GB1589220A

GB1589220A - Process for casting molten metal in casting machines having at least one casting belt

Info

Publication number: GB1589220A
Application number: GB37982/77A
Authority: GB
Original assignee: Hazelett Strip Casting Corp
Current assignee: Hazelett Strip Casting Corp
Priority date: 1976-09-13
Filing date: 1977-09-12
Publication date: 1981-05-07
Also published as: JPS613579B2; DE2740477A1; IT1085182B; JPS5335633A; ZA775237B; FR2364078A1; CA1089185A; YU217677A; BR7706012A; SE7710265L; ATA653877A; FR2364078B1

Description

(54) IMPROVED PROCESS FOR CASTING MOLTEN METAL IN CASTING MACHINES HAVING AT LEAST ONE CASTING BELT (71) We, HAZELETT STRIP-CASTING CORPORATION a corporation organised and existing under the laws of the State of Delaware. United States of America. of Malletts Bay. Winooski, Vermont ()54()4, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process for casting molten metal in casting machines having at least one endless casting belt. such as twin-belt casters and wheel casters.

In those machines, an endless casting belt revolves around pulleys and passes along a casting zone from the input end to the output end thereof; during its travel from the output end to the input end of the casting zone, the casting belt has to be covered on its casting side with a layer of a parting agent in order to avoid in the casting zone adhesion of the metal being cast to the casting belt: that parting agent may also be used as thermal barrier for controlling cooling conditions in the casting zone.

A known method for applying such a parting agent consists in exposing the casting side of the casting belt to a reducing flame, whereby a layer of soot is deposited on it. Soot being hygroscopic. this method presents the disadvantage that it may induce porosity in the cast metal. Moreover, this method is particularly air-polluting, since the entire environment of the casting machine becomes rapidly charged with very fine soot particles.

Another known method consists in applying upon the casting belt by spraying or brushing, a layer of a dispersion of a parting agent. e.g. a mixture of colloidal graphite and a resinous binder, in a highly volatile liquid such as trichloroethane (boiling point: 74,1 C), whereby the casting belt re-enters the casting zone. apparently in a completely dry state.

This method has been found by the Applicant to produce porosity in the cast metal.

It is an object of the present invention to provide a process for casting molten metal in a casting machine having at least one endless revolving casting belt, which process reduces porosity in the cast metal.

To this end and from one aspect, the present invention consists in a process of casting molten metal in a casting machine wherein at least one endless casting belt revolves around pulleys and passes along a casting zone from its input end to its output end and wherein the casting belt during its travel from the output end to the input end receives on its casting side a layer of a parting agent dispersed in a liquid, characterized by heating the casting belt during said travel to such an extent that the parting agent layer which enters into the casting zone is thermally stable in that zone.

By thermally stable is meant that the layer of parting agent does not give rise to gas formation either by volatilisation or by thermal decomposition at the tempeflitureof the casting belt in the casting zone.

The thermal behaviour of various commercially available parting agents has been studied in the laboratory. Casting belt samples measuring 0. 10 x (). I() metre have been provided on one side with a layer of a parting agent dispersion. the layer thickness (about 0,060 mm) being the same as that used normally in industrial casting operations. The samples have been subjected to a thermal treatment in an electrical furnace, then cooled in the air to about 100"C and finally reheated within the range of temperature to which casting belts are normally brought in the casting zone (250 - 350"C). Reheating has been done in an electric furnace equipped with a photoelectric cell for fume detection. Results obtained with a dispersion of Aqualon in trichloroethane (100 g. of Aqualon per liter of dispersion), Aqualon being the trade name for a colloidal graphite based parting agent sold by Prohag, Bamberg, West-Germany, are given in the table below.

TABLE thermal treatment reheating temp. "C. fume detected (samples held for 1 minute upon reheating temp. "C time in sec. at the given temp.) 350 6 350 yes 350 6 300 yes 350 6 250 yes 350 8 350 yes 350 8 300 yes 350 8 250 no 350 10 350 no 350 10 300 no 350 10 250 no 350 12 350 no 350 12 300 no 350 12 250 no 300 6 350 yes 300 6 300 yes 300 6 250 yes 300 8 350 yes 300 8 300 yes 300 8 250 yes 300 10 350 yes 300 10 300 no 300 10 250 no 300 12 350 yes 300 12 300 no 300 12 250 no 250 6 300 yes 250 6 250 yes 250 8 300 yes 250 8 250 yes 250 10 30() yes 250 10 25() no 250 12 300 yes 250 12 250 no Nearly the same results have been obtained with - a dispersion of Aqualon in water (100 g. of Aqualon per liter of dispersion); - a dispersion of Endugraco in trichloroethane (150 g. of Endugraco per liter of dispersion), Endugraco being the tradename for a graphite based parting agent sold by Etablissements Paul Lacroix, Liege, Belgium; - a dispersion of Foliac X in trichloroethane (100 g. of Foliac X per liter of dispersion), Foliac X being the tradename for a graphite based parting agent sold by Société Anonyme Morgan, Brussels, Belgium, and - a dispersion of Top Coat WO 133D in trichloroethane (100 g. of Top Coat WO 133 D per liter of dispersion), Top Coat WO 133 D being the tradename for a graphite based parting agent sold by Acheson Colloids B.V., Scheemda, The Netherlands.

It has surprisingly been found that such treatment does not affect the parting power of the layer of parting agent.

From another aspect, the present invention consists in a process of casting molten metal in a casting machine wherein at least one endless casting belt revolves around pulleys and passes along a casting zone from its input end to its output end and wherein the casting belt during its return travel from the output end to the input end receives on its casting side a layer of a parting agent dispersed in a liquid, characterized by heating the casting belt during said return travel for at least 10 seconds to a temperature which is at least equal to the highest temperature to which the casting belt is brought in the casting zone, whereby the parting agent layer which enters the casting zone is thermally stable in that zone.

It is particularly advantageous to have the casting belt re-entering the casting zone at a temperature of at least 100"C. Thus, condensation of air humidity upon the re-entering belt is avoided.

In order to avoid excessive local heating of the belt, the casting belt is preferably heated before as well as after applying said layer. For the same reasons, it is particularly useful to heat the belt on both its sides.

Heating may be carried out in any way; highly suitable heating means include electrical, steam, flame and hot air heating.

It may be useful to heat internally, preferably by means of steam or hot air, that pulley which deflects the casting belt towards the position wherein it receives said layer, especially if the casting belt's travel from the output end to the input end of the casting zone is short.

Water is preferably used as the dispersion liquid.

Suitable parting agents include those which contain at least one of bone ash (Ca3PO4), colloidal graphite, alumina and diatomite.

Thanks to the fact that casting belt heating is provided, the process of the present invention makes it possible to cool the cast metal as it leaves the casting zone by direct contact with a liquid coolant, e.g. by water spraying, whereby the capacity of the casting machine is increased; the coolant, which adheres then to the casting belt when the latter leaves the casting zone, is preferably wiped off before the belt is heated. When applying such cooling without belt heating, it would be impossible to have the belt reentering the casting zone in a dry state.

The process according to the present invention is particularly suited for the continuous casting of high melting point metals such as copper and steel.

In order that the invention may be more readily understood reference will now be made to the accompanying diagrammatical drawings which show two modes of carrying out the process according to the invention and in which: Figure 1 is a longitudinal section taken across a twin-belt caster, Figure 2 is a section, on a larger scale, of the casting device taken along line X-X of Figure 1, Figure 3 is a longitudinal section, taken across a wheel caster, and Figure 4 is a section, on a larger scale, of the casting device made along line Y-Y of Figure 3.

Referring to Figures 1 and 2 the casting zone 1 of a twin-belt caster to which molten metal is fed at 2 and from which cast metal issues at 3 is delimited by two endless casting belts 4 revolving around drive pulleys 5 and tension pulleys 6 and by two side dams 7 moving forward in the same direction as belts 4. A dispersion of a parting agent in a liquid is sprayed at 8 upon the belts 4.

Belts 4 are heated over their entire width by electrical or hot air heating devices 9. The cast metal is cooled at 3 by water sprays 10. Cooling water which adheres to belts 4 is wiped off at 11.

In Figures 3 and 4, the casting zone 12 of a wheel caster to which molten metal is fed in 13 and from which cast metal issues at 14 is delimited by the groove of a casting wheel 15 and by an endless casting belt 16 revolving around wheel 15 and pulleys 17. A dispersion of a parting agent is sprayed at 18 upon belt 16. Belt 16 is heated over its entire width by electrical or hot air heating devices 19.

Reference will now made to the following Examples.

Example 1 In a twin-belt caster of the type illustrated in Figures l and 2 having a casting zone with a length of 4 metres, a height of 0.05 metre and a width of 0.12 metres, a copper bar was cast at a maximum speed of about 14 metres/minute. There was no direct cooling of the bar at the exit of the casting zone. Maximum temperature of the belts in the casting zone was about 300"C and temperature of the belts at the exit of the casting zone was about 30"C.

After leaving the tension pulleys the belts were heated to about 220"C, then covered by spraying with a layer of an aqueous dispersion of Aqualon (6 litres/hour/belt) and finally reheated again to about 350"C for about 12 seconds before reaching the drive pulleys.

The casting belts re-entered the casting zone at a temperature of about 130"C. No porosity was found in the cast bar.

Example 2 The same method as in Example 1 has been used, except that the cast metal bar has been directly cooled at the exit of the casting zone by means of water at a temperature of 25 to 30"C and a flow rate of 850 to 1250 litres/minute, the cooling water adhering to the belts being wiped therefrom before the belts are heated. Tests have shown that this direct cooling of the cast metal allows an increase in the maximum casting speed of about 50%.

WHAT WE CLAIM IS: 1. A process of casting molten metal in a casting machine wherein at least one endless casting belt revolves around pulleys and passes along a casting zone from its input end to its output end and wherein the casting belt during its travel from the output end to the input end receives on its casting side a layer of a parting agent dispersed in a liquid, characterized by heating the casting belt during said travel to such an extent that the parting agent layer which enters into the casting zone is thermally stable in that zone.

2. A process of casting molten metal in a casting machine wherein at least one endless casting belt revolves around pulleys and passes along a casting zone from its input end to its output end and wherein the casting belt during its return travel from the output end to the input end receives on its casting side a layer of a parting agent dispersed in a liquid, characterized by heating the casting belt during said return travel for at least 10 seconds to a temperature which is at least equal to the highest temperature to which the casting belt is brought in the casting zone, whereby the parting agent layer which enters into the casting zone is thermally stable in that zone.

3. A process according to claim 2, wherein the casting belt is heated at a temperature of at least 250"C. for at least 10 seconds after receiving the parting agent layer.

4. A process according to claim 2, wherein the casting belt is heated at a temperature of at least 350"C. for at least 10 seconds after receiving the parting agent layer and the casting belt is at a temperature of at least 100"C. when it enters the casting zone.

5. A process according to claim 1, 2 or 3, wherein the casting belt re-enters the casting zone at a temperature of at least 100"C.

6. A process according to any one of claims 1 to 5, wherein the casting belt is also heated prior to receiving the parting agent layer.

7. A process according to claim 6, wherein the temperature to which the casting belt is heated prior to receiving the parting agent layer is less than the temperature to which it is subsequently heated.

8. A process according to claim 6 or 7, wherein the cast metal is cooled as it leaves the casting zone by direct contact with a liquid coolant whereby liquid coolant adheres to the casting belt when it starts said travel, the liquid coolant is wiped from the casting belt, and the casting belt is heated subsequent to such wiping and prior to receiving the parting agent layer.

9. A process according to any one of claims 1 to 8, wherein the casting belt is heated on its both sides.

10 A process according to any one of claims 1 to 9, wherein the casting belt is heated by electrical means, steam, flame or hot air.

11. A process according to any one of claims 1 to 10, wherein the pulley, which deflects the casting belt towards the position whereat the casting belt receives the parting agent layer, is internally heated.

12. A process according to any one of claims 1 to 11, wherein the liquid is water.

13. A process according to any one of claims 1 to 12, wherein the parting agent includes at least one of bone ash, colloidal graphite, alumina and diatomite.

14. A process according to any one of claims 1 to 13, wherein the cast metal is copper or steel.

15. A metal casting process according to claim 1 or 2, and substantially as hereinbefore described.

16. A metal casting process substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

17. A metal casting process substantially as hereinbefore described with reference to Figures 3 and 4 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. being wiped therefrom before the belts are heated. Tests have shown that this direct cooling of the cast metal allows an increase in the maximum casting speed of about 50%. WHAT WE CLAIM IS:

1. A process of casting molten metal in a casting machine wherein at least one endless casting belt revolves around pulleys and passes along a casting zone from its input end to its output end and wherein the casting belt during its travel from the output end to the input end receives on its casting side a layer of a parting agent dispersed in a liquid, characterized by heating the casting belt during said travel to such an extent that the parting agent layer which enters into the casting zone is thermally stable in that zone.

18. A metal casting process substantially as hereinbefore described with reference to

Example 1 or Example 2.

19. A metal casting apparatus when used for carrying out the process claimed in any preceding claim.