1. To save production cost.
Melting point of slag is about 1100°-1250° while basalt:1400° -1500° and dolomite:900° in China, depending on their content.
So usage of slag can firstly save energy consumption of melting to save production cost.
If fuel is coke, slag is more important. But for electric, it just affects a little .
Electric furnace price is much higher, so many rock wool factories use coke and slag to invest less and save more cost.
2. In China, slag was thought difficult to be handled years ago so rock wool factories got slag for free.
Although price of slag is higher than before, but factories still can get them easily now.
3. Some customers only need slag wool products, so some factories produce them, depending on the factory boss’s market positioning.
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