GB2099341A

GB2099341A - Production of thickwalled containers by casting metal

Info

Publication number: GB2099341A
Application number: GB8213142A
Authority: GB
Original assignee: Siempelkamp Giesserei KG
Current assignee: Siempelkamp Giesserei KG
Priority date: 1981-05-21
Filing date: 1982-05-06
Publication date: 1982-12-08
Also published as: CH660317A5; BE893222A; DE3120221A1; FR2506191A1; DE3120221C2; GB2099341B; FR2506191B1

Abstract

A foundry mould for use in a process for the production of a thickwalled container in nodular cast iron, e.g., for irradiated nuclear fuel elements, has a baseplate (1) moulding- box rings (2) and a core spindle (3), having a mould jacket (4) made from moulding sand and a core (5) preferably made from moulding sand, both the mould jacket and the core having cooling tubes (9) embedded therein adjacent the cavity faces at a distance not exceeding 100 mm, the cooling tubes (9) being connected to a cooling unit, to develop rapidly solidified surface skins adjacent to the mould jacket and core faces by active cooling in the molten iron, and thereby protect the mould jacket and the core from a proportion of the solidification pressure. <IMAGE>

Description

SPECIFICATION Production of thickwalled containers This invention relates to a process for the production of a thickwalled container in nodular cast iron, i.e., cast iron with nodular graphite, in which molten iron at the pouring temperature is poured into the cavity in a foundry mould comprising a core and a mould jacket formed from moulding sand, cooled in the mould and allowed to solidify. The invention further relates to a foundry mould for carrying out the said process. The term "thickwalled" is defined in the context of the invention as a wall thickness from, for example, 200 to 600 mm or more, and refers to containers which may have a height up to several metres, as used mainly for the protected transport and storage of irradiated fuei elements for nuclear reactors.

Known foundry moulds are constructed in the classical manner from moulding sand and binders.

Inside the mould, the molten iron cools to the knocking out temperature by heat transfer to the environment, - and cooling is consequently slow.

The mould is subjected to substantial loads and can sometimes lose the necessary strength conferred upon it by the binders. The loads are set up mainly by the so-called solidification pressure. It must be assumed that when molten iron cools below about 1340"C it will undergo more expansion than can be offset by thermal contraction. This occurs because of the precipitation of nodular graphite typical of nodular cast irons. The resulting positive pressure can distort the mould at a lower temperature. The mould jacket is particularly at risk. Distortion is an adverse effect, which can lower certain significant properties of the container. There is also a risk that sand will enter the molten iron.

The object of the invention is to provide a process for the production of a thickwalled container in nodular cast iron, in which damaging mould distortions are avoided, and a foundry mould particularly adapted to the said process.

According to the present invention, in a process for the production of a thickwalled container, in nodular cast iron, in which molten iron at the pouring temperature is poured into the cavity in a foundry mould comprising a core and a mould jacket formed from moulding sand, cooled in the mould and allowed to solidify, cooling tubes are embedded in the mould jacket and the core and connected to a cooling unit, to develop rapidly solidified surface skins adjacent to the mould jacket and core faces by active cooling in the molten iron and thereby protect the mould jacket and the core from a proportion of the solidification pressure.It is known in a completely different context, viz., to accelerate the solidification process for metallurgical or economic reasons or to protect permanent moulds, to cool the jackets of metallic moulds or more particularly the jackets of chill moulds; thus pipelines can be embedded in the chill-mould walls (German Patent Specification 425 132 and 725 674) or one can use chill moulds having an inner steel jacket, a surrounding cooling jacket and a space containing inserted cooling coils and a sand filling (German Patent Specification 855 151). It is also known to surround a metal mould externally with a pressed-on cooling jacket which is made from high-conductivity material and has a plurality of cooling channels running longitudinally and transversely (German Patent Specification 2317 151). In the casting of rolls, it has already been proposed (U.S.Patent Specification 1 173 955) to effect cooling from the roll axis zone. None of this prior art relates to the problems initially described of preventing damaging distortions in sand moulds for the basic process.

In most applications of the process of the invention, the cooling system is brought into action after pouring the molten iron. In certain cases, however, cooling can be started before pouring the mould with molten iron, by switching the cooling system on first. In all cases, the invention makes use of active cooling, which can be adapted without difficulty within the range of normal thermodynamic conditions for heat exchange so that damaging mould distortions no longer occur, because the active cooling develops rapidly solidified surface skins adjacent to the mould jacket and core faces and thereby protects the mould jacket and core from a proportion of the solidification pressure. It is preferable to use in the cooling unit any liquid or gaseous coolant whose temperature can be adjsted as required to attain the described effect.The solidification period for the molten iron to fall from the pouring temperature to the knocking-out temperature can be significantly shortened by cooling as described, for example, by as much as 80%. In generai, the cooling action is mantained only until the molten iron has transformed to austenite, pearlite and ferrite, and is then terminated. The cooling action can be started again after passing through the transformation range. In general, the invention is carried out with foundry moulds made from moulding sand, for both the mould jacket and the core.

However, it is also possible to use a metal core, e.g., steel or copper.

A foundry mould for carrying out the process as described incorporates a base-plate, moulding-box rings, and a core spindle, has both a mould jacket made from moulding sand and a core made from moulding sand, and both the mould jacket and the core have cooling tubes, which are embedded in the moulding sand, the cooling tubes being disposed adjacent the cavity faces of the mould jacket and the core, at a distance from the mould jacket and core faces not exceeding 100 mm.

The accruing advantages are to be seen in that damaging mould distortions are avoided. Strength is retained, since binder combustion in the moulding sand can only take place during the cooling period in the layers nearer the mould cavity than the cooling tubes. This contributes to the avoidance of damaging mould distrortions. Moreover, the mould is protected from the solidification pressure. Furthermore, the invention makes it possible to use the much cheaper silica sand instead of expensive chrome-ore sand. However, the invention also has advantages in the metallurgical respect. Thus graphite degeneration is prevented, so that the elongation and notched impact values are improved.

Moreover, trace-element segregation is avoided.

The nodular graphite develops in the form of very large numbers of small nodules, thereby improving the tensile strength, proof limit, elongation and notched impact values and the elasticity modulus.

The acceleration of cooling down to the austenitepearlite-ferrite transformation range has the effect of producing a ferritic cast structure, so that ferritising annealing can be omitted. One particular advantage of the invention is that moulds can be poured without feeders.

An embodiment of foundry mould for carrying out the process of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a longitudinal section through one-half of the foundry mould; Figure 2 is an enlargement of the area A in Figure 1; and Figure 3 is a section, taken on the line B-B of Figure 1.

The foundry mould shown in the drawings incorporates a base-plate 1, moulding-box rings 2, and a core spindle 3. It has both a mould jacket 4 made from moulding sand and a core 5 made from moulding sand. Molten iron is poured in through a pouring cup 6 and flows down the runner 7 to the lowest point in the mould cavity 8. Thus, the mould cavity 8 fills from the bottom upwards during pouring.

The mould jacket 4 and the core 5 both contain cooling tubes 9 embedded in the moulding sand and connected to a cooling unit (not shown). The cooling tubes 9 are disposed adjacent the cavity faces of the mould jacket 4 and the core 5, at a distance from the mould jacket and core faces not exceeding 100 mm.

The cooling tubes run vertically, but they could run in loops and/or be connected to distribution tubes, or the cooling tubes could be disposed in helical formation. Moreover, a plurality of cooling-tube systems could be used, the coolant running in opposite directions through them to achieve a uniform cooling action over the entire height of the foundry mould.

Claims

1. A process for the production of a thickwalled container, in nodular cast iron, in which molten iron at the pouring temperature is poured into the cavity in a foundry mould comprising a core and a mould jacket formed from moulding sand, cooled in the mould and allowed to solidify, cooling tubes being embedded in the mould jacket and the core and connected to a cooling unit, to develop rapidly solidified surface skins adjacent to the mould jacket and core faces by active cooling in the molten iron, and thereby protect the mould jacket and the core from a proportion of the solidification pressure.

2. A process as in Claim 1,wherein the solidification period for the molten iron is reduced by 80% by the cooling action.

3. A process as in either of Claims 1 and 2, wherein the cooling action is maintained only until the molten iron has transformed to austenite, pear lite and ferrite and is then terminated.

4. A process as in Claim 3, wherein the cooling action is started again after passing through the said transformation range.

5. A process as in any of Claims 1 to 4, wherein a metal core is used.

6. A foundry mould for carrying out the process as in any one of Claims 1 to 4, incorporating a baseplate, moulding-box rings, and a core spindle, having both a mould jacket made from moulding sand and a core made from moulding sand, and both the mould jacket and the core having cooling tubes, which are embedded in the moulding sand, the cooling tubes being disposed adjacent the cavity faces of the mould jacket and the core at a distance from the mould jacket and core faces not exceeding 100 mm.

7. Afoundry mould substantially as hereinbefore described with reference to the accompanying drawings.