The deformation process is completed by rolling the billet into the product required by the customer. The rolling process plays a decisive role in the quality of the product.
Rolled product quality includes: product geometry, dimensional accuracy, internal organisation, process mechanical properties and surface finish and several other aspects. Therefore, the rolling process must be based on product technical standards or technical requirements, production product characteristics and production technology and equipment capabilities, as well as production costs and labour conditions of workers and other aspects of the requirements, the development of the corresponding rolling process technical regulations and process management system. To ensure that the quality of rolling products and technical and economic indicators to achieve the most optimal
The billet section compression, semi-finished rolling deformation and finished product rolling functions, respectively. Finished mill hole type or finishing hole type for K1 holes, finished before the mill hole type for K2 holes, finished before the mill hole type for K3 holes, and so on below.
Continuous rolling mill and continuous rolling constants? Continuous rolling mill is a number of rolling mill seat in the direction of the rolling order into a line, rolling in several mills at the same time, rolling deformation, rolling speed of each frame with the increase in the length of the rolled parts and increase, and keep the metal in each mill in the second flow of equal or have a slight pile of pulling steel relationship rolling method called continuous rolling mill. Continuous rolling mill with high mechanization, automation, rolling speed and rolling accuracy, and thus high labour productivity and excellent product quality, is the bar, wire rod mill transformation and new direction. Keep the rolling unit time through the rolling volume of each mill equal rolling called continuous rolling.
Continuous rolling constants = F1D1N1= F2D2N2= F3D3N3= FnDnNn
Where: F – section area of the roll mm2
D-roll working diameter mm
N – number of roll revolutions (1/min)
The cold bed is the main cooling equipment for rolled bar products. The loose cooling rollway is the main cooling equipment for wire rod products.
The role of the cold bed and the loose cooling roller conveyor is to cool the high temperature rolled parts above 800°C to below 150-100°C in order to restore the inherent physical properties of the steel and to facilitate the quality of the shear and the operation of the subsequent processes.
The cooling methods are based on the chemical composition of the steel, the state of the organisation, the use of the application, and the defects that may arise after cooling, etc. The following cooling methods are identified.
Natural air cooling? Natural air cooling is a more common cooling method for carbon structural steel, low alloy structural steel, high quality carbon structural steel, and austenitic stainless steel, etc. This cooling method generally does not affect the physical properties of steel.
Forced rapid cooling? Forced rapid cooling is generally used to blow, spray, spray water and other methods, the process is characterised by a certain time to make the steel fast cooling to a certain temperature before the natural cooling. This cooling method can generally change the internal structure of the steel, which can affect the physical properties of the steel. Such as improving the mechanical properties of ordinary wire; eliminating steel reticulated carbides, etc.
Controlled slow cooling? The steel is generally cooled by controlled slow cooling, such as high-speed tool steel, martensitic stainless steel, high-alloy tool steel and high-alloy structural steel. This cooling method can prevent the steel organisation from changing and stress concentrating to produce cracking defects.
The rolling process of steel shearing: to cut off parts of the steel that affect its use (defects) such as the head and tail of the steel; to cut it to
the length required by the user.
Steel shearing equipment is divided into cold shears and hot shears. Hot shears are commonly used for cutting heads, tails or multiples of shears for semi-finished products.
Cold shear is often used for finished steel cutting head, tail or fixed (through) foot shear.
Steel inspection is a key Rolling process to ensure that the quality of the product meets the technical standards and technical conditions of the product. Product inspection usually includes: steel dimensions, surface quality, length, weight deviation, Rolling process properties, mechanical properties, etc. Steel that does not meet product quality standards must be picked out and sorted.
Common surface defects and preventive measures Rod and wire products are usually specified to have no surface defects such as cracks, folds, lugs, scars, delamination and inclusions
Characteristics: The surface of the billet or steel shows varying depths and dispersion of hairline, generally unevenly arranged along the rolling direction.
Causes: continuous casting billet subcutaneous bubbles, surface porosity, non-metallic inclusions, uneven heating temperature, steel temperature is too low or improper cooling after rolling (such as high-quality carbon structural steel).
Preventive measures: steelmaking should be good steel smelting and degassing work, reduce the temperature of steel, the use of protective casting, to avoid secondary oxidation; rolling steel should be reasonable control of furnace temperature and cooling rate.
Features: the steel surface along the rolling direction of the local longer or continuous near-crack defects. Generally in a straight line.
Causes: rolled semi-finished products appear ears, serious scratches or holes after the wrong roll rolling and then rolling the corner parts can not extend the expansion and cause.
Preventive measures: reasonable control of semi-finished rolling size, the production process should often use a wooden stick to check the roll seam on both sides of the rolling piece with or without ears and hole type wrong roll phenomenon; pay attention to observe the running condition of the rolling piece.
Characteristics: Steel roll seam on both sides or a single side along the rolling direction overfilled resulting in a local or continuous raised state.
Causes: finished before the hole rolled large material; import guide guard bias, loose, rolled incorrect support; roll axial movement; uneven heating or temperature is too low; finished hole type wear with a step bump.
Preventive measures: reasonable control of the heating furnace and semi-finished products size; strict adjustment of the guide device; improve the precision of the mill pre-assembly; regular quantitative reverse hole type.
Characteristics: The steel surface is lumpy or fish scale, uneven thickness, irregular shape of the “tongue-shaped” or “nail-shaped” scars. Closed or not closed; with or without roots. The scars usually have an iron oxide skin underneath. A warped scar is also known as a warped skin.
Causes: billets with scars, heavy skin, inclusions and other defects; semi-finished rolled parts with local bumps; hole block or trachoma; hole scoring or poor welding scars; rolled parts in the hole slip; external metal rolled into the surface of the rolled parts; semi-finished rolled parts by external objects scratched.
Preventive measures: unqualified billets are not allowed into the furnace; hole type to take the scoring or welding scars, scoring, welding scar shape and height should be smooth and round; strengthen the quality of roll inspection; reasonable hole design; low temperature, black head steel rolling is strictly prohibited; frequent inspection of hole wear and timely reverse hole type; roll delivery equipment and running place should be neat and smooth.
Characteristics: Steel surface with local or intermittent gouge marks, generally straight or arc-shaped.
Causes: improper processing and installation of inlet and outlet guides or scuffing of the rolling mill delivery equipment; unfavourable rolling off slot.
Preventive measures: the correct processing, installation, use of import and export guide facilities; rolled parts delivery equipment and running place should be neat and round.
Features: steel surface with local periodic or irregular concave defects.
Causes: rolling hole type with bumps or adhering with iron oxide; steel surface without root scar off; foreign metal items substituted into the hole type by rolling off the formation.
Preventive measures: hole cooling water should be clean, the amount of water should be sufficient; billet quality qualified; production environment free of debris.
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