Fourcault process

The Fourcault Process is a method of manufacturing flat glass. First developed in Belgium by Émile Fourcault during the early 1900s, the process was used globally. Fourcault is an example of a "vertical draw" process, in that the glass is drawn against gravity in an upward direction. Gravity forces influence parts of the process.

The Fourcault process requires a "pit" or drawing area and an assembly of machines to draw up the ribbon of glass while performing actions upon it that ensure desired quality and process yields. Today most glass manufacture has a "hot end" where the products are made. Fourcault is no exception.

The action in Fourcault happens "at the draw", or area where the glass is taken from a liquid state into the start of the process needed to make it into flat glass.

At the bottom of the draw is the "pit" or place where the molten glass is sufficiently cooled to be close to forming temperature. The cooling process uses a device known as a "canal". As the name describes, a canal is a box shaped structure which conveys the glass from the refining area to the pit.

The canal links the pit with the "refining" area, a section of the glass furnace that removes gas bubbles and other sources of imperfection. Since refining requires much higher temperatures to release gas bubbles than those required to form the glass it is not possible to draw directly from the refining area, hence the need for canals.

The Fourcault Process uses a ceramic die to shape fused (or molten) glass into a ribbon of rectangular cross section. The die, known as a Debiteuse, floats in the molten glass inside of the pit to a prescribed depth which slightly pushes a part of the molten glass slightly above the top surface of the die. A slot is cut through the center of the Debiteuse, which is shaped to produce the best quality of glass.

The Debiteuse is the starting point of the vertical draw, where the glass begins to change from a hot syrupy mass into useful flat glass. We will call the glass from the point of the Debiteuse until it is cut a "ribbon".

The base of the ribbon is shielded from heat radiation from the fused glass so that it continues to hold the shape imparted to it by the Debiteuse. This cooling preserves the rectangular cross section of the drawn glass by cooling the ribbon glass below the temperature where it would collapse into a column or break back into the melted glass. It is especially important to shield the outside edges of the ribbon from heat so that they are firmer and will hold the rest of the ribbon in a proper shape. In some cases manufacturers will allow the edges to form thicker "bulbs", which are removed after final cutting.

Immediately after being drawn the ribbon is cooled using mechanical coolers so that it maintains its rectangular shape in two dimensions, but assumes a ribbon like structure that extends down into the Debi and upwards into a drawing assembly. This mechanical cooling allows the ribbon to hold its integrity. In the author's experience the mechanical coolers used water, contained in specially shaped radiators, to remove heat radiated by the ribbon.

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