Magnesium-carbon bricks are made of high melting point alkaline oxide magnesia (melting point 2800 C) and high melting point carbon materials which are difficult to be soaked by slag, and various non-oxide additives are added. Non-burnt carbon composite refractory made of carbon binder. It is often used in lining of converter, AC furnace, DC arc furnace and slag line of ladle.
The raw materials for making magnesia-carbon bricks are sintered magnesia with 98% MgO content, fused magnesia with 91% MgO content and with 94-95% fixed carbon content and natural flake graphite of 5% ash content. The binder is a composite binder of thermosetting phenolic resin and thermoplastic phenolic resin. The technical indexes of heat-fixed phenolic resin are as follows: fixed carbon 80-89%, free phenol 5-6%, free formaldehyde 1.2-1.5%, moisture less than 10%. Additives are metal aluminium powder, silicon powder, SiC and Al+Si powder.
- When manufacture the magnesia-carbon bricks, special attention should be paid to two key points of technology:
Sintered magnesia and fused magnesia are crushed and screened separately, and part of sintered magnesia is ground into fine powder less than 0.088mm by a barrel mill. The amount of graphite added varies according to the brand of brick, generally 8-20%. The amount of additive is 3-6%.
- The raw materials are prepared in a predetermined proportion and mixed in a strong sand mixer. The order of feeding is magnesia aggregate – Binder – graphite – fine powder and additives, and the mixing time is 15 – 45 minutes. In order to mix evenly, phenolic resin is usually heated to 35-45 C before mixing. Forming is carried out on 800t friction brick press. In accordance with the principle of first priority, then priority and multiple pressurization, the volume density of brick blank is controlled at 2.9g/cm3 after 4 to 6 times of light pressing and 8 times of heavy pressing. Magnesium-carbon bricks are finished products after heat treatment at 150-200 C for no less than 32 hours. Products with special requirements can be lightly burned and impregnated with asphalt.