1.What is the essence of the Kaiping process?
The function of a leveling line (straightening machine) is to correct the shape of sheet metal, not to eliminate internal stress in the material. Its working principle involves repeatedly bending and deforming the steel sheet through a series of staggered rollers to achieve visual and measurable flatness.
This process actually redistributes internal stress: it transforms the originally uneven residual stress that caused sheet defects (such as waviness, camber, and warping) into a new, more uniform stress equilibrium. However, this equilibrium is "mechanical" and "forced," not it eliminates stress at its source.
2.What are the requirements for high-precision machining and dimensional stability?
Precision stamping/drawing: If the leveled sheet metal requires complex forming processes such as deep drawing or fine drawing, residual stress will be released during the forming process, leading to dimensional errors, shape distortion, slip lines (Lüders band), or orange peel texture. Stress-relief annealing can significantly improve forming stability.
High-precision machining: When used for precision mechanical parts, the rebalancing of internal stresses during machining can cause slow deformation of the workpiece, compromising machining accuracy. Stress relief treatment is essential beforehand.
As a substrate for molds or gauges: Extremely high long-term dimensional stability is required; internal stress must be completely eliminated.
3.What are the subsequent processing requirements involving high heat input?
Welding: This is the most common and intense requirement. Localized heating during welding generates enormous thermal stress, which, combined with the existing residual stress in the sheet metal, can easily lead to severe distortion and warping of the welded parts. Stress-relieving annealing of the sheet metal before welding is one of the most effective means of controlling welding deformation.
Laser Cutting/Plasma Cutting: Although the heat-affected zone is smaller, residual stress can still affect the shape of the cut sheet, especially for high-precision, thin-plate, or complex-shaped cuts.
4.What is the original state of cold-rolled coil?
Fully hardened (unannealed) cold-rolled coils: These have severe internal work hardening and extremely high residual stress levels. Although leveled, the material is very hard and has poor plasticity, making it virtually impossible to perform any forming processes. Recrystallization annealing (not only to relieve stress but also to restore plasticity) is necessary first, and then a secondary leveling may be required depending on the situation.
Annealed state (common commercial coils): These have already undergone annealing and have lower residual stress. Whether they meet usage requirements after leveling depends mainly on points 1 and 2 above.
5.Are there any special requirements for surface quality and mechanical properties?
Stress-relief annealing is typically performed at lower temperatures (below the recrystallization temperature, such as 550-650℃). Although slight oxidation may occur, it maintains the material's hardness essentially unchanged. If complete oxidation elimination and a glossy surface are required, bright annealing is necessary.