“…Particle size characteristics have also been measured by researchers [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ]. Figure 1 shows the results for 50 typical factories, including fastener processing factories [ 19 , 20 ], charging machinery processing factories [ 21 ], and machining factories [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. The blue triangles in the figure represent the minimum particle size, whereas the red triangles and black rhombuses represent the maximum, and mean particle size, respectively.…”