et up during World War II
resulted in the development and expansion of uses for ground shell
materials. Fine flours from walnut shells were needed as extenders in
plywood adhesives. Soft grits from various shells were used by the Army
Air Forces in the air-blast method for cleaning airplane engines and
parts. Grits were required for deburring metal stampings and
flash-removal from molded plastics. These uses have expanded
considerably to meet civilian needs since the war.

Grinding Nut Shells and Fruit Pits

As uses for ground shell products were developed the Laboratory sought
advice of grinding equipment manufacturers for information on the design
and construction of suitable grinding plants. Only limited tests had
been made and data were not readily available in any published form.
Consequently the Laboratory undertook an extensive study on grinding nut
shells and fruit pits as part of its research on agricultural residues.

These studies were not limited to grinding only, but included methods of
separation and classification based on physical characteristics of the
raw materials; the relation of associated mechanical operations; a
consideration of the hazards; the problems of labor, management, and
merchandising.

A number of fires have occurred in plants grinding nut shells, corncobs,
stock feeds, and similar materials. In most cases the causes of fire
have been other than the grinding operation. From a consideration of the
causes of fires a number of safety precautions have been developed. Good
plant housekeeping is paramount. This is essential, not only because of
influence of dust and dirt on the maintenance of motors and equipment,
but because of the highly explosive nature of shell dusts. The U. S.
Bureau of Mines has cooperated closely with the Northern Laboratory in
evaluating the explosive hazards of the shell dusts.

Many of the present operators of shelling-grinding plants have benefited
from the information and assistance available from this Laboratory. The
cooperation of equipment manufacturers has aided considerably in
extending the scope of the Laboratory's studies.

The Northern Laboratory has published bulletin AIC-336, "Dry Grinding
Agricultural Residues, A New Industrial Enterprise" that summarizes the
research conducted to date. This is the first time that such data on
engineering and design has been assembled and published to cover this
field. Copies of the bulletin may be obtained by ad