Hänvisningar finns i följande patent|
| US4318691 | 10 okt 1980 | 9 mar 1982 | | Furnace for expanding mineral ores | | US4347155 | 19 mar 1981 | 31 aug 1982 | Manville Service Corporation | Energy efficient perlite expansion process | | US4521182 | 21 jan 1982 | 4 jun 1985 | Grefco, Inc. | Method and apparatus for heating particulate material |
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