Forging heating furnaces are among the critical equipment in the forging industry. Due to high operating temperatures, significant temperature fluctuations, and exposure to intense vibrations and mechanical impacts during material loading and unloading, their working environment is extremely harsh. Consequently, traditional refractory brick-lined furnaces have a very short lifespan, particularly the furnace roof, which typically lasts only one year. This often necessitates emergency shutdowns for repairs, significantly increasing annual maintenance hours and costs. Following improvements in refractory material application methods, specialized refractory castables for heating furnaces were introduced for forging furnaces. These castables were used to fabricate easily replaceable prefabricated components for high-wear areas like furnace roofs and doors. This approach significantly extended furnace lifespan and yielded substantial economic benefits.
I. Usage Effects and Analysis
1. Specialized castable refractories for heating furnaces exhibit excellent high-temperature performance. The primary reason these castables significantly extend furnace lifespan lies in their quartz-based AIP04 matrix, which features a chain-like spatial polymer network structure with a melting point of approximately 2000°C. Consequently, beyond superior refractoriness, this matrix provides high-temperature toughness, impact resistance, wear resistance, and thermal stability. When furnace temperatures exceed 1400°C, physical-chemical reactions like sintering further enhance its strength. Consequently, this castable outperforms refractory brick masonry at temperatures above 1400°C.
2. The furnace body made of specialized heating furnace castable is easy to repair. Repairing a refractory brick-built furnace roof is difficult; local burn damage often leads to collapse, necessitating complete dismantling and rebuilding. In contrast, the precast furnace roof made of specialized heating furnace castable has good integrity and high high-temperature strength. Even if local spalling occurs, it does not cause the roof to collapse, and repairs are easy, while also extending the roof’s service life.
3. Reduced furnace repair frequency. The extended roof lifespan minimizes disruptions to other furnace components caused by roof dismantling and repair, consequently prolonging the overall furnace service life.
4. Impact of production operation modes. Both batch-type furnaces and continuous heating furnaces employ precast refractory castables for their roofs. The difference lies in batch operation, where drastic temperature fluctuations cause greater roof damage. Generally, higher Al₂O₃ content in refractories increases refractoriness but reduces thermal stability. Although heating furnace-specific castables exhibit superior thermal stability compared to general heavy-duty castables, chamber furnaces subjected to frequent significant thermal stresses are prone to cracking, spalling, and reduced service life. In contrast, continuous heating furnaces maintain stable temperature profiles during normal operation, resulting in minimal cracking and spalling, thereby extending furnace longevity.
II. Reduced Heat Loss
The reduction in heat loss is primarily due to the following two reasons:
1. The overall sealing performance of specialized castable refractories for heating furnaces is superior to that of brickwork. Refractory brick-built furnace bodies have numerous joints, which significantly impact furnace lifespan. Refractory mortar is prone to powdering and detachment under the combined effects of high-temperature furnace gas erosion, corrosion, and thermal expansion/contraction of refractory bricks. This leads to erosion and damage starting from the joints, thereby increasing heat loss from the furnace body. In contrast, castable materials form a seamless monolithic structure with low permeability, resulting in minimal heat loss.
2. Specialized heating furnace castables facilitate furnace insulation. Better insulation reduces the temperature difference between the furnace lining and the furnace body, lowering the high-temperature strength and increasing the risk of furnace softening and collapse. Therefore, insulation should be adjusted according to the high-temperature strength of the lining material. Although refractory bricks contain mullite crystals with a high melting point of 1870°C, these crystals are present in very small quantities as fine needles, isolated within a siliceous glass matrix that constitutes the majority of the mineral phases. This glass matrix softens between 1300°C and 1360°C. Mullite dissolves in the liquid phase, causing a sharp decline in the compressive strength of refractory brick products. Consequently, excessive insulation should be avoided in furnaces constructed with refractory bricks, particularly for the furnace roof. In contrast, castables maintain good high-temperature strength above 1400°C, allowing for appropriate insulation reinforcement in castable furnace structures.
