US2025336A - Method of forming large hollow castings - Google Patents

Description

Dec. 24, 1935.

A. w. BREARLEY 2,025,336

METHOD OF FORMING LARGE HOLLOW CASTINGS Filed March 25, 1934 2 Sheet-Sheet l dmrn y Dec. 24, 1935. A. w. BREARLEY 2,025,336

METHOD OF FORMING LARGE HOLLOW CASTINGS Filed March 25, 1954 2 Sheets-Sheet 2 Saw Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE METHOD OF FORMING LARGE HOLLOW oas'rmcs Arthur William Brearley, Sheffield, England Application March 23, 1934, Serial No. 717,067 In Great Britain March 24, 1933 3 Claims. (01. 22-200) 10 size, to cast the ingot solid and to remove thecentral unwanted portion by a machining operation.

fI'his process is unduly expensiveand diflicult because the weight oi metal required to be cast is greatly in excess of that which would be required 15 ii'the ingot were cast hollow, the ingot requires much greater time before removal from the mould and for annealing than if cast hollow and the machining operation is difiicult, laborious and expensive. Moreover in some cases of very large 2 ingots the extra weight involved by the unwanted central portion brings the total weight of the in-,

got above the load capacity 01' available lifting gear.

One of the main difiiculties to be overcome in the casting of large hollow ingots is the shrinkage oi. the casting after, it has been poured and has partly.- or wholly-irozen".- Such shrinkage is resisted by the core and undesirable internal strains, or, in some cases, actual cracks are formed 30 in the inset.

' A further difilculty arises in the casting of heavy hollow ingots owing to the tendency or the molten metal in very large bulk to erode a core of rammed sand or fire clay'and the liberation from such 5 cores, under. the intense heat, of gases such as water-vapour.

The present invention has torits object the provision of an improved process of casting heavy hollowingots, whether open at both ends oronly at one end.

Another object is the casting of such heavy hollowingots ln'such a manner that they are free from internal strains or cracks after they have cooled. r

A Anothenobject is the utilization of loose dry sand, as to rammed or moist coherent sand,v in, the casting of heavy hollow ingots.

Another object is'the provision of' a process of 50 casting heavy hollow ingots in which the core maintains its form rigidly so long as is required for the poured steel ingot to freeze sufliciently to become seli' maintaining as to its shape and the molten steel, when poured, does not come into 55 direct contact with the core which may evolve gases and may be eroded or disintegrated by the molten metal. I

Other objects and advantages of the invention will be appreciated from the following description and accompanying drawings. 5

It has heretofore been proposed, for the purpose of preventing blistering of the interior surface of a hollow ingot to cast it about a collapsible core comprising a thin nickel plated tube filled with loose sand or other refractory material. According 'to this proposal the thin nickel plated core tube became fused to the molten metal and, upon contraction, the loose packing of sand was crushed. .According to another prior proposal intended for the production of relatively light hollow castings, such as ordnance and projectiles therefore the core comprised sand rammed within a shell of sheet iron which melted and formed part of.the casting. In this latter process the sheet iron was for ,the purpose of providing a cleaner mould than would be provided by sand alone thusto prevent the formation of blow holes and irregularities in the casting. It has also been proposed to provide a ieeder head comprising an inner liner of thin sheet metal surrounded by loosely packed sand or other insulating material andto embed a closed case 01' sheet iron containing a. non-metallic or silicious body wholly within an ingot or other casting. Light tubular, articles such as iron pipes have been cast in a sand mould on to an internal shell of thinsheet steel or wrought iron filled with sand. All these proposals relate to comparatively light castings and not to heavy ingots of the nature of those with which the present invention is concerned. It has not hitherto .been practical to utilize sand v for heavy castings where the hydrostatic pressure of the large bulk of molten metal may exceed the stiffness of the sand.

According to the present invention in a process 40 of casting heavy hollow steel ingots about a core comprising a thin walled hollow protector of metal, capable of blending or alloying with the steel, filled with loose dry sand, the sand sinters at or near the melting point oithe steel, the hollow protector is only sufilciently thick to support the sand without melting until after at least the surface layers of the sand have been sintered by the intense heat 01' the molten steel, the steel is flowed into the mould at-the bottom and fills the mould' from the bottom upwards substantially without turbulence and the sand is .broken and loosened after the steel has frozen sufilciently to form in proximity to the core a solid wall of sufficient strengthto maintain the shape of the hollow ingot, thus permitting unimpeded contraction of the ingot as it cools further.

The functions'of the thin metal protector and of the sand are complementary to each other. The thin metal protector first supports and maintains the desired shape of the loose dry sand core, secondly it protects the loose sand core from being disintegrated by the molten steel and thirdly it permits the sand to be sintered without deformation of the core. The sand on the other hand, 'by the pressure exerted by it on the surface of the protector owing to its loose or mobile form prevents the collapse of the protector under the very great hydrostatic pressure of the molten steel. The sand moreover sinters before the protector melts, as it may in some cases, and thus forms a coherent wall of sufiicient strength to withstand the hydrostatic pressure of the still molten 'metal against it. It is of secondary importance whether or not the protector melts after the sintering of the sand because when the sand is sintered, the function of the protector is no longer necessary.

As above stated as soon as the cast steel has solidified sufiiciently to retain the shape of the ingot the sintered sand is broken and loosened, the contraction of the ingot thus being permitted to take place with little or no restraint as the ingot cools.

The flowing of the molten steel into, the bottom of the mould and filling of the mould from the bottom upwards substantially without turbulenceis of importance, since pouring the steel into the top of the mould would inevitably set up turbulence and splashing which might cause premature melting of the protector before the sand has sintered sufficiently to maintain its shape.

.In carrying out the invention a fracturing device is preferably embedded in the sand and, after the steel has frozen sufiiciently,'it is moved and preferably withdrawn to cause the sand to crumble. In casting a hollow ingot the steel may be poured through a central geat or conduit in known manner so that the molten steel is introduced through the center of the core to the bottom of the mould. In this case the geatis surrounded by a thin protector with an annular space between the geat and the protector filled'with loose dry sand and, after the steel has frozen sumciently, the sand is fractured and loosened by movement of the geat.

In casting a hollow ingot closed at one end the protector may be a sheet metal vessel having .a closed and an open end. It is filled with loose dry sand and supported in the mould with its closed end lowermost and above the base of the mould and with its open end above the top of the ingot to be cast. a

Other objects are to apply the invention to the casting ofslab ingots andcomposite ingots.

In the accompanying drawings:-- Figure 1 is a sectional elevation of an ingot mould and core according to the present invention. I

Figure 2 is a plan of Figure 1.

/ .Figure 3 is a view similar to Figure 1 illustrating a modification.

and a geat or conduit I2,for the molten metal is arranged at about the centre of the mould and is connected. with runner bricksv l3 fitted in the plate ll.

The geat illustrated is of the type in which dry granular packing I4 is poured into the annular 5 space between an outer metal case i 5 and an inher refractory liner tube l6. I

A protector in the form of a hollow cylinder ll of sheet metal is supported on the casting plate ll co-axial with the geat or conduit I2 and the 10 annular space between the protector I1 and the outer metal case l5 of the conduit is filled with dry sand l8 which is in a dry condition and may tector II.

It is advisable to feed the ingot through a number of equally spaced runner bricks l3, four of the feed apertures I! from such bricks being shown in Figure 2, so that the steel may be delivered at an equalized temperature in different parts of the ingot, thereby preventing the production of a relatively hot and cold side which may lead to cracking when the ingot freezes.

At a suitable interval after casting, depending on the mass of the ingot, the central conduit or geat I5 is drawn out, allowing the sand l8 to collapse. A flange or laterally projecting feet or the like 20 may be provided onthe outer metal case of the conduit to enable it to stand firmly on the casting plate II and to operate to fracture the sintered sand l8 when the conduit is extracted.

The'shape of the protector I1 may vary accord- 40 ing to circumstances and its thickness is governed by the mass and temperature of fluid metal in contact with it, its own melting point and the temperature at which the sand it! sinters.

In a specific example an ingot weighing from seven to twenty tons may thus be cast around a protector l1 made from mild steel sheet one sixteenth of an inch thick. In another example an ingot weighing three to five tons may be cast around a protector I1 made from mild steel sheet of twenty six gauge thick. In bothcases the outer orexposed surface of the protector remains solid, its inner surface'being'welded to the casting.

Whether the protector l1 melts wholly or partially during the pouring operation, it may be arranged to distribute the pressure of the fluid metal to the main body of the .sand ll (thus preventing the latter from crumbling) until it has frit or sintered and is in a condition to withstand that pressure without the aid of the protector.

In the modification illustrated in Figure 3 the geat or conduit 24 is disposed outside the mould 22 and a rod 2| is embedded in the sand 28 inside the protector 21. The rod 2| forms a fracturing or removing device so that on withdrawing it, after casting, the sand 28 will collapse and will oppose no resistance to contraction of the ingot as it freezes. The geat or conduit 24 may feed more than one mould, two-being shown in, Figure 3. The molten steel is fed to the base of the mould through runner bricks 25 provided with feed apertures 29as illustrated in Figure 3, arranged in the annular space between the protector 21 and the mould 22. f

Ifdesired the rod 2| may be provided with 75.

lateral projections to ensure that the sand shall plete core comprising the protector ll, 34, supporting the wall of sand 32 and containing the rod 33 is supported or suspended in an ingot mould 35, with its closed end 34 the'desired distance from the base of the mould and its open end'above the casting level or top of the ingots The inventionmay also be applied to the cor ing of castings other than ingots, especially where it is desirable that the core shall oppose no resistance to contraction of the casting.

The metal wall of the tube or protector must not be of such thickness that it may by itself,

when heated to the temperature of the molten metal in contact therewith, withstand the hydrostatic pressure of the metal, but on the other hand must require interior support at such temperatures in order to maintain its shape. On the other hand the metal wall of the tube must not be so thin that it will melt and permit penetration of molten metal to the sand core prior to the time when the layer of sand next adjacent I the same has been raised to a sintering temperature. By

the term thin used in the appended claims in describing the thickness of the wall of the tube is meant a tube having a wall the thickness of which lies between the limits above set forth. The actual thickness of the metal wall of the tube to be used in any particular instance may vary facing sheet of metal capable of blending or alloying withthe metal to be cast, said sheet being relativelythin so as to readily transmit heat from a body of molten metal to the sand, while at the same time preventing access of the molten metal thereto until the sand layer next adjacent the sheet has sintered and become self-sustaining against the action of molten metal and, after the molten metal has cooled sufficiently to become self-sustaining, destroying the core. g

2. The method of forming an axial cylindrical void or cavity in a large thick walled casting, during a casting operation, with the aid 'of apore of loose dry sand having the capacity to sinter under heat, which comprises the steps of protecting the loose dry sand core by a relatively thin cylindrical facing sheet of metal capable of blending or alloying with the metal to be cast, said sheet readily transmitting heat from a body of. molten metal to the sand, while at the same time preventing access of the molten metal thereto until the sand layer next adjacent the facing sheet has sintered and forms a rigid wall self-sustaining against the action and pressure of the surrounding body of molten metal and-after the molten metal has itself cooled suillciently to become self-sustaining, destroying the core, including the sintered outer wall, to permit free contraction of the casting.

. 3. The method of forming an axial void or cavity in a large thick walled casting, during a casting operation, with the aid of a core of loose dry sand having the capacity to sinter under' heat, which comprises the steps of protecting the loose dry sand core by a relatively thin facing sheet ,of metal capable of blending or alloying with the metal to be cast, said sheet readily transmitting heat from a body of molten metal to the sand, while at the sametime preventing access of the molten metal theretountil the sand-layer next adjacent the facing sheet has sintered and forms a rigid wall self-sustaining-against the ac- 40 L the,casting.

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