Abstract:
Fully dense long ingots are produced by the bottom pouring method and apparatus of the present invention. A solidification sequence is achieved which is conducive to eliminating solidification shrinkage and piping. The set-up of the bottom poured ingot molds facilitates a solidification sequence starting from the top and then down the ingot mold and then up the down pour pipe.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/059,393, filed Sep 19, 1997 and is a divisional of U.S. Application No. 09/156,835, filed Sep. 18, 1998. 
    
    
     BACKGROUND 
     The special alloys industry, requires a high quality, fully dense billet for rolling various product forms. Presently high quality specialty alloy bars are generally made by hot rolling round or square billets four or five inches in diameter to finished bars in a size range of tow inches or less. Such billets are generally produced for the specialty alloys industry by continuous casting, conventional static cast ingots, and VAR (vacuum arc remelting)/ESR (electroslag remelting) processed remelt ingots. 
     Continuous casting is the only method currently utilized that is capable of converting the liquid steel directly into solid semifinished forms. Continuous casting skips the intermediate step of forging the ingots for rolling mill feed stock and has higher yield. The disadvantages of continuous casting include the high cost of machinery and the requirement of large tonnage of the product. Many specialty mills cannot afford the large capital outlay required to purchase continuous casting equipment. Continuous casting is also not appropriate for all alloys because of macrosegregation problems. 
     The conventional static cast and VAR/ESR remelt ingot processes each include the added cost of open die or rotary forging to form the billet for feed stock. Ingot cross sectional dimensions are limited under static casting due to macrosegregation. Alloy macrosegregation in ingots can be greatly reduced using VAR/ESR remelting but at an added cost. 
     A bottom pouring process of casting long ingots could alleviate the need for open die or rotary forging by producing a billet suitable for feed stock to a rolling mill. Bottom pouring consists of pouring liquid alloy into a vertical cast iron downpour pipe or “trumpet”. The liquid alloy then flows out from the bottom of the downpour pipe and into horizontal runners attached to the base of the downpour pipe. The liquid alloy travels through the horizontal runners and flows into vertical cast iron ingot molds where the liquid completely fills the void within the mold. Such a bottom-pour set-up has the advantage of eliminating the turbulent splashing associated with normal top pouring set-ups. By eliminating turbulent splashing the bottom-pour set-up results in a smoother ingot surface. 
     The disadvantage to conventional bottom-pouring is discontinuous solidification that results in piping. Piping is a cavity usually found in the middle of the ingot, which results from the metal contracting as it cools in the mold. Shrinkage pipes are usually an incurable defect because the cavity formed by the pipe may be oxidized and thus the pipes will not weld shut during the rolling of the ingot. To cure the defect a portion of the ingot containing the shrinkage pipes must be cropped and returned to the electric furnace as scrap. If the defect is not cropped the ingot will produce a weakened finished steel product. 
     During casting, under the conventional bottom-pouring process, the horizontal runners and center down-pour usually cool too quickly. Such cooling deprives the bottom ingot portion of the liquid metal needed to fill any voids created in the solidifying upper portion of the ingot mold. As the top cools the metal contracts and voids (shrinkage pipes) form within the ingot and remain unfilled as new molten metal is prevented from entering the ingot mold. Shrinkage pipes are undesirable defects which often interfere with subsequent hot forming or remelting operations. To minimize solidification shrinkage, exothermic hot tops have been fitted into the top of the ingot molds to reverse the direction of solidification, unfortunately hot tops have met with little success. A method is needed that is capable of altering to normal solidification pattern of bottom-pouring so that fully dense ingots for feed stock can be cast. 
     SUMMARY 
     An object of the present invention is to facilitate a solidification sequence conducive to eliminating solidification shrinkage and piping. Another object of the present invention is to form fully dense long ingots using an innovative set-up of bottom poured ingot molds. 
     The present invention&#39;solidification sequence begins with the top of the ingots solidifying first. The solidification process then progressively descends down along the length of the side ingots until the ingots connect with lateral runners. The lateral runners feed the side ingot with molten metal. Solidification then proceeds from the runner to the center vertical down pour pipe, which originally received the molten metal. The metal then solidifies from the bottom of the down pour pipe to the top of the pipe. Through this process fully dense long ingots can be formed. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     These and other features, aspects and advantages of the present invention will become better understood with regard to the following description, and accompanying drawings where: 
     FIG. 1 shows a cutaway view of a mold setup for a bottom poured ingots apparatus; 
     FIG. 2 illustrates different setups for lateral runners, including a circular, square and triangular configuration; also illustrated is a ceramic insulating tube; 
     FIG. 3 shows a split mold configuration including clamps; 
     FIG. 4 illustrates a mold heating setup, including heating elements for down pour tube and ingot side molds; 
     FIG. 5 schematically shows the preferred direction of the solidification, the cap and compressed air being applied to the ingot molds; and 
     FIG. 6 illustrates the cap and the cap heating element which rest atop the pour cup. 
    
    
     DETAILED DESCRIPTION 
     As illustrated in FIG. 1, the present invention includes a central vertical down pour pipe  2  connected at the bottom by lateral runners  4 . At the outer ends of the runners  4  are vertical side ingot molds  6  extending parallel and in spaced relation to the vertical down pour pipe  2 . The present invention can be operated under a vacuum or at atmosphere. 
     The central down pour pipe  2  is preferably configured out of cast iron with a shell mold design to facilitate mold stripping operations. Cast iron is preferred, but any other material suitable for casting liquid metals may be used. The shell mold design forms a cavity within the center down pour pipe  2  by preferably joining at least two pieces, which are held together by metal clamps  12 . The down pour pipe  2  may also be used as a mold for forming an ingot. 
     The introduction of molten metal into the down pour pipe  2  is aided by a pour cup  8  formed from the upper portion of the down pour pipe  2 . The pour cup  8  is preferably configured as a funnel, with a wide end for receiving molten metal and a small end integral with and having the same diameter as the down pour pipe  2 . The bottom portion of the down pour pipe  2  is connected to lateral runners  4 . The down pour pipe  2  is connected to the lateral runners  4  so that liquid metal may flow from the down pour pipe  2  and into the lateral runners  4 . 
     The lateral runners  4  are configured out of cast iron with a shell mold design. The interior walls  24  of the lateral runners  4  form a cavity. A ceramic insulating tube  10  is fitted securely to the interior walls  24  of each of the runners&#39;  4  cast iron shells. The ceramic tube  10  insulator is preferably made of a ceramic oxide selected from the group consisting essentially of alumina, silica, and magnesia. The ceramic may also be either boron carbide or silicon carbide. Molten metal flows through the ceramic tube  10 . The ceramic tube  10  aids in preventing heat from being transferred from the molten metal. As illustrated in FIG. 2, the runners  4  may be dimensionally configured in appropriate shapes such as circles squares, or triangles. Runners  4 , dimensionally configured as triangles, have the advantage of being able to entrap ceramic particles that may break free of the insulation. Ceramic particles freed from the runners  4  and then mixed with the molten metal add unwanted inclusions to the metal ingots formed in the molds  6 . The apex of the triangularly shaped runner  4  is able to capture the majority of the particles and prevent them from reaching the ingot mold  6 . Filters can also be positioned within the runners to prevent ceramic particles from entering the ingot molds  6 . 
     The ingot molds  6  preferably have a split mold configuration in order to facilitate the mold stripping operation. As illustrated in FIG. 3, the split molds are preferably fastened together by metal clamps  12  and are generally formed from cast iron. Generally, a plurality of side ingot mold  6  elements are clustered around the down pour pipe  2  so that numerous ingots may be cast simultaneously. The ingot molds  6  are connected to the down pour pipe  2  by the lateral runners  4 . The bottom of each ingot mold  6  is connected to a lateral runner  4  and into the ingot mold  6 . Molten metal is supplied to the bottom of the ingot mold  6  and fills the mold from the bottom to the top. The ingot molds  6  can form the molten metal into ingots having any shape but cylindrical or cubical are most common. 
     The preferred ingot solidification sequence for the present invention, as illustrated in FIG. 5, is from the top of the ingot mold  6  then down the mold, to the runner  4 , and last up to the top of the down pour pipe  2 . Thus, the first place to solidify will be the top of the ingot molds  6  and the last place to solidify will be the top of the down pour pipe  2 . Such a pattern is designed to prevent piping or voids from being formed within the solidified ingot. 
     As illustrated in FIG. 4, the central vertical down pour pipe  2  is heated prior to filling in order to aid in establishing the preferred solidification pattern of the present invention. A down pour pipe heating element  14  is lowered into the down pour pipe  2  cavity to heat the surrounding walls of the pipe  2 . Preferably, only the middle portion to the upper portion of the down pour pipe  2  is heated by the element  14 . An example of a possible down pour pipe heating  14  element is a quartz rod radiation heater. The heater  14  is slowly lowered into the pipe  2  as it heats the walls of the pipe  2 . The heating element  14  may have a pour cup heat shield  16  at the upper end of the element so as to direct the heat downward. The pour cup heat shield  16  preferably rests upon the rim of the pour cup  8  once the element has been fully inserted. Other heating elements, such as natural gas or liquid hydrocarbon may also be used so long as the element is capable of being lowered into the down pour pipe  2 . The down pour pipe heating element  14  preferably preheats the down pour pipe  2  to a temperature that is below the particular metal liquidus temperature of the metal being formed. 
     The ingot molds  6  are heated by separate individual mold heating elements  18 . Like the vertical down pour pipe  2 , the ingot molds  6  are heated prior to the filling of the molds  6 . A mold heating element  18  is lowered into the open top of the ingot mold  6  and down into the mold  6  cavity. Preferably only the lower to middle portion of the mold  6  is preheated by the mold heating element  18 . The mold heating element  18  can have the same configuration as that used for the down pour pipe heating elements  14 , although alternative configurations are acceptable. The mold heating element  18  may have an ingot mold heat shield  24  at the upper end of the element so as to direct the heat downward. The ingot mold heat shield  24  preferably rests upon the rim of the side ingot molds  6  once the elements have been fully inserted. The mold heating elements  18  for the ingot molds  6  preferably only reheat the molds  6  to a temperature that is below the particular metal liquidus temperature of the metal being formed. 
     Once the heating elements ( 14  and  18 ) have been removed from the down pour pipe and ingot molds, molten metal can be poured into the center down pour pipe  2 . Once the molten metal reaches the bottom of the down pour pipe  2  it is dispersed into the individual lateral runners  4  connected at the base of the down pour pipe  2 . The lateral runners  4  then transfer the molten metal to the base of the ingot molds  6 . The ingot molds  6  are filled from the base of the mold to the top, in order to eliminate splashing and to promote a smoother ingot surface. 
     Once the present invention is filled with molten material, a cap  20 , as illustrated in FIG. 5, may be fitted upon the wide end of the pour cup  8  rim. If a cup  8  has not been formed, the cap  20  may be fitted upon the rim of the open top of the down pour pipe  2 . The cap  20  may be made of any material capable of withstanding the high temperature of the molten metal and should be able to provide an insulating barrier. The cap  20  may also be equipped with electric heating elements  26  to provide additional heat to the top of the metal in the pour cup. The cap  20  functions to retard heat loss and to aid in ensuring that the molten metal located at the top of the down pour pipe  2  will be the last molten metal to solidify within the bottom pouring apparatus. Also, to aid in the preferred solidification sequence of the present invention, compressed air  22  may be blown on the open top of the ingot mold  6 . The compressed air  22  accelerates the solidification of the exposed molten metal in the top portion of the ingot mold  6 . Thus the first molten metal to solidify will be the metal located at the top of the ingot molds  6 .