The main aim of the paper is to describe the design, functionality and the development of a coreless induction furnace. In administering the task much focus has been given in analyzing the coreless inductor to emphasize on the advantages over channel type inductor. The difference between the two types is the consideration of the technical information to identify the new benefits. Some of the benefits is the increased service life therefore maintenance of the furnace with the crucible inductor. It is important to acknowledge that there are two different types of induction furnaces; one for holding and casting metals while the other is used for smelting iron and steel (metals). These are coreless type induction furnace and channel-type induction surface. The focus of the paper notes the significance of the induction furnace in the steel making industry especially for the small scale production units. When it comes to installation, maintenance and operation, they are the easiest therefore a preference for many. In the coreless furnaces, smelting of the steel is facilitated through a charged material which produces heat from the electromagnetic field.
The paper will also discuss the coreless induction furnace parts which include a crucible, cooling system, shell, coil inductor, and the tilting machinery. The cylindrical crucible is made from the resulting material of the refractory, through which the lining of the coil is performed. The charged material is held by the cylindrical crucible in the subsequent melting processes. When choosing a refractory material determinant of the charge is based on the composition i.e. acidic, alkaline or neutral. Ultimately, the furnace was constructed and the final aim, which is melting the metal, was achieved.
Key words: Induction heating, coreless furnace, Equivalent circuit method.
Operation of Coreless Induction Furnace
Coreless induction furnace is the most popular kind due to its suitability in all the metal industries and more so it’s easy handling as a major advantage. It is for that reason that the paper has picked coreless induction furnace. In description, a coreless induction furnace has been constructed as the simplest unit which is made up of a helically wound coil which surrounds the refractory crucible that holds the molten charge. It follows a connection to the alternating excit ation system. Excitation occurs in the coil through alternating current which prompts the production of an axial magnetic field. The produced magnetic field experiences a variation resulting to a field of electric and eddy currents in the concentric paths on the axis. A rapid attenuation of the electromagnetic field is charged. In a computation, the determination of the depth of the induced decline of the density (/e) attests to its surface value. The formula applied in this computation
eddy currents are concentrated at the outer surface of the charge due to skin effect and heat is developed by the conventional ohmic losses.
Some of the heat produced in the furnace is lost to the surrounding medium, while the remnant is evenly distributed across the mass of charge in the effect of the thermal conduction. Additionally, there is a skin effect as a product which is distributed throughout the coil conductor.
A proximity effect is developed as a phenomenal occurrence due to the un-uniformity of the coil as the greatest current density is prompted in the sectional unit that lie so close to the charge. Following the above discussion it is evident that an induction furnace is developed on the basis of four principles i.e. Electromagnetic induction, skin effect, heat transfer and proximity effect.
Coreless induction furnaces are developed through a conceptual design of a cylindrical crucible encircled by charge coil where energy supply emanates directly or through the frequency converter. The surrounding coils generate the magnetic field which transfers the energy to the charge.
At the epicenter of the coreless induction furnace is the coil; it is composed of a depressed section of heavy duty facilitating high conductivity of the copper tubing that makes up the helical coil. The coil takes the shape that fits within the steel shell. In order to protect the coil from overheating cooling using the water is effected through recirculation from a cyclic cooling tower.
The crucible formation is done through ramming of a granular refractory that is found in between the coil and the internal void. All grades of steel and iron are the most raw materials used in the coreless induction furnace and undergo melting. In addition, non-ferrous alloys can be melted in the coreless induction furnace. It has proven to be an ideal furnace to facilitate remelting and alloying as it has a high capability to control exceeding temperatures and balance the chemistry composition. At the same time, the furnace inducts current providing a good circulation of the melt substance.
Radio frequency (RF) energy prompts a unique feature in part of the electromagnetic spectrum under infrared and microwave energy. This is because of the transferring of the produced heat via the electromagnetic waves since it never comes into contact with flame.
Usually to enable the functionality of the induction furnace there occurs a rapid, but non-polluting heat. However, the recirculation of the cooling water ensures that the induction coil remains cool throughout to avoid building up of heat.
FEATURES OF INDUCTION FURNACE
A coreless induction furnace is a electric and requires a electric enable coil to help in the production of a charge. Coils have the potential to fail and therefore are replaced. The failure of a coil can render a coreless induction furnace useless since no charge can be produced therefore unable to operate.
A crucible with the cylindrical structure that holds the melt steel is made of heavy duty material to resist the high heating temperatures. The use of a poor metal in the crucible lacks the ability to resist the immense heat. To ensure optimal resistance of the crucible the coil is usually cooled to prevent overheating (Ambade 153-160).
In consideration of the difference in level of productions, there are a range of induction furnace sizes that can handle low production to mass production of clean metal through smelting. The different sizes of induction furnaces also helps I various applications in the in the industry. There is a high advantage of using an induction furnace. One, it helps in the production of clean metal, achieve energy efficiency and has a well managed melting process that is easily controlled; no complexities involved. It is the best mean of metal melting in comparison to other available alternatives.
Due to their easy maintenance, the coreless induction furnaces are now used in the foundries and replacing the cupolas to facilitate the melting of cast iron. This is because the cupolas have been found to produce a lot of dust during the melting process thus significantly contributing to environmental pollution. On the other hand, the induction furnace is clean, therefore environmental friendly (Dey Vol 32)
With all the goodness found in the coreless induction furnaces, there is a major drawback that has been identified in its application in the foundry. The furnace lacks the capacity refine the final products.
The coreless induction furnace is made of technical and economical features. Each of the features has their functions to perform.
The technical feature assists in the adjustment of temperature and control processes. Another feature helps achieves high analytical accuracy and reproducibility, keeping check of the high melting rates and operational flexibility. The management of the melting point suitability is performed by the technical features and they have the capacity to handle a wide range of diversity of raw material compositions in alternation mode. The technical features allow maximum and effective management of metallurgical selectiveness capacity (Moreira et al 415-419).
The economic features relate to the enhancement of induction furnace efficiency in terms of energy and waste heat reduction. Through the installed features, there is a huge set of low energy consumption leading to maximum production. Waste heal is no longer a significant concern as the furnace experiences extremely low loss of melting heat. A coreless induction furnace is readily available, comes with a minimal installation cost in comparison to other furnace systems. Additionally, the ease in its maintenance and handling makes it a preference for many smelting companies (Moreira et al 415-419).
ADVANTAGES OF INDUCTION FURNACE
Coreless induction furnaces have been found to offer numerous advantages in comparison with other developed furnace systems. Some of the advantages realized by the users include
Production of high yields since it drastically reduces the oxidation losses which are significant in the production economics.
Faster start up procedure upon the availability of reliable power supply. The instant ability to startup helps in reducing the duration for optimal temperature required in the process.
The higher level of flexibility as no molten metal is needed to initiate the medium frequency of the coreless induction melting equipment. It helps in facilitating a repetitive cold start and the frequent changes of the alloys.
The induction furnaces provide a better working environment in that they are quieter than other gas furnaces, cupolas and arc furnaces. The lack of combustion gas helps in minimizing the loss of heat. In regards to energy conservation, coreless induction furnaces are the best due to their efficiency as the melting rates range from 55-75%.
DISADVANTAGES OF INDUCTION FURNACE
Induction furnaces lack the capacity to facilitate intensive refinement of the metal product as in Electric Arc Furnace (EAF). Secondly, it illustrates a low refractory lining in comparison to the EAF and selection of charges must be administered to produce final products with minimal impurities.
Coreless induction furnace has an advanced high-power medium frequency that is made up of the following features i.e.
Melting furnace, comprising
Furnace body including coil
Furnace tilting cradle (optional backward tilting)
Hydraulic power pack
Operator control desk
Electric power supply system, comprising
Process control system, comprising
Auxiliary and ancillary equipment,
Water recooling system with air cooler / cooling tower
Dust collection system
Charge make-up system
Crucible ejector system
Evaluation of Frequency
During the operation of a coreless induction furnace, eddy currents are produced due to the built up charge and as a result it prompts a stirring action. To improve the performance frequency, laminations of iron are provided externally so as to provide a primary wound that helps the creation of low reluctance platform for flux. It also contains a path to direct induced heavy currents to the stray field. The size of the furnace is used to determine the level of frequency to be employed (Moreira et al 415-419).
For furnaces with low capacities usually a higher frequency capacity is employed to an order of 3000Hz while those of higher capacity are brought down to 600Hz. Hollow copper tubes are wound in the water holding compartment to reduce losses of the metal.
In reference to the medium frequencies developed in the induction furnaces, the level of efficiency in production is expressed by taking to account the total, heat transfer and the deductible electrical loss achieved in the process. To accord a typical balancing of the equation, the electrical losses of transformers are considered, the condenser, coil, cable unit and the frequency converter. The heat loss experienced through conductivity of the furnace wall and the coil side causes radiation effect increasing the loss of heat from the melt surface. In order to reduce the prevalence heat loss, cooling water is directed to the coil through recirculation. Through the intervention heat efficiency is achieved since high and medium frequencies are attained in the furnace. Usually it is around (60%-70%) and for low frequencies furnace (58%-71%).
The refractory system succumbs to deterioration that occurs to a rubber tire. The feature is consumable as it gradually wears out. To resolve the problem and therefore requires to repair the lining to their minimum thickness to prevent failure.
The wearing out of the lining is referred to sidewall wear. This is due to thermal stress and continuous churning (stirring) of liquid metal.
Coreless induction furnace has a bottom that is prone to damage due to severe heat stress. The bottom is usually exposed to consistent chemical attack and has a severe damage on the weight charge (Fong).
When the features of an induction furnace fail they pose a risk to the workforce and also the environment. In many times the metal works are always risky and the workers are vulnerable to numerous kinds of accidents. Though improved designs the furnaces have been constructed in consideration of occupational safety and hazards to provide good working and safe environments. The designers have put focus in building energy efficiency furnaces that provide less hostile working environments. With recent increased concern for the natural environment, models and kits to help reduce noise and pollutant emissions have been incorporated to develop a healthy and clean production. However, it should be noted that despite the numerous measures to improve on safety and efficiency dangers have not been inherently eliminated. More especially workers should avoid being in close proximity to the molten metal.
Following the usual practice, checking the level of temperatures was used through tapping of heat manually using shovels or pressing of bundles of the low grade scrap. To ensure safety of the workers and avoid getting close to the molten metal, there is need for the use of safety measures such as using help of crane filled with low grade scrap and spreading them over the furnace space. As a result, the charge does not become dense since the furnace does not draw sufficient power.
Control on Furnace Power during De-slagging Operations
In reference to the power of the furnace, there need to making of control panels in the moments of de-slagging the molten bath.
Once the solid scrap (raw materials) will still be held in the bath, allowing the reduction of power in the potentiometer settings, the incorporation of this will lead to the prevention of overheating of the molten.
Globally, the designing of induction furnaces and rapid development and immense increase in the last decades. Significant growth in the sector has been noted in the utilization of the wind power. A number of factors that has contributed to the increasing drive in the sector that has seen the improvement in the wind turbine technology are rising environmental concern, especially climate change, cost reduction, and interest in decreasing reliance on non-renewable sources of energy (Kipepe 64-73)
By 2009, 86% of the total installed capacity can be accounted for the three markets. Despite the fact that the cost variation in the installation of the furnaces for steel production is trending globally, thus the use of coreless induction furnace in comparison to the channel-type induction surfaces and it is becoming more economical and competitive. Due to the economical benefits advantages that come with the use of coreless induction furnace it is the best alternative and a preference of the furnace and so far ascertains sustainability with no much complications in their maintenance.
The induction furnace and the industry have recorded much proliferation in advancement and can be considered to be the fastest growing industry. The amplified permeation of increased research in the improvement of the furnace has prompted efficiency and forges towards sustainability of the steel and iron industry (Tan and Bayindir 239-253). The relevant grid requirements need furnaces to perform correspondingly to improved melt plants. Particularly the necessities for the designing of induction furnaces to stay in connection to help the development of a technical empower to go beyond the prospective challenges in designing of induction furnaces. Coupled with challenges in the last decades, researchers has been motivated and prompted studies to be conducted focused on the development of improved induction furnaces and modern designs and control panels for purposes of efficiency and increase its’ potential to produce enough energy. It will also ensure all the grid requirements have met (Fong).
The paper has put focus on the development of improvement efficiency in steel melting industry. Through the analysis of the coreless induction furnace it is evident that the major concern is in reference to heat loss and energy efficiency. Considerably, there are milestone achievements to improve the efficiency of the induction surfaces. The paper has made recommendations molten metal delivery, preheating, and scheduling of operations.
Referring to the case of the coreless furnace induction has had significant fall backs in the system caused by ignorance of observing the lab safety guidelines to a point of unethical behavior that can lead to misdiagnosis of the subjects under their care. The company has an issue with its culture as illustrated.
On further assessment another problem exists. To ensure occupational safety labeling is critical and of great importance in ensuring the right specimen for a particular subjected is easily identifiable to avoid a mix up which could be detrimental. Instead of acquiring another system the staff compensates the only effective technique to track the achievements to proof of the unsafe practices in the industry which goes against the professionalism of working in a occupational hazards.
Notably, lab safety, rule and guidelines are being taken for granted by the staff. Rene notices that some of the staff taking food stuff in the lab which is very unhealthy and even unethical as they put a risk to their own life. Again, the protective gear is specifically meant for workforce uses only and should remain in the confines of the slide wall. Wearing the protective gear outside the smelt factory goes against the rules and guidelines that ascertain safety. It poses a threat of contamination of the safe environment from the external environment.
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