In order to intensively understand the interacting forces between solid particles, apparent viscosity was introduced to characterize the resistance of particles against movement. On this basis, a measuring method was developed, through which the torque exerted on a rotating blade inside a solid particle layer was measured. The apparent viscosity was then acquired based on the motion equations of the particles. The influences of various parameters such as type of blade tip, blade position inside the powder layer, particle size/shape, and temperature were discussed and analyzed. The results indicated that at room temperature, the shape of solid particles gives much more important effect on their apparent viscosity; while, under higher temperature, particle size tends to play a major role. The apparent viscosity of iron particles increases with increasing temperature. Good linear relationships between the logarithm of the apparent viscosity of iron particles with 75 mu m and the reciprocal of the temperature are observed over different temperature ranges. (C) 2015 Elsevier B.V. All rights reserved.