I. Scientific Selection of Pouring Temperature: A Key Parameter for Balancing Performance

Pouring temperature is the primary process factor affecting the quality of steel castings. Excessively high or low temperatures will cause a series of quality problems, which need to be accurately set according to the characteristics of the steel grade and the casting structure.

In terms of actual parameter setting, the pouring temperature of steel castings is usually controlled in the range of 40~80℃ above the melting point of the material. At the same time, the principle of "differentiated adjustment" must be followed: for steel grades with high viscosity, small-weight castings, thin-walled castings and complex-structured castings, the pouring temperature should be appropriately increased to ensure complete filling; on the contrary, for thick-walled, large-sized and simple-structured castings, the pouring temperature can be moderately reduced to reduce shrinkage defects.

II. Optimal Control of Pouring Speed: A Dynamic Strategy Adapting to Casting Characteristics

The speed of pouring needs to be comprehensively judged based on the structural characteristics, wall thickness and mold properties of the casting. Its core goal is to ensure smooth filling of molten steel while avoiding mold damage and casting defects.

In terms of speed selection, thin-walled castings and complex-structured castings are suitable for rapid pouring. By shortening the filling time, it can prevent the molten steel from being too cold during the filling process, which may cause the "misrun" defect. When the mold has a large upper surface, rapid pouring can reduce the peeling phenomenon of the mold surface caused by long-term radiation and baking of high-temperature molten steel, thereby avoiding the slag inclusion defect of the casting. For thick-walled and large-sized castings, the pouring speed can be appropriately slowed down to reserve sufficient time for gas floating and slag inclusion separation in the molten steel.

In terms of speed control methods, although the pouring speed can be fine-tuned through the operator's experience, it is more mainly affected by the diameter of the pouring outlet. The flow rate of molten steel at the pouring outlet of the ladle is proportional to the square of the diameter of the pouring outlet and the square root of the height of the molten steel level in the ladle, and will gradually decrease as the molten steel level drops. To achieve a stable pouring speed, it is necessary to configure a pouring outlet brick with an appropriate diameter according to the ladle capacity, molten steel volume and casting requirements. For multi-box pouring or large flow demand scenarios, a double-pouring outlet design can also be adopted to improve speed controllability.

III. Operation Points of the Whole Pouring Process: Standardized Control to Build a Quality Defense Line

Standardized pouring operation is the guarantee for the accurate implementation of process parameters such as temperature and speed. It needs to cover the whole process of pre-pouring preparation, pouring process control and post-pouring treatment, and each link must strictly follow the specifications.

1. Pre-pouring Preparation: Comprehensive Hidden Danger Inspection

Inspection of the environment and equipment is the primary task. It is necessary to verify the steel grade of the castings to be poured, arrange the sand boxes in order, and ensure that the pouring gates are distributed in a straight line to facilitate the operation of the crane and pouring. Small and medium-sized molds or molds for mid-to-late pouring should be arranged in areas close to the melting furnace, and sorted according to height and pouring start time; molds for early pouring and large molds should be arranged in areas far away. At the same time, it is necessary to confirm that the pouring channel is unobstructed, the working ground is free of water accumulation and damp areas, and there are no flammable and explosive materials, so as to ensure that the emergency evacuation channel is unobstructed.

For pit-molded castings, the parting surface should not be higher than the upper surface of the pit; if it is unavoidable, backing sand should be filled and rammed tightly and blown hard after pressing the weight to prevent molten steel from running out during pouring. The surrounding plane of pit castings (including cement pit castings) should be higher than the parting surface of the casting to be poured; otherwise, sand should be filled and rammed tightly, and a sufficient weight should be pressed to prevent molten steel from running out. For adjacent pit castings, the poured castings must not be pulled out of the pit before the pending castings are poured, so as to avoid damaging the mold of the pending castings or causing molten steel to run out during pouring. If there is water accumulation on the ground near the casting to be poured, which may cause water to enter the casting, pouring is strictly prohibited to prevent safety and quality accidents.

The preparation of molds and tools is also crucial. Half an hour before pouring, it is necessary to re-inspect the floating sand in the mold cavity and pouring channel, check whether the size of the pouring gate meets the requirements, and the preheating effect of the mold cavity that needs to be preheated; check whether the mold weights are sufficient and the box clamps are locked tightly to prevent molten steel from running out during pouring. At the same time, tools and materials such as crowbars, sample spoons, exothermic agents and heat preservation agents for risers should be prepared to ensure the smooth connection of the pouring process.

2. Pouring Process Control: Accurate Implementation and Dynamic Adjustment

In terms of organization and management, a special person must be assigned to command uniformly during pouring. The commander needs to master key information in advance, such as the material of the molten steel in the furnace, the gross weight of the casting, the amount of molten steel for pouring, the pouring height of the riser, the number of molds and the distribution of weights. For extra-large and important castings, a special meeting must be held to determine the pouring plan before pouring. The safety officer must supervise the site throughout the process and strictly control the number of people at the work site.

In terms of work guarantee, a suitable pouring platform should be built according to the position of the sand mold, the condition of the sprue and the size of the ladle. If the height exceeds 1.5 meters, upper and lower ladders must be provided to ensure smooth roads and facilitate the operator to evacuate quickly in case of emergency. The pouring operator should prepare 2-3 shovels and a sufficient amount of backing sand and covering agent, and wear labor protection equipment in accordance with regulations.

The core operation points include multiple aspects. In terms of temperature monitoring, the temperature of the molten steel must be measured before pouring, and the process regulations must be strictly followed. Usually, the pouring temperature in the early stage is relatively high, which is suitable for complex and thin-walled castings, while the temperature in the later stage is relatively low, which is suitable for simple and thick-walled castings. In terms of filling operation, the pouring outlet of the ladle must be accurately aligned with the pouring cup of the mold to prevent molten steel from pouring out of the mold; the distance between the pouring cup and the molten steel flow should not be too high to reduce the contact time between the molten steel and air and lower the risk of secondary oxidation. At the initial stage of pouring, a thin stream should be used to reduce the scouring of the mold and the splashing of molten steel, and then the flow rate should be gradually increased to keep the molten steel flow continuous, straight and smooth during the filling process.

The control of pouring sequence and riser should also not be ignored. Generally, the principle of "small castings first, large castings later; thin-walled castings first, thick-walled castings later; complex castings first, simple castings later" should be followed. If the ladle is not fully baked, considering that the temperature of the molten steel at the bottom may be low, a slightly larger casting can be poured first. When the molten steel rises to the riser, the flow rate should be slowed down and poured slowly to the specified height to prevent the molten steel from overflowing, the box from lifting or the molten steel from running out, and at the same time help compensate for the liquid and solidification shrinkage of the molten steel. For castings with open risers, after the molten steel rises, the pouring speed should be reduced and the covering agent should be added immediately; for castings with blind risers or high manganese steel castings, after being fully filled, 1-3 spot pourings should be carried out on the pouring gate. After pouring, 1-2 more heat preservation covering agents should be added to ensure that the riser does not "show red".

The handling of special scenarios must be standardized and orderly. During multi-box pouring, if each ladle of molten steel is used to pour 3 or more boxes, the remaining amount of molten steel must be detected with a steel brazing before pouring the 3rd box; if 2 or more boxes are poured and the amount of molten steel poured exceeds 80%, the steel brazing detection is also required before subsequent pouring. To ensure full-flow pouring of the castings poured later, oxygen burning tools must be prepared and the pouring outlet should be blown and burned in a timely manner when necessary. When multiple furnaces are used for combined pouring of large steel castings, it is necessary to coordinate the tapping sequence of each furnace, the distribution of cranes, the position of ladles and the pouring sequence, and strive to open all pouring outlets at the same time. The pouring temperature of the molten steel used for riser feeding should be 30-50℃ higher than that of the molten steel used for combined pouring.

In addition, air induction must be carried out immediately at the start of pouring to reduce the blowhole defect of the casting; a special person should be assigned to monitor the pouring process to prevent slag from entering the mold cavity. If molten steel leaks from the mold, measures should be taken to block it while maintaining a thin and slow flow, and the flow must not be interrupted to avoid cold shuts in the casting. If the process requires sampling for composition analysis during pouring, a sample spoon should be used to take molten steel for sampling, and the furnace number should be marked clearly.

3. Post-pouring Treatment: Improving Quality Traceability and Safety Guarantee

After the completion of pouring, the pouring time and heat preservation time should be clearly marked on the sand box to facilitate the connection of subsequent processes. For castings with a weight of more than 500 kg, alloy steel castings, trial castings and key castings, the furnace number mark should be inserted into the riser. A test bar should be poured for each furnace of molten steel to provide a basis for quality inspection and traceability.

For the remaining molten steel, it should be poured into the material-combining mold or dry pit prepared in advance at a fixed position. After pouring, no sand should be sprinkled on the surface to prevent personnel from stepping on it by mistake and causing safety accidents.

Conclusion

The core of the steel casting pouring process lies in "precision" and "standardization". From the scientific setting of parameters such as temperature and speed to the standardized operation of the entire process, every detail is related to the casting quality. Only by deeply combining process theory with practical experience and strictly controlling the technical points of each link can various casting defects be effectively avoided and high-quality steel castings that meet industry standards and application requirements be produced.