Vertical Bright Annealing (BA) Furnace for Stainless Steel Coil Tube
Product Overview
The Vertical Bright Annealing (BA) Furnace is an advanced heat treatment system developed by Wenzhou Jixing Metal Materials Co., Ltd. specifically designed for the bright annealing of stainless steel coil tubes (Coiltube). Unlike conventional horizontal annealing furnaces that rely on roller transport systems, this vertically oriented furnace utilizes gravitational force as the primary mechanism for coil tube movement through the heating and cooling zones. This innovative design eliminates contact-induced surface defects such as roller marks (roller impressions), delivering an exceptionally superior surface finish that meets the most demanding aesthetic and functional requirements in high-end stainless steel tube manufacturing.
As a critical process in the production of high-grade stainless steel coil tubes, the Bright Annealing furnace operates under a controlled reducing atmosphere, simultaneously achieving grain structure refinement, stress relief, and surface brightening without the formation of scale or oxide layers that would require subsequent pickling or mechanical polishing.
Material & Properties
Applicable Materials
- Austenitic Stainless Steels: AISI 304, 304L, 316, 316L, 321, 310S
- Duplex Stainless Steels: 2205, 2507
- Super Austenitic Grades: 904L, 6Mo
- Custom Alloys: Tailored compositions for specialized applications
Post-Annealing Mechanical Properties
- Grain structure refinement with uniform equiaxed grains
- Complete residual stress elimination from cold forming operations
- Improved ductility and formability for downstream processing
- Maintained yield strength and tensile strength in compliance with ASTM/ISO standards
- Superior corrosion resistance restored through full recrystallization
Surface Quality Achievements
- Surface Roughness (Ra): ≤ 0.2 μm achievable for mirror-grade applications
- Zero roller marks (roller impressions) — a distinguishing advantage over horizontal furnace systems
- Uniform surface brightness across the entire coil tube length
- No decarburization or scale formation under controlled atmosphere conditions
Specifications
| Parameter | Specification |
|---|---|
| Furnace Orientation | Vertical (Gravity-Driven Transport) |
| Maximum Tube Outer Diameter (OD) | Up to 1020 mm (configurable per project requirements) |
| Maximum Coil Weight Capacity | Up to 15,000 kg (dependent on tube dimensions and grade) |
| Heating Zone Temperature | 800°C – 1200°C (adjustable per material grade) |
| Temperature Uniformity | ± 10°C across heating zone |
| Atmosphere Type | Reducing atmosphere (H₂/N₂ mixture or endothermic gas) |
| Atmosphere Dew Point | ≤ -60°C (dew point control) |
| Heating Method | Induction heating or electric resistance heating |
| Control System | PLC-based automated temperature and atmosphere control |
| Heating Rate | Programmable, typically 50–200°C/hour |
| Cooling Rate | Controlled air cooling or forced convection cooling |
| Surface Finish After BA | 2B / BA / Mirror (HL) — depending on incoming surface condition |
| Energy Efficiency | High-efficiency thermal insulation with heat recovery system |
| Applicable Standards | ASTM A213, ASTM A269, EN 10216-5, GB/T 12771 |
Manufacturing Process
Process Flow
- Coil Loading: The stainless steel coil tube is loaded onto the vertical furnace's upper suspension mechanism. The coil is centered and secured using a non-contact gripping system to prevent surface damage.
- Pre-Heating: The coil tube is gradually pre-heated in a controlled atmosphere to avoid thermal shock and ensure uniform temperature distribution throughout the tube wall thickness.
- Recrystallization Heating: The furnace temperature is raised to the target annealing temperature (typically 1050°C–1150°C for austenitic grades). The coil tube moves downward through the heating zone via gravitational force, ensuring continuous and uniform exposure.
- Soaking: The coil tube is held at peak temperature for a specified duration to achieve complete recrystallization, grain refinement, and stress relief. The vertical orientation ensures uniform heat distribution without localized hot spots caused by roller contact.
- Controlled Cooling: The coil tube descends through the cooling zone under controlled atmosphere conditions. The cooling rate is precisely regulated to prevent re-precipitation of carbides and maintain optimal microstructure.
- Discharge & Coiling: The annealed coil tube is unloaded at the furnace base and re-coiled for downstream processing (cold drawing, polishing, cutting, or direct delivery).
Unique Process Advantages — Vertical BA Furnace
- Gravity-Uniform Heat Treatment: The vertical configuration leverages gravitational force for continuous, uninterrupted coil movement. This eliminates the stop-and-go transport mechanism inherent in horizontal furnaces, resulting in more uniform thermal exposure and consistent annealing quality across the entire coil length.
- Zero Roller Marks: Since the coil tube is suspended and moves freely under gravity, there is absolutely no mechanical contact with rollers, rolls, or transport mechanisms. This is the most critical differentiator for applications requiring pristine surface quality.
- Superior Surface Integrity: The absence of mechanical contact combined with a meticulously controlled reducing atmosphere ensures that the as-annealed surface retains its original finish quality. For mirror-grade applications, the surface roughness remains at or below the pre-annealing level.
- Enhanced Throughput: The continuous vertical movement enables higher production rates compared to batch-type or intermittent horizontal furnaces, particularly for large-diameter coil tubes.
- Reduced Energy Consumption: The vertical design allows for optimized thermal insulation geometry and heat recovery, resulting in lower energy consumption per ton of annealed product.
Applications
Primary Application Segments
- High-End EP (Electro-Polished) Tube Mother Pipe: The vertical BA furnace produces coil tubes with exceptional surface uniformity and microstructural homogeneity, serving as the ideal feedstock for electro-polishing processes. The absence of roller marks and surface defects ensures that the electro-polishing process achieves consistent, high-quality results without requiring extensive pre-polishing or pickling.
- Mirror Tube (Mirror-Finish Tube) Production: Dedicated to the manufacture of mirror-finish stainless steel tubes used in architectural applications, decorative interiors, and high-end consumer products. The vertical BA process preserves the surface finish through the entire annealing cycle.
- Medical Device Tubes: Tubes for medical equipment manufacturing requiring stringent surface cleanliness, corrosion resistance, and mechanical properties.
- Food & Pharmaceutical Industry: Process tubes and heat exchanger tubes where surface quality directly impacts product safety and regulatory compliance.
- Ornamental & Architectural Tubes: High-grade decorative tubes for building facades, interior design elements, and luxury applications.
- Precision Instrumentation: Tubes used in scientific instruments, analytical equipment, and laboratory apparatus requiring both mechanical precision and surface quality.
Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System compliance
- Product Standards: ASTM A213 (Seamless Ferritic, Austenitic, and Precipitation-Hardening Stainless Steel Tubing for High Temperature Service), ASTM A269 (Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service), EN 10216-5 (Stainless Steel Tubes for General Purposes), GB/T 12771 (Stainless Steel Seamless Tubes for Fluid Transportation)
- Material Certifications: EN 10204 3.1/3.2 material test certificates available upon request
- Surface Quality Testing: Ra surface roughness measurement, visual inspection under standardized lighting, and colorimetric evaluation
- Metallurgical Testing: Grain size analysis, tensile testing, hardness testing, and intergranular corrosion testing (ASTM A262 Practice E/A)
- Atmosphere Quality Monitoring: Continuous dew point monitoring and oxygen potential measurement to ensure process integrity
Key Differentiator: The Vertical BA Furnace represents a paradigm shift in stainless steel coil tube annealing technology. By eliminating all mechanical contact during the heat treatment process, it delivers a surface quality and microstructural uniformity that is unachievable with conventional horizontal furnace systems. This makes it the definitive solution for manufacturers of high-end EP tube mother pipe and mirror-finish tubes where surface integrity is non-negotiable.