Abstract:

Objective As one of the most widely used inorganic fiber, basalt fiber has the advantage of high strength, high modulus, excellent chemical corrosion resistance and anti-atomic oxygen properties. Thus,it can be used as a high-temperature resistant sewing thread material in aviation and military industries. However, its high brittleness and poor-wear resistance strongly restrict the processibility and final application of basalt fiber. In order to prepare basalt fiber based high-performance sewing threads, polyamide filaments were introduced to incorporate with basalt fiber for fabricating composites yarns.

Method Using a hollow spindle covering spinning mechanism, the polyamide filament yarn was used as the sheath to coat the double-stranded basalt filament yarn in both directions. In this case, the basalt core yarn was arranged vertically in the coating yarn and was coated by the outer polyamide filament. The outer coating yarn not only contributed to the strength but also provided strong wear-resistance, laying the foundation for the preparation of excellent sewing threads with both flexibility and high strength properties.

Results The overall strength of all five different double-coated yarns was increased over the core basalt yarn by about 23% to 29%. The basalt core yarn was axially arranged in the composite yarn retaining the core yarn strength, while the outer coating yarn also contributed to the strength resulting in enhanced strength of the composite yarn. The breaking force maximized when the wrapping twist was 650 twists/m (Tab. 2). At this twist, the yarn exhibited the highest breaking elongation, indicating that the yarn has good flexibility. When the twist increased to 750 twists/m, the breaking strength of the yarn decreased sharply by 3.20 cN/tex. The strength variations of three different yarn densities were compared by selecting the optimal strength at 650 twists/m (Tab. 3). It showed that the higher the density of the composite yarn, the higher the strength of the yarn. The coated yarn of 16.7 tex in this research had the highest break strength. The variation of twist of the composite yarn showed that the increase of twist would lead to the increase of coating density (Fig. 3). The three-dimensional microscopic fracture morphology indicated that the surface core yarns showed different magnitudes of protrusion at the wrapping spacing, and the core yarns broke into splits after a fracture. The results of the wear-resistance tests shown that at 650 twists/m the yarn has the smallest coefficient of variation (Tab. 4). The core yarn was protected by the sheath, and the low-twist sheath yarn also demonstrated strong wear-resistance in the test.

Conclusion As the twist increases, the composite yarn strength firstly increases and then decreases, and the higher the density of the outer yarn, the higher the yarn strength. The spiral coating structure of the outer yarn provides axial force in the radial direction and increases the clamping force. Continuously increasing the twist, the angle between the two-way sheath increases as well, causing smaller spacing between coating sheath strands, higher yarn density, but lower axial strength of the composite yarn. Further increase in twist could lead to lower strength because the core yarn can be damaged by too tight hold. The degree of wear-resistance tends to weaken and then increase with an increasing twist. At lower twist levels, the polyamide filament spacing is relatively long and the number of abrasion rollers rubbing against the polyamide filament increases. After increasing the twist degree, the pilling phenomenon tends to occur when grinding, and the number of grinding breaks decreases. Continuously increasing the yarn wrapping tightness makes it hold stronger, and the wear-resistance will gradually increase.

Key words: basalt filament, coated yarn, hollow spindle, twist, breaking force, polyamide filament