Why has the tank furnace drawing process become the mainstream production method for fiberglass?

01. What is Fiberglass?

 

Fiberglass, also known as glass wool or fiberglass, is a new type of reinforcing material commonly used in composite materials, electrical insulation, thermal insulation, circuit boards, and other sectors of the national economy. Its monofilaments range in diameter from a few micrometers to over twenty micrometers, equivalent to 1/20 to 1/5 the diameter of a human hair. Each bundle of fiber consists of hundreds or even thousands of monofilaments.

 

It is made from six minerals-pyrophyllite, quartz sand, limestone, dolomite, borosilicate, and boromagnesia-through high-temperature melting, drawing, winding, and weaving processes. It is a high-performance inorganic non-metallic material with many varieties. Its advantages include good insulation, strong heat resistance, good corrosion resistance, and high mechanical strength. However, its disadvantages include brittleness and poor wear resistance.

 

02. Composition of Fiberglass

 

The main components are silicon dioxide, aluminum oxide, calcium oxide, boron oxide, magnesium oxide, and sodium oxide. Based on the alkali content, it can be divided into:

 

① Alkali-free Fiberglass (0%~2% sodium oxide, aluminoborosilicate glass)

 

② Medium-alkali fiberglass (8%~12% sodium oxide, boron-containing or boron-free sodium-calcium silicate glass) and high-alkali fiberglass (sodium oxide 13% or more, sodium-calcium silicate glass).

03. Characteristics of Fiberglass

 

Characteristics: fiberglass has higher temperature resistance than organic fibers, is non-flammable, corrosion-resistant, has good heat and sound insulation, high tensile strength, and good electrical insulation. However, it is brittle and has poor wear resistance. Used to manufacture reinforced plastics or reinforced rubber, as a reinforcing material, Fiberglass has the following characteristics:

 

① High tensile strength and low elongation (3%).

② High elastic modulus and good rigidity.

③ Large elongation within the elastic limit and high tensile strength, thus absorbing a large amount of impact energy. ④ It is an inorganic fiber, non-flammable, and has excellent chemical resistance.

⑤ It has low water absorption.

⑥ It has excellent dimensional stability and heat resistance.

⑦ It has good processability and can be made into various forms such as strands, bundles, mats, and woven fabrics.

⑧ It is transparent and allows light to pass through.

⑨ It has good adhesion to resin.

⑩ It is inexpensive.

⑪ It is not easily flammable and can be melted into glass-like beads at high temperatures.

 

04. Fiberglass Production Process

 

There are two fiberglass production processes: two-stage molding - crucible drawing method and one-stage molding - tank furnace drawing method.

The crucible drawing method involves several steps. First, the glass raw material is melted at high temperature to form glass spheres. Then, the glass spheres are melted a second time and drawn at high speed to form fiberglass filaments. This process has many drawbacks, including high energy consumption, unstable molding process, and low labor productivity, and has been largely phased out by large-scale Fiberglass manufacturers.

 

The tank furnace drawing process involves melting raw materials such as pyrophyllite into a glass molten solution in a furnace. After removing air bubbles, the solution is transported through a channel to a porous stencil, where it is drawn at high speed into fiberglass filaments. The furnace can connect hundreds of stencils via multiple channels for simultaneous production. This process is simple, energy-efficient, provides stable forming, and is highly efficient and productive, facilitating large-scale, fully automated production. It has become the mainstream international production process, producing over 90% of global fiberglass.