This article describes the classification of rolls according to different directions, explains the rolls with different materials, and analyzes the rolls with different materials at home and abroad.
Key words: roll; classification; material selection
In order to meet the actual needs of steel rolling production, my country needs to spend a lot of foreign exchange to import rolls every year, importing about 30,000 tons of high-end rolls every year, and consuming about 200 million US dollars in foreign exchange. At present, my country’s roll consumption is 1.0 kg to 1.2 kg per ton of steel, and the annual consumption of various hot and cold rolls exceeds 900,000 tons, worth more than 15 billion yuan. Its massive consumption has caused a huge waste of resources and energy. Therefore, improving the quality of rolls and extending the life of rolls can not only save a lot of roll materials, reduce resource consumption and environmental pollution, but also save a lot of foreign exchange. Therefore, the continuous research and development of new composite roll manufacturing technology and equipment with simple process, high production efficiency and low equipment investment, in order to realize the production of low-cost, high-performance rolls, so as to manufacture new composite rolls with higher performance, is the future roll The direction of technological development.
Classification of rolls
There are many types of rolls, and their classification methods are not uniform, but they are generally classified according to the following three methods:
A. Classified by roll use:
1. Primary rolling roll
Slab blooming roll, billet blooming roll (these two rolls are replaced with the increase of continuous casting ratio)
2. Strip roll
Plate rolls, thin plate rolls, hot-rolled strip rolls, narrow strip rolls, cold-rolled strip rolls
3. Section steel roll
B. Classified by roll material
1. Cast iron roll
Chilled cast iron rolls, infinite chilled cast iron rolls, semi-chilled cast iron rolls, nodular cast iron rolls, high chromium cast iron rolls
2. Cast steel roll
Alloy cast steel rolls, alloy semi-steel rolls, graphite steel rolls, high chromium steel rolls, high speed steel rolls
3. Forged steel roll
Alloy forged steel rolls, high chromium forged steel rolls, forged high-speed steel rolls, etc.
4. Special rolls
Tungsten carbide roll, ceramic steel roll
C. Weight classification:
1. Large rolls, weighing more than 10 tons;
2. Medium-sized rolls, weight 3-10 tons:
3. Small rolls, weighing less than 3 tons;
Selection of roll material
The roll is an important consumable tool in the steel rolling production process. It directly affects the dimensional accuracy and surface quality of the rolled material. Since the rolling conditions of each rolling mill, the variety and specification of the rolled material are different, the correct design of the roll characteristics and reasonable Proper selection of roll material is very important.
Blooming mill roll
Blooming mills are mainly divided into slab mills and billet mills. Blooming mills use steel ingots as billets, and the as-cast structure of steel ingots is a coarse dendrite structure, which is prone to segregation. In order to eliminate the cast structure, a higher rolling temperature and a large amount of deformation are controlled to break the coarse grains. At the same time, the roughing mill has a large reduction and a large rolling torque. Therefore, the thermal crack resistance and strength of the roll are the key to the initial roll.
Before the 1950s, most foreign primary rolls used forged steel rolls. Later, some cast steel rolls were used instead. Although this type of roll has high strength, the main problem is that it is not wear-resistant on the one hand; on the other hand, it is poor in thermal crack resistance, and the roll is often broken due to ring cracks. In the blooming mill rolls, the application of nodular cast iron rolls is considered to be a very effective pioneering work. In 1958, my country was the first in the world to use nodular iron rolls on the blooming mill, and achieved satisfactory rolling results, making a fruitful contribution to the expansion of the application field of nodular cast iron. In the past, the hardness of cast steel initial rolling rolls was 27-35HSD, but the hardness of alloy ductile iron rolls can reach 43-48HSD, which has better durability.
Abrasion resistance and thermal crack resistance, but the disadvantage is that it is easy to slip. In terms of strength, as long as the spheroidization effect of the roll is good and the heat treatment is good, the strength of the roll is guaranteed.
Plate roll
There are two-high reversing mills, three-high Lauter mills and four-high reversing mills in terms of structural types: according to the number of stands, there are single-stand, double-stand and multi-stand semi-continuous rolling or full-continuous rolling. rolled.
In a three-roll Lauter-type mill, except the middle roll is a work roll, the upper and lower rolls are both backup rolls and work rolls. It is required that the rolls not only have good wear resistance and heat resistance, but also have good spalling resistance and Fracture resistance. Therefore, the roll should use low nickel chromium molybdenum or medium nickel chromium molybdenum infinitely chilled cast iron roll, and the surface hardness of the roll body is 60-70HSD.
The four-high reversing mill is the most widely used medium and heavy plate mill in modern times. It combines the advantages of the two-high and three-high Lauter mills, which not only reduces the rolling pressure, but also greatly enhances the rigidity of the rolling mill. The choice of rolls in this rolling mill has changed several times. The back-up rolls are usually cast steel rolls with a hardness of 45-52HSD. The use of rolls for this stand is a major feat. In the 1950s, the work rolls of the finish rolling stand were high-alloy infinite chilled cast iron rolls produced by the full flushing process in foreign countries, with a hardness of 75-82HSD. This material has continued to this day, but it is only in the form of graphite and the state of carbide. It has been improved, and the leveling roll adopts centrifugal composite high-alloy infinite chilled cast iron roll with a hardness of 70-80HSD.
Sheet rolling roll
At present, the stacked sheet rolling mill has been basically eliminated in the world, but there are still dozens of them in my country at this stage. This kind of rolling mill has the following characteristics:
1) Irreversible periodic rolling, the idling time of the rolled piece is longer.
2) Due to the small thickness and large surface area of the rolled piece, the heat dissipation is fast during the rolling process, coupled with the long empty running time, the temperature of the rolled piece quickly drops to a level that is not suitable for continuous rolling, and it often needs to be returned to the furnace for reheating .
3) Due to the limitation of the elastic deformation of the rolling mill, when the product thickness is less than 2 mm, it is necessary to carry out multi-sheet stack rolling, and the rolling thickness is generally between 0.28-4.0 mm.
4) In order to reduce the cooling of the rolled piece during the rolling process, generally the rolls are not water-cooled, and the working temperature of the rolls is 500-600°C.
5) The rolls need to be preheated and ironed before installation and normal steel rolling. The preheating temperature of the rolls is 380-420°C
6) The rolling pressure of the rolling mill is high, generally reaching more than 900 tons, and the maximum pressure can reach as high as 1600 tons.
According to the above characteristics, it can be seen that the working conditions of the rolls of the stacked thin plate mill are quite harsh. It is required that the roll has good thermal conductivity and peeling resistance, and the roll has high impact resistance and fracture resistance. Therefore, this kind of roll is usually made of CrMo infinite chilled nodular composite cast iron roll with low alloy content, and the hardness is 57-63HSD. The most prone problems of the roll are roll breakage and peeling.
Hot rolled strip rolls
Hot-rolled strip mills are divided into semi-continuous rolling, 3/4 continuous rolling, full-continuous rolling and thin-plate continuous rolling. Only one reversible roughing mill and a set of finishing mills are called semi-continuous rolling; Rolling mill, which has a reversible called 3/4 continuous rolling; continuous rolling mill with several roughing mills and a set of finishing stands is called full continuous rolling; The billet directly enters the continuous rolling mill for rolling, which is called thin plate continuous rolling.
The two-roller rough roll must have high resistance to twisting, bending strength and good thermal crack resistance, so most of them use integral cast alloy cast steel rolls with a hardness of 43-50HSD or high-strength alloys with a hardness of 55-60HSD Ductile iron rolls. In recent years, some foreign countries have adopted composite cast steel rolls whose outer layer is graphite steel. Good results have been obtained.
In the 3/4 continuous rolling mill and the full continuous rolling mill, because the roughing stand has backup rolls, there is no need to worry about the problem of work roll breakage. The key is the wear and tear of the rolls. In the 1960s and 1970s, the rough rolling stand of the hot strip continuous rolling mill mainly used nickel-chromium-molybdenum infinite chilled composite cast iron rolls or semi-steel rolls with a hardness of 50-55HSD. In the 1980s, Europe began to use high-chromium composite cast iron rolls and achieved rapid promotion. The hardness of the rolls also increased to 70-75HSD.
In the 1990s, semi-high-speed steel rolls were successfully applied in the roughing stands of hot-rolled strip mills. Semi-high-speed steel rolls have the following advantages: high wear resistance: good thermal crack resistance: good spalling resistance sex and bite.
The finishing stand is composed of 5-7 stands. Usually, the first stand is called F1, the second stand is F2, etc. The finishing mill is called a four-roll mill, and the back-up rolls are used to prevent the working rolls from bending due to rolling force. Back-up rolls generally use cast steel rolls with a hardness of 40-50HSD, and some countries use forged steel rolls with a hardness of 60-70HSD. In short, the selection of backup roll material must have good fatigue strength and fracture resistance. This is because the contact between the backup roll and the work roll is under great pressure, and work hardening occurs in each rolling cycle. If it cannot be removed in time, Will cause peeling.
The work rolls in the front section of finishing rolling (F1-F3) also experienced a revolution in the 1980s. When thick slabs were rolled, a phenomenon called roll sticking appeared, and black oxides would stick to the work rolls. Surface, until it reaches a certain critical thickness, it will start to fall off, and the peeled oxide will cause quality problems in the strip due to the rolling of the rolls. In order to solve this problem, high-chromium composite cast iron rolls with a hardness of 70-80HSD are used in the front section of finish rolling, and good results have been achieved. Of course, not all rolling mills can use this kind of roll. If the cooling water is insufficient or the water quality is not good, serious spalling will occur. When high-chromium composite cast iron rolls have not been widely used, high-speed steel rolls have achieved good results in the front stage of finishing rolling, and their service life is more than three times that of high-chromium cast iron rolls. Now they have basically completely replaced high-chromium cast iron rolls. . The selection of rolls for the same rolling mill is not uniform, and the most suitable rolls should be determined according to the specific usage and operating conditions of the rolling mill.
The work rolls in the post-finish rolling section (F4-F7) are used in the last few shifts, so the hardness, wear resistance, thermal crack resistance and spalling resistance of the rolls are the main performance requirements. Based on this characteristic requirement, almost all the work rolls in the finishing rolling section of the hot strip tandem mill at home and abroad are made of high-nickel-chromium-molybdenum infinite chilled composite cast iron rolls. Its hardness range is 75-85HSD. The most important feature of this type of roll is its excellent wear resistance, which ensures high dimensional accuracy and surface finish of the strip. However, with the development of materials, roll developers have achieved remarkable results by using high-speed steel materials in roll manufacturing. The roll changing cycle is 3-5 times higher than before, and the hardness of the roll can reach 80-90HSD. At present, not only F1-F3 frames generally use high-speed steel rolls, but also F4 and F5 frames all use high-speed steel rolls. F6 and F7 frames still use improved high-nickel-chromium-molybdenum infinite chilled cast iron rolls with a hardness of 78-83 HSD. The leveling roll adopts the centrifugal composite gold infinite chilled cast iron roll with a hardness of 70-80HSD.
Hot rolled narrow strip steel roll
Usually people call the strip steel with a width less than 500mm narrow strip steel. The frame form and layout of the narrow strip steel rolling mill are very similar to that of the hot strip continuous rolling mill. Therefore, the selection of rolls is basically similar. Rough rolling stands usually use alloy cast steel rolls with a hardness of 40-50HSD or alloy ductile iron rolls with a hardness of 45-55HSD.
The front section of the finishing rolling unit adopts bainite ductile iron rolls with a hardness of 60-70HSD or medium-high alloy infinitely chilled cast iron rolls; the rear section of the finish rolling unit uses high-alloy infinitely chilled cast iron rolls with a hardness of 75-85HSD or a hardness of 80-90HSD high-speed steel rolls. It is better to use semi-steel rolls for the back-up rolls.
Cold rolled strip rolls
The cold strip tandem mill consists of three to six stands, which are four-high mills with larger back-up rolls and smaller diameter work rolls. During cold rolling, emulsified oil is used to lubricate the steel strip and also to cool it. Forged steel rolls of 80-95HSD are used for cold rolling work rolls, and high-alloy infinitely chilled cast iron rolls with a hardness of 75-80HSD are used in some rolling mills. The advantage is that the roll shape is easy to control, but the disadvantage is that due to graphite, the strip steel is often used surface contamination. In recent years, the use of semi-high-speed steel rolls and high-chromium forged steel rolls for cold-rolled work rolls is another great breakthrough.
Large section steel roll
Large section steel rolling mills are generally divided into rough rolling, intermediate rolling and finishing rolling, so the materials of the selected rolls should also be different according to the different stands.
The rolls of the rough rolling stand are usually processed with deep grooves, and the rolling temperature is high and the rolling pressure is high, which requires the rolls to have high strength and heat resistance. Therefore, most foreign manufacturers use nickel-chromium alloys with grooves Molybdenum alloy cast steel rolls or graphite steel rolls. In recent years, in order to improve the surface quality of rolled materials, some manufacturers have begun to use alloy semi-steel rolls with a hardness of 45-50HSD. As long as the cooling condition of the roll is improved, the alloy semi-steel roll can achieve the best use effect when the roll temperature is controlled below 60°C during use.
The rolls used in the middle stand must have good thermal crack resistance and wear resistance at the same time, so the rolls of this stand generally use alloy ductile iron rolls with a hardness of 50-60HSD or cast alloy ductile iron rolls with grooves.
The rolling operation of the large section steel finishing stand is an important operation link to ensure the rolling according to the negative tolerance, reduce the allowable deviation, and improve the dimensional accuracy of the large section steel. Therefore, the rolls used in the finishing stands of large section steel mills should have certain strength and excellent wear resistance at the same time. Therefore, the roll basically chooses a pearlite ductile iron roll with good wear resistance or a high-carbon semi-steel roll.
Medium and small section steel rolls
Medium and small section steel rolls are generally divided into rough rolling, medium rolling and finishing rolling, and the material selection should be determined according to specific conditions such as the type of rolling mill, product specifications, and the number of rolling mills.
Roughing stands generally have deep grooves, requiring the rolls to have high strength and heat crack resistance. Therefore, most of them use alloy semi-steel rolls or high-strength alloy ductile iron rolls.
The rolls in the middle stand are heavily loaded during the rolling process, and the rolls are required to have good thermal crack resistance and certain wear resistance. Therefore, alloy nodular cast iron rolls or infinite chilled cast iron rolls are generally used.
The rolling pressure on the rolls of the finishing stand is relatively small, and it is generally not easy to cause roll breakage. However, this stand is the finished product stand or the finished front stand of the product. In order to ensure the dimensional accuracy of the rolled material and ensure that the rolling mill is rolled according to negative tolerances, the wear resistance of the rolls is the primary issue. Therefore, the rolls of the finishing stand usually use pearlitic ductile iron rolls, bainitic ductile iron rolls or nickel-chromium-molybdenum infinite chilled cast iron rolls with good wear resistance, and the hardness of the rolls is 65-75HSD.
Bar Roll
Bar mills belong to the small section steel mills. According to statistics, by the end of 2003, my country had successively introduced and self-made 118 sets of bar continuous rolling mills. Rolling technology, due to the long heating time of the rolls and the long length of the rolled material, the requirements for the rolls are not only good wear resistance and high strength, but also better thermal crack resistance and toughness.
The rolls of the rough rolling stand must firstly have a high strength due to the high rolling pressure of the rolling mill, the deep roll pass, and the high cutting force caused by the large reduction. On the other hand, due to the slow rolling speed of the stand 1. The roll has a long heating time, so it must have good thermal crack resistance and anti-stripping performance; at the same time, the roll must also have good wear resistance, impact resistance and bite resistance. Clearly, some of these properties are contradictory. Steel rolls have better bite and higher strength than ductile iron rolls, but their wear resistance and thermal crack resistance are not as good as ductile iron rolls. Some manufacturers use semi-steel rolls for rough rolling stands. Although they can meet the requirements of the rolling mill in terms of strength and wear resistance, the thermal cracks of the rolls are very serious. Therefore, most manufacturers currently use ferritic nodular cast iron rolls with a hardness of 45-50HSD for the first stand of rough rolling mills, and pearlitic nodular cast iron rolls with a hardness of 50-55HSD for other stands. In fact, the most ideal material for the roughing unit should be non-carbide bainite roll (NCC roll), with a hardness of 48-55HSD. This kind of roll has high wear resistance due to the absence of network carbide in the structure. Moreover, the ability to resist thermal crack expansion is strong, but the disadvantage is that the price is high.
On the one hand, the rolls of the middle rolling stand have a deep pass and a large rolling pressure, so the strength of the roll is still crucial; on the other hand, due to the large pass size of the roll, the cooling of the groove bottom cannot be fully carried out. Therefore, the thermal crack resistance and impact toughness of the roll still cannot be ignored. At the same time, compared with the rough rolling stand, the wear resistance of the rolls of this stand puts forward higher requirements, especially the hardness of the bottom of the groove should be similar to that of the top of the groove. Therefore, the hardness of the middle rolling stand is 60-68HSD. Pearlitic ductile iron rolls are ideal and economical, and the roll surface wear and thermal cracks are better after use. Although the acicular bainite ductile iron has better wear resistance, its thermal crack resistance is lower than that of pearlite. The body ball iron is slightly worse. The future development trend of mouth rolling stand rolls is to use semi-high-speed steel rolls with a hardness of 68-75HSD, whose wear resistance is twice that of acicular bainite ductile iron rolls.
The rolls of the finish car frame should not only ensure the normal operation rate of the machine, reduce the number of roll changes, increase the steel output, but also ensure the surface quality of the steel, that is, more steel and better steel. Therefore, the wear resistance of the roll is The key question. At the same time, due to the rolling of rebar, the toughness and spalling resistance of the roll are still very important, so the acicular bainite ductile iron roll with a hardness of 68-75HISD is generally used for this stand. Because the matrix structure of this roll is acicular bainite, the wear resistance and strength and toughness of the roll are good. In recent years, with the development of materials, high-speed steel rolls and tungsten carbide roll rings have become more and more popular in the steel rolling industry due to their excellent wear resistance and remarkable use effects, especially for the finished racks of bar continuous rolling mills. , Finished front frame, split frame and pre-cut frame are better. The wear resistance of high-speed steel rolls is 3-5 times higher than that of bainitic ductile iron rolls, and the wear resistance of tungsten carbide roll rings is 5-10 times higher than that of bainite ductile iron rolls, but the price of high-speed steel rolls is only It is one tenth of the tungsten carbide roller ring, with high price-performance ratio and broad prospects. At the same time, it also shows that the concept of roll selection in rolling mills has also changed. They are no longer keen on low-priced rolls, but value the price-performance ratio of rolls, the improvement of the operating rate of the rolling mill, and the improvement of the quality of rolled products.
High speed wire rod roll
The high-speed wire rod mill is also divided into rough rolling, intermediate rolling and finishing rolling, and there are 2-4 pre-finishing stands before finishing rolling. The rough rolling unit usually consists of 4-8 stands. Due to the high rolling temperature, large cross-section and deep mill pass, the rolls used in the rough rolling stand should have good resistance to breaking, heat cracking, and abrasion and good bite properties. Usually the rough rolling stand adopts pearlitic ductile iron rolls with a hardness of 50-60HSD or alloy semi-steel rolls with a hardness of 45-55HSD.
The rolls of the intermediate rolling mill are generally required to have good wear resistance and surface roughness resistance. Therefore, the rolling unit in the high-speed wire rolling mill generally uses pearlitic nodular cast iron rolls or bainitic nodular cast iron rolls with a hardness of 60-70HSD. Some manufacturers also use infinite chilled rolls, which should be determined according to the specific conditions of the rolling mill.
The pre-finishing rolling unit of the high-speed wire rod mill can reduce the rolling accidents of finishing rolling and improve the dimensional accuracy of the finished wire rod. Therefore, the principle of selecting roll materials for the pre-finishing mill should be that the rolls used in this unit can play a role in connecting the past and the future, and the main basis should be to ensure the wear resistance of the rolls. Improving the hardness of the working layer of the roll body, especially increasing the hard wear-resistant phase in the matrix structure of the working layer of the roll body is an effective way to reduce wear. Therefore, in the matrix structure of the working layer of the roll body, increasing the amount of the above-mentioned cemented carbide carbides and controlling their precipitation form is an important guarantee for improving the wear resistance of the pre-finishing roll (or roll damage). Most of the pre-finishing stand rolls are a combined structure, which is made up of a roll ring and a mandrel. At present, the selection of materials for roll rings in foreign countries is very complicated, such as high hardness acicular ductile iron, high chromium cast iron, high vanadium alloy cast iron, high tungsten chromium alloy cast iron, tungsten carbide composite roll rings, etc. Most of the pre-finishing roll rings of high-speed wire mills in my country use high-nickel-chromium-molybdenum infinitely chilled cast iron with an outer hardness of 75-80HSD, and centrifugal composite roll rings with alloy ductile iron inner layers, which have achieved good results. Some manufacturers also use tungsten carbide hard alloy roll rings. Although the wear resistance is good, the strength is low and fractures often occur. However, high-speed steel roll rings are more suitable for pre-finishing of high-speed wire rod mills because of their wear resistance three times that of high-nickel-chromium-molybdenum infinite chilled cast iron rolls and higher strength than tungsten carbide hard alloy roll rings.
The high-speed wire rod mill finishing unit is an important factor to ensure high-precision rolling of wire rods. Therefore, tungsten carbide roll rings with a hardness of 82-90HSD must be used in the finishing unit of the high-speed wire rod mill. Otherwise, the rolling speed and the wear resistance of the roll ring cannot be guaranteed. So far, there is no material that can replace the tungsten carbide hard alloy roll ring of the finishing unit of the high-speed wire rod mill.
The gap between domestic and foreign countries in the selection of rolls for bar continuous rolling mills
In the selection of rolls in the past few years, there is a big gap between domestic rolling mills and foreign countries. For example, the CIC tungsten carbide roll ring produced by Sweden’s Sandvik has been pushed to China in the early 1990s. After more than ten years of development At first, there were only a small number of trials in Shanghai No. 1 Iron and Steel Plant, and there are no more than 5 so far. Although many steel rolling mills are actively selecting imported tungsten carbide roll rings in recent years, they are all out of interest in the product for trial use. Few of them repeat the purchase. The biggest obstacle is limited to tungsten carbide roll rings. In terms of the price and use conditions of the ring, because the use effect of this kind of roll depends not only on the quality of the roll itself, but more importantly on the use conditions of the roll and the maintenance and maintenance of the roll. From this point alone, it is also unacceptable to roll users in the short term. Essentially, it’s a matter of using the roller concept. Two years ago, the British Steel Union in the United Kingdom and the bar tandem rolling mill finishing unit of the Barton Company in Germany all used high-speed steel rolls.
This year, when the leaders of Synnex Corporation in charge of export inspected many rolling mills in Japan, they found that Japanese rolling mills had a fundamental change in roll selection compared with two years ago. Pearlitic nodular cast iron rolls were generally used for rough rolling stands, and semi-high-speed rolls were used for medium rolling stands. Steel rolls and finishing stands are all high-speed steel rolls. The bar rolls supplied by Synnex to the United States are still pearlitic nodular iron rolls and bainitic nodular iron rolls, and even a certain amount of conventional rolls, but they think that after 3-5 years, they will be like Japan. The selection of materials will completely change. As far as our country is concerned, it will take a longer time to completely change the concept of roll selection.
Birth and development of centrifugal composite roll
When human beings created the rolling mill, there were rolls. The early rolls were integrally cast with sand molds, and metal mold casting was invented later. Roll manufacturing technology took a leap forward when rolls were poured with tangential gates from the bottom of the mold. With the development of the steel rolling industry, steel rolling workers have higher and higher requirements for the performance of the roll, which requires high hardness of the roll body, good wear resistance, good impact resistance and thermal crack resistance, and no slippage, while the requirements for the core of the roll It is high strength, continuous rolling and small deformation. These properties are often contradictory. In order to solve this problem, roll developers have thought of producing composite rolls by half flushing or full flushing.
The semi-flushing method is to pour alloy molten iron from the bottom of the mold, stop pouring when the molten iron reaches the junction of the upper roll neck and the roll body, let it stand for a period of time, and add the remaining molten iron in the ladle to a certain amount when the roll body forms a shell. A certain amount of ferrosilicon powder is stirred and then poured, so as to achieve the purpose of improving the strength of the roll core.
The full flushing method is to pour alloy molten iron from the bottom of the casting mold. When the molten iron reaches the junction of the upper roll neck and the roll body, stop pouring and let it stand for a while. When the roll body forms a shell, replace it with another bag of high-strength one. The core molten iron continues to be poured along the bottom gate, and the original core molten iron is replaced from the riser end. The birth of the composite roll made another leap forward in the production technology of the roll.
In 1968, Japan’s Kubota first announced the successful development of centrifugal composite cast iron rolls, making the manufacturing technology of composite rolls more perfect. Over the past 35 years, the manufacturing technology of centrifugal compound rolls has developed rapidly, and it can be said that eight generations of centrifugal compound rolls have been formed.
The first generation is chilled compound roll and infinite chilled compound roll. — That is, the outer material of the roll is chilled cast iron or infinitely chilled cast iron, and the core material of the roll is gray cast iron. The technical key of this generation of composite rolls is to solve the centrifugal composite process, the development of mold slag and the development of cold coating.
The second generation is the spherical core composite roll. — That is, the outer material of the roll is chilled cast iron or infinitely chilled cast iron, and the core material of the roll is ductile iron. The technical key of this generation of composite rolls is to solve the influence of the black line of the roll bonding layer on the anti-stripping performance of the rolls.
The third generation is the nodular composite cast iron roll. — That is, the outer layer material of the roll is alloy ductile iron, and the core material of the roll is also ductile iron. The technical key of this generation of composite rolls is how to prevent the nodular recession and remelting of the outer layer of ductile iron.
The fourth generation is high chromium composite cast iron roll. One by one, the outer material of the roll is high chromium cast iron, and the core material of the roll is nodular cast iron. The technical key of this generation of composite rolls is how to prevent or reduce the damage caused by the expansion of chromium in the outer layer to the core. Therefore, sometimes a three-layer composite has to be used.
The fifth generation is high chromium composite cast steel roll. — That is, the outer material of the roll is high chromium steel, and the core material of the roll is ductile iron or graphite steel. The technical key of this generation of clad rolls is still to reduce the diffusion of chromium from the outer layer to the core and to determine the parameters of the centrifugal clad process.
The sixth generation is composite cast steel or composite semi-steel roll. One – that is, the material of the outer layer of the roll is alloy steel or semi-steel, and the material of the core of the roll is ordinary cast steel or stone black steel. The technical key of this generation of composite rolls is the determination of centrifugal composite process parameters and the development of high melting point mold powder.
