Işık fiberini çekerken uygulanan kuvvet, fiberin kalitesini etkiler mi?
Fiber drawing tension in fiber manufacturing engineering is not only a factor that affects fiber quality, but also one of the core process parameters that determine the geometric dimensions, optical loss, and mechanical reliability of the fiber.
I. What is Fiber Drawing Tension?
Fiber drawing is typically performed on a drawing tower tens of meters high:
- Melt Deformation: A high-purity silica fiber preform is fed into a high-temperature drawing furnace (graphite resistance furnace or induction furnace, typically at 1900^\circ\text{C} \sim 2100^\circ\text{C}) where it softens and forms a neck-down region.
- Drawing into Fiber: A bottom capstan pulls downward at a set speed, stretching the preform, which is several centimeters in diameter, into a bare fiber with a nominal diameter of 125\ \mu\text{m}.
- Tension Definition: The axial tensile force experienced by the fiber in the melt forming zone and cooling section is the drawing tension (usually expressed in gram-force (gf) or millinewtons (mN), with common industrial control ranges generally between 30 \sim 150\ \text{gf}, depending on drawing speed, cladding diameter, and material composition).
The drawing tension F is directly related to the viscosity \eta of the glass melt in the neck-down region, the drawing speed v, and the geometric tapering rate:
F \approx 3 \pi \eta r^2 \frac{\partial v}{\partial z}
II. Specific Mechanisms of Drawing Tension’s Impact on Fiber Quality
Excessive or insufficient drawing tension can have multidimensional negative effects on the fiber:
1. Geometric Uniformity and Outer Diameter Fluctuation
- Excessive Tension: The molten zone is prone to capillary instability or rheological instability, leading to high-frequency radial jitter in the fiber’s outer diameter.
- Insufficient Tension: The fiber may sway at low frequencies in the furnace and cooling tube, causing delays in the feedback closed-loop control of the outer diameter, severely affecting the tolerance consistency and roundness of the cladding diameter (125 \pm 0.7\ \mu\text{m}).
2. Microscopic Defects and Optical Attenuation (Loss)
- Excessive Tension:
- High shear stress can cause bond breaking in the three-dimensional tetrahedral network structure of high-purity silica glass (\text{SiO}_2), creating point defects (such as non-bridging oxygen hole centers (NBOHC), oxygen defect centers (ODC), E’ centers, etc.). These color center defects can generate additional absorption peaks in specific ultraviolet, visible, and near-infrared bands.
- It also increases the non-uniformity of the glass’s microscopic density,