At Železiarne Podbrezová, we take pride in our production of seamless steel tubes, a tradition dating back to 1978. The heart of our rolling mill is the piercing press, which creates the initial cavity in the heated steel billet and prepares it for further forming in the elongator and the push bench.
The input material is a continuously cast steel billet from our steelworks, produced from steel scrap. After heating, the billet is inserted into the press, where the piercing mandrel gradually forms the internal cavity, creating a thick-walled shell. This shell then proceeds to the rolling line, where it is shaped into the final seamless tube through a series of forming operations.
Key Technological Aspects
Strict adherence to technological procedures is essential for us, including lubrication of the forming tools with a special graphite compound. Until now, the lubrication had been performed manually, which was demanding and monotonous for our operators.
The main forming tools—the die and the piercing mandrel—consist of a head that performs the actual forming process, and a body that transfers the force from the press crosshead. The heads were originally made of steel grade 19 678 with a hardness of 34 Rockwell, unchanged for years, which reflected in their service life and surface quality. The degraded surface of the head directly affected the internal quality of shells and the eccentricity of the finished tubes.
The mandrel bodies were manufactured from used mandrel bars that had endured thousands of thermal cycles on the extrusion press. Such material could no longer provide the stiffness and mechanical properties required during pressing. Another critical factor was the alignment between the head and the body of the mandrel—an issue that had not received sufficient attention prior to modernization.
Our Team and Solutions
In March 2025, under the initiative of the General Director, we created a research-technology team consisting of staff from production, technical departments, quality control, and our R&D organization. Led directly by the General Director, the team addressed all technological challenges, focusing primarily on head service life and tube quality.
We subjected the mandrel heads to technological testing—through heat treatment, we increased the hardness of the original 19 678 steel to 44 Rockwell. We also introduced the renovation of worn heads and their reuse. For the next stage, we prepared materials 19 720 and 19 740, from which we expect further improvements in service life. After evaluating all three materials, we will implement the head with the best results into final production.
Mandrel bodies are now manufactured from new mandrel bars, ensuring higher stiffness during pressing. We introduced shape control of the body and surface quality checks of the head after assembly, approving only those meeting strict criteria. Another innovation is the improved technology for mounting the head onto the body, significantly reducing misalignment risks. Increased attention is also given to the mandrel holder in the upper crosshead of the press, which must meet prescribed hardness and accuracy standards.
Supporting Innovations
In addition to material improvements, we introduced automatic lubrication of the head using the graphite compound. The system was tested in two versions: mechanical and pneumatic. Pneumatic dosing proved most effective and has been operating flawlessly for a month. In the second phase, we implemented automatic dosing based on the press’s operating data.
We also optimized head cooling. A non-contact thermal imaging system measures the head temperature after piercing each shell, and the cooling water flow is automatically adjusted according to billet length. This ensures optimal head temperature without overheating and minimizes water consumption.
Results of the Modernization
The modernization brought significant improvements: head service life increased nearly 2.5-fold, and mandrel replacement time was reduced by 166 minutes, which translates into an additional 80 tons of monthly production. The occurrence of internal defects decreased from 1.8% to 0.9%, and shell eccentricity improved from 5.2% to 4.7%.
This modernization demonstrates that the combination of traditional know-how, experienced people, and modern technologies can significantly improve production quality, efficiency, and safety. We are proud to move our steelworks one step further.
Article written by:
Ivana Malčeková
Marketing Department
malcekova@zelpo.sk
