Melting and Holding October 08

252 FTJ October 2008

Primary materials have become limited on the global market, causing an increase in prices that have reached a new level in 2008. But there are ready-to-use alternatives for foundries that can help economise in a difficult procurement situation.

Because of the hike in raw material prices for coke as well as for steel scrap that has been on-going since 2002, availability of these materials in the German market suffered badly, and foundry

coke was even apportioned for some time. After the situation had eased somewhat in 2007, a new hike of prices ensued at the beginning of 2008, mainly due to the growing dependence on China and other rapidly developing countries for raw material deliveries, such as foundry coke.

From that background, it is essential for foundries in Germany and across the EU to explore new ways to cope with the tight price situation on the world market and shortages of raw materials, plus changes in their quality in order to assure cost-effectiveness when melting in the cupola.

Meeting material requirementsImplementation of a consequent points-of-accrual-management (recyclers/foundries) is one way to ensure the increasing requirements for charge material are met and to provide such materials with consistent quality to foundries.

The aim of this publicly funded research project was to provide new ways of substitution for small and medium-sized foundries. Substitutes that were investigated included briquettes made from GJL, GJS and mixed GS / GJS borings and from grinding swarf, as well as alternative sorts of steel scrap such as micro-alloyed, shredded

Alternative charge materials for the cupolaIt doesn’t always have to be primary raw materials for cupola melting, say Gotthard Wolf, Herbert Löblich and Timo Wysocki from the Institut für Gießereitechnik IfG gGmbH, Düsseldorf.

Fig 1. C-bricks with mixed borings may be magnetised and then charged using

a magnet crane

Fig 2. HCS testing of self-reducing c-bricks (left) and apparatus (right). Specimen (hatched) is placed between two refractory pistons within a protective tube, heated up to the desired temperature and then loaded until breakage (left). (Photo courtesy of DIFK, Bonn)

FTJ October 2008 253

Melting and Holdingor electroplated steel scrap that are drawn into the focus of foundries.

In addition, fuel substitutes available on the market such as blast furnace coke, Chinese foundry coke or lime-malm bonded c-bricks were investigated and synthetic charge materials such as self-reducing c-bricks or c-bricks with admixed borings that make these briquettes magnetisable were developed especially for this project.

Pre-testing of the alternative charge materials was emphasised during the entire project. Testing methods included cold compressive strength (CCS) and hot compressive strength (HCS) at temperatures of 800°C, reduction under load (RuL) and drop shatter testing, fuel analysis, abrasion strength, analysis of the chemical composition of metallic charge materials and trace elements analysis.

Conditioning and briquetting technology for borings briquettes and c-bricks was investigated and optimised, including experiments using an industrial briquetting press with 150 tonnes maximum load.

Cupola melting trialsMelting trials were carried out in two NRW foundries equipped with cold-blast cupolas with respective melt rates of five and eight tonnes per hour. During these trials, emphasis was placed on the complete coverage of all input and output parameters. These included: iron temperature, blast pressure, iron, slag and gas composition, dust, inoculation and mechanical properties of the iron. The results showed most of the alternative charge materials can be used safely up to a certain amount. Borings from the machining of castings can be considered as an ideal substitute for the metallic charge if their chemical composition is consistent and they are briquetted.

Within the series of trials, briquettes made from borings with CCS of more than 20MPa were used to replace up to 60%

of iron without affecting blast pressure. From that, it was concluded that the briquettes remained sturdy until their meltdown. It was also possible to replace all the steel scrap and pig iron from the metallic charge with borings briquettes.

Furthermore, c-bricks with admixed GJS borings were developed as a substitute for both coke and the metallic charge, and self-reducing c-bricks made of coke breeze and iron oxide were developed as a substitute for steel scrap and pig iron. Aluminium phosphate was used as a binder for that, as the special advantages of this material compared to cement and other binders became apparent in preliminary experiments.

It was found safe to use these c-bricks in amounts up to about 10% of the metallic charge, providing compression strength exceeded 1.8MPa. For the self-reducing c-brick, a degree of reduction of 99% of the included Fe

2O

3 could be proven through

slag analysis. These bricks can be used for replacing steel scrap without problems.

C-bricks with admixed borings are also suitable and can be charged with the usual magnet crane (fig. 1), offering an advantage for small foundries in that no further investment cost for a second coke bunker is required when substituting foundry coke

with alternative fuels. They can be produced with moderate investment and manpower or purchased (which is likely to be the more economic solution for medium and small-sized foundries) from a commodity trader.

None of the alternative charge materials caused significant metallurgical disadvantages concerning trace elements, nucleation and chill depth when tested - even in high amounts during the trials. No increase in scrap was found in either foundry during the period of the trials.

Monitoring dust and odourDuring the trials, dust and odour emissions were observed at the de-dusting plants. Samples for analysis were taken directly from the undiluted raw gas from the stack and analysed with methods according to olfactometric standard EN 13725(1). Dust measurements in front of and behind the filter did not show significant changes in dust emission and composition during any of the trials, except for the trials with borings and grinding swarf briquettes.

For these materials, a relation between oil and cutting fluid residue and the odour emission was developed and it was shown that odour emission increased with an increase in total oil and cutting fluid residue charged (fig. 5). Nevertheless, it should be considered that the effective odour effluents in the neighbourhoods of the foundries are subjected to a variety of influences, such as weather, direction of the wind, moisture, height of the stack, distance between the foundry and its neighbours, topography of the surroundings etc.

Producers of briquettes made from borings are therefore required to ensure low enough oil and cutting residue, one possible solution being the combination of borings from dry and from wet machining to a mixture with low residue.

Cost-effectiveness of the alternative charge materials tested within this project depends on the market situation and on the availability of the alternative materials to the foundries. The

0

20

40

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4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 5.0

Apparent Density [g/cm!]

CC

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B502 (90 bar)

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Fig 3. Comparison between CCS at various compaction pressures and HCS of borings briquettes


Moulding and Coremakingare likely to increase further in the future, foundries will be able to flexibly adapt their charge composition with the results of this project.

Reference1. Helber J, ‘Odour emission

reduction in foundries - a report on the state of the art’, 66th World Foundry Congress, Casting technology - 5000 years and beyond, Vol 1, Istanbul, Turkey, Sep 6-9, 2004.

AcknowledgementsThis research project was funded by the NRW Ministry of Innovation, Research and Technology (funding no. 005-0410-0005, in responsibility of Forschungszentrum Jülich, file number PTJ-Az. 0410MW14). The authors also wish to express their gratitude to the foundries involved in this project for making the investigations possible during regular operation.

About the authorsThe authors are Dr-Ing Herbert Löblich (cupola melting, cast iron production); B E Timo Wysocki (briquetting technology, binder systems); and Dr-Ing Gotthard Wolf, IfG Institute of Foundry Technology, Düsseldorf (Germany).

Gießereiingenieur (BE) Metallurgie und Werkstofftechnik, Institut für Gießereitechnik IfG GmbH, Düsseldorf, Germany;Tel: +49 (0) 211 6871 327;fax: +49 (0) 211 6871 255;email: [email protected]

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0

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situation is likely to improve with rising demand for these materials, which should result in increased investment of re-cyclers and foundries into advanced briquetting technologies and to emphasising the closing of idle material cycles

in foundries. The latter is further accelerated through government subsidies for material effectiveness.

As prices for charge materials

Melting and Holding

Fig 4. Briquettes made from borings can be an ideal substitute for the metallic charge

Fig 5. Odour emissions increased with oil residue

NRW Ministry of Innovation, Science, Research and TechnologyThe Ministry of Innovation, Science, Research and Technology of the state of North Rhine-Westphalia (NRW) in its present form was established in June 2005. This is the first time that a German Ministry has focussed on a state’s potential for innovation as a top priority.

The Ministry is responsible for all NRW-based universities and polytechnics, university clinics, colleges of art or music, for non-university research institutions and for the promotion of technologies in the state.

The remit of the Ministry of Innovation, Science, Research and Technology reflects the entire innovation process ranging from higher education training to university and non-university research on developments and inventions and to industry’s activities aimed at making applications ready for the market and successfully marketing fundamental innovations.

The Ministry’s objectives include: achieving excellence in research and higher education teaching in NRW, boosting exchanges between the research and business communities, and considerably improving NRW’s technological capacity.

NRW boasts Europe’s most closely set research and higher education infrastructure. The NRW government is firmly resolved to bring the state to the forefront of scientific, technological and economic

progress and to turn NRW into Germany’s number one innovation state by the year 2015. www.innovation.nrw.de


Melting and Holding

Faced with increasing energy prices, in 2007 Alumasc Precision - the Burton Latimer, England, based aluminium diecaster, made a comprehensive review of its energy use and costs associated with melting and holding aluminium for its high-pressure diecasting facilities. A detailed appraisal showed that there would be significant cost savings and reduction of carbon emissions by installing a new high-efficiency bulk melting and holding furnace to replace some of the existing older gas-fired crucible furnaces. The new bulk melting furnace was supplied and installed by the German company ZPF therm GmbH of Siegelsbach.

Space was very limited in the chosen location in Alumasc’s high-pressure foundry, but ZPF’s very compact, highly efficient design meets Alumasc’s energy reduction targets, and complies with the latest mandatory emissions limits without the need for filtering systems.

Norbert Feth, marketing manager of ZPF therm GmbH explains: ‘The reason for such low emission lies in the unique design of ZPF therms furnaces. The core of the system is the combustion chamber, which is made of refractory concrete and weighs several tonnes. The thick encasement functions as a protective barrier between the thermal insulation layers and external steel casing on one hand, and the aggressive liquid aluminium on the other.

‘The heavy refractory lining also serves as a heat accumulator that helps to maintain a steady state interior temperature of the furnace. A sophisticated system of insulation keeps the thermal energy in the interior of the furnace and contributes significantly to energy saving.’

Reduction of emissionsAn unconventional exhaust gas flow from the melting chamber plays a very significant role in the reduction of the furnace’s emissions to air. Rather than being expelled directly to atmosphere from the melting shaft through a chimney as is typical in other furnaces, flue gases are first held in the interior of the self-contained system. In the process, residues from the charged material - particularly those from returns - are subsequently virtually combusted. This means that complex filtration systems are unnecessary.

The measured emissions values fall far below the statutory limits. ZPF claims that the proportion of particulate matter in waste gases is less than three milligrams per cubic metre, for nitrogen oxide, the value is about eleven

milligrams and only 0.4 milligrams for hydrogen fluoride.Herr Feth speculates: ‘Even if the limits become yet stricter in five

years time, we will still be able to meet without external filtering.’The longer dwell time of the hot gases in the furnace chamber

also contributes greatly to the high energy-efficiency of the furnace. ZPF therm say there is an average of 20 to 30% more performance capacity through this method of optimal heat utilisation rather than with open exhaust gas systems.

The furnace installed at Alumasc is rated to melt one tonne per hour of aluminium alloy and has a holding bath capacity of two and a quarter tonnes. The unique gas firing system employs two modulating nozzle-mixing gas burners with automatic air/gas ratio control. Both burners are used when the furnace is in the melting mode to give rapid melting which reduces metal loss. Only one of the burners is used when maintaining to give better turn-down and consequently more accurate temperature control.

Integrated chargingAn integrated charging machine automatically loads aluminium ingots and foundry returns that are pre-loaded in wheeled charge cars. The furnace is mounted on load cells giving the operators accurate information of the weight of metal in the furnace. The weighing system also controls the charging machine to automatically prevent over-filling the furnace.

Weight monitoring allows the PLC system to accurately calculate the melting time for each charge according to the weight and regulate the time on ‘high-fire’, which saves energy and prevents over heating and associated oxidation losses.

After a year’s continuous operation, the furnace has met Alumasc’s expectations regarding energy cost saving and reduced emissions. An inspection during the recent annual shut-down showed only minimal lining wear; the furnace needed only general cleaning of dross and metal residues.

Ramsell-Naber is the sales and service representative of ZPF for the UK and Ireland. ZPF specialises in gas- and oil-fired furnaces mainly for the aluminium casting industry. The company has a unique range of furnaces for bulk melting and holding, with melting rates up to five tonnes per hour and holding capacities up to 20 tonnes.

Ramsell-Naber Ltd; Tel: +44 (0) 1922 455521; fax: +44 (0) 1922 455277; web: www.ramsell-naber.co.uk

Focus on energy reductionLimited space did little to deter one aluminium diecaster from installing new melting facilities to improve energy efficiences and reduce emissions.

ZPF therm aluminium melting furnace


The Striko Westofen Group has been one of the leading companies producing and supplying a high efficiency range of melting plant on a worldwide basis.

The following article was prepared by Herr Klaus Malpohl of Striko Westofen Gmbh in 2006 to highlight several important points when buying new melting plant. But with ever-increasing raw material costs metal loss becomes a more important factor when installing new equipment. For this reason it is important to reconsider the figures.

When ordering new equipment, most customers first think of energy costs as the main consideration and then required manpower.

Striko Westofen knows that metal loss can often give greater savings than just those associated with energy. With aluminum costs staying high this, combined with the energy usage, can give very significant savings.

High efficiency aluminium melting with the STRIKOMELTER® technology With the STRIKOMELTER® with patented ETAMAX® technology, the caster has an outstanding tool at his disposal, which fulfils all requirements for the melting operation. The determination of operational data in a foundry has confirmed the efficiency and profitability again.

Against a background of constantly rising prices for raw materials and energy, the question of the metal supply plays an ever larger role for aluminium foundries in order to come up with the high market requirements.

However, individual aspects such as gas consumption or maximum efficient and qualitative metal yield should not be ignored in this overall view. The metal supply is a multi dimensional system, with the most important task consisting of supplying a casting operation with metal of suitable quality to optimise the yield of good castings; and of course, this must be achieved as economically as possible. In this connection there are numerous other requirements to be taken into consideration.

Some of these are: high melting rate with low energy consumption, minimum metal losses and/or high metal yield and a safe and largely automated operation. It is also necessary to consider both the current and future environmental and safety requirements. This view should also consider low breakdown and maintenance expenses and the potential lining life and replacement cost.

The STRIKOMELTER® fulfils all parameters by the multi graduated use of thermal energy of the burners as well as the innovative melting concept. This is realised through the physical separation into three zones: preheating, melting and holding together with ETAMAX® patented shaft and melting design, especially developed for the STRIKOMELTER®. The choked shaft design allows the consistent preheating of the charge material prior to melting. The hot exhaust gases from the holding bath pass through the melting zone and from there into the preheating zone and thus used several times.

The additional energy required for melting comes from burners located in the melting zone and focussed into the area at the base of the preheating area; exhaust gasses from these burners also exit through the charged material in the shaft and therefore ensure drying and a greater degree of preheating, and therefore greater speed and efficiency of melting efficiency. In that way, the charged material reaches the melting bath in small quantities. Compared to other furnace designs, this makes possible substantial savings in fuel consumption and consequent lower melting cost. In the practical foundry operation, a power requirement by only < 600 kWh/t was determined. This corresponds to a thermal efficiency of over 50%.

In order to ensure good casting quality, it is necessary to start with good metal quality. Since aluminium is usually supplied to good metallurgical quality standards, it is important to ensure that no contamination is introduced during the melting operation. This includes the absorption of hydrogen from the atmosphere and inclusion such as oxides and dross.

The primary source of contamination is

High efficiency Aluminium melting with the STRIKOMELTER® technology

With the STRIKOMELTER® with patented ETAMAX® technology, the caster has an outstanding tool at his disposal, which ful-fils all requirements for the melting opera-tion. The determination of operational data in a foundry has confirmed the efficiency and profitability again.

Against a background of constantly rising prices for raw materials and energy, the question of the metal supply plays an ever larger role for Aluminium foundries in order to come up to the high market requirements. However, individual aspects as gas con-sumption or maximum efficient and qualita-tive metal yield should not be ignored in this overall view. The metal supply is a multi-

dimensional system, whose most important task consists of supplying a casting operation with metal of suitable quality to optimize the yield of good castings; and of course, this must be achieved as economi-cally as possible. In this connection there are numerous other requirements to be taken into consideration. Some of these are high melting rate with low energy consumption, minimum metal losses and/or high metal yield and a safe and largely automated operation. It is also necessary to consider both the current and future environmental and safety requirements. This view should also consider low breakdown and mainte-nance expenses and the potential lining life and replacement cost.

STRIKOMELTER® MH II-T in tilting version

The STRIKOMELTER® fulfils all parameters by the multi graduated use of thermal energy of the burners as well as the innovative melting concept. This is realized through the physical separation into three zones: pre-heating, melting and holding together with ETAMAX®patented shaft and melting design, especially devel-oped for the STRIKOMELTER®. The choked shaft design allows the consistent preheating of the charge material prior to melting. The hot exhaust gases from the hold-ing bath pass through the melting zone and from there into the preheating zone and thus used several times.

The additional energy required for melting comes from burners located in the melting zone and focussed into the area at the base of the preheating area; exhaust

gasses from these burners also exit through the charged material in the shaft and therefore ensure drying and a greater degree of preheating, and therefore greater speed and efficiency of melting efficiency. In that way, the charged material reaches the melting bath in small quantities. Compared to other furnace designs, this makes possible substantial savings in fuel consumption and con-sequent lower melting cost. In the practical foundry operation, a power requirement by only < 600 kWh/t was determined. This corresponds to a thermal efficiency of over 50 %.

STRIKOMELTER® with conveyor charging system

Process visualization

In order to ensure good casting quality, it is necessary to start with good metal quality. Since aluminium is usually supplied to good metallurgical quality standards, it is important to ensure that no























Cost reduction in the foundryMelting and Holding


STRIKOMELTER® MH II-T in tilting version Process visualisation


moisture from storage of the returns or ingots, the result of this being an increase in the hydrogen content of the metal with its consequent quality problems in the cast parts. This is avoided in the STRIKOMELTER® by the separation of melting and preheating zones. Moisture and other contaminants are evaporated or burnt off in the shaft by preheating with exhaust gases, ensuring that only perfectly dry material reaches the melting chamber. A further advantage is the avoidance of excessive contact of the melt with atmospheric oxygen thereby reducing the tendency to form oxides. In order to minimise this danger the burners in the melt chamber are arranged to avoid direct metal impingement. This allows melting only on the hearth and for the metal to flow quickly but without turbulence into the holding bath. A third measure for the maintenance of metal quality is the avoidance of the contamination by impurities entering the metal holding bath. This is assured by allowing the metal to run laterally into the holding bath. In this way, dross and other impurities remain on the melt hearth to be removed during cleaning.

An additional advantage of the separation of the two chamber concept is a continuous availability of molten metal at a very consistent temperature (to +/- 5°C). This type of melting system guarantees continuous melting whilst tapping liquid metal. The automated charging contributes to achieving a molten metal availability of 98% during practical operation.

Measured data in foundry practice

The data stated by the manufacturer were confirmed in the industrial high pressure die-casting foundry of W Hesse & Bauckhage GmbH in Germany in the autumn of 2005. Since 2001 there have been two STRIKOMELTER® systems in use in this foundry; these are MH II-N 2000/1000 G-eg units and the investigation was based on the following operating conditions:

Alloy: 231 D, AlSi12Cu1 (Fe) EN-AC 47100 - StrikoWestofen GmbH – 239, EN-AC-43000 - customer -

Employment: 50% ingots 5-7 kg 50% dry returns, size - 0.3-2 kg with some flitter

Other: Flux was used on the melting ramp and in the holding bath

The investigation examined both the gross and the net metal yields. Using only ingot, a gross yield (ratio of initial metal weight to the metal weight at the tap) was determined at 99.75%.

Using a charge of 50% ingots and 50% returns the value was approx. 99.40%. The net yield refers to the metal after additional drossing operations in the ladle; for this, the weight of the 300-kg-ladle before and after drossing was measured on a precision weight scale. Table 1 contains the results of the net metal yields achieved in the foundry as well as previous reference values. They show that the metal losses were in all cases below 1%.

The manufacturer data for metal loss specified in brochures were therefore not only confirmed, but clearly exceeded.

Financial and technical advantages

Based on the determined values, the enormous advantages of the this particular system can be calculated as follows: • Metal price 2,400 €/t • Total melting times 6,600 h/a • Melting capacity 1 t/h • Increased metal yield by 1% • Savings / pa 158,000 €

The increased metal yield by only 1% permits a yearly saving of €158,000! In comparison to many older furnace units with metal losses of up to 8%, enormous saving potentials occur in connection to the clearly higher efficiency of the sysytem. The investment in the modern STRIKOMELTER® technology enables extremely short pay back periods of 6 to 12 months.

A further financial factor is the savings in energy due to the high efficiency of the ETAMAX® technology as well as a substantially low scrap rate due to the better molten metal quality.

StrikoWestofen GmbH, Wiehl, Germany, July 2006

contamination is introduced during the melting operation. These include the absorption of hydrogen from the atmosphere and inclusion such as oxides and dross.

The primary source of contamination is moisture from storage of the returns or ingots, the result of this being an increase in the hydrogen content of the metal with its consequent quality problems in the cast parts. This is avoided in the STRIKOMELTER® by the separation of melting and preheating zones. Moisture and other contaminants are evaporated or burnt off in the shaft by preheating with exhaust gases, ensur-ing that only perfectly dry material reaches the melting chamber. A further advantage is the avoidance of excessive contact of the melt with atmospheric oxygen thereby reducing the tendency to form oxides. In order to minimize this danger the burners in the melt chamber are arranged to avoid direct metal im-pingement. This allows melting only on the hearth and for the metal to flow quickly but without turbulence into the holding bath. A third measure for the maintenance of metal quality is the avoidance of the con-tamination by impurities entering the metal holding bath. This is assured by allowing the metal to run later-ally into the holding bath. In this way, dross and other impurities remain on the melt hearth to be removed during cleaning.

An additional advantage of the separation of the 2 chamber concept is a continuous availability of molten metal at a very consistent temperature (to +/- 5°C). This type of STRIKOMELTER® guarantees continuous melting whilst tapping liquid metal. The automated charging contributes to achieving a molten metal avail-ability of 98% during practical operation.

Measured data in foundry practice The data stated by the manufacturer were confirmed in the industrial high pressure die-casting foundry of W. Hesse & Bauckhage GmbH in Germany in the autumn of 2005. Since 2001 there have been two STRIKOMELTER® in use in this foundry; these are MH II-N 2000/1000 G-eg units and the investigation was based on the following operating conditions:

STRIKOMELTER® at Hesse & Bauckhage

Alloy: 231 D, AlSi12Cu1 (Fe) EN-AC 47100 - StrikoWestofen GmbH – 239, EN-AC-43000- customer -



salt salt

exhaust gas

initialmetalweight[ kg ]

returnmaterial,

+bulkymaterial

to DCM;output metal weight (net)

dross in the shaft

dross on the bath

outputmetalweight(gross)

dross in the ladlewith / without melttreatment

dross take-off from furnace

melttreatmentin the ladle:- adding of salts- impeller, …

salt

metalportion

salts +metal oxides

The investigation examined both the gross and the net metal yields. Using only ingot, a gross yield (ratio of initial metal weight to the metal weight at the tap) was determined at 99, 75%. Using a charge of 50% ingots and 50% returns the value was approx. 99, 40%. The net yield refers to the metal after additional drossing op-erations in the ladle; for this, the weight of the 300-kg-ladle before and after drossing was measured on a precision weight scale. Table 1 contains the results of the net metal yields achieved in the foundry as well as previous re-ference values. They show that the metal losses were in all cases below 1%.

Draft testing procedure

contamination is introduced during the melting operation. These include the absorption of hydrogen from the atmosphere and inclusion such as oxides and dross.

The primary source of contamination is moisture from storage of the returns or ingots, the result of this being an increase in the hydrogen content of the metal with its consequent quality problems in the cast parts. This is avoided in the STRIKOMELTER® by the separation of melting and preheating zones. Moisture and other contaminants are evaporated or burnt off in the shaft by preheating with exhaust gases, ensur-ing that only perfectly dry material reaches the melting chamber. A further advantage is the avoidance of excessive contact of the melt with atmospheric oxygen thereby reducing the tendency to form oxides. In order to minimize this danger the burners in the melt chamber are arranged to avoid direct metal im-pingement. This allows melting only on the hearth and for the metal to flow quickly but without turbulence into the holding bath. A third measure for the maintenance of metal quality is the avoidance of the con-tamination by impurities entering the metal holding bath. This is assured by allowing the metal to run later-ally into the holding bath. In this way, dross and other impurities remain on the melt hearth to be removed during cleaning.

An additional advantage of the separation of the 2 chamber concept is a continuous availability of molten metal at a very consistent temperature (to +/- 5°C). This type of STRIKOMELTER® guarantees continuous melting whilst tapping liquid metal. The automated charging contributes to achieving a molten metal avail-ability of 98% during practical operation.

Measured data in foundry practice The data stated by the manufacturer were confirmed in the industrial high pressure die-casting foundry of W. Hesse & Bauckhage GmbH in Germany in the autumn of 2005. Since 2001 there have been two STRIKOMELTER® in use in this foundry; these are MH II-N 2000/1000 G-eg units and the investigation was based on the following operating conditions:


Alloy: 231 D, AlSi12Cu1 (Fe) EN-AC 47100 - StrikoWestofen GmbH – 239, EN-AC-43000- customer -



salt salt

exhaust gas

initialmetalweight[ kg ]

returnmaterial,

+bulkymaterial

to DCM;output metal weight (net)

dross in the shaft

dross on the bath

outputmetalweight(gross)

dross in the ladlewith / without melttreatment

dross take-off from furnace

melttreatmentin the ladle:- adding of salts- impeller, …

salt

metalportion

salts +metal oxides

The investigation examined both the gross and the net metal yields. Using only ingot, a gross yield (ratio of initial metal weight to the metal weight at the tap) was determined at 99, 75%. Using a charge of 50% ingots and 50% returns the value was approx. 99, 40%. The net yield refers to the metal after additional drossing op-erations in the ladle; for this, the weight of the 300-kg-ladle before and after drossing was measured on a precision weight scale. Table 1 contains the results of the net metal yields achieved in the foundry as well as previous re-ference values. They show that the metal losses were in all cases below 1%.

Draft testing procedure

Melting and Holding

Draft testing procedures


Measured values at Hesse & Bauckhage

The manufacturer data for metal loss specified in brochures were therefore not only confirmed, but clearly exceeded.

Financial and technical advantages

Based on the determined values, the enormous advantages of the STRIKOMELTER® can be calculated as follows:

Metal price 2.400 €/t Total melting times 6.600 h/a Melting capacity 1 t/h Increased metal yield by 1% Savings / pa 158.000 €

The increased metal yield by only 1 % permits a yearly saving of 158.000 €! In comparison to many older furnace units with metal losses of up to 8 %, enormous saving potentials occur in connection to the clearly higher efficiency of the STRIKOMELTER®. The investment in the modern STRIKOMELTER® technology en-ables extremely short pay back periods of 6 to 12 months.

A further financial factor is the savings in energy due to the high efficiency of the ETAMAX® technology as well as a substantially low scrap rate du to the better molten metal quality.

StrikoWestofen GmbH, Wiehl, Germany, July 2006

StrikoWestofen GmbH Fritz – Kotz –Str. 2-4 D – 51674 Wiehl Tel + 49 / 2261 / 70 91 – 0 Fax + 49 / 2261 / 70 91 – 107 [email protected]

Charged material 100 % ingots 50 % ingots50 % returns

StrikoWestofen values EN AC-47100 / 231 DMetal yield %

99.55 % 99.20 %

HeBa values EN AC-43000 / 239Metal yield %

99.61 % 99.01 %

Measured values at Hesse & Bauckhage


BackgroundFuel prices have been rising at such a rapid rate in recent months that foundries everywhere are finding it increasingly difficult to remain cost effective and competitive, so they are looking to significantly reduce their energy consumption.

Morgan Molten Metal Systems is a global manufacturer and supplier of foundry crucibles, furnaces and associated metal handling and treatment products. With over 150 years in the foundry business, Morgan has developed a leading position and enviable reputation for its truly integrated crucible based metal melting and holding systems. The company says its success stems from the fact it designs and manufactures both the crucibles and the furnaces. Morgan understands that optimising the performance of any metal melting and holding process in the foundry is dependent on balancing a complex set of variables; the furnace, customer working practices, crucible and metallurgical processes all interact. So to achieve the balance required, the system needs application specific design for both the consumables and the equipment.

From this technological background, Morgan MMS was keen to address the concerns that foundries had expressed about their rising fuel bills so they set out to design a molten metal system that used fuel in a much more efficient way,

such that it could significantly reduce foundries’ fuel costs. To achieve this they looked to their own existing technology and how it could be redesigned and enhanced.

Recuperation on furnaces is not a new concept, having been around since the early 1900s. Take up of the technology accelerated during the 1970s oil crisis, which created similar problems to those being experienced today - rising energy costs and supply restrictions. Morgan was quick at the time to respond to the situation and developed a range of crucible furnaces incorporating a recuperation

technique which would utilise fuel more efficiently. To address the latest fuel crisis they took another look at recuperation and set out to improve the efficiency and cost effectiveness of the technology to breathe new life into the recuperator system.

So what is recuperation?A ‘recuperator’ recycles waste heat from the exhaust gases to pre-heat the combustion air to the burner. It achieves this via a counter-flow heat exchanger which, on a crucible furnace, replaces the standard exhaust stack. The recuperator transfers waste heat in the exhaust to the

Save Money with Morgan Recuperative Crucible Furnaces

Dr Andy Wynn, Global Technical Director, [email protected]

Bob Thomas, Chief Furnace Engineer, [email protected]

Tim Heeks, Furnace Design Engineer, [email protected]

Morgan Molten Metals Systems

Woodbury Lane

Norton

Worcester

WR5 2PU

INTRODUCTION

Does this sound familiar?

“My energy costs are rising out of control!”

“Our energy bill this year is double what it was last year!”

We hear these comments every day of the week when visiting non-ferrous foundries

all over the world.

Want to know how to reduce your energy bill and save money? Well don’t worry,

new technology is now available to solve this problem for you. Morgan’s new

recuperative crucible furnace range is the answer you’re looking for.

Morgan Recuperative

Gas Fired Crucible Furnace

Want to know how to reduce your energy bill and save money? New technology is now available to solve this growing problem and Morgan Molten Metal Systems say its new recuperative crucible furnace range is the answer.

Reduce your energy bill with new technology

Melting and Holding

BACKGROUND

Fuel prices have been rising at such a rapid rate in recent months that foundries

everywhere are finding it increasingly difficult to remain cost effective & competitive.

So foundries are looking to significantly reduce their energy consumption in order to

remain competitive.

Morgan Molten Metal Systems is a global manufacturer and supplier of foundry

crucibles, furnaces and associated metal handling and treatment products. With over

150 years in the foundry business, Morgan has developed a leading position and

enviable reputation in the market worldwide, as it can offer truly integrated crucible

based metal melting & holding systems. This is because it designs and manufactures

both the crucibles and the furnaces. Morgan understands that optimising the

performance of any metal melting and holding process in the foundry is dependent on

balancing a complex set of variables. The furnace, customer working practices,

crucible and metallurgical processes all interact. So to achieve the balance required,

the system needs application specific design for both the consumables and the

equipment.

From this technological background, Morgan MMS was keen to address the concerns

that foundries had expressed about their rising fuel bills. We set out to design a

molten metal system that used fuel in a much more efficient way, such that it could

significantly reduce foundries fuel costs. To achieve this we looked to our existing

technology and how we might redesign and enhance it.

Recuperation on furnaces is not a new concept, having been around since the early

1900’s. Take up of the technology accelerated during the 1970s oil crisis, which

created similar problems with rising energy costs and supply restrictions as we are

experiencing today. Morgan was quick at the time to respond to the situation and

developed a range of crucible furnaces incorporating a recuperation technique which

would utilise fuel more efficiently. To address our latest fuel crisis we took another

look at recuperation and set out to improve the efficiency and cost effectiveness of the

technology to breathe new life into the recuperator system.

Metallurgy Working

Practice

Furnace

EXCEL E

SO WHAT IS RECUPERATION?

A “recuperator” recycles waste heat from the exhaust gases to pre-heat the

combustion air to the burner. It achieves this via a counter-flow heat exchanger which

on a crucible furnace replaces the standard exhaust stack. The recuperator transfers

waste heat in the exhaust to the combustion air entering the fuel burner, thus

preheating it. Since the gases have been pre-heated, less fuel is needed to heat those

gases to the required furnace melting/holding temperatures.

The recuperator technique is used for heat recovery in many other industries, such as

chemical plants and refineries, in applications where there is fluid-fluid counter flow

and in closed system processes such as in refrigeration cycles. There are several other

systems of heat recovery available including the regenerative heat exchanger, the

rotating recuperator and energy recovery ventilation, but the standard recuperator is

the system that works best with fuel burner applications, to increase the overall

efficiency, and for this reason is used in gas turbine engines.

By recovering some of the energy usually lost as waste heat, the recuperator makes a

fuel fired crucible furnace significantly more efficient. Morgan’s unique position as a

designer of both furnaces and crucibles allowed us to significantly enhance the

efficiency of the design of the recuperative system as applied to fuel fired crucible

furnaces, through optimal selection of materials and components and true integration

of design. Instead of just bolting a recuperator system onto an existing furnace, we

understood that optimum efficiency would only come by starting from first principles,

and so we set out to create a design which truly integrated the recuperator with the

furnace and the crucible. The result of this development work is the new range of

Morgan Recuperative Furnaces, available as both static bale out and as tilting systems

to provide foundries with the lowest gas bills possible at both the casting and melting

stations.

Air and Gas Components


combustion air entering the fuel burner, thus preheating it. Since the gases have been pre-heated, less fuel is needed to heat those gases to the required furnace melting/holding temperatures.

The recuperator technique is used for heat recovery in many other industries, such as chemical plants and refineries, in applications where there is fluid-fluid counter flow and in closed system processes such as in refrigeration cycles. There are several other systems of heat recovery available including the regenerative heat exchanger, the rotating recuperator and energy recovery ventilation, but the standard recuperator is the system that works best with fuel burner applications, to increase the overall efficiency. For this reason it is used in gas turbine engines.

By recovering some of the energy usually lost as waste heat, the recuperator makes a fuel fired crucible furnace significantly more efficient. Morgan’s unique position as a designer of both furnaces and crucibles allowed them to significantly enhance the efficiency of the design of the recuperative system as applied to fuel fired crucible furnaces, through optimal selection of materials and components and true integration of design. Instead of just bolting a recuperator system on to an existing furnace, they understood that optimum efficiency would only come by starting from first principles, and so they set out to create a design which truly integrated the recuperator with the furnace and the crucible. The result of this development work is the new range of Morgan recuperative furnaces, available as both static bale out and as tilting systems to provide foundries with the lowest gas bills possible at both the casting and melting stations.

Performance benefitsDue to the integrated design, the range of recuperative furnaces gives a number of benefits to the foundry far beyond the key advantage of

lowering their gas bill and they are considered here.

Cost effectiveThe company says the new technology incorporated into the recuperative system makes it the most cost effective product of its kind. Existing recuperative products on the market quote a maximum of 25% energy reduction compared with an equivalent non-recuperative furnace. Morgan’s new recuperative technology provides a minimum of 35% energy reduction, and often higher. At some foundries, as high as 50% reduction in gas usage can be achieved, compared to their existing firebrick lined gas-fired furnaces.

The cost savings achieved by more efficient use of gas from the new recuperator technology are enhanced by incorporating the very latest refractory and insulation technology into the furnace design. Using the latest materials technology developed within the Morgan Crucible Group provides the lowest level of thermal conductivity available commercially, which minimises heat losses from the furnace chamber. Melting efficiencies as high as 40% are achieved, compared to conventional gas-fired crucible furnaces, where 20-25% is typical.

The new recuperative furnace also delivers more cost effective running costs in terms of longer consumable life. Crucible life is enhanced due to the fully modulating burner technology, which has two advantages in terms of crucible life. Firstly it

burns very close to stoichiometric combustion, so that no excess oxygen is present in the furnace chamber, which would otherwise attack the high graphite and carbon content of the crucible causing oxidation. Secondly it introduces a high velocity gas stream into the chamber, which creates an even heat distribution over the whole crucible, ensuring no hot spots exist that would otherwise cause thermal stresses, leading to distortion. This highly efficient thermal design feature is further enhanced by the hot face chamber lining, which incorporates Morgan’s patented gas radiant panel technology which radiates heat directly on to the crucible and thereby to the metal, rather than traditional brick designs, which allow more heat to be lost to the stack as waste.

The new integrated recuperative furnace design also facilitates fast commissioning times, minimising foundry downtime, if replacing a non-recuperative unit. Traditional recuperative designs are constructed using separate floor mounted components, with gas pipes trailing across the foundry floor. This leads to long and complicated installation and commissioning times and presents health and safety risks to the operator and risk of damage to the critical components from fork-lift traffic in the foundry.

Optimum metal qualityThe same technological features that minimise the running costs of the new recuperative furnace also contribute to delivering optimum metal quality. The fully modulating, high turn down ratio burner gives tight control of metal temperature typically down to ±5°C, allowing foundries to achieve the stringent quality controls required for modern automotive castings, reducing rejects and minimising costly metal losses. The gas flow design is such that the exhaust gases exit from the side of the chamber, not over the top of the crucible, ensuring that gases do not contact the molten metal, thus minimising the potential for gas pick up which would otherwise lead to porosity in castings.

Health, safety and the EnvironmentWith operator comfort and safety in mind the highly efficient insulation which helps minimise running costs also ensures that casing temperatures are low and that the ambient temperature of the working

Melting and Holding

PERFORMANCE BENEFITS

Due to the integrated design, the Morgan range of recuperative furnaces hosts a range

of benefits to the foundry far beyond the key advantage of lowering their gas bill;

COST EFFECTIVE

The new technology incorporated into the recuperative system makes it the most cost

effective product of its kind. Existing recuperative products on the market quote a

maximum of 25% energy reduction compared with an equivalent non-recuperative

furnace. Morgan’s new recuperative technology provides a minimum of 35% energy

reduction, and often higher. At some foundries, as high as 50% reduction in gas usage

can be achieved, compared to their existing firebrick lined gas-fired furnaces.

The cost savings achieved by more efficient use of gas from the new recuperator

technology are enhanced by incorporating the very latest refractory and insulation

technology into the furnace design. Using the latest materials technology developed

within the Morgan Crucible Group provides the lowest level of thermal conductivity

available commercially, which minimises heat losses from the furnace chamber.

Melting efficiencies as high as 40% are achieved, compared to conventional gas-fired

crucible furnaces, where 20-25% is typical.

The new recuperative furnace also delivers more cost effective running costs in terms

of longer consumable life. Crucible life is enhanced due to the fully modulating

burner technology, which has two advantages in terms of crucible life. Firstly it burns

very close to stoichiometric combustion, so that no excess oxygen is present in the

furnace chamber, which would otherwise attack the high graphite and carbon content

of the crucible causing oxidation. Secondly it introduces a high velocity gas stream

into the chamber, which creates an even heat distribution over the whole crucible,

ensuring no hot spots exist that would otherwise cause thermal stresses, leading to

distortion. This highly efficient thermal design feature is further enhanced by the hot

face chamber lining, which incorporates Morgan’s patented gas radiant panel

technology which radiates heat directly onto the crucible and thereby to the metal,

rather than traditional brick designs, which allow more heat to be lost to the stack as

waste .

Integrated Design

Gas Radiant Panel


environment is as comfortable as possible. The unique burner design also reduces noise levels during use of the furnace to unparalleled levels, with under 75dBA measured at 2m from the unit, which is below current regulations for the UK requiring PPE action.

The new burner technology in Morgan’s recuperative crucible furnace also has the added benefit of reducing ‘greenhouse’ gaseous emissions. Typical CO

2 emissions for a BT1300

size furnace are reduced to ~12 tonnes per year compared to ~20 tonnes per year for a non-recuperative equivalent furnace run under the same conditions. Raising the temperature of the input air by recuperation also raises the level of NO

x generated, such that conventional recuperative

forced air burners run above 400ppm. Input air is typically pre-heated up to 250°C in a recuperative crucible furnace. Under these conditions Morgan’s recuperative burner technology reduces NO

x

emissions below 125ppm.

Foundries save moneyInitial foundry trials of the new recuperative technology started in the UK, where the technology was developed. Following initial commercialisation in Europe, Morgan’s newest furnace technology is now being utilised successfully in other markets. In work with foundries across the world, typically, a project to optimise their melting and holding

foundry to find that the investment in new recuperative furnaces is paid for within two

years just by the reduction on their gas bill. On top of this, there is often additional

financial support available in terms of government grants and loans available to

support energy saving and carbon footprint reduction schemes. In the UK the Carbon

Trust provides interest free loans to fund the purchase of energy efficient capital

equipment to reduce carbon emissions. Similar schemes are available in a number of

other countries.

practices will start with a detailed audit of the foundry’s existing capabilities and a comparison with their energy costs, working practices and alloy demands. To complement the recuperative technology Morgan has developed a series of analytical tools which can help a foundry identify where it can save money on gas bills. Invariably, the biggest potential saving identified is replacement of the existing furnaces with this new recuperative furnace technology. Depending on the state of the furnaces being replaced and the gas price, it is not uncommon for a foundry to find that the investment in new recuperative furnaces is paid for within two years just by the reduction on the gas bill. On top of this, there is often additional financial support available in terms of government grants and loans to support energy saving and carbon footprint reduction schemes. In the UK the Carbon Trust provides interest free loans to fund the purchase of energy efficient capital

equipment to reduce carbon emissions. Similar schemes are available in a number of other countries.

For more information contact: Dr Andy Wynn, global technical director, e: [email protected] or Bob Thomas, chief furnace engineer, e: [email protected] or Tim Heeks, furnace design engineer, e: [email protected] at Morgan Molten Metals Systems, Woodbury Lane, Norton, Worcester WR5 2PU. UK.Web: www.morganmms.com

Melting and Holding

Introducing......the latest in improved technologyfor your foundry, MORGAN MOLTEN METAL SYSTEMS’Recuperative Furnace:

CRUCIBLE LTDMORGANITE

MORGANITE CRUCIBLE LTDWoodbury Lane

Norton, Worcester WR5 2PUTel: +44 (0) 1905 728200Fax: +44 (0) 1905 767877

Web: www.morganmms.com

Realize these benefits with this new furnace:� Up to 50% energy savings� Improved crucible life� Very low noise emissions� Environmentally

friendly emissions


Having an all steel construction up to 1,000kg capacity, the new compact furnace bodies can easily be connected to all brands of inverter system and in most cases without the need for any modification to existing brickwork.

Up to 1,000kg steel capacity, the industry has historically favoured unscreened box type tilting bodies, this trend has been largely down to economic and maintenance considerations. As a knock-on effect, today’s second-hand furnace market limits customers’ choice as to the brand and style of equipment available. In Meltech’s experience the market for furnace bodies outstrips whole-system sales by around two to one and in some cases has hampered sale potential because quite simply, ‘there were not enough loose bodies available at the time to meet demand’.

Limitations in availability and changing market trends were the catalyst which encouraged engineers at the UK based supplier to study the possibility of developing a furnace body. In order to succeed, the new system would have to meet an exacting specification to include features which were common to much larger steel frame or shell furnaces but with simplicity and build cost equal to, or better than, a box furnace.

Study complete . . furnace designedToday, some 12 months after that initial study was completed, the new furnace has been designed, built, tested and certified with the first two units now sold and completing commissioning trials.

The Mag-Melt furnace body has a fabricated steel construction, which is magnetically screened, utilising air cooled shunt gap technology offering improved efficiency compared to other steel shell or steel frame furnaces. Power ratings of well above 750kw on a 1,000kg body are achievable.

On the 500kg capacity units already constructed, fussy water manifold arrangements and shunt cooling circuits common to other steel furnaces have been completely designed out, leaving the

interior of the body uncluttered and free of pipe work. Each shunt is easily lifted out by undoing just two retaining bolts. Unlike most other furnaces, there are no shunt compression bolts present on the furnace either, inside or out.

In addition to the simplification of the water circuitry, there has been further development. This includes the almost total removal of combustible insulation materials within the furnace, anywhere other than on the coil itself, thus reducing ground fault problems associated with charred or burnt insulators. This is possible by the clever use of refractory within the body which has eliminated the need for coil backing materials, Mica, insulation tubes, top hat washers and so on.

While it is not possible to eliminate lining failure, metal run through and damage to any furnace, the Mag-Melt design does reduce potential electrical or ground fault problems. However, should they occur, the simplicity of the furnace construction also allows the damaged coil to be removed in minutes by undoing just four bolts and the power leads.

Certification conformityThe furnaces meet all current and proposed EMF regulations and come with a certificate

of conformity. Options include hydraulic lid, lip fume extraction, refractory push out and pre-tilt system for accurate pour control.

Steve Macey of Meltech explains the importance and the customer reaction to this new product line. ‘We accepted our first two orders for Mag-Melt furnace bodies several weeks ago. Customers seem impressed with the thought we have put into the product. For example, our access cover has proper lifting handles, big enough to take hands wearing heavy-duty gloves – a small but important point that demonstrates our complete attention to detail. Our design people have years of experience fixing all makes of systems and understand the advantages and disadvantages. They have been innovative and used a systematic approach to manufacture, and for that they must take the credit for this product.’

Meltech is also the service and sales agent for ABP induction and supply their induction melting and heating equipment to the UK and Ireland.

Meltech Ltd.Tel: +44 (0) 1902 722588;fax: +44 (0) 1902 730142;email: [email protected]: www.induction-furnaces.co.uk

New induction furnace body hits the market

Meltech Ltd has introduced a new range of compact furnace bodies designed specifically for the small and medium foundry. Mag-Melt furnaces meet all current and proposed EMF regulations and

come with a certificate of conformity

Melting and Holding October 08

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Transcript of Melting and Holding October 08