US1923000A - Production of metal castings - Google Patents

Description

1933- R. w. BAILEY 1,923,000

PRODUCTION OF METAL CASTINGS I Filed Nov. 17, 1931 Rchard lA/Bculeg BY v ATTORNEY Patented Aug. 15, 1933 PRODUCTION or METAL CASTINGS Richard William Bailey, Hale, England, as-

signer to Associated Electrical Industries Limited, a Company of Great Britain Application November 17, 1931, Serial No.

575,628, and in Great Britain December-23,

This invention relates to the production of metal castings and particularly, though not exclusively. to the production of ingots of cast steel.

In the production of castings, such'as steel ingots, particularly those of large size, variations in grain structure usually occur in various parts of the casting. These may result in segregation and cracks in the outer parts of castings of all shapes and, in the case of ingots of square and parallel cross section, of what are called ingot corner marks. Defects are also generally found in the axial region of an ingot, particularly in the upper part. It has already been suggested that such defects in castings, and particularly those likely to occur in the casting of steel ingots, may be avoided by introducing at a desired stage in the casting process a suitable low melting point metal or alloy into the space formed between the mould and the casting by the contraction of the casting and/or the expansion of the mould. t l

According to the present invention similar defects, or some of them. are avoided by introducing a low melting point metal or alloy into the mould prior to the pouring of the metal to be cast.

In carrying out-the invention a quantity of fusible metal, lead for example, in the case where steel ingots or castings are to be made, is introduced into the mould and allowed to solidify before the ingot metal is poured. or it may be placed in the mould as a solid of suitable form, a disc, slab or ring for example. The solid fusible metal is covered with a plate which forms a false bottom to the mould, and of which the thermal capacity and resistance to the flow of heat is such that the ingot can be wholly or partially poured before the fusible metal begins to liquefy. The plate may be made of any suitable material, for example cast iron. steel; or of two or more materials as for example cast iron faced on one or both sides with a refractory material of low thermal conductivity such as asbestos sheet. As liquefaction of the fusible metal takes place it will flow upwards under the weight of the ingot into the space formed between the ingot and the mould by contraction of the ingot in cooling and/or expansion of the mould due to heat. It

necessary the resistance to the flow of heat from be available for melting the fusible metal. The

"5 Claims. (01. zip-200) V cient to float'the ingot.

' The rate ofliquefaction of the fusible metal will determine the rate at which its level in the mould will ascend, and consequently the extent to which the cooling towards the bottom of the ingot is made more active than in the upper portion of the ingot. This graduated cooling may be varied by changing the construction of the mould, for example making the wall thicker towards the bottom of the mould, or by artificial cooling of the mould,for example moving air over 0 the surface of the mould in the direction from the bottomto the top.

In dealing with ingots or castings of small and medium size the risk of producing fissures, that is ingot corner defects in polygonal or square in- 5 gots, may be negligible or absent, and in such cases the invention is employed mainly for controlling the cooling of the ingot so that it proceeds in the direction from the bottom to the top thereof. In the case of ingots of large size where there may be a risk of fissure defects in the outer zone it is necessary to counteract the bursting action of the metal which still remains liquid within the solidified outer shell during casting by providing a fluid pressure in the space between the surface of the ingot and the mould as described in the specification of the application hereinbefore referred to.

In applying the present invention for this purpose the plate or false bottom above described may be of any convenient form. For example. it may be a plain plate or disc. or it may be dished or cup-shaped, and made with a comparatively small thermal resistance and capacity so that the fusible metal beneath it will liquefy shortly after the commencement of pouring and thereby rise between the ingot and the mould when the free surface of the cast metal has risen only a short distance in the mould. Graduated cooling of the ingot, decreasing in intensity from the bottom of the mould towards the top, can also be accentuated .or assisted ,as hereinbefore described. Gradual cooling may be effected by varying the level of the fusible metal in the mould, which may be done either by varying the quantity originally introduced as hereinbefore described or by allowin; a regulated quantity of the fusible metal to escape from the mould when desired through an orifice which is normally closed, for example by means of a screwed plug or other suitable device.

In some cases it is desirable to provide for melting the fusible metal in two stages, and in one method of doing this a certain quantity of the fusible metal is placed in the bottom of the mould and covered by a plate andthen a further quantity of fusible metal is introduced above the plate and covered by a second plate. The thermal capacity and resistance of the second plate is made low whereas that of the first plate is much greater. When the ingot is poured the fusible metal between the first and second plates quickly becomes fiuid and rises up in the space formed between the outside of the ingot and the mouldand fioats the ingot until completion of pouring and for a sufiicient period of time for the outer part of the ingot to become solid and capable of retaining its fluid inner portion without risk. Asufficient quantity of the fusible metal may then be permitted to run off from the mould through a suitably controlled tapping orifice until the ingot descends and is supported by the lower plate. The tapping orifice for the fusible metal is then closed, and by reason of the thermal resistance of the first or lower plate the fusible metal below it is slowly melted. Fused metal will then rise again between the ingot and the mould and during the final stages of solidification of the ingot cooling of the same from the bottom upwards may be obtained. I

In some cases it may be necessary to provide means for preventing the lower plate from fioating upwards when the first quantity of fusible metal liquefies. This may be done by the provision of ledges or projections in the bottom of the mould under which the plate is lodged, Where more than one plate or false bottom is provided said plates and/or the bodies of fusible metal located below them may be of different metals or have different specific heats or thermal conductivities and melting points. The plate or plates which overlies or overlie the body or bodies of fusible metal prevent the molten metal. when poured into the mould, from coming into direct contact with and immediately fusing the body or bodies of fusible metal, and yet such plate or plates will transmit heat from the molten metal to the fusible metal to melt the latter. Therefore a short interval of time will elapse between the beginning of the pouring of the molten metal and the fusing of the bodyor bodies of fusible metal and the molten fusible metal will be caused by the weight of the poured molten metal to rise, in a film between the periphery or peripheries of the plate or plates, to fill the space between the cast ingot and the walls of the mould as the ingot cools.

The accompanying drawing shows three vertical sections, somewhat diagrammatic, illustrating ingot moulds with plates of low melting point metal located therein in accordance with the invention.

In Fig. 1 the body of the mould is indicated at 1 and 2 is a plate of low melting point metaL'lead for example in the case of steel ingots, covered by a plate 3 forming a false bottom to the mould.

In Fig. 2 the low melting point metal is in two pieces, namely a plate 4 resting in a cavity in the bottom of the mould and a ring 5 located at a somewhat higher level andresting on a ledge formed near the bottom of the mould. .The pieces 4 and 5 may be of the same low melting point I metal or of different metals. and both are covered by a plate 6 of suitable formlin section forming a false bottom. The body of the mould l in this figure is shown as being thicker at the bottom than at the top.

In Fig. 3 two plates of low melting point metal 7 and 8 are shown located in the bottom of the mould being separatedby a plate of other material 9 of suitable thermal capacity and heat conductivity, and the upper plate 8 is covered by a plate 10 also of suitable thermal capacity and heat conductivity which may be different from that of the plate 9 and which forms a false bottom to the mould. An orifice 11 is provided in the body 1 communicating with the interior of the mould and adapted to be closed by a plug of the mould, this being generally preferable and advantageous, the invention is not limited to this location, as, if desired, one or more pieces of low melting point metal ,may be located at different levels or at or towards the top of the casting. The metal when melted by heat conducted from the casting flows by gravity into the gap formed between the casting and its mould, suitable means being provided to admit the low melting point metal to the said gap.

I claim:-

1. The process of producing metal castings, comprisingintroducing a low melting point metal into the lower portion of a mould, covering the metal with a plate, and pouring molten metal to be cast into the mould, said plate having a capacity to transmit heat from the molten metal to said low melting point metal at a rate which will cause the low melting point metal to melt after at least a part of the metal to be cast has been poured into the mould, whereby the low melting point metal is caused to fiow between the solidifying casting and the walls of the mould.

2. The process of producing metal castings, comprising introducing a low melting point metal into a mould, covering the metal with a plate of metal faced on at least one ofits sides with a refractory material of comparatively low thermal conductivityvand pouring molten metal to be cast into the mould, said plate and facing together having a capacity to transmit heat from the molten metalto said low melting point metal at a rate which will cause the latter metal to melt after at least a part of the metal to be cast has been poured into the mould, whereby the low melting point metal will be caused to flow between the solidifying casting and the walls of the mould.

3. The process of producing metal castings. comprising introducing a low melting point metal in a liquid state into a mould. permitting said metal to cool, covering the solidified metal with a plate. and pouring molten metal to be cast into the mould whereby the solidified low melting point metal is fused and is caused to fiow between the solidifying casting and the walls of the mould.

4. The process of producing metal castings, comprising introducing into the lower portion of a mould a lower quantity of metal having a low melting point, covering said lower quantity of Q metal with a plate having a high thermal capacity and resistance to the flow of heat, introducing into the mould above said plate an upper quantity of metal having a low melting point, covering said upper quantity of metal with a plate having a lower thermal capacity and a lower resistance to the flow of heat than those of the first-named plate, pouring into the mould the molten metal to be cast whereby said upper quantity of low melting point metal is fused before the lower quantity of low melting point metal is fused and said upper and lower quantities or

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