TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The total volume of the molten glass in the cooling part accounts for 40-60% of molten glass at half portion of the outlet. The distance at bottom of molten glass is at the depth of 1/2. The periphery place of the inner side wall of the heating device and temperature measuring device is located with refractory bricks to form circular bottom mounting arrangement. When the molten glass plane line shows rising and descending changes, the plane line of the glass also shows rising and descending changes in different degrees, or the volume of molten glass in the cooling unit changes, specifically, generation of large breakdown, or forming upper work section due to maintenance or operation error, or failure of molding part product, replacement of product, or change in the drawing amount, or change of product debugging time, glass product failure in molding process, breakdown in annealing step, or failure in cutting process, or failure of installation package. When the temperature measured in the temperature measuring device is less than the glass crystallization temperature at 50 degrees C, the heating device begins to heat and increases the power of the heating device. The depth of the molten glass in the cooling part is in the range of 0.15-0.9M, is calculated according to the plane of the glass area of the cooling liquid, and 1-5 heating devices are installed at the range of 0.2-3 cm2. The power in the heating device is 3-15 times higher than normal, when the large-scale production. EXAMPLE - 4 wt.% Sodium oxide, 25 wt.% aluminum oxide, 38.5 wt.% silica, 20.3 wt.% calcium oxide, 12.2 wt.% magnesium oxide, silicon oxide with content of 1.9 times that of calcium oxide, and calcium oxide with content of 1.66 times that of magnesium oxide were mixed and conveyed into the hopper. Glass raw materials were melted and conveyed into the cooling part. 30 Temperature-measuring devices and 30 heating devices were set in the space above the level of glass liquid in the cooling part, at a distance of 10-80 mm from the inner side of a refractory brick wall of the pool. The heating devices were heated when the temperature at the cooling part measured by the temperature-measuring devices was less than 50 degrees C of crystallization temperature of the molten glass, and the heating was terminated when the temperature at the cooling part measured by the temperature-measuring devices was more than 100 degrees C of crystallization temperature of the molten glass. The molten glass from the cooling part was directed to multiple holes in a high-temperature resistance porous metal plate, stretched at a high speed to form glass fibers, and cooled to obtain glass fiber product.