Abstract: This article introduces the application of SIEMENS' SINAMICS S120 series frequency converters in the hot continuous rolling of three-roll seamless steel tubes, and highlights the configuration and use of the SINAMICS S120 frequency converters.
Keywords: SINAMICS S120 Profibus-DP Basic Power Module (BLM), Non-Regulated Power Module (SLM), Regulated Power Module (ALM)
1. Project Background:
Continuous rolling mill is a high-efficiency rolling mill for producing seamless steel pipes. It involves placing a pierced tube onto a long mandrel and rolling it into a rough tube through a set of 4 to 11 (usually 5 to 9) continuously arranged two-roll (or three-roll) stands at 90° (or 60°) intervals. This achieves a highly mechanized and automated rolling process.
Three-roll continuous rolling mills produce more uniform deformation, lower rolling pressure, better surface quality of raw tubes, and higher dimensional accuracy, representing an advancement over two-roll continuous rolling mills. By adjusting the roll profile parameters, a set of rolls and mandrels can be used to produce finished products of adjacent specifications.
Our company undertook the entire transmission system and basic automation work for the 7-inch seamless steel pipe rolling mill project at Jiangyin Huarun Steel Co., Ltd., excluding the continuous rolling mill, sizing mill, pipe saw, and furnace.
2. Equipment Overview:
Figure 1. Schematic diagram of hot continuous rolling mill for three-roll seamless steel pipe.
After piercing, the tube is rapidly transported to the front of the continuous rolling mill by a transport mechanism. The mandrel is clamped and fed into the tube by a mandrel plate limiting trolley. The mandrel plate limiting trolley is driven by four motors through a reducer, which drives a limiting rack. The rack has a clamping device at the front. The tube is fed into the continuous rolling mill together by the limiting device and the clamping device. After the continuous rolling mill bites the steel, the rolls roll the tube and it enters the next stand in sequence. At the same time, the friction of the rolled metal drives the mandrel forward. The limiting trolley provides a reaction force, allowing the mandrel to run at a set constant speed throughout the rolling process. At the end of the rolling process, the blank tube is removed by the tube stripper, and the mandrel is quickly returned to its initial position by the mandrel limiting device. The blank tube is then transported to the sizing mill by the transport mechanism, where it is sized and extended to become a steel pipe. The simplified diagrams of the continuous rolling mill and the tube stripper are shown below:
Appendix 2: Simplified diagram of the pass profiles of the continuous rolling mill and the tube removal mill
Each stand of the main rolling mill, tube stripping mill, and tension reduction mill consists of three rolls, each with its own independent drive system. The sizing mill's pass shape and structure are basically the same as the tube stripping mill.
The use of this structure places higher demands on the dynamic characteristics and precision of the transmission system. Basic automation users choose to use SIEMENS PLCs as the control core for equipment, process, and transmission control. Some factory users will be expanding their existing plant space, and with limited reserved space in the electrical room, they require the electrical control system to occupy as little space as possible.
1. Selection of electric drive :
After considering the performance, price, technology, and specific requirements of mainstream frequency converters on the market, as well as the actual conditions of this project, we ultimately selected Siemens' SINAMICS S120 series frequency converter as the drive system for the AC motor. The SINAMICS S120 is an upgrade from the 6SE70, with its main advantages being a significantly smaller size, significantly lower noise, and the controller being independent of the drive unit. One controller can control four vector-controlled drive units, allowing many process interconnections that previously required a PLC to be completed within the drive controller. Since all the necessary information is stored in the central control unit, there is no need for time-consuming and laborious data transmission. Interconnection of each axis can be achieved within a single control unit, and configuration can be done simply by clicking the mouse in the STARTER commissioning tool.
2. Electrical drive scheme:
The drive unit adopts a shared DC bus structure with multiple drives using the SINAMICS S120 (AC/DC rectification + DC/AC inverter). The S120 AC/DC rectification has three types: basic power module (BLM), non-regulated power module (SLM), and regulated power module (ALM). Considering both rolling process requirements and project cost, this project selects a mixed configuration of basic power module (BLM) and non-regulated power module (SLM). The drive load and time curves are shown below:
Figure 3. Mill time and load curves
Figure 4. Limiting time and load curve
The load curves of the tube stripping mill and sizing mill are similar to those of the rolling mill. Based on the load curves, the transmission mechanism operates in the forward direction, requiring energy feedback only during equipment shutdown and emergency stops. Therefore, the AC/DC rectifier power of the rolling mill, tube stripping mill, and sizing mill is greater than the feedback power. The limiting mechanism operates in both forward and reverse directions, with the reverse direction providing energy feedback; its AC/DC rectifier power equals the feedback power. Each stand of the rolling mill, tube stripping mill, and sizing mill constitutes a transmission group. The process requires that the three motors in one stand operate at the same speed and have balanced torque. The four limiting motors must also maintain balanced speed and torque. Based on these process requirements, the 100 motors in the rolling mill, tube stripping mill, sizing mill, and limiting mechanism are divided into 33 control groups. Each group's inverter shares one controller (CU). The power calculation of the transmission device is based on the motor load conditions to determine the capacity of the inverter unit and rectifier, which will not be discussed further in this paper. A representative transmission single-line diagram is shown below:
Appendix 5: Single-line diagram of rolling mill drive
Appendix 6: Single-line diagram of limited-motion transmission
Appendix 7: Single-line diagram of the tube removal machine drive
5. Project Implementation
After adopting the SINAMICS S120 multi-drive solution, the wiring of the DP (Power Distribution Unit) is greatly reduced. One controller CU (Control Unit) requires only one DP connector, and one CU can connect to up to four vector control power units via DRIVE-CLiQ cables. For example, the attached diagram shows that each stand of the nine-stand rolling mill has only two DP contacts, while the previous 6SE70 unit required six DP contacts. The system's anti-interference capability has been significantly improved.
Figure 8. DP and DRIVE-CLiQ network diagram for each stand of the rolling mill.
The SINAMICS S120 separates the drive unit and controller, which helps reduce spare parts costs for users; one controller can control multiple drive units, making it easier to achieve master-slave speed and torque control, resulting in more ideal control effects and better quality assurance for finished products; the debugging interface is also more user-friendly, making programming in the controller easier.
Figure 9. Main drive speed setting
Figure 10. From the transmission setpoint
Figure 11. Drive activation droop function
The drive module of SINAMICS S120 has undergone significant design improvements compared to its predecessor, the 6SE70 frequency converter. The overall cabinet size after assembly is reduced by about one-third compared to the 6SE70, and the noise of the drive device is also greatly improved. With the new solution, the rectifier feedback device no longer needs an autotransformer, which greatly reduces the failure rate.
6. Conclusion
The SINAMICS S120 is a newly launched engineering-grade frequency converter from Siemens AG, Germany. Based on Drive CLiQ device-level intelligent networks and modular components, the S120 offers a flexible topology, greatly facilitating system configuration, diagnosis, and maintenance. The drive system in this project utilizes the SINAMICS S120, which perfectly meets the requirements of the three-roll seamless steel pipe hot continuous rolling production process and also accommodates the user's need to utilize part of the existing factory space.
About the author:
Yan Wenxiu (August 1975 - ), male, graduated from Taiyuan University of Science and Technology with a major in Industrial Automation, currently works as an engineer at the Rolling Mill Institute of the Technology Center of Taiyuan Heavy Machinery Group Co., Ltd. Tel: 13935155572, E-mail: [email protected]
