Corncob Information Overview

Corncob particles are valuable because they are highly absorbent and they are abrasive.  The various corncob products we offer are defined by the size of the particle and the portion of the cob from which they are made.

The largest particle is about one-fourth the size of a garden pea and the finest particles are flour-like in appearance.  There are three parts to a corncob:  Chaff, which is also called beeswing, is on the outside of the cob; Pith is the soft/spongy center portion; and Woody-Ring, which forms between the Chaff and Pith.

All three portions of the cob are absorbent, but the pith and chaff portions are the most absorbent.  Those portions have a bulk density of approximately 8 pounds per cubic foot and that compares to about 27 pounds for the woody-ring.  The difference in bulk densities allows us to separate the woody-ring from the pith & chaff portions.

Products made from the woody-ring portion are referred to as “grit” products and products made from pith and chaff are referred to as “PC” products.  

Both Grit products and PC products are:  all-natural; bio-degradable; renewable, and absorbent.  However, water absorbency for PC products can approach 300% on a weight-to-weight basis and that compares to grit products at about 100%.

Corncob particles are free-flowing and that combined with their absorbency makes them ideal for use as a “carrier” of other products.  In general, those products are liquid in form and they are absorbed by the corncob particles.  Examples of carrier applications include carrying the active ingredients of pesticides, animal medications, feed flavors, and feed nutrients.      

Grit particles are also used when the abrasive characteristic of corncobs is desirable.  Corncob grit is often characterized as being a “soft abrasive” because it is considerably less aggressive than other abrasive media.

In tumbling and vibratory finishing applications, the primary purpose for using corncob grit is to dry metal parts, but corncob grit also de-burrs and polishes the parts at the same time.  The grades most often used are 1014, 1420, and 2040 and the correct grade is usually the one where particles do not lodge in holes or cavities present in the parts.

As a pressure blast media, corncob grit is ideal for wood and aluminum substrates because it is considerably less aggressive than sand.  Corncob grit is also non-sparking and does not foul bearings.  In general, larger grit particles are more aggressive than smaller particles. Grit blasting can utilize grades 1014, 1420, 2040, or 3080.  Because the particles are larger, 1014 and 1420 are the most aggressive.  Log homes are most often grit-blasted with 2040 or 3080 and of those two, 2040 is larger and is therefore more aggressive.

Standard Corncob Grit Grades: +8, 814, 1014, 1020, 1420, 2040, 3080, 4060, -40

Unraveling the mystery of the grades is easy.  In the list above, +8 grade has the largest particles, and each successive grade has particles smaller than the grade that precedes it.  Particles are sized using U.S. Standard Sieves/Screens.  For +8 grade corncob, the vast majority of particles are above, or retained on, a #8 screen.  For 1420, the vast majority of particles pass through a #14 screen and are retained on a #20 screen.  For -40, the vast majority of particles pass through, or are below, a #40 screen.

Particle Sizes
The following table shows U.S. Standard Sieve numbers and the corresponding sieve opening sizes in inches and microns.