2008년 11월 07일
SMSDemag Breakout Prection System
New approaches to breakout prediction. (Continuous Casting).
By Arzberger, M
Date: Tuesday, October 1 2002
Date: Tuesday, October 1 2002
High-speed slab casting requires a more rapid response to caster control when potential breakout conventional speeds. SMSDemag are now employing a Field Bus based system to digitise data at the mould which, along with suitable algorithms, enables the caster to be stopped within two seconds to heal the strand and then automatically be ramped back to production speed. In addition to break out prevention, the system profiles the temperature of the whole mould and also monitors stopper movement to provide warning of nozzle clogging with its associated risk of inclusions causing poor surfaces and breakouts.
The task of detecting and preventing breakouts is as old as continuous casting itself. Of all the processes hitherto used to prevent breakouts (measurement of temperature; friction force; withdrawal force; vibration and structure-borne noise), the measurement of temperature by means of thermocouples at the mould copper plates has proved to be the most suitable and most reliable.
Thanks to close cooperation and full use of all the synergies between automation, mechanical design, process engineering, metallurgy and steelworks customers, a system has been created which has taken a pioneering role for breakout early-warning systems. This system is known as the SMSDemag Breakout Prediction System (BPS).
SMSDemag supplies the complete solution from one single source, the `Plug and Cast' concept, which also includes competent and long-term service to its customers.
DATA COLLECTION
The basis for a successful BPS is reliable data collection which, in the tough environment of continuous casting, transmits plausible measuring data at all times from the sensors installed in the mould.
With the growing need for top-class product quality, the number of sensors in the moulds has increased greatly. While at the beginning of the development it was customary to have two rows of thermocouples, nowadays three or more rows are generally used.
The focus is no longer exclusively on early detection of breakouts but now also on the monitoring of heat dissipation and the contact between the strand shell and the mould. It is therefore not unusual for individual moulds to be equipped with 100 or more thermo sensors. This large number of sensors necessitates a great deal of cabling and coupling. In addition to the high investment costs, the maintenance expenses are also considerable.
The standard design used today is the multifunction coupling shown in Fig 1 which was developed for use in a tough environment. Thus, for example, in a facility currently in use, four such multicouplings are required to connect about 100 temperature sensors. The sensors are connected to the multicouplings via temperature-resistant master cables.
[FIGURE 1 OMITTED]
Thanks to the data transmission system recently developed by SMSDemag, distinct progress has made with regard to minimising the cabling and maintenance expenses.
By using the new type of field bus modules (with IP67 type protection) for decentralised pre- processing of data, the values measured are directly recorded in digital form at the mould. The modules, which are each equipped with four channels, are connected via profibus (in cascade form). Fig 2 shows the opened water-cooled protective casing which houses the field bus modules.
[FIGURE 2 OMITTED]
The hitherto used multi-strand master cables are replaced by a so-called `hybrid cable' (bus and energy supply combined in one). Two special plug connectors, which were specially developed for the tough ambient conditions, replace the multi-pole multifunction coupling which is prone to failure, Fig 3.
[FIGURE 3 OMITTED]
To replace a thermocouple, only the sensor plug connector has to be released, the thermocouple removed and replaced by a new one. A mould equipped with this technology has already been fully tested in the workshop, (Fig 4).
[FIGURE 4 OMITTED]
This new technology can be used for new casters as well as when revamping existing ones. The newly developed concept was tested for several months in field trials and is now used in all products supplied by SMSDemag. Initial experience shows that the costs of maintaining the thermocouples and the pertaining cabling have dropped by more than 20%.
EVALUATION SYSTEM
The evaluation system uses a real-time database and also archives the history of events as a `flight recorder' type record for subsequent analysis if required.
In addition to the extensive measuring data on the mould, further process-related data are transmitted to the BPS. At the required cycle times--ranging from a few milliseconds (10ms for mould level and stopper position) to 250ms (for temperature signals), all data are saved in a real-time database and archived for several weeks. The evaluation programs procure the data required for active breakout recognition from this real-time database.
In addition to this on-line function, the system also enables the analysis of previously recorded data by playing back complete casting sequences (the flight recorder). This makes it possible to subsequently examine the process sequence and to optimise the system in respect of changed conditions (new grades of steel, different casting powder, casting speeds etc) by means of simulation. The plant operator obtains in-depth knowledge about the connections between breakout risks and operating practice (Fig 5).
[FIGURE 5 OMITTED]
THE ALGORITHMS
The algorithms employed provide quick reaction for high-speed casting.
The development of near-net-shape casting of thin gauges at high casting speeds has also resulted in the need for a BPS which is capable, within the shortest feasible time, of recognising potential breakout risks and introducing preventive measures. Breakouts are primarily caused by so-called `Stickers' which cause 80% of all failures.
The traditional method for recognising stickers uses certain temperature progressions (signal patterns) which have to first take place before an alarm is triggered. These are no longer sufficient for today's faster casting rates. This is clearly illustrated by the fact that with an active mould length of approximately 1m and a casting speed around 6m/min, an alleged sticker is within the mould for a maximum of 10 seconds only. If the strand is to be given a chance to be repaired before exiting the mould, the continuous caster must be stopped within just two seconds. Once the strand is healed, the caster speed can then be brought back to the required production speed with the help of suitable acceleration ramps.
Algorithms which can tackle this task are based on a rate-of-change process. The rate of increase of all incoming temperature measurements is continuously compared with threshold values. If the value is exceeded, the BPS enters a state in which it is ready to trigger an alarm. In this condition, the temperature progressions are monitored in the immediate vicinity of the initiator. If the threshold value is exceeded here too, the BPS immediately enters the alarm state and an active breakout alarm is triggered.
A further criterion for producing an alarm state is abnormal movements of the mould level and the stopper.
A newly developed algorithm compares the expected stopper position and movement as functions of material flow, tundish level and tundish and stopper geometry with the actual stopper position and is therefore able to recognise clogging deposits at the tundish spout at an early stage. The operating personnel are warned well in time about any possible wash out of me aeposas, winch upon entering the mould would then cause inclusions in the strand shell and consequently lead to breakouts. The implemented technological model records any factors insidiously affecting the submerged nozzle which in turn largely also influence the surface quality of the cast product.
PREVENTION
The active alarm is transferred to the caster's control system (Fig 6). The casting speed is reduced according to a predefined ramp such that a speed of approximately 0.5 m/min is reached within less than two seconds. After a short holding time, the casting speed is again automatically accelerated to the original production speed by using emergency delay ramps. Various types of emergency delay ramps are automatically activated, depending on the manner of formation of the sticker and the steel grade (Fig 7).
[FIGURES 6-7 OMITTED]
The changes in speed take into account the past experiences with various production facilities. The reactions have to be adapted depending on the various steel grades and the pertaining casting powders as well as on the different operating situations. While production is continued after a preventive measure during the casting process, it may be necessary in the event of a breakout alarm being triggered in the startup phase to immediately initiate a sequence abort with automatic withdrawal. A coordinated reaction from the caster control system and the BPS is essential for this purpose. This is how maximum protection against damage can be attained with minimum loss of production.
THE TRANSPARENT MOULD
In addition to the function of the BPS described above, the sensor system on the mould is being increasingly used to monitor the casting process. With Mould Temperature Mapping (MTM), SMSDemag has developed a system which gives the operating personnel on-line information on the heat dissipation from the mould as well as on the contact between the strand shell and the copper plates (Fig 8). The temperature measurements which are distributed over a network in the mould serve as points of calculation for the temperature of the copper plates and provide information on the contact between the strand shell and the mould. At locations which have an abnormally low temperature, a gap will have been formed between the strand and the mould, thereby hampering the necessary heat dissipation and the continuous growth of the strand shell. In the area of the mould corners, this could be an indication of incorrect taper. As a rule, the risk of breakout is greater in such operating conditions.
[FIGURE 8 OMITTED]
A user-friendly visual display system shows the temperature maps measured and allows the user to continuously estimate the quality of the casting process.
Thanks to this additional complementary function, the breakout detection system has progressed from the plain BPS to become the SMSDemag Mould Monitoring System--MMS and is thus the prerequisite for the `Transparent Mould'.
THE VISUAL DISPLAY
In addition to the direct reaction of the automation system for the prevention of breakouts, a user-friendly visual display of measured data and operating states is extremely important. The visual display system for operation and observation purposes is directly linked to the database, Fig 9. A graphics editor facilitates the creation of the screen display which can be adapted to meet the individual requirements of the users.
[FIGURE 9 OMITTED]
In addition to the depiction of the operating condition of the mould and the availability of the entire MMS, the process data must also be displayed in a suitable manner, (Fig 10). The green background colour in Fig 10 indicates trouble-free operation. Yellow and red draw the user's attention to abnormal situations which could jeopardise casting. Furthermore, essential information is also show in the form of process data such as mould level, stopper position, casting speed and integral heat dissipation,
To analyse historical data, the system allows the compilation of any number of trend curves and signals.
[FIGURE 10 OMITTED]
TELESERVICE SUPPORT
Assisting customers in the maintenance and optimisation of the automation systems is an integral part of the SMSDemag service. BPS incorporates the hardware and software components which enable remote diagnosis. The maintenance staff as well as SMSDemag's service staff can access the system via teleservice and analyse the entire system.
A RESULT
The Mould Monitoring System (comprising BPS and MTM) is an interdisciplinary development from all the departments of SMSDemag. A technological system has been developed which, in a consistent and logical manner, takes account of all aspects, ranging from plant operation to maintenance and down to the minimisation of damage losses.
Caster operators benefit from these achievements by:
--Prevention of sticker breakouts;
--Thorough monitoring of the heat transfer in the mould;
-- Further development of casting technology;
-- Lower expenses on maintenance;
-- Quick mould change times;
-- Steep acceleration curves;
--Thorough monitoring of the heat transfer in the mould;
-- Further development of casting technology;
-- Lower expenses on maintenance;
-- Quick mould change times;
-- Steep acceleration curves;
-- High product quality;
-- High operational reliability.
CONTACT
SMSDemag
Automation Division,
SMSDemag Ag, Eduard
Schloemann-Strasse 4,
40237 Dusseldorf,
Germany, Tel +49 27
33 25 95 Fax +49
27 33 29 10 11
Automation Division,
SMSDemag Ag, Eduard
Schloemann-Strasse 4,
40237 Dusseldorf,
Germany, Tel +49 27
33 25 95 Fax +49
27 33 29 10 11
5 Cause for breakouts
Breakouts caused by
Stickers 8O%
Slag 8%
Bleeders 6%
Mould level waving 4%
Others 2%
Stickers 8O%
Slag 8%
Bleeders 6%
Mould level waving 4%
Others 2%
Note: Table made from pie chart.
# by | 2008/11/07 12:42 | Automation | 트랙백 | 덧글(0)
☞ 내 이글루에 이 글과 관련된 글 쓰기 (트랙백 보내기) [도움말]