Thesis (M.S.)--Virginia Polytechnic Institute, 1964. / Vita. Abstract. Includes bibliographical references (leaves 65-66). Also available via the Internet.

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Central-hopper spreaders are widely used to apply dry fertilizer. Uniformity of distribution is severely limited by the centrifugal-fan and boom-type distributors used on these spreaders. The purpose of this study was to investigate the application of automatic control principles to an experimental auger-boom-type distributor, To facilitate the use of automatic controls, a distributor of special design was developed, It consisted of an auger conveyor with a U-shaped cross section. Eighteen discharge openings were located on 6-inch centers along its length. Small compartments at the Location of each opening, agitators on the auger flighting, and a control slide along the length of the boom, controlled the discharge from the boom. The control system consisted of a flow-level detector at the outboard end of the boom and a controller and linear actuator to operate the control slide. Basic performance characteristics of the distributor were measured on a laboratory test stand using manual-remote control. Coefficients of variation for discharge patterns along the length of the boom varied from 4.63 to 12.22 percent under various combinations of auger speed, discharge opening size, and boom inclination. Discharge rate was more sensitive to opening size than auger speed. Regression coefficients and tests of independence indicated that discharge rate was not greatly influenced by fertilizer flow level. Minor segregation of dry-blended fertilizers was noted. In tests with automatic control, errors in slide position were corrected. However, slow oscillation of the slide occurred after the initial correction. An improved flow-level detector and controller are needed for acceptable field performance of the system. / Master of Science

Centrifugal distributors are used extensively for the broadcast application of granular materials such as seed, granular fertilizer, and agricultural chemicals. A major problem with this equipment is nonuniform spreading which frequently results in reduced crop yield. The object of this study is to provide information required for more satisfactory design of spreading equipment. The equations representing the motion of granular particles along the blades of three centrifugal distributor configurations were solved with the aid of an electronic analog computer. Straight, forward and backward-pitched blades and logarithmically spiraled blades, all on flat distributor bases, were studied. Straight radial blades on a concave, cone-shaped base were also investigated. The results of this study were presented in graphs. Displacement, velocity, and departure angle versus the angular rotation of the distributor were plotted for a large range of parameters for each configuration. These variables were expressed in dimensionless form. From a study of the graphs it was noted that of all configurations investigated, the radial-blade arrangement requires the smallest 1·rotational displacement of the distributor to impart a specified velocity to granular material. As the pitch is increased, greater rotation is required. For a given amount of distributor rotation, higher values of the coefficient of friction cause a reduction in both displacement of the particle along the blade and its final velocity. The effect of increasing the ratio of gravity induced friction force to centrifugal force is similar but smaller than the effect of increased friction alone. / Master of Science