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Basic knowledge of roll

Description:roll is a tool to produce plastic deformation of metal. It is an important consuming part to determine the efficiency and quality of rolling mill.

Roll types can be divided into casting roll and forging roll according to forming method: integral roll, metallurgical composite roll and composite roll according to process method. Integral roll is divided into integral casting roll and integral forging roll. Metallurgical composite casting rolls mainly include semi flushing composite casting, overflow (full flushing) composite casting and centrifugal composite casting. In addition, there are also composite rolls manufactured by special composite methods such as continuous pouring process for cladding, spray deposition, hip – hot isostatic pressing and electroslag fusion welding. The combined roll is mainly the insert sleeve combined roll.

Title:Basic knowledge of roll

Keyword:roll, Roll type,

rolling-mill-rolls

2 – what is an integral roll?

The integral roll is relative to the composite roll. The outer layer, center and neck of the integral roll are made of a single material by casting or forging. The different structures and properties of the outer layer and neck of the roll are controlled and adjusted by casting or forging process and heat treatment process.Forged roll and static casting roll belong to integral roll.

3 – what are the main categories of rolls according to material?

According to the manufacturing materials, rolls are mainly divided into three categories: cast steel series rolls, cast iron series rolls and forging series rolls.

4 – what are casting rolls and what are the main types of casting rolls?

Casting roll refers to the type of roll manufactured by casting molten steel or molten iron directly. Casting roll can be divided into cast steel roll and cast iron roll according to material; it can be divided into integral casting roll and composite casting roll according to manufacturing method.

5-which rolls are suitable for integral casting production?

The rolls used by blooming mill, billet continuous mill, large section steel and rail beam mill, scale breaking and edging mill of hot strip mill, edging mill of section steel universal mill, as well as roughing stand of small section steel and wire and bar mill are mostly produced by integral casting method. This kind of roll has thick layer and deep pass. In addition, the two high coarse roll of hot strip mill is also suitable for integral casting production. The process method of integral casting roll is relatively simple and the manufacturing cost is low

6-What is composite casting roll?

Composite casting roll means that the outer layer, core and neck of the roll body are made of two or more materials. The outer layer and neck of the roll body obtain the required microstructure and properties through the composition design and heat treatment process of different materials respectively. There are three kinds of composite casting methods: semi flushing composite casting, centrifugal composite and overflow composite. The composite casting roll needs special process equipment, the process is relatively complex, the control is difficult, and the manufacturing cost is high.

7- Which rolls are suitable for compound casting?

Compound casting is suitable for producing rolls with large working load and high rolling quality requirements. The performance requirements of this kind of roll body and roll neck are very different. The surface hardness of roll body is required to be high, and the roll neck requires high strength and toughness. For example, work roll and support roll of hot strip mill; Work roll of medium and heavy plate and wide and heavy plate rolling mill: work roll and support roll of leveling mill: roll ring of section steel universal rolling mill; Finishing roll of small section steel and bar mill, continuous pipe roll and stretch reducing roll ring of seamless steel pipe mill, etc, In recent years, centrifugal composite high chromium cast iron small vertical roll has been more and more used in hot strip mills at home and abroad, showing excellent wear resistance and obviously prolonging the roll change cycle.

8- what is cast steel roll and what are the varieties of cast steel roll

Rolls made of iron-based materials with carbon content less than 2.2% are collectively referred to as cast steel rolls. The cast steel with the total amount of alloy elements not greater than 0.8% is called carbon steel; the cast steel with the total amount of alloy elements greater than 0.8% is called alloy cast steel; the alloy cast steel with the carbon content not less than 1.3% is called semi steel. The main varieties of cast steel roll include carbon cast steel roll, alloy cast steel roll, semi steel roll, graphite steel roll, high chromium steel roll, composite cast steel support roll, high speed steel roll, semi high speed steel roll, etc.

 

9 what is carbon steel roll and what are its structural characteristics?

Carbon steel roll is a kind of hypoeutectoid steel composition roll with low alloy content (no more than 0.8%), such as z-u70, zu80, zu70mn listed in gb1503-89 cast steel roll. It is a kind of cast steel roll used in early China. The matrix structure is pearlite, but there are a large number of massive or strip ferrite in the matrix structure, which reduces the impact toughness and wear resistance of the matrix. At present, domestic horizontal section mill Carbon steel rolls are still used in double a heavy wire rod mills and some bad continuous rolling mills, which tend to be eliminated.

 

10 – what is alloy cast steel roll and what are its structural characteristics?

Alloy cast steel roll is a kind of cast steel roll with composition in the range of eutectoid steel and hypereutectoid steel and alloy content greater than 0.8%. Its carbon content is generally between 0.4% – 1.3% and contains some alloy elements such as chromium, nickel,, vanadium, etc. its matrix structure is generally controlled as sorbite and tempered sorbite through normalizing + tempering heat treatment process. Typical materials such as 60CrMnMo, 65crnimo, 70Mn2Mo, 75crmo, 75crnimo, etc.

 

The matrix structure of alloy cast steel roll is mainly pearlite type, containing a small amount of carbides, and the hardness range is hs35-50: due to a small amount of secondary carbides in the matrix, the tracking resistance of sensitive carbon steel wheel roll is greatly improved. At the same time, the impact toughness of roll is improved due to the elimination of massive strip ferrite in the matrix. The performance characteristics of alloy cast steel roll are high strength, good toughness, good thermal crack resistance and impact resistance.

The material of alloy cast steel roll has the trend of reducing carbon content and improving alloying degree. A variety of microalloying technologies are adopted, and the metallurgical quality is further improved, so that the alloy cast steel roll can better meet the needs of different rolling mills.

11- What are the main uses of alloy cast steel rolls?

Alloy cast steel rolls are used for square / slab blooming mill, roughing of large section steel billet and rail beam mill, two high roughing mill of plate and strip steel, large vertical roll of scale breaking frame, roughing mill of section steel, rod and wire mill, etc. The backup rolls of integral casting and composite casting belong to alloy cast steel rolls in a strict sense. The carbon content is controlled according to the hardness requirements and different alloy elements are added. The alloy cast steel material for the backup roll contains high alloy elements such as chromium, molybdenum and vanadium. With the increase of alloy content, the matrix structure changes from sorbite to bainite or martensite, It also contains secondary carbides with high hardness in the hardness range of HS 55-70 Excellent wear resistance and peeling resistance.

12-What is the production process and process of alloy cast steel roll?

Alloy cast steel rolls are mostly integrally cast rolls. The traditional production process adopts roll body cold sand hanging, bottom injection and normalizing and reheating heat treatment. It is mainly used to produce carbon steel roll and ordinary alloy cast steel roll used in ordinary 3-high section steel mill, double double bar and wire mill, etc. In order to strengthen the roll body performance of alloy cast steel roll and obtain good casting structure of roll body working layer, most of them are changed from cold mold sand hanging to cold mold coating spraying, and electric heating process is adopted for riser feeding. With the improvement of roll alloying degree, high temperature diffusion and spheroidization are added to roll heat treatment. There are two production processes of alloy cast steel roll: one is smelting casting heat treatment processability

Energy, flaw detection and other detection of a finished product: second, smelting – casting – rough machining – heat treatment – finish machining – performance, flaw detection and other detection of a finished product.

In 1986, German GP (gontennann peipers GmbH) roll manufacturing technology was introduced in China to produce large square / slab alloy cast steel primary rolls by no flow casting process. The roll has been successfully applied to Baosteel’s 1300mm I blooming mill.

In 1997, Masteel and Caigang imported 600000 T and 500000 T / a section steel from Germany and Japan respectively. According to the structure of section steel, universal rolling mill, roll and special service conditions, domestic

Wanliji alloy cast steel BD beonp is produced under static casting conditions, so that the alloy cast steel can be applied with no flow casting process and electric heating riser in the heart of grid political attack. Thus, the development and BD roll realize sequential solidification in the solidification process, and the rolling quality of alloy cast steel is improved

Manufacturing technology of roller. What types of heat treatment are commonly used for bottles

The commonly used heat treatment types of rolls include stress annealing, isothermal spheroidizing annealing, diffusion annealing, normalizing, tempering, quenching and cryogenic treatment.

 

14 – why does metallurgical cast steel roll undergo high temperature diffusion treatment?

During the solidification of cast steel roll, due to the existence of dendritic crystallization, it will cause the intracrystalline segregation of alloy components. This segregation is caused by the failure of sequential solidification of the upper, lower, inner and outer layers of the roll during the solidification process. The larger the roll body diameter, the longer the roll body length and the larger the solidification temperature gradient, the more serious the alloy solidification segregation is caused. With the increase of alloy content of alloy cast steel roll, the segregation index during solidification increases, and the degree of composition heterogeneity is also greater. Therefore, in order to fully diffuse the atoms of alloy elements and obtain the austenite structure with uniform composition, it is necessary to heat the high alloy cast steel roll to 150-250c above AC3 for a certain time. This heat treatment method is called high temperature diffusion treatment.

 

15-Why do alloy cast steel rolls undergo spheroidizing annealing heat treatment?

The spheroidizing annealing heat treatment of alloy cast steel roll is mainly to improve the cutting performance of roll, improve cutting efficiency and make corresponding organizational preparations for subsequent quenching treatment. Spheroidizing annealing makes the carbides in the structure change from flake to spherical, that is, spherical or granular carbides are evenly distributed on the ferrite matrix to become spherical pearlite structure. The spheroidizing temperature is generally slightly higher than the AC1 critical point. If the temperature is too low, the spheroidization time is too long, and if the temperature is too high, granular pearlite with different particle sizes will appear.

 

16-Why do alloy cast steel rolls need quenching heat treatment?

Quenching of alloy cast steel roll is a heat treatment process in which it is heated above the critical temperature (ACM or AC1), fully austenitized for a certain time, and then rapidly cooled to the bainite transformation zone at a cooling rate greater than the critical cooling rate, so as to obtain bainite structure in the working layer of the roll body. The purpose of quenching heat treatment of alloy cast steel roll is mainly to obtain good applicable structure of roll working layer, give full play to the role of alloy elements in roll and improve the hardness and wear resistance of roll body working layer.

Work rolls

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