by robert g. sperry m.s. graduate john h. wilhoit extension associate professor dave ash

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 Tobacco

Operations Labor Required, Conventional (wk*hr/ac)

Labor Required, Enhanced (wk*hr/ac)

Plant Production

6 2

Field Prep. & Cult.

22 22

Transplanting 11 11

Topping 8 8

Cutting 26 26

Load & Haul 8 8

House 26 14

Cure 3 3

Bulk & Load 12 12

Strip & Bale 73 51

Load & Market 2 2

Total 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 11

Topping 8 8

Cutting 26 26

Load & Haul 8 8

House 26 14

Cure 3 3

Bulk & Load 12 12

Strip & Bale 73 51

Load & Market 2 2

Total 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 11

Topping 8 8

Cutting 26 26

Load & Haul 8 8

House 26 14

Cure 3 3

Bulk & Load 12 12

Strip & Bale 73 51

Load & Market 2 2

Total 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

PlantEfficiency

(%)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 6.1

Average 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.