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    The bushing is rectangular shaped platinum alloy box with a large top opening and a multiplicity of orifices or tips in the base.  The bushing is electrically heated and the bushing acts as a “thermal valve” and accurately controls the flow of glass through it over a long period of time.   Thermocouples attached to the bushing send a control signal to a PID controller, which then controls a SCR Power Pack used to regulate the supply voltage to a highly turned down special water cooled transformer.  Large copper buss bars and clamps complete the circuit between the transformer and bushing.  From the economic point of view, it is desirable to flow as much glass as possible through the tips and convert efficiently to fiber.  From the technical point of view, the draw-down ratio should be kept as low as possible for optimum stability of the process.  The bushing should operate with the smallest orifice, which at the highest temperature possible consistent with stable conditions will give the desired throughput.  In practice this is limited by the rate at which the surface of the glass cones will cool.  GSI designs bushings and the supporting hardware and also uses  McCormick & Associates for custom designs.



Fiber Forming Systems:

In all types of Fiber Forming Systems designed by GSI the forehearth refractory and support structure are integrated into the forming room design.  The furnace channels/forehearths, support structure and the forming room are not treated as separate components but coordinated in an overall design.  Equipment mounts and utility supply conduits depend on the forehearth support frame for support.

The GSI forming room is very open and allows for bushing access from any side.  The GSI bushing area is completely open on all sides for clear access to all cooling devices on double-bottom bushings.  There are no rear or side sheet metal walls around the upper level bushing area.  There are normally some screens around the upper bushing area to block heat radiation on the operator and direct air flow towards the bushing.  Low velocity cooling air is directed toward the front and rear of the bushing from ducts located more than a meter away.  That controlled cooling air is used to establish a constant environment around the bushing tip area and also to supply clean air to be drawn into the tip region during attenuation.  The GSI Open Forming System allows the horizontal running of multiple strands to direct chopping machines along the rear of the applicator while adjacent strands travel downward to winders without interference. 




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