Metal sampling method and apparatus

Abstract

A method of sampling a molten metal, the method comprising: pouring a stream of the molten metal; moving a plurality of sample pots under the molten metal stream during pouring, whereby a portion of the molten metal stream is poured sequentially into each of the plurality of sample pots and repeating such that each sample pot holds multiple portions of the molten metal stream; and heating the plurality of sample pots during the pouring process such that the molten metal within the plurality of sample pots remains molten during the pouring process.

Description

[0001] METAL SAMPLING METHOD AND APPARATUS

[0002] Field

[0003] The present specification relates to a method of sampling metal materials and to apparatus for sampling metal materials. The present specification is particularly useful in platinum group metal (PGM) sampling, assaying, and refining applications.

[0004] Background

[0005] Rotary sample dividers (also called spinning riffles or riffle sample splitters) are known for sampling of dry powder materials. Such an apparatus typically comprises a ring of sample pots which are rotated during sampling. Dry powdered material can be continually poured into the sample pots as the ring of pots rotates to divide the dry powdered material into a plurality of different sample pots. Each sample pot is only partially filled during each pass / rotation and is gradually filled up in a stepwise manner by multiple passes under the stream of powdered material. As such, any single sample pot will contain powder from a plurality of portions of the powder stream being poured into the rotating ring of pots.

[0006] The method is based on the principles that the powder should be sampled when in motion as a stream of powder and that a sample should be taken from many short increments of the stream of powder in preference to a single section of the powder stream. This method is used to produce accurate representative samples efficiently and consistently.

[0007] In contrast to the above, molten metal sampling can be done using a dip sampling technique to extract a sample of material from a molten metal batch. However, dip sampling can be prone to errors associated with inhomogeneities. While mixing of molten metal in an induction furnace can be used to improve the homogeneity of a melt such that a more representative sampling can be taken, this method is still prone to errors associated with inhomogeneities.

[0008] Alternatively, grain sampling can be used for molten metal sampling. Grain sampling can be achieved by pouring molten metal onto a slowly oscillating surface to form droplets which then fall into a bath of water. On entering the water bath, the droplets are quenched and frozen, forming solid grains. Depending on the size of the water bath available, this is often only suitable for small volume melts, as the water gradually heats over the process. To further reduce the risk of homogeneities, the resultant metal grain can be processed via a representative sample splitter (e.g. a spinning riffle as previously described), adding a further operational step to the sampling process. This type of grain sampling methodology can thus be slow and labour intensive.

[0009] It is an aim of the present specification to provide an improved method of sampling molten metal which will ensure representative sampling (low errors associated with inhomogeneities) and which can be implemented quickly and easily with relatively low manual input.

[0010] Summary

[0011] According to the present specification there is provide a method of sampling a molten metal, the method comprising: pouring a stream of molten metal; moving a plurality of sample pots under the molten metal stream during pouring, whereby a portion of the molten metal stream is poured sequentially into each of the plurality of sample pots and repeating such that each sample pot holds multiple portions of the molten metal stream; and heating the plurality of sample pots during the pouring process such that the molten metal within the plurality of sample pots remains molten during the pouring process.

[0012] The present methodology is advantageous over current methods of sampling molten metal materials. When compared to dip sampling it is less susceptible to sampling errors caused by inhomogeneities and when compared to grain sampling it is quicker and less labour intensive. In some respects, the method is similar to the rotary sample dividers (spinning riffles or riffle sample splitters) which are known for sampling of dry powder materials and have been demonstrated to minimise sampling errors very effectively. However, such prior art rotary sample dividers are not suitable for sampling of molten metal materials. The challenge with molten metal sampling is keeping the metal molten during the sampling activity. By actively heating the sample pots, it is possible to prevent metal freezing during pouring and bridging between pots, which would cause uneven distribution of the sample between pots and also introduce operational difficulties associated with removing metal from the pots. Induction heating can be used, and the sample pots can be constructed from an induction coupling material such as graphite or silicon carbide. Using such a configuration, the sample pots can be safely heated to temperatures up to around 1600°C during the sampling process, which maintains sufficient heat within the melt to ensure it remains fluid for PGM-containing alloys sampled by induction melting. Since sampling metallic customer feed is a core operation for a PGM refining business, having a more efficient and representative sampling method will aid in de-risking customer assays and improving the efficiency of the refining process.

[0013] The present specification also provides a molten metal sampling apparatus configured to perform the method as described herein. The molten metal sampling apparatus comprises: a molten metal pouring section for pouring a stream of the molten metal; a plurality of sample pots configured to move under the molten metal stream during pouring, whereby a portion of the molten metal stream is poured sequentially into each of the plurality of sample pots and repeating such that each sample pot holds multiple portions of the molten metal stream; and a heater configured to heat the plurality of sample pots during the pouring process such that the molten metal within the plurality of sample pots remains molten during the pouring process.

[0014] Brief Description of the Drawings

[0015] For a better understanding of the present invention and to show how the same may be carried into effect, certain embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

[0016] Figure 1 shows a simple schematic representation of an example of a metal sampling apparatus according to the present specification; Figure 2 shows another example of a metal sampling apparatus according to the present specification; and

[0017] Figure 3 shows another example of a metal sampling apparatus according to the present specification.

[0018] Detailed Description

[0019] As described in the summary section, the present specification provides a method of sampling a molten metal, the method comprising: pouring a stream of molten metal; moving a plurality of sample pots under the molten metal stream during pouring, whereby a portion of the molten metal stream is poured sequentially into each of the plurality of sample pots and repeating such that each sample pot holds multiple portions of the molten metal stream; and heating the plurality of sample pots during the pouring process such that the molten metal within the plurality of sample pots remains molten during the pouring process.

[0020] For example, the plurality of sample pots can be maintained at a temperature of at least 800°C, 1000°C, 1200°C, 1400°C, 1500°C, or 1600°C during the pouring process. Such high temperatures can be achieved and maintained during the sampling process by, for example, constructing the sample pots from an induction coupling material (e.g., graphite or silicon carbide) and heating via induction heating.

[0021] Figure 1 shows a simple schematic illustration of a sampling apparatus according to the present specification. In this configuration, the plurality of sample pots is in the form of a ring of sample pots which is rotated such that the sample pots sequentially and repeatedly pass under the stream of molten metal in a cyclical fashion during the pouring process. Molten metal 2 is poured via a tun dish 4 to provide a stable stream of molten metal 6 to the plurality of sample pots 8. The ring of sample pots 8 is made of an induction coupling material such as SiC or graphite to enable induction heating at high temperature (e.g., up to around 1600°C). The ring of sample pots 8 rotates during sampling as illustrated by the arrow R in Figure 1 . The molten metal stream 6 flows into the sample pots sequentially and cyclically as the ring of sample pots 8 is rotated under the molten metal stream 6 and the ring of sample pots is heated such that the metal remains molten during the sampling process. As such, each sample pot includes multiple different segments or portions of the stream of molten metal 6 to ensure that a representative sample is collected accounting for any inhomogeneities.

[0022] An induction heater can be utilized to provide the induction heating, the induction heater being located below and / or around the plurality of sample pots. For example, the sample pots can be located on a turntable which is driven to rotate the ring of sample pots underthe stream of molten metal and an induction heater can be located on the turntable under sample pots and / or located in a ring around an inner and / or outer circumference of the ring of sample pots.

[0023] Figure 2 shows a simple schematic illustration of a sampling apparatus in which a ring of sample pots 8 is placed on an induction heater 10 on a turntable 12 which has a driver 14 to rotate the turntable. The induction heater 10 heats and maintains the temperature of the sample pots 8. The turntable 12 is spun throughout the sampling operation. Figure 3 shows a simple schematic illustration of another sampling apparatus in which a ring of sample pots 8 is placed on a turntable 12 which has a driver 14 to rotate the turntable. An induction heater 10 heats and maintains the temperature of the sample pots 8. The turntable 12 is spun throughout the sampling operation. In this configuration, an induction coil 10 is located around the ring of sample pots to provide the induction heating. Heat is applied by the induction coil around the outside of the sample pots.

[0024] Advantageously, the stream of molten metal is poured into the plurality of sample pots at a uniform flow rate and the sample pots are moved under the molten metal stream at a uniform rate during pouring. This ensures that a uniform volume of molten metal is poured into each sample pot. The apparatus and methodology is particularly useful for sampling molten metals comprising one or more platinum group metals. The method may further comprise assaying the metal in one or more of the sample pots to determine platinum group metal content, and recycling the metal on the basis of the platinum group metal content determined by the assaying.

[0025] In summary, embodiments of the present specification provide a molten metal spinning riffle sampler. Such a sampler may comprise a powered turntable supporting a ring of sample pots, with a method for induction heating of the pots (either a coil surrounding the ring of sample pots, or a loop under the ring). Molten metal is poured via a tun dish, to maintain a stable stream of molten metal, into the sample pots as the turntable rotates. The rotating causes the molten metal stream to be split between all the pots evenly, hence accounting for material inhomogeneity. This method allows for representative primary samples of metal to be taken with relatively low manual effort. While spinning riffles already exist for powder sampling and have been demonstrated to minimise sampling errors very effectively, the challenge with molten metal sampling, is keepingthe metal molten duringthe samplingactivity. By actively heatingthe sample pots, it is possible to prevent metal freezing during pouring and bridging between pots, which would cause uneven distribution of the sample between pots and also introduce operational difficulties associated with removing metal from the pots. If the pots are constructed from an induction coupling material such as graphite or silicon carbide, then the pots can be safely heated to temperatures up to temperatures around 1600°C during the sampling process, which maintains sufficient superheat within the melt to ensure it remains fluid for PGM-containing alloys sampled by induction melting. Since sampling metallic customer feed is a core operation for a PGM refining business, having a more efficient and representative sampling method will aid in de-risking customer assays and improving the efficiency of the refining process.

[0026] While this invention has been particularly shown and described with reference to certain examples, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

Claims1 . A method of sampling a molten metal, the method comprising: pouring a stream of the molten metal; moving a plurality of sample pots under the molten metal stream during pouring, whereby a portion of the molten metal stream is poured sequentially into each of the plurality of sample pots and repeating such that each sample pot holds multiple portions of the molten metal stream; and heating the plurality of sample pots during the pouring process such that the molten metal within the plurality of sample pots remains molten during the pouring process.

2. A method according to claim 1 , wherein the plurality of sample pots is maintained at a temperature of at least 800°C, 1000°C, 1200°C, 1400°C,1500°C, or 1600°C during the pouring process.

3. A method according to claim 1 or 2, wherein the pots are constructed from an induction coupling material and the heating is via induction heating.

4. A method according to claim 3, wherein the induction coupling material is selected from graphite or silicon carbide.

5. A method accordingto claim 3 or4, wherein an induction heater provides the induction heating, the induction heater being located below and / or around the plurality of sample pots.

6. A method accordingto any preceding claim, wherein the plurality of sample pots is in the form of a ring of sample pots which is rotated such that the sample pots sequentially and repeatedly pass under the stream of molten metal in a cyclical fashion during the pouring process.

7. A method accordingto claim 6, wherein the sample pots are located on a turntable which is driven to rotate the ring of sample pots underthe stream of molten metal and an induction heater is located on the turntableunder sample pots and / or located in a ring around an inner and / or outer circumference of the ring of sample pots.

8. A method accordingto any preceding claim, wherein the molten metal is poured via a tun dish to provide a stable stream of molten metal to the plurality of sample pots.

9. A method accordingto any preceding claim, wherein the stream of molten metal is poured into the plurality of sample pots at a uniform flow rate; and the sample pots are moved under the molten metal stream at a uniform rate during pouring, whereby a uniform volume of molten metal is poured into each sample pot.

10. A method accordingto any preceding claim, wherein the molten metal comprises one or more platinum group metals.

11. A method accordingto claim 10, wherein the method further comprises assayingthe metal in one or more of the sample pots to determine platinum group metal content; and recycling the metal on the basis of the platinum group metal content determined by the assaying.

12. A molten metal sampling apparatus configured to perform the method according to any preceding claim, the molten metal sampling apparatus comprising: a molten metal pouring section for pouring a stream of the molten metal; a plurality of sample pots configured to move under the molten metal stream during pouring, whereby a portion of the molten metal stream is poured sequentially into each of the plurality of sample pots and repeating such that each sample pot holds multiple portions of the molten metal stream; and a heater configured to heat the plurality of sample pots during the pouring process such that the molten metal within the plurality of sample pots remains molten during the pouring process.

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