Compared with conventional lost foam casting (full-mold casting), the key advantage of the hollow-shell lost foam precision casting process lies in the use of liquefaction. Liquefaction makes the foam pattern "disappear," thereby solving the pain point of conventional lost foam casting—carbon defects. This makes the lost foam process applicable to high-grade steel castings. Ningbo Qianhao New Material Technology Co., Ltd. is one of the first companies in China to apply this unique liquefaction process to steel casting production, and has achieved large-scale manufacturing.
Principle of the liquefaction process: The EPS foam pattern is heated, softens, and melts into a liquid state, which flows out of the shell mold by gravity through pre-formed drainage outlets. The distinctive feature here is that the process is slow and low-temperature—rather than high-temperature combustion and vaporization.
1. Advantages of the liquefaction process over burn-out-then-pour or direct pouring
1.1 "No carbon defects"
Whether using burn-out-then-pour or direct pouring of molten metal, the EPS pyrolyzes and generates large amounts of carbon-rich tar and residual carbon, which adhere to the inner wall of the shell mold. This makes castings highly prone to carburization, surface wrinkling, and slag inclusions. The liquefaction process converts the foam into a liquid that flows away, leaving no residual carbon in the mold cavity, and significantly improving the surface quality and mechanical properties of the castings.
1.2 Environmentally friendly, with centralized treatment
Because liquefaction is carried out at low temperature, the EPS never reaches the conditions for combustion and gasification, so only minimal gas is generated inside the liquefaction furnace. The liquefied foam residue is collected and returned to the EPS manufacturer for recycling. The small amount of fumes generated is treated jointly with the high-temperature roasting furnace: after full combustion, it is discharged through the exhaust gas treatment system.
1.3 Reduced risk of shell cracking
Direct combustion of EPS generates a large volume of flue gas in a short time, causing a sudden pressure rise inside the shell mold that can burst the coating shell before it has developed sufficient strength. Liquefaction drains the pattern slowly and keeps internal pressure low, making it suitable for thin-walled castings with complex internal cavities.
2. Engineering control elements of the liquefaction process
2.1 Pattern loading configuration and drainage
When loading the furnace, the drainage outlets face downward to make full use of gravity; multiple drainage outlets are provided at different locations for complex parts. Blind cavities and high points must be provided with additional drainage channels to prevent foam from being trapped in dead corners and solidifying inside the shell after cooling.
2.2 Heating curve control
EPS liquefaction range: 160–280 °C (EPS softens and melts; above 300 °C it begins to pyrolyze violently, generating gas).
Heating rate: 80–150 °C/h; rapid heating is strictly prohibited. If the temperature rises too quickly, moisture in the coating and the EPS, as well as rapidly generated gas, cannot escape in time, easily causing blistering and cracking of the coating shell.
A longer holding time should be set at the constant-temperature stage to ensure that thick foam sections and deep internal cavities fully melt and drain out slowly; the holding time is adjusted according to product wall thickness and structural complexity.
Furnace atmosphere control: weakly oxidizing / slight ventilation—no strong oxidation. This prevents the EPS from burning and coking; slight ventilation only removes water vapor and will not cause airflow erosion of the shell mold.
Conclusion
In summary, liquefaction is the core and critical process step of the hollow-shell lost foam steel casting process. Unlike conventional burn-out or direct pouring processes, it suppresses carbon defects at the source through low-temperature melting and drainage. In production practice, drainage outlet layout, the heating curve, and furnace atmosphere constrain one another; only strict implementation of process control parameters and smooth drainage of the molten EPS foam can consistently produce low-residual-carbon, high-quality steel castings. In actual production, the process should also be flexibly adjusted according to casting wall thickness and structural complexity, balancing shell safety with product quality, so as to fully exploit the technical advantages of the shell precision casting process.
Qianhao New Material Foundry - Qianhao's sixth factory and one of the four core production bases, it is located in Dongchen Township of Xiangshan County, about an hour drive from the headquarters. It covers a land area of 40,000 square meters with a factory floor area of 30,000 square meters. The site is equipped with automated hollow-shell lost-foam casting lines designed for an annual capacity of 30,000 tons, serving as Qianhao's production hub for medium and large castings.
WYD, CTO of Qianhao Casting October 8, 2026