The essence of the backup roll is to support the work roll, and the work roll can reduce the diameter of the work roll and increase the rigidity of the work roll through the contact of the work roll. The backup roll is an important part of the rolling mill, used to support the work roll or the intermediate roll, in case the work roll is deflected and deformed, which affects the output and quality of the plate and strip. The quality characteristics of the back-up roll are high surface hardness, good hardness uniformity, deep hardened layer of the roll body, good strength and toughness of the roll neck and the body of the roll body; the quality characteristics of the back-up roll are high wear resistance, peeling resistance Good and accident resistant.
With the development of high-speed, large-scale, and high-precision cold and hot rolling mills, the requirements for backup rolls are also increasing. In view of the requirements of hard layer depth and residual stress, it is more appropriate to choose forged steel backup rolls. Compared with composite cast steel backup rolls, forged steel backup rolls have the characteristics of uniform material, better wear resistance, and peeling resistance. Large forged steel backup rolls are high-value-added products with high technical requirements, complex processes, difficult manufacturing, many production processes, and long cycle times. Therefore, only a few enterprises can produce them.
Back-up roll working conditions and performance requirements
1. During the rolling process, the backup rolls support the work rolls to ensure high rigidity and small deformation of the work rolls. Therefore, the backup rolls should have good stiffness.
2. During use, the backup roll is always in rolling contact with the work roll or the intermediate roll, which is very prone to work hardening. When overloaded, the local yield causes subcutaneous micro-cracks at the bottom of the hardened layer, and the expansion of the micro-cracks eventually causes the roll body to peel off. The backup roll is required to have high contact fatigue strength, reasonable stress state, and crack growth resistance.
3. The middle part of the backup roll will form a concave shape due to wear, and the contact stress at both ends of the roll body will increase sharply, resulting in peeling. Therefore, the roll is required to have excellent wear resistance to delay and reduce the formation of the concave roll shape.
4. The service life of the backup roll is long, and the roll neck is subjected to alternating bending stress for a long time. In order to prevent the roll neck from breaking, the roll neck is required to have good yield strength, toughness, and fracture resistance.
In a word, the perfect combination of the high wear resistance, high yield strength, and high peeling resistance of the roll body and the high strength, high toughness, and fracture resistance of the roll neck is the necessary performance of the backup roll
Production technology and equipment of large forged steel backup roll
The production process of large forged steel backup rolls is as follows:
Raw materials→steelmaking (electric furnace smelting, ladle refining)→vacuum ingot casting→forging→post-forging heat treatment→rough machining→first ultrasonic flaw detection→preparatory heat treatment (quenching and tempering)→semi-finishing→second ultrasonic flaw detection→final heat treatment (Quenching and tempering of the surface of the roll body)→finishing→comprehensive inspection (including final ultrasonic flaw detection)→painting and delivery