GB1595737A

GB1595737A - Casting metal ingots

Info

Publication number: GB1595737A
Application number: GB4957/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1978-02-07
Filing date: 1978-02-07
Publication date: 1981-08-19
Also published as: WO1979000596A1; FR2448951B1; SE431833B; BR7906448A; DE2934887C2; JPS55500084A; DE2934887T1; EP0009028A1; FR2448951A1; SE7908283L

Abstract

A method of casting metal comprising teeming molten metal into an ingot mould with a hot-top, the hot-top having a metal inner wall which is thin compared to the thickness of the mould wall and is surrounded by a heat insulating barrier, the resulting thermal expansion of the hot-top forming a gap between the inner wall of the hot-top and the shell of solidified metal on the ingot without external manipulation.

Description

(54) IMPROVEMENTS IN OR RELATING TO CASTING METAL INGOTS (71) I, ENN VALLAK, a Swedish Subject of 15 rue Sautter, CH-1205 Geneva, Switzerland, hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following state ment :- The present invention concerns casting metals in an ingot mould with the use of a so-called hot-top positioned on the mould to reduce pipe-formation in the solidified ingot.

A hot-top is a device which can be situated at the upper end of an ingot mould for preventing the upper part of an ingot in the ingot mould from cooling too rapidly.

Such a method is described in U. S. patent specification No. 3766965. In this U. S. patent specification molten metal is poured into an ingot mould having a hot-top. After a shell or layer of solidified metal has been formed the hot-top is moved mechanically so as to provide a gap between the inner wall of the hot top and the shell. This gap acts as insulation to prevent the upper portion of the ingot from cooling too rapidly.

Accordingly in one aspect the present invention consists in a method of casting metal ingots comprising teeming the molten metal in an ingot mould with a hot-top positioned on the mould, the hot-top having a metal inner wall which is thin compared to the thickness of the mould waTt and which is surrounded by a heat insu barrier, the resulting thermal expansion of the hot-top due to the temperature of the molten metal forming a gap between the inner wall of the hot-top and the shell of solidified metal on the ingot without external manipulation.

In a second aspect the invention consists in a hot-top for use with an ingot mould in the casting of metal ingots, the hot-top being capable of carrying out the method set forth above and comprising a hollow body having a base adapted to be positioned at the upper end of an ingot mould, the body having an upper opening and being formed from an inner wall of metal heat conductive material surrounded by a heat barrier of ceramic material.

In order that the present invention may be more readily understood, an embodiment thereof will now be described by way of example and with reference to the single Figure of the accompanying drawings, which Figure is a cross-section through an ingot mould and an associated hot-top.

The Figure shows an ingot mould 1, a hot-top 2 and a cover plate 3 and is divided into two by a line A so that two stages of the casting process can be shown. The left hand side of the Figure shows the mould just after molten metal 4 has been poured into the mould. The molten metal will normally be steel or iron, though non-ferrous metals may also be cast in a similar manner.

The hot-top 2 has a metal inner wall 5 having a thickness which is small compared to that of the mould walls. The inner wall 5 is surrounded by a heat barrier 6 made from a (heat resistant) ceramic fibre material. It is essential that the thickness of the inner wall 5 be chosen in relation to the capacity of the mould 1 such that the wall will not melt or become fused with the poured molten metal. The inner wall 5 should have a melting point which is not more than 300 C below the casting temperature of the molten metal being cast. The mner wall 5 may be 10 to 30 mm thick. Thus the thickness of the inner wall of the hot top should be chosen in relation to the capacity of the ingot mould in such a manner as to prevent melting or fusion of the inner wall during the casting of molten metal in the mould. The inner wall is also thin compared to the thickness of the mould wall. A suitable metal is cast iron but of course the material of the inner wall will depend on the metal being cast. As shown in the Figure the hot-top tapers from its base to its open top which is closed by the top cover 3. This taper is not, however, essential.

An additional heat barrier 9 is provided around the lower edge of the inner wall 5 to prevent heat transfer between the inner wall and the ingot mould. This additional heat barrier may not always be needed.

The hot-top is surrounded by a metal head case 10 provided with lifting lugs by means of which the hot-top and head case can be mounted on or removed from the ingot mould.

The metal may be poured either uphill or downhill. In the latter case the cover plate 3, which may be as described in U. K. patent specification No. 1,496,348; is placed on the hot-top after pouring.

As previously mentioned the left-hand side of the Figure shows the molten metal immediately after teeming. Shortly after the poured metal contacts the inner wall 5 a thin outer layer or shell of solidified metal is formed on the poured metal due to heat being conducted away from the molten metal by the mould 1 and the inner wall 5 of the hot-top.

The heat absorbed by the inner wall 5 causes the hot-top to expand. However because of its lower mass with respect to the mould 1 the hot-top 2 will expend substan tially more rapidly than the mould 1. Thus the hot-top is moved off the ingot without external manipulation to form a gap 7.

Because of the above mentioned difference in masses the gap 7 between the hot-top 2 and the ingot will be formed more rapidly and will be larger than the gap between the ingot and the mould.

The metal is then allowed to cool until it is solid. This is the situation shown in the right-hand side of the Figure. The hot-top 2 and the cover 3 remain in position throughout the entire cooling process. The gap 7, together with the insulation provided by the heat barrier 6 ensure that the upper portion of the ingot does not cool too rapidly with respect to the remainder of the ingot. Furthermore there is no need to introduce exothermic material into the gap 7 during cooling of the cast metal because of the thermal insulation provided by the gap 7 and heat barrier 6.

It will be appreciated that the hot-top described is reusable and also avoids the necessity of special provision being made to move the hot-top mechanically during the casting operation.

Several modifications of the hot-top described herein are wall of metal heat conductive material surrounded by a heat barrier of ceramic material.

Claims

8. A hot-top is claimed in claim 7, wherein the ceramic material is fibrous.

9. A hot-top as claimed in either claim 7 or claim 8, wherein the inner wall of the hot-top is coated with a parting or heat re flective material.

10. A hot-top as claimed in any one of claims 7 to 9, wherein the inner wall is made from a number of metal plates inter connected by means for causmg increased thermal expansion of the hot-top.

11. A hot-top as claimed in any one of claims 7 to 10, wherein the hot-top tapers inwardly from its base to its upper opening.

12. A hot-top as claimed in claim 10 or claim 11, wherein the means for causing increased thermal expansion comprise cop per or bimetallic material interposed bet ween the plates.

13. A hot-top as claimed in any one of claims 7 to 12 wherein the lower edge of the