A small-scale mobile jaw-crusher unit with a throughput of 1-1.5 tons of aggregates per hour has been designed, manufactured and tested at the Department of Chemical and Processing Engineering, University of Dar es Salaam. The equipment is aimed at reducing the drudgery and hardships faced by artisanal miners, mostly women, who spend long hours in quarrying sites excavating and crushing aggregates using manual tools.
The aim was to design a low-cost unit powered by bicycle pedals however this objective was defeated by economic constraints like labor cost and product price, as well as, technical limitation of the human physique and stamina to sustain pedaling of heavy inertial flywheels required to overcome the actual load and intermittent shock-loads. Instead a simple air-cooled engine 2.94 kW was used causing a 25% increase in investment cost but had 6 fold improvement in productivity over bicycle power and 30 fold boost over manual tools like sledge hammer, pickaxe and crowbars previously used by miners.
The crusher was successfully field tested for 3 months by Umoja ni Nguvu women group at Kunduchi Mtongani quarry site to crush 6-8” limestone rocks to aggregates of various sizes ½”, ¾” and 1” required for road and building construction of roads on the outskirts of Dar es Salaam city. Based on the field data and an investment cost of Tshe 3.5 million, a financial profitability analysis indicated that the crusher project has a daily net-inflow of Tshs 259 thousand and a pay-back period of two months. Since the unit requires low level of technical skills and is not capital intensive it is recommended for micro- and medium scale aggregates miners and can be deployed in peri-urban quarries or remote villages without electricity grid.
The technology and equipment for size reduction such as jaw- crushers , gyratory crushers, hammer mills, and ball mills have been in application for the past 70 years (Coulson and Richardson, 1999). Some are automated and operated by open- or closed-circuit grinding mode which includes conveyer belts, bucket elevators and screening and classification equipment. Due to its capital intensiveness, the application of size reduction technology in Sub-Saharan Countries has been limited to few players mainly international foreign companies which construct roads, build houses, or operate large-scale mining . In the middle of 1990s Tanzania witnessed a huge upswing of building construction activities which created a demand for aggregates beyond that could be supplied by existing large-scale quarries. This prompted a new vocation of aggregate miners, mostly women, who use manual tools like pickaxe, crow-bars and sledge hammers to mine and process limestone or granite rocks to feed the booming construction industry
Crushing and grading limestone aggregate products.
In Tanzania artisanal aggregate quarrying activities can be seen almost everywhere in small towns and big cities like Dar es Salaam, Mwanza and Arusha where men, women and children work round the clock in quarry sites. In Dar es Salaam they scavenge limestone rocks left behind by large-scale miners in open-pit mines located in Kunduchi Mtongani, Boko and Salasala areas. In Arusha they crush granite stones in semi-commercial quarries in Sombetini and Sakina areas located a few metres off the Arusha-Nairobi highway. It is estimated that more than 15,000 people countrywide earn their livelihood through artisanal quarrying activities (Elisante, 2003).
In developed countries the construction of roads and houses is undertaken by large-scale contractors, who procure bulk aggregates from commercial quarries. A typical jaw-crusher grinding 3-20 tons per hour costs US$ 20-50,000 for equipment (MachineRoll, 2008); plus US$ 20,000 for working shade, concrete foundation and purchase of 25-50 Hp prime movers. Due to high capital cost the technology it is not very affordable in developing countries like Tanzania. As a result, there have been attempts to de-scale jaw-crushers and other size reduction equipment to match budgets of small-scale miners or road contractors using labor based technologies. The
New Dawn Engineering of South Africa developed a manually operated portable jaw-crusher (Crispin, 1997); which costs about US$ 3,000. However the crusher has a low throughput producing about one ton per day and is physically tasking requiring two people to operate comfortably. In this work a simple jaw-crusher is proposed and developed for small-scale aggregate miners,
the aim is to simplify complex and massive large-scale equipment to obtain a technology that can be manufactured using technical skills and engineering resources (Peters et al., 2005) available in developing countries.
For the sake of brevity, detailed engineering issues pertaining to design and manufacture of components and sub-systems are not included here, only major issu es like choice of technology and estimation of power requirements are reported, other pertinent information is outlined in Itika and Elisante (2004).
Although miners earn their livelihoods (Jambiya et al., 1997) through sale of aggregates, the occupation is undertaken under adverse conditions and characterized by:
1. Low productivity as it takes a man 3 weeks and a woman 4 weeks to produce a 7 ton lorry of limestone aggregates worth US$ 80 less production costs.
2. Health risks and safety hazards that cause bodily injury of fingers by sledge hammers, eye injury from flying stone chips, and respiratory ailments due to dust inhalation (Elisante, 2003).
3. Drudgery and hardship involving over 10 hours per day of toiling on hot sunshine.
Simplification of Jaw crusher for Artisanal Aggregates Miners
Simplification of Jaw crusher for Artisanal Aggregates Miners
A small-scale mobile jaw-crusher unit with a throughput of 1-1.5 tons of aggregates per hour has been designed, manufactured and tested at the Department of Chemical and Processing Engineering, University of Dar es Salaam. The equipment is aimed at reducing the drudgery and hardships faced by artisanal miners, mostly women, who spend long hours in quarrying sites excavating and crushing aggregates using manual tools. The aim was to design a low-cost unit powered by bicycle pedals however this objective was defeated by economic constraints like labor cost and product price, as well as, technical limitation of the human physique and stamina to sustain pedaling of heavy inertial flywheels required to overcome the actual load and intermittent shock-loads. Instead a simple air-cooled engine 2.94 kW was used causing a 25% increase in investment cost but had 6 fold improvement in productivity over bicycle power and 30 fold boost over manual tools like sledge hammer, pickaxe and crowbars previously used by miners.
The crusher was successfully field tested for 3 months by Umoja ni Nguvu women group at Kunduchi Mtongani quarry site to crush 6-8” limestone rocks to aggregates of various sizes ½”, ¾” and 1″ required for road and building construction of roads on the outskirts of Dar es Salaam city. Based on the field data and an investment cost of Tshe 3.5 million, a financial profitability analysis indicated that the crusher project has a daily net-inflow of Tshs 259 thousand and a pay-back period of two months. Since the unit requires low level of technical skills and is not capital intensive it is recommended for micro- and medium scale aggregates miners and can be deployed in peri-urban quarries or remote villages without electricity grid.
INTRODUCTION
The technology and equipment for size reduction such as jaw- crushers , gyratory crushers, hammer mills, and ball mills have been in application for the past 70 years (Coulson and Richardson, 1999). Some are automated and operated by open- or closed-circuit grinding mode which includes conveyer belts, bucket elevators and screening and classification equipment. Due to its capital intensiveness, the application of size reduction technology in Sub-Saharan Countries has been limited to few players mainly international foreign companies which construct roads, build houses, or operate large-scale mining . In the middle of 1990s Tanzania witnessed a huge upswing of building construction activities which created a demand for aggregates beyond that could be supplied by existing large-scale quarries. This prompted a new vocation of aggregate miners, mostly women, who use manual tools like pickaxe, crow-bars and sledge hammers to mine and process limestone or granite rocksto feed the booming construction industry.
Although miners earn their livelihoods (Jambiya et al., 1997) through sale of aggregates, the occupation is undertaken under adverse conditions and characterized by:
1. Low productivity as it takes a man 3 weeks and a woman 4 weeks to produce a 7 ton lorry of limestone aggregates worth US$ 80 less production costs.
2. Health risks and safety hazards that cause bodily injury of fingers by sledge hammers, eye injury from flying stone chips, and respiratory ailments due to dust inhalation (Elisante, 2003).
3. Drudgery and hardship involving over 10 hours per day of toiling on hot sunshine.
Estimation of power requirements
The major challenge faced in developing the crusher was to choose the appropriate power source and thus size of equipment. Too high power input from electric motors or diesel engines may give equipment with high throughputs but too expensive to be affordable by the target group.
On the other hand, low power input from humans or animals may result into a cheaper crusher but with low productivity comparable to manual tools (Elisante and Itika, 2004). In general size reduction equipment are highly energy intensive whereby it is estimate that only 0.1-2% of energy is utilized effectively (Coulson and Richardson, 1999), the rest is lost as sound, heat and friction. Efficiency depends on the magnitude and manner of energy application, that is, compressive, impact, shear or attrition.
Choice of technology
The basic data and information gathered from Kunduchi Mtongani quarry site such as type of tools and techniques used by artisanal miners (Table 1) formed the basis for design of the jaw-crusher. However the choice of technology was also influenced by a matrix of other socio-economic and technical factors like:
1. Gender non-displacement due to introduction of new technology.
2. Feed size of 3-6 inches consistent with existing techniques and tools used by miners as shown in Table 1.
3. Product size range of ½-1 inch consumed by the local construction industry.
4. A throughput that is economical in terms of time and investment.
5. Wide applicability to crush different rocks from softer materials like gypsum and dolomite to hard and abrasive like quartz, limestone and granite.
Conclusion and Recommendations
A mobile jaw-crusher unit has been developed for artisanal aggregates mining. The unit is suitable for application in labor-based road construction projects, low-cost housing sector and in small-scale mining such as:
i) Crushing gold ore prior to panning.
ii) Crushing limestone or dolomite before burning in kilns.
iii) Crushing coal lumps for briquette making.
The crusher has been field tested for crushing limestone rocks and was found to be technical viable and economically feasible with a pay-back period of two months. The engine seemed to perform well based on field observation like sound during heavy loads and absence of over-heating even for non-stop crushing of 3-4 h. However more tests are needed to validate the engine using different raw-material like gold ore, gypsum or granite which has a higher working index and abrasion index compared to limestone as shown in Table 2.
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Simplification of Jaw crusher for Artisanal Aggregates Miners
A small-scale mobile jaw-crusher unit with a throughput of 1-1.5 tons of aggregates per hour has been designed, manufactured and tested at the Department of Chemical and Processing Engineering, University of Dar es Salaam. The equipment is aimed at reducing the drudgery and hardships faced by artisanal miners, mostly women, who spend long hours in quarrying sites excavating and crushing aggregates using manual tools.
The aim was to design a low-cost unit powered by bicycle pedals however this objective was defeated by economic constraints like labor cost and product price, as well as, technical limitation of the human physique and stamina to sustain pedaling of heavy inertial flywheels required to overcome the actual load and intermittent shock-loads. Instead a simple air-cooled engine 2.94 kW was used causing a 25% increase in investment cost but had 6 fold improvement in productivity over bicycle power and 30 fold boost over manual tools like sledge hammer, pickaxe and crowbars previously used by miners.
The crusher was successfully field tested for 3 months by Umoja ni Nguvu women group at Kunduchi Mtongani quarry site to crush 6-8” limestone rocks to aggregates of various sizes ½”, ¾” and 1” required for road and building construction of roads on the outskirts of Dar es Salaam city. Based on the field data and an investment cost of Tshe 3.5 million, a financial profitability analysis indicated that the crusher project has a daily net-inflow of Tshs 259 thousand and a pay-back period of two months. Since the unit requires low level of technical skills and is not capital intensive it is recommended for micro- and medium scale aggregates miners and can be deployed in peri-urban quarries or remote villages without electricity grid.
The technology and equipment for size reduction such as jaw- crushers , gyratory crushers, hammer mills, and ball mills have been in application for the past 70 years (Coulson and Richardson, 1999). Some are automated and operated by open- or closed-circuit grinding mode which includes conveyer belts, bucket elevators and screening and classification equipment. Due to its capital intensiveness, the application of size reduction technology in Sub-Saharan Countries has been limited to few players mainly international foreign companies which construct roads, build houses, or operate large-scale mining . In the middle of 1990s Tanzania witnessed a huge upswing of building construction activities which created a demand for aggregates beyond that could be supplied by existing large-scale quarries. This prompted a new vocation of aggregate miners, mostly women, who use manual tools like pickaxe, crow-bars and sledge hammers to mine and process limestone or granite rocks to feed the booming construction industry
Crushing and grading limestone aggregate products.
In Tanzania artisanal aggregate quarrying activities can be seen almost everywhere in small towns and big cities like Dar es Salaam, Mwanza and Arusha where men, women and children work round the clock in quarry sites. In Dar es Salaam they scavenge limestone rocks left behind by large-scale miners in open-pit mines located in Kunduchi Mtongani, Boko and Salasala areas. In Arusha they crush granite stones in semi-commercial quarries in Sombetini and Sakina areas located a few metres off the Arusha-Nairobi highway. It is estimated that more than 15,000 people countrywide earn their livelihood through artisanal quarrying activities (Elisante, 2003).
In developed countries the construction of roads and houses is undertaken by large-scale contractors, who procure bulk aggregates from commercial quarries. A typical jaw-crusher grinding 3-20 tons per hour costs US$ 20-50,000 for equipment (MachineRoll, 2008); plus US$ 20,000 for working shade, concrete foundation and purchase of 25-50 Hp prime movers. Due to high capital cost the technology it is not very affordable in developing countries like Tanzania. As a result, there have been attempts to de-scale jaw-crushers and other size reduction equipment to match budgets of small-scale miners or road contractors using labor based technologies. The
New Dawn Engineering of South Africa developed a manually operated portable jaw-crusher (Crispin, 1997); which costs about US$ 3,000. However the crusher has a low throughput producing about one ton per day and is physically tasking requiring two people to operate comfortably. In this work a simple jaw-crusher is proposed and developed for small-scale aggregate miners,
the aim is to simplify complex and massive large-scale equipment to obtain a technology that can be manufactured using technical skills and engineering resources (Peters et al., 2005) available in developing countries.
For the sake of brevity, detailed engineering issues pertaining to design and manufacture of components and sub-systems are not included here, only major issu es like choice of technology and estimation of power requirements are reported, other pertinent information is outlined in Itika and Elisante (2004).
Although miners earn their livelihoods (Jambiya et al., 1997) through sale of aggregates, the occupation is undertaken under adverse conditions and characterized by:
1. Low productivity as it takes a man 3 weeks and a woman 4 weeks to produce a 7 ton lorry of limestone aggregates worth US$ 80 less production costs.
2. Health risks and safety hazards that cause bodily injury of fingers by sledge hammers, eye injury from flying stone chips, and respiratory ailments due to dust inhalation (Elisante, 2003).
3. Drudgery and hardship involving over 10 hours per day of toiling on hot sunshine.
Simplification of Jaw crusher for Artisanal Aggregates Miners
Simplification of Jaw crusher for Artisanal Aggregates Miners
A small-scale mobile jaw-crusher unit with a throughput of 1-1.5 tons of aggregates per hour has been designed, manufactured and tested at the Department of Chemical and Processing Engineering, University of Dar es Salaam. The equipment is aimed at reducing the drudgery and hardships faced by artisanal miners, mostly women, who spend long hours in quarrying sites excavating and crushing aggregates using manual tools. The aim was to design a low-cost unit powered by bicycle pedals however this objective was defeated by economic constraints like labor cost and product price, as well as, technical limitation of the human physique and stamina to sustain pedaling of heavy inertial flywheels required to overcome the actual load and intermittent shock-loads. Instead a simple air-cooled engine 2.94 kW was used causing a 25% increase in investment cost but had 6 fold improvement in productivity over bicycle power and 30 fold boost over manual tools like sledge hammer, pickaxe and crowbars previously used by miners.
The crusher was successfully field tested for 3 months by Umoja ni Nguvu women group at Kunduchi Mtongani quarry site to crush 6-8” limestone rocks to aggregates of various sizes ½”, ¾” and 1″ required for road and building construction of roads on the outskirts of Dar es Salaam city. Based on the field data and an investment cost of Tshe 3.5 million, a financial profitability analysis indicated that the crusher project has a daily net-inflow of Tshs 259 thousand and a pay-back period of two months. Since the unit requires low level of technical skills and is not capital intensive it is recommended for micro- and medium scale aggregates miners and can be deployed in peri-urban quarries or remote villages without electricity grid.
INTRODUCTION
The technology and equipment for size reduction such as jaw- crushers , gyratory crushers, hammer mills, and ball mills have been in application for the past 70 years (Coulson and Richardson, 1999). Some are automated and operated by open- or closed-circuit grinding mode which includes conveyer belts, bucket elevators and screening and classification equipment. Due to its capital intensiveness, the application of size reduction technology in Sub-Saharan Countries has been limited to few players mainly international foreign companies which construct roads, build houses, or operate large-scale mining . In the middle of 1990s Tanzania witnessed a huge upswing of building construction activities which created a demand for aggregates beyond that could be supplied by existing large-scale quarries. This prompted a new vocation of aggregate miners, mostly women, who use manual tools like pickaxe, crow-bars and sledge hammers to mine and process limestone or granite rocksto feed the booming construction industry.
Although miners earn their livelihoods (Jambiya et al., 1997) through sale of aggregates, the occupation is undertaken under adverse conditions and characterized by:
1. Low productivity as it takes a man 3 weeks and a woman 4 weeks to produce a 7 ton lorry of limestone aggregates worth US$ 80 less production costs.
2. Health risks and safety hazards that cause bodily injury of fingers by sledge hammers, eye injury from flying stone chips, and respiratory ailments due to dust inhalation (Elisante, 2003).
3. Drudgery and hardship involving over 10 hours per day of toiling on hot sunshine.
Estimation of power requirements
The major challenge faced in developing the crusher was to choose the appropriate power source and thus size of equipment. Too high power input from electric motors or diesel engines may give equipment with high throughputs but too expensive to be affordable by the target group.
On the other hand, low power input from humans or animals may result into a cheaper crusher but with low productivity comparable to manual tools (Elisante and Itika, 2004). In general size reduction equipment are highly energy intensive whereby it is estimate that only 0.1-2% of energy is utilized effectively (Coulson and Richardson, 1999), the rest is lost as sound, heat and friction. Efficiency depends on the magnitude and manner of energy application, that is, compressive, impact, shear or attrition.
Choice of technology
The basic data and information gathered from Kunduchi Mtongani quarry site such as type of tools and techniques used by artisanal miners (Table 1) formed the basis for design of the jaw-crusher. However the choice of technology was also influenced by a matrix of other socio-economic and technical factors like:
1. Gender non-displacement due to introduction of new technology.
2. Feed size of 3-6 inches consistent with existing techniques and tools used by miners as shown in Table 1.
3. Product size range of ½-1 inch consumed by the local construction industry.
4. A throughput that is economical in terms of time and investment.
5. Wide applicability to crush different rocks from softer materials like gypsum and dolomite to hard and abrasive like quartz, limestone and granite.
Conclusion and Recommendations
A mobile jaw-crusher unit has been developed for artisanal aggregates mining. The unit is suitable for application in labor-based road construction projects, low-cost housing sector and in small-scale mining such as:
i) Crushing gold ore prior to panning.
ii) Crushing limestone or dolomite before burning in kilns.
iii) Crushing coal lumps for briquette making.
The crusher has been field tested for crushing limestone rocks and was found to be technical viable and economically feasible with a pay-back period of two months. The engine seemed to perform well based on field observation like sound during heavy loads and absence of over-heating even for non-stop crushing of 3-4 h. However more tests are needed to validate the engine using different raw-material like gold ore, gypsum or granite which has a higher working index and abrasion index compared to limestone as shown in Table 2.