C SeedRupture

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.

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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

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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

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g 6

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4

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2

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PERCENT

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SEED RUPTURE

lO'^VELOCITY,

EACH POINT

AVERAGE

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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.

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