Application and improvement of hss rolls in hot-rolled strip production

This paper studies and analyzes the application of high-speed steel rolls in the production of hot-rolled strips, and predicts the broad prospects of hss rolls with the help of wear resistance, chemical composition, heat resistance and mechanical properties. Solutions and good suggestions are put forward for the problems existing in the production of steel rolls in hot-rolled strips.

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

Improvement of High Speed Steel Rolls

By changing the chemical composition of the roll and improving the matrix structure, the wear resistance of the roll can be improved. After more than ten years of updating and perfecting the technology, high-speed steel rolls have begun to be used in hot strip finishing mills. The application of this new technology in combination with the lubrication process not only improves the product quality to a certain extent, but also achieves a very obvious effect in reducing the production cost. The combination of the core of the high-speed steel roll and the outer layer of the roll is a defect-free metallurgical bond. The core of the high-speed steel composite roll has high tensile strength and the strength of the bonded layer is high, which can increase the bending load of the roll, so that the plate can be obtained more Good shape.

Good wear resistance

Through horizontal comparison, high-speed steel rolls exhibit good wear resistance under the same frame and the same use condition. Based on the good condition of the surface of the high-speed steel roll after being off the machine, we increase the number of times the roll is used after a single grinding. This not only reduces the workload of the grinding machine, but also reduces the production cost. Compared with the high-chromium steel, the millimeter rolling capacity of high-speed steel has been greatly improved, which is about 26 to 28 times that of the original, and the cost performance has been greatly improved. .

Good thermal cracking resistance

Due to its unique organizational characteristics, high-speed steel can effectively suppress the generation of cracks. In actual use, it is found that high-speed steel rolls do have better thermal cracking 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 adding a small amount of grinding, so that the processing process is simplified and the cost is saved.

The friction coefficient of high-speed steel rolls is 0.4 to 0.44, which is higher than that of high-chromium iron rolls on average. When the high-speed steel roll is arranged on the F stand, the biting state can be obviously changed, and the rolling force will be improved. We can combine the use of process lubrication to reduce the rolling force of high-speed steel rolls in use.

Optimization and detection of hss rolls use

Because the high-speed steel roll has good wear resistance, high hardness and friction coefficient, it directly brings certain difficulties to grinding and quality control. For example, the reduction of grinding efficiency, the vibration marks are easy to occur during grinding, the control of roll shape is difficult, and the roughness is re-determined. In this regard, the manufacturer can re-select the material of the grinding wheel, and by adjusting various parameters such as the hardness and particle size of the grinding wheel, the grinding efficiency can be greatly improved. In terms of controlling the grinding quality, by optimizing the grinding parameters, such as controlling the feed rate and grinding current during fine grinding, using periodic variable speed control technology and controlling the smooth grinding pass and smooth grinding current, etc., the high-speed steel roll The surface quality of the machine fully meets the production requirements.

Use of process lubrication

The purpose of rolling with lubricating oil in the finishing mill is to reduce rolling force, reduce rolling energy consumption, reduce roll wear, reduce roll consumption, improve roll surface condition, and improve strip surface quality. In order to improve the rolling state and improve the surface quality of the product, the process lubrication system should be invested. Process lubrication mixes oil and water, and sprays the mixed oil and water to the surface of the roll with a nozzle. A certain concentration of emulsion is formed as a lubricant. When the work roll is cooled and closed during use, the lubricant is sprayed on the surface of the work roll on the day-entry side, and a continuous, uniform, and firm lubricating oil film is formed when the roll is in contact with the strip to reduce work. The friction coefficient between the roll and the strip can reduce the rolling force, reduce the vibration of the rolling mill, and reduce the wear of the work roll. This technology is used in conjunction with the roll gap spray (anti-oxidation film shedding), which can effectively reduce the oxide film shedding of the work roll. , reduce the temperature of the surface of the work roll in the deformation zone, reduce the thermal cycle stress of the work roll, and thus prevent the occurrence of cracks.

In actual production, the combination of process lubrication and high-speed steel rolls not only eliminates the increase in rolling force caused by the high friction coefficient of high-speed steel rolls, but also improves product quality and reduces roll consumption and energy consumption. showed a very obvious effect.

Detection of high-speed steel rolls

In order to ensure the normal working condition of the high-speed steel roll, it must be strictly tested. The accidents of high-speed steel rolls generally come from two aspects,

Mechanical Collision: When a mechanical collision occurs. Mechanical cracks sometimes occur on the surface of the roll.

Production Accidents: When a steel stacking accident occurs, because the high-speed steel roll has good thermal crack resistance, if the operator responds quickly and handles it in time, generally no surface cracks will occur. However, sometimes the working layer is detached due to the impact of stacked steel. This necessitates confirmation of surface defect detection with eddy current testing after an accident. Once a crack is found, it must be ground, and the working layer is inspected by ultrasonic flaw detection to confirm that there are no defects or that the existing defects do not expand within the safe range. Another method is to use surface wave testing instead of eddy current testing. When cracks are detected, confirm the cracks with color penetrant inspection or magnetic particle inspection, and then use the angle probe to determine the 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. Once mechanical cracks appear, they must be ground, otherwise there will be dangers of roll spalling, falling blocks or even broken rolls during production. Therefore, when a mechanical collision occurs to the roll, it is necessary to carry out eddy current flaw detection or surface wave flaw detection in time to ensure that there are no mechanical cracks and ensure the safety of production.

PC FC board shape control optimization

Since the physical and chemical properties of high-speed steel rolls are different from those of high-chromium rolls or ICDP rolls, adjustments to the roll shape must be made. The physical and chemical properties refer to thermal expansion coefficient, friction coefficient, elastic modulus and hardness. When the rolling ends, stop the water immediately, and record the water stop time, and then replace the high-speed steel roll. Measure the temperature after about 2ML from the time when the water is cut off. Take the middle of the roll body as the origin of the coordinates, take points on both sides, divide the roll body into 21 equal parts for every 10ML measurement point, and measure the temperature of each point. According to the measured value, the temperature distribution map of the roll body is drawn to optimize the temperature model: then the work roll is hoisted to the roll room for air cooling. After air-cooling to room temperature, the wear curve is measured by the grinding machine, and then fed back to PC FC to optimize its wear model.

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. But there are also some disadvantages. Therefore, we must constantly summarize the experience of using high-speed steel rolls.

HSS ROLLS

Service life and flaw detection standard of cold-rolled work rolls and cold-rolled intermediate rolls

The main links in the manufacturing process of cold-rolled work rolls and cold-rolled intermediate rolls are smelting, forging, heat treatment, processing and inspection.

Cold-rolled work rolls and cold-rolled intermediate rolls have to bear a lot of rolling stress during the working process. In addition, problems such as welds, inclusions, and edge cracks in the rolled piece can easily lead to instantaneous high temperatures, which make the work rolls subject to strong thermal shocks. Cause cracks, sticking, peeling and even scrapping. 

Therefore, cold-rolled work rolls and cold-rolled intermediate rolls must have the ability to resist cracking and spalling caused by bending stress, torsional stress, and shear stress, and also have high wear resistance, high contact fatigue strength, and high Fracture toughness and thermal shock strength, etc. 

Therefore, how to improve the service life of the roll has always been a major problem faced by the roll manufacturing industry.

Non-destructive testing of rolls is usually carried out with ultrasonic flaw detectors. In the flaw detection standards of cold-rolled work rolls and cold-rolled intermediate rolls, the roll body is usually divided into a surface area, a central area and an intermediate area according to the stress, and then the critical size of the allowable defects in each area is specified according to the principle of fracture mechanics. Flaw detectors should have knowledge of roll manufacturing in order to determine the nature of defects, and should also have knowledge of roll use in order to estimate whether these defects may cause service damage under specific conditions of use.

Leading Manufacturer of High-Performance Work Rolls - LMM GROUP 

What is the requirement of high efficiency continuous casting for the copper mould tube taper ?

At present, the taper values of high-efficiency copper mould tubes used by various steel mills are generally 0.6-0.9. When the low-carbon steel and low-alloy steel are pulled, the taper value is taken as the middle and lower limit, and the drawn medium carbon steel and high carbon steel are the upper limit of the taper value. 

In order to ensure that the inner cavity of the copper tube is consistent with the cooling shrinkage of the slab throughout the length of the crystallizer, the inner cavity of the crystallizer copper tube should be a parabolic continuous taper. When casting low carbon steel and low alloy steel, the apex of the parabola should be designed at the lower end of the copper tube. At the same time, the taper distribution of the high-efficiency crystallizer should also match the other process parameters in the drawn steel.

LMM GROUP 

What is adamite roll？

 

Adamite rolls are a type of rolling mill roll made from a material that combines the properties of both steel and cast iron. They are known for their excellent wear resistance, toughness, and ability to withstand high temperatures, making them suitable for various rolling mill applications. Here are the key aspects of adamite rolls:

Adamite roll Composition and Properties

Material Composition:

Carbon Content: Adamite rolls typically have a carbon content ranging from 1.2% to 2.3%.

Alloying Elements: They contain alloying elements such as chromium, nickel, molybdenum, and vanadium, which enhance their mechanical properties and wear resistance.

Microstructure: The microstructure of adamite rolls consists of a mixture of pearlite and carbide phases, providing a balance between hardness and toughness.

Properties:

Wear Resistance: Adamite rolls have good wear resistance, which helps in reducing roll wear and extending roll life.

Toughness: They exhibit high toughness, making them resistant to mechanical shocks and impacts during the rolling process.

Thermal Stability: Adamite rolls can withstand high temperatures, making them suitable for hot rolling applications.

Hardness: They have a hardness range typically between 40 to 60 HRC (Rockwell Hardness Scale), depending on the specific alloy composition and heat treatment.

Adamite roll Manufacturing Process

Casting: Adamite rolls are produced through a casting process, where molten metal is poured into molds to form the desired shape.

Heat Treatment: After casting, the rolls undergo heat treatment processes such as annealing, quenching, and tempering to achieve the desired mechanical properties.

Machining and Grinding: The rolls are then machined and ground to achieve the required dimensions, surface finish, and profile.

Applications

Adamite rolls are used in various rolling mill applications, including:

Hot Rolling Mills: Suitable for rolling hot metal slabs, billets, and blooms into desired shapes and sizes.

Section Mills: Used in rolling mills that produce structural sections such as beams, channels, and angles.

Bar and Wire Rod Mills: Employed in mills that produce bars and wire rods from billets.

Plate Mills: Used in rolling mills that produce metal plates of various thicknesses.

Roughing Stands: Often used in the roughing stands of rolling mills, where the initial deformation of metal takes place.

Advantages

Durability: The combination of wear resistance and toughness results in long-lasting rolls that require less frequent replacement.

Versatility: Suitable for a wide range of rolling mill applications, including hot and cold rolling.

Cost-Effective: The extended roll life and reduced maintenance requirements contribute to cost savings in rolling mill operations.

Consistent Performance: Adamite rolls provide consistent performance under varying rolling conditions, ensuring high-quality rolled products.

Author: LMM GROUP

Coke Oven Door And Frame

The coke oven doors of coke ovens are generally iron-on-iron self-sealing, that is, knife-edge doors. The tightness of the doors is closely related to preventing smoke and fire, as well as the deformation and failure of the furnace frame and furnace columns. Therefore, the furnace door, which is not usually a furnace protection device, is actually a very important furnace protection device.

 

Analysis of Factors Affecting the Life of Mold Copper Tubes

This article describes the reasons that affect the life of the mold copper tube and the corresponding measures to be taken.

Key words: copper mould tube; service life of copper tube; countermeasures

Main reasons restricting the service life of copper tubes

Copper mould tube vibration table

The billet continuous casting machine adopts the semi-plate spring imitation positive rotation vibration system, but due to the occurrence of steel leakage accidents in actual production, the vibration frame exposed to the lower mouth of the copper mould tube is most likely to be adhered by molten steel or residual steel residues enter the vibration mechanical parts , affect the accuracy of the vibration parameters, and even produce polarization phenomenon, which will cause the leaf spring to break in severe cases, which will bring great hidden dangers to the quality of the billet and the normal use of the copper tube.

When the vibrating leaf spring has a long service life, the leaf spring produces linear plastic extension, and the arc of the copper tube in the copper mould tube does not coincide with the basic arc of the casting machine, resulting in excessive resistance during casting, resulting in transverse cracks, and the service life of the copper tube shorten.

Assembly of tension leveler

Billet continuous casting machine drawing and leveling machine system is mainly composed of a set of drawing and leveling upper and lower rolls, a set of free rolls, a set of stripping upper rolls and lower rolls and frame, base, transmission system, hydraulic cylinder, etc., for Five-roller two-point straightening structure, but due to the relatively weak maintenance force of our factory and limited technical level, it often happens that the dummy bar deviates from the lower mouth of the copper mould tube when feeding the dummy, which cannot ensure the accuracy of arc alignment and artificially increases the billet The resistance increases the wear of the chrome-plated layer of the copper tube.

copper mould tube assembly

The key parameter of mold assembly is the adjustment of the water gap. Whether the water gap is even on both sides directly affects the quality of the billet and the service life of the mould. Quality accidents such as deformation and corner cracks, and single-strand production accidents such as breakouts, severely restrict production and affect the quality of billets and the service life of mold copper tubes.

copper mould tube reverse taper

The size of the taper of the mold must be appropriate. Excessive taper will cause the mold to squeeze the billet shell, resulting in concave corners, increased friction between the billet shell and the copper tube of the mold, and aggravated the wear of the copper tube. For copper, hot spots can form in the corner area due to air gaps, causing shell thinning and cracking. If the taper is small, the air gap will increase, the heat flow will decrease, the billet shell will become thinner, and steel breakout will easily occur. In addition, if the taper is too small, the rotation of the corner will be aggravated, and subcutaneous cracks and longitudinal depressions will appear.

Corresponding measures taken

(1) Strengthen spot checks on the copper mould tube vibration device. Every time the copper mould tube is replaced or overhauled, a special person will check the gap between the leaf spring and the stand to prevent mold slag, cold steel, etc. from entering and causing copper mould tube polarization. In addition, after thecopper mould tube is replaced, the anchor bolts of the copper mould tube are fastened in place.

(2) The workshop and the factory strengthen the training of maintenance-related knowledge and operational ability to ensure that the basic data such as the longitudinal centerline and outer arc reference line of the continuous casting machine are identified during the continuous casting repair and overhaul.

(3)copper mould tube assembly.

a. For the off-line copper mould tube, do a good job of confirming the inner wall of the copper tube, dismantling it, checking the aging of the sealing rubber ring, whether there is any abnormal change in the water joint between the copper tube and the water jacket, and whether there are foreign objects in the copper mould tube, etc., and analyze the specific Make a record of the reason for the offline.

b. The inspection of new copper pipes and water jackets is strictly in accordance with the requirements of the drawings, and all spare parts of the copper mould tube are measured, and they can only be put on the line if they meet the requirements. To ensure the accuracy of spare parts when the copper mould tube is repaired.

c. During the process of dismantling and assembling copper pipes, two key points must be ensured: stability and accuracy. Prevent pits from appearing due to local stress on the copper pipe, and deformation of the water joint adjustment device, which will ultimately affect the assembly accuracy of the copper pipe. It is strictly forbidden to use sharp objects in the installation of the sealing rubber ring to prevent the damage of the rubber ring that is not easy to observe.

d. The adjustment of the water joint is the core content of the repair of the copper mould tube. The upper water joint of the copper pipe should be positioned with the matching copper pipe and water jacket before assembly. The deviation of the upper water joint is not allowed to exceed 0.5mm, and the lower water joint of the copper pipe The seam deviation does not exceed 0.2mm to ensure the water seam accuracy during assembly. Avoid billet defects caused by uneven cooling in copper pipes due to uneven water seams.

e. After the assembled copper mould tube is tested for water and pressure for 30 minutes, it can be put into use without leakage or loss of pressure, and records should be made.

Other measures to increase the steel passing capacity of copper pipes

(1) In the process of dismantling and inspecting the copper mould tube, foreign objects occasionally appear in the water chamber, and protective measures should be implemented in time according to the different foreign objects. Such as the water flushing method of the copper mould tube, the water quality management method of the copper mould tube, and the installation of pipeline filters, etc.

(2) During the maintenance process, focus on the arc calibration accuracy of the casting machine, adjust the guide edge spacing of the secondary cooling guide roller, and take measures such as water bar alignment, which effectively reduces the impact on the life of the copper tube due to eccentric wear.

(3) Adjust the production organization mode, reduce the number of stop flow, stabilize the casting speed, and effectively reduce the impact of start stop flow on the life of the copper tube.

LMM GROUP Online Automatic Steel Bar Counting And Separation System

 

1) The counting accuracy of our rebar counting machine is as high as 0.02%.

2) The system could work 24 hours/day continuously, Increasing productivity.

3) The system could control the number/weight of every bundle, and decrease the production cost.

4) The system’s cost is very low, and the spare parts are also inexpensive.

5) It will achieve Full Automation, and enhance the plant’s image.

6) Fast Installation and easy operation: It only needs 15 days to install and commission and 5 days to teach your worker how to operate.

7) It could install on stop time, not influence the production.

8) The free warranty period of one year, life-long free update system.

LMM GROUP Online Automatic Steel Bar Counting And Separation System