High temperature flexural strength of magnesia carbon brick

There are many factors that affect the high-temperature flexural strength of magnesia carbon brick, the most important of which is the purity of raw material, carbon content, binder, matrix composition and organizational structure of magnesia carbon brick. The purity of raw material is relatively simple, the purity of magnesia is high, the crystal scale is large, the low melting point phase content distributed in the periclase grain boundary is low, the direct bonding degree is high, the high-temperature flexural strength is better; the purity of graphite The research on matrix composition, microstructure and other aspects is relatively complex, and it is also the most concentrated research field to improve the high-temperature flexural strength of magnesia carbon brick, which is roughly divided into the following three directions.

1、Add metal powder

In the aspect of improving the flexural strength at high temperature, the metal powders mainly include A1, Si, etc

① Al4C3 and SiC are formed by the reaction of metal Al and Si with graphite and resin carbon in magnesia carbon brick, strengthening the combination of carbon and carbon, and improving the strength;

② whiskers and fibers are formed in MgO-C brick by metal Al and Si, which strengthen the material matrix;

③ The formation of magnesia alumina spinel and the improvement of ceramic bonding

2、In situ formation of carbide, nitride and other whiskers

The improvement of high temperature flexural strength of MgO-C brick is usually achieved by in-situ formation of carbide and nitride whiskers.

Whiskers are generally one-dimensional crystalline materials of nanometer or submicron scale, with few internal defects, and the strength and modulus are close to the theoretical value of crystal materials. At the same time, the net distribution of whiskers in the brick or the pinning and locking effect in the microstructure of MgO-C brick also endow the material with a better mechanical properties Good strength. For example, yijingguang et al. Found that with the increase of heat treatment temperature, the high-temperature flexural strength and residual flexural strength of MgO-C brick added with metal Si powder and Al powder increased, while the flexural strength of the sample after heat treatment at 1400 ℃ was larger.

Through the analysis of microstructure, it was found that there was not only needle like AlN formation in the brick, but also inlaid on the surface of magnesia particles at 1400 ℃, At the same time, there are a large number of SiC whiskers and acicular β – Sin whiskers. In such a microstructure, when the material is subjected to external force, the stress can be transferred from the matrix to the whisker through the interface layer, and the whisker disperses the stress on the matrix and reduces the damage effect.

When the crack size of the sample under the action of thermal stress is small, the whisker plays a bridging role, When the crack increases, the whisker at the crack tip will be further destroyed, and the whisker will be pulled out of the matrix to consume energy. At this time, the pull-out effect will give the magnesia carbon brick high temperature mechanical properties

3、Generation or addition of nano carbon in magnesia carbon brick

Carbon nanotubes are new materials which appear in recent years, and their mechanical properties are very outstanding. Therefore, in the aspect of improving the high-temperature flexural strength and microstructure of MgO-C brick, some scholars have formed carbon nanotubes in the material by introducing catalysts and other ways, and achieved good results.

For example, we ì and other scholars modified phenolic resin and prepared low-carbon MgO-C brick by introducing Fe nano sheets. It is found that doping 0 A large number of carbon nanotubes with a diameter of 50-100nm and a length of micrometer are produced by the MgO-C brick with a mass fraction of. 5%. Compared with the sample without doping Fe nano sheet, the high-temperature flexural strength increases from 8.29mpa to 10.29mpa with a amplitude of about 24%, reaching the highest value. The presence of a large number of carbon nanotubes firmly locks the MgO particles.

When the stress is applied to the blank sample, the For the 0.5% doped sample, when the crack passes through the MgO particles, the carbon nanotubes can absorb and release the stress at the crack tip through the bridging and crack deflection mechanism due to its high strength and toughness.

In addition to the formation of carbon nanotubes in MgO-C brick, nano carbon is also introduced to improve the microstructure of MgO-C brick and improve the high-temperature flexural strength of materials. For example, on the basis of 3% mass fraction of graphite, by introducing different proportions of nano carbon and graphite, the high-temperature flexural strength (hMOR) increases with the increase of nano carbon content, and its value increases from 2.5MPa When it reaches 4.5MPa (0.9% mass fraction) and keeps constant when the nano carbon is further increased, as shown in Figure 21. Further analysis shows that with the increase of the content of nano carbon, the filling and compaction effect is better. At the same time, the nano carbon has very high reactivity and can form carbides at a higher rate when contacting with the gold additive, with stronger binding force and higher strength.

LMM GROUP

The influence of mill rolls on product quality in the production of plate steel and strip steel

In the rolling process, the quality of the rolls is very important. Often due to the poor quality of the roll itself or improper operation, many rolling accidents occur, which bring losses to the steel mill. The following is a detailed analysis of the phenomena and causes of several rolling accidents that may occur.

What is the cause of mill rolls sticking?

The sticking mill roll is caused by excessive local pressure, broken strip fragments and folded strip steel entering the rolling mill. Generally, the slightly sticky mill roll can continue to be used after manual grinding with grindstone. When the strip surface require is high, the mill roll must be changed.

What are the material requirements for the cold mill rolls?

During the cold rolling process, the surface of the roll bears great squeezing and intense wear. Steel jamming and over-burning during high-speed rolling will cause cracks on the roll surface. Therefore, cold-rolling work rolls should have extremely high and uniform hardness, a certain depth of hardened layer, and good wear resistance and crack resistance. The roll has good resistance to over burning and crack resistance is the main factor to extend the life of the roll.

What are the effects of insufficient mill rolls hardness on the rolling process?

The roll hardness is not enough, the elastic flattening is large during rolling, and the contact area between the roll and the strip surface is increased. To obtain the same thickness of the product, the rolling pressure must be increased, but the large rolling pressure is not good for the adjustment of the plate shape. The roughness of the roll is large, and the friction coefficient between the roll and the strip steel surface increases during rolling, which causes the friction force and the rolling pressure to increase.

How to use bending rolls to eliminate “both sides waves” and “middle waves”?

When waves appear on both sides of the strip during rolling, it means that the rolling pressure on both sides of the strip is too large. At this time, positive bending rolls are used to eliminate the waves on both sides. When there is an middle waves, it means that the original crown or thermal crown of the roll is too large. At this time, use a negative bending roll to eliminate.

How to prevent the skewing when the strip passes through the gap of the roll

First of all, before the strip passes through the gap of the roll, it must be minimize the clearance between upper and lower rollers, given a standard roll gap, it looks like the quality of the material, whether there are edge waves, and observe the strip running condition. In the rolling process, the deviation of the strip generally occurs during the strip passes through the gap of the roll or tail flicking. The main reasons for the skewing of the strip are as follows:

1）Due to the shape of the incoming material is not good, and there are serious edge waves, so that the strip edge control device cannot be accurately and timely adjusted effectively, causing the strip to deviate in the first pass. The measure to be taken is that control the rolling speed don’t be too high! Control the clearance between upper and lower roller, swing adjustment in time or stop in time.

2) Operational reasons: The unreasonable adjustment of the swing due to the the clearance between upper and lower roller causes the strip to run out of direction.

3) For electrical reasons, the coiler tension suddenly decreases or disappears during the rolling process, causing the strip to run off and break.

4) Due to the serious taper of the roll after the roll is ground, the clearance between upper and lower roller is inaccurate. During the rolling, the reduction and swing of the operation increase the difficulty. The lighter one will produce serious side waves and cause the plate shape defect, and the heavy one will cause deviation and broken strip.

5) The strip edge control device failure, the deviation device, the lamp tube or the pollution of the receiving device, etc., make the deviation device failure and cause the first deviation.

What quality defects can occur in rolls grinding? What are the undesirable consequences in the rolling process?

1) The roll body has a taper: the reduction cannot be corrected, and it is easy to cause a side wave, and the plate shape is difficult to control. The roll body taper is required to be less than 0.1mm.

2) Grinding is not round: the roll body has ellipticity. Vibration occurs during the rolling process, the rolling pressure fluctuates, and the strip thickness varies along the length direction.

3) Crown: The roll is required to be a flat roll in the process of the unit. If the roll has a crown,In the rolling process, it is easy to produce the middle wave and the second rib wave of the strip steel.

4) The surface roughness of the roll is too large. During the rolling process, the rolling pressure increases, the strip shape is difficult to control, and the surface quality of the strip is affected.

5) The roll body cracks, because the cracks have not been ditched and ground. The rolls were not inspected for flaw detection, and protruding rolling marks with crack shapes were generated on the surface of the strip during the rolling process.

LMM GROUP

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.