Ultrasonic Degassing Molten Glass
New generation ultrasonic NIMA generators for the molten glass industry
Ultrasonic treatment of molten glass can substantially improve their properties
Recently, we have introduced a new ultrasonic generator ánd a proprietary ceramic sonotrode which enable us to treat large volumes of highly viscosity molten glass up to 1,600 degrees Celsius.
Principle of ultrasonic degassing in molten glass
The gas bubbled rise to the surface and are expelled. An alternative approach involves subjecting the melt to reduced pressure, but both processes have environmental and economic drawbacks.
During ultrasonic degassing, the microbubbles that form during the low-pressure cycle provide nuclei for the formation of hydrogen bubbles. Essentially, hydrogen diffuses to these bubbles. Assisted by ultrasonically induced acoustic flow and streaming, the hydrogen bubbles rise to the melt surface and are expelled.
This process has many advantages over the traditional methods, including reduced environmental cost and improved efficiency. Effectively ultrasonic degassing reduces the porosity of the cast increasing both strength and ductility.
Glass Making Process
There are currently two primary methods of making glass containers: the blow and blow method for narrow-neck containers only, and the press and blow method used for jars and tapered narrow-neck containers.
In both methods, a stream of molten glass, at its plastic temperature (1,050–1,200 °C [1,920–2,190 °F]), is cut with a shearing blade to form a solid cylinder of glass, called a gob. The gob is of predetermined weight just sufficient to make a bottle. Both processes start with the gob falling, by gravity, and guided, through troughs and chutes, into the blank moulds, two halves of which are clamped shut and then sealed by the “baffle” from above.
In the blow and blow process, the glass is first blown through a valve in the baffle, forcing it down into the three-piece “ring mould” which is held in the “neckring arm” below the blanks, to form the “finish”, [The term “finish” describes the details (such as cap sealing surface, screw threads, retaining rib for a tamper-proof cap, etc.) at the open end of the container.] The compressed air is blown through the glass, which results in hollow and partly formed container. Compressed air is then blown again at the second stage to give final shape.
Containers are made in two major stages. The first stage moulds all the details (“finish”) around the opening, but the body of the container is initially made much smaller than its final size. These partly manufactured containers are called parisons, and quite quickly, they are blow-molded into final shape.
The “rings” are sealed from below by a short plunger. After the “settleblow” finishes, the plunger retracts slightly, to allow the skin that’s formed to soften. “Counterblow” air then comes up through the plunger, to create the parison. The baffle rises and the blanks open. The parison is inverted in an arc to the “mould side” by the “neckring arm”, which holds the parison by the “finish”.
As the neckring arm reaches the end of its arc, two mould halves close around the parison. The neckring arm opens slightly to release its grip on the “finish”, then reverts to the blank side. Final blow, applied through the “blowhead”, blows the glass out, expanding into the mould, to make the final container shape.
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