Scottish Branch Weekend Conference

Peebles plays host to Branch once more

Delegates to the Scottish Branch weekend conference were treated to an excellent weekend of good company, good food and fine surroundings at Peebles Hotel Hydro in May. Attendees were welcomed to the conference by Branch President, Ian Young OBE, FICME MA BCom and by Branch Vice President, Tom Paterson, FICME FIMMM CSci who chaired the technical sessions.

The formal conference kicked off on Saturday morning with a talk by Grant Cullen, Capital Refractories Ltd on ‘Gas Purging in the Induction Furnace – a Technology for the 21st Century.’ A technology that is well known in both the steel making and non-ferrous casting industries, through the use of ladle gas diffusers, Grant’s presentation was about the use of gas purging in the induction furnace, primarily, but not exclusively, for steel casting production. A porous plug of alumina is embedded in the lining and connected to an argon gas, supply. The inert gas is then bubbled gently through the liquid metal.

Grant described the manufacture of the plugs and pointed out the fact that the plugs need to last the same time as the lining. Installation and operation of the plugs is straightforward and safe, as both a kit and on-going technical support are provided by the company. Standard welding purity Argon, with up to 8% CO2, may be used as the gas which means that the technology may be applied wherever welding gases are readily available and makes it cost effective. The technology can be applied to almost any size of furnace, through the use of different sized plugs or more than one plug in larger furnaces.

Although primarily introduced for high alloy steel casting production, the advantages of the technology are also offering benefits to high alloy iron (MoCrV) casting producers, the Ni-Hards and Ni-Resists as well as to the producers of special high temperature metals, Monels, Inconel and Incalloy as well as aluminium and other non ferrous metals.

The advantage of the porous plug as opposed to the use of a lance is primarily associated with the fact that the gas bubbles emanating from a porous plug are much finer and more evenly distributed in the melt, giving a much higher efficiency.

The main benefit that arises from the technology is the improvement in the metal quality since the gas bubbles pick up non-metallics as they float to the surface of the melt, leading to fewer slag and other non-metallic inclusions. However these are not the only benefits through the use of the technology. The gas also forms a protective ‘blanket’ across the top of the melt, shielding it from atmospheric gases, effectively acting like a poor man’s vacuum melter, and this leads to reduced nitrogen levels which can be harmful in certain castings. This can lead to a reduction in scrap rates for the foundry.

But apart from cleaner metal, users of the technology and Capital’s own trials have indicated that the use of the gas purge also led to other tangible benefits which he was able to show through various case studies. One company, who were melting special metals were suffering from severe erosion in one part of the furnace wall. The use of gas purging effectively stirred the melt, eliminating the problem through temperature homogenisation. Another company were suffering from very high scrap levels due to N2 pickup, a problem which was exacerbated due to returns being remelted and which necessitated the use of an extra process step as the company were required to remelt and degas their returns in an AOD at another site. Again, gas purging was able to bring the N2 as levels down from around 0.04% to less than 0.022%.

Increases in lining life of up to 80% in some cases, due to more efficient slag removal is also a benefit that was not anticipated by the company but is being reported by users of the technology.

The majority of the installations to date, and there have been around 1000, have been retrofits to existing vessels but the company is now in talks with furnace manufacturers about fitting the technology into new furnaces. New developments on the horizon include the use of dual layer (duplex) plugs whereby the steel outer casing, or can, is replaced with an outer layer of impermeable ceramic. This fully ceramic plug would be able to withstand the higher temperatures experienced where the diffuser is close to the active zone of the induction coil.

This presentation was followed by more than 20 questions and an hour of discussion about the technology and its application to the industry to the delight of the organisers and Grant Cullen of course.

Jack Gunning gave the vote of thanks on behalf of the branch.

On Sunday morning the technical presentation was from Don Tittensor, Technical Manager of A&S Metallurgical Resources Ltd, who spoke about ‘Monitoring Metal Condition using ATAS’. The session was chaired by John Paterson, MICME.

ATAS stands for Adaptive Thermal Analysis System and its development originally started as a project between NovaCast and the Swedish Foundry Association. The aim was to develop an efficient control method for cast iron based on thermal analysis. Cast iron alloys are very complex and several of the mechanisms behind crystallisation and growth of austenite and graphite are still only partially understood. At the time the project began, most commercial thermal analysis systems were based on monitoring the cooling and solidification of samples in tellurium-coated test cups, the tellurium being present to chill the iron making it solidify "white". By doing this, liquidus and especially the "white" eutectic temperature were easy to trace. Regression analysis proved that the carbon equivalent, carbon and silicon could be estimated using these two temperatures. The method works fine but it does not indicate how the carbon precipitates into graphite, which is one of the most important features of cast irons.

The ATAS system uses test cups without any tellurium, allowing the metal sample to solidify "grey", i.e. according to the stable phase diagram. It is used for grey and ductile irons and also more recently has been applied to compacted graphite cast irons, CGI. Artificial intelligence methods are then used to interpret the cooling curves individually for each alloy being sampled; for example differentiation and integration of the cooling curves is performed to obtain the important change of rate points which are the points at which different phases start or finish forming. The aim of the technology is therefore to enable the foundryman to have library of comparative curves that he can use to identify changes and modifications that need to be made to each melt to optimise its solidification characteristics and hence it microstructure. It is therefore adaptive since interpretation of the cooling curves must be adapted to the particular conditions for each foundry.

Don explained that traditional methods of control, such as normal thermal analysis using a spectrometer, do not provide the levels of accuracy required, for example there is a trade off between carbon content and silicon content and the presence of other elements which can lead to variations in the predicted liquidus temperature. Chemical analysis does not provide the detailed understanding required since while alloying elements may alter the physical properties of cast iron, the final properties and especially the behaviour of the alloy when poured in a mould cannot be fully predicted and controlled by chemical analysis alone. The practical foundryman experiences this daily in the form of unexpected casting defects, low yields and variations in mechanical properties.

The amount and precipitation patterns of austenite and graphite influence the behaviour of grey, ductile and compacted graphite iron during mould filling and solidification and the detailed cooling curves obtained using the ATAS system enable fine details of the solidification characteristics to be seen and interpreted.

This knowledge can then be used to:
Reduce casting defects
Increase yield (reduce trial and error and over-feeding/risering)
Reduce costs (scrap, rework, reduced levels of treatments such as inoculants and nodularisers).
Indeed Novacast are able to claim 50 uses for the technology (source: Novacast website).

A&S Metallurgical Ltd have been using the system since 2002, at which time they had one unit. The company now uses three representatives who travel with ATAS units to foundries solving metallurgical problems. The system is not cheap and would not therefore suit every ferrous foundry; at present there are 3 units currently in use in the UK but interest in the rest of the world is much greater as foundries invest in the latest technology to compete internationally. For example Don was able to report that there are nearly 20 foundries in Turkey using the technology. It also does require some training of operators to optimise the use of the systems although increasing more information is embedded in the software to aid melting shop personnel and on-going support is provided by A&S Metallurgical Ltd.

(For further information about the use of advanced thermal analysis please refer to two recent articles in the FTJ:
• Advances in the melting of high quality grey iron automotive castings at Precision Disc Castings, M Macnaughtan, D Eggleston and N Richardson, Foundry Trade Journal, Vol 180, No 3637, Sept 2006, pp231.
• Production of ductile iron casting without feeders, R Sillen, Foundry Trade Journal, Vol 180, No 3644, May 2007, pp147.)
Once more there was a lively discussion following the presentation and the vote of thanks was given by Steve Waring.
Following Don’s presentation, Dr Tom Paterson gave an entertaining presentation about his year as National President of ICME, which thankfully has not put off the President-in-Waiting, Willie Howson, currently ICME Senior Vice President.

Around 50 delegates to the weekend were all able to enjoy the branch hospitality during a drinks reception and formal dinner on the Saturday evening, with dancing in the hotel ballroom.

The branch was also delighted to have Peter Nix, ICME National President and his wife Ruth in attendance. Peter was keen to encourage all those present and beyond to support the institute and in particular to try to all bring in one new member during the next 12 months.

The branch officers would like to thank the sponsors, Archibald Young Ltd, A&S Metallurgical Resources Ltd and Capital Refractories Ltd for supporting the event.

The photo shows from left, Ian Young, Peter Nix and Willie Howson