Rolling Mill

In metalworking , rolling is a metal forming process in which a metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to provide a desired mechanical property. . The concept is similar to the rolling of dough . Rolling is classified according to the temperature of the metal being rolled. If the temperature of the metal is above its recrystallization temperature, the process is known as hot rolling . If the temperature of the metal is lower than its recrystallization temperature, the process is known as cold rolling., In terms of usage, hot rolling processes more tonnage than any other manufacturing process, and cold rolling processes the highest tonnage of all cold working processes. [1] [2] Roll stands are pairs of rolls grouped together in rolling mills that convert metals, usually steel , into products such as structural steel ( I-beams , angle stock, channel stock), bar stock , and rails . can be processed quickly. , Most steel mills have rolling mill divisions that convert semi-finished casting products into finished products.

There are several types of rolling processes, including ring rolling , roll bending , roll forming , profile rolling , and controlled rolling .

iron and Steel

The invention of the rolling mill in Europe can be attributed to Leonardo da Vinci in his paintings. [3] The earliest rolling mills in crude form but the same basic principles were found in the Middle East and South Asia as early as 600 BC. The earliest rolling mills were slitting mills, which were introduced to England from Belgium in 1590 . These used to pass flat bars between rolls to form iron plates, which were then passed between grooved rolls (slitters) to make iron rods. [4] The first experiments on rolling iron for tinplate occurred about 1670. In 1697, Major John Hanbury built a mill at Pontypool .To roll ‘pontypool plates’ – blackplate . Later it was rolled and tinned again to make tinplate . In Europe, earlier plate iron was not produced in rolling mills, but in forges.

The slitting mill was adapted for the production of hoops (for barrels) and iron with half-rounds or other sections, which was the subject of two patents of c. 1679.

Some of the early literature on rolling mills can be traced back to the Swedish engineer Christopher Polheim in his Patriista Testament of 1761 , where he mentions rolling mills for both plate and bar iron. [5] He also explains how rolling mills can save time and labor as a rolling mill can produce 10 to 20 or more bars at the same time.

In 1759, Thomas Blockley of England was granted a patent for the polishing and rolling of metals. Another patent was granted in 1766 to Richard Ford of England for the first tandem mill. [6] A tandem mill is one in which the metal is rotated in successive stands; Ford’s tandem mill was for heating wire rods.

other metals

Rolling mills for lead seem to have come into existence by the end of the 17th century. By the end of the 18th century copper and brass were also rolled.

modern rolling

The pioneering efforts of modern rolling practice can be attributed to Henry Cort of the Funtley Iron Mills, near Fareham in Hampshire , England. In 1783, a patent was issued to Henry Court for the use of grooved rolls to rotate iron bars. [7] With this new design, mills were able to produce 15 times more per day than hammers. [8] Although Cort was not the first to use grooved rolls, he was the first to combine the use of many of the best features of various ironmaking and shaping processes known at the time. Thus modern writers have called him “the father of modern trend”.

The first rail rolling mill was established in 1820 by John Birkenshaw at Bedlington Ironworks in Northumberland , England , where he produced fish-bellied wrought iron rails 15 to 18 feet in length. [8] With the advancement of technology in rolling mills, there was a rapid increase in the size of rolling mills as well as an increase in the size of the products. An example of this was at The Great Exhibition in London in 1851 , where a plate measuring 20 feet long, 3 1/2 feet wide and 7/16 inch thick and weighing 1,125 pounds was displayed by the Concett Iron Company . [8]Further development of the rolling mill occurred in 1853 with the introduction of three-high mills, which were used to roll heavy sections.

hot and cold rolling

hot rolling

Hot rolling is a metalworking process that occurs above the recrystallization temperature of the material. After the grains deform during processing, they recrystallize, which maintains a fine equiaxed metal and prevents work hardening. The starting material is usually large pieces of metal, such as semi-finished casting products, such as slabs, blooms and billets. If these products came from a continuous casting operation the products are usually fed directly into rolling mills at the appropriate temperature. In smaller works, the material starts at room temperature and must be heated. This is done in a gas or oil-powered soaking pit for large workpieces; For small workpieces, induction heating is used. As the material is working, the temperature must be monitored to ensure that it remains above the recrystallization temperature. one to maintain a safety factorThe finishing temperature is defined as above the recrystallization temperature; This usually occurs at 50 to 100 °C (90 to 180 °F) above the recrystallization temperature. If the temperature drops below this temperature the material must be reheated before further hot rolling. [9]

Hot rolled metals generally have very little direction in their mechanical properties and deformation induced residual stresses. However, in some cases non-metallic inclusions will provide some directionality and workpieces less than 20 mm (0.79 in) thick often have few directional properties. In addition, non-uniform cooling will induce a lot of residual stresses, which usually occurs in shapes that have a non-uniform cross-section, such as I-beams. While the finished product is of good quality, the surface is covered in mill scale, which is an oxide that forms at high temperatures. It is usually removed through the pickling or smooth clean surface (SCS) process, revealing a smooth surface. ^[10] Dimensional tolerance is usually 2 to 5% of the overall dimension. ^{[11 1]}

It seems that hot-rolled mild steel has a wider tolerance for the amount of carbon involved than cold-rolled steel, and is, therefore, more difficult for a blacksmith to access. Also for similar metals, hot-rolled products seem to be less expensive than cold-rolled products. 

Hot rolling is mainly used to produce sheet metal or simple cross-sections such as rail tracks. Other specific uses of hot rolled metal: ^[13]

• truck frame
• Automotive Clutch Plates, Wheels and Wheel Rims
• pipe and tube
• water heater
• farm equipment
• strappings
• Stamping
• compressor shells
• metal buildings
• Railroad Hopper Car And Railcar Components
• doors and shelving
• Disc
• Guard Rails for Roads and Highways

shape rolling design

Rolling mills are often divided into roughing, intermediate and finishing rolling cages. During shape rolling, an initial billet (round or square) with an edge diameter typically between 100–140 mm is continuously deformed to produce a definite finished product with small cross section dimensions and geometry. Starting with a given billet different sequences can be adopted to produce a certain final product. However, since each rolling mill is quite expensive (up to 2 million euros), a specific requirement is to contract the number of rolling passes. Various approaches have been acquired, including empirical knowledge, the employment of numerical models, and artificial intelligence techniques. Lambius et al. ^[14] [15]Validated a finite element model (FE) to predict the final shape of a rolled bar in a round-flat pass. One of the major concerns when designing rolling mills is minimizing the number of passes. One possible solution to such requirements is the slit pass , also known as a split pass , which splits the incoming bar into two or more subsections, thus reducing the cross section reduction ratio per pass as reported by Lambius. Actually enhances. ^[16] Another solution to reduce the number of passes in rolling mills is the use of automated systems for roll pass design as proposed by Lambius and Langella. ^[17]Later, Lambius developed an automated system based on artificial intelligence, and in particular an integrated system, consisting of an inference engine based on genetic algorithms, a knowledge database based on artificial neural networks trained by a parametric finite element model, and To optimize and design automatically. rolling mills. ^[18]

cold rolling

Cold rolling occurs with the metal below its recrystallization temperature (usually at room temperature), which increases strength through stress hardening by up to 20%. It also improves surface finish and has tighter tolerances. Commonly cold rolled products include sheets, strips, bars and rods; These products are usually smaller than the same products that are hot rolled. Because of the smaller size of the workpieces and their greater strength, compared to hot rolled stock, four-high or cluster mills are used. ^[2] Cold rolling cannot reduce the thickness of a workpiece as much as hot rolling in a single pass.

Cold-rolled sheets and strips come in a variety of conditions: full-hard , half-hard , quarter-hard , and skin-rolled . Full-hard rolling reduces the thickness by up to 50%, while others have less reduction. Cold rolled steel is annealed to induce ductility in cold rolled steel which is known as cold rolled and close annealed . skin-rolling, also called skin-closeAlso known as , contains the least reduction of: 0.5-1%. It is used to produce a smooth surface, uniform thickness, and reduce yield point phenomena (by preventing Luder bands from forming in post-processing). This closes the dislocations on the surface and thereby reduces the possibility of Luder band formation. It is necessary to create a sufficient density of unpinned dislocations in the ferrite matrix to avoid the formation of Luders bands. It is also used to break up spangles in galvanized steel. Skin-rolled stock is typically used in subsequent cold-working processes where good ductility is required.

If the cross-section is relatively uniform and the transverse dimension is relatively small, other shapes can be cold-rolled. Cold rolling shapes require a series of shaping operations, usually along the lines of shaping, cracking, roughing, semi-roughing, semi-finishing and finishing.

If processed by a blacksmith, the smoother, more consistent and lower levels of carbon contained in steel make it easier to process, but at the cost of being more expensive. ^[19]

Typical uses of cold rolled steel include metal furniture, desks, filing cabinets, tables, chairs, motorcycle exhaust pipes, computer cabinets and hardware, home appliances and components, shelving, lighting fixtures, hinges, tubing, steel drums, lawn mowers, Electronics are included. Cabinetry, water heaters, metal containers, fan blades, frying pans, wall and ceiling mount kits, and a variety of construction-related products. ^[20]

Procedures

roll bending

Roll bending plate or steel produces a cylindrical shaped product from metals. ^[21]

Making Role

Making Role

Roll forming, roll bending or plate rolling is a continuous bending operation in which a long strip of metal (usually coiled steel) is passed through a successive set of rolls, or stands, of only an incremental portion of each turn. perform, until the desired cross-section profile is obtained. Roll forming is ideal for producing long lengths or large quantities of parts. There are 3 main processes: 4 rollers, 3 rollers and 2 rollers, each of which has different advantages according to the desired specifications of the output plate.

flat rolling

Flat rolling is the most basic form of rolling with starting and ending materials having a rectangular cross-section. Material is fed between two rollers , called working rolls , which rotate in opposite directions. The gap between the two rolls is less than the thickness of the starting material, causing it to deform. The material becomes elongated due to the decrease in the thickness of the material. Friction at the interface between the material and the roll causes the material to be pushed through. The amount of deformation possible in a single pass is limited by the friction between the rolls; If the change in thickness is too great the rolls just slip over the material and don’t stretch it in. ^[1]The final product is either a sheet or a plate, with the former less than 6 mm (0.24 in) thick and the latter being greater; However, heavy plates are manufactured using a press, which is called forging , rather than rolling . ^{[ citation needed ]}

The roll is often heated to aid the workability of the metal. Lubrication is often used to keep the workpiece from sticking to the rolls. ^{[ citation needed ]} To fine-tune the process, the roll speed and the temperature of the rollers are adjusted. ^[22]

h is sheet metal with a thickness of less than 200 microns (0.0079 in). ^{[ citation needed ]} Rolling is done in a cluster mill because smaller thicknesses require smaller diameter rolls. ^[9] To reduce the need for smaller rolls, pack rolling is used, which rolls multiple sheets together to increase the effective initial thickness. As the sheets of foil come through the rollers, they are trimmed and cut with a circular or razor-like knife. Trimming refers to the edges of the foil, while cutting involves cutting it into multiple sheets. ^[22]Aluminum foil pack is the most commonly produced product through rolling. This is evident from the two different surface finishes; The shiny side is on the roll side and the dull side is against another sheet of foil. ^[23]

ring rolling

Ring rolling is a special type of hot rolling that increases the diameter of the ring . The starting material is a thick-walled ring. The workpiece is placed between two rolls, an inner idler roll and a driven roll , which press the ring outward. As rolling occurs, the wall thickness decreases as the diameter increases. Rolls can be shaped to form various cross-sectional shapes. The resulting grain structure is peripheral, providing better mechanical properties. The diameter can be as large as 8 m (26 ft) and the height of the face can be up to 2 m (79 in). Common applications include railway tyres, bearings, gears, rockets, turbines, airplanes, pipes and pressure vessels. ^[10]

structural shape rolling

Cross-sections of continuously rolled structural figures showing the changes induced by each rolling mill.

controlled rolling

controlled rollingIs a kind of thermomechanical processing integrating controlled deformation and heat treatment. The heat that brings the workpiece above the recrystallization temperature is also used to heat treatment so that any subsequent heat treatment is unnecessary. Types of heat treatment include production of fine grain structure; Controlling the nature, size and distribution of various transformation products (such as ferrite, austenite, pearlite, bainite and martensite into steel); hard rain inducing; and, controlling hardness. To achieve this the entire process must be closely monitored and controlled. Common variables in controlled rolling include starting material composition and structure, deformation level, temperature at various stages, and cool-down conditions. The benefits of controlled rolling include improved mechanical properties and energy savings. ^{[11 1]}

forge rolling

Forge rolling is a longitudinal rolling process that reduces the cross-sectional area of ​​hot bars or billets by moving them between two opposite rotating roll segments. The process is primarily used to provide optimized material delivery for subsequent die forging processes. Due to this better material utilization, less process force and better surface quality of parts can be achieved in die forging processes. ^[24]

Basically any forgeable metal can also be forge-rolled. Forge rolling is primarily used to preform long-scale billets through targeted mass distribution to parts such as crankshafts, connection rods, steering knuckles and vehicle axles. The narrowest manufacturing tolerances can only be partially achieved by forge rolling. This is the main reason why forge rolling is rarely used for finishing, but mainly for preforming. ^[25]

Features of Forge Rolling: ^[26]

• High productivity and high material utilization
• Good surface quality of forge-rolled workpieces
• Extended Tool Life-time
• Smaller equipment and lower equipment costs
• Better mechanical properties due to optimized grain flow especially compared to die forged workpieces

mills

A rolling mill , also known as a reduction mill or mill , has a general construction that is independent of the specific type of rolling:

• work roll
• Backup Roll – Intended to provide the rigid support required by the working roll to prevent bending under rolling load
• Rolling Balance System – to ensure that the upper work and back up roll are maintained in the proper position relative to the lower roll
• Roll changing equipment – use of an overhead crane and designed to attach a unit to the neck of the roll which can be removed or inserted from the mill.
• Mill protection device – to ensure that forces applied to backup roll chocks are not of such magnitude as to fracture the roll neck or damage the mill housing
• Roll Cooling and Lubrication System
• Pinion – gear to split power between two spindles, rotating them at the same speed but in different directions
• Gearing – to set the desired rolling speed
• Drive Motors – Rolling Narrow Foil Product to Thousands of Horsepower
• Electrical control – constant and variable voltage applied to motors
• Coiler and Uncoiler – for opening and rolling metal coils

Slabs are the feed material for hot strip mills or plate mills and feed billets in large sections in a billet mill or structural mill. The output from the strip mill is coiled and, later, used as feed for a cold rolling mill or directly used by fabricators. The billets are then rolled in a merchant, bar or rod mill for re-rolling. Merchant or bar mills produce a variety of shaped products such as angles, channels, beams, rounds (long or coiled) and hexagons.

layout

Mills are designed in a variety of configurations, with the most basic being two-high non-reversing , meaning there are two rolls that only turn in one direction. There are two high aft mill rolls that can rotate in both directions, but the disadvantage is that the roll must be stopped, reversed, and then brought back to rolling speed between each pass. To solve this, three-highThe mill was invented, which uses three rolls rotating in one direction; The metal is fed through two rolls and then returned through the second pair. The disadvantage of this system is that the workpiece must be raised and lowered using a lift. All of these mills are commonly used for primary rolling and roll diameters range from 60 to 140 cm (24 to 55 in). ^[9]

A four-high or cluster mill is used to reduce the roll diameter . A smaller roll diameter is beneficial because less roll is in contact with the material, resulting in less force and power requirement. The problem with a smaller roll is the decrease in stiffness, which is overcome by using a backup roll . These backup rolls are larger and contact with the rear of the smaller roll. A four-height mill has four rolls, two small and two large. A cluster mill consists of more than 4 rolls, usually in three tiers. These types of mills are commonly used for heating wide plates, for most cold rolling applications and for rolling foil. ^[9]

Historically mills were classified by the product produced: ^[28]

• Blooming, cogging and slabbing mills are the initial mills for rolling a finished rail, shape or plate, respectively. If reversed, they are 34 to 48 inches in diameter, and if three-tall, 28 to 42 inches in diameter.
• Billet mills, three-height, 24- to 32-inch diameter rolls used to reduce flowers to 1.5×1.5-inch billets, are newpreparatory mills for bars and rods.
• Beam mills, three-height, 28 to 36 inches in diameter, roll to produce heavy beams and channels 12 inches and up.
• Roll rail mills from 26 to 40 inches in diameter.
• Shape sills with rolls of 20 to 26 inches in diameter for smaller sizes of beams and channels and other structural shapes.
• Get merchant bars with rolls of 16 to 20 inches in diameter.
• Small merchant bar mills with finishing rolls 8 to 16 inches in diameter are usually arranged with a larger roughing stand.
• Rod and wire mills with finishing rolls 8 to 12 inches in diameter are always arranged with a sizable roughing stand.
• Hoop and cotton tie mills, similar to small merchant bar mills.
• Meet armor plates with a diameter of 44 to 50 inches and a body roll of 140 to 180 inches.
• Mill plates with 28 to 44 inch diameter rolls.
• Mill sheets in rolls of 20 to 32 inches in diameter.
• Universal mills for the production of square-edge or so-called universal plates and various wide flanged shapes by a system of vertical and horizontal rolls.

tandem mill

A tandem mill is a special type of modern rolling mill where rolling is done in a single pass. In a conventional rolling mill, rolling is done in several passes, but in a tandem mill there are several stands (>=2 stands) and the cuts are sequential. The number of stands ranges from 2 to 18. Tandem mills can be of hot or cold rolling mill type.

Defects

In hot rolling, if the workpiece temperature is not uniform, the material flow will be higher in the hot parts and less in the cooler. If the temperature difference is high enough, cracking and tearing may occur. ^[9]

flatness and shape

In a flat metal workpiece, flatness is a descriptive characteristic indicating the extent of geometric deviation from a reference plane. Deviation from perfect flatness is a direct result of workpiece relaxation after hot or cold rolling, due to the non-uniform transversal compressive action of the roll and the internal stress pattern caused by the uneven geometrical properties of the entering material. The transverse distribution of differential stress/elongation-induced stress with respect to the average applied stress of the material is commonly referred to as the size. Because of the strict relationship between shape and flatness, these terms can be used interchangeably. In the case of metal strips and sheets, Flatness refers to the differential fiber elongation across the width of the workpiece. This property must be subject to a precise reaction-based control to guarantee the machinability of the metal sheets in the final transformation processes. Here are some technical details about the feedback control of flatness.^[29]

profile

The profile is made up of crown and wedge measurements. The crown is thicker at the center than the average thickness at the edges of the workpiece. Nail is a measure of thickness on one edge as opposed to the other. Both can be expressed as an absolute measure or a relative measure. For example, one might have a 2 mil crown (the center of the workpiece is 2 mil thicker than the edges), or one might have a 2% crown (the center of the workpiece is 2% thicker than the edges).

It is generally desirable to have some crown in the workpiece as this will pull the workpiece towards the center of the mill, and thus move with higher stability.

flatness

It is difficult to maintain a uniform gap between the rolls because the rolls deflect under the load required to deform the workpiece. The deflection causes the workpiece to become thinner at the edges and thicker in the middle. This can be overcome by using a crowning roller (parabolic crown), although a crowned roller will only compensate for a set condition, particularly material, temperature and amount of deformation. ^{[11 1]}

Other methods of compensating for roll deformation include Continuous Differential Crown (CVC), pair cross rolling and work roll bending. CVC was developed by SMS-Cimag AG and involves grinding third-order polynomial curves into work rolls and then moving the work rolls laterally, evenly and oppositely to each other. This has the effect that there will be a gap between the rolls that is parabolic in shape, and will vary with lateral shift, thus allowing the crown of the roll to be dynamically controlled. Pair cross rolling involves using crown rolls flat or parabolically, but shifting the ends at an angle so as to increase or decrease the gap between the edges of the roll, thus allowing for dynamic crown control. Work roll bending involves using hydraulic cylinders at the ends of the rolls to counteract roll deflection.

Another way to address deflection issues is to reduce the load on the roll, which can be done by applying a longitudinal force; This is essentially a drawing. Other methods of reducing roll deflection include increasing the elastic modulus of the roll material and adding a back-up support to the roll. ^{[11 1]}

There are various classifications for flatness faults:

• Symmetrical edge wave – The edges on both sides of the workpiece are “wavy” because the material at the edges is longer than the material in the center.
• Asymmetric edge wave – An edge “wavy” as the material on one side is longer than the other.
• Middle Buckle – The center of the bandage is “wavy” because the bandage in the center is longer than the bandage at the edges.
• Quarter Buckle – This is a rare defect where the fibers are elongated in the quarter regions (the part of the strip between the center and the edge). This is usually attributed to using excessive roll bending force as the bending force cannot compensate for the roll deflection across the entire length of the roll.

It is important to note that a flatness defect can occur even with workpieces of equal thickness in width. In addition, one may have a fairly high crown or wedge, but still produce material that is flat. To produce flat material, the material must be reduced in width by the same percentage. This is important because the mass flow of the material must be conserved, and the more the material shrinks, the longer it elongates. If a material is uniformly elongated in width, the flatness at the mill will be preserved at the exit of the mill.

draft

The difference between the thickness of the initial and the rolled metal piece is called the draft. Thus if is the initial thickness and is the final thickness, then the draft is given by

t_{0}t_{f}d

d=t_{0}-t_{f}

The maximum draft which can be achieved by means of rollers of radius between the roller and the metal surface with the coefficient of static friction is given by

Rf

d_{max}=f^{2}R

This is the situation when the frictional force on the metal from the inlet contact matches the negative force from the exit contact.

surface defect type

There are six types of surface defects: Lap This type of defect occurs when a corner or wing is bent and rolled but not welded into the metal. ^[31] They appear as seams on the metal surface. grinding mill These defects are in the form of feather-like lap. rolled-in scale This occurs when the mill scale is driven into the metal. scabs These are long patches of loose metal that are rolled into the surface of the metal. fast They are open, broken lines that run along the length of the metal and are caused by the presence of scale as well as the roughness of the roughing mill. slivers Major surface breakage.

surface defect prevention

Many surface defects can be removed from the surface of semi-finished rolled products before further rolling. Methods of scarring include hand chisels (18th and 19th centuries); Peeling and grinding operated with air chisel and grinder; burning with an oxy-fuel torch, the gas pressure of which blows molten metal or slag from the flame; and laser scarring.