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YUAN HUI
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Use and improvement of high-speed steel rolls in hot-rolled plate and strip production

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This article studies and analyzes the application of high-speed steel rolls in hot-rolled strip production, and predicts the broad prospects of high-speed steel rolls with the help of characteristics such as wear resistance, chemical composition, heat resistance, and suction properties. At the same time, solutions and good suggestions were also put forward for the problems existing in the production of hot-rolled strips with high-speed steel rolls.

Keyword:Hss rolls

hss rolls

High chromium cast iron material is generally used to cast the work rolls of the front-end frame of the finishing mill in hot plate and strip rolling mills. It is used to extend the service life of the roll by forming a layer of high-chromium oxide film with high hardness and wear resistance on the surface of the roll through the contact between the roll and the high-temperature strip steel. The process of forming this oxide film is a dynamic process. The cooling conditions and rolling conditions will directly affect the density and thickness of the oxide film. Because the entire process is difficult to master, it is difficult to meet the conditions for the formation of the oxide film. Therefore, when high-speed steel rolls are used in hot-rolled strip production, the oxide film will fall off, which directly affects the surface quality of the strip and the service life of the rolls.

Improvement of HSS rolls

By changing the chemical composition of the roll and improving the matrix structure, the wear resistance of the roll can be improved. High-speed steel rolls have begun to be used in hot plate and strip finishing units. The combined application of this new technology and technology not only improves product quality to a certain extent, but also achieves very obvious results in reducing production costs. The combination of the core of the high-speed steel roll and the outer layer of the roll is a flawless metallurgical bond, so the core of the high-speed steel composite roll has high tensile strength and the strength of the bonding layer is high. This can increase the bending load of the roll, so that the plate can obtain a better shape.

Good wear resistance

Through horizontal comparison, high-speed steel rolls show good wear resistance in the same frame and in the same use condition. By measuring the wear curve after a single shutdown, it can be concluded that the wear value of high-speed steel rolls is approximately that of high-chromium cast iron rolls and shows good wear resistance. If the surface of the high-speed steel roll is in good condition after being removed from the machine, we will increase the number of uses of the roll after a single grinding operation. This not only reduces the workload of the grinder, but also reduces production costs. Compared with high-chromium steel, the millimeter rolling amount of parallel-mesh high-speed steel has been greatly improved, about 26 to 28 times. In actual use, it was found that high-speed steel rolls indeed have better thermal crack resistance than high-chromium cast iron rolls. In this way, if a general production accident occurs, the impact of the accident can be eliminated through constant grinding or a small additional grinding, making the processing process simpler and cost-saving.

The friction coefficient of high-speed steel rolls is 0.4 ~ 0.44, which is higher on average than high-chromium iron rolls. When the high-speed steel roll is arranged in the F, frame, the bite state can be significantly changed, but the rolling force will be increased. We can combine the use of I technology to reduce the rolling force of high-speed steel rollers when in use.

hss rolls

Optimization and detection of HSS ROLL use

Since high-speed steel is expensive, this requires us to take it more seriously during grinding, machine use, dismounting and inspection after accidents.

Grinding optimization of high-speed steel rolls

Due to the good wear resistance, high hardness and friction coefficient of high-speed steel rolls, it directly brings certain difficulties to grinding and quality control. For example, the grinding efficiency is reduced, vibration marks are easily generated during grinding, the roll shape is difficult to control, and the roughness must be re-determined, etc. In this regard, the manufacturer can reselect the grinding wheel material, and by adjusting various parameters such as grinding wheel hardness and particle size, the grinding efficiency can be greatly improved. In controlling the grinding quality and imitation surface, we can optimize the grinding parameters, such as controlling the feed-level grinding current during fine grinding, using periodic variable speed control technology and controlling the number of polishing passes and polishing current, etc., so that the high-speed steel roll can be The surface quality of the machine fully meets the production requirements.

Use of technology

The purpose of using oil rolling in the finishing mill is to reduce the rolling force, reduce rolling energy consumption, reduce roll wear, reduce roll consumption, improve the surface condition of the rolls, and improve the surface quality of the strip. In order to improve the rolling state and improve the surface quality of the product. The process mixes oil and water, and sprays the mixed oil and water onto the surface of the roll with a nozzle. Form an emulsion of a certain concentration as an agent. When in use, the work roll is cooled and closed, and the agent is sprayed on the surface of the work roll on the incoming side to form a continuous, uniform, and firm oil film when the roll contacts the strip to reduce the friction coefficient between the work roll and the strip and reduce the rolling force. , reduce rolling mill vibration and reduce work roll wear. This technology is used in conjunction with roll gap spraying (anti-oxidation film shedding), which can effectively reduce the shedding of the oxidation film on the work roll, reduce the temperature of the roll surface in the deformation zone, reduce the thermal cycle stress of the work roll, and thus prevent the occurrence of cracks. . In actual production, the process is used in conjunction with high-speed steel rolls. Not only does it eliminate the increase in rolling force caused by the high friction coefficient of high-speed steel rolls, but their combined effect can improve product quality, reduce roll consumption and energy consumption, etc., showing very obvious effects.

Inspection of high-speed steel rolls

In order to ensure the normal working condition of high-speed steel rolls, they must be strictly tested. Accidents of high-speed steel rolls generally come from two aspects, the impact of shovel accidents and the impact of mechanical collisions. When a collision occurs, mechanical cracks will sometimes occur on the surface of the roll.

When a steel pile accident occurs, because the high-speed steel roll has good resistance to thermal cracking, if the operator responds quickly and handles it promptly, surface cracks will generally not occur. However, sometimes the impact of piled steel may cause the working layer to detach and reveal the original defects. This necessitates surface defect detection and confirmation using eddy current testing after the accident. Once cracks are found, they must be ground away, and the working layer must be inspected with ultrasonic flaw detection to confirm that there are no defects or that the existing defects have not expanded within a safe range. Another method is to use surface wave testing instead of eddy current testing. When a crack is detected, the crack is confirmed by using color penetrant inspection or magnetic particle inspection. The bottle uses an oblique probe to determine its depth, determine the appropriate grinding amount, and process the roll to ensure the normal operation of the roll.

Although high-speed steel rolls have good thermal crack resistance, they are very sensitive to mechanical cracks. -But if there are mechanical cracks, they must be ground clean, otherwise there will be a risk of the roll peeling off, falling off pieces or even breaking the roll during production. Therefore, when a mechanical collision occurs on a roll, eddy current flaw detection or surface wave flaw detection must be carried out promptly to ensure that there are no mechanical cracks and to ensure the safety of production.

PC FC board shape control optimization

Since the physical and chemical properties of high-speed steel rollers are different from those of high-chromium rollers or ICDP rollers, the roller shape must be adjusted. The physical and chemical properties mainly include thermal expansion coefficient, friction coefficient, elastic modulus, suction hardness, etc. Stop the water immediately after the rolling is completed, record the water stop time, and then replace the high-speed steel roll. Starting from the time when the water is stopped, measure the temperature after about 2 ml. Take the middle of the roller body as the coordinate origin, take points from both sides, divide the roller into 21 equal parts for every 10ML-measurement point, and measure the temperature of the sea point. The temperature distribution map of the roll body is drawn based on the measured values, and is fed back to the first level to optimize the temperature model, and then the work roll is hoisted to the roll room for air cooling. After the air is cooled to room temperature, the wear curve after the machine is removed is measured by the grinder, and then fed back to PC FC to optimize its wear model.

The continuous application of new technologies to improve the quality and precision of rolled products and reduce production costs is the development direction of today’s rolling technology. High-speed steel rolls have good wear resistance and thermal crack resistance, which can improve product quality and reduce production costs. However, there are also some disadvantages, such as increased rolling force due to higher friction coefficient, sensitivity to mechanical cracks, lower grinding efficiency, and difficulty in grinding quality control. As long as we continue to summarize the experience in using high-speed steel rolls, we will be able to further increase the utilization rate, improve the surface quality of the strip, and reduce production costs.

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Product advantage

The world No. 1 in crude steel production steel plant, over 70% of the HSS for bar and wire are from us.

LMM high-speed steel rolls have higher steel passing per groove (times) due to their good wear resistance, which saves roll changing time, improves rolling mill operation rate, reduces roll consumption, and improve the overall efficiency of the factory.
Generally, the amount of steel passing in a single groove (times) is 3 to 5 times that of cast iron rolls.

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