Casting characteristics of thick-walled seamless steel pipes

The production of cast thick-walled seamless steel pipes requires a careful balance between process structure, performance, and quality control. Achieving high productivity while maintaining strict quality standards is crucial to ensure the integrity and functionality of the finished product. Here are the key characteristics and considerations during the production process.

Production Process and Quality Control
The key to producing high-quality thick-walled seamless steel pipes lies in managing both the production process structure and the product's performance. Productivity improvements must not come at the expense of quality. During production, the integrity of the pipe must be checked thoroughly to ensure it is defect-free. Any defects must be repaired before use. Additionally, when removing molds, the knocking force should be carefully controlled. Using a wooden block to strike the aluminum mold helps reduce damage and ensures a smoother production process.

Strict Control of Furnace and Raw Materials
When manufacturing thick-walled seamless steel pipe fittings, the quality of the furnace and the packaged raw materials must be strictly monitored. This includes inspecting and accepting the composition, block size, and physical and chemical properties of the materials as per specified standards.

Inspection and Defect Prevention
Regular inspections are essential to identify defects in thick-walled seamless steel pipes. When defects are detected, their causes should be analyzed, and timely corrective measures should be taken to minimize the occurrence of such defects during production.

Pre-Pouring Processes and Continuous Casting
Before pouring the molten steel, it is essential to inoculate the casting water and remove any slag. The casting process should be continuous and stable to prevent sand holes caused by sand washing. In case of fire or leakage in the casting process, it is important to block the leaking casting water and replenish it promptly to reduce defects like cold shuts and insufficient pouring.

Molding Sand Performance
The quality of molding sand directly affects the surface quality of thick-walled seamless steel pipes. The molding sand must exhibit good air permeability, wet strength, fluidity, plasticity, and yieldability to produce smooth, defect-free pipe fittings.

Improving Molding Sand Performance
Bentonite has a higher hot wet tensile strength than ordinary clay, and when combined with materials such as coal powder or sawdust, it improves the ability to resist sand inclusion and sticking. This helps produce pipe fittings with smooth surfaces. The moisture content of the molding sand should be around 6% to optimize its comprehensive performance.

Surface Finish Treatment
To achieve a good surface finish on thick-walled seamless steel pipes, the sand on the pipe surface can be removed through cleaning drums or by shot blasting. The sticky sand on unprocessed surfaces must be cleaned properly to avoid defects that could affect the pipe’s usability.

Drying Process for Molds
For the dry mold process, following the proper operational procedures is critical. Molds should be dried for at least 8 hours to avoid defects such as sand inclusion and pores, which can occur due to incomplete drying.

Cooling Time and Mold Removal
After casting, the pipe fittings must be fully cooled before they can be removed from the mold. This process usually requires a cooling period of at least 3 hours. Removing the pipes too early may result in surface chilling, leading to increased hardness and difficulty in cutting. Additionally, large thick-walled seamless steel pipe fittings are more susceptible to thermal cracking and internal stress, which can cause deformation and negatively impact the external dimensions of the pipe.

In summary, producing high-quality cast thick-walled seamless steel pipes requires strict control over the entire production process, from raw material selection and molding to inspection, cooling, and finishing. Each stage is critical to ensuring the pipes meet the necessary standards for performance and durability.