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Long-distance camera and non-contact temperature measurement can be well combined in some steel processes, such as furnaces and rolling mills. High-temperature camera thermometers provide excellent tools for optimizing monitoring and temperature measurement functions because of their flexible combination of unique video imaging and infrared temperature measurement. This combination opens up new avenues for steel mills that have not used video cameras before, especially making it easier to maintain the furnace. The following focuses on the potential applications of high-temperature camera thermometers in steel plants, and describes the measurement of solid and liquid steel temperatures.
Iron & Steel Industry & Temperature Measurements In general, the use of infrared thermometers to measure the temperature of steel is difficult because of the low radiative properties of steel. Radiation is a property of matter, it shows that the same black object (it is an emissivity of 1 object, it represents an excellent radiation) compared to how much infrared radiation is emitted. The higher the radiation value, the higher the energy reaching the detector. Basically, the higher the emissivity, the easier it is to measure the temperature of the object.
For steel products, the emissivity varies with temperature, surface conditions, and the chemical composition of the steel. One variable that has a large effect on emissivity is surface conditions. For example, the emissivity of non-oxidized stainless steel (if processed in a factory) is approximately 0.4. For highly oxidized (more "dark") surfaces, this value rises to 0.8. For a planed (very "bright") surface, the emissivity drops to 0.2. Since the high-temperature camera thermometer provides a flexible method of changing the emissivity for the cursor selectable area on each terminal screen, a reliable measurement temperature can be obtained as long as we know the parameters and specifications of the processed raw material. 
Another problem to understand is the heat reflection from the hot furnace wall on the surface of the steel, which is more important for applications where the steel is in a solid state, such as steel in furnaces and annealing furnaces. There is a large temperature difference between the steel surface and the furnace wall, combined with the high reflectance properties of the steel (such as the same mirror), making it difficult to measure absolute temperatures in these applications. However, it is possible to periodically observe changes in the product or its processing with related measurements. In steel melting applications, this issue is not important. Especially the electric furnace, it is not affected by this problem, because the furnace wall is not the hottest part in the process. The following sections detail the potential applications and potential difficulties of high temperature camera thermometers in the steel industry.
Blast Furnace The blast furnace is the beginning of the steel production process and is a place where continuous operation is required. It is a container in which iron ore is mixed with limestone, coke (a solid material obtained from the residue of coal, asphalt, and petroleum). These mixtures are heat-treated in a blast furnace to produce molten iron which then falls on the bottom of the furnace. The molten mixture is moved by the ladle to the next step in the process. This is an extremely dusty environment with very poor visibility. Installing the camera in the blast furnace area has little value.
Unless at the tuyere, or when the mill uses pulverized coal as a fuel, a surveillance camera with a temperature measurement function is very useful in order to control the combustion in the furnace "cavity" (combustion zone). The camera installed in this position is not used to observe the product, nor to look at the fireball. Because the flame is full of particles, it is possible to measure their temperature. Knowing the temperature and size of the furnace "cavity" is very valuable, and it is also a very important control tool. The potential for low fuel costs and the use of crushed coal as a fuel in combination with blowing oxygen to promote its combustion have become very popular in European society.
In the blast furnace there are two (container) sections that can be easily repaired by the use of a high-temperature camera thermometer. One is the furnace body and the other is a fish-shaped ladle. The furnace body is a container for generating hot air for the furnace. It is a high-cylindrical structure made of heat-resistant bricks. A large furnace produces heat that is stored before it is sent to the air used as a blast. Each blower unit has 3-4 furnaces. Fire life is critical, with some plants imaging infrared with very small hot spots and then using black-and-white photos to locate the actual point in the furnace. The high temperature camera thermometer is useful in this application by identifying the location of the hot spot (using a red-purple-yellow color palette) and then setting the cursor zone to the maximum temperature mode to identify the temperature at this point. Fish-shaped ladle is used to send hot metal products from a blast furnace to a steel production furnace. In general, it is a large cylindrical object made of refractory material and mounted on a wheel. No burning occurs at this stage. If it has not been empty for a long time, the appearance of hot metal is enough to provide sufficient brightness for using the camera. Continuous monitoring of fire bricks is normal, but it is difficult to observe all the contents inside. However, a high temperature camera thermometer equipped with a 78′′ vertical lens can successfully see every corner of it. The temperature measurement function of the high temperature camera thermometer with visual images can help you decide which brick needs to be replaced. The stability and integrity are critical, and failures in transit can cause serious damage, such as complete damage to containers, rails, work areas, etc., resulting in expensive downtime – any of them is paid for. Great.
There are three commonly used steel production processes in the iron and steel production process: oxidation, open hearth furnaces and electric furnaces. At this stage, iron from the blast furnace is converted to low grade steel and then an ingot or billet is formed.
(1) Oxidation process The oxidation process involves mixing the liquid hot metal of the blast furnace with the flux, and then transferring it together with a large amount of oxygen into a large insulated casting spoon. In industry, this is usually identified as Basic Oxygen Furnace or BOF. Basically, no combustion is taking place during this batch process. In spite of the lack of flame, the high-temperature camera thermometer can effectively measure the temperature of the charge. It is a key parameter, and it decides when to release the molten metal and another key parameter to monitor the height of the liquid in the casting spoon. At present, it is the most common method to insert a thermocouple into a bath to measure the temperature of the charge. We have received inquiries about how to use a high-temperature camera thermometer in this process. There is potential here, but we cannot make an experimental demonstration to prove this theory. In addition to maintenance and bricklaying, the feedback results corresponding to this process are more difficult to determine.
(2) Open hearth process Open hearth furnace is the most efficient steel production process (mainly manifested in the ability to handle raw materials for pieces/waste). Basically, this process is responsible for the melting of iron, chip/waste limestone charge and different fluxing agents during the batch process. This process takes place in a large insulated rectangular furnace with a sloping floor. The flame on the charge is ignited from one end of the furnace to the other, melting all the components. In such a furnace, the charge is a mixture of solid and molten metal having different temperatures, so it is necessary to set different emissivities for the purpose of accurately measuring the temperature.
During this process, a high-temperature camera thermometer installed under the flame generator will provide the operator with:
The temperature measurement of the furnace wall at the point of view of the melting process - it is useful for measuring the life of bricks - multiple temperature measurement end-point temperatures of the contents - in controlling and obtaining the desired metallurgical properties and once the steel is ready and It is important to ensure that the long cooling process in the furnace is eliminated after pouring.
(3) In this process, the electric current is used to generate an electric arc from the welding rod to the charge to generate a powerful heat and to rapidly melt it. There is no need to use oxygen to burn, but the heat is intense and can be strictly controlled. This provides the most flexible way to produce steel and most of the steel can only be produced in electric furnaces, such as (1) high manganese steel, (2) a large number of stainless steel alloys, (3) super alloys for high temperatures steel.
We successfully installed a S-high-temperature camera thermometer in an iron-free alloy arc melting furnace - similar to an iron and steel production furnace. This system is used to monitor the melt zone. It can be used to monitor the size of the melt zone as well as to monitor the wear of the firebrick. In this application there is no problem with heat reflection and there is no change in the emissivity due to oxidation. As for the video image, there is a big difference in full power and starting power of the welding electrode under bright conditions. If the camera aperture of the high-temperature camera thermometer is not variable, it is difficult to see the product under certain conditions. In order to solve this problem, we have developed a product with a remote control auto iris. Because a strong magnetic field is generated during this process, installing a video monitor in an environment such as a control room becomes a good idea. Because if the monitor is close to an arc, the image is likely to be affected.
The soaking furnace is used to make the temperature of the steel ingot uniform. As discussed earlier, the ingot is cast at the exit of the furnace. This is necessary to ensure the metallurgical properties of the entire product and the bulky structure before hot working and further processing in the breakdown (damaged) rolling mill.
In this process, a dozen or so ingots and firebricks must be aligned in a large pit, and the whole body is heated. There is no continuous movement in the furnace, so there is less need for camera monitoring. However, if the camera is installed to observe the flame, then the high-temperature camera thermometer's control of the fuel is helpful.
The normal temperature range for heating the ingot is between 1175°C and 1345°C. The exact temperature depends on the grade of the steel and the characteristics of the rolling mill. In order to preserve the fuel here, it is important to measure the temperature of the ingot, which prevents the surface from overheating. At present, temperature measurement is mostly done by thermocouples. The ingots took about 8-12 hours for "same soaking/soaking." This process results in a large amount of oxidation of the ingot surface and due to the nature of the emissivity during the operating time, it is difficult for the infrared thermometer to obtain a good viewing angle.
The reheat furnace steel sheet is the result of the production of a rolling mill that breaks (damaged). A typical steel plate is produced at 25 feet in length and 4" in thickness. During the passage of the steel plate through a breakdown (damaged) roller, the raw material loses a lot of heat and becomes fragile and less flexible. Based on this The steel plate needs to be reheated for further processing, at least 1200°C steel plate temperature is required and this temperature can be reached in the reheating furnace.
The design of continuous furnaces varies with plate advancement mechanisms, such as simple mechanical thrusters, rotary hearths, or walking conveyors. These mechanisms lift the steel plate through the furnace. The hearth (blow light) is directed in the opposite direction to the movement of the steel plate. The reheat furnace is located in the path of the rolling stock material. Because the reheating furnace may become a production bottleneck, continuous temperature measurement of the steel plate is necessary. Steel plates always travel in the furnace (sometimes slow) and contact thermometry through thermocouples is difficult.
Because of these difficulties, infrared thermometers are often used in these applications. The requirements of infrared thermometers are the radiation emission compensation from the surface of the steel to the pyrometer (produced by particularly hot surrounding objects). The difference of 100°C or less between the furnace wall and the steel plate makes the value read by the monochromator at 0.8 mm higher than the actual 30°C. The temperature difference of 200°C between the furnace wall and the steel plate makes the value read by the monochrome thermometer 120°C higher than the actual one. The specific data will change with the furnace. If the relative temperature of the steel plate or the uniformity of the heating is important, since the absolute temperature is not the main parameter of this industry, the high temperature camera thermometer can provide useful information. The progress of the steel plate in the furnace can only be observed by the camera monitor. In some places, up to three cameras are used in each furnace to achieve complete observation of the movement of the steel plate.
Application in rolling mills The final processing of steel production is rolling, hot rolling and cold rolling. First, the heated steel plate passes through the hot rolling mill. The basic function here is to reduce the thickness of the steel plate by 40%. Second, the steel plate advances to the final step of steel production—cold rolling—and it is named because unheated metal passes through the rolling mill. Through this process, the final thickness required for steel sheet products such as automotive steel sheets, steel sheets for beverage containers, building materials, and the like can be obtained. Cameras have been widely used in rolling mills (hot and cold) for monitoring between rolling mills.
Temperatures need to be measured at both the inlet and the outlet of the rolling mill (hot and cold rolling). The temperature of the steel plate at the entrance determines the "gap" (force of isolation), which is useful for the operator during rolling. The temperature at the outlet determines the mechanical properties of the final steel product. Infrared thermometers have been used in these two places. The high-temperature camera thermometer at the entrance completes the auxiliary monitoring function by providing a picture when the plate enters the rolling mill; it is necessary for tracking. When the steel plate stays for almost 30 seconds before it enters the first stand, the six temperature measurement areas of the high-temperature camera thermometer will measure the temperature difference along the length of the plate before it enters the rolling mill. This is a potentially large application for high-temperature camera thermometers because observation and temperature measurement are equally important.
Other parts of the industry may require continuous casting—for example, in some mills. In these applications, there is a large furnace to melt the steel before the steel is poured in (these furnaces may also be inclined). Pour the stream into a series of tanks and distribute the melted metal onto a movable conveyor belt to produce steel plates directly. There is a need to see the flow of raw material along the processing path. Infrared thermometers have been used to monitor the solidification process of the steel at the end of the conveyor belt.
The structural changes imposed on the raw material during the cold rolling process of the annealing (toughening) furnace make it necessary to "anneal (toughen)" (relax) the steel structure before it is formed. Without the annealing step, the steel sheet product is brittle during any forming process. There are two types of furnaces: closed annealing and continuous strip annealing. Closed annealing is a batch process that uses hot air to heat a set of cold mill coils. There is no critical temperature requirement for moving without raw materials. Applying our products here does not bring much value.
On the other hand, heating and cooling units are built into towers in a continuous strip annealing furnace, so there may be potential applications because our system will bring real benefits to the operators of the rolling mills. Steel moves in a continuous path and quickly passes through heating and cooling towers (some with 5 floors). Steel travels back and forth around the rollers at the top and bottom of the tower to increase the time of the steel itself in the furnace. Finally, the steel is "cooled" (freezing the molecular structure of the steel at this time) to its final temperature.
As for the alloy, the steel needs to reach a temperature of between 730°C and 1050°C. The uniformity of the temperature over the width of the steel sheet determines the mechanical properties of the steel and it is a very important parameter. Because the speed of the raw material is changing (up to 7 m/s), the temperature information from the high-temperature camera thermometer can be set at different points, so the high-temperature camera thermometer can also view the steel plate on the large annealing line. At present, there is no way to determine where the edge of the strip is related to the roller. As long as there is enough light, this observation is very beneficial for the operator to control the movement of the steel plate.
However, some of the furnace's lens tubes are under controlled air and the use of non-automatic gas, so it is necessary to cool the camera in these annealing furnace applications.
Summary The above description refers to the traditional application of many cameras and high-temperature camera thermometers in integrated steel plants. There are also ancillary applications such as melting furnaces for waste, electroplating lines, extrusion lines and coating lines, where the application of cameras is beneficial to operators and rolling mills. These processes do not exist in every steel plant. They are generally found in factories that produce special products.
Temperature measurement is required in many processes in the steel industry. Thermocouples are used in most cases, however, contact measurements are not feasible in some applications because of the presence of moving solid steel or the use of contact probes in their environment. These special applications will undoubtedly benefit from the use of high temperature camera thermometers for image temperature measurement applications.
Figure 1 Interior of a glass furnace viewed through a Spyrometer
Figure 2 Internal view of a power boiler viewed through a Spyrometer