US1812172A - Production of castings free from pipes and blow-holes - Google Patents

Description

W. ROHN June 30, 1931.

PRODUCTION OF CASTINGS FREE FROM PIPES AND BLOW HOLES Filed Sept. 16, 1927 aoooodoooo v//////////////////n1 .rlfll/w -1:

Inventor: W

o oooooooo Patented June 30, 1931 1 W'ILHEIJM BORN, OF HANAU-ON-THE-MAIN, GERMANY PRODUCTIQN OF CASTIIIGS FIE-3E FBOIVI PIPES AND BLOW-HOLES Application filed September 16, 192., Serial No. 220,054, and in Germany December 28, 1925.

Blocks, sheets and articles of other shapes were hitherto produced in such a manner that the molten smelt from the furnace or the crucible was cast into a suitably selected mould and allowed to solidify therein. In .this method there is always observed the disadvantage t-hat the cast articles which are 'ol t-ained,.in spite of the casting methods which have been modified a considerable numit her of times, are never obtained free from pipes and blow-holes. so that a considerable waste occurs by reason of the lost head. There will now he described a method of producing such articles in a convenient. manner and free from pipes and blow-holes.

The fundamental idea of the. invention is not to pour the. molten metal into a separate mould. but to allow it'to solidify in the crucible itself. and to so select the cooling conditions that no pipes or blow-holes can be formed. On the same principle is also based for example, the production of the single crystals of salt and metal smelts butthe y use of such a. method of operation for the production of blocks free from pipes and blowholes wasnot known hitherto. The problem under consideration can be solved by causing the smeltto solidify from the bottom upwards. This can be effected by mounting the f t crucible on a vertically movable support.

After the termination of the smelting process this sup iort is lowered, and the crucible is fthlls brought with the bottom firstgradually into colder'zones, in such a manner that the bottom. of the crucible first comes into the lower temperature, and the cooling of the crucible proceeds from the bottom upwards.

In order to enable the cooling to be better I controlled it is preferable to provide in the lower part-of the furnace, or under the bottom thereof stationary copper tubes, which pass round the support in circles and through which cooling water flows.

The-same result can be obtained for example in anelectrically heated furnace by subvidmg the heat-ingkcoil. and after the com- ..pletion of the fusion cutting this outin sections. beginning at the bottom at suitably h selected periods of time. Ir an inductively heated electric smelting lurnace the same resultcan be obtained by switching off the windings of the induction coil gradually. separately. or in groups, from the bottom, until finally the whole coil has been cut out. The action can also be supported or controlled by increasing the thickness of layer from the bottom upwards, of the refractory material between the smelt and the oven coil, which, for example. is water-cooled. In order to prevent a too early freezing of the upper layers of the smelt. there is preferably suppliul to the upper coils. which still remain in operation. somewhat more energy than is actually required by them for participating in the complete-operation of the furnace. Finally, such control may also be obtained by slowly raising the complete induction coil or the furnace casing.

A constructional example for an induction furnace, free from iron. is illustrated in Figs. 1- tofl. In these. (1 indicates the crucible which is mounted on the support 7). which is passed through an opening I in the bottom of the furnace. and for example can be. moved vertically by toothed wheel gear I]. so that "after the completion of the smelting the support-.7). together with the crucible a can gradually'be lowered from the top downwardly. f indicates the. windings of the primary coil. Underneath this may be provided a cooling device in the form of copper pipes through which watercirculated. In the form of construction according to Fig. 2 the primary coil. after completion of the smelting. is raised at a suitably selected speed by a suitable device. for example by weights guided over rollers. According to Fig. 3 the coil f is provided with tapping points g. (I, which enable sections of the coil to be cut out in stages. In the example of the circuit illustrated in the drawing the two lowermost windings are disconnected by moving the switch h from the segment 1 to the segment 2, on movement to segment 3 the next two windings and so forth. The production of the desired action may, if necessary. also be promoted by allowing a sufiiciently thick plate of refractory and heating insulating material to float on the surface of the smelt or by placing simply on the surface of the smelt a layer of granular, refractory material. A suffciontly thick layer of slag of suitable composition may also act in this respect.

For this method of operation. the smelting vessel. particularly when a high-frequtaicy furnace is used as the smelting furnace. may

he of any suitable. shape. so that it. is possible to obtain moulded articles of any suitable character. The heating winding or primary coil i:-= preferably arranged to snit the moulded article to lo produced. In this manner it is possible to obtain with -full certainty moulded castings free from blow-holes. A |ulrti ularly suitable application is the direct l'u'odu tion ol' slab blooms free from blowhol s. which directly hate the most suitable shape for rolling plates.

It may be mentioned that a very advantageous method of operation is obtained when the above method is combined with the preparing method according to British specification Xo. 2:26.801. For this purpose itis advisable to adapt the method of operation according to British specification No. 22(530]. in the manner illustrated in Fig. 4 in accordance with the requiiementsof the new method ofoperation. For example. in induction furnaces. free from iron. the lower opening of the somewhat cylindrical induction coil 1' is closed by a chamotte plate Zr. 7. formed of one or more parts. Onto this chamotte plate. is firstly charged up to a pre-determintal depth of the layer a granular or sandy material 7 such as ground bauxite which at the temperatures occurring during the operation is not capable of sintcring. There is then placed inside the 'coil on this layer a thin railed sheet-metal cylinder space bet ween the J11. and the intermediate sheet-metal cylinder in and the inthiction coil 5 is filled with the same granular or sandy material which doesl'iot sinter at the temperatures which occur. Into the interior of the sheet-metal cylinder there is then placed for example. a sheet-metal cas .a ldition. if nos-iced, of powdered mg 'n. of which the outer shape t -orrespomls with the surface of the. casting to be subsequently produced. according to British Patent 226.801 and in the interior of which is placed the :aterial to be fused. mediate space between this sheet-metal templateyli and the sheet-metal cylinder in is filled with a granular or sandy material such as ground magnesite. or alumina. with the glass or horic acid which at the temperatures occurring during the operation, is capable of sintering and retaining its shape. After the charging of the furnace ha been completed in the manner indicated, the sheet-metal cylinder in is withdrawn. whereby the two layers of non-sinteri|;g granular or sandy material 7. and the sinteringmaterial 0 are notintermixed. but simply put in contact with one another. This material 0. by reason of the fact that it sinters at temperatures The interthe fusion point of the alloyto be extent. a shapewhich are somewhat below of the metal to be fused. or fused, thus forms to some retaining crucible. In the upper opening of the induction coil ithe temperature under the circumstances will not be suiliciently high in order to ell'ect u sutlicient sintering of the shape retaining material 0. It may consequently be adrisable when setting up the furnace to insert at. this pointa tubular section of refractory material as is indicated in the drawing of the. furnace at p. Iirorder to obtain a sufficient increase in temperature in these upper zones it may be advisable to cover the upper opening oi. the fusion chamber by a thick refractory plate or to apply a layer of granular or sandy refra ct ory material.

During the fusion process the material Z will still be, capable of crumbling. as this mass is ot adapted to sinter at. the temperatures which occur during operation. The mass 0 however, will sinter together into a. shape-retaining crucible of like body at; tempertures which are. below the temperature at which the. fusion commences. After the completion of the fusion the separate sections of the induction coil. commencing from the bottom. are disconnected in stages at suitable. intervals of time and thus the smeltis caused to solidify from the bottom upwards. free from bimv-holes and pipes. After the completion of the smelting and solidification the chamotte plate l' is partly or wholly drawn to one side and the. material 7. which is still capable of crumbling. is allowed to run out downwardly. As soon as this has been done the casting which has been produced in the interior of the induction coil. with its surrounding sintered layer a is freely exposed. v and can be I'(.'t (lll removed. either upwardlv or do\\'n\\':u'dl from the. induction coil. whereupon the furnace. can be recharged. The layer 7. which has notsiut-ered and which has remained capable of crumbling, and is between the siutered part- 0 and the coil or the heating element. also serves as a. protection. against furnace breahages. Should a crack occur in the sintered layer 0 for any reason. this could not be continued through the layer 7 as this layer remains crumbly and would thus I'HCfttll the passage of metal to the coil. Finally it is advisable also to combine the method of operation with that according to which the outer space between the coil or the heating element and the furnace casing is filled with a crumbly. sandy mate rial. H in the cast! of an accident. there should be such a collapse of the materials I and 0 that. the molten smelt should come in contact with the induction (:oil or the heatingelemcnt then the smelt could not. pass into the space outside the induction coil or the heating element, and consequently could not;

zone adjacentthe iii Zii

come into contact with the furnace casing and thus damage this.

Finally it is possible to work a furnace oprated in accordance with the construction bove described readily in a gas-tight casing (see Fig. l) and to allow the fusion operation to take place in a protecting atmosphere or in a vacuum. As in accordance with the im'ention. the block, free from pipes and blmv-holes. is produced at the place of fusion without casting, itis not necessary to provide separate devices for carrying out the casting in a protecting atmosphere or a vacuum, or to arrange the furnace together with the easing so as to be capable of being tilted for this urpose. This is of considerable importance in the case of induction furnaces free from iron as in such uses, as is well known. the

casing must either consist of a non-comluctlag material (for example, earthenware) or of a 1ioor-comlucting metallicmaterial which in addition must also be subdivided in a suitable manner so as to be electrically non-conducting. lloth in the case of earthen "are casings and subdivided metal casings the device for tilting causes considerable difliculties by reason of the mechanical strains to which the furnace is subjected, and it is therefore to be regarded as a technical improvement that the above described construction and methods of operation enable blocks 2 nd ':i.-ting;-: free from pipes and blow-holes to be produced in a constantlystationary furnace.

While 1 have shown and described my improved process and the-means for producing castings free from blmv-holes and pipes as pointed out. above, I do not wish to limit my' self to the exact steps and nit-ans described as I am aware that two or more of the steps described may be combined and man minor changes may be made in them without dcpariing from the spirit of my inventi n. and I claim such equivalents as may suggest themselves to those skilled in the art.

I claim:

1. The method of producing castings free from pipes and blow-holes in smelting furuaces, which consist in melting the metal in the furnace. particularly in electrically heated furnaces such as resistance furnaces or induction and high-frequency furnaces and gradually solidifying the entirely molten metal from the bottom upwards in the smelting vessel.

2. The method of producing castings free from pipes and blow-holes in electrically heated smelting furnaces which consists in thoroughly melting the material in the furnace and then successively eliminating at an adjustable speed the action of the heating device from the bottom of the smelting vessel upwards.

3. The method of producing castings of a determined shape free from pipes and blowholes such as slab blooms for rolling plates which consists in smelting the metal or the solidifying the thoroughly liquefied metal from the bottom upwardly in the smelting vessel.

The method of producing ferrous metal castings free from pipes and blow holes in a ceramiclined smelt-lug furnace particularly in electrically heated furnaces such as resistance furnaces or induction and high frequency furnaces which consists in melting the metal in the furnace. and gradually solidify ing the entirely molten metal from the bottom upwardly in the smelting vessel.

(3. The method of producing castings free from pipes and blow-holes in electrically heated smelting furnaces such as resistance or induction and high-frequence furnaces which consists in first forming a sheet-metal casing of which the outer shape corresponds with the surface of the casting to be produced, surrounding the said casing with a.

layer of a granular material capable of sintering closebelow the melting temperature of the material to. be smelted, surrounding the said layer with a layer of a granular material not sintering at the said temperature, then introducing the metal to be smelted into the interior of the metal casing, heating the 'metal by means of an electric current up to the molten state and gradually solidifying the molten metal, after completing the melt, from the bottom upwards in the smelting vessel.

7. The method of producing castings free from pipes and blow-holes in electrically heated smelting furnaces such as resistance or induction and high-frequency furnaces. which consists in first forming a sheet metal casing of which the outer shape corresponds with the surface of" therasting to be produced, surrounding the said casing with a layer of a granular refractory material capable of sintering close below the meltin temperature of the material to be smelted:

surrounding the said layer with a further layer of a granular material not sintering at the temperature produced between the layer being capable of sintering and the heating devices. then introducing the metal to be smelted into the interior of the metal casing, heating the metal by means of an electric current up to the molten state, gradually solidim: H m

fying the molten metal, after completing the melt, from the bottom upwards in the smelthe method of producing castings free from pipes and blow-holes in electrically heated smeltim furnaces such as resistance or induction and 1gh-f equency furnaces which materinl capable of sintermg close below the melting temperature of the material to be smcltwl, and an upper, smaller part with a. tube of refractory material, surrounding the m layer of granular material, not sintering at I an electric current up to molten state, and

I 25 gradually solidifying the molten metal, aftif; V er completing the melt, from the bottom upwards in the smelting vessel.

. gg, 9. The method of producing castings free 5x: from pipes and blow-holes in electrically as heated smelting furnaces such as resistance as duced, surrounding the said casing with a 49 granular material. extending to the outer to e smeltedinto the interior of' the metal 4.; casing, heating the metal bv mean's of an wards in the smelting vessel. 50 n testimony whereof I aflix my signature WILHELM ROHN.

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