In the process of drawing fiberglass in a tank furnace, why is the fiber root the core key to fiberglass forming?

Basic Principles of Fiber Forming

 

In the tank furnace fiber drawing process, molten glass, under hydrostatic pressure, flows out in droplets from a precision nozzle at the bottom of a platinum alloy baffle. A high-speed drawing machine, located directly below the nozzle, rotates at a constant high speed, applying a strong stretching force to the falling glass droplet. The key to this process lies in the dynamic equilibrium zone formed at the droplet exit-the fiber root:

 

1. Fiber Root Formation:

Below the nozzle exit, the surface tension of the molten glass (attempting to maintain the droplet's spherical shape) and the stretching force of the drawing machine (attempting to stretch the droplet) reach a dynamic equilibrium. This causes the molten glass to form a unique, crescent-shaped region at the nozzle exit. The diameter of this region gradually tapers from the nozzle exit.

 

2. Fiber Forming Line:

The distance from the nozzle exit until the molten glass is stretched and solidified, and the fiber diameter reaches its final and no-longer-changing point, is called the fiber forming line. The space encompassing this line is the fiber forming zone. Within this zone, the molten glass undergoes a dramatic viscosity change, solidifying from a viscous fluid into solid fibers.

 

3. Fiber Drawing Line:

This refers to the total distance from the nozzle outlet to the fiber winding point on the drawing machine. This distance can be manually adjusted according to process requirements (such as cooling needs and operating space), and is usually much longer than the actual fiber forming line length.

The stability of the fiber root and fiber forming line is a decisive factor in producing high-quality glass fibers, directly affecting:

 

◉ Uniformity of fiber diameter

◉ Breakage rate

◉ Production efficiency and cost

 

Key process parameters affecting forming stability:

* Liquid level: Determines the hydrostatic pressure of the molten glass at the nozzle, affecting the outflow rate and initial fiber root morphology.

* Shutter temperature: Precisely controlling the viscosity of the molten glass is fundamental to obtaining suitable tensile properties.

* Drawing speed: Directly determines the magnitude of the draw force and the final fiber diameter.

* Molten glass properties: Chemical composition determines its viscosity-temperature characteristics, surface tension, crystallization tendency, etc.

* Cooling conditions: Affects the temperature gradient and solidification rate in the fiber root region, crucial for stability and fiber performance.

* Draw ratio: The ratio of the nozzle orifice diameter to the final fiber diameter, reflecting the degree of drawing.

 

Airflow control: Affects the temperature field distribution and cooling efficiency in the fiber root region.

 

Pool Furnace Fiber Drawing Process Equipment and Layout

 

Achieving stable and efficient fiber forming relies on a series of process devices precisely arranged vertically (from top to bottom):

 

1. Spindle:

Contains and regulates the temperature of molten glass, and controls the flow of molten glass through the spout.

 

2. Fiber Root Cooler:

Located directly below the spindle, close to the fiber root region. Typically uses air cooling (high-pressure air curtain) or water cooling (indirectly) to rapidly and controllably force-cool the high-temperature, viscous fiber roots, accelerating the solidification and shaping of the molten glass. It is a key piece of equipment for stabilizing the fiber roots.

 

3. Raw Fiber Sprayer:

After the fiber has initially solidified, it sprays water mist or air onto it for auxiliary cooling.

 

4. Monofilament Oiler:

Before the monofilaments are bundled into raw filaments, a wetting agent (bundling agent, lubricant, coupling agent, etc.) is uniformly applied to the surface of each monofilament. The sizing agent plays a crucial role in protecting the fibers, bundling them into strands, and bonding them to subsequent composite materials.

 

5. Bundler:

Ensuring that the monofilaments flowing from different nozzles are spatially separated, preventing them from sticking together or colliding.

 

6. Bundler:

Gently bundling multiple oiled and bundled monofilaments (typically tens to thousands) into a continuous filament.

 

7. Slow-Pull Roller:

Located below the bundler, it applies slight tension to the bundled filament, allowing it to smoothly transition to the high-speed drawing machine area.

 

8. Airflow Diffuser:

Located above the drawing machine inlet, it disperses or guides the airflow, preventing turbulence generated by the high-speed rotating drawing machine head from interfering with the stable operation of the fibers above.

 

9. Drawing Machine:

The power core of the forming system. Its high-speed rotating head (winding head) generates strong drawing force, stretching the molten glass into fibers and winding the solidified filament into a bobbin (yarn). The forming process position line refers to the relative vertical and horizontal layout of the aforementioned key devices (mainly the stencil, oiler, bundler, drawing machine winding wheel, and head). This layout design directly affects the fiber's running path, tension distribution, and cooling effect.

 

Single-layer layout: All forming operations (from the stencil to winding) are basically completed on the same operating plane. The structure is relatively simple, but the operating space may be limited.

 

Double-layer layout: The process is divided into upper and lower operating zones (common in large tank furnace drawing lines). Upper zone: Typically includes the stencil, fiber cooler, sprayer, oiler, bundler, and bundler, for high-temperature forming and preliminary treatment.

 

Lower zone: Mainly includes the slow-drawing roller, airflow diffuser, and drawing machine for fiber winding. This layout optimizes space utilization, improves the operating environment (especially the isolation of the high-temperature zone), and facilitates automation.

 

Summary

Glass fiber forming is an art of precisely balancing surface tension and mechanical tensile force at high temperatures. Understanding the formation and stabilization mechanism of "fiber roots" is the core of mastering the process. By precisely controlling key parameters such as liquid level, temperature, speed, and cooling, and utilizing a precision device system consisting of a baffle plate, cooler, oiler, bundler to drawing mechanism, along with a reasonable "forming process position line" design, viscous molten glass can be efficiently and stably transformed into high-performance continuous glass fibers.