Generally we have commercially today three foaming recipes for closed cell cellular glass. First there was the carbon system, which works under a reducing atmosphere. This system is still dominant in the production of boards. Later on, there was the SiC foaming agent and the organic foaming agent, dissolved in water glass. SiC is only used for the production of foamed glass gravel while the organic foaming agent in water glass shows up in gravel and boards.
The SiC system involves rather high foaming temperatures above 900°C, which shortens the life of the expensive belt on which the foaming happens. The carbon system involves a strong reducing atmosphere, which includes a rather low combustion efficiency. Both are dry methods, which generate a lot of dust during production.
The glycerin / water glass foaming agent is an alternative, which foams in a neutral atmosphere (high combustion efficiency) below 800°C, without generating any dust thanks to the water glass. This foam can be cut or broken after foaming without inducing any decoloring or other damage, which is important for gravel and board production. For board production from a continuous ribbon, annealing becomes a lot easier due to this cutting after foaming because temperature gradients only acts on the sawed stroke and not on the full ribbon. On top of that, the water glass improves the sintering behaviour of the glass powder, which is translated in a reduced grinding of the glass cullet.
From the above, it is clear that the glycerin / water glass foaming system is the future and this foaming system is indeed booming with boards and gravel. Reduced production cost, reduced investment and improved ecology are the main reasons.
Therefore, we came interested to find the brilliant inventor of this process. We found a patent from Millcell AG in Switzerland with Otto Anton Vieli as inventor and also a US-patent version. The patent was filed in 1978 and was expired in 1998. Today, this process is booming without any royalties in Germany, Austria, Switzerland and Russia with at least 1000000 m³ cellular glass yearly.
The patent mentions that the organic foaming agent has to be dissolved in the water glass which is basically the reason why it can be used in a neutral atmosphere and sawing / cutting is possible at higher temperature without burning out of the foaming agent causing decoloring of the foam. Glycerin is the typical example of an organic foaming agent.