In the continuous casting process of iron and steel production, many prioritize the "explicit performance" of copper mould tubes—such as material composition and thermal conductivity—while overlooking a critical "invisible indicator": geometric accuracy. In reality, this accuracy directly determines whether continuous casting billets can form successfully: even with high-quality materials, a 0.2 mm deviation in inner diameter or 0.1% deviation in taper may cause billet square loss, surface depression, or catastrophic breakout accidents.
I. Why Geometric Accuracy Is the "Lifeline of Billet Forming"?
A single continuous casting machine processes hundreds of heats of molten steel daily, and each copper mould tubes operates in direct contact with 1300°C+ molten steel, enduring intense cooling from circulating water and frictional forces during billet withdrawal. Its inner wall profile and dimensional tolerances govern the "molten steel–copper tube–cooling water" balance:
- An oversized inner diameter leaves insufficient shrinkage space for molten steel, increasing steel adhesion risks.
- Uneven wall thickness causes localized overcooling (thinner sections) or undercooling (thicker sections), leading to surface cracks.
- Inaccurate taper creates fluctuating billet-tube gaps, disrupting cooling and elevating breakout risks.
Statistics from a large steel mill show defects from substandard geometric accuracy (e.g., square loss, bulging) account for over 35% of total billet defects. A single taper-induced breakout can shut down production for 2 hours, with direct losses exceeding RMB 100,000. This makes geometric accuracy a non-negotiable bottom-line requirement, not a "value-added feature."
II. Core Geometric Accuracy Indicators: Rigorous "Millimeter-Level" Standards
Copper mould tubes accuracy falls into three key categories, each stricter than conventional mechanical component standards:
1. Dimensional Tolerance: Minute Deviations, Severe Consequences
Critical for matching billet cross-sections and caster configurations:
- Inner diameter & length: For 150 mm×150 mm square billets, inner diameter tolerance is ≤±0.1 mm (149.9–150.1 mm); length tolerance aligns with mold height (≤±0.5 mm) to avoid jams or breakouts.
- Wall thickness uniformity: Full-length deviation ≤0.1 mm (e.g., 11.9–12.1 mm for 12 mm designed thickness) to ensure uniform cooling—deviations of 0.3 mm have caused 10% crack rates in single heats.
- Taper accuracy: Reverse taper (for shrinkage compensation) requires 0.4%–0.8%/m (square billets) or 0.2%–0.5%/m (slabs), with deviation ≤0.05%/m to prevent jamming or surface depressions.
2. Geometric Tolerance: Ensuring Structural Integrity
- Straightness: Full-length (2–4 m) deviation ≤0.1 mm/m (max 0.2 mm for 2 m tubes) to avoid uneven billet force and shape defects (e.g., rhomboidal square billets).
- Coaxiality: Inner-outer wall concentricity deviation ≤0.1 mm to prevent localized thinning and cooling issues.
3. Surface Quality: Preventing Scratching & Steel Adhesion
- Inner wall roughness: Ra ≤0.8 μm (mirror finish) to reduce friction and steel adhesion—Ra=1.6 μm causes micro-scratches and extra grinding costs.
- Defect-free requirement: No air bubbles, scratches, or inclusions (even 0.1 mm deep); outer walls must be dent-free to avoid cooling jacket gaps.
These rigorous standards demand reliable verification methods to ensure every tube meets operational needs. The following article will explore the key inspection technologies that underpin this quality assurance.