Design and Reform of the On-line Monitoring System for Bearing Temperature of Finishing Mill

Xuanlong high-speed wire finishing mill adopts domestic top-crossing 45° rolling mill, with a designed maximum speed of 115m/s and a guaranteed speed of 90m/s. In the high-speed finishing mill, bearings are one of the key components, among which real-time monitoring of the temperature rise of motor bearings can reliably reflect the stability of its operation. However, there is no real-time monitoring of bearing temperature in the existing monitoring system, and it is difficult to detect hidden dangers of bearing failure early by relying only on irregular inspections. It is an effective means to ensure the safe and stable operation of the finishing mill to measure the bearing temperature signal and input it into the human-machine interface through the rolling mill production line automation network system to keep track of the bearing temperature changes at any time, make timely judgments and take necessary measures.

1. System Configuration

The automation system of Xuanlong High-speed Railway consists of three-level control systems and two-layer communication networks. The secondary control system consists of human-machine interface (HMI), basic automation system and speed control system, which respectively complete different control functions. In this renovation, the human-machine interface and basic automation system are fully utilized.

1. Human-machine interface (HMI)

It is composed of a high-performance microcomputer, which mainly realizes the human-machine interface function of the automation system, dynamically displays the collected parameters, makes fault alarms and records them, generates, stores and prints production reports, etc.

2. Basic automation system

The latest Siemens PLC S7-400 and PLC S7-300 series products are used. SIEMENS S7 series products are powerful and flexible in configuration, with the following outstanding features: (1) High speed. The extremely short instruction execution time makes S7-400 and S7-300 stand out from the competition; (2) Sturdy. Even in harsh and unstable industrial environments, the fully enclosed template can still work normally, and fanless operation reduces installation costs; (3) Complete and powerful functions. It allows multiple CPU configurations, with stronger functions and faster speeds. At the same time, it is equipped with a full range of functional templates to fully meet on-site needs; (4) Strong communication capabilities. The distributed internal bus allows fast communication between the CPU and the central I/O, the P bus exchanges data with the input/output template, and the K bus transmits large amounts of data to the functional template and communication template.

The CPU selected for this system is equipped with a ProfiBus-DP interface, which ensures fast data exchange for distributed I/O. The powerful communication template allows point-to-point communication and can communicate via industrial Ethernet.

ET200M is a modular I/O station with IP20 protection level. It can be expanded with signal templates and function templates of S7-300 programmable controller. Due to its wide range of installable templates, ET200M is suitable for special and complex automation tasks. ET200M is a slave station on ProfiBus-DP fieldbus with a maximum transmission rate of 12Mbps.

2. Design transformation

1. Temperature detection

The temperature signal is measured by a platinum thermal resistor PT100 sensor placed in the temperature measuring hole inside the bearing of the finishing mill. Its temperature measurement range can reach -200~850℃, and it has the advantages of high measurement accuracy and good stability.

2. Signal transmission between ET200M and PLC

An analog input template is added to the remote I/O station ET200M near the finishing mill, and a platinum thermal resistor is connected to any channel to receive the temperature signal. Since the PLC can read the signal status of the remote I/O station template in real time, it can reliably ensure the rapid transmission of the signal, so that the temperature signal can be transmitted to the PLC in real time without distortion.

ProfiBus-DP communication network is used between PLC and its remote I/O stations and speed control transmission. ProfiBus network is a real-time, open industrial fieldbus network. Its characteristics are the use of digital transmission, easy to receive and error check correctly, ensuring the reliability and accuracy of data, and helping to reduce the cost of cable connection between low-level equipment in the factory. It is easy to install, maintain and expand, can detect faults in time, and is easy to handle early. The biggest advantage is that it can make full use of the capabilities of intelligent devices.

The communication protocol of the ProfiBus network card allows high-speed cyclic communication of small amounts of data, so the bus cycle scan time is extremely short, which can be less than 2ms under certain circumstances.

3. Signal transmission between PLC and human-machine interface

The PLC programs and processes the analog signal read from the remote station, obtains the actual value of the required finishing mill bearing temperature, and sends it to the display screen of the human-machine interface.

The human-machine interface and PLC communicate via Ethernet to exchange information with each other.

3. Software Function Implementation

This system monitors the bearing temperature of the finishing mill online 24 hours a day and manages the data effectively. It has the functions of fault alarm and preliminary automatic emergency processing.

l. Real-time signal acquisition, processing, alarm and fault auxiliary processing functions

The graphic software adopts ifix monitoring software, which has real-time monitoring, provides historical trend charts, reports, fault information, good human-computer interface, rich graphic library, and also has process control and mathematical function functions.

The actual value of the bearing temperature is displayed digitally and in large font for easy viewing. In the case of abnormal temperature, temperature alarm and fault alarm will appear in a prominent position on the main screen. When the temperature reaches the set temperature of the first-level alarm value (the alarm temperature can be adjusted according to the temperature change), a yellow alarm flashing light pops up on the screen; when the temperature reaches the set temperature of the second-level alarm value, a red alarm flashing light pops up on the screen and an audible alarm sounds. In the case of extremely fast temperature rise and the operator has no time to react, the automatic control program will interlock and start the high-pressure oil top equipment of the finishing mill in real time to supply lubricating oil in time to cool the bearing and protect the equipment.

2. Trend analysis function

Through the FIX screen system, the historical trend of the real-time feedback temperature value is recorded and analyzed.

In addition to immediate display, the online monitoring data collected in real time also automatically records trends and is stored for approximately one month. Based on its operating cycle, the daily trend data and dynamic curves are archived and retained as historical data to facilitate future analysis and comparison.

The trend curve can better reflect the temperature rise status. The screen also provides the function of modifying the time coordinate axis, which can display the trend curve in any time period for easy analysis and comparison.