Qingdao Xinshengyuan Roller Co.,Ltd.

Hot rolling and cold rolling are two important metal processing methods in the metallurgical industry, the following is their detailed introduction:

Hot rolling

· Definition: Hot rolling is the process of metal working by heating a metal material to a high temperature above the recrystallization temperature so that it has good plasticity and low deformation resistance, and then rolling it into a product of the desired shape and size by applying pressure to the metal through the roll of the rolling mill to produce plastic deformation.

· Process features

· Good shaping: metal materials have good plasticity at high temperature, which is conducive to the processing of large deformation, and can realize the forming of complex shapes and the production of large-size products.

· Low deformation resistance: due to the low deformation resistance of the material at high temperature, the rolling force required in the rolling process is relatively small, which reduces the load of the rolling equipment and is conducive to the smooth rolling process.

· Recrystallization: in the hot rolling process, the metal deformation at the same time will occur dynamic recrystallization, can eliminate the work hardening phenomenon, fine grain structure, improve the comprehensive mechanical properties of the material.

· Application: Hot rolling is widely used in the production of various kinds of steel products, such as hot rolled steel plate, hot rolled profiles, hot rolled steel pipes and so on. These products are widely used in construction, machinery manufacturing, automotive industry and other fields. For example, hot-rolled steel is often used in construction and bridge construction; Hot rolled profiles are used to manufacture mechanical parts and steel structures.

Cold rolling

· Definition: Cold rolling is a metalworking process that causes plastic deformation of metallic materials at or near room temperature. It is usually carried out after hot rolling, and the hot rolled product is further processed to improve the dimensional accuracy and surface quality of the product.

· Process features

· High precision size: cold rolling can precisely control the size of the product, the thickness, width and length tolerances are very small, can meet some special industries for high precision requirements of metal materials.

· Excellent surface quality: the surface of the product after cold rolling is smooth, bright, and has few surface defects, which is very suitable for the application scenarios with high surface quality requirements, such as the production of automotive panels and electrical shell.

· Work hardening: in the cold rolling process, due to the large deformation of the material at room temperature, the work hardening phenomenon is obvious, the strength and hardness of the material are increased, but the plasticity and toughness are reduced.

· Application: Cold rolled products are widely used in precision machinery parts manufacturing, electronic components production, auto parts manufacturing and high-grade building materials and other fields. For example, cold-rolled steel is an important material in the manufacture of automobile bodies and home appliance casings; Cold-rolled stainless steel strips are widely used in the production of kitchenware and decorative materials.

Temperature: Hot rolling is performed at high temperatures, while cold rolling is performed at or near room temperature. Surface quality: The surface of the cold-rolled material is smooth and the size is more accurate. Mechanical properties: Cold-rolled materials generally have higher strength and hardness, but lower plasticity and toughness. Cost: Low cost of hot rolling, high cost of cold rolling

Hot rolling and cold rolling as an important metal processing process, their main differences are as follows:

Working temperature

· hot rolling: The metal material is processed above the recrystallization temperature, taking steel as an example, usually the temperature is about 1000° C-1200 °C, so that the metal is in a state of high plasticity and low deformation resistance, which is convenient for large deformation processing.

· cold rolling: The metal is processed at or near room temperature (generally below 200°C) under the condition of high temperature, without the aid of high temperature, the plasticity of the metal is relatively poor, and the deformation resistance is large.

Equipment requirements

· Hot rolling: need to withstand high temperature and high rolling force equipment, equipment strength and heat resistance requirements are high, the structure is often large and complex to adapt to the high temperature environment of large deformation rolling.

· cold rolling: The precision of the equipment is very high, equipped with a precision control system, used to precisely control the size and surface quality of the product, while the equipment must be rigid enough to withstand large rolling forces.

Product characteristics

· Appearance and dimensions

· hot rolling: suitable for the production of large size, thick specifications of products, such as wide and thick steel plates, large profiles, but the product surface is relatively rough, large dimensional tolerances.

· cold rolling: mainly produces thin specification and high precision products, such as thin steel plate, narrow strip steel, etc. The product has smooth surface and high dimensional precision, which can meet the strict requirements of precision applications.

· mechanical properties

· Hot rolling: dynamic recrystallization occurs in the process of hot rolling, which refines the grain of the material, and the toughness and ductility of the product are good, but the strength and hardness are relatively low.

· cold rolling: due to the work hardening phenomenon, the strength and hardness of the product are greatly improved, but the plasticity and toughness are reduced compared with that of the hot-rolled product.

Production cost

· Hot rolling: The production process is relatively simple, the equipment cost is relatively low, but heating the metal to high temperatures requires a lot of energy, and the energy cost is high.

· Cold rolling: requires high-precision equipment and complex process, equipment investment and maintenance costs are high, but there is no need for high temperature heating, compared with hot rolling, energy consumption cost is lower.

Application scenario

· Hot rolling: widely used in the construction industry of steel structure, bridge construction, shipbuilding industry hull manufacturing, and general machinery manufacturing of large parts production, such as hot rolled I-steel for construction, hot rolled steel plate for shipbuilding.

· Cold rolling: It is mainly used in fields requiring high precision and surface quality, such as precision machinery manufacturing, electronic equipment manufacturing, body and parts production in automobile manufacturing, shell manufacturing in home appliance industry, such as cold-rolled steel plate for automobile body and cold-rolled steel strip in electronic equipment.

Hot and cold rolled alloy rolls have important applications in many fields, as follows:

Application field of hot rolled alloy rolls

· Iron and steel industry: used to roll billets into various hot rolled steels, such as medium plate, hot rolled coil, H-shaped steel, channel steel, Angle steel and other profiles, as well as bar, wire and so on. These hot-rolled steels are widely used in building structures, bridge construction, and large component manufacturing in machinery manufacturing.

· Non-ferrous metal industry: in the processing of aluminum, copper, nickel and other non-ferrous metals, used for hot rolling metal ingot or billet into sheet, strip, foil and so on. For example, in aluminum processing, aluminum ingots are hot-rolled into aluminum slabs to provide raw materials for subsequent cold rolling or other processing processes; In copper processing, hot rolling can produce copper strip billets for wire and cable, electronic components and other fields.

· Composite materials industry: For some metal matrix composites or other composites, hot rolled alloy rolls can be used to roll the composite body, densify it, improve the microstructure properties, and obtain a certain shape and size for aerospace, automotive and other fields of parts manufacturing.

Application field of cold rolling alloy rolls

· Automobile manufacturing industry: used to produce cold-rolled steel sheet and steel strip for automobile body. These cold-rolled products have high precision, good surface quality and mechanical properties, and can meet the requirements of lightweight, high strength and appearance quality of automobile body. It is also used to manufacture high-precision cold-rolled steel for automotive engines, transmissions and other parts.

· Home appliance industry: It is a key tool for the production of cold-rolled steel plates for home appliance shell, inner liner and other components. For example, the housing of refrigerators, washing machines, air conditioners and other home appliances is usually made of cold-rolled steel plates to obtain a flat, smooth surface and good formability.

· electronic industry: used for rolling the production of various precision parts of electronic equipment required metal materials, such as mobile phones, computers and other electronic products in the metal shell, shielding cover, connectors and other copper strip, steel strip, etc., the material is required to have extremely high dimensional accuracy, surface finish and good electrical conductivity, thermal conductivity and other properties

· Precision machinery manufacturing industry: providing high-precision cold-rolled steel for manufacturing precision machinery parts, such as various shaft, gear, CAM and other parts, cold-rolled alloy rolls can ensure the rolled materials with high dimensional accuracy and low surface roughness, which is conducive to improving the assembly accuracy and operation performance of precision machinery.

The use of alloy rolls is mainly based on its excellent performance in strength, wear resistance, corrosion resistance, thermal stability and other aspects, which can meet the high requirements of modern rolling processes for the following reasons:

Improve strength and toughness

· Withstand high rolling forces: In the rolling process, the roll needs to withstand huge rolling forces. Alloy roll by adding alloying elements, such as chromium, molybdenum, vanadium, etc., can form a special alloy structure, effectively improve the strength of the roll, so that it can maintain shape stability under high pressure, avoid deformation, fracture and other problems, to ensure the smooth rolling process.

· Adapt to complex conditions: the rolling roll will also be subjected to various impact loads during the rolling process, the high toughness of the alloy roll can make it difficult to crack when bearing the impact, improve the impact resistance of the roll, extend the service life of the roll, and reduce the risk of production interruption caused by roll damage.

Enhanced wear resistance

· Reduce wear and loss: there is strong friction between the roll and the metal material during rolling, and the ordinary roll is easy to wear in a short time, resulting in an increase in the surface roughness of the roll and a decrease in dimensional accuracy. The alloying elements added to the alloy roll can form hard point phases, such as carbide, nitride, etc. These hard point phases are distributed in the roll matrix, which greatly improves the hardness and wear resistance of the roll, reduces the wear rate of the roll, reduces the roll replacement frequency, and improves the production efficiency.

· Ensure product quality: roll wear will directly affect the surface quality and dimensional accuracy of rolled products. The use of alloy rolls can maintain the finish and dimensional stability of the roll surface, so as to produce rolled products with good surface quality and high dimensional precision, and meet the strict requirements of product quality in different industries.

Improved corrosion resistance

· Adapt to special environment: in some special rolling process, the roll may come into contact with corrosive media, such as lubricants and coolants used in some non-ferrous metal rolling process may contain corrosive components, or in some humid, acid and alkali and other corrosive atmosphere in the production environment, the ordinary roll is vulnerable to corrosion and damage. The chromium, nickel and other elements added to the alloy roll can form a dense oxide film on the surface of the roll, improve the corrosion resistance of the roll, so that it can work normally in the harsh working environment.

· prolonging service life: the improvement of corrosion resistance can effectively prevent the surface of the roll from peeling and rusting due to corrosion, keep the performance of the roll stable, extend the service life of the roll and reduce the production cost.

Improved thermal stability

· Resistance to thermal fatigue: in the process of hot rolling, the roll is repeatedly subjected to the cyclic action of high temperature and cooling, which is easy to produce thermal fatigue phenomenon, resulting in cracks and other defects on the roll surface. The alloying elements in the alloy roll can improve the thermal stability of the roll, enhance its ability to resist thermal fatigue, make the roll maintain good performance under high temperature environment, reduce the generation of thermal fatigue cracks, and extend the service life of the roll.

· Maintain dimensional accuracy: alloy rolls with good thermal stability are not easy to change and deform at high temperature, which can ensure the dimensional accuracy and shape accuracy of rolled products and improve product quality.