proficiency testing numbered NIFDC-PT-242 were unsatisfactory,and the results of the sample for measurement audit numbered NIFDC-MA-2020-148 were satisfactory.In view of the unsatisfactory results,the laboratory analyzed and summarized from the aspects of“human,machine,material,method and environment”,providing reference for the laboratories participating in proficiency testing and measurement audit..
文摘The aim of this paper was to study the reaction between a Ti-6Al-4V alloy and boron nitride based investment shell molds used for investment casting titanium. In BN based investment shell molds, the face coatings are made of pretreated hexagonal boron nitride （hBN） with a few yttria （Y2O3） and colloidal yttria as binder. The Ti-6Al-4V alloy was melted in a controlled atmosphere induction furnace with a segment water-cooled copper crucible. The cross-section of reaction interface between Ti alloys and shell mold was investigated by electron probe micro-analyzer （EPMA） and microhardness tester. The results show that the reaction is not serious, the thickness of the reacting layer is about 30-50 μm, and the thickness of α-case is about 180-200 pro. Moreover the α-case formation mechanism was also discussed.
基金financially supported by the Technical Development Foundation of China Academy of Machinery Science and Technology under project:Investment Casting Technology Research for TiAl Alloy Turbocharger Turbine
文摘At present, most TiAl components are produced by an investment casting process. Environmental and economic pressures have, however, resulted in a need for the industry to improve the current casting quality, reduce manufacturing costs and explore new markets for the process. Currently, the main problems for investment casting of TiAl alloys are cracks, porosities, and surface defects. To solve these problems, many studies have been conducted around the world, and it is found that casting defects can be reduced by improving composition and properties of the shell molds. It is important to make a summary for the related research progress for quality improvement of TiAl castings. So, the development on refractory composition of shell molds for TiAl alloy investment castings was reviewed, and research progress on deformability of shell mold for TiAl alloy castings both at home and abroad in recent years was introduced. The existing methods for deformability characterization and methods for improving the deformability of shell molds were summarized and discussed. The updated advancement in numerical simulation of TiAl alloy investment casting was presented, showing the necessity for considering the deformability of shell mold during simulation. Finally, possible research points for future studies on deformability of shell mold for TiAl alloy investment casting were proposed.
文摘The correlation between the impact toughness and microstructural characteristics of a large bainitic steel bloom has been investigated. The study focuses on microcrack nucleation and propagation in the basic cleavage plane. To analyze the phase transformation during the wind-cooling process, the temperature field of the bloom was acquired by computer simulation, and a continuous cooling transformation experiment was conducted. The results show that compared with the surface of the bloom, the toughness of the bloom’s core is decreased by the increase in proeutectoid ferrite and the coarsening of tempered martensite–austenite constituents. The proeutectoid ferrite decreases the toughness via its effects on carbide precipitation, the formation of martensite–austenite constituents, and the bainite transformation. The relatively large tempered martensite–austenite constituents are conducive to microcrack nucleation and propagation.
文摘The influence of submerged entry nozzle clogging on the behavior of molten steel in continuously cast slab molds was studied using commercial code CFX4.3. The results indicate that clogging at the top part of the nozzle port not only increases the velocity of molten steel, but also enhances the wall shear stress, F number and heat flux. This clogging has the greatest effect on the behavior of molten steel. However, clogging at the top 1/3 of the nozzle only increases the velocity of molten steel and has little influence. Clogging at the bottom of the nozzle almost has no influence.
基金the 13th Five-Year Common Technology Equipment Development Project(No.41423040206)the Industry-University-Research Cooperation Annual Plan of Shanghai(No.CXY2016004)
文摘The permeability of a new investment casting mold system prepared by adding needle cokes has been investigated in this work.The permeability tests of the molds were carried out at the temperature of 25—1200℃The results showed that the addition of needle cork could significally increase the permeability of the molds by a factor of about 4 because the burning of needle cokes increased the porosities of the molds.Meanwhile,the needle coke modified molds exhibited higher green strength and greater thickness both on flat section and at sharp edges compared with the full fused silica mold.Taking account of the mold thickness,the needle coke modified molds had increased adjusted fracture load(AFL)by a factor of about 2 at the test temperature of 25—1200℃.The addition of needle coke significally improved the permeability of the molds during both autoclaving and casting,and optimized the correlation between the permeability and green strength of the molds.
文摘In order to improve the performance of plaster molds for investment casting,a diverse content of glass fiber and polypropylene(PP)fiber was incorporated into the slurry for the preparation of a fiber-reinforced mold.The green and fired bending strengths,thermal expansion properties,permeability,and thermal shock resistance of the mold were examined,and the scanning electron microscope(SEM)with energy dispersive spectrometer(EDS)was applied for the observation of fracture morphology.With appropriate content,the introduction of glass fiber was proved to increase the green bending strength and fired bending strength,restrain the thermal expansion and improve the thermal shock resistance of the mold,while the polypropylene fiber added was able to raise the green bending strength and the permeability,reduce the thermal expansion and heighten the thermal shock resistance as well,though the fired bending strength would be weakened slightly.Evenly distributed fibers were capable of enhancing the mechanical properties of the matrix,but agglomerations and bundles of fibers resulting from excessive addition had a negative impact.Meanwhile,it was also manifested that micropores left by ablative polypropylene fibers could improve the permeability and reduce the thermal expansion of the mold,and the fired bending strength would be decreased slightly by the deterioration of continuous structure.Three different ratios of hybrid fiber were employed in plaster molds,which can meet altered requirement of castings.The samples modified with hybrid fiber possessed lower thermal deformation,higher air permeability,and better resistance of thermal shock,while the mechanical strength was equal to the fiber free sample or slightly increased.
文摘In order to develop super-board and super-thick slabs, the flow and temperatur fields were studied in slab continuous casting molds under different practical conditions, such as slab dimensions, with-drawing slab speed, design of nozzles, and superheat tempera-ture. The results showed that it is preferred to incline nozzle bores downwards and the submerged depth of the nozzles is best kept be-tween 250-300 mm. In addition, the solidified shell is thicker at the wide face than that at the narrow face, while the thin points alongthe wide face ekist both in the center and in the some area toward each respective end.
