Effect of Moisture Content on Frictional Properties of SomSelected Grains in Indonesia

The frictional property of grains is one of the most important engineering parameters in developing solid bulk handling of grains. It is necessary for designing agricultural facilities and production process activities. These properties are expressed as internal friction angle
(φ) and wall friction angle (θ), which are known to be affected by the moisture content of the grains. This research investigates the effect of moisture content on the values of φ and θ of some selected grains. In the research, some indigenous Indonesian grain types, including rough rice, white rice, corn, soybean, and coffee, each in three varieties and three level of moisture contents, were used as the research samples. Those angles were measured using a self-constructed direct shear cell apparatus. Three different normal loads for each grain type were used with three replications. It is concluded that φ and θ of the
tested grains increase with moisture contents with different trends of increments. The relationship of those angles with moisture contents can be expressed as linear regression
equations. The slope of the regression lines for both φ and θ is significantly affected by grain type (p<0.05). For φ, coffee (Excelsa) is the most susceptible to the change in
moisture content, while dent corn (Hibrida) is the least affected one. For θ, soybean (Galunggung) is the most susceptible to the change in moisture content, while rough rice (Mapan 5) is the least affected one.