Design, Construction and Testing of a Charcoal Fired Crucible Furnace for Melting 10kg of Aluminum
Chapter One
AIM AND OBJECTIVES OF THE WORK
The work aims to improve the technology of local foundry men in the melting of aluminium. The research is expected to come up with a portable, safe and economical crucible furnace, which is going to be used in small-scale casting industries with maximum efficiency (i.e. efficient use of heat energy with minimum loss of heat energy).
The specific objectives of this research are as follows:
- To design a portable charcoal-fired crucible-type furnace that can melt 10 kg of aluminium.
- To construct the furnace using local materials.
- To test the furnace constructed.
- To carry out performance evaluation of the furnace.
CHAPTER TWO
LITERATURE REVIEW
INTRODUCTION
It is clear that despite the advances in the mode of melting metal scrap (aluminum), the charcoal fired crucible furnace is commonly used in Nigeria due to the fact that it can easily be operated, is available all over the country and its construction materials are readily available. The charcoal fuel used is readily available in all parts of the country.
In any foundry, large or small, heat is required to melt different metals and alloys for casting.
This has resulted in the utilization of many types of melting furnaces for ferrous and non-ferrous metals and alloys
A furnace is a device in which the chemical energy of a fuel or electrical energy is converted into heat which is then used to raise the temperatures of materials. Furnaces operating at low temperatures are often called ovens depending on their purposes and there are other furnace used at higher temperatures for various materials and purposes. (Folayan, 2001).
Furnaces are refractory lined vessels that contain the material to be melted and provide the energy to melt it. Modern furnace types include electric arc furnaces (EAF), induction furnaces, cupolas, reverbetory, and crucible furnaces. The furnace choice is dependent on the materials and quantities processed. For ferrous materials, EAFs, cupolas and induction furnaces are commonly used. Reverberatory and crucible furnaces are common for aluminum castings. (Beeley,2001).
A crucible furnace is among the oldest and simplest furnaces used in the foundry; it is primarily used to melt smaller amounts of nonferrous metals but can also be used for ferrous metals. It is mostly used in small foundries or for specialty alloy lines. The crucible or refractory container is heated in a furnace, typically fired with natural gas or liquid propane, although coke, charcoal, oil, or electricity can be used. (www.industrialmetalcasting.com)
A crucible furnace is a type of furnace which uses the crucible as a metal container for melting purposes. The crucible is made from the material of higher refractory properties with higher melting temperature than the materials being melted and it is normally made from clay.
Metals are cast into shapes by melting them, pouring the molten metal into a mold, and removing the molded material or casting after the metal has solidified and cooled. The most common metals processed are aluminum and cast iron. However, other metals, such as bronze,
steel, magnesium, copper, tin, and zinc, are also used to produce castings in foundries. (Beeley 2001).
Folayan (2001), improved on the gas fired crucible type method of melting by designing a coal fired crucible furnace. He observed that charcoal remains the most available fuel as coal is not available in many parts of the country, whereas charcoal is always available everywhere and is cheaper than both gas and coal.
Charles, (2000) constructed an electric line crucible-type aluminum melting furnace featuring quiet “Buzzer” venturi burners. This furnace offers the cleanliness of gas heat, operates economically, does not require the maintenance of compressed air and will continue to operate
during power failures. The furnace consists of sectioned cast iron furnace rings and a steel lined jacket.
Okada, Sasaki and Yoshikawa, (2004) conducted research on the development of an innovative continuous melting and holding crucible furnace. A high performance continuous aluminum smelting and holding crucible furnace was developed. It has a compact single-body combining the features of both a melting and holding crucible furnace. Continuous melting at minimum temperature in a crucible contributes to less generation of aluminum oxide and less metal loss.
The ideal temperature for casting is achieved and higher metal quality with a lower number of hard spots is obtained. The utilization of exhaust heat improves energy saving. The furnace also provides a better work environment and other benefits for the realization of efficient in-house continuous melting and holding of aluminum ingots, and higher returns.
CHAPTER THREE
MATERIALS AND METHODS
Materials and Material Selection.
A large number of materials are available for engineering applications. The choice of amaterial for a given application can determine, to a large extent, the ultimate success or failure of the system as it is the final practical decision in the design process. Hence in selecting the
materials suitable for use in this work, the physical properties of the materials were used as the basic parameters guiding the selection. The factors, properties used include cost effectiveness, availability, high or low tensile, strength as may be required, rigidity and/or flexibility, heat and corrosion resistance, etc.
The following materials were obtained for the construction of the crucible furnace: mild steel sheet of 3mm thickness, mild steel sheet 1.5 mm thickness, iron, charcoal, scrap aluminum, rubber belt, ball bearings, spindle shafts (12 mm) diameter, mild steel angle iron of 5
mm thickness, asbestos, clay sand, stainless steel plate of 2 mm thickness, stainless steel pipe 45 mm diameter, screws, bolts and nuts, aluminum bicycle wheel of (550 mm) diameter. The materials were purchased at Zaria.
Material for the furnace unit
The material used for the furnace is a 3mm thick mild steel sheet selected based on the design calculations and specifications. It was selected to meet the following requirements:
– Ability to withstand internal pressure. Steel possesses high tensile strength ranging from 276Mpa – 2070Mpa (Singh, 2003) which is more than sufficient to withstand the internal pressure developed during operations.
– Ability to withstand the relatively high operational temperature both in the furnace unit and combustion chamber.
– Ease of machining and fabrication.
CHAPTER FOUR
RESULTS
Experimental results
Having fabricated the furnace it was tested in a three different ways to determine the time it takes to raise the temperature up to 660 OC and above for melting of aluminum in each of the tests conducted. The three tests that were conducted are:
1. No load test of the furnace
2. Furnace with Load of 10kg at once test
3. Continuous load test.
The results obtained are as follows
CHAPTER FIVE
DISCUSSION OF RESULTS
From the results obtained from the various (three) test carried out, showed that;
No-load test
During this experiment the furnace was tested with the crucible empty without load of aluminum, Figure 4.1 shows that temperature of the crucible rose from room temperature of 28 OC to the aluminum melting point of 660 OC in 30 min, and it consumed only 1 kg of charcoal.
With load test
Figure 4.2 shows the trend of temperature –time for this experiment, the furnace was tested under the load of 10 kg at once, the load of 10 kg of aluminum was put in to the crucible furnace at once and tested the furnace performance, it was observed that the crucible temperature rose to the melting point of 660 OC in 55 min and it was maintained and held for 10 min while steering the aluminum to ensure the complete melting of aluminum, this test consumed 2.5 kg of charcoal.
CHAPTER SIX
CONCLUSION AND RECOMENDATIONS
CONCLUSION
In developing countries like Nigeria, where job opportunities are very scarce, it is not wise to allow the few operating ones to close down. Therefore, Based on the results obtained from the performance test carried out on the fabricated crucible furnace the set objectives of the research was achieved, such as fuel economy, health hazard reduction and time required for the operation, the following conclusions can also be made:
1. The crucible furnace proved to be effective for melting of aluminum.
2. Melting aluminum in the crucible furnace proved to be more economical and time saving during operation.
3. It can be concluded that the device is suitable for use in small scale foundries and tertiary institutions.
4. The fabricated crucible furnace reached a temperature of 700 OC and produced 67,943.16kJ of heat in 1:33min.
5. The practical performance of the fabricated crucible furnace was in accordance with the efficiency value gotten from the calculation.
This research work has shown that with this simple device, the problem of casting in the small scale foundries in Nigeria will be solved.
RECOMMENDATIONS
1. Further research is recommended to ease the operation of the system.
2. The capacity of the combustion chamber should be increased to accommodate more fuel for longer operation period.
3. A seat should be designed for the operator for convenience of operations.
4. An awareness campaign should be undertaken to encourage the use of crucible furnace
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