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So, you want to store some corn? Here is some information about corn storage that will help you compute your storage structure needs. Perhaps it is way more information than you need but it will give you some background understanding of grain storage and volume.
What this page does not cover:<br />
Ventilation, <a href="http://www.iburncorn.com/content/view/20/31/">rodents and bugs</a>, and moving grain. Those will be topics to come as I get time.
Corn is normally purchased by the bushel, though you can buy it bagged as well. Bagged corn generally weighs fifty pounds per bag which means .89 bushels. When buying bulk corn however you purchase by the bushel. A bushel of high grade #2 corn weighs fifty six pounds. There can be a considerable price bump for the convenience of buying bagged corn. Today the local co-op is charging $4.20 for a bag of corn, that would be $4.71 per bushel. On the other hand, bulk corn today is going for $1.43 per bushel.
Quite a savings that would pay for some sort of bulk storage in short order.
Bagged corn asside, corn is generally bought and sold by weight. To calculate bushels by weight, you actually weigh the grain, divide total weight by the standard weight per bushel 56lbs, measure grain moisture, and finally adjust the number of bushels to the number that you would have at the moisture value specified by the buyer.
Test weight is the weight of the corn per unit of volume and is usually expressed as pounds per volume bushel. This value can be used to estimate bushels by weight from bushels by volume. In the rare case that grain test weight (lb/vol bu) equals the standard bushel weight, in this case 56lbs/bu (lb/weight bu), bushels calculated by volume will equal bushels determined by weight. In most cases, however, bushels estimated by volume differ slightly from bushels calculated by weight. Volume calculations can be used to get a reasonable estimate of the number of bushels, but it is always more accurate to weigh grain and measure its moisture content and calculate bushels by weight.
Here are some figures to get you started. A bushel of grain is 1.25 cubic feet, or, to put it the other way, one cubic foot of grain is 0.8 bushels.
1 Bushel Corn = 1.25 cubic feet (cu ft), or
1 cu ft of corn = 0.8 bushel
To determin the bushels of corn by volume, calculate corn volumen in cubic feet and divide by 1.25 or multiply by 0.8
Most storage structures can be visulaized as some simple geometric shape, or combination of shapes. You can estimate storage voulme by totaling the volumes for each seperate shape.
Rectangular bins or buildings
To calculate the volume of a rectangular-shaped pile with a level top surface,
volume = length x width x height
Cylindrical bins or cribs
To calculate the volume of a round bin or crib with a level top surface,
volume =
[(pi x diameter squared) x height<br />
(3.14 x diameter x diameter) x height<br />
0.785 x diameter x diameter x height<br />
Angle of repose
The angle of repose, or angle with a horizontal surface formed when
free-flowing grain comes to rest, can be used to estimate the height or
width of grain piles. Angle of repose depends on things like size and shape
of kernels, moisture content, fines and foreign material content, presence
of mold, and filling or emptying method, and can vary greatly. For example,
the angle of repose for dry corn can range from 15 to 26 degrees. However,
the standard angle of repose for healthy dry corn is 23 degrees.<br />
The tangent of an angle (abbreviated tan) is the ratio of the length of the
side of a right triangle (triangle that contains one 90-degree angle) that
is opposite the angle to the length of the side of the triangle that is
adjacent to the angle. This means that for grain dropped into a pile from an
overhead spout, the tangent of the angle of repose is equal to the height of
the pile divided by half the width of the pile.
For any right triangle,
tangent of angle = opposite side of triangle adjacent side of
triangle
For a grain pile,
tangent of angle of repose = pile height ï¿1Ž2 (0.5 x pile width or
diameter)
To get pile height if you know the width,
pile height = tangent of angle of repose x (0.5 x pile width or diameter)
To get pile width or diameter if you know the height,<br />
pile width or diameter = pile height ï¿1Ž2 (0.5 x tangent of angle of
repose)
<b>Sloped sides and round base (cone)</b><br />
<br />
These examples use some big numbers, far more bushels than you will use to
heat your home but you might be buying corn from a grain elevator that has a
pile like this and I think it is good to get some idea of the bushels
contained in some of these grain piles. To get the volume of a peaked pile
that has a round base and no sidewalls, volume =<br />
<br />
1/3 x [(pi x diameter squared) ï¿1Ž2 4] x height<br />
0.262 x diameter x diameter x height<br />
<br />
Example calculations for a cone-shaped pile: Corn is dropped from a
permanently fixed 30-ft high spout on to a flat asphalt pad that has no
retaining walls. Estimate the expected diameter and bushels contained in the
pile.<br />
<br />
We see that for corn, the expected angle of repose is about 23 deg (tan =
0.42). pile diameter =<br />
<br />
pile height ï¿1Ž2 (0.5 x tangent of angle of repose)<br />
30 ft ï¿1Ž2 (0.5 x 0.42) = 143 ft<br />
<br />
The volume of a cone-shaped pile is volume =<br />
<br />
0.262 x diameter x diameter x height<br />
0.262 x 143 ft x 143 ft x 30 ft = 160,729 cu ft<br />
<br />
The estimated number of bushels in the pile is<br />
vol bu = 0.8 x volume = 0.8 bu/cu ft x 160,729 cu ft = 128,583, or about
128,600 vol bu<br />
<br />
<b>Partially empty cylindrical bin (cylinder with cone missing)</b><br />
<br />
To estimate the volume of grain remaining (and help you figure out if you
are going to makein a round bin after grain stops flowing out of a center
unloading sump, volume =<br />
<br />
volume of a cylinder - volume of a cone<br />
(0.785 diameter x diameter x height) - (0.262 diameter x diameter x
height)<br />
0.523 x diameter x diameter x height</p>
<p><img height="203" width="500" alt=""
src="http://www.iburncorn.com/images/stories/bushelsfig4.jpg" /></p>
<p><b>Converting Bushels by Volume to Bushels by Weight</b> You can
estimate weight bushels from volume bushels (and vice versa) if you know the
grain's test weight. Test weight is an expression of grain bulk density,
which is weight per unit of volume. Test weight is affected by things like
grain moisture, grain variety, growing conditions, presence of disease
(scab, for example) and method used to fill the vehicle, pile, or storage,
and so can vary greatly from one batch of grain to another, and even within
a given batch of grain. This means that using test weight to convert volume
bushels to weight bushels provides only a rough estimate of actual grain
weight.<br />
<br />
Grain test weight affects the amount of grain that occupies a given amount
of space, but when you sell grain, test weight is not used to calculate the
quantity of bushels. Test weight is used, however, as a quality indicator,
and discounts are applied if test weight is low. Test weight usually
increases as grain dries, but the exact relationship between moisture and
test weight depends on drying conditions and grain characteristics and is
difficult to predict.<br />
<br />
Test weight is determined by weighing the amount of grain that it takes to
fill a standard dry one-quart cup. A conversion factor is used to convert
the weight of grain in the one-quart cup to pounds per volume bushel, or
pounds per 1.25 cubic feet of grain.<br />
<br />
To estimate weight bushels from volume bushels, multiply volume bushels by
test weight and divide by the standard bushel weight for that grain. In the
rare case that test weight equals the standard bushel weight, volume bushels
equal weight bushels.<br />
<br />
weight bu = (volume bu x test weight) ï¿1Ž2 standard bushel weight<br />
<br />
Example of estimating grain weight from volume: About how many bushels of
corn (by weight) would you expect to sell from the cone-shaped pile used in
an earlier example if the corn test weight is 52 lb/bu? (Assume that the
grain is dry.)<br />
<br />
volume bu = 128,583 vol bu<br />
<br />
weight bu = (128,583 vol bu x 52 lb/vol bu) ï¿1Ž2 56 lb/weight bu
= 6,686,316 lb ï¿1Ž2 56 lb/weight bu = 119,399 or about 119,400 weight bu
Remember, this is only an estimate and the actual number of bushels determined by weighing the grain and applying the buyer's shrink factor could differ substantially from this value.<br />
Sections of the text above were heavily borrowed from a paper written by:<br
/>
Bill Wilcke, Extension Engineer<br />
University of Minnesota Extension Service</p>
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