摘要 |
Tunnel furnace for foaming glass material, comprising heating elements chosen among electrical and gas based heating elements. The tunnel furnace comprises at least the following temperature zones: a preheating zone (8) suitable for heating the feed material to a temperature in the range 400 - 900 ~C and a foaming zone (9) suitable for heating the glass material to a temperature above 900 ~C. The furnace also typically comprises a cooling zone (10) suitable for reducing the temperature from the elevated temperature in the foaming zone. According to the present invention the preheating zone (8) is at least 15 % longer than the foaming zone (9).
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