In glass fiber production, molten glass flows through a funnel and is drawn and cooled and cured into very fine fibers by a high rate of downward pulling gravitational force at the outlet of the funnel. For the fiber forming process to be stable, there are specific requirements for certain properties of the glass solution. These properties include crystallization properties, surface tension, viscosity and other rheological properties, hardening speed and the wetting properties of the glass liquid on the nozzle material.

  1. the crystallization properties

  Glass fiber production on the greater impact of crystallization performance, refers to the upper limit temperature, crystal growth rate, the maximum crystal growth rate of the temperature and the first and second precipitation of the crystal phase (i.e., the initial and subsequent precipitation of crystals category).

  2. viscosity and hardening speed

  Viscosity is one of the important operational properties of glass, the production of any glass products, including glass melting and clarification, product forming and annealing, etc., are related to viscosity. The viscosity requirements for the production process of continuous glass fibers are: (1) The drawing operation temperature Tw should be low. This will enable the fiber to be formed at a lower funnel temperature, thereby reducing energy consumption, improving the operating environment and extending the service life of the platinum alloy funnel. The tensile strength and creep life of platinum alloys both decrease with increasing temperature. For example, Pt-Rh alloy, the temperature of 1100 ℃, its tensile strength of 5.6kg / mm, 1200 ℃, the tensile strength is reduced to 4.4kg / mm ; when the temperature from 1200 ℃ to 1300 ℃, the creep life is shortened from 16h to 2.6h. (2) Drawing operation temperature than the upper limit of the crystallization temperature is at least 40 ~ 50 ℃ higher (i.e., Tw-TL>40 ~ 50℃). Otherwise, the drawing process may produce precipitation and affect the drawing operation. Some glass components are difficult to do this, it is necessary to use special measures in the drawing process, such as enhanced cooling and other methods. Glass hardening rate in addition to the factors directly affected by the composition of glass, of course, also affected by the quality of the glass being cooled, the ratio of surface area to mass and the cooling medium (such as air) temperature and flow rate. When fiberglass is formed, the surface area to mass ratio is very large, so the hardening rate is faster. Generally, after the glass composition is determined, the temperature-viscosity curve is not easy to change, and the heat capacity and thermal conductivity rarely change, but the iron oxide in the glass is unavoidable.

  3. Surface tension

  Surface tension is the work required to increase a unit area of a liquid in contact with another phase at the phase interface (generally referred to as the liquid-gas interface) at constant temperature and volume. It is usually expressed as σ in units of 10-3N/. Silicate glass liquid surface tension is generally 0.220 ~ 0.380N / m. Glass clarification process, the greater the surface tension, the glass liquid bubble growth and rise the slower the rate of discharge; conversely, the faster. The speed of diffusion and dissolution of streaks and nodules in the glass liquid also depends on the relative size of the surface tension of streak glass and base glass.

  4. Rheological properties

  This is some property of a material that causes it to flow or deform when subjected to an external force. A liquid will flow when subjected to a force and a solid will deform (both elastically and permanently) until it breaks. However, under certain conditions, brittle solids will also flow and liquids will break brittlely. Here the time of application of the force and the time of stress relaxation in the material play a very crucial role. The stress relaxation time of a liquid is very short, but if the force is applied for a shorter time than the stress relaxation time, the liquid behaves like a solid and will also fracture. A solid has a long stress relaxation time, but if the force acts for a longer time than that, the solid will also flow. The mountains of hard rock on earth flow from a geologic conception of time. Similarly, during fiberglass forming, since the force acts for a short time, it is possible to produce brittle fractures in the viscous state even before the glass liquid is fully solidified. Therefore, stress relaxation time is a very important rheological property.

  5. Wetting properties

  In glass fiber production, glass liquid and leakage plate material (generally platinum alloy, also used nickel-based high-temperature alloys) between the degree of wettability, on the wire drawing operation is affected. Good wettability, flow through the leakage nozzle flow is small, more importantly, will be in the leakage nozzle outlet wall to the surrounding dispersion, the formation of the so-called "diffuse flow", serious so that the wire drawing operations can not be carried out. Therefore, poorer wetting on the contrary, drawing is favorable. Wetting phenomenon is the liquid phase, solid phase and gas phase with each other - a kind of interfacial force balance phenomenon.