John H Wilhoit Extension Associate Professor Dave Ash Engineer Aid Biosystems and Agricultural Engineering University of Kentucky 2012 DEVELOPMENT AND EVALUATION OF A BURLEY TOBACCO MECHANICAL STRIPPING CONCEPT UTILIZING STRING TRIMMERS ID: 699650
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ByRobert G. SperryM.s. Graduate John H. Wilhoit Extension Associate ProfessorDave AshEngineer AidBiosystems and Agricultural Engineering,University of Kentucky2012
DEVELOPMENT AND EVALUATION OF A BURLEY TOBACCO MECHANICAL STRIPPING CONCEPT UTILIZING STRING TRIMMERSSlide2
Standard Labor Requirements for Burley TobaccoOperationsLabor Required, Conventional (wk*hr/ac)
Labor Required, Enhanced
(wk*hr/ac)
Plant Production62Field Prep. & Cult.2222Transplanting1111Topping88Cutting2626Load & Haul88House2614Cure33Bulk & Load1212Strip & Bale7351Load & Market22Total 197159Slide3
Standard Labor Requirements for Burley TobaccoOperationsLabor Required, Conventional (hours/acre)
Labor Required, Enhanced (hours/acre)
Plant Production
62Field Prep. & Cult.2222Transplanting1111Topping88Cutting2626Load & Haul88House2614Cure33Bulk & Load1212Strip & Bale7351Load & Market22Total 197159Slide4
Harvesting (48-60 wk*hr/ac) and stripping (51-73 wk^hr/ac) are by far the biggest labor requirementsOperations
Labor Required, Conventional (hours/acre)
Labor Required, Enhanced (hours/acre)
Plant Production62Field Prep. & Cult.2222Transplanting1111Topping88Cutting2626Load & Haul88House2614Cure33Bulk & Load1212Strip & Bale7351Load & Market22Total 197159Slide5
GradingBased on stalk positionEach grade takes up a length of stalkLeaves for each grade stripped off by hand seperatelySlide6
Manually stripping tobacco is very labor intensiveSlide7
New MethodCombining major elements of proven systemsStraight line conveyorsPlants conveyed at even spacesGrading based on stalk positionUsing new tobacco stripping technology
String trimmers to remove leaves
Flexible brushes to align leaves
Slide8
Basic configuration of stripping machine conceptSlide9
Leaf Alignment
Brushes used for aligning and holding leaves
Cams open brushes to allow stripped leaves to fallSlide10
Leaf Alignment
Brushes used for aligning and holding leavesSlide11Slide12
VideoSlide13
ObjectivesDevelop 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. Slide14
Coverage
5 in. string (7 in. radius)
7 in. string (9 in. radius)
9 in. string (11 in. radius)Slide15
Single Grade Testing ProcedureString length (in.)
Motor speeds (rpm)
5
3000340038004200
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 restSlide16
Resulting Efficiencies
Motor Speed (rpm)
3000
340038004200Trial 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
3000Trial 168.595.595.899.3Trial 279.192.397.096.2Trial 353.394.295.295.6Average67.094.096.097.0
9
IN. STRING LENGTHSlide17
Machine Stripping 3 GradesFlyings are removed by handLug, leaf and tip are removed with string trimmers7 in. string length used for proper coverage and grading on 44 in. plantSlide18
3 Grade Machine Stripping ResultsPlant
Efficiency (%)
Average Efficiency
194.697.0%
2
98.0
3
94.1
4
98.3
5
96.7
6
97.8
7
98.0
8
99.8
9
95.8
Note: The stripping efficiency results for plant 10 contained an error and were left out.Slide19
Leaf DamageSmall pieces make up 5.6% of total weight removedSlide20
Particle DistributionPlant
Stripping 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
11.9
2
95.7
91.6
3.5
4.9
3
92.5
95.5
1.9
2.5
4
99.3
89.5
3.5
7.0
5
97.2
89.7
4.5
5.8
6
99.8
89.7
5.0
5.3
7
99.7
91.9
3.4
4.7
8
93.9
93.4
3.1
3.5
9
94.8
91.3
4.3
4.3
10
98.4
86.5
7.3
6.1
Average
96.9%
90.1%
4.3%
5.6%Slide21
ConclusionsSignificant difference in efficiency for faster speeds at given string lengthResults for 3 grade stripping with 4th grade stripped by hand showed 97% efficiencyParticle 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.Slide22
Potential ProductivityConveyor 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 sPotential productivity: Assume 85% field efficiency Approximately 1100 plants/hr
370 lb/hr
Approximately 3,000
lbs per 8 hour dayApproximately 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/acSlide23
Cost and PaybackLabor costs for crew of workers are $10-15 per hour per workerPotential savings with this machine $5,000/year for 20 acre crop at $10/hr labor rateAt $15/hr, savings could be $7,500/yearIf machine cost $10,000, pay back period could be 1.5 to 2 years, twice that if cost is $20,000Slide24
Further work needed to develop operational prototypeAutomatic opening and closing of stalk-holding cups for faster loadingAutomatic ejection of stalks from stalk-holding cupsAutomatic opening of brushes to eject detached leavesShielding between gradesPossible conveyor speed variations
More detailed look into the power requirements and usage
Investigate issue of foreign matter (from plastic string) in tobaccoSlide25
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 leavesShielding between gradesPossible conveyor speed variationsMore detailed look into the power requirements and usageInvestigate issue of foreign matter (from plastic string) in tobaccoSlide26
Modifications to Stalk-Holding CupsA cam opens spring-loaded cups over an 18 in. distance at the front end of the machine to facilitate continuous loadingSlide27
Modifications to Stalk-Holding CupsAnother cam at the end of the machine opens the cups again as for ejecting the stalks after strippingSlide28
Ejection WheelsRotating rubber wheels grasp stalks as they come around to ensure that they are ejected from the cupsSlide29
Modifications to brushesBristle 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.Slide30Slide31
Results of Preliminary Tests Conducted in 2012Tests 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. Slide32
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. Slide33
Further work needed for reliable operational strippingTo 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.