jagomart
digital resources
picture1_Induction Furnace Pdf 180107 | 3 Item Download 2023-01-30 09-38-18


 140x       Filetype PDF       File size 0.06 MB       Source: staff.futminna.edu.ng


File: Induction Furnace Pdf 180107 | 3 Item Download 2023-01-30 09-38-18
au j t 9 2 83 88 oct 2005 design analysis of an electric induction furnace for melting aluminum scrap k c bala mechanical engineering department federal university of technology ...

icon picture PDF Filetype PDF | Posted on 30 Jan 2023 | 2 years ago
Partial capture of text on file.
             AU J.T. 9(2): 83-88 (Oct. 2005) 
              
                            Design Analysis of an Electric Induction Furnace  
                                           for Melting Aluminum Scrap 
                                                                  
                                                          K. C. Bala 
                         Mechanical Engineering Department, Federal University of Technology 
                                                 Minna, Niger State, Nigeria 
                                                                  
                                                           Abstract 
                          
                         The advancement of any nation technologically has been influenced and elevated 
                   by the extent to which it can usefully harness and convert its mineral resources. The 
                   productions of metal in foundries and in all human lives have also become a general 
                   practice. Different melting techniques are in practice with different energy sources. The 
                   cleanliness and availability of electrical energy sources in Nigeria is of paramount 
                   importance to its use in foundries, hence the need for this design. This paper deals 
                   principally with the mechanical and electrical requirements for induction furnace 
                   production. The mechanical aspect gives consideration to the geometrical components, 
                   cooling system, and the tilting mechanism. The electrical aspect deals with the furnace 
                   power requirement to make it functional. The design was achieved through 
                   consideration of relevant theories and their practical application. 
                          
                         Keywords:  Electrical, Mechanical, Induction, Furnace, Aluminum, Heat energy, 
                   Charge, Melting 
                                                                          
                                Introduction                       display a marked decrease in performance level 
                                                                   after some years of service and have to be 
                   In the production of mineral resources,         discarded. 
             the melting of metals has become one of the                 The re-melting of these scraps product of 
             tremendous industrial practices in the forefront.     aluminum will go a long way to enhance the 
             This is because metals are versatile elements         availability of the product without over reliance 
             whose fields of application are very wide in          on the foreign market, and thereby improving 
             human lives.                                          the foreign reserve. Similarly, the acquisition 
                   Of all metals, iron production has              of melting equipment for this purpose has also 
             developed substantially, such that different          become a very difficult thing such that there is 
             types of furnaces ranging from blast furnaces,        a need to look inward for fabrication of some 
             open-hearth furnaces, to converters and electric      vital components for our technological growth. 
             furnaces for steel production are in use today        It is in view of this, that different methods of 
             worldwide. Here in Nigeria, Ajaokuta Steel            melting aluminum are being used in the 
             Company and Delta Steel Company are  country, such as crucible furnaces, either on 
             examples of steel making companies that use           industrial or local small scale, by burning of 
             these types of furnaces.                              fossil or organic fuels. These have the 
                    Aluminum being the most abundant               disadvantage of producing low quality products 
             metallic element, forming about 8% of the             as a result of the impurities present in the fuel. 
             solid portion of the earth’s crust, is rarely               In recognition of these facts, and 
             available as rich ores. Hence most countries are      considering the availability of electricity - a 
             dependent  on supplies of it being imported.          cleaner source of power in Nigeria, the design 
             Nigeria, for instance, uses aluminum in all           of an Electric Induction Furnace for Aluminum 
             aspects of human endeavor (Abubakre 2001),            scrap melting and indeed any metal is in the 
             be it transportation, machine components,             right direction worth undertaking (Mastrukov 
             cooking utensils alloying etc. these components       1986). 
                                                               83
             AU J.T. 9(2): 83-88 (Oct. 2005) 
              
                   A furnace is an apparatus in which heat is                     Basic Components 
             liberated and transferred directly to solid or              
             fluid charge mass, for the purpose of effecting            The induction furnace consists basically 
             a physical or chemical change, through cycle         of a crucible, inductor coil, and shell, cooling 
             involving temperature in excess of 400°C.            system and tilting mechanism.          
             There exist various classifications of furnaces            The crucible is formed from refractory 
             based on the purpose and energy source.              material, which the furnace coils is lined with. 
                   In the early nineteenth century, the           This crucible holds the charge material and 
             phenomenon of induction heating was applied          subsequently the melt. The choice of refractory 
             to the experimental melting of metals. The           material depends on the type of charge, i.e. 
             early furnace consisted of circular hearth or        acidic, basic or neutral. In this design a neutral 
             trough, which contained the molten metal of an       refractory is use and based on effectiveness, 
             annular ring. This formed a short circuited          availability and practical application in 
             single turn secondary winding of a transformer       Nigerian foundries, zirconium oxide (ZrO ) is 
             which was energized by a supply of alternating                                                   2
             current at normal line frequency. This design        implored. The durability of the crucible 
             has inherent defects, such as mechanical force       depends on the grain size, ramming technique, 
             set up by the current flowing in the molten          charge analysis and rate of heating and cooling 
             metal which tended to cause contraction and          the furnace. 
             could result in the interruption of the current,           The inductor coil is a tubular copper coil 
             thereby posing operational difficulties. This        with specific number of turns. An alternating 
             effect was called ‘pinch effect’ (Shrets et al.      current (A.C) passes through it and magnetic 
             1987), and a lot of attempts to solve it were not    flux is generated within the conductor. The 
             successful until in the early 1900’s, when Ajax      magnetic flux generated induces eddy currents 
             Wyatt removed the difficulty by placing the          that enable the heating and subsequently the 
             secondary channel in the vertical plane. The         melting process in the crucible. In order to 
             weight of the metal in the bath was then             eliminate electrical breakdown the turns are 
             sufficient to overcome the forces, which caused      insulated by wrapping with mica tape, this 
             the pinch effect.                                    serve as a good insulator. 
                   It was later that a new approach was                 The shell is the outer part of the furnace. 
             made by Dr. E. F. Northrup, who substituted a        This houses the crucible and the inductor coils, 
             crucible containing the metal charge in place of     and has higher thermal capacity. It is made of 
             the channel (Hammond 1978) surrounded with           rectangular parallelepiped with low carbon 
             a multi-turn coil through which current was          steel plate and joined at the corners by edge 
             passed at high frequency. The development of         carriers from angular pieces and strips of non-
             these types of furnaces, the core-type and the       magnetic metal. 
             core-less type, the former for brass and the               The cooling system is a through-one-
             latter for steel were extremely rapid, and many      way- flow system with the tubular copper coils 
             hundreds of thousands of kilowatts of capacity       connected to water source through flexible 
             are installed throughout the world today.            rubber hoses. The inlet is from the top while 
                    The poor development of foundries in          the outlet is at the bottom. The cooling process 
             Nigeria today reported in (Bala 1998) extends        is important because the circuit of the furnace 
             to the fact that science and engineering infra-      appears resistive, and the real power is not only 
             structure was not provided at the beginning of       consumed in the charged material but also in 
             its national independence. However, today            the resistance of the coil. This coil loss as well 
             there is a good thrust to foundry technology         as the loss of heat conducted from the charge 
             and the trend of induction furnace application       through the refractory crucible requires the coil 
             is just in its prime age. Its application is mostly  to be cooled with water as the cooling medium 
             in smaller foundries for iron melting.               to prevent undue temperature rise of the copper 
                                                                  coils. 
                                                                        Tilting of the furnace is to effect pouring 
                                                                  of the melt as a last operational activity before 
                                                              84
                  AU J.T. 9(2): 83-88 (Oct. 2005) 
                   
                  casting. Since this furnace is of small capacity,                                         b = thickness of bottom refractory 
                                                                                                               t
                  a manually operated tilting mechanism is                                        lining, (b = 25.5mm for 10kg capacity). 
                                                                                                               t
                  adopted. The furnace is hinged on at the spout                                            
                  edge with a shaft and bearings. At one side to                                           The slag height is calculated thus: 
                  the bearing is pinion and gear system to give a                                                  4
                                                                                                           h = Vs ..............................................7   
                  gear reduction, so that when the handle is                                                 s    πd2
                  turned clockwise, the furnace is tilted to                                                           m
                                                                                                  where, V  = volume of slag in one heat, taken 
                  achieve a maximum angle of 90 degrees for                                                     s                     3
                  complete pouring of the molten metal.                                           as 8% of total charge, m . 
                                                                                                            
                                            Design Analysis                                               Height of inductor holding poles: 
                                                                                                           Hp = Hin + 2Tf .....................................8    
                                                                                                  where, T = flange thickness, taken as 3mm. 
                  Geometrical parameters                                                                       f
                                                                                                            
                           The analysis is based on a 10kg capacity.                              Heat Energy and Electrical Parameters 
                  The shape of the crucible is cylindrical. The                                             
                  internal diameter of the crucible and the height                                         The required theoretical heat energy 
                  of melt is determined by the furnace capacity                                   (Ilori 1991), consumed during the first period 
                  (melt volume), with considerations that the                                     of melt is given by: 
                  ratio:                                                                                   Qth =Qm +Qsh +Qs +Qen −Qex ............9
                            Hm =(1.6−2.0)........................... 1                               
                                                                                                  where, Q  = amount of heat energy to  
                             D                                                                                  m
                                c                                                                                     melt 10kg of charge material, J; 
                  where  H  = height of molten metal, m; 
                                 m                                                                           Q  = amount of heat energy to  
                             D  = diameter of crucible, m;                                                      sh
                                 c                                                                                    superheat the melt to temperature 
                                                                                                                      of superheat, J; 
                           Volume of metal charge is given by:                                                        Q = heat required to melt slag 
                                    πd2H                                                                                 s
                           V =          m    m ............................    2                             forming materials, J; 
                              m          4                                                                            Q  = energy required for 
                                                                                                                         en
                  where d = diameter of molten metal = D .                                                   endothermic process, J; 
                                m                                                 c                                   Q  = amount of heat energy 
                                                                                                                         ex
                           The thickness of the refractory lining                                            liberated to the surroundings as a result 
                  (Voskoboinikov, et al. 1985), of the crucible in                                           of exothermic reactions, J. 
                  the middle of the crucible can determine from                                             
                  the relation                                                                            Theoretically Q  = Q . 
                                                                                                                                  en       ex
                            B =0.084 T ........................................ 3                 Where 
                              r                                                                            Q =Q +Q +Q ........................... 10    
                  where  T = furnace capacity in tonnes.                                                      th       m       sh        s
                           The internal diameter of the inductor can                              and, 
                  be calculated from the equation:                                                         Qm = MC(θ1 −θ0)+ Lpt ......................11
                            Din = Dc + 2(Br + Bins) ...........................4                     
                   where  BB  = thickness of refractory lining, m;                                where, M = mass of charge, kg; 
                                r                                                                            C = specific heat capacity of charge  
                            B = thickness of insulation layer. 
                                ins                                                               material, (for aluminum, C = 1100J/kg K); 
                            (B  is such that 5 ≤ B  ≤ 6 [mm]). 
                                ins                           ins                                          L  = amount of heat to accomplish phase 
                           Height of inductor coil is given by:                                              pt
                                                                                                  transformation, (for pure aluminum L = 0, no                   
                            Hin =(1.1−1.2)Hm ..................................5                                                                            pt
                  The height of furnace from bottom of the bath                                   phase transformation); 
                  to the pouring spout is:                                                                   θ1 = melting temperature of charge, (for 
                            H =H +h +b ..................................6                        aluminum θ1 = 660°C); 
                                f       m       s       t                                                    θ0 = ambient temperature, 25°C; 
                    where, h  = height of slag formed, m; 
                                 s                                                                          
                                                                                            85
                   AU J.T. 9(2): 83-88 (Oct. 2005) 
                    
                             Similarly,                                                                            L = H = length of coil in metres, m; 
                                                                                                                              in
                                                                                                                   μ  = permeability of free space = 4 π x 
                             Q =MC θ .................................12                              
                                 sh           m sh                                                                    o
                                                                                                            -7       -1
                   where, C  = average heat capacity of molten                                          10  Hm ; 
                                  m                                                                                μ  = relative permeability of charge 
                   Aluminum, (= 992J/kg K);                                                                           r
                                                                                                        material, (for non-magnetic material  μ  = 1). 
                               θsh = amount of superheat temperature,                                                                                                  r
                   taken as 40°C.                                                                                Therefore, 
                             and,                                                                                 N = BmaxL ...........................................           19
                             Qs = KsGs .......................................13                                           μoI
                   where, K  = quantity of slag formed in (kg),                                            
                                  s
                   taken as 8% of furnace capacity;                                                              The resistance of the copper coil inductor 
                              G = heat energy for slag = 18kJ/kg.                                       at ambient temperature is given by: 
                                  s
                                                                                                                  R =ρcl .......................................... 20
                             Total heat energy induced (Hammond,                                                    θo       A
                   1978), in charge due to eddy current is given                                                               t
                   by:                                                                                      
                                       π3 f 2H B2 d4                                                    where, ρ = resistivity of copper 
                             Q =                    m max m .................. 14                                     c             -8
                                 ec               8ρ                                                              =1.72 x 10 Ωm at 25°C; 
                             where,  f = frequency of power supply,                                                l = total length of copper tube, m; 
                                                                                                                   = πD N 
                   50Hz;                                                                                                    in
                              B  = maximum flux density, H;                                                       
                                  max                                                                            Resistance at any temperature θ is given 
                               ρ = resistivity of charge metal, ( for                                   as: 
                                                           -8
                   aluminum, ρ = 2.83 x 10 Ωm).                                                                   R =R [1+αθ (θ −θ )] ..................21
                             Therefore,                                                                             θ        θo            o           o
                                                 8ρQ                                                       
                              B       =                 ec           ....................15                              
                                max         π3f 2d4H                                                    where, αθo = temperature coefficient of copper 
                                                       m     m                                          at 25°C; 
                   Also                                                                                                                     -3    -1
                                       Q                                                                                   = 3.9 x 10  K . 
                             Q = th ........................................ 16                                   
                                 ec       t                                                                      Coil loss due to resistance is: 
                   where,             t = time in seconds to attain                                               P =I2R              ...........................................22
                                      maximum flux.                                                                 c           θ
                             The allowable current density in the                                         
                   inductor is given by:                                                                         Heat loss through conduction (Shrets et 
                                      I                                                                 al. 1987), from furnace walls to copper coil: 
                              J =           ............................................... 17                                                    H (              )
                                     A                                                                                                         π m θ2 −θ
                                       t                                     2                                    QL = 1 1                d          1        D          1         d
                             (J ranges from 20 to 40A/mm ).                                                                   [       ln    2 +          ln      in +         ln     3 ]
                   where, I = current in inductor in amperes, A;                                                            2 λzi         Dc       λas        d2        λcu       Din
                                A = cross sectional area of conducting 
                                  t             2                                                                                           ....................................... 23
                                tube (mm ), take external diameter of                                      
                                inductor coil, d  = 8mm and internal 
                                                          t2                                            where, λ = thermal conductivity, with 
                                diameter of inductor coil, d  = 6mm. 
                                                                           t1                           subscripts for zircon, asbestos, and copper 
                                                                                                        respectively; 
                             The number of turns of the inductor can                                               λ  = 2.093w/m K; λ  = 0.117w/ m K; 
                   be determined from:                                                                                zi                              as
                                                                                                        and         λcu = 380w/m K; 
                                         μ μ NI                                                                   d = outer diameter of crucible = D  + 
                              B       = r o             .....................................  18                     2                                                         c
                                max                                                                     2B, m; 
                                               L                                                             r
                                                                                                                  d = inductor diameter surrounding 
                    where, N = number of turns of inductor coil;                                                      3
                               I = current in coil in amperes, A;                                       crucible +  2 thickness of coil, m; 
                                                                                                  86
The words contained in this file might help you see if this file matches what you are looking for:

...Au j t oct design analysis of an electric induction furnace for melting aluminum scrap k c bala mechanical engineering department federal university technology minna niger state nigeria abstract the advancement any nation technologically has been influenced and elevated by extent to which it can usefully harness convert its mineral resources productions metal in foundries all human lives have also become a general practice different techniques are with energy sources cleanliness availability electrical is paramount importance use hence need this paper deals principally requirements production aspect gives consideration geometrical components cooling system tilting mechanism power requirement make functional was achieved through relevant theories their practical application keywords heat charge introduction display marked decrease performance level after some years service be discarded metals one re these scraps product tremendous industrial practices forefront will go long way enhance ...

no reviews yet
Please Login to review.