Runner bricks, as the name suggests, are refractory bricks through which molten steel flows. They have a distinctive shape - some are hollow with a bottom - and pressing them into shape presents considerable difficulty. Furthermore, during sintering, whether the temperature is too low or too high, the result is invariably poor wall strength.
Runner bricks come in many shapes. Straight-flow runner bricks are relatively easier to form, whereas funnel-shaped, three-way, and bottomed types used in short-process steel casting - particularly the bottomed pouring basin bricks - present greater forming difficulties. For high-pressure forming, funnel-shaped runner bricks are hard to press because of their thin walls. Since they are round and thin-walled, the process requires first mechanical pressing to expel air, then hand-ramming with a thin roller during the beating stage, and finally pressing on a mechanical press. Without this sequence, porosity develops, and the walls crumble at the slightest touch.
Large funnel bricks are even harder to press. They must be hand-rammed with iron rods and then mechanically pressed to achieve sufficient density. Compared with standard refractory bricks, the forming speed is much slower: standard bricks can be produced at 8 tons per 8-hour shift, whereas only 300–400 runner bricks can be made per shift, making the forming labor cost several times higher.
During sintering, if the temperature is too low, the thin walls develop uneven coloration and inconsistent strength, making the bricks prone to breaking in service. If the firing temperature is too high, the entire brick becomes over-fired, turning dark and crumbling when lightly scraped. Typically, manufacturers conduct trial pressing and trial firing on each batch of raw materials before commencing mass production; otherwise, the product yield can fall to zero.
Therefore, runner bricks are priced considerably higher than standard refractory bricks of the same material, and their forming requires highly skilled workers. The firing temperature is a key technical parameter that the technical team must determine through trials on each raw-material batch in order to produce qualified finished products.