Description
The brazing surface width of the sealing bar refers to the horizontal width where the sealing bar fits against the separator (clad aluminum plate) to form a brazed joint. Two mainstream processes are distinguished: vacuum aluminum brazing (flux-free) and NOCOLOK controlled atmosphere brazing.
I. Industry-General Optimal Recommended Values (Mass-Production Mature Range)
- Normal working conditions (oil coolers, battery chillers, general liquid-cooled radiators, design pressure ≤3.0 MPa)
✅ Preferred range: 3.0 ~ 3.5 mm
- Vacuum brazing: 3.0 mm preferred
- NOCOLOK controlled atmosphere brazing: 3.2 ~ 3.5 mm preferred
2.High-pressure working conditions (energy storage cooling, hydraulic coolers, cryogenic heat exchangers, design pressure 3 ~ 6.3 MPa) ✅ Preferred range: 4.0 ~ 5.0 mm Improved pressure resistance and reduced risk of seal failure; width exceeding 5.0 mm is not recommended.
✅ Preferred range: 4.0 ~ 5.0 mm
Improved pressure resistance and reduced risk of seal failure; width exceeding 5.0 mm is not recommended.
3.Lightweight compact products (server micro liquid-cooled cores, small heat dissipation modules)
✅ Extreme lower limit: 2.5 mm
⚠️ Risk Warning: The 2.5 mm narrow sealing bar design imposes stringent requirements on incoming flatness, assembly clearance and furnace temperature uniformity. Intermittent brazed joints and leakage are highly likely. Only applicable for low-pressure products (≤1.6 MPa).
II. Pros & Cons Analysis for Different Widths
- Width ＜ 2.5 mm
Disadvantages: Insufficient effective brazed joint area; minimal tolerance for filler metal wetting. Minor assembly deviations lead to incomplete bonding and penetrating leakage, with low pressure resistance and high rework rate. Not recommended for mass production.
2. 3.0 ~ 5 mm (Optimal Range) ✔ Advantages:
- Sufficient spreading of brazing filler metal with adequate process tolerance;
- Moderate sealing bar material consumption, controlling core weight and overall dimension;
- Balanced sealing performance, structural strength and lightweight design;
- Stable mass production feasible for both vacuum brazing and NOCOLOK controlled atmosphere brazing; this is the standard specification adopted by most domestic plate-fin heat radiator manufacturers.
3. Width ＞ 5.0 mm
- Higher material consumption for sealing bars and increased weight, conflicting with lightweight targets;
- Large contact surfaces tend to trap oil contaminants and oxide films, resulting in porosity within brazed joints;
- Molten brazing filler metal is prone to extensive runoff, causing fin erosion;
- Occupied core space reduces the effective heat transfer area.
III. Minor Differences: Vacuum Brazing vs. NOCOLOK Brazing
- Vacuum Brazing Capillary wetting performance is inferior to NOCOLOK brazing. Values toward the upper limit of 3.0 ~ 5.0 mm are recommended; avoid 2.5 mm narrow sealing bars as far as possible.
- NOCOLOK Controlled Atmosphere Brazing Flux assists oxide removal and delivers superior filler metal wettability. The lower limit can be extended to 2.8 mm; 3.2 mm is sufficient for stable regular production.
IV. Key Supporting Design Constraints
- Assembly brazing clearance: 0.03 ~ 0.08 mm; clearance exceeding 0.1 mm greatly increases the risk of incomplete bonding.
- Sealing bar height tolerance: controlled within ±0.03 mm. Fins shall be 0.02 ~ 0.04 mm slightly higher than sealing bars to ensure tight compression contact.
- Sealing bar cross-section: rectangular bars are preferred. Sealing bars with small flow guide grooves may be adopted for high-pressure products to optimize filler metal flow.
- Corner regions: local width expansion to 10 mm is suggested at four corners of the core, as corners are high-risk leakage locations.
V. Concise Selection Summary
- Low-pressure lightweight products (≤1.6 MPa): 2.5 ~ 3.0 mm (only if robust process control is available)
- General new energy / oil radiators (≤3.0 MPa): 3.0 ~ 3.5 mm 【Recommended standard value: 3.2 mm】
- High-pressure hydraulic / cryogenic heat exchangers (3 ~ 6.3 MPa): 4.0 ~ 5.0 mm
