Can the float glass technology be used for the continuous foaming?

logo_smallWe are currently studying the technology to produce float glass. In a lot of cases, float glass is used as base material to foam directly or to remelt with addition of other raw materials and to be foamed later on.

logo-cnud-efcoBut since GFT joined CNUD EFCO, we are also interested about the tin bath. Molten tin and hot glass cannot be mixed and for that reason, we can produce window glass direcly on the molten tin. But could we do this also with cellular glass?

DownloadCould we put a glass powder with foaming agent on the molten tin and let it foam? In that case, we don´t need a belt or a mold, which are expensive parts in the production process. They have to be replaced regularly and are also heated to 850°C in the foaming process, consuming a lot of primary energy. Also the complete investment of rollers and drive systems can be skipped. On top of that, the typical belt coating with kaoline is not needed anymore, the glass foam does not stick on the molten tin.

The technology to protect the molten tin for oxidation can be used for the foaming with carbon black, where a reducing atmosphere is always needed. The foaming processes with glycerin can probaly skip or reduce  the use of water glass while the SiC process can remain unchanged.

imagesThe use of (graphite) fenders for thicker glass is now available to make a perfect rectangular foam (low waste) while top rollers can be used to stretch the cellular glass for an improved thermal conductivity or even to compress the cellular glass for an improved compressive strength without changing density. The bottom of the foam does probably not need any facing improving the efficiency of the process even more. I guess a foaming  efficiency close to 90% becomes possible (90 % of the glass is sold as foam).

Heating above the glass can be done with gas burners, which are also generating the reducing atmosphere. Heating under the foam has to be done in another way, keeping the temperature of the bottom of the foam equal to the top.

The largest part of the above is already published in an old US3361550 patent from 1964, when commercial float glass was born. The general remark on this idea is that a tin bath is too expensive compared with a normal foaming furnace. It is my conviction that a much simpler tin bath can be constructed for this purpose because we don´t have to produce perfect transparant glass without any distortion. The payback is made with less primary energy and refractory steel use and a larger flexibility. The answer on the above question is YES, this is the second generation continuous foaming.

patent

And if we combine this with a small glass melting furnace, we could foam on a molten glass plate. This cellular glass should have one absolutely hard surface, which is frost resistant, could have any color wanted and is absolutely flat. If a less smooth surface is allowed, we could work with two layers of powder: one non-foaming and one foaming. The idea for a new generation cellular glass is born.

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