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.


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.


New recipes to foam glass

logo_smallWe found some papers with new recipes to foam glass. The first paper was written at the Iran University of Science and Technology in Teheran, which seems also to step into cellular glass.  Hereunder, you will find the abstract:

Foam glasses are encountered as one of the most promising solutions for waste glasses recycling issues. Homogeneous pores distribution and high mechanical strength are two main characteristics of these products which many investigations have been done for their optimization. High flexural strength glass foams were fabricated by usage of oxidant agents like Fe2O3 and Co3O4 besides soda lime glass wastes and SiC as a
foaming agent. Glass foams containing 4 wt % SiC and foamed at 850°C for 1 h had 90% porosity and bending strength of 0.75 MPa. Bending strength of specimens using increased to 6.82 MPa and porosity was decreased to 80% by addition of 1.2 wt % Co3O4. Moreover, the effects of Fe2O3 and Co3O4 on porosity, microstructure and mechanical properties of foam glasses were studied. Based on the results, the finest porosities with the highest size distribution homogeneity were observed in foam glasses contained Fe2O3 and Co3O4. Furthermore, Co3O4 addition produced slightly narrower pores size distribution in comparison with Fe2O3.

IUST_GATEThe same university also did some foaming of Cathode Ray Tube glass from old televisons. This is given in the following paper with abstract:

In the present study, the effect of temperature and oxidising agents such as Fe2O3 and Co3O4 on physical and mechanical properties of glass foam is investigated. The glass foam is made of panel glass from dismantled cathode ray tubes and SiC as a foaming agent. In the process, powdered waste glass (mean particle size below 63 mm) in addition to 4 wt-% SiC powder (mean particle size below 45 mm) are combined with Fe2O3 and Co3O4 (0?4, 0?8 and 1?2 wt-%) have been sintered at 950 and 1050uC. The glass foamed containing 1?2 wt-% Co3O4 has good physical properties, with porosity more than 80% and bending strength more than 1?57¡0?12 MPa. However, by adding different amounts of Fe2O3 in comparison with samples without iron oxide, little changes in porosity and strength are obtained.

Iyte_entrance_gateAnother paper  was written in Turkey at the Izmir Institute of Technology with abstract:

The foaming behavior of a powder residue/waste of a soda-lime window glass polishing facility was investigated at the temperatures between 700 and 950 C. The results showed that the foaming of the glass powders tarted at a characteristic temperature between 670
and 680 C.  The maximum volume expansions of the glass powder and the density of the foams varied between 600% and 750% and 0.206 and 0.378 gcm3, respectively. The expansion of the studied glass powder residue resulted from the decomposition of the organic compounds on the surface of the glass powder particles, derived from an oil-based coolant used in the polishing. The collapse stress of the foams ranged between 1 and 4MP aand the thermal conductivity between 0.048 and 0.079WK1 m1. Both the collapse stress and thermal conductivity increased with increasing the foam density. The foams showed the characteristics of the compression deformation of the open cell brittle foams, which was attributed to the relatively thick cell edges.

In the last paper, the foaming agent is the coolant used for the polishing of the glass. That is an interesting observation.


GLAPOR is 10 years … alive and kicking

logo_smallWe got an invitation from GLAPOR to join the tenth birthday in their factory. It means that 10 years ago Walter Frank founded this company to produce and sell cellular glass gravel and boards.

In his philosophy, boards are an extension of the succesfull cellular glass gravel, based on 100% recycled glass with a minimum energy and zero waste production. Today, this philosophy is changing the cellular glass world by putting an enormous price pressure to obtain: “cellular glass for everybody”, which is the mission of BELGLAS.


GLAPOR is not only a cellular glass producer but also a multicultural family, which is celebrating this 10 years old relationship. In that perspective, all family and shareholders are present to enjoy this unique culture. Pimpy Panda is the multicultural music group, which is already announcing the show on YouTube.

74px-Wappen_Mitterteich.svgGLAPOR is based in Mitterteich, a municipality in the district of Tirschenreuth, in BavariaGermany. In fact, GLAPOR is located in the old porcelain factory of Mitterteich, saving and renewing the old experience to work with minerals, furnaces and high temperature equipment. About the old porcelain factory on the GLAPOR site, I copied the following:

Porzellanfabrik Mitterteich A.G. (1917 until 2006)

mitterteich-02-01To match constantly rising demand, a second facility (‘Werk B’) was in 1925 constructed on Hüblteichstrasse and the total number of workers increased to just over 300 in the same year. The second facility was in 1937 followed by a third, ‘Werk C’, located on Schulgartenstrasse. The whole factory used standard coal-fired kilns before completely switching to gas-fired tunnel kilns early in the 1950’s.

mitterteich-02-32A huge fire completely destroyed the ‘Werk C’ part of the facility in 1988 and the required reconstruction took until 1989. With all three locations fully operational again, the factory had a production area of 20,000 square meters and a workforce of around 800 people. The Mitterteich A.G. seemed to cope quite well with the overall situation on the German market. But in August 2005 the small city was rocked by the news that the company, represented by the board of directors, had to file for bankruptcy. For the 360 workers (70 percent of these female), it came as a shock. The small hope of an investor being able to save the company was destroyed by the local banks, who did not want to support the Mitterteich facility any longer. On March 1st 2006 the doors leading to the factory closed for the last time.

In 2007, Walter Frank founded GLAPOR and used the old buildings and infrastructure.                GLAPOR _logo




Cellular concrete versus cellular glas

logo_smallCellular concrete is much better known under the name autoclaved aerated concrete (AAC) and is nothing less than foamed concrete. Glass and concrete are both mineral but glass is vapour tight while concrete allows transport of vapour. It makes sense to compare both products which is done on the basis of this document in Dutch.

220px-AAC_blocks_fed_in_to_autoclaveWhile the lowest density for AAC is about 350 kg/m³ , cellular glass can be foamed to 100 kg/m³. As a consequence, the thermal conductivity of AAC is much larger (0.11 W/mK) in comparison with GLAPOR cellular glass (0.050 W/mK) even in case of an equivalent compressive strength (0.06 W/mK). It means that we need the double thickness with AAC to obtain the same thermal resistance.

220px-Autoclaved_aerated_concreteAAC needs about 200 kWh/m³ primary energy for the production while GLAPOR cellular glass is satisfied with 400 kWh/m³, however for a much better (halve) thermal conductivity (and so reduced thickness). GLAPOR cellular glass is 100% foamed from recycled glass while AAC uses predominatly fresh raw materials.

AAC can be produced in blocks and large panels and this is also the case for GLAPOR cellular glass. A recent pricelist shows that AAC blocks are costing 170€/m³ for 0.1 W/mK while low cost cellular glass with 0.050 W/mK can be bought for 250 kg/m³ regardless of the dimension. AAC panels up to 2.4 m length are costing 240€/m³. It is clear that GLAPOR cellular glass is a price competitive product as a building brick and panel if we consider the distinct smaller thermal conductivity.

Both products started once around1920 with smaller blocks and evoluted to larger panels and both claim also to be able to recycle all old material. In fact, everything which could be produced in AAC can be produced in GLAPOR cellular glass. We have just to look to cellular glass in the same way as to AAC, namely as a (insulating) brick / panel and not only as thermal insulation of a brick / concrete structure.

Cellular glass gravel or boards?

logo_smallThe current shortage of PIR and PUR makes that customers and investors are looking for alternatives. These alternatives are mostly mineral and in this way, low cost cellular glass like GLAPOR comes into the picture.

RDSIn that case, it is not clear whether it will be boards or gravel. Like shown in this GLAPOR document, the cellular glass gravel is used for floor insulation, road and railway construction and even landscaping. The boards are mainly used in the building industry from private homes to larger buildings. The combination of boards and gravel, the well known GLAPOR RDS system is today a very performant floor thermal insulation, which in principle can be used also for tankbase bottoms of small and even larger tanks.

In fact, the answer is clear: a low cost cellular glass factory must include gravel and board production lines. Indeed, the waste of finishing cellular glass boards cannot be used again for the board production due to crystallisation after a few cycles but is perfect for the (one cycle) production of gravel. A low cost cellular glass factory with gravel and board lines runs with 95% recycled waste glass and does not generate any waste by itselves. It is the perfect recycled glass absorber by converting it into ecologic durable recycable thermal insulation.


Australia: terra incognita for low cost cellular glass

logo_smallLow cost cellular glass involves a short distance between market, production and recycled glass combined with a confident energy source. The following article explains how the import of cheap bottles is the reason why recycled glass remain in stock instead of being used in Australia.

world-mapNevertheless, Australia is familar with reycling of glass like shown in this link. Even more, glass is considered as ecologic.

  • This list of material life times gives 1 million years as life time for glass in sea water while plastic foam (EPS) survives 50 years. The short life time of plastic is a big problem for the health of people, who likes to eat fish.
  • Recycling glass fact sheet explains why glass has to be used and how it is recycled within the classical glass industry.
  • This document explains focuses on the many times glass can be recycled if not contaminated and how to avoid contamination. It shows also the advantages of recycling for the environment.
  • Last but not least repeats the above and mentions that glass is already 2500 years old.

8776548-3x2-700x467It is clear that a cellular glass plant, converting recycled glass into cellular glass boards and gravel would be the ideal solution to value the recycling efforts of the Australian citizens. Indeed, cellular glass resists the harsh climate of Australia by its high softening point (above 700°C) and all kind of animals, which are halted by cellular glass boards.