The present invention relates to an improved method and apparatus for centrifugally forming filaments from molten glass or other thermoplastic materials such as polyester and polypropylene.
It is well known in the art to produce large quantities of fibers by supplying a stream of molten material to a high speed centrifuge or rotor having a plurality of orifices about its peripheral face through which the molten material flows by centrifugal force. The eminating streams of material are then subjected to a gaseous blast to attenuate the molten streams or primary fibers into fine filaments.
The production rate at which filaments may be formed is a function of the number of orifices about the rotor periphery. To increase the number of orifices it is generally necessary to increase the peripheral surface area of the rotor where the orifices are located. The peripheral surface area can be increased by increasing the depth of the rotor and/or increasing the diameter thereof. Also the production rate can be increased by manipulating the size of the orifices in the rotor and the force generated by the gaseous attenuation blast and/or the speed of the rotor.
Increasing the rotor depth can cause material flow and thermoequilibrium problems resulting in undesirable fiber properties. On the other hand, by increasing the rotor diameter, the fluid dynamics downstream of the rotor may be adversely affected. The low pressure region directly downstream of the rotor influences the stability of the primary fiber/filament veil in that the unstable veil tends to wobble aimlessly about the downstream extension of the rotor's axis of rotation. Such wobbling can affect the flow parameters in the attenuation zone and coarse non-uniform and undesirable filaments can be produced thereby.
The phenomenon of veil instability is not necessarily restricted to large diameter rotors. Generally speaking, the instability phenomenon may be observed for various attenuating momentums depending upon the vortex strength immediately downstream of the rotor.
Typical prior art disclosing techniques aimed at diminishing the effect of the low pressure region downstream of the rotor may be found in U.S. Pat. Nos. 3,114,618; 3,285,723; 3,179,507; 3,372,011; 2,855,626; 3,040,337; and 4,046,539.