- Email: [email protected]
Purification of Aluminum melt in Crucibles by Bubble Flotation
Available online at www.sciencedirect.com Available online at www.sciencedirect.com
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Available Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Procedia Manufacturing 00 (2019) 000–000 Procedia Manufacturing 00 (2019) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Manufacturing 37 (2019) 438–442 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
9th International Conference on Physical and Numerical Simulation of Materials Processing (ICPNS’2019) 9th International Conference on Physical and Numerical Simulation of Materials Processing (ICPNS’2019)
Purification of Aluminum melt in Crucibles by Bubble Flotation Purification of Aluminum melt in Crucibles by Bubble Flotation
a b c a Manufacturing Engineering Society International Conference 2017, MESIC 2017, 28-30 June Qiang Li a, Kezhun Heb, Ni Wuc,Jianmin Zenga* 2017, Vigo (Pontevedra), Spain Qiang Li , Kezhun He , Ni Wu ,Jianmin Zeng * a
Key Lab. of nonferrous Materials and New Processing Technology, Guangxi University, Nanning, 530004, China b Key Lab. of nonferrous Materials and New Processing Technology, University, Nanning, 530004, China Alnanaluminum CO., LTD, Nanning, Guangxi 530031, China b c Alnanaluminum CO., LTD, Nanning, 530031, China NationalAluminum Metal Product Quality Supervision and Inspection Center, Baise, 532000, China c NationalAluminum Metal Product Quality Supervision and Inspection Center, Baise, 532000, China
a
Costing models for capacity optimization in Industry 4.0: Trade-off between used capacity and operational efficiency Abstract A. Santanaa, P. Afonsoa,*, A. Zaninb, R. Wernkeb Abstract According to the principle of bubble floatation, of A356 aluminum casting alloy has been studied by purging a University purification of Minho, 4800-058 Guimarães, Portugal According the the principle of bubble floatation, purification of Chapecó, A356 casting alloy hasmolten been studied by and purging b nitrogen gastointo A356 alloy melt through a patented porous sprayeraluminum which is immerged in the aluminum can Unochapecó, 89809-000 SC, Brazil nitrogen agas intoquantity the A356 melt micro through a patented porous which immerged in the molten aluminum generate large of alloy dispersed bubbles to absorb the sprayer hydrogen and is carry the nonmetallic inclusions in theand meltcan to generate a large quantity of dispersed microhave bubbles absorb out the in hydrogen carry the in the melt to the surface of the melt. The experiments beentocarried differentand capacity of nonmetallic crucibles forinclusions the assessment of the the surfaceofofeffectiveness. the melt. The experiments carried out 4inmin, different of 10 crucibles for the assessment of the evaluation 5 samples were have takenbeen at 0 min, 2 min, 6 min,capacity 8 min and min, respectively, to measure evaluation of effectiveness. 5 samples Ⅱ were taken at tester 0 min,in2 min, 4 min, 6 min, min and min, respectively, measure Abstract hydrogen content through HYSCAN hydrogen the temperature of 8720C. The10experiments results to show that the hydrogen contentofthrough HYSCAN hydrogen in the temperature ofcontents 720C. The results thatlasts the removing effects hydrogen and oxideⅡinclusion aretester remarkable. The hydrogen reachexperiments the minimum whenshow purging removing of hydrogen and oxide inclusion are remarkable. The hydrogen contents reach minimum when lasts 10, 8 and 4 minutes for 280kg, 160kg and 40kg, respectively. The inclusions are also removed along with thepurging removal of Under theeffects concept ofthe "Industry 4.0", production processes will be pushed to be the increasingly interconnected, 10, 8 and 4 minutes for athe 280kg, and 40kg, respectively. inclusions are In also removed along with the removal of hydrogen. information based on real time 160kg basis and, necessarily, muchThe more efficient. this context, capacity optimization hydrogen. goes beyond the traditional aim of capacity maximization, contributing also for organization’s profitability and value. © 2019 The Authors. Publishedand by Elsevier B.V. improvement approaches suggest capacity optimization instead of Indeed, lean management continuous © 2019 2019 The Authors. by Elsevier B.V. © The Authors. Published by Elsevier B.V. This is an open accessPublished article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) This is is an an open open access access articleof under the CC CCoptimization BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) maximization. The study capacity and costing models is an important research topic that deserves This article under BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility ofthe the scientific committee of the 9th International Conference on Physical and Numerical Peer-review under responsibility of the and scientific committee of the 9th This International Conference Physicala and Numerical contributions from both the practical theoretical perspectives. paper presents and on discusses mathematical Peer-reviewonunder responsibility of the scientific committee of the 9th International Conference on Physical and Numerical Simulation Processing Simulation on Materials Materials Processing based on different costing models (ABC and TDABC). A generic model has been model for capacity management Simulation on Materials Processing
developed and it was analyze idle capacity and to alloy. design strategies towards the maximization of organization’s Keywords:Aluminum cast used alloy; to purification; bubble floatation, A356 Keywords:Aluminum cast capacity alloy; purification; bubble floatation, A356 alloy.efficiency is highlighted and it is shown that capacity value. The trade-off maximization vs operational optimization might hide operational inefficiency. © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency
Introduction *1.Corresponding author. Tel.:+86-771-3232200; fax: +86-771-3234560. * E-mail Corresponding author. Tel.:+86-771-3232200; fax: +86-771-3234560. address:[email protected] E-mail address:[email protected] The cost of idle capacity is a fundamental information for companies and their management of extreme importance
2351-9789© 2019 The Authors. Published by Elsevier B.V. in modern production systems. In general, it is defined as unused capacity or production potential and can be measured 2351-9789© 2019 Thearticle Authors. Published Elsevier B.V. Thisseveral is an open access the CC by BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) in ways: tons ofunder production, available hours of manufacturing, etc. The management of the idle capacity This is an open access article under CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the 9th International Conference on Physical and Numerical Simulation on * Paulo Afonso. +351 253of 510 fax: +351 253 604of741 Peer-review underTel.: responsibility the761; scientific committee the 9th International Conference on Physical and Numerical Simulation on Materials Processing E-mailProcessing address: [email protected] Materials
2351-9789 Published by Elsevier B.V. B.V. 2351-9789 ©©2017 2019The TheAuthors. Authors. Published by Elsevier Peer-review underaccess responsibility of the scientific committee oflicense the Manufacturing Engineering Society International Conference 2017. This is an open article under the CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the 9th International Conference on Physical and Numerical Simulation on Materials Processing 10.1016/j.promfg.2019.12.071
2
Qiang Li et al. / Procedia Manufacturing 37 (2019) 438–442 Author name / Procedia Manufacturing 00 (2019) 000–000
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1. Introduction Molten aluminum reacts with water vapor and oxygen in the air to result in the formation of aluminum oxide and hydrogen during the melting and mould filling. Casting defects such as pinholes, oxide inclusions and dross in the casting were formed because of the precipitation of resolved hydrogen and oxide inclusions [1-4]. Mechanical properties of materials will also been seriously deteriorated due to stress concentration around the pinholes and inclusions in the casting. The purpose of purification is to decrease the harmful inclusions and hydrogen to an acceptable level and improve the mechanical performance of the casting. Basically there are two industrial techniques used to perform melt purification: flotation and filtration [5-7]. Flotation techniques have been widely used in the foundry industry because this process was effective in reducing hydrogen and inclusion contents in the melt. Bubble floatation is a very efficient purification technology of aluminum melt, in which a hundred and thousand of bubbles were purged into the aluminum melt, the flush of inert gas bubbles brings the inclusions in suspension to the melt surface to be skimmed off. In the present paper, a porous ceramic sprayer was employed to generate dispersed bubbles in the melt. The relationship between purging time and hydrogen contents, along with removal of oxide inclusion, has been investigated with different capacity of the A356 melt. 2. Experimental setup A356 aluminum cast alloy was employed for experiment material. The chemical compositions of alloy are 7.5% Si, 0.43% Mg and 0.08% Ti with aluminum balanced. A burden of 40Kg, 160kg and 280kg was melted, respectively in the electric resistance furnace and the temperature of the melt was maintained at 720C for use. The purging device comprises a nitrogen gas tank A, a relief valve B, a manometer C, an air filter D, a molecular sieve E, a gas flow-meter F and a porous sprayer P, as shown in figure 1.
Fig. 1. The schematic of the flotation device.
The nitrogen gas in the tank A enters into tank D and E for drying and filtrating to remove water via the relief valve B to decrease the pressure. The dried nitrogen gas then enters into the porous sprayer via the flow-meter by which the flow rate of the gas can be adjusted accurately. In the experiment, the flow rate was set to 0.2m3/h. sampling were done at 0 min, 2 min,4 min,6 min,8 min and 10 min, respectively to measure hydrogen contents in the melt and 5 tests were performed. The device at our pilot workshop was seen in figure 2. The pressure of nitrogen gas was set to 0.2MPa. Figure 3 showed an immerged sprayer was working with A356 melt in a crucible. The bubbles can be seen on the surface of the melt from figure 3. HYSCAN Ⅱ hydrogen tester was used to detect the hydrogen content in the A356 melt. A sample of the molten alloy (100g) is poured into a small, stainless steel chamber and the pressure reduced within several seconds to 10 -1 mbar by a vacuum pump. The chamber and associated vacuum system is then isolated from the pump and the sample allowed to solidify. As hydrogen is released during cooling, its partial pressure is measured by a calibrated Pirani gauge from which the hydrogen content in the sample is calculated.
Qiang Li et al. / Procedia Manufacturing 37 (2019) 438–442 Author name / Procedia Manufacturing00 (2019) 000–000
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3
Fig. 2. Flotation equipment at our pilot workshop
Fig. 3. An immerged sprayer was working.
3. Results and analysis The relationship between nitrogen purging time and hydrogen content in A356 melt was shown (a), (b) and (c) in figure 4. It can be seen that hydrogen contents decrease as the purging time increases. The times for minimum hydrogen concentration were about 10 min, 8 min and 4 min for the aluminum melts of 280kg, 160kg and 40kg, respectively. The degassing efficiency was remarkable. The hydrogen contents were decreased by approximately 60% on average for the three capacity of melt. According to the diffusion theory, the hydrogen removing efficient can be expressed by the mass transfer coefficient K [5]:
K
Du D e
(1)
where, D is the diffusion coefficient; u is the rising speed of the bubble and De is the equivalent diameter of the bubbles. The hydrogen in the melt will diffuse into the bubble under the partial pressure difference until the hydrogen partial pressure reached balance. During the flotation, the bubbles float, taking with the inclusions to the liquid surface to be skimmed off. It can be seen from the equation (1) that hydrogen removing efficient depends mainly on the diameter of the bubble. The small the bubble is, the higher hydrogen removing efficient is. As the hydrogen concentration difference between the melt and the bubble was so tremendous that the degassing speed was fast in the beginning period. With the increasing of the purging time, the hydrogen content continue to decrease but the speed was slow down due to the less hydrogen concentration difference between the melt and the bubble. From the figure 4, the hydrogen content reaches the minimum value at 10 min, 8 min and 4 min for the capacity of 280kg, 160kg and 40kg melt, respectively, with the hydrogen being near to 0.1ml/100gAl.
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Qiang Li et al. / Procedia Manufacturing 37 (2019) 438–442 Author name / Procedia Manufacturing 00 (2019) 000–000
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Under ordinary melting conditions a wide variety of inclusions can be found in an aluminum melt. However, most inclusion is aluminum oxide which is usually present as flake and flocculent, as shown in figure 5. In castings, pore nucleation can be possible to occur primarily at heterogeneous sites which are linked with inclusions. Microstructures before and after melt treatment can be compared in figure 6 in which (a) is before purification and (b) is after purification for the case of 40kg melt. It can be seen that the oxide inclusion (the black) is also decreased drastically.
(a)
(b)
(c) Fig. 4. The relationship between degassing time and hydrogen content in melt (a) 280kg melt, (b) 160kg melt and (c) 40kg melt.
Fig. 5. Oxide inclusion in A356 cast alloy.
Qiang Li et al. / Procedia Manufacturing 37 (2019) 438–442 Author name / Procedia Manufacturing00 (2019) 000–000
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(a)
5
(b)
Fig. 6. The microscopic image of A356 alloy, (a) before and (b) after purification treatment.
4. Conclusions A simple method of purification has been proposed. In which, a porous ceramic prayer is immerged into the aluminum melt and nitrogen gas is ejected from the micro holes, dispersed in the melt. Hydrogen contents decrease with the increasing of purging time. At 10, 8 and 4 minutes, the hydrogen content get to the minimum for 280kg, 160kg and 40kg melt, respectively. The aluminum oxide inclusion is also decreased drastically. This lightweight device is very suitable for small foundry workshops. Acknowledgements The authors gratefully acknowledge the support of Major Science and Technology Projects in Guangxi (Guike AA17204012-2) and the support of the project in the collaborative innovation of ecological aluminum industry in Guangxi. References [1] J.M. Zeng, Ping Gu, Youbing Wang, Investigation of Inner Vacuum Sucking method for degassing of molten aluminum Materials Science and Engineering B, 177 (2012) 1717-1720. [2] J.M. Zeng, Yaohe Zhou, A New Sand Casting Process with Accelerated Solidification Rate, Mater. Sci. Forum, 686 (2011) 765-769. [3] Z.B. Xu, Y.Z. Zou, W.C. Wang, X.Z. Pang and J.M. Zeng, An Investigation on the Impurities of Aluminum Alloy in Melt Furnace, Advanced Materials Research, 97-101 (2010) 1045-1048. [4] Y. Li, Z.B. Xu and J.M. Zeng, Effect of hydrogen content on impact property of A357 alloy, Materials Science Forum, 704-705(2012) 12011204. [5] C.G.Hao, D.Z.Li and J.M.Zeng, Research on Porous sprayer for Refining of Aluminum Melt, Advanced Materials Research, 418-420 (2012) 1856-1859. [6] H.H.Zhan, J.M.Zeng, P.P.Chen, Z.Y.Lin, A New porous Mullite Nozzle for Refining Molten Aluminum, Applied Mechanics and Materials 117-119 (2012) 1701-1704. [7] J.M. Zeng, D.Z.Li, Z.B.Xu and Y.B.Wang, Hydrogen Diffusion in Molten Aluminum A206 Casting Alloy, Advanced Science Letters, 4 (2011) 1-5.
ScienceDirect ScienceDirect
Available Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Procedia Manufacturing 00 (2019) 000–000 Procedia Manufacturing 00 (2019) 000–000
ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Procedia Manufacturing 37 (2019) 438–442 Procedia Manufacturing 00 (2017) 000–000 www.elsevier.com/locate/procedia
9th International Conference on Physical and Numerical Simulation of Materials Processing (ICPNS’2019) 9th International Conference on Physical and Numerical Simulation of Materials Processing (ICPNS’2019)
Purification of Aluminum melt in Crucibles by Bubble Flotation Purification of Aluminum melt in Crucibles by Bubble Flotation
a b c a Manufacturing Engineering Society International Conference 2017, MESIC 2017, 28-30 June Qiang Li a, Kezhun Heb, Ni Wuc,Jianmin Zenga* 2017, Vigo (Pontevedra), Spain Qiang Li , Kezhun He , Ni Wu ,Jianmin Zeng * a
Key Lab. of nonferrous Materials and New Processing Technology, Guangxi University, Nanning, 530004, China b Key Lab. of nonferrous Materials and New Processing Technology, University, Nanning, 530004, China Alnanaluminum CO., LTD, Nanning, Guangxi 530031, China b c Alnanaluminum CO., LTD, Nanning, 530031, China NationalAluminum Metal Product Quality Supervision and Inspection Center, Baise, 532000, China c NationalAluminum Metal Product Quality Supervision and Inspection Center, Baise, 532000, China
a
Costing models for capacity optimization in Industry 4.0: Trade-off between used capacity and operational efficiency Abstract A. Santanaa, P. Afonsoa,*, A. Zaninb, R. Wernkeb Abstract According to the principle of bubble floatation, of A356 aluminum casting alloy has been studied by purging a University purification of Minho, 4800-058 Guimarães, Portugal According the the principle of bubble floatation, purification of Chapecó, A356 casting alloy hasmolten been studied by and purging b nitrogen gastointo A356 alloy melt through a patented porous sprayeraluminum which is immerged in the aluminum can Unochapecó, 89809-000 SC, Brazil nitrogen agas intoquantity the A356 melt micro through a patented porous which immerged in the molten aluminum generate large of alloy dispersed bubbles to absorb the sprayer hydrogen and is carry the nonmetallic inclusions in theand meltcan to generate a large quantity of dispersed microhave bubbles absorb out the in hydrogen carry the in the melt to the surface of the melt. The experiments beentocarried differentand capacity of nonmetallic crucibles forinclusions the assessment of the the surfaceofofeffectiveness. the melt. The experiments carried out 4inmin, different of 10 crucibles for the assessment of the evaluation 5 samples were have takenbeen at 0 min, 2 min, 6 min,capacity 8 min and min, respectively, to measure evaluation of effectiveness. 5 samples Ⅱ were taken at tester 0 min,in2 min, 4 min, 6 min, min and min, respectively, measure Abstract hydrogen content through HYSCAN hydrogen the temperature of 8720C. The10experiments results to show that the hydrogen contentofthrough HYSCAN hydrogen in the temperature ofcontents 720C. The results thatlasts the removing effects hydrogen and oxideⅡinclusion aretester remarkable. The hydrogen reachexperiments the minimum whenshow purging removing of hydrogen and oxide inclusion are remarkable. The hydrogen contents reach minimum when lasts 10, 8 and 4 minutes for 280kg, 160kg and 40kg, respectively. The inclusions are also removed along with thepurging removal of Under theeffects concept ofthe "Industry 4.0", production processes will be pushed to be the increasingly interconnected, 10, 8 and 4 minutes for athe 280kg, and 40kg, respectively. inclusions are In also removed along with the removal of hydrogen. information based on real time 160kg basis and, necessarily, muchThe more efficient. this context, capacity optimization hydrogen. goes beyond the traditional aim of capacity maximization, contributing also for organization’s profitability and value. © 2019 The Authors. Publishedand by Elsevier B.V. improvement approaches suggest capacity optimization instead of Indeed, lean management continuous © 2019 2019 The Authors. by Elsevier B.V. © The Authors. Published by Elsevier B.V. This is an open accessPublished article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) This is is an an open open access access articleof under the CC CCoptimization BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) maximization. The study capacity and costing models is an important research topic that deserves This article under BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility ofthe the scientific committee of the 9th International Conference on Physical and Numerical Peer-review under responsibility of the and scientific committee of the 9th This International Conference Physicala and Numerical contributions from both the practical theoretical perspectives. paper presents and on discusses mathematical Peer-reviewonunder responsibility of the scientific committee of the 9th International Conference on Physical and Numerical Simulation Processing Simulation on Materials Materials Processing based on different costing models (ABC and TDABC). A generic model has been model for capacity management Simulation on Materials Processing
developed and it was analyze idle capacity and to alloy. design strategies towards the maximization of organization’s Keywords:Aluminum cast used alloy; to purification; bubble floatation, A356 Keywords:Aluminum cast capacity alloy; purification; bubble floatation, A356 alloy.efficiency is highlighted and it is shown that capacity value. The trade-off maximization vs operational optimization might hide operational inefficiency. © 2017 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the scientific committee of the Manufacturing Engineering Society International Conference 2017. Keywords: Cost Models; ABC; TDABC; Capacity Management; Idle Capacity; Operational Efficiency
Introduction *1.Corresponding author. Tel.:+86-771-3232200; fax: +86-771-3234560. * E-mail Corresponding author. Tel.:+86-771-3232200; fax: +86-771-3234560. address:[email protected] E-mail address:[email protected] The cost of idle capacity is a fundamental information for companies and their management of extreme importance
2351-9789© 2019 The Authors. Published by Elsevier B.V. in modern production systems. In general, it is defined as unused capacity or production potential and can be measured 2351-9789© 2019 Thearticle Authors. Published Elsevier B.V. Thisseveral is an open access the CC by BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) in ways: tons ofunder production, available hours of manufacturing, etc. The management of the idle capacity This is an open access article under CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the 9th International Conference on Physical and Numerical Simulation on * Paulo Afonso. +351 253of 510 fax: +351 253 604of741 Peer-review underTel.: responsibility the761; scientific committee the 9th International Conference on Physical and Numerical Simulation on Materials Processing E-mailProcessing address: [email protected] Materials
2351-9789 Published by Elsevier B.V. B.V. 2351-9789 ©©2017 2019The TheAuthors. Authors. Published by Elsevier Peer-review underaccess responsibility of the scientific committee oflicense the Manufacturing Engineering Society International Conference 2017. This is an open article under the CC BY-NC-ND (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer-review under responsibility of the scientific committee of the 9th International Conference on Physical and Numerical Simulation on Materials Processing 10.1016/j.promfg.2019.12.071
2
Qiang Li et al. / Procedia Manufacturing 37 (2019) 438–442 Author name / Procedia Manufacturing 00 (2019) 000–000
439
1. Introduction Molten aluminum reacts with water vapor and oxygen in the air to result in the formation of aluminum oxide and hydrogen during the melting and mould filling. Casting defects such as pinholes, oxide inclusions and dross in the casting were formed because of the precipitation of resolved hydrogen and oxide inclusions [1-4]. Mechanical properties of materials will also been seriously deteriorated due to stress concentration around the pinholes and inclusions in the casting. The purpose of purification is to decrease the harmful inclusions and hydrogen to an acceptable level and improve the mechanical performance of the casting. Basically there are two industrial techniques used to perform melt purification: flotation and filtration [5-7]. Flotation techniques have been widely used in the foundry industry because this process was effective in reducing hydrogen and inclusion contents in the melt. Bubble floatation is a very efficient purification technology of aluminum melt, in which a hundred and thousand of bubbles were purged into the aluminum melt, the flush of inert gas bubbles brings the inclusions in suspension to the melt surface to be skimmed off. In the present paper, a porous ceramic sprayer was employed to generate dispersed bubbles in the melt. The relationship between purging time and hydrogen contents, along with removal of oxide inclusion, has been investigated with different capacity of the A356 melt. 2. Experimental setup A356 aluminum cast alloy was employed for experiment material. The chemical compositions of alloy are 7.5% Si, 0.43% Mg and 0.08% Ti with aluminum balanced. A burden of 40Kg, 160kg and 280kg was melted, respectively in the electric resistance furnace and the temperature of the melt was maintained at 720C for use. The purging device comprises a nitrogen gas tank A, a relief valve B, a manometer C, an air filter D, a molecular sieve E, a gas flow-meter F and a porous sprayer P, as shown in figure 1.
Fig. 1. The schematic of the flotation device.
The nitrogen gas in the tank A enters into tank D and E for drying and filtrating to remove water via the relief valve B to decrease the pressure. The dried nitrogen gas then enters into the porous sprayer via the flow-meter by which the flow rate of the gas can be adjusted accurately. In the experiment, the flow rate was set to 0.2m3/h. sampling were done at 0 min, 2 min,4 min,6 min,8 min and 10 min, respectively to measure hydrogen contents in the melt and 5 tests were performed. The device at our pilot workshop was seen in figure 2. The pressure of nitrogen gas was set to 0.2MPa. Figure 3 showed an immerged sprayer was working with A356 melt in a crucible. The bubbles can be seen on the surface of the melt from figure 3. HYSCAN Ⅱ hydrogen tester was used to detect the hydrogen content in the A356 melt. A sample of the molten alloy (100g) is poured into a small, stainless steel chamber and the pressure reduced within several seconds to 10 -1 mbar by a vacuum pump. The chamber and associated vacuum system is then isolated from the pump and the sample allowed to solidify. As hydrogen is released during cooling, its partial pressure is measured by a calibrated Pirani gauge from which the hydrogen content in the sample is calculated.
Qiang Li et al. / Procedia Manufacturing 37 (2019) 438–442 Author name / Procedia Manufacturing00 (2019) 000–000
440
3
Fig. 2. Flotation equipment at our pilot workshop
Fig. 3. An immerged sprayer was working.
3. Results and analysis The relationship between nitrogen purging time and hydrogen content in A356 melt was shown (a), (b) and (c) in figure 4. It can be seen that hydrogen contents decrease as the purging time increases. The times for minimum hydrogen concentration were about 10 min, 8 min and 4 min for the aluminum melts of 280kg, 160kg and 40kg, respectively. The degassing efficiency was remarkable. The hydrogen contents were decreased by approximately 60% on average for the three capacity of melt. According to the diffusion theory, the hydrogen removing efficient can be expressed by the mass transfer coefficient K [5]:
K
Du D e
(1)
where, D is the diffusion coefficient; u is the rising speed of the bubble and De is the equivalent diameter of the bubbles. The hydrogen in the melt will diffuse into the bubble under the partial pressure difference until the hydrogen partial pressure reached balance. During the flotation, the bubbles float, taking with the inclusions to the liquid surface to be skimmed off. It can be seen from the equation (1) that hydrogen removing efficient depends mainly on the diameter of the bubble. The small the bubble is, the higher hydrogen removing efficient is. As the hydrogen concentration difference between the melt and the bubble was so tremendous that the degassing speed was fast in the beginning period. With the increasing of the purging time, the hydrogen content continue to decrease but the speed was slow down due to the less hydrogen concentration difference between the melt and the bubble. From the figure 4, the hydrogen content reaches the minimum value at 10 min, 8 min and 4 min for the capacity of 280kg, 160kg and 40kg melt, respectively, with the hydrogen being near to 0.1ml/100gAl.
4
Qiang Li et al. / Procedia Manufacturing 37 (2019) 438–442 Author name / Procedia Manufacturing 00 (2019) 000–000
441
Under ordinary melting conditions a wide variety of inclusions can be found in an aluminum melt. However, most inclusion is aluminum oxide which is usually present as flake and flocculent, as shown in figure 5. In castings, pore nucleation can be possible to occur primarily at heterogeneous sites which are linked with inclusions. Microstructures before and after melt treatment can be compared in figure 6 in which (a) is before purification and (b) is after purification for the case of 40kg melt. It can be seen that the oxide inclusion (the black) is also decreased drastically.
(a)
(b)
(c) Fig. 4. The relationship between degassing time and hydrogen content in melt (a) 280kg melt, (b) 160kg melt and (c) 40kg melt.
Fig. 5. Oxide inclusion in A356 cast alloy.
Qiang Li et al. / Procedia Manufacturing 37 (2019) 438–442 Author name / Procedia Manufacturing00 (2019) 000–000
442
(a)
5
(b)
Fig. 6. The microscopic image of A356 alloy, (a) before and (b) after purification treatment.
4. Conclusions A simple method of purification has been proposed. In which, a porous ceramic prayer is immerged into the aluminum melt and nitrogen gas is ejected from the micro holes, dispersed in the melt. Hydrogen contents decrease with the increasing of purging time. At 10, 8 and 4 minutes, the hydrogen content get to the minimum for 280kg, 160kg and 40kg melt, respectively. The aluminum oxide inclusion is also decreased drastically. This lightweight device is very suitable for small foundry workshops. Acknowledgements The authors gratefully acknowledge the support of Major Science and Technology Projects in Guangxi (Guike AA17204012-2) and the support of the project in the collaborative innovation of ecological aluminum industry in Guangxi. References [1] J.M. Zeng, Ping Gu, Youbing Wang, Investigation of Inner Vacuum Sucking method for degassing of molten aluminum Materials Science and Engineering B, 177 (2012) 1717-1720. [2] J.M. Zeng, Yaohe Zhou, A New Sand Casting Process with Accelerated Solidification Rate, Mater. Sci. Forum, 686 (2011) 765-769. [3] Z.B. Xu, Y.Z. Zou, W.C. Wang, X.Z. Pang and J.M. Zeng, An Investigation on the Impurities of Aluminum Alloy in Melt Furnace, Advanced Materials Research, 97-101 (2010) 1045-1048. [4] Y. Li, Z.B. Xu and J.M. Zeng, Effect of hydrogen content on impact property of A357 alloy, Materials Science Forum, 704-705(2012) 12011204. [5] C.G.Hao, D.Z.Li and J.M.Zeng, Research on Porous sprayer for Refining of Aluminum Melt, Advanced Materials Research, 418-420 (2012) 1856-1859. [6] H.H.Zhan, J.M.Zeng, P.P.Chen, Z.Y.Lin, A New porous Mullite Nozzle for Refining Molten Aluminum, Applied Mechanics and Materials 117-119 (2012) 1701-1704. [7] J.M. Zeng, D.Z.Li, Z.B.Xu and Y.B.Wang, Hydrogen Diffusion in Molten Aluminum A206 Casting Alloy, Advanced Science Letters, 4 (2011) 1-5.