Sensors are moving front and center as mills work toward greater optimization, but complexity of retrofitting can hamper use of latest devices.
Steel mills and other major metals companies are seeking more intelligent devices, says Dave Welch, vice president and co-founder of Midwest Engineering & Automation, based in Wadsworth, Ohio.
In this context intelligent means connected by high-level communication protocols to enable to operator to get access to information more easily. One of our suppliers, LMI, makes a laser profiler that has been very successful in steel mills for dimensional data.
He also cites Wenglor laser-based sensors among those able to gather data quickly.
Gathering data quickly and easily is always a challenge on the shop floor regardless of the technology or device manufacturer. High-temperatures, dust, and gases can affect both sensors and readings. All sensors in the hot-metal processes have to be rugged and fast, says Welch.
To that end, many sensor makers are shifting to 24-volt sensors from 124-volt. Most manufacturers are using 24-volt, but many mills want to keep operating in the 124-volt, alternating-current world, says Welch. The low-voltage devices have the advantages of lower power use, less heat generation, and also are not subject to the arc-flash rules.
Those are standards set by the Occupational Health & Safety Administration, based on standards from the National Fire Protection Association. Devices that could arc and cause a flash are subject to the rules, which mandate that operators nearby and maintenance personnel carry safety gear and have special training.
Despite the apparent attractiveness of newer devices that obviate special safety rules, Welch reports that more than a few mills are not just reluctant but resistant to adopt the new sensors. That is because the different power systems mean they cannot just swap one sensor for another, but must change the entire electrical and communications system.
Compared to that recalcitrance, modifying sensor environments to enhance readings is relatively simple. Any laser-based sensor operating in an optically harsh environment such as a steel mill or aluminum smelter is going to content with particles, gas, and heat, says Welch. It is often possible to have an enclosure for air purge, or even just a fan, but the greater question is always: what is the best technology? That varies with the device and with the environment.
Which leads to the question of specifications. Often that term is used interchangeably with the term standards, but in practice the two are not necessarily synonyms. In case of an outage, the quickest replacement may just be the same or updated version of the previous sensor. In a broader maintenance turn, there may be an opportunity to change sensor technologies in a line or furnace. In general, the trend is to less and less contact, says Welch, but that varies greatly.
With the downturn in the global steel industry, there is some price pressure on components, including sensors, but Welch reports that there remains good competition among device makers. Many types of sensors are applicable in several different industries, so they continue to develop overall. Laser dimensional sensors are a prime example. Those were adapted for steel forms from other industrial sectors.
With specifications varying not just country to country or mill to mill but sometimes line to line, it is not difficult to imagine that the sensor business is crowded with small, mostly privately held regional or national manufacturers. One of the few global majors in the sector is Delta Sensor, based in Paris. Most of the device assembly is also done at plants in France, but the company has some specialized manufacturing in the U.S. and in China.
There are two major trends today in sensors in all regions of the world, says Julien Fuchs, sales and marketing manager for Delta. The first is the need of mills to have easy maintenance and long life. The second is for faster and more responsive communications protocols. In maintenance, steel makers want a long life for the sensor. They also want reliability in the mechanism and in the software.
That is often the latest software or new materials, but it can be as simple as a snap, literally. In one case we replaced a screw with a draw latch, says Fuchs. Now maintenance does not need a screwdriver, just a finger. In communication, he adds that the focus is on two-way flows of data, so that operators can change parameters or query the sensor if necessary.
Overall Fuchs says the sensor business into the primary metals industry is flat worldwide, but that smooths over considerable regional differences. Over the last three or four years we have been able to maintain our turnover. That does not sound so great, but it is not bad considering how things are in the steel business.
Reviewing individual regions and countries, Fuchs details that the U.S. is a strong market currently, but that Europe is generally low. Germany and France are off a bit, while Italy is down more substantially. The Middle East is up in demand, and that includes Turkey; notwithstanding recent financial press reports that Turkeys economy may cool if geopolitical disputes with Russia move to sanctions or boycotts. Russia itself is flat as a market for sensors in steelmaking, as is India.
Fuchs confirms that while Delta and other makers continue to invest in developing new technologies, mills are generally not early adopters, like consumers with the latest mobile devices. The broader trends are clear, he notes, for example, lasers are a more important part of our business than they were a few years ago. But overall mills tend to be happy with what they have. If a customer has something that is working, they want to keep it and dont want to change.
That does not stop them from window shopping, however. Stefan Koch, global lead for metals at control systems giant SAP says that the recent Steel Day in Germany featured a great deal of equipment and interest in sensor technology, especially those for carbon dioxide balances in the furnace.
Incremental advances in sensor technology is part of a larger and more strategic change in process control, optimization, and enterprise-wide systems linking the shop floor to the front office, even the executive suite. That change is not without complications.
The link between the physical world of the plant and the digital world of process control is the sensor, says Koch. More intelligent sensors and more intelligent systems mean more data, but more data is also a bigger headache. One big headache is timing. Time-stamps on readings from sensors become meta-data that must be tracked and correlated with the reading. When outliers are reported, the time stamps must be accurate. Without that, the problem in the system can be corrected, but the batch or form cannot be identified.
With all the complications, the tends are still toward sensors collecting more data faster, and communicating back and forth with the control systems on up through the enterprise. Predictive capabilities need very precise data in real time, says Koch. One example are new heat-distribution models inside a blast furnace, with the focus on secondary heating. If the data is wrong, you can simulate anything you like, but it wont work.
With refreshing frankness, Koch notes that in some situations, the physical world can move faster than the sensors and control systems can handle. In a coating mill, for example, sensors detect coating thickness; in a cold-rolling mill sensors detect holes, thin spots, or cracks.
The sampling frequency is often every meter, but the newest materials handling machines are moving too fast. So the sensors and the system miss one, then catch up and try to harmonize. It is funny that the physical plant is running too fast for the electronics sometimes.
The challenge, he explains, is not the sensors or the control systems per se, but the harmonization and interpretation. Not only do measurements have to go from the physical world to the digital world in some useful way, but then corrective actions have to go back. All in real time. Much can go astray in the cycle of information from sensor to system, from physical to digital and then to physical againall in order, with time stamps and records up to management.
As noted, standards are essential. But no single standard exists, says Koch. The operators are responsible for the machine control. There is an automation layer above that, and may even be a layer below. Then up the layers finally to storage. As a global enterprise system provider, SAP is on home territory at those layers.
Back on the shop floor, metals makers have specifications for standard reporting, but they vary not region to region or type of plant, but client by client, sometimes hot mill to cold mill, says Mike Falk, president and chief executive officer at Falk PLI Engineering & Surveying, based in Portage, Ind.
He also notes that in some cases mill operators are already overwhelmed with data, so they look for a new sensor, but not necessarily a better sensor. In a recent example, a client installed a new laser tracker. It started detecting anomalies, and their response was, well, we never had this problem before. I had to tell them, yes, you did, you just did not know it.
Sensors also figure into a demographic shift in metals making. There is a lot of age and experience leaving the industry, says Falk. The youngsters who are coming in have a thing for fancy technology. That can be a double-edged sword.
Sensing is an essential part of process optimization and continuous improvement, says Falk. That is on us as much as it is on our clients. The key is how to develop a consultative relationship, [rather than a device- or system-based relationship.] How to break into these issues is as much psychology as it is engineering.
At the device level, one continuing trend in sensors is streamlining the proximity to the process. That could be either using remote sensing to remove the hazard and complication of probes in or on the furnace or machinery. In other cases it could be more-robust sensors that can go on or in the process, in that case to give more immediate readings and eliminate laboratory testing with its attendant delays and complications in tracking and tracing.
Our sensors measure the concentration in liquids directly in the process, says Rebecca Dettloff, head of marketing for SensoTech, based in Magdeburg-Barleben, Germany. They are installed directly in the pipe without bypass, or in the vessel or bath. There is no need of manual sampling and lab analysis. The data will be provided on line, and for process automation the data can be sent to the control system via fieldbus (Profibus DP or Modbus), 4-20 mA signal, digital outputs or Ethernet.
In the event of deviations from the production reference value, a signal will be sent immediately, so the metal maker can take counter measures. The focus is on preventive quality management to ensure an optimum product and no waste, says Dettloff. To have detailed information on the process parameters increases the safety and facility utilization.
In-line liquid concentration measurement is essential in at least four major steel mill operations: pickling (acid or base concentration and salt concentration in the pickling bath), acid regeneration (acid concentration), cold rolling (rolling oil concentration), electrolytic galvanizing (zinc salt and acid concentration), and roller chrome plating (chrome acid and sulfuric acid concentration).
In pickling baths the operator knows when to add fresh acid, how much acid and when to change the bath, says Dettloff. Measuring the rolling oil concentration the manufacturer knows how much oil and water he needs to add in the emulsion tank to keep the oil concentration on a constant optimum level.
SensoTechs devices are based on sonic velocity measurement, which is has been around for many years, but is finding new applications when coupled with latest-generation communications and process-control systems. This measuring method is safe, convenient and reliable, says Dettloff, in opposite to other measuring methods like radiometry, due to radiometrys high running costs and requirements of the regulatory authority.
SensoTech cites AMAG, Nucor, Arcelor-Mittal, Posco, Salzgitter, and ThyssenKrupp, as customers.