by robert g. sperry m.s. graduate john h. wilhoit extension associate professor dave ash
Post on 23-Feb-2016
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B YR O B E R T G . S P E R R Y
M . S . G R A D U AT E
J O H N H . W I L H O I T E X T E N S I O N A S S O C I AT E P R O F E S S O R
D AV E A S HE N G I N E E R A I D
B I O S Y S T E M S A N D A G R I C U LT U R A L E N G I N E E R I N G ,U N I V E R S I T Y O F K E N T U C K Y
2 0 1 2
DEVELOPMENT AND EVALUATION OF A BURLEY TOBACCO MECHANICAL STRIPPING
CONCEPT UTILIZING STRING TRIMMERS
Standard Labor Requirements for Burley TobaccoOperations Labor
Required, Conventional (wk*hr/ac)
Labor Required, Enhanced (wk*hr/ac)
Plant Production
6 2
Field Prep. & Cult.
22 22
Transplanting 11 11Topping 8 8Cutting 26 26Load & Haul 8 8House 26 14Cure 3 3Bulk & Load 12 12Strip & Bale 73 51Load & Market 2 2Total 197 159
Standard Labor Requirements for Burley TobaccoOperations Labor
Required, Conventional (hours/acre)
Labor Required, Enhanced (hours/acre)
Plant Production
6 2
Field Prep. & Cult.
22 22
Transplanting 11 11Topping 8 8Cutting 26 26Load & Haul 8 8House 26 14Cure 3 3Bulk & Load 12 12Strip & Bale 73 51Load & Market 2 2Total 197 159
Harvesting (48-60 wk*hr/ac) and stripping (51-73 wk^hr/ac) are by far the biggest labor requirements
Operations Labor Required, Conventional (hours/acre)
Labor Required, Enhanced (hours/acre)
Plant Production
6 2
Field Prep. & Cult.
22 22
Transplanting 11 11Topping 8 8Cutting 26 26Load & Haul 8 8House 26 14Cure 3 3Bulk & Load 12 12Strip & Bale 73 51Load & Market 2 2Total 197 159
Grading
Based on stalk position
Each grade takes up a length of stalk
Leaves for each grade stripped off by hand seperately
Manually stripping tobacco is very labor intensive
New Method
Combining major elements of proven systems Straight line conveyors Plants conveyed at even spaces Grading based on stalk position
●Using new tobacco stripping technology String trimmers to remove leaves Flexible brushes to align leaves
Basic configuration of stripping machine concept
Leaf Alignment
Brushes used for aligning and holding leaves
Cams open brushes to allow stripped leaves to fall
Leaf Alignment
Brushes used for aligning and holding leaves
Video
Objectives
Develop a mechanical system for removing a single grade of burley tobacco from the stalk utilizing string trimmer technology.
Determine the best combination of motor speeds and string lengths for optimal stripping efficiency.
Strip tobacco leaves into three appropriate grades based on stalk position and linear progression along the length of the machine using multiple string trimmers.
Evaluate the stripped leaves for damage due to shredding by classifying potential losses.
Coverage
5 in. string (7 in. radius) 7 in. string (9 in. radius) 9 in. string (11 in. radius)
Single Grade Testing Procedure
String length
(in.)Motor speeds (rpm)
5 3000 3400 3800 4200
7 2800 3000 3200 3500
9 2200 2500 2800 3000
5 in. String 7 in. String 9 in. String
Strip first 14 in. Strip first 12 in. Strip first 10 in.
Leave 10 in. Leave 14 in. Leave 18 in.
Strip the rest Strip the rest Strip the rest
Resulting Efficiencies
Motor Speed (rpm)
3000 3400 3800 4200
Trial 1 49.9 74.4 92.0 96.7
Trial 2 73.4 42.2 91.8 91.6
Trial 3 62.1 66.2 94.8 84.8
Average 61.8 60.9 92.9 91.0
5 IN. STRING LENGTH
Motor Speed (rpm)
2800 3000 3200 3500
Trial 1 86.4 95.2 91.0 84.8
Trial 2 96.1 97.2 96.4 93.2
Trial 3 82.6 94.7 91.7 92.3
Average 88.4 95.7 93.0 90.1
7 IN. STRING LENGTH
Motor Speed (rpm)
2200 2500 2800 3000
Trial 1 68.5 95.5 95.8 99.3
Trial 2 79.1 92.3 97.0 96.2
Trial 3 53.3 94.2 95.2 95.6
Average 67.0 94.0 96.0 97.0
9 IN. STRING LENGTH
Machine Stripping 3 Grades
Flyings are removed by hand
Lug, leaf and tip are removed with string trimmers
7 in. string length used for proper coverage and grading on 44 in. plant
3 Grade Machine Stripping Results
Plant Efficiency (%)
Average Efficiency
194.6
97.0%
298.0
394.1
498.3
596.7
697.8
798.0
899.8
995.8
Note: The stripping efficiency results for plant 10 contained an error and were left out.
Leaf Damage
Small pieces make up 5.6% of total weight removed
Particle Distribution
PlantStripping Efficiency
(%)
Whole Leaf Particles
(%)
Particles larger than 1x1 in. but
smaller than whole leaves
(%)
Particles 1x1 in. and
smaller (%)
1 97.6 81.8 6.2 11.92 95.7 91.6 3.5 4.93 92.5 95.5 1.9 2.54 99.3 89.5 3.5 7.05 97.2 89.7 4.5 5.86 99.8 89.7 5.0 5.37 99.7 91.9 3.4 4.78 93.9 93.4 3.1 3.59 94.8 91.3 4.3 4.3
10 98.4 86.5 7.3 6.1Average 96.9% 90.1% 4.3% 5.6%
Conclusions
Significant difference in efficiency for faster speeds at given string length
Results for 3 grade stripping with 4th grade stripped by hand showed 97% efficiency
Particle size distribution test results showed 5.6% by weight pieces smaller than 1 in. x 1 in.
With modifications, the current setup could be turned into a fully operational field prototype with the potential to significantly reduce stripping labor requirements.
Potential Productivity
Conveyor Speed was timed: 2.73 s/plant (cups holding plants spaced 24 in. apart)
With two people hand-stripping flyings and feeding machine, each person would process 1 plant/5.5 s
Potential productivity: Assume 85% field efficiency Approximately 1100 plants/hr 370 lb/hr Approximately 3,000 lbs per 8 hour day Approximately 1.25 acres stripped per day (depending on yield)
With 4 person crew stripping rate is 26 wkr*hr/ac Conventional hand stripping 51-73 wkr*hr/ac
Cost and Payback
Labor costs for crew of workers are $10-15 per hour per worker
Potential savings with this machine $5,000/year for 20 acre crop at $10/hr labor rate
At $15/hr, savings could be $7,500/year
If machine cost $10,000, pay back period could be 1.5 to 2 years, twice that if cost is $20,000
Further work needed to develop operational prototype
Automatic opening and closing of stalk-holding cups for faster loading
Automatic ejection of stalks from stalk-holding cups
Automatic opening of brushes to eject detached leaves
Shielding between grades
Possible conveyor speed variations
More detailed look into the power requirements and usage
Investigate issue of foreign matter (from plastic string) in tobacco
Modifications Made for 2011-2012 Season
Automatic opening and closing of stalk-holding cups for faster loading
Automatic ejection of stalks from stalk-holding cups
Automatic opening of brushes to eject detached leaves
Shielding between grades
Possible conveyor speed variations
More detailed look into the power requirements and usage
Investigate issue of foreign matter (from plastic string) in tobacco
Modifications to Stalk-Holding Cups
A cam opens spring-loaded cups over an 18 in. distance at the front end of the machine to facilitate continuous loading
Modifications to Stalk-Holding Cups
Another cam at the end of the machine opens the cups again as for ejecting the stalks after stripping
Ejection Wheels
Rotating rubber wheels grasp stalks as they come around to ensure that they are ejected from the cups
Modifications to brushes
Bristle brushes have been replace by sheet rubber, and they pivot to open in between every plant so detached leaves can fall instead of being pushed into the string trimmers.
Results of Preliminary Tests Conducted in 2012
Tests conducted with additional string trimmer added for stripping tip grade, to better handle taller plants.Tip grade was stripped first rather than last.Trials 3 and 4 conducted at higher motor speeds.
Results of Preliminary Tests Conducted in 2012
Note low stripping efficiencies for a few plants that reduced average efficiencies.Based on observations, the cause was usually a stalk that was poorly seated in the cup so that the string trimmers caused the stalk to bend over significantly.
Further work needed for reliable operational stripping
To achieve stripping efficiencies comparable to hand stripping (95%-100%), the machine needs to effectively strip nearly every single plant.
The key to such reliability seems to be that the stalk ends be securely seated in the cups so that the stalks remain vertical as they pass all of the string trimmers.
Further work is needed to determine optimum string trimmer placement to give full stripping coverage for a range of stalk heights.
Once reliable operational stripping is achieved, efforts will be directed at working out shielding for grade separation and assessing grading accuracy.
Efforts will also be directed at assessing foreign matter in the tobacco (from the plastic string), and developing methods for minimizing it if necessary.
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