研究了聚碳硅烷(PCS)熔体在Y型喷丝孔中的挤出胀大机理、 膨胀模型以及膨胀比对Y型碳化硅纤维异形度的影响. 结果表明: 采用圆形喷丝孔时PCS的膨胀比为1.02$\sim$1.15, Y型喷丝孔时膨胀比为1.02$\sim$1.43, 在与圆形喷丝孔成形条件相当的情况下, Y型喷丝孔的膨胀比比圆形孔的高出约15\%, Y型口模周边的剪切应力分布不均、剪切应力内外差异和区域差异是造成其膨胀比增大的根本原因. PCS熔体温度降低或软化 点提高, 其出口挤出胀大效应增大. 由于模口膨胀的影响, Y型PCS纤维的异形度比喷丝孔异形度下降10\%$\sim$20\%.
The die--swell mechanism of polycarbosilane(PCS) melt for a spinneret with Y--shaped orifice and the effect of die swelling of PCS on the profile degree ($PD$) of Y--shaped SiC were investigated. For a spinneret with circular holes, the die--swell ratio was in the range of 1.02$\sim$1.15, while for a spinneret with Y--shaped orifices, the ratio is 1.02$\sim$1.43. The die--swell ratio for a spinneret with Y--shaped orifices was about 15\% higher than that with circular holes in the same forming condition. The asymmetric distribution of shear stress in the circumference of the Y--shaped orifice and the different shear stress in the orifice profiles were the fundamental reasons for the increase of the die--swell ratio for the Y--shaped orifice. In comparison with the $PD$ of the orifice, there was a reduction of 10\%$\sim$20\% in the $PD$ of the fibers.
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