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Carbolite furnaces play key role in sample preparation at Diamond Light Synchotron
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Diamond Light Source, the UK’s national synchrotron facility in Oxfordshire, has taken delivery of seven Carbolite electric furnaces designed to provide researchers with a broad spectrum of high-quality thermal equipment for sample preparation and processing.
Diamond, the largest UK scientific investment for 40 years, is a third-generation light source with an electron beam energy of 3 Giga electron volts (three thousand million volts). At its heart is a circular vacuum chamber, half a kilometre in circumference, through which electrons travel at just below the speed of light. Passing the electrons through specially designed magnet arrays produces infra-red, ultra-violet and X-ray beams of exceptional quality and brightness, which enable researchers to study the basic structure of many materials, down to the scale of molecules and atoms. |
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 | | Within the doughnut-shaped building 14 experimental stations are currently located (known as beamlines) with eight more due for completion by 2012. The beamlines are supported by laboratories that provide researchers with comprehensive in-house facilities for performing cutting-edge experiments into a very wide range of fields, including health research, engineering, environmental science, sustainable energy, cultural heritage and fundamental physics. Plans for a further ten beamlines are currently under review.
Carbolite furnaces have been previously supplied for sample preparation and related activities at the Synchrotron Radiation Source (SRS) at Daresbury, Cheshire. The equipment supplied by the company to Diamond Light Source includes a specially |
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designed high-vacuum tube furnace, four conventional tube furnaces and two chamber furnaces. Maximum operating temperatures are between 1200°C and 1500°C. These furnaces are mainly used for heat treatments commonly used for inducing structural and phase changes, which is essential for material, engineering and environmental science. The tube furnaces allow additional species to be introduced or intercalated into the structure of materials, which can then be examined using X-ray diffraction.
The vacuum tube furnace has silicon carbide heating elements which provide a maximum operating temperature of 1500°C, with control provided by a Carbolite 301 PID instrument that allows temperature ramp rates and dwell periods to be pre-set for different procedures. Samples are held in a 50mm diameter 450mm long work tube. Reliable vacuum performance is achieved by means of a rotary vane roughing pump combined with a high-vacuum oil diffusion pump. Models with a turbo-molecular high-vacuum pump and fully oil-free roughing pump are also available from Carbolite.
The four tube furnaces provide heating capabilities up to 1500°C in air or inert atmosphere and include two models with three-zone control which allow temperature gradients to be applied or very accurate control of long heated lengths to be achieved. The two chamber furnaces have operating temperatures up to 1300°C and 1500°C, the higher-temperature model having a rapid-heating capability.
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Developments in microwave heating technology
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.jpg) | | Famously discovered accidentally by Dr Percy Spencer of the Raytheon Corporation when a chocolate bar mysteriously melted in his pocket while working on a new device for radar applications, microwave heating has been around since World War II. Given that length of time and the speed with which many new technologies have been applied during the last 60 years, industrial microwave heating could be considered a somewhat slow developer.
Microwave heating is actually a form of dielectric heating, another being radio frequency (RF) heating. Today we all know the domestic microwave which |
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| enables us to re-heat the cup of coffee we left for too long or make porridge without using a saucepan, but even that relatively simple product took more than two decades to develop and become widely available. Commercial uses of microwave technology also developed slowly and initially were restricted to simple heating and drying applications, either at laboratory scale or in a production system. Food, paper, textiles, wood, rubber, chemicals, semi-conductors and ceramics – that is, typically non-metals with poor thermal conductivity -- are among the materials that are now commonly processed by microwave heating equipment. But other materials, including metals, are continuously joining the list, and the temperatures and complexity of the processes are also steadily increasing. |
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One of the reasons for the initial slow development of microwave technology for industrial applications was perhaps the incomplete understanding of the mechanisms involved. Dr Percy Spencer’s chocolate bar melted when he was working with a magnetron, which is still the predominant mechanism for generating microwaves, but for many years the way microwaves acted on a given material was not understood. Even now research is continuing into some of the features, and new potential benefits associated with this technology are still becoming apparent.
A magnetron is an oscillator capable of converting electric power, usually in the form of high-voltage DC current, into high-frequency radiant energy. The polarity of the emitted radiation changes between negative and positive at high frequencies, and material within the radiation field heats up through ‘molecular friction’ as the dipoles within it try to re-orientate themselves. By international agreement, certain microwave frequencies are reserved for industrial, scientific and medical (ISM) applications, each having a specific wavelength.
The standard frequency used in domestic microwave ovens is 2450 MHz, with the magnetrons producing typically 800 W or so at maximum power. This frequency is also used for industrial systems with power ratings commonly up to 20kW and occasionally higher. Larger industrial heating systems use 896 MHz or 915 MHz magnetrons, although there is some overlap of the power ratings of magnetrons at these two frequencies. Wave-guides transfer the generated energy from the magnetron to the processing chamber, where a device known as a mode stirrer may be used in order to improve energy distribution, depending on the cavity design.
Microwave heating has some very particular characteristics and is quite different in many ways from conventional radiant heating. First, it is volumetric -- that is, energy is generated directly within the body of the material itself instead of the interior gradually heating up through conduction from the external surface as occurs with radiant heating. Some materials are more susceptible than others to microwave energy and heat more readily, so preferential heating may take place, which can provide process advantages. Volumetric heating can also result in energy being used very efficiently, as only the target material is heated.
Second, in many materials heating is almost instantaneous and takes place without the need for radiating elements to heat the air or any container.
And third, heating is highly specific, with different materials displaying different ‘susceptibilities’ to microwave energy, as we know from our kitchen microwave: water usually heats relatively quickly, while other materials – some plastics, for example -- heat very slowly. This differential can be used to advantage in microwave processing – for example, pharmaceuticals can be sterilised in their packaging without the plastic heating up. And wet areas of a product will take up heat more than dry areas, so moisture content will equalise.
However, the optimum frequency for any given material may not be constant over the entire temperature range encountered during heating. Therefore, it is very important to match the system and experimental process design to the material.
The advantages of microwave heating can be summarised as:
- Energy-efficiency, because power is only applied to the material;
- Higher quality through avoidance of case-hardening and other surface damage;
- Selective heating, giving processing benefits in some cases;
- Direct heating of the sample body, reducing process times.
Despite the advantages offered by microwave heating, it can sometimes, when applied in isolation, be less successful at higher temperatures, such as those required for firing or sintering ceramics. This is because once a sample heats up, it will generally be at a higher temperature than the surrounding atmosphere, and heat can be lost from the material’s surface. This in turn can create temperature gradients within the material, albeit the reverse of those associated with radiant heating, and the gradients increase as the component becomes hotter. This limiting factor can be particularly significant for materials requiring high structural integrity.
Various ways of overcoming the temperature profile problem have been investigated, the most successful being to apply a combination of radiant and microwave heating to materials, especially those that need to be processed at temperatures above 800°C. C-Tech Innovation Ltd, based near Chester, has been at the forefront of microwave-assisted heating technology (MAT), in which microwaves provide an additional heating mechanism in support of conventional gas or electric radiant heating. With the MAT technology, while the microwaves provide a thermal equalising effect, the radiant heating retains the controllability essential for many advanced materials, and this approach is now being used successfully for batch and continuous processes and at laboratory and production scales.
This combined approach has been found to have significant advantages over both radiant-only and microwave-only systems. More consistent product properties, greater strength, improved yield, reduced formation of undesirable phases and lower quantities of harmful emissions can all be achieved through the use of MAT.
The specific process developed by C-Tech Innovation was patented by the company and Carbolite has now concluded a technology transfer and licence agreement with C-Tech to manufacture and sell equipment with the MAT heating technology in Europe. The first models with the combined microwave and radiant equipment are laboratory-scale chamber furnaces with maximum temperatures between 1200°C and 1600°C. Molybdenum disilicide elements are used in these furnaces in order to avoid the microwave uptake that would occur with the more common silicone carbide elements. James Roper, who is leading Carbolite’s MAT product development programme, expects the laboratory-scale equipment to lead to production-scale units as processes are developed and validated by research programmes.
He has identified a number of applications where MAT heating could speed up processing times or produce more consistent results, from precious metals assaying to burning off wax moulds for foundry castings. Development work has also revealed that MAT heating has a beneficial effect on the properties and performance of some materials – for example, sintering high-performance ceramics such as zirconia in a MAT furnace has been found to produce more consistent grain size, which is particularly important for semi-conductor applications and nano-materials. It can also give better control of hardness, toughness and translucency than conventional radiant heating.
Another advantage of MAT heating is the ability to scale up easily from laboratory to production capacities, according to Mr Roper. ‘It is very difficult to scale up microwave-only systems because of the problem of maintaining high power densities over a large area, but scaling-up is relatively straightforward with the MAT heating system’, he explains.
Microwave heating may have taken some time to find full acceptance in the commercial sector, but Carbolite believes that developments such as MAT heating open a whole new spectrum of applications that could make it as widely used as conventional radiant heating has been in the past.
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Special furnaces simulate aero-engine conditions
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 | | Five specially designed Carbolite furnaces are enabling Vibro-Meter UK to perform long-term thermal test programmes that simulate conditions experienced by thermocouples in gas turbine aero-engines. Vibro-Meter UK is part of Meggitt plc and one of the leading manufacturers of sensors for the aerospace sector.
The furnaces were bought to enable the company to carry out research into the stability and accuracy of thermocouples as a result of long-term exposure to temperatures up to 1100°C in aero-engines. An important aspect of the equipment is the ability to simulate working conditions by cycling the thermocouples for long periods between typical operating temperatures and ambient temperatures. |
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In order to achieve this, the Carbolite furnaces have an automatic actuator mechanism that pushes and pulls bundles of thermocouples in and out of the heating zone of a horizontal tube furnace. The five furnaces have a maximum temperature of 1200°C and three heated zones in order to ensure precise temperature control at the centre of the 38mm diameter tube where the thermocouples are heated.
Each thermocouple is typically 2mm in diameter and usually 15 are tested at a time. |
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Test programmes typically involve holding the samples in the furnace for 30 minutes at a temperature between 700°C and 1050°C, extracting them and exposing them to ambient air for five minutes and then re-inserting them into the furnace again for 30 minutes. This sequence is generally repeated 4000 times before the samples are analysed and calibrated to determine the effects.
The furnace design allows entire cyclic programmes lasting over 2000 hours to be carried out automatically once the temperature and time data has been input into the control system. The five furnaces allow Vibro-Meter to carry out several programmes in parallel at the same time.
The equipment is compact and convenient to use in a laboratory situation, with double skin construction helping to keep the outer case cool and high-quality insulation optimising thermal efficiency. A high-precision PID temperature controller, timer and associated power control equipment are housed within an integral control box.
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High temperature oven ensures ultra clean glassware
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 | | Purifying glassware in a high-temperature Carbolite oven has enabled ELGA LabWater to stop using chromic acid for the preparation of samples in the R and D laboratory where new high-purity water systems are designed.
Minimal total organic carbon (TOC) levels, which are used as an indicator of overall organic purity, are a key requirement for users of pure water in laboratories. ELGA’s PURELAB Ultra system achieves TOC levels as low as 1 μg/litre.
In order to stop water samples being contaminated by organic compounds on the glassware, ELGA used to soak it in chromic acid, which is both toxic and corrosive. Now, following the recommendations in Preparation and Testing of Reagent Water |
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in the Clinical Laboratory (CLSI 4th edition, 2006), sample bottles are rinsed in ultra-pure water and then heated to 450°C for two hours in the high-temperature Carbolite oven. Tests have shown that any organic contamination present after this procedure is not detectable, according to Dr Paul Whitehead, R&D laboratory manager.
The equipment has a maximum temperature of 500°C and a 60-litre capacity stainless steel chamber. A PID controller is fitted to ensure temperature stability, and fan-assisted air circulation gives temperature uniformity better than ±5°C, as well as fast heat-up and recovery times. |
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Carbolite manufactures high-temperature LHT ovens, in three sizes – 30, 60 and 120 litres, each with a choice of 400°C, 500°C and 600°C maximum temperatures.
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Furnaces expand Daresbury laboratory facilities
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‘The Daresbury Laboratory is a world-class facility that is used by researchers at the cutting edge of materials science, so our equipment and services have to be of the highest quality’, said Ray Jones, the Materials Science Laboratory manager.
‘Access to use of the Synchrotron Radiation Source is usually very limited, so sample preparation and other associated activities have to be exceptionally reliable to ensure the experimental time is successful. Temperature accuracy, temperature uniformity and repeatability between sample batches are extremely important’. |
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 | | Off-line preparation, analysis and support services for users of the Synchrotron Radiation Source (SRS) at the Daresbury Laboratory in Cheshire have been expanded and upgraded with the installation of two Carbolite chamber furnaces.
The Daresbury SRS is a world-class facility that delivers radiation with wavelengths from the infrared to hard X-rays and is used by over 1300 scientists a year from some 25 countries for multiple simultaneous experiments. The SRS is supported by a Materials Science Laboratory which has a broad spectrum of sample preparation and analytical equipment, including a dedicated furnace room for calcination, sintering and other procedures. |
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The two chamber furnaces supplied by Carbolite have maximum temperatures of 1300°C and 1700°C and temperature uniformity within ±5°C. The CWF1300 unit has a chamber capacity of 5 litres and is heated by free-radiating coiled wire elements within moulded alumina-based carriers on either side the chamber. Elements are graded to compensate for heat loss and to optimise uniformity. The HTF1700 furnace, which has a 10-litre chamber, is heated by U-shaped molybdenum disilicide elements, which are extremely durable at high temperatures but can also be easily replaced when required.
The HTF1700 has an eight-segment programmer, while the CWF model has a PID controller. Both units have over-temperature protection and are linked to PCs to allow pre-programmed processing cycles to be run automatically without staff supervision.
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Carbolite furnaces expand Siemens laboractory facilities
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 | | Seven chamber furnaces from Carbolite have expanded laboratory facilities for evaluating nickel-based superalloys and associated coating materials at the Siemens Industrial Turbomachinery factory at Lincoln, UK.
The furnaces are used for long-term thermal and atmospheric exposure of the alloy substrates and coatings used for components in hot-end sections of industrial gas turbines. They work alongside a custom-built thermal rig with a maximum operating temperature of 1500°C, also manufactured by Carbolite, which is used to subject coating materials to heating and cooling cycles.
The chamber furnaces are used to hold samples at specific temperatures |
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between 700°C and 1100°C for thousands of hours, with sections being removed periodically for analysis. They have five-litre capacity chambers and a maximum temperature of 1200°C, provided by heating modules on either side of each chamber. The modules consist of alumina-based carriers housing coiled wire elements which are graded to compensate for heat loss and optimise temperature uniformity. Hard-wearing refractory brick is used around the entrance and in the base of the chamber, and secondary insulation reduces power consumption.
The equipment has replaced a number of existing Carbolite furnaces which had been in use at the factory for nearly 20 years.
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High specification ovens boost production capacity and quality
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 | | Two high-specification Carbolite ovens have been installed by specialist sealing solution provider Greene, Tweed and Co Ltd to increase the capacity and consistency of the raw material sintering operation at its UK manufacturing facility.
Greene, Tweed is a world leader in the supply of polymer-based engineered solutions to market leaders in industries such as defence, aerospace, chemical processing, medical equipment and oil and gas production and has been experiencing a growing demand for its products. The company uses a wide variety of proprietary PTFE formulations for its products, which are moulded in both tube and bar form in the facility, before being sintered and then machined to custom designs required by customers. |
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The two new ovens, which join two existing units that have been in the factory for over ten years, have a maximum volumetric capacity of 1.73m³ and have a maximum operating temperature of 425°C. Temperature uniformity is guaranteed to be better than ±5°C and is typically as good as ±3°C.
The tube and bar that are being processed stand on rotating tables, ensuring that heat is applied very evenly to all the material. The tables, which are perforated to improve air circulation throughout the chamber, rotate approximately once every two minutes. Heating is provided by Incoloy-sheathed, mineral-insulated rod elements located behind side duct sheets. Air is circulated by heavy-duty fan impellers on either side of the chambers.
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Furnace tests hydrogen storage materials
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 | | A Carbolite tube furnace is playing a key role in a research programme at the Risø National Laboratory in Denmark to investigate the potential of metal hydrides for hydrogen storage.
While the advantages of hydrogen as a fuel are well recognised, suitable ways of storing it, particularly for mobile applications such as cars, have yet to be developed. The Institute has installed a special experimental rig to test the capacity, kinetics, thermodynamics and stability of hydrides that could be used for this purpose.
In order to prevent samples being exposed to air, they are tested in a sealed reactor that is loaded and unloaded in a glove |
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box with an inert atmosphere and then heated in the Carbolite furnace at temperatures up to 500°C. The MTF model used is particularly compact and is mounted on rails on the work-bench so that it can be moved from side to side to give access to the reactor.
The maximum operating temperature of the furnace is 1200°C, has a 250mm long heated zone and is used with a 25mm diameter work tube. Low thermal mass insulation ensures rapid heat-up, and a microprocessor-based digital controller delivers precise, repeatable temperatures.
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Carbolite furnaces speed high-quality drill production
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 | | Dormer Tools is one of the world’s largest producers of high-speed-steel cutting tools, with five major manufacturing centres in the UK, Sweden, Italy and Brazil. Since buying the company in 1993, the Sandvik Group has maintained a policy of product development and investment in advanced manufacturing facilities which has secured its reputation for quality and service.
One of the most recent investments in production equipment is at the UK factory at Worksop, Nottinghamshire, which specialises in the manufacture of high-quality twist drills for production engineering and maintenance applications. A new Carbolite furnace line has been installed to carry out double-tempering of hardened HSS cut pieces, in a continuous process |
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without intermediate handling, in volumes up to 7000 per hour. The tempering furnace joins an existing Carbolite furnace used for hardening drill blanks at temperatures up to 1250°C.
The Worksop factory produces 6500 different types and sizes of twist drill at a rate of around 600,000 finished products a week. The raw material arrives in the form of annealed bar, with diameters ranging from 3mm to 25mm, before being cut to length. At this point, the cut pieces are hardened using one of three procedures currently used in the factory – a Carbolite electric rotating hearth furnace, several electric vacuum furnaces and salt baths. |
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Salt baths have been used for heat treatment for many years by Dormer and are widely used by other tool manufacturers. They are simple and robust, but expensive to run due to their high power consumption. They also have a number of other environmental disadvantages, including the need to store and dispose of the barium chloride salts used.
The vacuum furnaces are sophisticated and flexible – they can be used for hardening only or tempering only or hardening and tempering in a single continuous process. However, productivity is relatively low, and the 1200°C required for hardening the cut pieces damages the furnace linings, which frequently need to be repaired and replaced. A complete hardening and double-tempering cycle takes approximately 11 hours. | |  |
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For some years, most of the hardening has been performed in a Carbolite rotary hearth furnace. This equipment has a much higher throughput than a vacuum furnace without any reduction in quality and provides far better working conditions than the salt baths, according to Eddie Dabill, Technical Manager.
To complement the Carbolite hardening furnace, Dormer recently invested in a tempering unit from the same company in order to further increase the productivity of the heat treatment processes in the factory. The two units, which Dormer is planning to link together to form a continuous production line, are used for processing the material used for the main product sizes – from 5mm to 13mm diameter and 86mm to 150mm in length. Dormer also intends to install more Carbolite hardening and tempering furnaces in the future, which will allow the salt baths to be removed completely. |
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 | | The Carbolite hardening furnace has a rotating hearth with three heating zones operating up to 1250°C, and provision for a nitrogen atmosphere to prevent oxidation of the material. Each of the heating zones has four temperature controllers and two over-temperature instruments to optimise temperature uniformity, which is guaranteed to be no more than ±10°C.
After hardening and fully cooling, the drill blanks are placed manually in hoppers above the mesh conveyor belt that carries them through the new Carbolite tempering furnace. This is 13.5 metres long and includes two three-metre-long heating sections and two cooling sections for the double tempering required for these products. |
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The heating and cooling parameters have been tailored by Dormer Tools to significantly reduce the overall tempering time, thus achieving significant savings in reduced inventory and lead-time. The line has a nominal throughput capacity of over 150 kg/hr, and a typical tempering cycle from loading to unloading takes approximately 40 minutes. The processing speed can be adjusted to match the output from the hardening furnace.
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Furnaces provide accurate heat treatment of turbine components
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 | | The Rolls Wood Group, one of the world’s leading companies specialising in the servicing of gas turbines for industrial applications, has increased its heat-treatment capabilities with the addition of two specially designed electric furnaces from Carbolite.
The company is a joint venture between a well-known aerospace company and the Wood Group, employing about 400 people in Scotland, Canada and the USA and specialising in the repair and overhaul of aero-derived engines such as the RB211, Avon, Olympus and 501 used in the oil, gas and power-generation industries. The furnaces were ordered in order to meet a growing need for accurately controlled diffusion and solution heat treatment of turbine blades and nozzle guide vanes at the Aberdeen headquarters. |
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| Both the Carbolite furnaces are top-loading units with inconel alloy retorts, 600mm diameter x 1000mm high internally, which allow the use of gas atmospheres. One unit has a maximum nominal temperature of 1200°C and is designed for use with argon, while the other heats to 1250°C and can be used with argon and hydrogen if a surface cleaning effect is required. Temperature uniformity on both furnaces meets RPS953 inside the retorts at 50°C below maximum. |
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Components to be processed are placed in a ‘cake stand’ style jig before being loaded into the retort from above. After fitting a gas-tight water-cooled sealing flange, the retort is lifted from its cradle by a crane and lowered into the furnace chamber. The operator can then start one of a number of pre-set programmes held in the digital control system or set a new programme to suit the material to be processed. Both furnaces are rated to heat a 50kg load to 50°C below their maximum temperatures in three hours.
At the end of the heating cycle, the retorts are lifted on to a separate frame to cool.
Temperature accuracy and uniformity throughout the heating chamber are achieved by the use of a cascade control system with a master multi-segment programmer linked to two end-zone controllers which inter-communicate with each other. Over-temperature instruments are also fitted, and an eight-channel chart recorder provides a hard-copy record of each cycle.
A sophisticated gas control system is included on the furnace with argon and hydrogen gas facilities, to ensure that hydrogen can only enter the retort when the temperature is above 800°C. The retort is also automatically purged with argon before and after hydrogen is admitted.
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Thermal rig puts brake systems to the test
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 | | AP Braking, a division of AP Hydraulics Ltd, has expanded and upgraded its R & D facilities with the installation of a specially modified Carbolite thermal chamber suitable for long-term test programmes involving flammable liquids.
The new equipment is an upgraded version of an existing chamber used by the company for several years and is designed to accept rigs for thermal stroking tests on components such as brake cylinders and calipers. These components can incorporate a number of different metals and plastics, as well as various fluids and greases.
Thermal stroking tests are carried out by attaching components to jigs fixed inside the chambers, with hydraulic pipework |
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passing through the oven walls to external actuators. Up to four components can be tested at a time. A typical SAE (Society of Automotive Engineers) test requires brake cylinders to be subjected to 1000 strokes per hour for 70 hours at a temperature of 120°C to simulate conditions in an engine compartment.
The chamber has a maximum temperature of 200°C and can be programmed to provide temperature cycling if required. It is integrated with the test rigs, so it automatically switches off if a fault develops, and an explosion relief panel is also fitted. |
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Should a component fail, surfaces that could come into contact with flammable liquids are below their auto-ignition temperature, and elements are positioned away from flammable vapours. The chambers are also sealed to prevent liquid escaping. Internal lighting has been fitted so that staff can see clearly when setting up equipment.
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Thermal chambers test Airbus hydraulic systems
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 | | FR-HiTEMP, one of the UK’s leading aerospace component manufacturers, has installed two special Carbolite thermal cycling chambers for testing hydraulic systems on the Airbus A380 ‘super-jumbo’.
The company, which specialises in fuel, ducting, actuation and control systems for aero engines, missiles and military vehicles, supplies most of the world’s aircraft manufacturers and also supports airlines & air forces in the field. Current contracts on the A380 include supplying hydraulic system components, which operate at pressures up to 5000psi (345 bar).
On the A380 some of the hydraulic pipe-work and associated components are positioned around the massive Rolls-Royce Trent engines, while other sections are in the wings, involving a range of temperatures from -55°C to +90°C. The thermal chambers are used to replicate these service temperatures while components are subjected to pressure impulse testing up to 6000psi (400 bar), sometimes for several days at a specific temperature. |
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The chambers are 1000mm wide x 1000mm deep x 1000mm high internally and have a thermal range from -70°C to +150°C. Heating is by means of mineral-insulated metal-sheathed elements with a low surface watt loading to prolong service life. The chambers are cooled by directly injecting liquid nitrogen, and the equipment includes pressure relief valves & exhaust vents. Temperature stability & uniformity are better than ±5°C. A digital indicating microprocessor-based three-term time/temperature programme controller is fitted, which allows thermal cycles lasting up to 99 days to be programmed. A cut-out operates if pre-set temperatures are exceeded.
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Furnaces support efficient chemical analysis
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 | | One of the world's leading independent laboratories uses Carbolite furnaces for a wide variety of analytical procedures and applications.
Alfred H Knight International, one of the world's leading independent laboratories specialising in metals and minerals analysis for the mining and refining industry, uses Carbolite furnaces for a wide variety of analytical procedures and applications within its ISO/IEC 17025 accredited laboratory.
The laboratory at the company's St Helens head office provides a comprehensive analytical service for minerals and ferrous and non-ferrous metals. Some 100 scientists, chemists and laboratory technicians employ a combination of traditional chemical techniques and the most modern instrumental procedures to produce accurate results quickly and efficiently for commercial transactions in the metal commodity market. For the classical fire assay analysis of precious metals the laboratory uses six Carbolite cupellation furnaces, regarded as one of the leading furnace designs for this application. |
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More recently eight ashing furnaces were supplied for loss-on-ignition analysis of precious metal bearing catalyst commodities and routine analytical calcination procedures. These furnaces have calibration ports in the front door mechanism to supplement temperature calibration for optimum temperature quality control, as required for British UKAS accredited laboratories.
The AAF furnaces are designed for a wide variety of uses in a laboratory environment and are successfully used for ashing food, animal fats & natural fibres, as well as materials such as plastics, coal & other hydrocarbons which generate aggressive fumes requiring extraction. Models are available in three sizes, all with a maximum temperature of 1100°C. The air passing through an AAF furnace is pre-heated to ensure optimum temperature uniformity throughout the chamber. High regulated airflows help to remove fumes effectively, with large furnace chambers allowing many samples to be processed at a time. |
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The GSM model, which has a fused quartz chamber, has been developed for procedures where a dust-free environment is particularly important. The design of this model also protects the elements from harmful vapours and minimises leakage if gases are used.
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Furnace provides precise economical heating
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 | | Hindustan Aeronautics Ltd, one of India’s leading aerospace component manufacturers, has upgraded its production facilities with a specially designed Carbolite furnace for heating titanium and stainless steel parts before forging.
The equipment has been designed to a high specification to meet Rolls-Royce forging specifications and EU machinery directives in a compact unit that is easy to operate and requires little maintenance. Maximum operating temperature is 1150°C, and temperature uniformity is ±8°C, which is better than Rolls-Royce Technical Specification RPS953. Provision has been made for inert atmospheres, and an oxygen probe is included to monitor the atmosphere in the chamber at temperatures above 750°C. |
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The furnace consists of a 1200mm OD rotating hearth inside a gas-tight square cabinet with a single door that is raised and lowered pneumatically. The hearth, which is ceramic, rotates through a sand seal and is driven by a mechanism that can be disconnected to allow the hearth to be turned by hand for maintenance. Hearth speed is adjustable between 3 and 20 minutes per rotation.
The door is controlled by a pair of foot pedals – one for opening it and the other for closing it -- and has a fail-safe mechanism so that it only moves when one of the pedals is pressed.
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Carbolite equipment for thermal coatings research
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 | | A specially designed thermal cycling rig (TCR) and seven chamber furnaces have been supplied by Carbolite to the Siemens Industrial Turbomachinery factory at Lincoln to expand facilities for research and development work on thermal barrier coatings.
The Lincoln factory manufactures small industrial gas turbines for power generation and mechanical drive applications with outputs from 3mW to 13mW. The Carbolite equipment is being used to evaluate coating materials such as yttria-stabilised zirconia (YSZ) bonded to cast and wrought nickel-based super-alloys used in the production of hot gas path components.
While the chamber furnaces provide isothermal exposure for this work, enabling samples to be heated to a temperature, held and then cooled, the TCR allows samples to be subjected to long cycles of heating and cooling that accurately simulate thermal conditions within a turbine. The equipment has a maximum operating temperature of 1500°C, but the maximum temperatures used by Siemens are generally between 1000°C and 1300°C. In future the company may also use the equipment for thermal fatigue testing. |
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The TCR consists of a heating zone above a loading and quench zone, with an actuator that raises and lowers samples between the two. In a typical long-term test a sample is lifted into the heating zone, heated to a pre-set temperature, held at that temperature and then lowered into the quench area where it is air-cooled before being raised again into the heating zone for another cycle.
Time and temperature are controlled through a cascade system, with over-temperature protection provided for the heating chamber. A probe thermocouple in the centre of the lifting rod provides temperature readings for the control system and is also linked to a six-channel digital-display chart recorder. The heating elements used have been designed to increase resistance to oxidisation and to provide easy replacement when required. |
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Rather than the silicon carbide elements usually used for this type of application, Carbolite has installed wire wound elements, which are less expensive and last longer. The elements are mounted horizontally above the hearth and controlled in three zones by three-term digital instruments with over-temperature protection. As the elements remain on when the furnace door is opened, an internal guard has been fitted so they cannot be touched by operators loading and unloading. Low thermal mass insulation enables the furnace to heat up quickly when it is switched on.
Components are protected from oxidation by a controlled flow of nitrogen gas that passes into the chamber to maintain an inert atmosphere. The nitrogen also flows through holes above and below the door to create a gas curtain that reduces air-flow into the chamber when the door is open.
The furnace controls are located in a separate free-standing cabinet, which also houses a chart recorder.
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Furnaces ensure high quality ceramic sheet production
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.jpg) | | GE Infrastructure Sensing, a leading manufacturer of thermisters, has increased its production facilities with the addition of a fourth Carbolite top-hat furnace for processing ceramic sheet at temperatures up to 1300°C.
The thermal sensors manufactured by the company, which are widely used in the automotive industry and in heating, ventilation and refrigeration equipment, incorporate several types of ceramics to suit different applications. The materials are produced from metal oxides mixed with binders, which are formed into thin sheets and then fired in the Carbolite furnaces.
Heating the sheets to 400°C over four hours burns off the polymer binders, after which the material is sintered at between 1200°C and 1300°C to form the new crystal structure. Sintering can last up to 20 hours, depending on the formulation and the performance characteristics required. After cooling, the sheets are cut with a diamond saw to the size required for the finished assembly.
The hearth, which can hold many sheets at a time, runs on a track and is driven by an electric motor, so it can be moved in and out of the furnace. The heating elements are in a ‘top hat’ structure, which is lowered over the hearth when a charge is being processed and raised at the end of a cycle. |
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The success of the sintering process depends on heating the material to very accurate and uniform temperatures, so the furnaces have been designed to provide a working area within the chamber 200mm wide x 600mm long x 350mm high where temperature uniformity is ±2°C at 1200°C. Access ports allow thermocouples to monitor load temperatures in the chamber.
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Multi-strand heat treatment furnace gives high throughput strip processing
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Azmüsebat, one of Turkey’s biggest razor blade producers, has increased throughput at its factory in Istanbul with the installation of a second specialised heat-treatment furnace from UK manufacturer Carbolite.
The furnace, which is designed to harden and temper four strands of thin stainless steel strip simultaneously in a continuous process, joins an existing unit with similar specifications built by Carbolite three years ago. Processing four strands of strip simultaneously has been found to bring considerable cost/throughput benefits compared with single-strand equipment. When strip 22.5mm wide x 0.1mm thick is processed at 12.5 metres per minute, typical throughput is 50kg/hour.
The equipment is designed to produce sufficient hardness in the strip for it to retain a sharp edge without being brittle and hard to work. The material also has to remain flat at the end of the process, despite the potential for distortion. The 6000mm long hardening section has a maximum temperature of 1150°C and is divided into six independently controlled zones, allowing a temperature profile to be created, generally between 750°C and 1100°C. Temperature uniformity at 1000°C is guaranteed to be better than ±10°C. The power rating allows a fast heat-up to operating temperature from cold.
Each strand runs in a rectangular stainless steel tube, which is designed to minimise friction and is also tensioned to ensure it remains straight when hot. The strip and tubes are protected from corrosion and discolouration by injecting a nitrogen and hydrogen gas mixture into the tubes. After passing through a quench unit, the four strands are tempered in a 1000mm-long section with a maximum operating temperature of 500°C. This section incorporates four special heat transfer plates, designed to give rapid heating and to maintain product flatness and straightness. It also has two heating zones to give accurate control of temperature. After tempering, the four strands are cooled again and coiled.
The furnace has separate control and over-temperature instruments operating off independent thermocouples fitted to each heating zone. The controller is a microprocessor-based PID unit with dual display of set-point and measured value. |
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