The Additional Processing Steps In The Manufacture Of Cold Rolled Sheets

The Additional Processing Steps In The Manufacture Of Cold Rolled Sheets

The cold-reduced coil, as it exists, is very hard and possesses very limited applicability. It is very stiff and exhibits high amounts of spring back when bent. Therefore, this steel must be annealed (heated to high temperatures) to soften it and make it useful.

During the process of heating, the steel will be soft and can subsequently be used for a multitude of applications. Continuous annealing involves passing the steel through a high-temperature furnace in the form of a continuous ribbon. That is to say, the coil is fed from a payoff reel into the furnace. It reaches a high temperature when its passage through the furnace. The steel sheet cooled, and recoiled at the exit end of the furnace.

Whether the steel is batch annealed or continuously annealed, the specific properties of the steel sheet, after annealing, depend on the steel chemistry, the temperatures used during hot rolling, the amount of cold reduction, and the annealing cycle (time and temperature).

Whichever method of annealing is used, the steel is maintained under a protective (non-oxidizing) atmosphere using hydrogen and nitrogen to prevent oxidizing the steel while it is at high temperature. Furthermore, to prevent oxidation, the protective atmosphere is designed to clean the steel by breaking down the oils that are present after cold rolling and entraining the oil vapors in the hydrogen/nitrogen gases that are passed through the furnace.

The New Method Of Combining Emulsion And Neat Oil Lubrication In Cold Rolling Lubrication

The New Method Of Combining Emulsion And Neat Oil Lubrication In Cold Rolling Lubrication

One of the key processes in cold rolling is known as the cooling and lubrication process(cold rolling lubrication), it is not only determined the surface quality and strip shape but also reduced the rolling power consumption, and extends the life of the roll even during high-speed operation. 

As we discussed, a new method combining emulsion lubrication and neat oil lubrication was applied to solve the problems related to individual passes. Plenty of tests on stainless steel strips came to the conclusion that this new lubrication method can improve the surface quality of the strip, and control the rolling friction in the deformation zone, and it has the great potential of making lubrication systems simpler, easier to operate, all those while reducing the negative environmental impact from the processing. 

In direct supply lubrication, oil and water are mixed and then sprayed on the strip surface in the inlet zone directly, and there is a separate cooling system, therefore is most of them used for high-quality, tinned thin strips. 

Recirculated supply lubrication, as we knew, is mainly used for relatively thick strips and an emulsion sprayed on the roll and the strip acts as both a coolant and a lubricant.

However, in combined supply lubrication, the high-concentration emulsion is sprayed on the strip, and the low-concentration is sprayed on the rolling process. As generally known, high-concentration emulsions are better at cooling. Both of them are circularly used for relatively thick strips.

Although the above two methods have their merits, with the growing consumer demand for different types of high-quality products and the need for increased production, improvements in cooling and lubrication method are necessary and inevitable. So, the new method of lubrication that combines neat oil and emulsion lubrication takes advantage of its merits.

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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.

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.

Please contact stella@hanrm.com for a quotation.
And free send inquiry to us.
Email: stella@hanrm.com   stellarollingmill@gmail.com
Whatsapp/Wechat:+8615877652925

Hot Rolling VS Cold Rolling

 

Hot Rolling VS Cold Rolling

Both hot rolling and cold rolling are the forming processes of section steel or steel plate. They have a great influence on the structure and properties of steel. The rolling of steel is mainly hot rolling, and cold rolling is only used to produce small section steel and thin plate. 

Hot Rolling

Advantages: 

It can destroy the casting structure of ingot, refine the grain size of steel and eliminate the defects of microstructure so that the structure of steel is compact and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction so that the steel is not isotropic to a certain extent. The bubbles, cracks, and porosity formed during pouring can also be welded under the action of high temperature and pressure. 

Disadvantages: 

1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) in steel are pressed into thin sheets, resulting in stratification (interlayer). Layering deteriorates the tensile properties of steel along the thickness direction, and interlaminar tearing may occur when the weld shrinks. Local strain induced by weld shrinkage often reaches several times of yield point strain, which is much larger than that caused by the load.

2. Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress without external force. Hot rolled section steel of various sections has such residual stress. The larger the section size of general section steel, the larger the residual stress. Although the residual stress is self-balanced, it has some influence on the performance of steel members under external forces. For example, it may have adverse effects on deformation, stability, and fatigue resistance. 

Cold Rolling

Cold rolling refers to the process of cold drawing, cold bending, and cold drawing of steel sheets or strips into various types of steel at room temperature.

Advantage:

With fast forming speed, high yield, and no damage to the coating, it can be made into various cross-section forms to meet the needs of service conditions. Cold rolling can make steel produce large plastic deformation, thus improving the yield point of steel. 

Disadvantage:

1. Although there is no hot plastic compression in the forming process, there are still residual stresses in the section, which will inevitably affect the overall and local buckling characteristics of steel;

2. Cold-rolled section steel generally has an open section, which makes the free torsional stiffness of the section lower. Torsion is easy to occur in bending, flexural-torsional buckling is easy to occur in compression, and torsional resistance is poor;

3. Cold-rolled formed steel has a smaller wall thickness and no thickening at the corner of the plate connection, so it has a weak ability to withstand local concentrated loads.

The main differences between hot rolling and cold rolling as following:

Local buckling of the cold-rolled section is allowed to take full advantage of the post-buckling bearing capacity of members, while local buckling of the hot-rolled section is not allowed.

The causes of residual stresses in hot rolled and cold rolled sections are different, so the distribution of residual stresses in sections is also very different. The distribution of residual stress on the section of cold-formed thin-walled steel is bending, while that on the section of hot-bonded steel or welded steel is a thin film.

The free torsional stiffness of hot-rolled section steel is higher than that of cold-rolled section steel, so the torsional resistance of hot-rolled section steel is better than that of cold-rolled section steel.

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