What is Hot Rolling?

What is Hot Rolling?

Rolling mill is a metalworking process which divided into two types: hot rolling and cold rolling. Here we will analyze the hot rolling cause we had discussed cold rolling before.

In many theory books, which called hot rolling is a metalworking process that occurs above the recrystallization temperature of the material. On the contrary, it means that below the recrystallization temperature of the metalworking process is called cold rolling.

But what is hot rolling besides of this word. Here we have the detail explanation about it. After the grains deform during processing, they recrystallize, which maintains an equiaxed microstructure and prevents the metal from work hardening. The starting material is usually large pieces of metal, like 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 the rolling mills at the proper temperature. In smaller operations, the material starts at room temperature and must be heated. This is done in a gas- or oil-fired soaking pit for larger workpieces and for smaller workpieces induction heating is used. As the material is worked the temperature must be monitored to make sure it remains above the recrystallization temperature. To maintain a safety factor, finishing temperature is defined above the recrystallization temperature; this is usually 50 to 100 °C (90 to 180 °F) above the recrystallization temperature. If the temperature does drop below this temperature the material must be re-heated before more hot rolling. All of this above, just part of the hot rolling actually.

Hot rolled metals generally have little directionality in their mechanical properties and deformation induced residual stresses. However, in certain instances, non-metallic inclusions will impart some directionality and workpieces less than 20 mm (0.79 in) thick often have some directional properties. Also, non-uniformed 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 the forms at high temperatures. It is usually removed via pickling or the smooth clean surface; process, which reveals a smooth surface.  Dimensional tolerances are usually 2 to 5% of the overall dimension.

Hot rolled mill steel seems to have a wider tolerance for amount of included carbon than cold rolled, making it a bit more problematic to use as a blacksmith. Also for similar metals, hot rolled seems to typically be less costly.

Hot rolling is used mainly to produce sheet metal, rebar, wire rod or other products. In a words, hot rolling is very popular used in the steel industry.

Since 1989 Hani Tech has been always involved in design, engineering, manufacturing and installation of complete hot rolling mill plant for long products (re-bars, SBQ bars, wire rod, small and medium sections), as well as revamping and upgrading of existing plants. 

Hani Tech is the one-stop manufacturer & supplier able to design, manufacture, install and commission your hot rolling mill plant from A to Z.

Bar & Wire Rod Rolling Mill Production Line Process Flow (Complete Version)

Bar & Wire Rod Rolling Mill Production Line Process Flow (Complete Version)

1. Bar Rolling Mill Production Line Process Flow 

Billet acceptance → reheating → rolling →double length shear → cooling → shear → inspection → packaging → metering → warehousing

2. Process Flow of Wire Pod Production

Billet acceptance → reheating →rolling → laying head → bulk coil cooling → coil collection → coil pressing → inspection → packaging → metering → warehousing

The process of acceptance, reheating and rolling of billet in wire rod production is basically the same as that of bar mill production, but the cooling of wire rod is carried out by the scattered cooling roller. The cooled bulk wires need to be collected into discs by the coiler and then compacted by the coiler and packed in small discs. Then the inspection classification is packed into large bales and measured in storage.

3. Analysis and Treatment of Bar and Wire Rod Production Process Fault

Can not rolling

1. Causes: 

1.Rolled piece rotten head, split head, black head, etc. 

2. Improper or too small installation of inlet guide; 

3.There are sticky iron or foreign bodies in the inlet guide; 

4. The roll over angle is too large or too small; 

5.Rolling guide wheel does not rotate or bearing burns out; 

6.Roll does not turn due to breakage or connection; 

7.Improper adjustment of roll gap or unsatisfactory size of incoming material; 

8. Roll pass friction coefficient is too small (new pass), etc.

2. Analysis and Treatment and Preventive Measures

(1) Analyse the reason why the rolled piece is not in progress, strengthen the inspection of the head defect of the rolled piece and dispose of it in time;

(2) After installation of the inlet guide, measure the width and dimension of the inlet cavity with the internal caliper; Illuminate with light and check whether the inlet guide is centered on the hole pattern from the outlet direction and tighten the guide bolts;

(3) Check and measure the solid size of the rolled piece with calipers to ensure the correct size of incoming material;

(4) Roll gap size is strictly adjusted according to rolling requirements;

(5) Check rolling guide wheel and twist outlet frequently and replace in time; Check import guide regularly for sticking of iron night and depositing of iron oxide scale or debris;

(6) New hole pattern shall be tested with small material first.

Rolling Heap Failure

Steel heap failure refers to stagnation after accumulation of rolled pieces between rolling mills or rolling mills, which is called steel heap failure.

1. Causes

A. The size and section area of incoming roll are too large; The rolled piece itself has surface or internal quality defects.

B. The friction coefficient of roll pass is not enough, causing slippage of the rolled piece;

C. Volume flow per second of incoming mill is greater than that of receiving mill.

D. Electrical control system is wrong or out of control.

E. Installation of mechanical running part or photoelectric control instrument of automatic looper system is wrong, out of control or out of function.

2. Analysis and Treatment and Preventive Measures

A. Adjust the size and area of incoming material to satisfy the reasonable continuous rolling constant relation;

B. Monitor the running condition of the rolled piece dynamically and tightly and adjust it in time;

C. Ensure the quality of the ingot; Disposal of semi-finished rolled parts with quality defects in time;

D. Check the rotational speed, looper system and electrical control system of each rolling mill regularly to ensure the stable and normal running equipment and electrical control system.

Steel Pulling Failure of Rolled Parts

Steel pulling failure refers to the phenomenon that the rolled pieces are too tight or broken between rolling mills or rolling mills, which is called steel pulling failure. Due to the failure of steel drawing, the dimension of the rolled piece often changes, and even the shape dimension or roundness of the finished product is out of tolerance, causing scrap.

1. Causes

A. The size and section area of incoming roll are too small;

B. Volume flow per second of incoming mill is less than that of receiving mill.

C. Electrical control system is wrong or out of control.

2. Analysis and Treatment and Preventive Measures

A. Adjust the size and area of incoming material to satisfy the reasonable continuous rolling constant relation.

B. Ensure that the electrical and electronic control equipment systems work properly.

What Is Steel Rolling Mill Machinery?

What Is Steel Rolling Mill Machinery?

The steel rolling mill machinery is a mechanical device that realizes the metal rolling process. It refers to the equipment that completes the whole process of rolling material production, including main equipment, auxiliary equipment, lifting transportation equipment and auxiliary equipment.

Steel rolling mill machinery can be divided into two parts: main rolling mill equipment and rolling mill auxiliary equipment.

Steel Rolling Mill Machinery Main Equipment

The main equipment of the steel rolling mill machinery includes the main motor, the working machine base and the main transmission (reducer, gear base, coupling, coupling shaft, etc.).

The steel rolling mill machine working machine seat is composed of a roll, a roll bearing, a frame, a rail seat, a roll adjusting device, an upper roll balancing device and a roll changing device.

Steel Rolling Mill Machinery Auxiliary Equipment

Auxiliary equipment for steel rolling mill machinery includes:

Transport equipment, such as the roller conveyor for longitudinal transport of rolled products, the lifting platform for transporting rolling stock in the vertical direction, and the steel pulling machine and steel moving machine for transversely transporting rolled stock.

Processing equipment, such as shearing machines (flying shear, gripping shear) and hot saw machines for cutting rolled products, straightening machines for straightening rolled products, and coilers for taking up rolled products.

Other finishing equipment, such as a steel turning machine for reversing rolling stock, a rotary table for revolving rolling stock, and a cooling bed for cooling rolled products.

And various mechanical equipment used in the processes of collection, pickling, printing, packaging, etc.

In general, the higher the degree of mechanization, the greater the proportion of auxiliary equipment weight to the total weight of the rolling mill workshop machinery.

Therefore, the degree of application of auxiliary equipment is also one of the important signs of the degree of mechanization of the rolling process.

High-Speed Wire Rod Mill Production Line Process Flow

High-speed Wire Rod Mill Production Line Process Flow

Billet preparation: 150 mm *150 mm *14 000 mm continuous casting billet.

Reheating furnace: The billet is heated to austenite temperature to facilitate rolling. 

High-pressure water descaling: After the billet is heated in the reheating furnace, before entering the roughing rolling mill, it is necessary to descaling with high-pressure water to remove the oxide scale and secondary oxide scale on the billet surface, so as to avoid defects on the pressed surface. 

Roughing mill, medium rolling mill, and finishing rolling mill rolling: the size of finished products, including 6 roughing rolling mills, 6 medium rolling mills, 4 pre-finishing mills, 10 finishing mills, a total of 26 rolling mills on this high-speed wire rod mill production line.

Flying shear head and tail: Before entering each set of rolling mills, the work of cutting head and tail must be carried out in order to remove the head with too low temperature to avoid damage to the roll surface and prevent the head of the rolling piece from being stuck in the inter-stand guide device. The stuck shear is used to crush and break the rolling event before the medium rolling mill, the pre-finishing mill and the finishing mill in the accident state.

Water cooling: In order to reduce the rolling temperature entering the finishing mill, a water tank is set before the finishing mill to control the finishing temperature. 

Rolling: Rolled wires are rolled into rolls after cooling through water, forming loose rolls through spinning.

Stelmore uncoiled cooling: The cooling speed of the controlled cooling line is controlled according to different steel grades and product uses, so as to obtain the corresponding product quality. 

Finishing and transportation: including coiling, dressing, inspection, sampling, baling and rolling, weighing and hanging tags, using the coiling device to collect loose rolls, and hanging them on the C-hook on the P-S transport line, completing the process of coiling, dressing, inspection, sampling, baling and rolling, weighing and hanging tags in turn, and then unloading and entering the warehouse.

What is Walking Beam Cooling Bed?

What is Walking Beam Cooling Bed?

Walking Beam Cooling Bed Introduction: 

(1) The Usage of Walking Beam Cooling Bed: Arranged behind the rolling mill for cooling of finished steel and bar products. Cooling finished product specifications Φ10 ~ 40mm rebar, Φ10 ~ 50mm round steel. The steel grade is plain carbon steel, excellent carbon steel, and low alloy steel. The speed of the large finished product is 16m/s and the annual production capacity is 600,000 tons.

(2) The rolling mill cooling bed type is the walking beam type of the rack. The effective size of the bed is 96000×9500mm. The large length of the steel is 90m, the pitch of the tooth is 100mm, the thickness of the rack is 18mm, the spacing of the static rack is 300/600mm, and the distance between the racks is 300/. 600mm.

(3) Walking beam cooling bed input roller: roller diameter Φ188mm, roller length 190mm, roller distance 1200mm, inclination angle 12°, drive type single machine drive, variable frequency speed regulation, irreversible, roller line speed 4.5~20m/s(max), motor YVPG100L2-4 , 2.2KW, 1500rpm, each motor with axial flow fan 125FZY2-S, 25W, 220V, 50HZ, the number of 115; 6 free rolls.

(4) Walking beam cooling bed dial-in mechanism: the width of the dial-in block is 150mm, the length of the dial-in block is 138m, the angle between the dial-in block and the horizontal is 35°, the angle between the dial-in block and the vertical is 12°, and the speed of the dial-in block is 0.15~0.3m/s. The dial-in block is lifted and hydraulic cylinder Φ63/Φ45x90. Pneumatic gear cylinder QGAIIΦ80×20-MP4, 1; compressed air working pressure 0.4~0.6Mpa, cycle 4s~12s.

(5) Walking beam cooling bed surface drive: main motor Z4-280-21, 132kW, speed 750/1600rpm, 2 sets; photoelectric encoder LAKESHORE, 2; reducer A=508mm, I=41, 4 sets; eccentric wheel eccentricity 50mm. The rack moves once the steel stroke by 100mm.

(6) Alignment roller path: roller diameter Φ225/165mm, roller length 810mm, effective number of teeth 6, roller surface speed V=1.1m/s, roller spacing 1200mm; reducer BWD1.5-18-11, I=11 , motor Y90L-4, 1.5KW, 1400rpm, the number is 45; the number of free rollers is 18.

(7) Chain type steel transfer machine: Transfer steel specifications ф12 ~ ф50mm. The length of the steel is 90m, the width of the chain transfer machine is 1500mm, the chain spacing is 1200mm, the chain speed is 0.2m/s, the stepping distance is 20~70mm, the transmission motor is YTSP160M-4, 11KW, 1500rpm, AC380V, 2 sets. The center distance of the reducer is 349mm, the transmission ratio is I=1:75, and the number is 2.

(8) Transport trolley: the width of the trolley is 1000mm, the lifting time of the trolley is 1~2s, the round-trip speed of the trolley is ~0.5m/s, the transmission motor: YTSP132S-4, 5.5KW, 1500rpm, AC380V, 2 sets, reducer: A=349mm, I = 1:45, 2 sets. The trolley is lifted and used with a hydraulic cylinder.

(9) Output roller path: roll diameter: Φ188 mm, roll length: 1000 mm, roll distance: 1200 mm, roll line speed: 2 m/s, number of rolls 86, 6 free rolls. Roller motor: YGb112L2-4, 1.5KW, 1450rpm, AC380V, 80 units, reversible.

What Should The Rolling Mill Need To Pay Attention To During The Shutdown?

What Should The Rolling Mill Need To Pay Attention To During The Shutdown?

In the production process of the rolling mill, what should be noticed after the rolling mill is shut down when there is a downtime overhaul or an unexpected situation?

1. After the rolling mill stops, stop the feeding of steel, and take the gas cutting and cutting out of the online rolling parts to avoid the stress on the rolls and cause damage.

2. If the rolling mill needs long-term shutdown, the best method is to open the lubrication system to keep the main bearing lubricated, and then close it in to avoid dust and debris entering the bearing.

3. Cut off the power supply of the rolling mill and auxiliary equipment.

4. Drain the water in the cooling tube to avoid freezing the cooling water pipe when it is cold.

5. Protect the lubrication system, motor, air clutch and slow drive from dust, but not tightly sealed to avoid moisture accumulation. Use a small heater or protect the bulb to prevent moisture buildup.

6. Place bagged desiccant in all control and electrical panels to prevent moisture build-up and safely seal the control panel.

The above need to pay attention to is that the rolling mill production enterprises need to pay special attention to it. Only when the rolling mill is under maintenance, the rolling equipment can better complete the production task during the production period, improve the rolling efficiency and extend the usage time of rolling mill.

What's The Difference Between Hot Rolling And Cold Rolling?

What's The Difference Between Hot Rolling And Cold Rolling？

Hot rolling has the following characteristic, low intensity, good extension, the surface is not shinning.

Cold rolling has the following characteristic, high intensity, high hardness, shining surface.

Hot rolling mill: though high heating, then rolling it to the certain structure.

Cold rolling mill: not heating, in common temperature, normally below critical point.

The mechanical property through hot rolling and cold rolling is different.

Cold rolling is in low hardness, easy to process, with good intention, easy to form cold stress, hot rolling is for high hardness, high intention, difficult to process, not easy to deformation. 

Hot rolling needs to be heated, normally temperature should above the critical point, the processing is under high temperature, make the steel recrystallization happen, but not changing the steel structure.

Cold rolling is under normal temperature, roll it into aiming thickness, compare with hot rolling , cold rolling has high accuracy, smooth surface, better mechanic characteristic, especially processability, because the raw material of cold rolling is very crisp and hard, not suitable for processing, normally, cold rolling steel plate should be acid pickling and surfacing, then can send them to final customer.

The difference between cold rolling and hot rolling is not in the process, but the temperature, hot rolling is easy to roll, and high efficiency, but hot rolling makes steel oxidation, surface gray and not shining; cold rolling requires high power motor, low efficiency, high cost, but with very shining surface, can be used as the final product directly, widely used.