1.What are the core standards and their classifications?
Standard Precision (PT.A)
Higher Precision (PT.B)
Many large steel mills (such as Baosteel and Ansteel) typically have stricter enterprise standards than national standards, and further subdivide them into grades. Common grades include:
Standard Grade
High Grade (or "Stamping Grade")
Ultra-High Grade (or "Fine Stamping Grade")
2.What impact do specific tolerance ranges have?
Width Influence: For the same thickness, the wider the steel coil, the more difficult it is to roll, and the tolerance will be appropriately relaxed. For example, the tolerance value for materials with a width > 1500mm will be slightly larger than that shown in the table above.
Condition Influence: The above tolerances usually refer to finished steel products in the "annealed + leveled" state. For coils in the "cold-hardened" state, the thickness tolerance will be stricter because the slight changes that annealing may bring are omitted.
"Same-Plate Difference": In addition to the above "deviation from nominal thickness," there is another important indicator called "same-plate difference," which refers to the thickness difference between the beginning, middle, and end, or the edge and middle of a steel plate or coil. High-grade materials also have strict requirements for this.
3.What are the key factors affecting thickness fluctuations?
Mill Capacity: Modern six-high HC/UCM mills offer significantly higher control precision than older four-high mills. The presence of an AGC (Automatic Thickness Control) system is crucial.
Raw Material (Hot-Rolled Coil) Quality: The thickness uniformity of hot-rolled incoming material is fundamental to cold-rolling precision.
Rolling Process: The stability of rolling force, tension, and speed directly affects instantaneous thickness fluctuations.
Roll Condition: The grinding precision, thermal crown control, and wear condition of the rolls.
Annealing and Leveling: The annealing process may produce slight adhesion or yield plateaus, requiring leveling to improve sheet shape and thickness uniformity.
4.How do I determine your specific permitted scope?
Review the contract and technical agreement: This is the most fundamental basis. The contract must clearly specify:
Product standards (e.g., GB/T 708-2019, or enterprise standards Q/BQB, etc.)
Precision grade (e.g., PT.B, or "High")
Special requirements (e.g., "Thickness controlled by three-point difference")
Consult the supplier: Obtain the corresponding grade and specification's "Product Tolerance Table" from the steel mill or large distributor.
Select the grade as needed:
Ordinary structural parts, cabinets: Ordinary precision (PT.A) is usually sufficient.
General stamped parts, electrical panels: Higher precision (PT.B) is recommended.
Deep-drawn parts, precision components, high-end appearance parts: "High" or "Ultra-High" precision must be selected and specified in the contract.
5.What suggestions do you have?
Thickness tolerance in cold-rolled coils is a systematic, graded specification. For most commercially available cold-rolled sheets (such as SPCC, approximately 1.0 mm thick), a high-precision (PT.B) tolerance of approximately ±0.05 mm to ±0.07 mm is a common control level.
Our key advice: When conducting procurement or technical verification, never simply ask "What is the thickness tolerance?" Instead, clearly state:
"Delivery according to [standard number], [grade], thickness [specific value] mm, width [specific value] mm, [precision class], please provide the permissible thickness deviation value."