Abstract:
Transfer system for liquid metals such as aluminum, zinc and magnesium. The system is used to transfer liquid metal in a casting process from a furnace to a casting machine while extending the life term of the transfer conduit. The canal replaces the use of gas burners with electric heat generating means in order to maintain the constant temperature of the liquid metal transferred. The system allows to automatically maintaining the liquid metal level and a constant temperature during said liquid metal transfer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a transfer system for liquid metals such as aluminum, zinc and magnesium. The invention also refers to a canal used in the transfer of such liquid metals and a method of transferring liquid metals using the transfer system.  
         [0003]     2. Description of the Related Art  
         [0004]     The use of canals in the transfer of liquid metals from the furnace to the casting machine is widely known and used. In the past, these canals were made of refracting concrete but the use of such material generated a great loss of temperature in the liquid metal during its transfer. Due to the enormous amount of materials available nowadays, there are at least two conditions that must comply when choosing the correct material in the process of making the canals. The first condition that a chosen material chosen must comply is that the loss of temperature of the liquid metal when transferred from the furnace to the casting machine must be minimum. The second condition that a chosen material must meet is the resistance to chemical attack deriving from the molten metal transferred.  
         [0005]     Most of the processes that in the past where made inside the furnace were converted into continuum process incorporating specific equipments for filtering and removing contaminating gases for the metal. Due to this modification, the length of the canals transporting the melted metal had to be lengthened, increasing therefore the loss of temperature during the transfer of liquid metal. In order to reduce such loss of temperature, the common solution was to increase the temperature of the liquid metal at the furnace, rendering a reduced loss of temperature of the liquid metal during its transfer. However, this obvious solution made the liquid metal to oxidize at a faster rate, rendering it to a more chemical aggressive material hence reducing the life of the canals. It is also important to mention that the increase of temperature in the liquid metal generated the incorporation of several contaminants such as hydrogen which solubility increased with the rise of the temperature.  
         [0006]     At the late  70 &#39;s, ceramic fibers were incorporated into the world of technological material. By using ceramic fibers in the construction of canals, the results of durability were surprisingly increased. However, the use of such canals was only useful in short casting process usually lasting between 4 to 5 hours. After that period the canals had to be replaced. As the use of aluminum was increased over time, the industry developed new equipments known as continuous casting machines, where the duration of the casting process can last up to several days.  
         [0007]     The problem encountered, when using the canals made of ceramic fiber in the continuous casting process, was that after every casting period the canals had to be replaced, therefore generating an increase in the final cost of the product. A partial solution to such problem was to develop canals using materials with increased resistance to the chemical attack but the problem encountered then was that using such materials also increased the loss of temperature in the liquid metal. Therefore, the canals included improved thermal insulation in order to obtain a satisfactory result. However, at the beginning of the continuum casting process the use of gas burners had to be applied in such process. Gas burners are widely known and use in the casting process, but it is also widely known that the expose of a material to a constant and powerful flame stream reduced the life term of such material producing cracks and clefts. Alternatively, in the near zones of the burners it could be found a temperature difference within several hundreds of degrees which generates tensions and micro cracks shortening the life term of the canal. In order to avoid the use of gas burners to maintain the temperature with in the canal, the use of electrical heaters were implemented reducing the deterioration of the canal.  
         [0008]     Due to the constant deterioration of the canals and the casting equipment where the liquid metal passes through, the maintenance schedule to follow in order to continue with the normal casting procedure requires several stopping times, which is inadmissible in continuous casting process. By using conventional canals, the average temperature of the liquid metal is sometimes greater than 100° C. which is more that the normal temperature needed for casting. This represents a loss of 5° to 10° C. by meter in the length of the canal. This loss of temperature can also generate the reduction or even the loss of the casting process. In the event that the casting process includes several hours, the interruption of a casting process due to parametrical miscalculations in the process can generate an important economic damage.  
         [0009]     As stated before, transferring canals are made of ceramic fibers and the same are placed in a metal cradle which is used to support the canal and abut the canal with an adjacent one by means of a bridle in order to conform a full canal for transferring the liquid metal. Another important factor to consider is the great difference between the thermal expansion coefficient of the canal and the metal cradle, which generates metal leaks in the junction between abutting canals increasing the leakage during several casting processes.  
         [0010]     Another important factor to consider is the level of the liquid metal during the transfer between the furnace and the casting machine. When the liquid metal gets in contact with the mould a thin layer of solid is formed which contains the remaining of the liquid metal. This is a dynamic process where the solid layer generated is removed at constant speed and the new liquid metal arrives at the mould. The quality of the obtained piece depends mostly on the stability of the solid/liquid interaction and its contact with the mould in the process of solidification. The variation in the metal level at the feeding system of the moulds modifies the liquid pressure and disarrays the contact between the thin solid layer and the mould. The final result becomes a noticeable reduction in the length of the casting process  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention relates to a transfer system for liquid metal from a furnace to a casting machine wherein the system lengthens the life term of the transfer canal while used on several casting process.  
         [0012]     The present invention also relates to a transfer canal to be used for transferring liquid metal from a furnace to a casting machine wherein the canal replaces the use of gas burners in order to maintain the constant temperature of the liquid metal transferred.  
         [0013]     In accordance with still another important feature of this invention, it provides a method for controlling the liquid metal transfer between a furnace and a casting machine allowing to automatically maintaining the liquid metal level during said liquid metal transfer.  
         [0014]     The above-discussed and other features and advantages of the present invention will be appreciated and understood by those of ordinary skill in the art from the following detailed discussion and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     Referring now to the drawings, wherein like elements are numbered alike in the several FIGURES:  
         [0016]      FIG. 1 a  schematic view of the system in accordance with the present invention;  
         [0017]      FIG. 2  is a front elevation view, partly in cross-section, of a canal in accordance with the present invention;  
         [0018]      FIG. 3  is a schematic drawing of the use of the method of the present invention with the system of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]     Referring initially to  FIG. 1  the transfer system of the present invention comprises a central operation panel  2  which controls and commands a PLC (Programmable Logic Controller)  3 . As stated on  FIG. 1 , the PLC controls the performance of a hydraulic central  4  which commands the movement of a balanced valve  5 . This balanced valve actuates on a hydraulic cylinder  6  controlling the tilt of a casting furnace  7 .  
         [0020]     A laser sensor  8  detects the liquid metal level in the conduit  9  when the liquid metal is poured from the furnace  7  towards the casting machine  22  ( FIG. 3 ). The data acquired by the laser sensor  8  is sent to the PLC  3  to adjust the furnace&#39;s tilting. The sensor  8  must be configured to detect the presence of liquid metal at a pre settled level bearing that the level  0  is the base of the canal. Said level can be settled according to the specific configuration of the casting process. The laser sensor  8  should be placed near the outlet of the furnace  7  but said sensor  8  can be used in any available position where it can be determined the level of the liquid metal in the conduit  9 .  
         [0021]     Making reference to  FIG. 3 , the conduit  9  is build based on a plurality of adjacent canals  10  abutted each other by means of nuts and bolts. Between every abutment a compressible gasket  11  made of ceramic fiber is placed in order to reduce the leakage of the liquid metal once is transferred from the furnace  7  towards the casting machine  22 . Any skilled in the art could notice that the use of bolts and nuts as a mean for abutting several canals  10  in order to make the conduit  10  is just an example and that any means for joining two or more canals such as welding, riveting, clinching and so, can be used without leaving the scope of the present invention. However, it is preferable to use any means to adjoin two or more canals that will allow performing a fast replacement of the damaged canals and thus maintaining the modular condition of the conduit  9 .  
         [0022]     The canal  10  showed in  FIG. 2  comprises a first U shape profile  12  in which a second U shape profile  14  is placed, being separated both profiles by an insulate layer  13 . The profile  14  defines a path for the liquid metal to be transferred from the furnace  7  to the casting machine  22 . In the present embodiment, the first profile  12  is made of a steel alloy while the second profile  14  is made of a refracting ceramic material. Moreover, the insulated layer  13  can be made of any insulate material such as fiber glass, ceramic fiber, microporous insulation panels, asbestos, refracting mud or the combination thereof. A lid  15  is placed on top of first and second profiles protecting the edges of such profiles from breakage when cleaning the conduit  10  once the casting process is over.  
         [0023]     As seen on  FIG. 2 , a cover  17  is attached with a hinge  18  to the first profile  12 . The cover is actuated by pneumatic or hydraulic means (not shown) controlled by said PLC  3 . Said cover includes heat generating means  16  attached to the internal portion of the cover by an insulate layer  19 . The insulate layer  19  can be made of the same material as the insulated layer  13 . Said heat generating means  16  are defined by electric resistance heating elements  20  enclosed in metal tubes that emit heat in the form of infrared rays. Even though the number of electrical resistance heating elements  20  illustrated in  FIG. 2  are only two, the number of such heating elements  20  can be as many as needed depending on the particular casting process. On the other hand, even if it is possible to replace said heating elements  20  with gas burners, the use of such gas burners can compromise the safety of the whole casting line. However, the use of heating elements  20  as means for generating heat in the canals  9  cannot be considered as limiting the scope of the invention, since it will be obvious to any skilled in the art replacing the heating elements  20  by any other heating source available. As seen on  FIG. 3 , the transfer system of the present invention comprises at least two heat sensors  23 . Said sensors  23  are placed preferably one near the outlet of the furnace  7  and the other near the inlet of the casting machine  22 . This sensor deployment allows the system to strictly control any differential of temperature along the total transfer of the liquid metal over the conduit  10 . It can be appreciated that the use of more than two heat sensors is included within the bound of the scope of the invention, since it will be obvious to any skilled in the art to notice that the greater the number of heat sensors the better the result in maintaining the temperature level would be. On the other hand, the heat sensors  23  can be any sensor commercially available such as laser beam sensor, thermocouple or a combination of both.  
         [0024]     From the safety point of view, the transfer system includes a complex electrical wiring (not shown) including current and voltage detectors that controls any variation such as in the heating elements  20  or heat sensors  23 , allowing the operator of the casting line to control the temperature process. As it is shown in  FIG. 2 , canals  9  are placed over a double T beam  21 . Such beam  21  is used as a strong and firm support platform for the total length of the conduit  10 .  
         [0025]     For a better comprehension of the present invention, an explanation of the use and functionality of the whole system will be explained in detail using all the figures mentioned before. As every casting process, the same begins at the furnace  7 . The metal in liquid form is placed inside said furnace  7  kept at a melting point until it is ready to be poured in the conduit  10 . For the present embodiment, the casting process will be explained using aluminum as the metal to be transferred. The aluminum in liquid form is kept in the furnace at approximately 720° C. Once the furnace  7  is tilted the pouring of the liquid metal in the conduit  10  occurs. This pouring method is based on a gravity pouring and the tilting degree is graduated and maintained by the hydraulic cylinder  6 . Once the furnace  7  is tilted and the pouring begins, the laser sensor  8  controls the level of the metal poured and acquires data about the minimum and maximum levels and sends them to the PLC unit  3 . The PLC unit then verifies that said data sent by the sensor  8  is within the parameters already configured in the PLC unit. In the event that the data sent by the sensor  8  is either over or below the parameters configured, the PLC unit sends the instructions to the hydraulic central  4  to command, by means of the balanced valve  5 , the corresponding hydraulic cylinder  6  to either increase or decrease the tilt degree of the furnace  7 . Once the data sent by the sensor  8  is within the parameters configured in the PLC unit, the tilting of the furnace  7  stops.  
         [0026]     Once the liquid metal starts flowing through the conduit  10  in order to reach the casting machine, the breach in the temperature from the furnace&#39;s outlet and from the casting machine&#39;s inlet is increased proportionally to the length of the conduit  10 . Therefore, sensors  23  gather the temperature in both places and each one sends the information to the PLC unit. The PLC unit compares the data received with the parameters previously configured. In the event that the temperature drops a few degrees, the PLC unit sends the instructions to a hydraulic center (not shown) which commands the closing of the covers  17  in order to reduce the loss of temperature. If the temperature keeps dropping the sensors  23  detect such drop and send the information to the PLC unit. Afterwards, the PLC unit processes the information and controls the ignition of the heating elements  20  in order to rise and maintain the heat of the liquid metal within the temperature parameters. In order to keep the temperature as homogenous as possible in the total length of the conduit  10 , the PLC unit can individually control the ignition of the heat elements  20  in each canal  9 , thus keeping a stricter control on the temperature range.  
         [0027]     Once the casting procedure is finished, which as stated before it could last several days, the maintenance routine commences. This routine comprises the complete checking and control of each and every canal  9 . In the event that one or more canals  9  show any sign of major attrition such canal can be easily replaced by a new one thanks to the modular construction concept that the conduit  10  has. On the other hand, if one or more canals  9  shows any small sign of ware, such as cracks in the ceramic fiber surface in the second profile, the same can be replaced in situ. This is possible since each canal has an easy construction configuration which allows the replacement of any part involved in the construction of the canal  9 . As experience shows, the second profile is the part which suffers greater deterioration between several casting processes. Fixing in situ or replacing such second profile reduces the costs of maintenance of the casting process.  
         [0028]     Finally, it is important to mention that even though the length of the canals  9  was not mentioned, the same can vary depending on the casting line to be used and also said canals can be formed in different shapes, not only straight line canals, but also Y shaped canal, curves or any desirable form needed to evade any obstacle in the process of building a casting line.