Beckham, S.

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Mississippi State University Scholars Junction Proceedings of the Short Course for Seedsmen 4-1-1988 Mechanical Damage - Causes and Solutions S. Beckham Follow this and additional works at: https://scholarsjunction.msstate.edu/seedsmen-short-course Recommended Citation Beckham, S., "Mechanical Damage - Causes and Solutions" (1988). Proceedings of the Short Course for Seedsmen. 1. https://scholarsjunction.msstate.edu/seedsmen-short-course/1 This Article is brought to you for free and open access by Scholars Junction. It has been accepted for inclusion in Proceedings of the Short Course for Seedsmen by an authorized administrator of Scholars Junction. For more information, please contact scholcomm@msstate.libanswers.com. 59 MECHANICAL DAMAGE - CAUSES AND SOLUTIONS Steve Beckham1 After a seed reaches physiological maturity, essentially everythIng that we do lowers Qua II ty. The best that we can hope to do is maintain QUality. Since damage is cumulative, we cannot Improve the Qual lty of an individual kernel. However, we can prevent further damage and there are several tools that we can use to remove those seed that are cracked, broken or deteriorated. The purpose of this paper is to examine the causes of mechanical damage and suggest solutions for damage prevention. For seedsmen, a major concern with regard to mechanical damage is that germination is lowered. Often germination will be lowered before an obvious crack develops. Unfortunately, most of the research on mechanical damage has been done on grain. Since many of the causes of damage to seed and grain are the same, the results from research on grain are directly transferable to seed. It is hoped that a review of mechanical damage on seed wi I I be of benefit both to the seedsmen and the elevator operator. Types of Mechanical Damage There are two basic types of mechanical damage - abrasion and impact. Abrasion is caused by friction of the seed or grain sliding over a surface. For the most part, abrasion results In very I ittle actual damage. The major problem resulting from abrasion is dust. As we wl I I later see, many times in designing a grain handling system we wi I I try to convert an impact situation to abrasion. Abrasion is somewhat affected by the coefficient of friction of the graIn. However, most research In thIs area has been to minimize the effect of the sliding grain on the eQuipment. Our concern is to minimize the effect of the eQuipment on the grain. Impact is the major cause of mechanical damage. In physics we learned that Force - t.tass x Acceleration (acceleration eQuals velocity sQuared) or F-t.txV. Grain is a fragl le commodity that we are continually impinging against hard, immovable objects. The force caused by impact has the most immediate effect on the grain. When we 1President, Amos, Inc., Lafayette, IN. 60 impact grain, we lower its capacity to germinate or we break it, or both. From the force eQuation , it can be seen that in order to decrease force we must either tower the mass or slow down the seed . Obviously, in the case of seed or grain our only hope of decreasing force is to slow the velocity of the grain as it goes through a handling system. Our other strategy for decreasing mechanical damage is to temper the seed or grain so that it Is I ess suscept I b I e to impact. Research data wi II be shown on how changes in moisture content and temperature affects susceptibi I lty to damage. Sources of Damage Mechanical damage begins with the harvest of the grain. This is especial ty obv ious wi th soybeans . Soybeans combined at a moisture content less than 12% a re very susceptible to mechanical damage . In order to minimize this damage, it is cr it ical that the seedsman starts harvest as early as possible. Soybeans can be combined at 16% moisture if faci I ities are avai table to safely dry the beans . Research at the University of Kentucky showed that air with a relative humidity less than 40% contributes to cracked seed coats. Caution is reQuired to be sure that the drying air doesn't cause internal stresses that result In mechanical damage. Since at I seed cannot be harvested at ideal moisture levels, steps must be taken to reduce harvest damage. CombInes can be adjusted to minimize impact. First, reduce cylinder speed, then increase concave clearance . What we are t r y ing to do is cause the seed to be threshed by rubbing plant material together instead of beating the seed out of the pods . A device is availab le that allows a combine operator to directly measure splits on the combine. This insures that proper adjustments are made before too much damage is done. ThIs dockage tester has a screen for sifting out splits. The percentage splits are then directly read from the tester . Drying any grain at high temperatures wi I I cause stress cracks that predispose the grain to breakage. Drying processes and techniQUes are beyond the scope of th Is paper. However, it is much easier to prevent broken kernels if the kernels do not contain stress cracks . Most mechanical damage occurs when the grain Is either dropped or thrown against a hard surface . Foster and Holman did a series of studies on the effect of dropping grain (Table 1). They also measured some of the effects of bucket elevators on mechanical damage. Traditional ty, most people felt that the best way to minimize 61 Table 1. Breakage in grain from free-fa 11. Corn Drop Height Discharge Orifice Impact 12.6 at 15.2 at (feet) Diameter Surface 25 31 100 12 Concrete 12.01 6.87 70 12 Concrete 7.07 2.54 40 12 Concrete 3.59 0.27 100 8 Concrete 13. 82 9.55 70 8 Concrete 10.83 5.03 40 8 Concrete 5.86 0.86 100 8 Grain 12. 53 7.11 70 8 Grai n 7. 74 4.00 40 8 Grain 4.35 0.25 *From Foster and Holman 62 mechanical damage was to drop grain on grain . However, Foster and Holman found that at drop heights greater than 40 feet, the damage was essent i a II y the same whether corn was dropped on corn or con-crete . They a I so documented the effect of grain moisture and tem-perature on mechanical damage . Corn at 12.6~ to 13~ resulted in a three-fold increase in damage ; decreasing temperature from about ·soF to near 40F doubled breakage. Mechanical damage to grain is cumulative. What this means is that if a certain process results in "X" amount of damage, the same "X" amount of damage will occur each time the same lot of grain is handled in that same process. Martin and Stephens found a continuous and relatively constant Increase in corn breakage with repeated handlings (Figure 1). They moved corn from one bin to another 21 times. Each handling produced a 0.6% increase in breakage. Simi Jar results were reported by Foster and Holman. The bucket elevator is a common source of mechanical damage. Foster and Holman examined two aspects of bucket elevator use, percent bucket fi I I and down-leg verses up-leg fl I I lng . Their results (Table 2) shows that damage is reduced when the buckets are ful I and the bucket elevator is fed on the down leg. Both of these methods reduce the force of Impact on the individual kernel. The fuller a cup is fi I led the less is the I ikel lhood that an individual kernel touches the cup . Likewise, impact is reduced when grain is int roduced with the bucket (down leg) versus against the bucket (up leg) . Bucket speed is a factor in damage. Slower belt and bucket speeds w I I I reduce both the impact during f i I 1 I ng and dIscharge. However, it is critical that the head be designed for a given bucket speed. Ideal head pulley diameter and discharge throat placement will vary with bucket speed. Slowing the belt speed of an existing leg may very wei I increase damage if down legging occurs. Reducing Damage Reducing mechanical damage from dropping corn into a bin is accomplished by instal I ing bin ladders. A bin ladder reduces damage by not allowing the velocity of the fa I I ing grain to reach a thresh-old which results in damage. Bin ladders are available which either mount on the side wal I of a bin or are free standing in the bin. The free standing ladders have the advantage of being less expensive to install and come in 63 20 1-z w • 0 15 0:: w a.. I w <.9 <! ~ 10 <t w 0:: (D 5 0 ~-----------------------------------0 5 ro 15 ·20 NUMBER OF HANDLINGS Figure 1. Breakage accumul ated from repeated handling of corn. After Martin and Stephens 64 Table 2. Corn breakage in bucket elevator tests. Test Condition Belt speed (f.p.m.) 650 940 Bucket loading: Fu 11 • • • Half full Feeding method: Front (up leg) •• Back (down leg) 32 Tests for each test condition. Average Percent 1.1 1.1 1.0 1. 2 1.2 1.0 Breakage Range Percent 0.2-3.5 .3-3.4 .2-3.5 .2-3 . 4 . 2-3.5 .2-3 .4 65 larger capacities than the side mounted ladders. Both types of bin ladders have an additional advantage in that the fines are evenly distributed within a bin . Without bin ladders, more fines or broken kerne Is are produced pI us they are concentrated in the center of a bin (Figure 2). Mechanical damage in grain spouting may be reduced by using grain retarders or decelerators. Work by McKenzie and Foster has shown that the effectiveness of different retarders varies greatly. They found that the commonly used cushion box was no better than nothing at al 1. Grain retarders which were most effective were those which gradually slowed down the grain. Results are shown in Table 3 and examples are i I lustrated in Figure 3. In summary, the key to minimizing mechanical damage is to handle grain using methods which eliminate impact. We must reduce the velocity of the grain so that, if and when impact occurs, it is below a threshold level for damage. The threshold level for damage is a function of temperature and moisture content of the grain. References 1 . Foster, G. H. and L. E. Holman. 1973 . Grain Breakage Caused by Commercial Handling Methods. USDA. ARS Marketing Research Report •968. 2. McKenzie , B. A. and G. H. Foster. 1979. Grain Decelerators for Reducing Grain Breakage. American Society of Agricultural Engineers Paper •79-3036. 3. Martin, c. R. and L. E. Stephens . 1976. Broken Corn and Dust Generated During Repeated Handling. American Society of Ag-ricultural Engineers. Paper •76-3026. 4. Miles, D. "Soybean Seed Storage . " Unpubl lshed Paper . 5 . Thompson, R. A. and G. H. Foster. 1963. Stress Cracks and Breakage in Artificial IY Dried Corn . USDA Agricultural Marketing Service. Marketing Research Report •631. 66 Hopper & Flow Channclizct· From the time your product enters the AMOS ladder, modern tcchnoloCY :tnd innovative design arc working !or you. · The hopper and Clow c:hannclizcr collect the product and direct it into the ladder. Product spillage, damage and waste arc prevented to keep profits up. Air Baffle The baCOcs on the AMOS ladder are a combination of unique design and highly abrasion resistant rubber. forming a soft air cushion between the rubber pad and the s~l ba!Cle. This air cushion acts as a shock absorber to protect your fragile product from damage as it is loaded into the bin. Discharge Ducts The AMOS unloadin&' ducts protect your product by unloading the bin !rom the top. one layer at a time. Stresses created by {lowing materials are minimized, allowing the ladder to be center mounted in the bin. The AMOS unloading duets eliminate the danger oC su!Coc:ation in an unloading bin because oC the top unloading system and the size of the duets. Universal Mounting System The universal moun tin&' system allows the AMOS ladder to be easily mounted in any bin. Adjustable supports make precise fitting to any bin dimensions a snap. The universal mounting system provides custom mountin&' in Oat bottom bins with or without perforated Cloors or sweep augers. and in hopper bottom bins. Figure 2. Center mounted bin ladder. Table 3. Summary of corn breakage in 1977 drop tests using var i ous spout-end decelerating devices. Breakage* 67 Amount Reduction** Test No. 4 7 6 3 9 5 2 1 8 Test Date Test Device 7/03/77 None-straight drop 7/21/77 None-straight drop (lbs) (%) 19.3 25.3 STRAIGHT DROP AVERAGE 22.3 7/21/77 7/03/77 8/23/77 7/05/77 6/17/77 6/15/77 8/16/77 45 cushion box Parallel (vertical) cushion box Grain brake Bucket Cascade 90 elbow-rubber sock 90 elbow-30" cyclone 90 involute-belt deflector 22.3 19.3 13.0 12.5 12.4 10.2 5.1 0 13 42 44 44 54 77 * Breakage separated from approximately 2000 lbs. of corn by a rotating cleaner with a 5-mesh hardware cloth screen. ** Percentage reduction from average breakage without decelerator. 32"------i -i~l/4" ~aM~ A. Jd· t 2+r.!' t ~· 21" " 7" 1 ~= OFGRAJN -CAFPED END B. Figure 3. (A) Dimens ions of cyclone grain declerator; (B) Typical 45° angle "c1:1shion box" or dead head for use on angled gravity spouts. Capped end section holds a quantity of grain for descending grain to impact onto, to reduce grain velocity and minimize tube wear. m OJ 

Mechanical Damage - Causes and Solutions

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Mechanical Damage - Causes and Solutions

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