Solution to Environmental Protection Problems of Intermediate Frequency Furnace

1. Dust removal of intermediate frequency electric furnace

Since the charge of induction heating furnace usually contains dust and oil, soot will rise from the furnace mouth when the charge is added to the furnace. If the charge contains zinc-plated materials and waste materials, the dust produced will also contain zinc or tin oxides. The smoke and dust generated in the operation of the intermediate frequency heating furnace is harmful to the human body and the production environment, so a dust removal system must be used to discharge the harmful smoke and dust outdoors. The amount of soot produced is related to the size of the intermediate frequency equipment and the cleanliness of the charge. The air volume of the dust removal system should be large enough to generate a large amount of negative pressure at the furnace mouth.

The dust removal system consists of an induced draft fan, a dust collector, a cyclone separator, a flue gas temperature adjustment device, and pipelines. In order to ensure that the temperature of the flue gas entering the precipitator does not exceed the value that the precipitator can withstand, the flue gas temperature adjustment device can adjust the amount of cold air mixed to control the temperature of the flue gas entering the precipitator. The flue gas of the intermediate frequency furnace through the dust removal system should meet the national standard GB9078-1996 "Industrial Kiln Air Pollutant Emission Standard". In order to capture the smoke and dust, the intermediate frequency electric furnace is generally equipped with a furnace mouth dust removal ring or a full cover type dust removal furnace cover. The dust removal ring at the furnace mouth is not as good as the full cover dust removal furnace cover, but it is suitable for electromagnetic chuck or manual feeding, so it is more used on furnaces less than 5t. The full hood dust removal furnace cover has a better ability to capture smoke and dust, and needs to be used in conjunction with a charging car, usually used for furnaces with larger specifications.

For the dust removal of the intermediate frequency electric furnace, it is very important to select a dust removal system with good performance. However, the maintenance of the dust removal system is also very important. The dust collector and pipes should be cleaned regularly to maintain the system with a good dust removal effect.

2. Noise of intermediate frequency furnace

During the operation of the intermediate frequency electric furnace, noise is mainly generated from the intermediate frequency power supply, furnace body and hydraulic pump. Secondly, the noise level generated by transformers and water pumps is relatively small. Generally, it is required that the noise at the furnace working platform 1m away from the furnace body and the height of 1m should be ≤85dB (excluding background noise).

At present, most of the equipment layout of intermediate frequency electric furnaces place the intermediate frequency power supply, furnace body, hydraulic pump station and water pump station under the working platform (in a semi-underground pit), which is helpful to reduce the noise at the operating station on the working platform. Improving the operating environment of workers plays a big role.

When the furnace with high power density is in operation, the noise is relatively large due to the vibration of the induction coil, yoke and other components. If necessary, the furnace body structure can take some measures to reduce noise, such as lining the inner wall of the furnace shell with sound insulation material, repair hole cover plate with rubber pad, and filling in the cavity of the furnace body structure. The hydraulic pump is noisy when it is working, so it should be shut down in time when it is not in use. For this reason, there is a stop button on the hydraulic operation console, so that the operator can stop the hydraulic pump in time, or configure a timer to shut down the hydraulic pump on time.



3. Harmonic problem of intermediate frequency furnace

Solid-state intermediate frequency power supplies use electronic devices such as thyristors, diodes, and IGBTs for rectification and inversion, which will cause harmonic interference to the power supply grid. With the widespread application of electronic devices such as electronic computers and numerical control machine tools, the requirements for power quality of the power grid are getting higher and higher. In modern industrial production, the use of various converter equipment is increasing, and the capacity is also increasing. The harmonics generated by it are injected into the power grid, distorting the voltage waveform of the public power grid, affecting the quality of power, and threatening the safe and economic operation of various electrical equipment. To this end, the country formulated the national standard GB/T14549-1993 "power quality, harmonics of the public grid". This standard specifies the allowable value of harmonics injected into the grid.

The harmonic interference produced by the solid-state intermediate frequency power supply mainly depends on the form of its rectifier circuit.

The rectification of the voltage feedback series resonant intermediate frequency power supply adopts a bridge-type uncontrollable rectifier circuit, which generates fewer harmonics than the current feedback parallel resonant intermediate frequency power supply.

In addition, the use of multi-phase rectification methods, such as 6-phase 12-pulse rectification, 12-phase 24-pulse rectification, and the rectifier transformer windings are equalized, can greatly reduce the harmonic interference of the intermediate frequency electric furnace.

4. Magnetic field of intermediate frequency electric furnace

Alternating current passing through the coil of the induction heating furnace will generate an alternating magnetic field. The strength of the magnetic field depends on the power of the electric furnace. At present, the working frequency of the intermediate frequency electric furnace is 100-3000 Hz. This frequency is not a radio wave transmission frequency, and generally does not cause interference to radio communications. However, if technical measures are not taken to limit the alternating magnetic field generated by the induction coil, the alternating magnetic field will heat the metal parts near the furnace, causing harm to workers operating on the furnace (especially for metal dentures). , Metal artificial joints, etc.), so the intermediate frequency electric furnace needs to use a yoke to restrict the magnetic field from radiating outward. Modern coreless induction furnaces are surrounded by multiple yokes around the induction coil. The length enclosed by the yoke in the circumferential direction of the coil reaches 60% to 65% of the circumference of the coil.

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Factors Affecting Energy Consumption of Intermediate Frequency Furnace

The intermediate frequency furnace has the advantages of high electrical and thermal efficiency, short melting time, power saving, less floor space, lower investment, easy process automation, and production flexibility. Compared with other melting furnaces, such as industrial frequency furnaces, intermediate frequency furnace has lower energy consumption and higher production efficiency. However, the low energy consumption is relative to other equipment. For enterprise production, it is of course to achieve the maximum benefit as the goal and minimize energy consumption. Therefore, it is necessary to increase the production base and reduce the total energy consumption.

To reduce the energy consumption of the intermediate frequency furnace, it is necessary to understand the factors that affect the energy consumption of the intermediate frequency furnace. The main factors affecting the energy consumption of the intermediate frequency furnace are as follows:

1. Power

The power density configuration of the induction furnace. High configuration, fast melting speed and good energy-saving effect. Whether the electric furnace can maintain high power and continuously send power to the furnace will affect the level of energy consumption; the messy arrangement of the power cord of the intermediate frequency furnace will affect the processing capacity of the power supply, resulting in unstable power, low power conversion efficiency, and energy consumption.

2. Melt

The cleanliness of the surface of the charge, if there are 5% impurities, it will consume 5% of the electrical energy to melt these impurities, which will also affect the life of the furnace lining; whether the length of the charge block is appropriate will affect the electric efficiency and melting quality of the electric furnace, generally 200～ 300mm block size is appropriate.

3. Refractory materials

Using a suitable crucible can increase the melting rate. Quartz crucibles are resistant to high temperatures, and when used with intermediate frequency furnaces, the metal materials in the crucible can generate heat by induction heating, which can reduce the consumption of heat transfer.

4. The improper operation causes high energy consumption

The molten metal is overheated, and the furnace is discharged continuously. Not only is it unsafe, but it is also wrong in terms of energy consumption and the melting process. Generally, electric furnace sensors are divided into upper and lower parts. When the molten metal level in the furnace is lower than half of the upper sensor, due to the change of resistance, the upper sensor no longer has induced current to pass, and all are concentrated in the lower sensor, making the lower molten metal overheating, scouring the furnace wall, the life of the furnace lining drops sharply.

Understanding these four major factors that affect the energy consumption of intermediate frequency furnaces and improving them in production can avoid unnecessary consumption, reduce production costs, and improve production efficiency.

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Intermediate Frequency Furnace VS Electric Arc Furnace?

Intermediate frequency furnace 
Intermediate frequency furnace is a power supply device that converts 50HZ power frequency alternating current into intermediate frequency (above 300HZ to 20K HZ). It converts three-phase power frequency alternating current into direct current after rectification, and then converts the direct current into adjustable intermediate frequency current. The medium frequency alternating current flowing in the capacitor and the induction coil generates high-density magnetic lines of force in the induction coil, and cuts the metal material contained in the induction coil, which generates a large eddy current in the metal material.

This kind of eddy current also has some properties of intermediate frequency current, that is, the free electrons of the metal itself flow in the resistive metal body to generate heat. For example, if a metal cylinder is placed in an induction coil with alternating intermediate frequency current, the metal cylinder is not in direct contact with the induction coil, and the temperature of the electrified coil itself is already very low, but the surface of the cylinder is heated to redness or even melting , and this redness and melting speed can be achieved only by adjusting the frequency and the strength of the current. If the cylinder is placed in the center of the coil, then the temperature around the cylinder is the same, and the heating and melting of the cylinder will not produce harmful gas or bright light to pollute the environment.

Smelting furnace characteristics of intermediate frequency furnace series:

(1) High melting efficiency, good power saving effect, compact structure, strong overload capacity

(2) The temperature around the furnace is low, there is less smoke and dust, and the working environment is good.

(3) The operation process is simple and the melting operation is reliable.

(4) The metal composition is uniform.

(5) The melting temperature is fast, the furnace temperature is easy to control, and the production efficiency is high.

(6) The furnace utilization rate is high and it is convenient to change the varieties.

(7) The long arc-shaped yoke shields the magnetic flux leakage and reduces the external magnetic resistance. There is magnetic leakage at both ends of the shielded coil. The inner side of the yoke section is arc-shaped and seamlessly adheres to the outer wall, which increases the effective magnetic permeability area and makes the lower ring Get better support. The unique positive and negative coils greatly improve the efficiency of the system.

Intermediate frequency furnace series diathermic furnace features:

●Fast heating speed, high production efficiency, less oxidation decarbonization, saving materials and forging die costs

●Excellent working environment, improving workers' working environment and company image, no pollution, low energy consumption

●The heating is uniform, the temperature difference between the core and the surface is very small, and the temperature control accuracy is high

Intermediate frequency furnace heating device has the advantages of small size, light weight, high efficiency, excellent thermal processing quality. It is rapidly eliminating coal-fired furnaces, gas furnaces, oil-fired furnaces and ordinary resistance furnaces. It is a new generation of metal heating equipment.

The intermediate frequency furnace is the main equipment of the foundry, forging and heat treatment workshop. The stability, reliability and safety of its work are the guarantee for the normal and stable operation of the casting, forging and heat treatment production line of the flow operation.

Electric arc furnace

An electric furnace for smelting ores and metals using the high temperature generated by the electrode arc. The energy is concentrated when gas discharge forms an arc, and the temperature of the arc zone is above 3000 ℃. For smelting metals, electric arc furnaces are more flexible than other steelmaking furnaces, can effectively remove impurities such as sulfur and phosphorus, furnace temperature is easy to control, and the equipment occupies a small area, which is suitable for smelting high-quality alloy steel. Electric arc furnaces can be divided into three-phase electric arc furnaces, consumable electric arc furnaces, single-phase electric arc furnaces and resistance electric arc furnaces according to the arc form. The furnace body of the electric arc steelmaking furnace is composed of a furnace cover, a furnace door, a tapping trough and a furnace body, and the furnace bottom and furnace walls are built with alkaline refractory materials or acid refractory materials.

Electric arc steelmaking furnaces are divided into ordinary power electric arc furnaces, high power electric arc furnaces and ultra-high power electric arc furnaces according to the transformer capacity per ton of furnace capacity. Electric arc furnace steelmaking is to input electric energy into the electric arc steelmaking furnace through graphite electrodes, and the electric arc generated between the electrode end and the charge is used as the heat source for steelmaking. The electric arc furnace uses electric energy as the heat source, and the atmosphere in the furnace can be adjusted, which is extremely beneficial to the smelting of steels that contain more oxidizable elements. Soon after the invention of electric arc furnace steelmaking, it was used to smelt alloy steel and has been greatly developed.

With the improvement of electric arc furnace equipment and the improvement of smelting technology, the development of electric power industry, the cost of electric arc furnace steelmaking continues to decline. Now electric arc furnace steelmaking is not only used for the production of alloy steel, but also for the production of ordinary carbon steel. The proportion of output in the total steel output of major industrial countries continues to rise.

The cost of electric arc furnace is very expensive, but the product quality is good, the public frequency furnace consumes the most electricity, the intermediate frequency furnace is 800-900 degrees/ton below 2000KW, and the large furnace is 600-700 degrees/ton. These are just normal conditions, plus human factors ( operation proficiency, equipment maintenance level), equipment aging, various compensation, harmonic control, and other factors will affect power consumption.

Compared with electric arc furnace, the cost of intermediate frequency furnace steelmaking is lower, and it is suitable for small and medium-sized enterprises (small workshops). However, the steel produced by it has many impurities and high carbon content, so the steel produced is not pure, and those with low requirements can choose The steel produced by the intermediate frequency furnace is usually more than 3 tons in volume. Therefore, the electric arc furnace is only used by enterprises with a certain scale, and the steel produced by it is relatively pure.

The electric arc furnace uses power frequency electricity, while the intermediate frequency electric furnace uses intermediate frequency electricity.


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Electric Arc Furnace Steelmaking Process

1. Feeding

The operation of adding molten iron or scrap steel to the electric furnace is the first step of the electric furnace steelmaking operation.

2. Slagging

The operation of adjusting the slag composition, alkalinity, viscosity and reaction ability in steel and iron production. For example, the oxygen blowing operation is to generate slag with sufficient fluidity and alkalinity, which can transfer enough oxygen to the metal surface, so as to reduce the sulfur and phosphorus below the upper limit of the planned steel grade, and the amount of splashing and slag spilling during oxygen blowing should be minimized.

3. Slag discharge

It refers to the slagging operation taken during the smelting process in the electric arc furnace steelmaking according to different smelting conditions and purposes. For example, when single slag method is used for smelting, oxidation slag must be removed at the end of oxidation; when double slag method is used to make reduction slag, the original oxidation slag must be completely released to prevent phosphorus from returning.

4. Molten pool mixing

Supply energy to the molten metal pool to make the molten metal and slag move to improve the kinetic conditions of the metallurgical reaction. The stirring of the molten pool can be achieved by means of gas, mechanical, electromagnetic induction and other methods.

5. Dephosphorization

It’s the chemical reaction to reduce the phosphorus content in molten steel. Phosphorus is one of the harmful impurities in steel. Steel with too much phosphorus, when used at room temperature or lower, is prone to brittleness, which is called "cold brittleness". The higher the carbon content in steel, the more serious the embrittlement caused by phosphorus. Generally, it is stipulated that the phosphorus content of ordinary steel does not exceed 0.045%, and high-quality steel requires less phosphorus.

6. Electric furnace bottom blowing electric furnace bottom blowing

Blow N2, Ar, CO2, CO, CH4, O2 and other gases into the molten pool in the furnace through the nozzle placed at the bottom of the furnace to accelerate the melting and promote the metallurgical reaction process. The use of bottom blowing technology can shorten smelting time, reduce power consumption, improve dephosphorization and desulfurization operations, increase the amount of residual manganese in steel, and increase the yield of metals and alloys. And can make the molten steel composition and temperature more uniform, thereby improving steel quality, reducing costs, and increasing productivity.

7. Melting period

The melting period of steelmaking is mainly for open hearth and electric furnace steelmaking. The melting period of electric arc furnace steelmaking starts from the time of electrifying to the time when all the accompanying materials are melted, and for open hearth steelmaking, it is called melting period from the end of hot metal mixing to the end of furnace burden melting. The task of the melting period is to melt and heat up the charge as soon as possible, and make the slag in the melting period.

8. Oxidation period and decarbonization period

The oxidation period of ordinary power electric arc furnace steelmaking usually refers to the process stage from dissolution of the charge, sampling and analysis to the completion of the oxidation slag. Some think it started from blowing oxygen or adding ore to decarbonize. The main task of the oxidation period is to oxidize the carbon and phosphorus in the molten steel; remove the gas and inclusions; make the molten steel uniformly heated. Decarburization is an important process in the oxidation period. In order to ensure the purity of steel, the amount of decarburization is required to be greater than about 0.2%. With the development of refining technology outside the furnace, most of the oxidation refining of the electric arc furnace is moved to the ladle or refining furnace.

9. Refining period

The steelmaking process uses slagging and other methods to select some elements and compounds that are harmful to the quality of steel into the gas phase or discharge or float into the slag through chemical reactions, so that they are excluded from the molten steel. The continuous casting machine discharges the billet.

10. Restoration period

In ordinary power electric arc furnace steelmaking operations, the period from the completion of slagging at the end of oxidation to tapping is usually called the reduction period. Its main task is to create reduced slag for diffusion, deoxidation, desulfurization, control of chemical composition and temperature adjustment. High-power and ultra-power electric arc furnace steelmaking operations have canceled the reduction period.

11. Refining outside the furnace

The steelmaking process in which the molten steel initially made in a steelmaking furnace (converter, electric furnace, etc.) is transferred to another vessel for refining is also called secondary metallurgy. Therefore, the steelmaking process is divided into two steps: primary smelting and refining. Primary refining: The charge is melted, dephosphorized, decarburized and main alloyed in a furnace with an oxidizing atmosphere. Refining: Degas, deoxidize, desulfurize, remove inclusions and fine-tune the composition in a container of vacuum, inert gas or reducing atmosphere. The advantages of dividing steelmaking into two steps are: it can improve the quality of steel, the steelmaking workshop can shorten the smelting time, simplify the process and reduce the production cost. There are many types of out-of-furnace refining, which can be roughly divided into two types: out-of-furnace refining under atmospheric pressure and out-of-furnace refining under vacuum. According to different treatment methods, it can be divided into ladle processing type furnace refining and ladle refining type furnace refining.

12. Molten steel stirring

The stirring of molten steel during the refining process outside the furnace. It homogenizes the composition and temperature of molten steel and can promote metallurgical reactions. Most metallurgical reaction processes are phase interface reactions, and the diffusion rate of reactants and products is the limiting link of these reactions. When molten steel is in a static state, its metallurgical reaction speed is very slow. For example, it takes 30 to 60 minutes to desulfurize molten steel in an electric furnace; while it takes only 3 to 5 minutes to stir the molten steel in furnace refining. When molten steel is in a static state, the inclusions are removed by floating upwards, and the removal speed is slow; when the molten steel is stirred, the removal speed of the inclusions increases exponentially and is related to the stirring strength, type, and characteristics and concentration of the inclusions.

13. Feeding wire in ladle

Feed the steel ladle with deoxidation, desulfurization and fine-tuning powders, such as Ca-Si powder, or directly fed into aluminum wire, carbon wire, etc., to deep desulfurize, calcium and fine-tune the molten steel into the steel ladle The method of carbon and aluminum components. It also has the function of cleaning molten steel and improving the shape of non-metallic inclusions.



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How to Choose Cardan Shaft?

The choice of coupling mainly considers the speed of the required transmission shaft, the size of the load, the installation accuracy of the two connected parts, the stability of rotation, the price, etc. We should refer to the characteristics of various couplings, and choose a suitable coupling joint. The following points can be considered when making specific choices:

1. Due to manufacturing, installation, load deformation and temperature changes, it is difficult to maintain strict and precise alignment of the two shafts after installation and adjustment. There is a certain degree of displacement in the X and Y directions and the deflection angle CI. When the radial displacement is large, you can choose a slider coupling, and when the angular displacement is large or the connection of two intersecting shafts, you can choose a universal shaft. When the two shafts produce a large additional relative displacement during the working process, a flexible coupling should be used.

2. The working speed of the coupling and the centrifugal force caused by it. For high-speed transmission shafts, couplings with high balance accuracy, such as diaphragm couplings, should be used, rather than eccentric slider couplings.

3. The size and nature of the torque to be transmitted and the requirements for the function of damping vibration. For example, gear couplings can be used for high-power and heavy-duty transmission. For severe impact loads or transmissions that require the elimination of shaft torsional vibration, tire couplings can be used. Most couplings have been standardized or standardized. The designer's task is to choose, not design. The basic steps for selecting a coupling are as follows:

According to the size of the transmission load, the shaft speed, the installation accuracy of the two parts connected, and referring to the characteristics of various types of couplings, a common type of coupling is selected. The following points can be considered in the specific selection:

1) The size and nature of the torque to be transmitted and the requirements for the buffer and vibration reduction function. For example, for high-power and heavy-duty transmissions, gear couplings can be selected; for transmissions that require severe impact loads or to eliminate shaft torsional vibration, tire couplings and other couplings with high elasticity can be selected.

2) The working speed of the universal joint shaft and the centrifugal force caused by it. For high-speed transmission shafts, couplings with high balance accuracy, such as diaphragm couplings, should be used, rather than eccentric slider couplings.

3) The magnitude and direction of the relative displacement of the two axes. When it is difficult to maintain strict and precise alignment of the two shafts after installation and adjustment, or when the two shafts will have a large additional relative displacement during the working process, a flexible coupling should be used. For example, when the radial displacement is large, you can choose a slider coupling, and when the angular displacement is large or the connection of two intersecting shafts, you can choose a Cardan shaft.

4) The reliability and working environment of the universal joint shaft. Generally, couplings made of metal elements that do not require lubrication are more reliable; couplings that require lubrication are easily affected by the perfect degree of lubrication and may pollute the environment. Couplings containing non-metallic components such as rubber are sensitive to temperature, corrosive media and strong light, and are prone to aging.

5) Manufacturing, installation, maintenance and cost of couplings. Under the premise of meeting the convenience of use, couplings with convenient assembly and disassembly, simple maintenance and low cost should be selected. For example, rigid couplings are not only simple in structure, but also easy to assemble and disassemble, and can be used for low-speed, rigid drive shafts. General non-metallic elastic element couplings (such as elastic sleeve pin couplings, elastic pin couplings, plum-shaped elastic couplings, etc.), due to their good comprehensive capabilities, are widely used in general medium and small power transmission.

If you are interested in our Cardan shaft, please contact me.
Email: marketing2@hanrm.com; Whatsapp / Wechat: +8618392033938.

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Requirements for Roll Performance of Bar Rolling Mill

With the progress of steel rolling technology and the improvement of equipment level, the bar production line has gradually moved towards continuous, automatic and efficient production, and the requirements for wear resistance and thermal stability of rolls are also higher and higher.

All kinds of ductile iron rolls used in the past can not meet the higher requirements, especially the production line based on hot-rolled ribbed steel bars. In addition to the special requirements for the hardness and toughness of the roller for the finished stand, the slitting rolling technology is mostly adopted for the small-sized varieties, and the requirements of the pre-slitting and cutting passes on the rolls are sometimes even more stringent than the requirements for the finished rolls of the ribbed bars.

At present, the traditional cast iron roll is still widely used in most bar production lines. Centrifugal casting high Ni Cr acicular bainite ductile iron roll is generally used in the finishing mill. The single-groove steel passing capacity of the finished roll is only 50 ~ 400t / groove according to the rolling specifications and process conditions.

This means that a bar production line with a single shift (8h) output of about 1000t has to replace the rolling groove 3-5 times per shift, resulting in a long cumulative time for roll changing and groove changing, frequent adjustment of rolling mill and frequent production accidents. As a result, the operation rate of the whole production line is reduced, the technical and economic indicators such as yield are poor, the product size fluctuates greatly and the comprehensive production cost is increased.

Therefore, the development and application of high wear-resistant and long-life rolls is an important means to improve the production efficiency of the bar production line. At present, this kind of roll mainly includes centrifugal casting high-speed steel composite roll, forging high-speed steel roll ring combined roll and tungsten carbide roll ring combined roll.

The main performance indexes of the roller are core strength and wear resistance of the working layer. In addition to considering the economy and the matching of roll changing and groove changing period with shutdown time, it is more important to reasonably select rolls with different performance characteristics from the pass difference of each set of stands, the deformation characteristics of rolled pieces and the requirements of product accuracy.

The main task of the roughing stand of the bar mill is to reduce the cross-section at high temperature, which has a high rolling force and low rolling speed. Generally, the roll performance should be considered from the two aspects of ensuring the roll strength and hot cracking resistance. For general steel grades and normal rolling temperature, centrifugal casting ordinary ductile iron roll can be selected.

The medium rolling mill of bar rolling mill generally adopts an ellipse round pass system, which mainly undertakes the task of extending the rolled piece and providing an accurate profile for the finishing mill. The rolling force is moderate and the pass wear is uniform. Therefore, centrifugal casting ordinary ductile iron roll or medium nickel-chromium alloy ductile iron roll is generally selected. In order to ensure the stability of the size of the exported rolling pieces of the unit, the export stand can also choose high nickel-chromium alloy ductile iron rolls or high-speed steel composite rolls.

There are many varieties of bar finishing mill, complex pass shape, uneven distribution of deformation, high rolling speed and large variation of rolling force. Therefore, the performance requirements of the roller mainly wear resistance and toughness, and both hot cracking resistance and strength are taken into account.

For the extended pass of the simple section, high nickel-chromium alloy ductile iron rolls are generally used, and high-speed steel composite rolls can also be used. For the finished front hole of round steel or ribbed steel bar, it is recommended to select high-speed steel composite roller or tungsten carbide composite roller with higher wear resistance.

As the finished hole of round steel is very small, the tungsten carbide composite roller with the best wear resistance and the high-speed steel composite roll with higher surface hardness should be selected. The finished hole of the ribbed steel bar is affected by the transverse ribs, and it is very easy to produce thermal cracks or micro-cracks during use.

In general, all transverse ribs must be turned off, and the amount of heavy vehicles is large. Therefore, the economy of the expensive tungsten carbide combined roll will be greatly affected. It is better to select a high-speed steel composite roll. Due to the serious non-uniform deformation in use, the high-speed steel composite roller with good toughness and wear resistance and moderate hardness or the tungsten carbide composite roll with good toughness and wear resistance should be selected.

Due to the existence of slitting wedge, not only good wear resistance and toughness, but also reliable hot cracking resistance are required. It has been proved that the present high-speed steel composite roll and tungsten carbide composite roll do not have this characteristic, and the phenomenon of splitting wedge spalling easily occurs in use. Therefore, only high nickel-chromium alloy ductile cast iron rollers can be used.

If you are looking for rolls of rolling mills, please contact me.
Email: marketing2@hanrm.com; Whatsapp / Wechat: +8618392033938

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Roller FAQs

What Is the Difference between Submerged Arc Furnace and Electric Arc Furnace?

Electric arc furnace is a kind of power-frequency electric furnace that uses electric arc energy to smelt metal. Electric arc furnaces used in industry can be divided into three categories: the first type is a direct heating type. The arc occurs between the special electrode rod and the smelted charge, and the charge is directly exposed to the arc heat. It was mainly used for steelmaking, and secondarily used for smelting iron, copper, refractory materials, refined molten steel, etc.

The second type is indirect heating. The arc occurs between two special electrode rods. The charge is only radiated by the arc and is used for smelting copper and copper alloys.

The third type is called submerged arc furnace, which uses ore with high resistivity as raw material, and the lower part of the electrode is generally buried in the charge during operation. The heating principle is that not only the heat flux generated by the resistance of the charge when the current passes through the charge, but also the heat generated by the arc between the electrode and the charge is used. Submerged arc furnace is a kind of electric arc furnace.

Ⅰ. properties:

1. Electric arc furnace: an electric furnace that uses the high temperature generated by the electrode arc to smelt ores and metals.

Industrial furnaces in which electric arc furnaces generate electric arc heating by metal electrodes or non-metal electrodes are called electric arc furnaces. Electric arc furnaces can be divided into three-phase electric arc furnaces, consumable electric arc furnaces, single-phase electric arc furnaces and resistance electric arc furnaces according to the arc form. The furnace body of the electric arc steelmaking furnace is composed of a furnace cover, a furnace door, a tapping trough and a furnace body, and the furnace bottom and furnace walls are built with alkaline refractory materials or acid refractory materials.

Electric arc steelmaking furnaces are divided into ordinary power electric arc furnaces, high power electric arc furnaces and ultra-high power electric arc furnaces according to the transformer capacity per ton of furnace capacity. Electric arc furnace steelmaking is to input electric energy into the electric arc steelmaking furnace through graphite electrodes, and use the arc generated between the electrode end and the charge as the heat source for steelmaking. The electric arc furnace uses electric energy as the heat source, and the atmosphere in the furnace can be adjusted, which is extremely beneficial to the smelting of steels that contain more oxidizable elements. After the invention of electric arc furnace steelmaking, it was used to smelt alloy steel and has been greatly developed.

With the improvement of electric arc furnace equipment and the improvement of smelting technology, the development of electric power industry, the cost of electric arc furnace steelmaking continues to decline. Now electric arc furnace steelmaking is used not only to produce alloy steel, but also to produce ordinary carbon steel. The proportion of output in the total steel output of major industrial countries continues to rise.

2. Submerged arc furnace: also known as electric arc furnace or resistance electric furnace. It is an industrial electric furnace with huge power consumption.

According to the structural and working characteristics of the submerged arc furnace, 70% of the system reactance of the submerged arc furnace is generated by the short network system, and the short network is a high-current working system, the maximum current can reach tens of thousands of amperes, so the short network The performance of the submerged arc furnace determines the performance of the submerged arc furnace. For this reason, the natural power factor of the submerged arc furnace is difficult to reach above 0.85. The natural power factor of most furnaces is between 0.7 and 0.8, which is relatively low. The power factor not only reduces the efficiency of the transformer, but also consumes a lot of useless work, and is charged with additional power fines by the power department. At the same time, due to the manual control of the electrodes and the stacking process, the power imbalance between the three phases increases, and the highest imbalance is The power can reach more than 20%, which leads to low smelting efficiency and higher electricity bills.

Therefore, increasing the power factor of the short network and reducing the imbalance of the grid has become an effective means to reduce energy consumption and improve smelting efficiency. If appropriate measures are taken to improve the short-network power factor, the power consumption can be reduced by 5-20%, and the output can be increased by 5%-10%.

This will bring good economic benefits to the enterprise, and the investment in transformation costs will be recovered in the short-term and in the short term.

In general, in order to solve the problem of low natural power factor of submerged arc furnaces, China mostly adopts the method of reactive power compensation on the high-voltage side to solve the problem. High-voltage compensation only improves the power factor of the high-voltage side, but due to the short-circuit system of the low-voltage side, the reactive power generated by the huge inductive reactance still flows in the short network system, and the three-phase imbalance is due to the strong phase of the short network (the short network is shorter, so the inductive reactance is smaller, so the loss is smaller, and the output is larger. Namely strong phase) and weak phase.

Therefore, high-voltage compensation cannot solve the problem of three-phase balance, nor can it offset the reactive power of the short-circuit system and improve the power factor of the low-voltage end. Because the inductive reactance of the short-network accounts for the inductive reactance of the entire system. Therefore, it cannot reduce the loss of the low-voltage side and increase the output of the transformer, but it can avoid fines, which is only meaningful for the power supply department.

Compared with high-voltage compensation, the advantages of low-voltage compensation are mainly reflected in the following aspects in addition to improving the power factor:

1) Improve the utilization of transformers and high-current lines, and increase the effective input power of smelting.

For arc smelting, the generation of reactive power is mainly caused by the arc current. Move the compensation point forward to the short network to compensate the large amount of reactive power consumption of the short network on site, increase the power supply input voltage, increase the output of the transformer, and increase the smelting effective input power.

The melting power of the material is a function of the electrode voltage and the specific resistance of the material, which can be simply expressed as P=U2/Z material. As the load capacity of the transformer is improved, the power input from the transformer to the furnace is increased, which can increase production and reduce consumption.

2) Unbalance compensation, improve the strong and weak phase conditions of the three-phase.

Because the three-phase short network layout and furnace body, charge and so on are always unbalanced, the three-phase different voltage drop and different power lead to the formation of strong phase and weak phase phenomenon. The reactive power compensation is carried out by single-phase parallel connection, the compensation capacity of each phase is adjusted comprehensively, the power density of furnace core and the uniformity of crucible are improved, the effective working voltage of three-phase electrode is consistent, the electrode voltage is balanced, the feeding of three-phase is balanced, the strong and weak phase conditions of three-phase are improved, and the purpose of increasing production and reducing consumption is achieved. 

At the same time, the three-phase unbalance phenomenon is improved, the working environment of furnace is improved, and the service life of furnace is prolonged.

3) Reduce high-order harmonics, reduce the harm of harmonics to the entire power supply equipment, and reduce additional losses of transformers and networks.

4) Improved power quality, improved system electrical parameters, and improved product quality. The figure below reflects the flow direction of reactive power during high-pressure compensation and low-pressure compensation. It can be clearly seen from the figure that the high voltage compensation cannot reduce the loss and increase the output of the transformer.

However, due to a large number of switching switches with traditional compensation switching technology (such as the use of AC contactor switching), the cost is high, and the service life is greatly affected due to the harsh working environment. According to survey statistics, the existing ones use traditional The low-voltage compensation service life of the switching method is difficult to exceed one year, so it brings a large amount of maintenance to the enterprise, and the investment recovery period is prolonged. Due to the high follow-up maintenance cost, the overall benefit is not good.

BWKN-3500 reactive power compensation controller (special type for submerged arc furnace short network), a reactive power compensation controller specially developed and designed for submerged arc furnace system (submerged arc furnace short network) to adapt to the working characteristics of submerged arc furnace Special type), the controller has the ideal function of improving power quality, mainly has the functions of improving the power factor of the submerged arc furnace, saving energy, providing voltage support, and reducing flicker. The controller has the following salient features:

▲Compensation for the three phases separately to reduce the three-phase imbalance and effectively increase production and reduce consumption.

▲ Greatly improve voltage sag and flicker.

▲Achieve free switching at any time.

▲High reliability, maintenance-free and unattended.

▲Multiple protection design avoids damage to capacitors and electronic switches to the greatest extent. (Developed according to different customers)

▲Significantly improve the utilization rate of the power supply system.

▲Main technical parameters: the main basis of the controller

Design specification: DL/T597-1996; rated voltage: 220V; fundamental frequency: 50Hz; controlled physical quantity: reactive power Q; power factor COSΦ; reactive power compensation capacity single channel setting value: 0---9999K VAR working system: Continuous work; Ambient temperature: -5℃～+70℃; Relative humidity: daily average not more than 95%, monthly average not more than 90% (indoors), non-condensing; compensation method: phase separation and grading compensation. (Can be customized according to customer needs)

▲Performance characteristics can be divided into phases, grades, cycles, electronic switch switching; phase separation and graded compensation can be used. Equipped with complete protection functions; automatic control of switching, device operation without manual intervention, safe and efficient.

Ⅱ. Features:

1. Electric arc furnace: The electric arc furnace is more flexible than other steelmaking furnaces. It can effectively remove impurities such as sulfur and phosphorus. The furnace temperature is easy to control, and the equipment occupies a small area. It is suitable for melting high-quality alloy steel.

2. Submerged arc furnace: Its working feature is to use carbonaceous or magnesia refractory materials as the furnace lining and self-cultivation electrodes. The electrode is inserted into the furnace charge for submerged arc operation. It uses the energy and current of the electric arc to pass through the charge. The energy is generated by the charge resistance to smelt the metal. It is an industrial electric furnace with continuous feeding and intermittent tapping of iron slag.

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How to Choose the Right Roll?

Residual stress and thermal stress will occur in the preparatory process before the roll is manufactured and used. During application, it was further subjected to various periodic stress effects, including tortuosity, change, shear force, contact stress and thermal stress. The distribution of these stresses along the roll body is uneven and constantly changing. The reason is not only the planning factors, but also the continuous changes in the wear, temperature and roll shape of the roll in use. In addition, rolling conditions often exhibit abnormal conditions. Improper cooling of the rollers after application will also be endangered by thermal stress.

Therefore, in addition to wear, the roll often exhibits various partial damages and appearance damages such as cracks, fractures, flaking, and indentation. A good roll should have a better match between its strength, wear-resistance and various other performance indicators. In this way, it is not only durable under normal rolling conditions, but also less damaging when presenting some abnormal rolling conditions. Therefore, when making rolls, the metallurgical quality of the rolls must be strictly controlled or supplemented with external measures to enhance the bearing capacity of the rolls.

Various types of rolling mills produce long products. Therefore, the selection and layout of rolling mill types, the selection of roll materials, and the determination of roll sizes are also very wide. At the same time, the rolls selected by different rolling mills are also different, and the rolls need to be selected according to production requirements.

Before choosing the right roll to increase productivity and improve product quality, you need to fully understand the types and configurations of various mills.

1. Bar and small section rolling mill

Generally speaking, bar and small section rolling mills can use either steel ingots with a size range of 80 to 150 mm or continuous casting billets with the same size range to produce small profile and bars. The initial feed temperature of the bar and small profile rolling mill is 1200°C. The rolling mill can be produced either semi-continuously or fully continuously. Continuous rolling mill is the current development trend, during which there are rough rolling, intermediate rolling and finishing rolling stands. The roughing stands are arranged in horizontal/vertical order, which mainly depends on the product composition. The intermediate stand and the finishing stand can be either vertical or horizontal. For the bar, the rolling mill constitutes more vertical stands, while for other small profiles, the horizontal stand is often used.

In the small profile rolling mill, the diameter of the selected roll is 300-600mm, and the length of the roll body is 700mm according to the difference between the raw materials fed and the final product size. For product tolerances, users generally require one-third of international tolerance standards, and products must have a good surface finish. For small profile, the rolling speed of the rolling mill is from 12m/s to 20m/s, while for the bar rolling mill, the rolling speed has been increased to 36m/s.

2. Wire rod rolling mill

Wire rod rolling mills have rough rolling stands and intermediate stands similar to small profile rolling stands. Compared with small profile rolling mills for two-line rolling, these mills are generally designed to perform split rolling for simultaneous rolling of up to four lines. However, the current development trend is to use single-line high-speed rolling. Modern wire rod rolling mills generally have 8 to 10 non-twisting stands, which are arranged at an angle of 90° to each other in the finishing mill.

At present, the diameter of the rolls used in wire rod mills is limited to 200mm. The rolling speed can be as high as 140m/s.

3. Medium profile rolling mill and large profile rolling mill

After the rough rolling stand, the medium profile rolling mill has two sets of continuous stands. Continuous rolling mills can be arranged horizontally or vertically according to the pass design. For the section steel and channel steel with parallel edges, there is also a universal frame. When rolling other profiles, the universal frame can be replaced with the horizontal frame. The rolls of the horizontal frame have a deep hole pattern, but the universal frame does not.

The larger-diameter horizontal roll determines the shape of the section steel, and the smaller-diameter pair of vertical rolls are used to roll the edge. When the billet passes through the finishing rolls of the traditional stand and the universal stand, a good surface finish and dimensional tolerance can be obtained.

Roller parameter selection

-Rolled steel grade

The rolled steel type is the key factor for selecting the roll. Its deformation resistance varies with the chemical composition of the billet, which is mainly reflected in the size and change of the deformation load at each stage of rolling. The roller must be selected according to the determined strength and hardness.

-Rolling mill layout and pass design

The position of the stand on the production line and the design of the pass has a great influence on the choice of rolls. Depending on the position of the stand, the force mode and performance of the rolls can vary greatly. This is because the rolls applied to the rough rolling stand and the finish rolling stand have very different stress modes, resulting in expected changes in roll performance. In addition, the time interval between the passage of a billet and the next billet and the productivity of the rolling mill also has a great influence on the choice of rolls. It can be observed through experiments that roll bending and torsional stress combined with high rolling pressure are the factors that determine the selection of rolls for rough steel stands. However, in the finishing stand, hardness, wear-resistance and surface quality are the key factors for roll selection.

-Friction between roller and billet

Due to the difference between the circumferential speed of the roll and the billet speed, friction plays a very important role, especially at low speeds, such as blooming mills and roughing stands. Therefore, the relevant data creates conditions for the proper selection of rolls to suit a particular stand.

-Hot state

The thermal conditions of the rolls and rolled billets are also very important. The main reason is that the temperature of the roll is much lower than that of the rolled billet. Therefore, the roll is susceptible to high thermal shock in a short period of time, resulting in the formation of burnt cracks on the roll surface and further spread to form fatigue cracks. Therefore, the selection of rolls should take into account that roll cracks are minimally generated and propagated under rolling conditions.

-Roller cooling

The effectiveness of the roll is also related to the layout of the rolling mill coolant. The thermal conductivity of the roll material has a great influence on the cooling of the roll. The higher the thermal conductivity of the roll material, the higher the requirement for effective cooling, mainly to avoid the occurrence of cracking, resulting in a reduction in roll life.

Choose the roll according to the type of rolling mill

The selection of rolls is very skillful. The experience of the rolling mill operator plays a decisive role in the selection of rolls.

-Bar and small rolling mill

The requirements of this type of rolling mill for rolls are ① relatively good bending strength against impact; ② uniform hardness of the roll; ③ higher wear resistance; ④ better resistance to cracking.

If you are looking for rolls of rolling mills, please contact me.
Email: marketing2@hanrm.com; Whatsapp / Wechat: +8618392033938

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How to Improve Success Rate of Heat Exchange of Tundish of Continuous Casting Machine

In order to reduce the cost and increase the operating rate of the continuous casting machine, when the tundish reaches the service life, it is necessary to carry out the hot-swapping operation of the tundish. During the hot-swapping of the tundish, the casting billet drawing speed is stopped, and the casting billet is still in continuous spraying In the cooling state, if the heat exchange time of the bale is too long, it is likely that the slab is cooled too much, which makes the slab hard and causes stagnation, interrupts production, and may even cause a frozen slab accident. At present, there is a hot-swapping operation for the tundish in the CCM of the steel plant, but there is no specific description of the control range of each operation.

This article aims at the continuous casting of slabs in steel mills and the pulling speed during the hot exchange of the tundish, which makes the slab continuously cooled by spraying, resulting in excessive hardening of the slab cooling and production problems in the slab. The method improves the success rate of heat exchange and the operation rate of continuous casting machine, reduces the labor intensity, and plays an active role in demonstrating energy saving and consumption reduction of enterprises.

The purpose of this method is to improve the success rate of the heat exchange of the continuous casting machine, control the heat exchange time of the tundish within 5 minutes, reduce the cost and improve the operation rate. The following are the specific contents:

Step1 The ladle waiting time is 5-10min, the ladle reaches the continuous casting platform temperature 1590-1600°C;

Step2 The pulling speed of the tundish molten steel is reduced by one gear every 20 seconds, and the pulling speed is reduced to 0. 3m/min within 8min;

Step3 Measure the liquid level of the tundish. When the liquid level of the tundish is 300-500mm, drive the standby tundish to the heat exchange preparation area. When the tundish stops pouring, move the standby tundish and the pouring tundish to the other side start simultaneously on the side;

Step4 After the spare tundish car is opened to the pouring position, quickly install the red hot immersion nozzle (the bake time of the immersion nozzle is 2h longer), adjust the position of the tundish car so that the immersion nozzle is in the middle of the crystallizer, and install the blind plate After that, adjust the height of the tundish car to ensure that the bottom of the immersion nozzle is 150-180mm away from the upper mouth of the crystallizer;

Step5 When the tundish is ready, the ladle is opened, after pouring 10 tons of molten steel, 150-200kg of covering agent is added to the tundish, and the temperature of the open tundish is measured, which requires> 1550°C;

Step6 When the ladle is poured 20 tons, the tundish starts pouring, and the tundish molten steel is poured into the crystallizer;

Step7 After the pouring of the tundish, the emergence time is controlled at 80-120S. When the molten steel in the crystallizer reaches 115-125mm from the bottom of the immersion nozzle, that is, the molten steel has not passed the immersion nozzle, the pulling start operation is carried out, and the pulling speed after starting 0. 3m/min, 0. 3m/min pulling speed is maintained for 1min, and then the pulling speed is increased to the normal value of 0.9m/min; from the first tundish stop to the start of the second tundish, the time is controlled at 4 -5min.

The operation points of the present invention: coordinate the rhythm of molten steel, control the time of molten steel preparation ladle and reach the temperature of continuous casting platform, control the speed drop time and control the liquid level height of tundish; Simultaneously start the standby tundish and the pouring tundish at the same time. After the standby tundish is opened to the pouring position, the submerged nozzle is quickly installed and centered. After the blind plate is installed, the large tundish is poured; from the first tundish The total pouring time from the pouring stop to the replacement of the tundish is controlled within 5min; this method shortens the hot exchange time of the tundish as much as possible to avoid the stagnation phenomenon caused by the excessive cooling time of the casting slab, and demonstrates the technological progress.

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