Stainless Steel Coil Tube — Intermediate Baking Oven Heat Exchanger
Product Code: JX-CT-495 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat transfer component specifically designed for intermediate baking oven systems in automotive paint coating processes. This product represents an advanced solution for improving thermal efficiency, reducing energy consumption, and extending service life in high-temperature industrial environments. The coil tube serves as the core heat exchange element, facilitating uniform heat distribution across the oven chamber during the intermediate drying and curing stages of automotive paint application.
Product Overview
Automotive paint coating processes require multi-stage thermal treatment, including pre-heating, intermediate baking, and final curing. The intermediate baking oven (Intermediate Baking Oven, IBO) plays a critical role in removing solvent residues and partially curing the paint film before the final cure. The stainless steel coil tube heat exchanger is the primary heat transfer medium within this system, carrying hot water or steam through coiled configurations to maximize the heat exchange surface area within a compact footprint.
The JX-CT-495 coil tube product incorporates design improvements derived from extensive engineering studies on heat exchanger optimization, including enhanced coil geometry, improved material selection for thermal cycling resistance, and refined manufacturing tolerances. These improvements address common industry challenges such as thermal fatigue cracking, scaling-induced heat transfer degradation, and uneven temperature distribution across the oven zone.
Key Design Philosophy
- Maximized Heat Transfer Surface: The coiled configuration provides a high surface-area-to-volume ratio, enabling efficient heat dissipation into the oven atmosphere.
- Thermal Fatigue Resistance: Material selection and manufacturing process are optimized to withstand repeated thermal cycling between ambient and operating temperatures of up to 250°C.
- Compact Integration: The coil geometry allows dense packing within oven boundaries without obstructing airflow patterns critical for uniform paint drying.
- Maintainability: Modular coil assembly design facilitates replacement of individual sections without full system shutdown.
Material & Properties
Primary Material Grades
The coil tube is fabricated from austenitic stainless steel grades selected for their combination of thermal stability, corrosion resistance, and mechanical integrity under sustained high-temperature exposure. The following grades are available depending on application-specific requirements:
- SUS304 (UNS S30408): General-purpose austenitic stainless steel with excellent corrosion resistance and formability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni). Suitable for intermediate baking ovens operating below 200°C.
- SUS316 (UNS S31608): Enhanced austenitic stainless steel with 2–3% Molybdenum (Mo) addition, providing superior resistance to chloride-induced pitting and intergranular corrosion. Recommended for environments with elevated humidity or chemical vapor exposure.
- SUS310S (UNS S31008): High-temperature austenitic stainless steel containing elevated Chromium (25–27%) and Nickel (19–22%) content. Suitable for intermediate baking ovens operating at sustained temperatures up to 250°C with exceptional oxidation resistance.
- SUS321 (UNS S32108): Stabilized austenitic stainless steel with Titanium (Ti) addition, providing superior resistance to intergranular corrosion and thermal cracking during prolonged heat exposure.
Mechanical Properties (Typical — Annealed Condition)
| Property | SUS304 | SUS316 | SUS310S | SUS321 |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥520 | ≥520 | ≥520 | ≥520 |
| Yield Strength (MPa) | ≥205 | ≥205 | ≥205 | ≥205 |
| Elongation (%) | ≥40 | ≥40 | ≥40 | ≥40 |
| Density (g/cm³) | 7.93 | 8.00 | 7.95 | 7.98 |
| Thermal Conductivity at 100°C (W/m·K) | 16.3 | 14.6 | 31.4 | 16.8 |
| Thermal Expansion Coefficient (10⁻⁶/K, 20–100°C) | 17.3 | 16.0 | 18.0 | 17.1 |
| Maximum Continuous Service Temperature (°C) | 870 | 870 | 1150 | 870 |
Chemical Composition (Wt%, Maximum Unless Noted)
| Element | C (Carbon) | Cr (Chromium) | Ni (Nickel) | Mo (Molybdenum) | Ti (Titanium) | Si (Silicon) | Mn (Manganese) |
|---|---|---|---|---|---|---|---|
| SUS304 | 0.08 | 18.0–20.0 | 8.0–10.5 | — | — | 1.00 | 2.00 |
| SUS316 | 0.08 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | — | 1.00 | 2.00 |
| SUS310S | 0.08 | 24.0–26.0 | 19.0–22.0 | — | — | 1.50 | 2.00 |
| SUS321 | 0.08 | 17.0–19.0 | 9.0–12.0 | — | 5×C (min 0.40) | 1.00 | 2.00 |
Specifications
Geometric Dimensions
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | Φ12 mm, Φ14 mm, Φ16 mm, Φ19 mm, Φ22 mm, Φ25 mm, Φ32 mm (custom sizes available) |
| Tube Wall Thickness | 0.5 mm – 2.0 mm (standard); up to 3.0 mm for high-pressure applications |
| Coil Inner Diameter (CID) | Φ100 mm – Φ500 mm (configurable per oven design) |
| Coil Pitch (Center-to-Center Spacing) | 1.5× OD to 3.0× OD (optimized for airflow and heat transfer balance) |
| Coil Length (Total Tube Length) | Up to 200 meters per continuous coil assembly |
| Coil Height (Axial Dimension) | 100 mm – 800 mm (depending on number of layers) |
| Number of Layers | 1 – 6 layers |
| End Connection Type | Flanged, threaded (NPT/BSP), welded stub, or socket-weld connection |
| Surface Finish | 2B (cold rolled and annealed) or No. 4 brushed finish; Ra ≤ 0.8 μm available upon request |
Thermal and Operating Parameters
| Parameter | Specification |
|---|---|
| Operating Temperature Range | -20°C to +250°C (continuous); peak excursions to 300°C (short-term) |
| Maximum Operating Pressure | 1.6 MPa (PN16); 4.0 MPa (PN40) for heavy-wall configurations |
| Heat Transfer Medium | Hot water, steam (low-pressure), or synthetic thermal oil |
| Design Heat Flux | Up to 15 kW/m² (surface heat flux) |
| Thermal Cycling Resistance | ≥10,000 cycles (20°C to 250°C) without degradation of mechanical integrity |
| Design Life | ≥15 years under normal operating conditions |
Manufacturing Tolerances
| Dimension | Tolerance |
|---|---|
| Tube OD | ±0.10 mm (for OD ≤ 25 mm); ±0.15 mm (for OD > 25 mm) |
| Wall Thickness | ±10% of nominal |
| Coil Pitch | ±1.0 mm |
| Coil Diameter | ±2.0 mm |
| Straightness (per 1 m) | ≤1.0 mm |
Manufacturing Process
Process Flow Overview
The manufacturing of the JX-CT-495 stainless steel coil tube follows a rigorously controlled multi-stage process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality suitable for demanding thermal cycling applications:
-
Raw Material Procurement and Inspection:
Stainless steel strip or seamless tube stock is sourced from certified mills (e.g., Outokumpu, Nippon Steel, POSCO, or domestic equivalents). Incoming material is verified through spectroscopic analysis (Optical Emission Spectrometry, OES) for chemical composition compliance and accompanied by mill test certificates (Mill Test Reports, MTRs).
-
Surface Preparation:
Strip material undergoes degreasing and surface cleaning to remove mill scale, oils, and contaminants. For seamless tube stock, internal and external surfaces are inspected for defects using visual and magnetic particle inspection (MPI) methods.
-
Coil Forming (Cold Bending):
The stainless steel tube or formed strip is cold-bent into the specified coil geometry using precision CNC-controlled coil winding machines. The bending process is executed with controlled bend radii (minimum 3× OD) to prevent cross-sectional distortion, wall thinning, or micro-cracking. Springback compensation algorithms ensure dimensional accuracy after release.
-
Welding and Joining:
For formed coil construction, longitudinal seams are welded using Argon Arc Welding (Tungsten Inert Gas, TIG) or laser welding techniques under controlled atmospheric conditions. Weld seams are oriented away from the primary heat transfer surface to minimize thermal stress concentration. All welds undergo 100% visual inspection and are subject to random ultrasonic testing (UT) or dye penetrant testing (PT).
-
Heat Treatment (Annealing and Pickling):
Following forming and welding, the coil assembly undergoes solution annealing at 1050–1100°C in a protective atmosphere (nitrogen or argon) to restore full austenitic microstructure, relieve residual stresses, and ensure optimal corrosion resistance. This is followed by acid pickling and passivation to remove oxide scales and restore the chromium-rich passive film on the surface.
-
Dimensional Verification:
Finished coil assemblies are inspected using coordinate measuring machines (CMM), laser scanners, and manual measurement tools to verify compliance with specified dimensional tolerances. Key parameters include coil diameter, pitch uniformity, tube straightness, and end connection alignment.
- Pressure Testing and Leak Detection: