Cottonseed Rupture from Static Energy and Impact Velocity
I. W. Kirk and H. E. McLeod Assoc. MEMBER ASAE
WHETHER cottonseed is to be used for planting or as a raw material
for any one of many products, sound, high-quality seed is necessary. Rupture of the seed coats may cause seed potentially of the highest quality to become almost worthless. There are points throughout many of the cotton-handling and processing o p e r a t i o n s that may cause mechanical damage to the seed.
Collins (2)* states that mechanical injury from improper handling practices that result in seed-coat rupture may adversely affect germination, particularly strength of germination. Seed-coat rupture permits a rise in the free fatty acid content of cottonseed. The fatty acid content is a matter of importance in seed deterioration from the standpoint of seed for planting purposes. Rusca (9) states that the relationship between free fatty acid content and cottonseed germination is that seed with high free fatty acid content has low germination and seed with low free fatty acid content has high germination. Simpson (11) found that cottonseed failed to germinate when seed lots contained more than 1.8 percent free fatty acid. An increase in free, fatty acid content of cottonseed increases the amount of soap stock produced as a by-product, which in turn reduces the quantity of high-quality oil refined during commercial processing.
A study of cottonseed and seed-cotton handling and processing systems reveals that there are two general conditions by which cottonseed may be damaged. The seed coat may be ruptured by a static force or by an impact force. The latter is the more prevalent of the two and occurs in conveyance systems when a seed moving at high velocity strikes a rigid object. Impact may also occur in cleaning systems when a rigid object, moving at a high velocity relative to the seed, strikes a seed. Some
Paper prepared for publication in the TRANSACTIONS of the ASAE. Approved for publication by the Director of the South Carolina Agricultural Experiment Station as Technical Contribution No. 609.
The authors—I. W. KIRK and H. E. McLEOD -—are agricultural engineer, AERD, ARS, USDA, Auburn University, Auburn, Ala. (formerly graduate student, Clemson University); and formerly associate professor of agricultural engineering, Clemson University.
* Numbers in parentheses refer to the appended references.
Author's Note: The research study on which this paper is based was made possible by a fellowship grant provided by the National Cotton Council of America and was conducted under the facilities of the South Carolina Agricultural Experiment Station.
1967 • TRANSACTIONS OF THE ASAE
FIG. 1 Seed-loading frame for static rupture tests.
knowledge of the physical properties of a cottonseed that may be related to these types of seed damage is needed so steps may be taken to reduce or eliminate the damage. This investigation was initiated to (a) determine the rupture force, deformation, and energy absorption of cottonseed for static loading conditions at different seed moisture contents, (b) determine the relationship between seed impact velocity and percent seed-coat rupture at different seed moisture contents, and (c) relate impact velocity to impact energy absorption and relate impact energy absorption to static energy absorption.
PROCEDURE
Cottonseed for the Tests
The cottonseed used in all the tests were from cotton which had been stored in a wire basket since the 1958 harvest season. Tests were conducted in July and August 1960. The cotton was roller ginned and the seed were collected for the tests. No visual difference was noted in the amount of linters left on the seed as compared to conventional saw-ginned upland cottonseed. The seed were conditioned at a temperature of 70 F and 65 percent relative humidity for a period of not less than 10 days.
Each seed was visually examined for previous damage. Those that had been cracked or damaged in any way were
discarded. The remaining seed were divided into 100-seed lots to be selected at random for the various tests.
The moisture content of the seed after the ten-day conditioning treatment was approximately 10 percent. This was chosen as one of the moisture levels for the tests. A moisture content lower than 10 percent and one higher were also desired. The lower moisture content (6 percent) was obtained by placing the conditioned seed in an oven for 15 minutes at a temperature of 190 F. The higher moisture content (14 percent) was obtained by placing the conditioned seed in a chamber for ten hours where the temperature was from 82 to 92 F. and the relative humidity was 98 percent. The dominant effect of the conditioning humidities and temperatures was a change in seed moisture content. The possible additional effects of the conditioning treatments on seed coat strength were not considered in this study.
Static Rupture Tests
A seed load frame (Fig. 1) was designed so that a compressive force could be applied to an individual seed. The loading frame was equipped with two strain-gage transducers: a force transducer and a deformation transducer. Two Brush amplifiers, type RD 5612 00, and a Brush dual-channel, recording oscillograph, type RD 2322 00, were used as amplification and recording instruments for the signals from the transducers. The force transducer was calibrated for load (oscillograph-pen deflection) and the deformation transducer was calibrated for deformation (oscillograph-pen deflection). With this equipment, a continuous recording of force applied and the corresponding seed deformation could be obtained for each seed tested.
Static rupture tests were made on cottonseed at dry-basis moisture contents of 6, 10, and 14 percent. Twenty-five seed were randomly selected from a 100-seed lot from each m o i s t u r e group. Each seed was individually placed in the seed loading frame and was slowly loaded until the seed coat ruptured. Rupture was usually indicated by a noticeable cracking sound and could be easily distinguished on the oscillograph chart. A continuous recording of applied force and seed deformation was made for each seed tested.
217
FORCE, POUNDS
FIG. 2 Curves indicating general relationship between forces applied and the deformation of cottonseed at three moisture contents.
Ten points of corresponding force and deformation between the no-load point and the rupture point were taken from the chart for each seed. These points were plotted on force - d e f o r m a t i o n charts. T y p i c a l fo rce - deformation curves for the three moisture contents are shown in Fig. 2. The area under each force — deformation curve to the rupture point was planimetered to obtain the energy absorption of each seed.
3000 4 0 0 0 5000 6000 SEED VELOCITY, FEET PER MINUTE
FIG. 4 Average percent cottonseed rupture due to seed impact at various velocities.
Impact Rupture Tests
A pneumatic apparatus was designed to accelerate a single seed to a given velocity and impact it against a flat steel plate. The apparatus (Fig. 3) consisted of an air-pressure regulator and gage, a seed-drop chamber, a blowpipe and an impact cage. The blowpipe was a y2-in. brass pipe 12 ft long. The blowpipe was connected to an air line from an air compressor. An air-pressure regulator with the pressure gage on the outlet was used to regulate air flow through the pipe. The system was under pressure at the pipe inlet so it was necessary to use an airtight chamber in order to drop the seed into the airstream. The drop chamber was designed so that one seed at a time could be made to enter the air stream. The seed were made to impact against a flat steel plate placed perpendicular to the direction of seed travel and one inch from the end of the blowpipe. A cage was placed around the plate and the free end of the pipe so that the seed could be recovered and examined.
The blowpipe was first calibrated for air velocity (pressure-gage reading). A full-range calibration was made with a precision air-velocity meter. Stroboscope pictures of seed after they left the blowpipe outlet were used to obtain a calibration of seed velocity. A stroboscope with an auxiliary high-intensity light source was used in conjunction with a 35-mm camera to take multiple time exposures of a seed moving against a fixed scale. A full-range
218
calibration of seed velocity for various pressure-gage readings was determined from the distance between seed images and the time between flashes of the light source. With these calibrations, an air velocity or a seed velocity could be estimated from any pressure-gage reading.
Cottonseed were subjected to direct impact on a steel plate to determine the resulting percent of seed rupture at seed velocities of 3,000, 4,000, 5,000 6,000 and 8,000 fpm. Three replications were made at each of the three moisture contents (6, 10, and 14 percent) used in the static rupture tests. A replication was made up of 500 seed, 100 seed at each indicated velocity. A lot of 100 seed was placed in the drop chamber. The pressure regulator was then set to give the desired seed velocity. Each seed was pushed into the blowpipe through the opening in the bottom of the drop chamber where it entered the airstream and was accelerated to the desired velocity as it passed through the blowpipe. The seed struck the steel plate in the impact cage as they emerged from the blowpipe and were collected from the impact cage after each 100-seed run. The percent of seed coat rupture was then determined by a visual examination of each seed in the 100-seed group. The seed were evaluated for rupture, with
out additional treatment, immediately after they were subjected to impact. A seed was considered ruptured if a crack could be found in the seed coat.
RESULTS AND DISCUSSION
Static Rupture Tests
Averages were taken for the rupture force, deformation, and energy absorption for each moisture content. These values are presented in Table 1.
TABLE 1. AVERAGE STATIC RUPTURE FORCE, DEFORMATION, AND ENERGY
ABSORPTION FOR COTTONSEED Moisture ,-, content*, F o r cS» r ^ ™ ^ pounds
Deformation, , E n exgy inches absorption,
inch- poun as
10 14
18.845 15.589 12.853
0.06028 0,07513 0.09926
0.714 0.696 0.691
FIG. 3 Seed blower for impact rupture tests.
* Dry-basis moisture content.
It may be seen from Table 1 that the rupture force and deformation vary considerably w i t h m o i s t u r e content. This was first noticed while the tests were being conducted. It was evident from the oscillograph trace of force and deformation that, for high moisture content, the rupture force was low and the rupture deformation h i g h . F o r low moisture content, the rupture force was high and the rupture deformation low. Even though there was considerable variation in the rupture force and deformation, the mean energy absorption at each moisture content was essentially the same. The coefficient of variation for energy absorption ranged from 0.41 to 0.49. The effect of moisture content was very small; however, the trend was to lower energy absorption at higher moisture contents.
Impact Rupture Tests
The average percent seed rupture for each velocity at the three moisture contents is presented in Table 2. The percent seed rupture was found to be independent of moisture content within the sensitivity of the test and the range of moisture contents and veloci-
TRANSACTIONS OF THE ASAE • 1967
ties tested. The average percent seed rupture due to impact velocity for all the tests was 1.22, 2.89, 7.44, 17.00, and 55.55 for seed velocities of 3,000, 4,000, 5,000, 6,000, and 8,000 rpm, respectively. Fig. 4 is a graphical presentation of percent seed rupture versus seed velocity.
An effort was made to establish an algebraic relationship between percent seed rupture and impact velocity. The average percent seed rupture, for all the tests, at each velocity was plotted on a logarithmic chart as shown in Fig. 5. The points formed a line indicating a relationship of the type Y = cXn. The equation of the graphically fitted line, the relationship between percent seed rupture and seed velocity, was found to be:
4.77 X 10 - 1 6 S 4.38 R where
R = percent seed rupture S = seed velocity, feet per minute.
The percent seed rupture at any seed velocity may be estimated with this equation. However, it must be kept in mind that the equation is valid only over the range of velocities tested in this investigation.
All of the indicated velocities have been seed velocities and not air velocities. Any application of the results of this investigation would ultimately have to be made on the basis of air velocity. The relationship between air velocity and seed velocity for the test system was: seed velocity = 0.71 air velocity. However, the authors do not suggest that this relationship would apply to a c o m m e r c i a l pneumatic-conveyance system.
TABLE 2. AVERAGE PERCENT COTTONSEED RUPTURE DUE TO DIRECT IMPACT
FOR FIVE SEED VELOCITIES AND THREE MOISTURE CONTENTS
(Each entry represents an average for 300 seed)
Seed velocity,
fpm 3,000 4,000 5,000 6,000 8,000
Dry-basis seed moisture content,
6 0.67 3.00 8.00
18.67 58.00
percent 10 14
2.00 1.00 2.00 3.67 8.33 6.00
15.00 17.33 52.33 57.33
top
90
80
70
60
50
40
30
20
H
RC
EN
QL
iu'10
5 9 1 8
UJ
g 6
5
4
3
2
-
-
"
-
PERCENT
4.77 X
SEED RUPTURE
lO'^VELOCITY,
EACH POINT
AVERAGE
1
-FEET PER MINUTE}4'3' —,
\ /
REPRESENTS /
FOR 900 SEED. /
. / 1 1, . J, , 1 ._L
: ---
/ -/ -/ -
-
-
-
--
-
_J L_iJ
Velocity-Energy Absorption Analysis
The energy absorption of a cottonseed upon impact was not experimentally measured in this investigation. A theoretical analysis of the relationship between impact velocity and impact energy absorption is presented below.
The kinetic energy of a body moving in coplanar translation may be determined by the basic dynamic relationship, Ek = ta2, where Ek is the kinetic energy of the body, m is the mass of the body, and v is the velocity of the body.
During the instant of impact, the total kinetic energy is absorbed by the
1967 • TRANSACTIONS OF THE ASAE
2 3 4 9 f 7 8 9 10
SEED VELOCITY, THOUSAND FEET PER MINUTE
FIG. 5 Logarithmic relationship of percent cottonseed rupture and seed-impact velocity.
cottonseed if the assumption is made that the energy absorption of the steel plate is negligible. This is a reasonable assumption from a consideration of the relative properties of the two materials. The impact is partially elastic, so the cottonseed rebounds and releases part of the absorbed energy. Even though part of the energy is given up, the total energy absorbed upon impact is the important consideration from the standpoint of impact energy required for rupture.
Rearrangement of the basic equation gives:
v = (2 E k /m)%
The average weight of a single cottonseed of the type used in these tests was 0.11 grams at a dry-basis moisture content of 10 percent. The average static energy absorption for cottonseed at a dry-basis moisture content of 10 percent was 0.696 in-.lb. Substitution of these values into the equation gives a velocity of 7,460 fpm. This velocity produces the same amount of energy as the mean energy absorption capacity of the cottonseed at 10 percent dry-basis moisture content.
The preceding analysis was made with a mean seed weight and a mean energy absorption capacity. Such an analysis would be expected to give a velocity that would rupture the "average" seed. A mean rupture velocity could not be determined from the test
data because 100 percent seed rupture was not obtained. However, the velocity at the median rupture percent (50 percent) should be reasonably close to the mean in a distribution such as the one obtained for percent rupture versus seed velocity. It can be seen from Fig. 4 that the indicated velocity of 7,460 fpm is only about 250 fpm away from the velocity at the median rupture percent. This indicates that a static energy absorption distribution could possibly be used to predict a velocity — percent rupture curve. However, further tests and a more complete analysis would be necessary to substantiate the preceding statement.
Conclusions
The following conclusions are valid within the range of moisture content and impact velocity used in this investigation:
1 The force to rupture cottonseed and the resulting seed deformation under static loading were quite variable with moisture content. However, the total energy absorption to rupture was approximately constant (0.70 in.-lb).
2 The percent seed-coat rupture of cottonseed due to impact at a given seed velocity was independent of seed moisture content and could be estimated by the equation:
R = 4.77 X 10 ~ 1 6 S 4 3 8
where R = percent seed rupture S = seed velocity in feet per min
ute.
3 It was indicated that a static energy-absorption distribution curve could be used to estimate percent seed-coat rupture for given impact velocities.
References
1 Bennett, C. A. Cottonseed handling with small air pipes. USDA Cir 768 (revised), 1953.
2 Collins, E. R. A fresh look at Tarheel cotton. Typewritten report. North Carolina State College extension service, ca. 1959.
3 Creswell, C. F. Composition of cottonseed. USDA Bui 948, 1921.
4 Eyes for industry . . . stroboscopic techniques. 9th ed. Cambridge, Mass., General Radio Co., 1957.
5 Franks, G. N. and Oglesby, J. C , Jr. Handling cotton planting-seed at cotton gins. USDA Production Research Report 7, 1957.
6 Johnson, T. J. Cotton ginner's handbook. Biytheviiie, Ark. Arkansas-Missouri Cotton Gin-ners Assn., Inc., 1955.
7 Kirk, Ivan W. Static energy and impact velocity requirements for cottonseed rupture. Unpublished M.S. thesis. Clemson, S.C. Clemson University Library, 1961.
8 Pearson, N. L. Relation of seed-coat structure to rupture in ginning. Journal of Agricultural Research 58:865-873, 1935.
9 Rusca, Ralph A. and Gerdes, Francis L. Effects of artificially drying seed cotton on certain quality elements of cottonseed storage. USDA Cir. 651, 1942.
10 Saunders, De Alton. Ginning as a factor in cottonseed deterioration. USDA Bui. 288, 1915.
11 Simpson, D. M. Factors affecting the longevity of cottonseed. Journal of Agricultural Research 64:407-419, 1942.
12 Weisbach, Julius. Mechanics of engineering —theoretical mechanics. New York. D. Van Nos-trand Co., 1889.
219
Top Related