The electronic hopper scale, as one of the important measuring devices in industrial automation,
is widely used for weighing various materials. In the application of metallurgical processes,
the advantages of the electronic hopper scale not only lie in its high-precision measurement capability,
but also in its real-time monitoring of the production process. It
Through precise measurement and control, real-time monitoring and automatic recording of the weight of the alloy ingredients are achieved, ensuring the accuracy of material ratio and feeding during the production process. In the metallurgical process, the alloy ingredient scale, as a type of electronic hopper scale, not only enables production personnel to promptly understand the consumption of raw materials, ensuring the rational use of alloy ingredients during the production process and reducing waste, but more importantly, it guarantees the accuracy and reliability of alloy ratio weighing during the production process, ensuring that each raw material is added in accordance with the standard ratio and avoiding product quality issues caused by improper ingredient addition. Therefore, it is extremely urgent and necessary to conduct regular calibration and interim verification of the alloy ingredient scale. However, the alloy ingredient scale in the metallurgical process is subject to the design of the production line, and its structure has characteristics such as a high installation position and a small operating space, making it difficult to use standard weights for verification in accordance with the JJG539-2016 "Digital Indicating Scale" regulations. Therefore, the calibration method for the electronic hopper scale in a limited space needs to be improved to ensure the accuracy and reliability of the alloy ingredient scale.
1.
The current situation of calibration of electronic hopper scales in limited spaces
The Long Products Division, Steelmaking Branch One of MaSteel Company uses 8 alloy ingredient scales to measure the alloy ingredients for steel water batching. The maximum weighing capacity Max = 1000 kg, accuracy grade, and graduation value e = 0.5 kg. Do
As an important measuring equipment for the long-section materials division, the weighing accuracy of this equipment directly affects the control of the steel water composition, and consequently relates to the quality of the wire products of MaSteel Company. The alloy batching scale adopts a suspended structure, as shown in Figure 1, and the silo and hopper are in a fully enclosed state. During calibration, it is impossible to load standard weights in the silo into the hopper. At the same time, since there are no conditions for installing cranes and other lifting equipment above the alloy batching scale, it is also impossible to use lifting equipment to load 500kg or 1000kg standard weights for calibration, and the surrounding space of the alloy batching scale is narrow. There are supporting steel structures on the top and bottom sides, and only a 2-meter-wide passage is available for operation, as shown in Figure 2. For a long time, only two 20kg weights were placed on the inclined surface of the hopper for calibration, and the weight of the loaded weights was far from meeting the requirements, making it impossible to conduct standardized calibration and interim verification work. To explore a safe and reliable calibration method that can be implemented in a limited space, the Ma'anshan Institute of Measurement and Testing and the calibration operation area of MaSteel Testing Center jointly conducted various attempts. Finally, by loading a dedicated weight set on the hopper of the alloy batching scale for calibration, this problem was solved.
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Brief Introduction of Practical Cases Based on the Replacement Method
In the JJG539-2016 "Digital Indicating Scale" verification regulation, there is a detailed description of the replacement of standard weights: "When the scale is being verified at its location, a substitute (stable load) can be used to replace part of the standard weights. If the repeatability of the scale is greater than 0.3e, the mass of the used standard weights should be at least 1/2 of the maximum scale capacity. If the repeatability of the scale is greater than 0.2e but less than 0.3e, the mass of the used standard weights can be reduced to 1/3 of the maximum scale capacity. If the repeatability of the scale is less than or equal to 0.3e, the mass of the used standard weights can be reduced to 1/5 of the maximum scale capacity." This
It provided us with the ideas for solving the above problems. If the repeatability of the electronic hopper scale meets the requirements of the regulations, can we look for substitutes (stable loads) to replace part of the standard weights to calibrate the electronic hopper scale? According to the calibration requirements: First, the calibration value should cover the common weighing range of the mixing alloy scale, that is, it should reach at least half of its weighing range to meet the requirements of daily verification. Second, the assigned value accuracy of the substitute (stable load) should be higher than the display graduation value of the mixing alloy scale, and it is expected to be able to calibrate and mark when the indication value deviates. Therefore, we made 9 steel calibration special weights of size (150×150×300) mm (see Figure 3), each weighing about 50 kg. The mass of the calibration special weights was set at 50 kg because the space was limited, and it was not possible to use lifting equipment to add or remove the weights. The height of the hopper from the ground was only 1.1m, and a weight of 50 kg was just enough for two people to move. To facilitate loading and unloading, we welded a 1000mm×600mm×120mm steel tray, with a 50mm high triangular base at the center of the bottom to facilitate the transportation by a small forklift. We drilled holes at the four corners of the tray, and inserted steel wires into the holes, with one end connected to the holes in the corners of the tray and the other end connected to the hook. As shown in Figure 4. Since there was no hanging point on the hopper, to ensure the stability of the tray hanging, we welded 4 hanging holes under the sensor base plate of the alloy scale, as shown in Figure 5. During calibration, the tray hook can be connected to it to make the hopper evenly stressed. The special weights and the steel tray together constitute the substitute (stable load) for the calibration of the electronic hopper scale. The measurement range of the alloy scale is (0~1000) kg, with a graduation value of d = 0.5 kg. The mass of the special weight group not only meets the requirement that the calibration weight of the alloy scale is greater than 50% of its measurement range during calibration, but also has an assignment value accuracy that is one order of magnitude higher than the graduation value of the alloy scale, and can be flexibly combined to meet the calibration requirements of these 8 alloy scales for mixing. Before calibration, close the mixing alloy scale hopper, clear the hopper, and use a small forklift to transport the steel tray to the bottom of the alloy scale. Then, hang the 4 steel wires on the tray on the hanging holes, slowly lower the fork arm, and make the steel tray smoothly suspended below the alloy scale hopper. At this time, by uniformly placing the special weights on the steel tray, complete the calibration work of the alloy scale step by step, as shown in Figure 6. Note
During the calibration process, interference factors such as personnel movement, air turbulence, and the contact of the hoisting steel wire rope with the scale body need to be excluded to ensure the reliability of the calibration results. A calibration method using dedicated weights instead is adopted for the alloy scale in confined spaces, although it has certain limitations. However, it demonstrates the improvement of the method and effectively solves the difficult problems of "impossible measurement, inaccurate measurement, and incomplete measurement" in electronic hopper scale weighing, reducing the labor intensity of the calibration work, eliminating the accident隐患 of manual weight handling， and can be widely applied to the calibration work of weighing equipment in spaces with limited positions and restricted calibration operation space， unable to load sufficient weights to meet the specified calibration weight standards， such as electronic hopper scales and measuring tanks. This ensures the accuracy and reliability of related measurements in the production process and avoids the impact on product quality or quality due to measurement errors.