1. Field of the Invention
The present invention relates to the Vello process and draw-down process for making glass products from a glass melt and, more particularly, to a sleeve-type agitator for the glass melt for preventing schlieren formation and for homogenizing the glass melt in the Vello process and draw-down process. The invention also relates to a method and apparatus for feeding a glass melt in order to make glass products, especially glass tubes or pipes, from the glass melt without schlieren formation in the glass melt.
2. Description of the Related Art
The Vello tube drawing process is a vertical drawing process for glass tube or pipe, in which the tube or pipe is drawn down from a circular nozzle. The glass melt flows through a nozzle with a cylindrical opening which is located at the bottom of a feed channel and over a funnel-shaped conical body which is adjustable in its height and which widens downward. The conical body is hollow and connected with a longitudinally extended pipe to a blower for air. The glass mass located around this valve body is held open when air is supplied through this pipe. The freely suspended glass is then drawn downward as a glass tube into a temperature regulated compartment or guided with the help of guide members into a horizontal orientation and drawn from the drawing machine.
The draw-down process operates exactly the same way that the Vello process does, except that the glass tube is not guided into a horizontal orientation, but instead is removed vertically from the drawing machine.
In the Vello head and draw-down head used in these glass product manufacturing processes schlieren are produced on the side facing away from the channel, which currently can be reduced only by connecting a head overflow. It is necessary to draw off the schlieren extending around the product with a head overflow duct in conventional feed heads. Faulty products would otherwise be produced with the schlieren extending around the product. Drawing the product with the schlieren thus causes glass losses.