The effect of the particle size distribution of filler on the flowability of thermosetting plastics molding compounds in narrow channels is investigated. The flowability of compounds is evaluated by the flow length of slit flow tests. Our experimental results showed that the relation between the slit flow and the thickness of channel is divided into 3 regions according to the channel thickness. In the region of small channel thickness, the slit flow length increases with the channel thickness. In the intermediate region of channel thickness, the slit flow length remains nearly constant regardless of the channel thickness. In the region of large channel thickness, the slit flow length again increases with the channel thickness. The boundaries of these regions are given by the filler size, i. e., at 5-10% and 70-80% of the cumulative undersize distribution of the filler. The slit flow length is expressed by the product of the 10% diameter of particle size distribution, the frequency of coarse particles larger than the channel thickness, and the packing fraction of filler.
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