Mid- to Small-Sized Castings: Upgrading and Reforming the Steel Casting Industry

Mid- to Small-Sized Castings: Upgrading and Reforming the Steel Casting Industry

Medium- and small-sized castings: China's annual output of steel castings has reached 11 million tons, with the molding sand primarily composed of hard sand, ester-hardened alkali phenolic resin self-hardening sand, and ester-hardened water-glass sand. Among these, 8 million tons of steel castings are produced using the water-glass sand molding (core-making) process, while the remaining ones utilize alkaline phenolic and resin sands. Large hydroelectric generators and thermal power units—due to their demanding requirements for high quality, precision, and performance—are particularly challenging to manufacture, making it difficult to meet these exacting standards. As a result, numerous large and medium-sized steel castings are employed in their production. Meanwhile, driven by ongoing advancements in cleanliness, energy efficiency, lightweight design, digitalization, and智能化 technologies, the steel industry is increasingly focusing on R&D initiatives aimed at achieving low-carbon emissions, energy conservation, and reduced pollution—key priorities for sustainable development in the sector.

Mid- to Small-Sized Castings: Upgrading and Reforming the Steel Casting Industry

For small to medium-sized castings, the surfaces of large steel castings typically use specialized sands such as chromite sand, which are significantly more expensive than the steel itself. Consequently, chromite sand separation technology and quartz sand regeneration systems are also critical technologies. However, for casting cores, pearl sand will replace zircon sand.

Currently, ester-hardened water glass sand is widely recognized as a viable option for wet-sand molding of steel castings. It is colorless, odorless, and non-toxic, producing no irritating smells or harmful gases during mixing, shaping, casting, or sand preparation—making it completely safe for human health while delivering excellent casting performance. As a result, it has gained widespread acceptance within the casting industry. However, one major drawback remains: its difficult recyclability, which leads to significant solid waste pollution. If the challenge of recycling water glass sand can be effectively addressed, this technology will undoubtedly take the lead in advancing toward green casting practices. Crucially, ongoing improvements and upgrades to casting equipment will also play a vital role in realizing this transition.

Facing the vast demand for large cast steel components in China's future, foreign manufacturers are accelerating their efforts to secure a foothold in the Chinese market by leveraging their advanced capabilities in intelligent casting equipment production. Domestically-based companies should seize these opportunities, embrace the challenges, and proactively implement strategies to stay competitive.

Small and medium-sized castings: Rules for thermal inspection of cast steel—given the complex shapes of valve castings, which are prone to deformation and cracking, carbon steel castings are typically used for heat treatment during annealing. Key inspection points include monitoring the supplier’s adherence to the following heat-treatment specifications, as well as verifying the hardness values of the castings.

Due to the complex shapes of carbon steel castings during the heating process, when the furnace temperature rises to between 650 and 800°C, it is essential to heat slowly or hold the casting at this temperature for a certain period. Within this temperature range, carbon steel undergoes significant volume changes and phase transformation stresses. If the temperature increases too rapidly, it can easily lead to temperature differences between the thin-walled sections of the casting and its surface and core layers, thereby intensifying thermal stresses and increasing the risk of cracking in the castings.

The holding time is sufficient to maintain a constant temperature throughout the casting, allowing ample time for microstructural changes. Consequently, thick-walled castings require a longer holding period compared to thin-walled ones. 1.3 Carbon steel castings are typically cooled in the furnace.