When I found the description of Neoporm for the first time on Internet, I simply did not believe it. The paper claims that it is possible to make the highest quality cellular glass from waste glass without remelting. For about 26 years, I believed that this is not possible and as a consequence, I never did research in that direction. Wrong, very wrong. Walter Frank from GLAPOR expressed once his will to make high quality cellular glass from waste glass without remelting years ago and I told him: impossible. I still remember when I met Andrei from STES and Oleg from LFG in Dusseldorf. They had a few samples for me and I was impressed, I made immediately my congratulations to inventor Andrei.
I learned that day that these black samples were foamed in air, another surprise. They invited me in Wuppertal and I watched the foaming of white powder to a black foam in an electric furnace under an air atmosphere. Andrei took a Russian patent but I still don’ t know how they achieve such a fine cell structure and good properties without remelting. I assume that prolonged grinding is the main key for this invention. Today, it is my challenge to find out.
The advantages of this process compared with the traditional carbon black process are enormous:
- no reducing atmosphere needed and so serious improved combustion in the foaming furnace
- no remelting of glass, generating a huge cost reduction
The production cost of this product could be easily 30% lower than the carbon black process. Today, STES is building a factory in Vladimir, Russia.
Every physicist, working with glass, is fascinated by the glass transition. This glass transition range is responsibe for the residual stress on the glass. In this range where the glass is not purely elastic but also not purely viscous, behaves the glass strange. Its properties depends on the way it is cooled. Thermal expansion, viscosity and specific heat depends largely on the cooling rate through the transition range. The first ones to find that experimentally were L.R.Troussart and P.Gérard from Belgium.
The first ones, who could describe theoretically the glass transition were P.Gilard and J. De Bast, also from Belgium. With their equations, the residual stress, being the sum of relaxed stress and structural stress could be calculated. The structural stress is a consequence of the fact that the surface of the glass has another cooling history as the bulk of the glass through the transition range and so slightly other properties.
The structural part becomes very large for tempered glass, due to the very fast cooling but becomes negligible for the relative slow cooling of cellular glass. This slow cooling is a consequence of the fact that temperature gradients are easily developed in cellular glass due to its low thermal conductivity.
For most cellular glass people, the annealing is the most difficult job because it is a black box where you can’t see what is happening. Also for float glass, CNUD EFCO is market leader for annealing furnaces. The gravity point of cellular glass and for float glass lehrs is already a long time in Belgium. Probably is that the heritage of Gilard and De Bast, great guys ….
Industrial historical research is always fascinating. Although you know the instrument, it is nice to find the original patent. In this case, this brilliant invention was patented in 1953. There is still a lot of handwriting on the patent, found by Google Scholar, also a fantastic instrument.
The patent explains first which problem is solved with the invention. Indeed, the powdered batch does not sinter homogeneously but in small and large parts, all irregular shaped. After sintering, when the foaming starts and the parts are expanding, it happens easily that two parts touch and are also lifting each other, inducing a fold because everything is confined in a mold. A fold in a glass foam disturbs the cellular structure and so the mechanical stability, reducing largely the productivity.
By using this dicer, regular blocks of powder are formed, which will also sinter in a regular homogeneous shape. During foaming, the sintered blocks touch but lifting is less probable and so the formation of the fold. By working with small blocks, the heat can better penetrate into the little blocks for a more homogeneous sintering and foaming.
By using a dicer, we can expect an improved productivity by less folds and faster sintering. The patent also mentions (column 5, line 31) that the patent is not only valid in a mold but also on a belt conveyor. The dicer could be replaced by rotating devices like for example a series pizza knifes.
This patent is a typical example of very intelligent research: simple with enormous excellent consequences. After so many years (61 years), it is still used by Russians and Chinese cellular glass producers. The picture showed a “diced” block from the STESS factory in Russia.
If we put a compressive stress on cellular glass, we would expect random phenomena of breaking cells. With piezo-electric sensors on the material, we are able to registrate these breaking cells, because they all emit acoustic waves in the structure. This measurement technique is acoustic emission and it is used to study the behaviour of steel welds, rocks, concrete, … . In that way, we can check whether the phenomena are random or not.
But in the case of many heterogeneous brittle materials, the distribution of amplitudes of these waves show a power law correlation. A Physical Review paper shows that this is also the case for cellular glass like it happens also for earthquakes. In the latter case, we speak about the Richter-Gutenberg law. For earthquakes, there is also the Omori law for the time interval between the after shocks. This distribution is also a nice power law and it is also present in cellular glass over many decades from microseconds to several minutes. In region with many earthquakes, there is also another power law about the distribution of distance between the epicentra of consecutive earthquakes. These three power laws in magnitude, time and space domain have the same coefficients for cellular glass as the earthquakes around San Francisco.
It is clear that the breaking of cellular glass under a compressive load is not a random but instead a correlated process, which has a limited but not negligible predictability. And this predictability allows us to define a safety factor between the short time compressive strength (1 min) and the long term mechanical stability. For cellular glass, a safety factor 3 is generally accepted and the above description is a method to prove that.
Solid glass has a much higher safety factor because one crack gives always complete failure while in the case of cellular glass, the interaction between the cells halts microcopic cracks inducing the low safety factor. This means that under a certain load under the safety factor, cellular glass does not not creep at all, while XPS, EPS, PIR, PUR and other foams always keep creeping and are never stable. This interaction between the brittle cells, as demonstrated with acoustic emission, gives cellular glass its perfect mechanical stability. Cellular glass is indeed smart …
Natural convection is a mechanism that is only present with a gas, gravity and a temperature gradient. The resulting movement of the gas is an effective heat transport mechanism. Thermal insulation is always eliminating this natural convection by confining the gas, allowing only brownian movement of the gas molecules.
The simplest example is using fibers in the way birds build a nest. A typical example is ROCKWOOL® , where the fibers are made from melting rocks or ISOVER® with glass fibers. But if we need more mechanical stability, we need to use a cellular material. Expanded polystyrene (EPS) , Extruded Polystyrene (XPS) are again typical examples. But these materials are combustible and still allow diffusion of water vapour because they are organic. In case we need also a perfect vapour tightness (against internal condensation) and non-combustibility on top of mechanical stability and thermal resistance, we have to use cellular glass with closed cells. GLAPOR® is a very good example of that. Some of the above materials have a very large ecological footprint while cellular glass can have a very low one. Some materials have an extreme low thermal conductivity like SPACELOFT®, others have no ecological impact at all like sheep wool, flax wool or wood wool.
It is very difficult to define “the best thermal insulation”, because a certain weight to the different properties is to be assumed. As a consequence, the “best thermal insulation” does not exist.
It is the conviction of BELGLAS that the “best thermal insulation system” to the customer’s wish is a sandwich of different thermal insulation materials, where a layer of GLAPOR® is replacing the vapour screen and forms the first cm’s thermal insulation. Any other thermal insulation can be added to value the wish of the customer, which can be to get
- the lowest price
- the lowest ecological foot print
- the thinnest system for a certain thermal resistance
- the best inverted roof
BELGLASCZ realizes that a full thickness with cellular glass, although maybe the highest quality, is becoming too expensive and simply too thick (not elegant) to realize today’s requested thermal resistance. A sandwich of GLAPOR® with another thermal insulation contains all the intrinsic properties of cellular glass and even more.
Polydros is already working a long time with what they call a ceramic belt. Their last patent was expired in 2008 and is now public domain information, free for everybodyto use.
The idea is to fill a typical lehr belt with clay by pressing the substance in the holes. After a drying time, the clay is fired and becomes a ceramic solid. This solid does not fall out of the belt during turning of the belt. It allows to transport powder or granulates through a high temperature furnace if the used steel for the belt is also temperature resistant. For that reason, it can be used to foam glass like applied by POLYDROS.
The development of this belt by POLYDROS was a fundamental step in the continuous foaming of glass.