Collection of nut shells for grinding operations is a relatively simple procedure, particularly where grinding is done at a cracking plant. Where shells must be collected over large areas both rail and truck transportation are used. If fruit pits are considered, provisions should be made for removal of residual flesh or pulp before the pits leave the canneries. In the cases where the pits have been cut during processing of the fruits, the released kernels should be removed before shipping the shells. Pit kernels are valuable for their oil content.
Shell Use During World War II
The production and maintenance schedules set 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 addressing requests to the Northern Regional Research Laboratory, Peoria, Illinois.
Plants designed to produce at least 1-1/2 tons per hour of ground shell products will cost upwards of $60,000. A well-engineered plant of such size will require three to five men per shift. Among other factors, the working capacity of a grinding plant depends upon the quantity of shells available and the ability of the organization to merchandize its products. The plant should be located in an area in which at least 5,000 tons of nut shells or fruit pits are annually available at low transportation costs.