Description: The roll is the most important process part in steel rolling production. The direct contact between the roll and the rolling piece causes the rolling piece to undergo plastic deformation, thus completing the rolling process. The other components of the rolling mill are all set up for installation, support, adjustment and replacement of rolls, as well as for guiding and controlling the correct entry and exit of rolled pieces into and out of the rolls. Rolls often work under harsh conditions such as high temperature, high pressure, chilling and heat, and impact. It is a severe test for the quality and performance of the rolls such as strength, surface hardness, wear resistance, and thermal cracking resistance. In order to reduce the investment of rolls and reduce the consumption of rolls, the selection of roll material, roll design and use are discussed.
Keyword: Rolling mill rolls material
Rolling mill rolls overview
The position and structure of the roll in the work stand
Central position: The other components and mechanisms of the stand are designed to install, support and adjust the rolls, and guide the rolling stock into and out of the rolls correctly.
(1) Roll body: The part where the roll contacts the rolled piece and causes plastic deformation of the metal.
(2) Roll neck: The support part of the roll, which is installed in the bearing and placed in the frame, and the rolling force is transmitted to the frame through the bearing seat and the pressing device.
(3) Roller head: It transmits the torque of the rolled piece by connecting with the coupling.
Mill Rolls classification
(1) Strip mill roll
The roll body is round: general rolling mill
Dimpled roll body: hot rolling, compensation of thermal expansion, control of plate shape.
Slightly convex roll body: cold rolling, compensating for stress bending, and controlling the shape of the plate.
S, cigar and other special curved roll body: CVC rolling mill, UPC rolling mill.
(2) Section steel mill roll :
There is a rolling groove (pass type) on the roll body
(3) Special rolls :
Generally used in special or special rolling mills such as piercing machines, wheel rolling mills, gear rolling mills, and cross wedge rolling mills. The rolls have various shapes.
The working characteristics of the roll and the requirements for the roll
|When working, it bears a large rolling force and moment, accompanied by a strong dynamic load.||Strength↑ Stiffness↑Surface Hardness↑|
|To work under conditions of high temperature and large temperature changes||Thermal Stress Stability↑|
|Severe wear and tear: hot rolling is accompanied by hard oxide scale, which makes the roll surface easily damaged; cold rolling, especially when rolling thin plates, the roll is often in a state of elastic flattening, which makes the contact stress huge, and the roll is also very easy to damage||The surface chill layer is deeper|
Roll main parameter design
The basic parameters of the roll
Roll nominal diameter (or nominal diameter) D, roll body length L, roll neck diameter d, roll neck length l. Roller head diameter d1.
Regarding roll diameter:
Nominal diameter: center moment of gear seat; blooming mill:
Outer warp of roll ring or central moment of finishing roll
Working Diameter: Groove Bottom Diameter (Section Steel Mill)
Maximum diameter: new roll diameter
Minimum diameter: old roll diameter
Determination of the nominal diameter of the roll and the length of the roll body
Blooming mill and section steel mill
First determine the diameter of the roll body, and determine the principle:
I In order to avoid too deep cutting of the pass groove, the ratio of the nominal diameter of the roll to the working diameter is generally not greater than 1.4;
II maximum bite angle
III roll strength (n=5)
|Rolling condition||maximum bite angle||maximum ratio||Friction coefficient between roll and rolling piece|
|Hot roll||Rolling blooms and billets in scored and welded rolls||24~32||1/6~1/3||0.45~0.62|
|Automatic pipe rolling machine hot rolled steel pipe||12~14||1/60~1/40||—|
|Cold rolled strip in lubricated condition||Rolled on smoother rolls||5~10||1/130~1/23||0.09~0.18|
|Rolled on well ground rolls||3~5||1/350~1/130||0.05~0.08|
|Lubricated with palm oil, cottonseed oil or scallion oil||2~4||1/600~1/200||0.03~0.06|
Length determination principle:
I Number of pass arrangements
II Strength Conditions
Principle: Set L first, then D
Hot rolled strip
Medium plate: L/D=2.2—2.8
|ratio||Common Ratio||ratio||Common Ratio||ratio||Common Ratio||According to the statistics of 165 four-high rolling mills with the length of the roll body in the range of 1120~5590mm|
|Heavy plate mill||3.0~5.2||3.2~4.5||1.9~2.7||2.0~2.5||1.5~2.2||1.6~2.0|
|Wide Strip Mill||roughing mill||1.5~3.5||1.7~2.8||1.0~1.8||1.3~1.5||1.2~2.0||1.3~1.5|
|Clod plate mill||2.3~3.0||2.5~2.9||0.8~1.8||0.9~1.4||2.3~3.5||2.5~2.9|
Cold rolled strip
The maximum diameter of the work roll is also limited by the minimum thickness of the rolled strip.
Determination of roll neck size
plain bearings, rolling bearings, liquid bearings
Determination of the size of the roll head
a torx hub, b cardan hub, c hub with keyway, d cylindrical hub, e hub with platform
Selection of roll material
Principles of Roll Material Selection
According to the working characteristics and damage mode, the performance of the roll (strength, wear resistance, heat resistance, etc.) is strictly guaranteed.
Roll damage form
Common materials for rolls
(1) alloy forged steel: (JB/ZQ4289-1986)
Hot Roll: 55Mn2, 55Cr, 60CrMnMo, 60SiMnMo, etc.
Cold Roll: 9Cr, 9Cr2, 9Cr2W, 9Cr2Mo, 60CrMoV, 80CrNi3W
Advantages and disadvantages: the comprehensive mechanical properties are better, but the price is expensive and the processing and manufacturing are difficult.
(2) Cast steel: ZG70, ZG70Mn, ZG8Cr, ZG75Mo
(3) Cast iron: ordinary cast iron, alloy cast iron, nodular cast iron.
Depending on the casting type, different hardness can be obtained: semi-chilled, chilled, and infinitely chilled.
Advantages: cast iron has high hardness, smooth surface, wear resistance, simple manufacturing process and cheap price.
Disadvantages: The strength is lower than that of steel rolls, and only ductile iron has better strength.
(4) High speed steel
Advantages: good wear resistance, good surface roughness resistance. New developments in the past 20 years have broad application prospects.
Selection of roll material
(1) Blooming mills, billet mills, thick plate mills, large rail and beam mills, section steel roughing mills:
Generally, forged steel rolls are used, and alloy steel rolls are used for higher requirements. Cast steel rolls are mostly used in section steel roughing mills.
Reason: Large reduction, large rolling force, and impact load require the rolling mill to have high strength and a large friction coefficient (because it is easy to bite, thereby increasing the reduction)
(2) Finishing stand rolls of small and medium-sized rolling mills:
Most of them use cast iron rolls, and some use ductile iron.
Reason: This type of rolling mill emphasizes hardness and wear resistance, so that the product size is accurate, the surface quality is good, and the number of roll changes can be reduced to increase productivity.
3) Wire rod mill
Rough mill stand: softened annealed pearlitic ductile iron or ordinary cast steel,
If hot cracking problem is the main problem: its hardness value is lower (HS=38～45)
If the wear resistance problem is the main problem: choose a slightly higher hardness (HS=45~55).
Cast iron is preferred, the reason: for rolls with the same hardness, the service life of softened and annealed ductile iron rolls is twice as long as that of ordinary cast steel rolls.
Intermediate rolling stand: pearlitic ductile iron or bainite ductile iron is preferred, with slightly higher hardness (HS=60~70).
Pre-finishing stand: high-nickel-chromium centrifugal casting composite roll, tool steel, tungsten carbide, etc.
Finishing stand: generally hard alloy of tungsten carbide. Because it has good thermal conductivity, it has the characteristics of small hardness drop at high temperature, good thermal fatigue resistance, good wear resistance, and high strength.
(4) Hot strip mill:
Working rolls: Cast iron rolls are mostly used. Reason: The hardness of the roll surface is the main requirement.
Support roller: Forged steel with chromium alloy is mostly used. Reason: The work mainly bears the bending moment, and the diameter is large, so the strength and hardenability of the roll should be considered emphatically.
(5) Cold-rolled strip mill:
Working rolls: High-strength alloy cast steel or composite rolls with hard alloy roll sleeves are mostly used. Reason: There are high requirements for the hardness and strength of the roll surface.
Support rolls: similar to hot-rolled strip steel, chromium-containing alloy forged steel is mostly used. But the hardness is higher (HS=50~65) Reason: The work mainly bears the bending moment, and the diameter is larger, so the strength and hardenability of the roll should be considered emphatically.
|category||Features of the working layer of the roll surface||Features of the working layer of the roll surface|
|chilled cast iron roll||Hard and brittle, high wear resistance, smooth rolling surface can be obtained in the finished passCast white iron rolls belong to this category, and can have a pass||Small load finishing roll rough rolling and intermediate stand|
|Infinite chilled cast iron rolls||Moderate wear resistance, thermal crack resistance and strength||All kinds of hot-rolled plate and strip mill work rolls, small and wire rod rolls.|
|Ductile iron rolls||Chilled Ductile Iron Rolls||Two-roll stacked thin plate and three-roll Lauter towel roll|
|Infinite Chilled Ductile Iron Rolls||Various section steel rolls, work rolls for hot-rolled strips with heavy loads, backup rolls for tempering mills|
|Ductile cast iron initial rolling roll, high strength and toughness, thermal cracking resistance and wear resistance are better than steel rolls||Primary roll|
|Semi-chilled cast iron rolls||Hardness drop is small, deep grooves can be opened||Large and medium-sized steel rolls, small rough rolls, hot-rolled pipe mill rolls|
|cast steel roll||High strength, but poor wear resistanceComposite cast iron rollers (cast steel inside) also belong to this category, with a slightly higher alloy content, and are more wear-resistant than ordinary cast steel||Preliminary rolls Large and medium-sized roughing stand rolls, hot-rolled strip backup rolls, vertical rolls, piercing mill rolls|
|semi-steel roll||Both strength and wear resistance, small drop in hardness, can open deep grooves, there are also forged products in this category, high strength, can reduce roll breakage accidents||Small and medium load primary rolls, various section steel rolls, various hot-rolled strip work rolls, hot-rolled tube rolls|
|forged steel roll||For hot rolling, strength quotient, not easy to stick to rolls (for non-ferrous metals)For backup rolls, high strength, wear-resistantFor cold rolling, it has high strength, good wear resistance and surface quality, and the steel type varies according to the application||Bloom rolls, hot non-ferrous metal rolls, backup, cold work rolls|
|High chromium steel roll||Good musk resistance, high strength and toughness||Work rolls before rough rolling and finish rolling of hot-rolled strip steelCold-rolled strip work rollsSmall and wire finishing rolls|
|Tungsten Carbide Rolls||Excellent wear resistance, minimal elastic flattening, and high surface precision of the roll||Small round steel, grain steel and wire rod rolls, high-speed wire rod mill roll rings, twenty-high mill work rolls|