Section steel pass design sets the foundation for shaping profiles on universal rolling mills. تتحكم ممرات الدرفلة المخصصة التي يتم تشكيلها على لفات في الشكل النهائي لمنتجات الصلب. تشرح هذه المقالة ثلاثة مفاهيم أساسية: استطالة, انتشار وتوزيع التشوه.
1. What Is a Rolling Pass for Section Forming
A pass refers to the cavity machined on rolls, with a shape matching the cross-section of rolled stock. When two rolls close, the pass restricts metal flow and gradually shapes the workpiece into the target profile pass by pass.
Key components: adjustable roll gap, collar lock (anti-twist), fillet radius (reduce stress and avoid cracks), roll collar (separate passes and bear axial force).
2. Elongation Coefficient: Pass Reduction Allocation
Elongation coefficient μ = incoming cross-sectional area / outgoing cross-sectional area. Total elongation equals the product of elongation coefficients of all passes. It determines the total number of passes from billet to finished product.
| Allocation Principle | Explanation |
|---|---|
| Bite limitation | The elongation of the first pass cannot be excessive, restricted by the maximum bite angle. |
| Descending distribution | Heavy reduction in early passes and lighter reduction in later passes. Smaller sections show higher deformation resistance, so elongation decreases gradually. |
| Equal strength / equal load | Balance rolling force of each pass to maximize equipment capacity. |
3. Spread: Metal Flow Control
Under compression, metal flows longitudinally (استطالة) and transversely (الانتشار). Three spread classifications:
- Free spread: No side constraint, such as flat rolls and early box passes.
- Restricted spread: Confined by pass sidewalls, widely adopted for sections (butterfly passes, universal passes).
- Forced spread: Specially shaped passes force metal to expand, used for flange forming.
Engineers estimate spread via empirical and semi-empirical models (Bakhtinov, Gubkin formulas). Restricted spread dominates section rolling. Precise control based on pass geometry is essential. Improper control causes insufficient flange filling or fin defects.
4. Deformation Distribution: Core Design Difficulty
The biggest design difficulty lies in coordinated deformation between webs and flanges. Within one single pass, both web and flange elongate and expand. Their metal flows interfere with each other.
Poor distribution leads to various defects: web cracking due to excessive thinning, incomplete flange filling, fins or folds.
Designers distribute elongation for each part following constant metal volume rules. Coordinated deformation of webs and flanges in every pass brings billets closer to finished dimensions. This is the core problem solved by universal pass systems and rolling simulation.
5. Common Pass Systems Used in Section Steel Pass Design
| Pass System | Typical Application |
|---|---|
| Box pass | Breakdown rolling, large reduction and scale removal |
| Diamond-square / جولة بيضاوية | Square bars and round steel |
| Butterfly pass | Form flanges of channel steel and I-beams |
| Angle pass | Equal and unequal angle steel |
| Universal pass | عوارض H, القضبان الفولاذية, bulb flat steel (discussed in Chapter 2.2) |
6. Complete Design Workflow
Section decomposition → Pass system selection → Confirm pass schedule and elongation → Spread calculation & deformation distribution → Pass dimension calculation → Check bite condition and roll collar strength → Modification based on trial rolling