GB2099339A - Improvements in dam-blocks for continuous metal casting - Google Patents

Abstract

A side dam-block (1) for twin belt casting machines, particularly for continuously casting copper, is formed with a core (5), preferably of a copper alloy, and at at least two adjacent working corners (6) are coated with a wear resistant metallic material having a hardness greater than the core. Preferred wear resistant materials include chromium or refractory steel and may be applied by electric arc deposition in an inert atmosphere. Various core and coating alloy compositions are provided. <IMAGE>

Description

SPECIFICATION Improvements in dam-blocks for continuous metal casting The present invention relates to improvements in dam-blocks for forming a casting side dam for use in twin belt casting machines for continuously casting molten metal, and particularly for casting molten copper.

In general, the upper and lower surfaces of the continuous casting mould of such twin belt machines are defined by a pair of spaced endless flexible belts travelling along, above and below the mould region. These belts are provided with a pair of spaced endless flexible side dams that travel along with and between the upper and lower casting belts and define the two lateral sides of the moving mould. Each of these side bands are formed by a multiplicity of slotted dam-blocks which are mounted on flexible straps.

Twin belt continuous casting macines which utilise side dams comprised of dam-blocks are described in U.S. Patent Specifications Nos. 2,904,860; 3,036,348 and 3,955,615. These prior Patent Specifications should be referred to if a fuller understanding of twin belt casting machines and the casting process is required.

The dam-blocks of the prior art are fabricated from a homogeneous material. Generally, the prior art dam-blocks are in the form of a massive piece of copper alloy which has undergone a structured hardening treatment in order to increase its mechanical strength.

More specifically, these known dam-blocks are made of a cooper alloy, such as, copper-nickel-silicon-ironchromium. These dam-blocks should have a minimal hardness of 200 HV10 (i.e. 200 Vickers hardness under a 10kg load). This minimal hardness is necessary in order for the dam-blocks to sustain the pressure stresses which they will be subjected to during the operation of the mould. However, in order to prevent too high a brittleness, the dam-blocks should not have a hardness exceeding 220 HV10. The alloys used in dam-blocks must also have sufficiently high thermal conductivity characteristics in order to allow for a rapid cooling of the cast bar. Generally, their thermal conductivity is measured by ascertaining their electrical conductivity which should be about 35% IACS.

One alloy which has the above described required properties is sold under the name "BRONZE CORSON" which is a Trademark of the Applicants (Usines a Cuivre eta Zinc de Liege). The alloy has the following composition.

Constituent % By Weight Nickel 1.7-2.0 Silicon 0.5-0.9 Chromium 0.2-0.4 Iron 0.1-0.2 Copper Balance This composition may undergo a structural hardening which involves the precipitation of Ni2Si.

Another alloy from which dam-blocks may be formed is copper-beryllium.

These alloys and the design of such dam-blocks made from the above-mentioned alloys allow a continuous casting of molten copper under good conditions. However, it appears that dam-blocks and side dams which are comprised of the known alloys undergo severe wear, especially at the edges of the blocks.

This wear reduces the life expectancy of such blocks. Another result of such wear is used during casting is the infiltration and leakage of molten metal copper, such as, between abutting ends of the blocks, which are being tightly pressed together in an end-to-end abutting relationship along the casting zone. This excessive wear will either cause spacing or deposition of copper between these dam-blocks, which will necessitate the replacement of the worn out blocks and cause an interruption in production.

The present invention seeks to overcome the above discussed disadvantages and other deficiencies of the prior art by providing improvements including a novel composite dam-block and a method of manufacture thereof.

According to this invention, we provide a blockforforming a casting side dam in a twin-belted casting machine wherein a plurality of abutting blocks are mounted to an endless belt, the block comprising a metallic core of generally rectangular shape in section which is coated on at least a pair of adjacent working corner edges with a metallic material having a hardness which exceeds that of the core material.

Preferably, the metallic core of the body comprises a copper alloy.

Accordingly, by this invention a composite dam-block is comprised of a massive core of a copper alloy which has in those regions which are subject to mechanical wear an outer coating of material with a hardness greater than that of the underlying copper alloy.

The preferred copper alloy material useful in formation of the body of a dam-block in accordance with the present invention is either a copper-nickel-chromium-silicon-iron alloy or a copper-beryllium alloy, which may possibly contain nickel. It has also been found that a copper-cadmium alloy having an electrical conductivity in the range of 90 to 70% of the electrical conductivity of electrolytically deposited copper is suitable.

The preferred seating material may be selected from either pure or substantially pure chromium or a refractory steel. As used herein the term "refractory steel" is a generic term for an iron alloy containing varying percentages of chromium and nickel with possible trace amounts of silicon and carbon.

In accordance with the present invention the dam-blocks are provided with the coating material only in the regions which are subjected to the excessive wear. The surfaces which are exposed to excessive wear are the corner edges of the blocks. By coating only the working edges of the blocks the required thermal conductivity of the block is maintained.

The preferred method of manufacturing a composite dam-block in accordance with the present invention involves first cutting each corner edge of the block to provide a triangular prism section or groove. The wear resistanct material for coating is then applied into this section by electric deposition in the presence of an inert gas. This process involves establishing potential difference between the core of copper alloy and the wear resistant material. This creates an electric arc between the materials which melts the wear resistant material to fill the prism section.

As far as we know, prior attempts to produce dam-blocks having the necessary mechanical strength and thermal conductivity with a sufficient wear resistance have been unsuccessful, and this invention provides a significant technical advance.

The composite dam-blocks of the present invention do not show any separation or splitting of the copper alloy from the wear resistant material in spite of the severe thermal variations to which the blocks are subjected during a continuous casting process; wherein the temperature varies between 1150"C and approximately 120 -200 C.

The present invention thus has as one of its many advantages the provision of dam-blocks and resulting side dams which have the necessary wear resistance without any loss of mechanical strength and thermal conductivity.

Another advantage of the present invention is to provide wear resistant dam-blocks and resulting side dams which have enhanced service life whereby the necessities of replacement and associated production stoppage are reduced.

The present invention may be better understood and its objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawings wherein like reference numerals refer to like elements in the several Figures and wherein: Figure 1 is a cross-sectional view of a composite dam-block in accordance with one embodiment of the present invention; Figure 2 is a side elevation view of the dam-block of Figure 1; Figure 3 is a top view of the dam-block of Figure 1; and Figure 4 is a graph illustrating the difference of Vickers hardness (HV10 under a 10 kg load) between a composite dam-block in accordance with the present invention and the prior art dam-blocks of copper-beryllium alloy and copper-nickel chromium-silicon-iron alloy following heating to certain temperatures.

Reference to Figures 1 to 3, a composite dam-block 1 is for use in a process such as aforementioned for continuously casting a molten metal, preferably copper. The block 1 is provided with a slot 2 for receiving a metal strap (not shown), and a plurality of such blocks 1 would be positioned along this strap, with the side faces 3 of adjacent blocks abutting each other. It is along the side faces 3 where the most excessive wear occurs. This end-to-end arrangement of blocks 1 forms the lateral walls of the continuous mould of the apparatus and process as mentioned previously.

The block 1 is made of a core of metallic material 5, preferably a copper alloy, which has a good mechanical strength and good thermal conductivity. These characteristics are essential in order to produce the lateral walls of a continuous mould useful for continuously cssting a molten metal. Block 1 has a generally rectangular shape. The working corner edges of the block 1 are provided with a wear resistant coating 6. The coating 6 reduces the excessive wear of the block 1, without adversely affecting the necessary thermal and mechanical properties.

Copper alloys which are useful in forming core 5 in the practice of the present invention are a nickel-silicon-chromium-iron-copper alloy, a copper-beryllium alloy, which may possibly contain traces of nickel, or a copper-cadmium alloy. The copper-cadmium alloy should have a respective electrical conductivity in the range of 90% to 70% of the electric conductivity of electrolytic copper.

The coating material 6 is preferably a refractory steel but may also be either pure or substantially pure chromium.

The preferred method of applying the coating material 6 is by an electric deposition process in the presence of an inert gas. In this process the block 1 is formed from the core material 5. A triangular prism section is removed from the core material 5, along each working edge of the block 1. This section has a dimension of, for example 5 x 5 millimetres. A potential difference is established between the coating material 6, which is preferably in the form of a wire, and the core material 5. As the wire is advanced towards the core material 5 an electric arc is created which causes the coating material 6 to melt into triangular cutaway section of the core material 5. The wire is in the form of a disposable eiectrode and is preferably advanced with an envelope of inert gas preventing oxidation of the molten metais. After the process is completed any unevenness of the resulting block 1 is corrected by machining.

The following examples illustrate various compositions of the core 5 and the material 6.

Example 1 The core material 5 had the following composition: Constituent % By Weight Nickel 1.6-2.2 Silicon 0.4-0.8 Chromium 0.3-0.6 Iron 0.1-0.2 Copper Balance The working edges were coated with the following composition: Constituent % By Weight Chromium 25 Nickel 20 Carbon 0.08 Iron Balance The final product is then tooled to the desired shape of the dam-block 1. The hardness of the coating material 6 is 230-260 HV10 while the core material 5 has a hardness of 206 to 220 HV10.

The resulting dam-block 1 was used in a twin-belt casting machine for continuous casting of copper. The temperature ofthe castcopperwas 1115 C (1110 to 11200) whilethe copper bar atthe exitofthe casting machine was at a temperature of 1000"C. The pressure on the steel belts was six metric tons and the cross-sectional area of the cast bar was 130 x 60 millimetres.

The speed of travel of the blocks 1 during the process was 10,500 millimetres per minute. Thus the blocks 1 travelled through a whole cycle 1.08 times per minute. During each cycle of the continuously practised process the blocks were cooled down from the 1000 C+ temperature to about 120"C by a water spray. After numerous runs the blocks were examined. It was found that there was no splitting or blistering between the coating material 6 and the core material 5. It was observed that small irrelevant plastic deformation had occurred at the lower edges of the blocks. The blocks prepared according to the above compositions were used for 24 hours before examination.

The expected mean life of dam-blocks prepared in accordance with the above composition is 44 times 24 hours of continuous operation. The following two examples (2 and 3), were also prepared and run through a twin belt casting machine for the continuous casting of copper under the same conditions as per Example 1.

Again observation showed no cracking or splitting between the coating and core materials.

Example 2 The core material 5 had the following composition: Constituent % By Weight Nickel 1.7-2 Silicon 0.5-0.9 Chromium 0.2-4 Iron 0.1-0.2 Copper Balance A block formed in according with the above composition had its working edges coating with a layer of pure chromium, the resulting thickness of the chromium being between 0.5 and 4 micrometres.

Example 3 Example 3 The core material 5 had the following composition: Constituent % By Weight Nickel 1.7-2 Silicon 0.5-0.9 Chromium 0.2-0.4 Iron 0.1-0.2 Copper Balance The working edges of a block having the above composition had its working edges coated with a layer having the composition of: Constituent % By Weight Beryllium 0.3-0.6 Nickel 2.2-2.7 Copper Balance As stated above the preferred method of applying the wear resistant material is by electric deposition and the following example was prepared by this method.

Example 4 The core material 5 had the following composition: Constituent % By Weight Nickel 1.6-2.2 Silicon 0.4-0.8 Chromium 0.3-0.6 Iron 0.1-0.2 Copper Balance Refractory steel having the following composition was used as the coating material 6; Constituent % By Weight Chromium 29 Nickel 9 Iron Balance The coating material 6 was in the form of a wire. A triangular prism section was then removed from each working edge of the block, this section having a dimension of 5 x 5 millimetres. A potential difference of 30 volts was established between the block and the wire of refractory steel. This potential difference was established by passing a current, with an intensity of 300 amps through both the wire and the block. The wire was then advanced towards the block, preferably at a speed of 250 millimetres per minute, until an electric arc was generated.The distance between the wire and the block was then permanently fixed, in order to maintain the arc and to ensure continuous melting of the wire into the sectional cutout. In order to prevent oxidation of the metal an atmosphere of argon, an inert gas, was established surrounding the block and wire while the electric arc was present. After this process was completed and the metals were cooled down, the composite block was tooled to the desired final shape of the dam-block.

Three composite blocks of the present invention, prepared by the above-discussed process, were placed in a chain of prior art blocks, which had the composition of nickel-silicon-chromium-iron-copper, and were used in a continuous process similar to those aforementioned. After a production of about 4800 tons of copper, which had been accidentally overheated, all the prior art blocks were destroyed by plastic deformation along their edges and the formation of a parasitic cast of copper between the blocks. Only the three composite blocks according to the present invention, resisted the plastic deformation and excessive wear along their edges, which would have resulted in the parasitic cast. These three composite blocks were further used to produce about 30,000 tons of copper.

With reference to Figure 4, the graph illustrates the Vickers hardness, under a ten kilogram load, of three types of dam-block compositions which had been heated to different temperatures and maintained at such temperatures for 1 hour and thereafter cooled to room temperature for hardness testing.

Curves 1 and 2 relate to the prior art dam-blocks having the composition of copper-beryllium and copper-nickel-silicon-chromium-iron, respectively. Curve 3 relates to a composite block, prepared according to the given Example 4.

The graph clearly illustrates that while the composite block of the present invention has maintained its hardness despite heating to the different temperatures, whilst the blocks prepared according to the prior art show a sharp decrease in hardness after heating to the higher range of the temperatures.

Although in the embodiments described, all four working edges of the block are coated with a metallic material having a hardness exceeding that of the core, the coating could be applied to the two working edges such as presented in the mould to the molten face of the metal.

The advantages arising from the present invention and the long-life expectancy of the dam-blocks in service will be appreciated by those skilled in the art.

Claims (12)

1. A blockforforming a casting side dam in a twin-belted casting machine wherein a plurality of abutting blocks are mounted to an endless belt, the block comprising a metallic core of generally rectangular shape in section which is coated on at least a pair of adjacent working corner edges with a metallic material having a hardness which exceeds that of the core material.

2. A block according to claim 1 wherein all four working corner edges are coated.

3. A block according to claim 1 or claim 2 wherein the metallic core of the block is a copper alloy.

4. A block according to claim 3 wherein the copper alloy is selected from the group consisting of: a copper-beryllium alloy; a nickel-silicon-chromium-iron-copper alloy; and a copper-cadmium alloy having an electrical conductivity in the range of 70% to 90% of the conductivity of electrolytically deposited copper.

5. A block according to any one of the preceding claims wherein the metallic coating material is chromium.

6. A block according to any one of claims 1 to 4 wherein the metallic coating material is refractory steel.

7. A block for forming a casting side dam in a twin-belted casting machine, the block being substantially as hereinbefore described with reference to Figures 1,2 and 3 of the accompanying drawings.

8. A block for forming a coating side dam in a twin-belted casting machine according to claim 1 and wherein the composition of the metallic core is substantially as given in any one of the Examples 1,2 or 3 hereinbefore.

9. A block for forming a casting side dam in a twin-belted casting machine according to claim 1 wherein the composition of the metallic coating is substantially as given in any one of the Examples 1,2 or 3 herein before.

10. A method of making a block as claimed in claim 3 wherein a rectangular block is formed from the copper alloy, a triangular prism section is cut from the block along the four corner edges, and the triangular prism sections are filled with a metallic coating material having a hardness greater than that of the copper alloy.

11. A method according to claim 10 wherein an atmosphere of inert gas is established around a prism section of the block and a member comprised of the metallic coating material, an electrical potential difference is established between the block and said member, the member is located at a position wherein an electric arc is struck between the member and the block and the member is melted to fill the prism section.

12. A method of making a block for forming a casting side dam in a twin-belted casting machine according to claim 1, the method being substantially as herebefore described with reference to any one of the Examples.