Articles

Russula, an engineering company specialized in automation solutions, has developed a new application that improves the shear cut cycle control in long product rolling mills.

Driven by Russula´s R & D progam, this new development involves combining a standard hardware product in the market with a tailor made software solution. The flexibility in interfacing the best technology on the market with a steel producer´s current control system can reduce the tolerance cut length by 70%.

Control of Cutting Shears:

The complete cut cycle of a shear from start to stop occurs in the range or 0.1 to 1 seconds. Therefore specialized software and hardware is necesarry to guarantee the repetitivity and accuracy of every cut.

There are four control phases to make a cut:

• Acceleration
• Cutting
• Braking
• Positioning

The problem:
Historically, Rusula used the rolling mill control system supplier´s provided hardware modules to meet the required accuracy of short cut cycle times. The disadvantages to using the control system suppliers hardware module for shear cutting control:

Every customer has different hardware modules (counter boards, shaft positioning boards, ect.) The funcionality of the hardware modules vary widely and may not have the most advanced technology Specific hardware modules are not compatible with the more advanced families of controllers

Therefore it became evident that using the rolling mill control system supplier´s hardware module, limited the flexibility of implementing a more functional and cost effective solution.

The alternative hardware solutions: Russula identified four options to meet the cutting shear process control requirements :

• Develop a specific electronic card not available in the market.
• PLC with good communication abilities and minimum hardware requirements
• Shaft controller with flexible parameterization flexible to support different functions
• Siemens T 400 control card with a flexible interface to communicate with all types of control systems used in rolling mill processes.

When a new project with different model of controller appears, it is clear that a “universal” solution will decrease the development and testing phase which allows a faster implementation of the project to the market. In addition, selecting a standard hardware base then changing the software configuration allows greater flexibility in adapting to the needs of the client.

When evaluate the options, Russula discarded developing a specific card as it has a higher development investment and longer lead time before it can be delivered to the market. The Siemens T400 combines the advantages of a shaft controller, which has high performance and a moderate price, and also the flexibility of programming like a PLC.

The selected hardware solution:

Based on the evaluated criteria Russula selected the Siemens T400 Control card as the hardware base to improve the shear cutting control. Another advantage in using the Siemens T400 card is that it easily networks with Profibus. Profibus is one of the field bus standards widely accepted by the main PLC manufacturers in the European market.

The card has built-in an Profibus-DP slave interface. Through the interface between the card and the control system Russula was able to control every function of the shear. The main data communicated is:

• Work mode
• Material speed reference
• Interlocks
• Enabling of different functions (head cut, tail cut, divide cut, cobble cut, trim, etc)
• Parameters for these functions (cut length, over speed, etc)
• Speed calibration factor
• Status of T400 and alarms

The selected software solution:

Normally the Siemens T400 card is supplied as a physical support for a standard shear cut control solution. Russula replaced the standard Siemens software solution with a tailor made solution based on an accumulated 20 years of experience with issues in controlling the start/stop cycle of shears. This solution removed the limitations of a typical non programmable system while keeping the high positioning performance from a positioning controller.

The advantage:

Russula utilized special functions of the Siemens T400 card to achive a higher level of accuracy in the cut length. Material speed calibration - The card uses the material speed sent by the PLC, but this speed usually has a small percentage of error due to the difficulty in reading the effective roll diameter. To compensate for this error, the T400 card can calibrate this signal using two photocells (or Hot Material Detectors). This calibration generates a correction factor that is sent back to the PLC.
Function time measurements- T400 can measure accurately the time required to accelerate and travel up to the cutting blade´s cross point. This measurement compensates for dead time, delays or non-linealities that usually introduce errors in the cut length. Also this measured value is corrected when the speed reference for cut changes.

The cut control application has been designed to control every type of shear by only changing the configuration parameters and not the application software. This parameterization control features such as:

• Dynamic performance of shear
• Working modes
• Auxiliary functions for digital outputs

The methodology of only changing the parameters creates a universal solution which saves times and costs during the implementation phase.

Results -factories using technology:

Russula has implemented this flexible solution for cutting shear control at 3 customer manufacturing sites. The technology functioned on different rolling mills including a rod and bar mill, bar mill and a medium section mill. Customer feedback from one of these sites stated that there was a reduction of 70% in the tolerance of cut length compared to the previous solution.