Glass fiber forming unit

In a glass fiber forming unit including a hollow-cylinder-shaped rotating spinner having (a) a bottom, (b) a surrounding wall having upper and lower outer surfaces and with a number of molten glass projecting orifices where the molten glass projects from each orifice such that a transition cone of the glass is formed with its base at the orifice and primary filaments of the glass extending from the apex of the cone, and (c) an upper annular flange extending inwardly from the upper edge of said surrounding wall;

• and an attenuating blast burner with jet flame orifices for attentuating primary filaments formed at the tips of transition cones of molten glass projecting from said rotating spinner into secondary filaments where the jet flame comprises an inner cone of flame surrounded by an outer cone of flame, the speed of the inner flame being greater than that of the outer flame, the improvement comprising
• said jet flame orifices in said attenuating blast burner being so positioned with respect to the surrounding wall hollow-cyliner-shaped rotating spinner that, for each jet flame from each jet flame orifice, (1) the inner cone of flame (a) contacts said primary filaments to attenuate them into the glass fibers due to the high speed of this flame and (b) does not contact said transition cones sufficiently to break them even though the speed thereof is sufficient to do so and (2) the outer cone of flame is in substantial contact with only the lower outer surface of said surrounding wall of said hollow-cylinder-shaped rotating spinner where the speed of said outer cone of flame is such as to not break said transition cones, and
• a heating burner disposed inside said upper annular flange of said hollow-cylinder-shaped rotating spinner for jetting a flame in a direction which is along the prolongation of said upper annular flange and which is in parallel with the surface of said upper annular flange, said flame from said heating burner heating said rotating spinner in such a manner that said flame goes along at least the upper surface of said upper annular flange to transmit heat to at least a corner where said upper annular flange of said hollow-cylinder-shaped rotating spinner and said surrounding wall meet such that the heat supplied to the upper surface of the surrounding wall by the heating burner and the heat supplied to the lower surface thereof by said outer cone of flame results in a substantially uniform temperature of the surrounding wall to thereby enhance fiber glass uniformity.