Building an extensive business refurbishing and upgrading second-hand furnaces from through the noughties has introduced expertise and entrepreneurship at Meltech Ltd which saw them swiftly move on to build their own coreless induction furnaces, including the development of their own invertor system. Now, 23 years later, the company has become synonymous with IGBT technology.
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Now occupying a 1,000sq mtr site, with the capability of even further expansion, the company is riding high thanks to its refinement of IGBT inverter technology and ability to offer a wide range of induction melting furnace bodies including tilting, rollover and crucible drop coil styles, plus a vast range of spare parts and service for various brands of furnace and melting equipment. Commercial director Steve Macey details the history: 'We had built a very nice business refurbishing existing equipment and bringing it up to modern standards, then when Electro Magnetic field emission standards came into effect in the s, we were faced with the dilemma that the cost of rebuilding and upgrading older equipment was becoming prohibitive. So, we decided to make new furnace bodies.'
The foray into part-new machines then led to the inevitable, as Macey puts it: 'We got a taste for making new stuff.' As a team of experienced electronic and mechanical engineers, the desire to find solutions to customers' induction melting dilemmas demanded a more all-encompassing approach. Thus, by Meltech had developed their own range of induction furnace bodies which were branded as Mag-Melt, an abbreviation for magnetic melting. Soon after the company ventured into IGBT inverter technology. 'We learned pretty quickly that this technology was noticeably faster and more efficient,' Macey explains. 'By we had developed our first IGBT invertor which was out for trial at Yeovil Precision Castings (now Tritech UK). When we accessed the performance data, we discovered it was significantly better than previous systems. Melt time was significantly reduced, as was energy consumption. We then went on to sell more.'
REMOTE MONITORING
There then followed constant product development with bigger machines being built up to 750kW power rating. Extra functionalities were also incorporated with constant software improvements. Auto sinter, interconnectivity, data download and monitoring, fault finding ' all able to be accessed remotely using portable devices. 'Basically, we have made the system totally flexible,' Macey says. 'The software lives with the machine and always evolves thanks to the upgrades we undertake as we service each machine, essentially the system or its software never becomes obsolete.' The extension to the life of machines has been a real bonus for customers and has enabled Meltech to grow the business, as has the adoption of digitised control which has further extended the flexibility of the furnaces.
The move into digital technology and remote monitoring has been an ongoing trend in recent years and this is very much a part of standard thinking now. The equipment and software has been designed for ease of detection and solution. Macey says: 'Everything the machine is doing is being measured constantly. There are multiple sensors which are constantly monitoring and displaying the system conditions, in the event of a fault, pressing the HMI indicator brings up the relevant page on the digital manual and suggests possible causes and solutions. There is also a detailed alarm history on the machine, both can be analysed online and by USB backup. We and the customer can access the machine remotely from anywhere in the world, we can advise how to fix a problem or we can initiate a call-out.'
INTEGRATED SYSTEM
Having mastered the melting technology, the next step has been integrating into the auxiliary equipment such as PLC control and water cooling systems. 'The inverter now talks directly to the water cooling PLC,' Macey explains. 'Everything on the system ' temperature, overrun times, settings ' are all set up and run from the HMI on the inverter. It also controls the water cooler with individual controls for every single fan ' this means that you only run the individual fans that you need, rather than having pairs or triple sets running. It's such a bonus in terms of energy efficiency.'
Efficiency is very much the order of the day and another tweak to original thought process that aids this is the use of magnetic shunts in each furnace body. Instead of butting up against the induction coil, In smaller furnaces Meltech advocates pushing the shunts away from the coil in order to reduce magnetic field density and enable the furnace to run cooler, another advantage is that there is a significant reduction in the use of insulators which reduces the chance of coil arcing whist making maintenance simpler and quicker.
'Our systems consume less energy than equivalent SCR or thyrister driven induction furnaces,' Macey says. 'It's all about melting for less cost and less energy.'
Macey puts the company's success down to their many years of working with a range of furnaces and customer requirements plus their adoption of IGBT technology which, he says has been widely adopted elsewhere. 'In other industries, IGBT's have wiped out SCR technology as a switching device. For example, all electric vehicles are IGBT driven along with almost all AC motor drives. SCR's have been superseded by IGBT transistors in most industries.
'In terms of our product lines, below 750kW most mainstream melting tends to be IGBT although higher power systems are in development right now.' This transformation has been a positive for Meltech, having got on board with the technology early on it has seen a decline on the company's original primary business. 'Up until eight years ago we were the foremost supplier of rebuilt furnaces in Europe, but as IGBT sets were introduced customers were given a compelling choice to make, at double the cost of a rebuilt second hand machine, an IGBT system could pay back that difference in less than three years in reduced energy costs, furthermore UK tax incentives introduced for capital equipment purchases during and after Covid, have enabled foundries to invest in the latest melting technology, and we are thankful for that.'
The company also still houses an extensive spare parts facility, carrying parts for a wide range of their own and competitor equipment and operates an easy to use spare parts online catalogue. Indeed, such has been the demand for new furnace technology that the company has expanded into the full 1,000sq mtr of its site in Haverhill, Suffolk (UK), including extra production and administration space, a new boardroom and increased test room facilities.
MODULAR INSTALLATIONS
In recent years, Meltech has become particularly experienced in the provision of modular systems, where platforms are part of the installation. Furnaces are pre-assembled in the Meltech factory, then dismantled, transported and re-assembled at customer's sites as a modular install ' an overall design that has been embraced by many customers requiring a quick installation. Andrew Drage, sales manager, says repeat orders are now a significant part of the company's business. 'Around half of our orders now come as a result of the customer buying their first Pulsar IGBT then realising the benefits, decide to replace their other SCR' sets.' he says.
Back in early Archibald Young Ltd invested in a brand new Meltech induction melting system to replace a now unreliable machine which dated back to the s, the new furnace comprised of 150Kw Pulsar IGBT Inverter with a twin crucible body drop coil arrangement at 100kg and 200kg capacities. As managing director Andrew Young explains: 'The technology offered with this system was a departure from the existing equipment and the benefits were quickly felt with an improved efficiency and shorter melt time. So much so, when deciding to invest in new furnaces at our subsidiary company, Peel Jones Copper Products Ltd, the purchasing decision was an easy one and we installed another Pulsar IGBT Inverter, this time with two off 500kg fixed body tilting units'.
Andrew Drage says: 'We are also known for special products such as carousel furnaces, Pre Tilt systems for accurate pouring and of course our IGBT power share where a single control panel feeds two furnaces simultaneously. This is a recent development for us, and I am not aware if any other company does this with a series driven IGBT inverter.' From humble beginnings to cutting edge technology, Meltech has invested in an efficient and controllable future for induction melting needs and continues to grow the business to support its extensive customer base.
Contact: Andrew Drage, sales manager, Meltech Ltd, : + 44 (0) , : [ protected] web: www.induction-furnaces.com
IGBT
Used as switching devices in the inverter circuit ' for DC to AC conversion ' for driving small to large motors, IGBT is considered an option to improve efficiency. With lower on-state resistance and conduction losses, and an ability to switch high voltages at high frequencies without damage, IGBT is ideal for driving inductive loads such as coil windings, electromagnets and DC motors.
Andrew Drage, sales manager at Meltech explains why the company's Pulsar IGBT inverters have been making a difference in recent years. 'The IGBT technology is all about efficiency and speed, with some installations having shown savings of up to 30 per cent via improvements in energy consumption and melt times. The Pulsar inverter is a thoroughbred IGBT series inverter, so it offers better efficiency like for like than other traditional SCR or thyristor driven system. The Pulsar IGBT can connect directly to a standard distribution transformer to drive all makes and types of induction furnace body.
'During customer installations, there have been instances where melt times have been reduced from 90 minutes to 55 minutes. While the performance exhibited during the melting and holding cycle has in certain circumstances reduced energy consumption to give the customer a very tangible cost saving and payback. One customer noted a decrease in power consumption from 125 to 60kW during their holding cycle.'
One major advantage of the coreless furnace design is that significantly higher outputs can be achieved. As a result, coreless furnaces for iron and steel with more than 20 MW power rating and melting rates in excess of 40 t/h are successfully in use.
Even if induction furnaces can be operated carbon-free when powered by electricity from renewable sources, the foundries using them still strive to minimize their electricity consumption. This is done with sustainable resource conservation in mind, and also with a view to improving the profitability of foundries and factories manufacturing semi-finished products, especially in the face of rising energy costs. Liquefying ferrous or aluminum materials requires approx. 500-560 kWh/t, which means that energy costs are often a decisive factor in the manufacture of castings and semi-finished products.
So how can a foundry save energy during the melting process? There are three main influencing factors:
- Dimensioning of the system and the terms of the electricity supply contract
- Operating regime of the melting furnaces in practice
- Analysis of digital melting process data
Rating and dimensioning of the system and considering the terms of electricity supply contracts
Today's electricity supply contracts usually apply demand charges, unit charges and reactive demand charges. The costs associated with the demand charge can be reduced by ensuring that the system draws energy from the grid as consistently as possible. Utilities charge hefty mark-ups for peak energy demands, for which after all they have to make provisions on the power generation side and grid side. It therefore makes sense to rate and dimension a melting furnace in such a way that the planned liquid metal requirement is covered, but the temporary maximum requirement is achieved where possible through additional production times. Maximum-power monitoring systems, which ensure that previously-defined loads are throttled when the power limit is reached, are also helpful in this regard. Induction furnace systems with pulse width modulated IGBT inverters offer an advantage for this mode of operation because they have a constant power factor cos phi even in the partial load range, while maintaining very good electrical efficiency of the parallel resonant circuit converter. Series resonant circuit converters too achieve a constant mains power factor. With these, however, the high uncompensated furnace current must be fed through the entire inverter, leading to additional losses and increasing the strain on components.
The unit charge in the electricity supply contract determines the price per kWh consumed, which must be paid by the foundry. For example, if this is 20 cents per kWh and the furnace consumes 550 kWh per tonne of liquid metal, the unit charge per ton of cast or semi-finished products would be ' 110.
In some grids, the unit charge may also vary depending on the time of day or day of the week. In such cases, it may make sense to install a holding furnace or a furnace system with two or three crucibles to store liquid metal that was produced during a low-tariff period.
Whether additional costs have to be paid for the reactive power used depends on the one hand on the consumption of reactive power permitted by the energy supplier and, on the other hand, on whether the induction furnace has a constant cos phi of 0.99, for example, at the converter input also in the partial load range.
If the unit charge does not have a low tariff and the liquid metal demand is relatively constant, it is better to avoid installing additional holding furnaces where possible. For instance, a 60-tonne holding furnace for iron, designed as a channel-type induction furnace, has an annual energy demand of approx. 2 million kWh. Based on the example of 20 cents per kWh, this equates to energy costs of ' 400,000 per annum.
Operating regime of the melting furnaces in practice
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Just like smart driving habits will maximize a car's fuel economy, a significant proportion of the energy needed to operate an induction melting furnace can be saved simply by adopting smart operating strategies. This starts with the chosen method and further processing of the charge material.
Savings measures can therefore be divided into two categories: Optimization of the type and quality of the charge material and optimization of the process flow.
Often no particular attention is paid to surface contamination because there is no visual difference. The material seems to melt just as well as clean metal. After the melting process, the non-metallic impurities are removed in the form of slag.
The fact is, however, that these impurities result in a poorer overall coupling of the scrap to the induction field. In the case of oxides, these do not even couple at all, which leads to poorer overall power utilization.
In practice, such insights are usually only gained by evaluating the production data. If irregularities are detected in the process or in the product quality, action needs to be taken and the process must be systematically examined.
Below are some examples of process situations and corresponding orientation values for potential energy savings when melting down a batch, as calculated in various iron foundries.
1) Sand in the charge material
After the molds have been shaken off, varying amounts of molding sand still adhere to the recycled material. If these are not adequately removed by blasting, sand will get into the melt. The formation of slag from the sand also takes energy. With a realistic quantity of 25 kg of sand per tonne of iron, this results in an increased requirement of 25 kWh/t.
2) Rusty charge material
Depending on how the scrap used is stored, rust (iron oxides) can form and be introduced into the crucible. The poor coupling leads to a lower power input. The iron oxide must be heated to the melting temperature in an energy-intensive process. For the furnace stated in the table (s. figure 4), this means an additional consumption of 30 kWh/t.
3) Low packing density
The packing density of the charge material also affects energy consumption: The higher the packing density, the lower the energy consumption.
Tests in practical operation showed a lengthening of the melting process by approx. 8 % and an increase in energy consumption by approx. 25 kWh/t with a reduction in packing density from 2.0 t/m3 to 1.3 t/m3.
4) Carburizing after melting
If the carburizing agent is not added at the beginning of the melting process along with the metallic feedstock, but only introduced into the liquid bath after melting, this results in a significantly higher energy consumption. Based on practical experience, it has been ascertained that an additional 1 to 2 kWh/kg is required if the carburizing agent is added later. With a realistic value of 1 % carburizing agent per batch, a higher energy requirement of up to 5 to 10 kWh/t iron can therefore be expected.
5) Melting with reduced power density
Based on theoretical considerations, the most energy-efficient way to operate the furnace is with the maximum
available electrical power and thus a high power density. Systematic tests carried out clearly confirm this. Batch times are shortened, thermal losses are reduced, and consequently, electricity consumption is lower. For example, if the furnace in the table operated at only 50 % of the maximum power, this results in an additional electricity consumption of 20 kWh/t.
6) Melting with a sump
If medium frequency technology is used, a sump can be dispensed with
and small-sized charge material can be melted. Due to the better
electromagnetic coupling of the solid feedstock (this only applies to cast iron materials), 5 % less energy is required in batch-only operation,
as a significantly higher coil efficiency is achieved up to the Curie point.
7) Holding with the lid open
If a furnace is operated with the lid open for longer than necessary, a considerable amount of heat escapes into the shop. This energy has to be replaced. The small thermal loss of originally only around 275 kW (for a 15-tonne furnace) then rises to around 600 kW. If the lid is left open for a period of 20 minutes, this results in an increased energy requirement of 15 kWh/t in total.
8) Unthrottled extraction
The extraction volume of the flue gas cleaning system should be adapted to the process steps of the furnace. Thus, if no flue gases are to be extracted or only small amounts are produced, the extraction volume can be throttled.
If the filter system is always operated at full capacity, energy is unnecessarily 'sucked' out of the furnace. In unfavorable cases, this can increase energy consumption by around 2 %. In the example in the table below, this is estimated at 8 kWh/t.
9) Unnecessary superheating
If the superheating of the iron is not checked in good time during the final melting phase in manual mode, the desired or sufficient casting temperature may be exceeded unnecessarily. By avoiding an excessive temperature increase of 50 K, for example, approx. 20 kWh/t can be saved.
If a digital furnace control system is used, the final temperature can be maintained with an accuracy of up to 5 K in automatic mode. This helps prevent unnecessary superheating.
To illustrate this, the table shows energy values for a furnace with a capacity of 8,000 kg of cast iron, operated at a maximum power of 7,000 kW.
Of course, these individual cases never all arise at the same time. However, the total sum shows that the required energy demand could even be exceeded by more than 35 % in the worst case.
Based on the initially assumed electricity costs of 20 cents per kWh,
this increases the cost of producing one tonne by about ' 30. For an annual production of 50,000 metric tons, this results in avoidable additional costs of approx. ' 1,500,000.
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