The prepared picture tube glass is stored in Mainz before being re-used.
From Tube to Funnel
As one of the biggest European television glass manufacturers, SCHOTT has taken the initiative regarding recycling. The goal is clear: special glass should no longer land in the dump, rather should be used as a valuable secondary raw material.
At a recent meeting, international specialists met in Mainz to discuss the future of the CRT or cathode ray tube (SCHOTT info 94/2000). At a second conference 80 experts came together for a closely related topic: the recycling of end-of-life picture tubes. The host on both occasions was SCHOTT GLAS. As one of Europe’s biggest television glass manufacturers with production of more than 200,000 tonnes of TV glass annually and as one of the pioneers in the recycling of special glass, SCHOTT is heavily involved in both areas. And the recycling of picture tubes will without doubt grow in importance.
One thing which underlines this is the fact that the good old cathode ray tube still has a long life ahead, even if flat screens are gaining ground in PCs and televisions. Up to 2005, according to forecasts by the American market research institute Stanford Resources Inc., the number of CRT units produced worldwide will continue to increase significantly from the latest figure of 275 million to 349 million – an increase of 27%.
On the other hand, it was the general opinion of all those attending the symposium that the current practice of dumping used television glass as special waste, cannot continue to be the solution. Also using it as mining infill or as a building material for roads has not proved to be a very promising outlet.
In Germany alone, approximately 1.8 million tonnes of electrical and electronic appliances are scrapped every year. A significant proportion of this waste is accounted for by television sets and monitors, the main component of which is the picture tube. “For this reason all manufacturers of television glass jointly carry the responsibility for the re-use of high-quality end-of-life glass in their production of new glass”, explains Franz Puder, whose responsibilities in the German Federal Environmental Agency include matters affecting the glass industry. And in fact more than four fifths of a television set consists of two sorts of glass: the tube neck and funnel are made of lead glass, which accounts for around 25% of the weight and glass containing barium and strontium is used for the panel, which accounts for up to 60% of the total weight of a picture tube.
Composition of funnel glass standardized
An obstacle to the recycling of material is the fact that the different television set suppliers all use their own glass recipe for the two types, while very tight specifications have to be adhered to for new glass. An important step towards a closed circuit was taken when the European picture tube glass producers Philips, Samsung, Thomson, NEC and SCHOTT reached agreement on the composition for funnel glass aimed at facilitating as high a recycling quota as possible. SCHOTT was the first to implement this composition and has developed its own process for reusing the glass in cooperation with picture tube glass processors.
In 1999 the Mainz glass specialists began using a mixture of one third funnel glass and two thirds panel glass in the melt for new funnels. Recycled material in the required quality, in other words free of metals, rubber, plastics and ceramic, is currently supplied by two processors, GRIAG Glasrecycling AG and RtG Recycling technischer Gläser. “We use this material in our funnel tank at a constant rate of 6% of the total melt”, explains Dr. Eckart Doering, Manager Batch Supply. However, as approximately two thirds of the mixture is panel glass, the quantity added cannot be increased arbitrarily.
Processing panel and funnel glass separately
SCHOTT uses cullet from used picture tubes as a raw material for new funnels.