Frame Seal Bar Radiator Manufacturing: 7 Key Process Controls

Frame seal bars form the closed sealing structure of a plate-fin radiator core. Their dimensional accuracy, assembly gaps, cleanliness, brazing quality, and post-brazing inspection directly affect pressure resistance and leakage performance.

For manufacturers of aluminum plate-fin radiators, controlling the following seven stages can significantly reduce brazing defects and leakage risks.

1. Seal Bar Cutting and Forming

Dimensional accuracy is the foundation of reliable brazing.

• Length tolerance: ≤±0.3 mm
• Height tolerance: ≤±0.02 mm
• Frame corner angle: 90°, with deviation below 0.5°
• Brazing surface flatness: ≤0.1 mm
• Burr height after cutting: ≤0.02 mm
• Recommended edge radius: approximately R0.2
• Brazing surface roughness: Ra 1.6–3.2 μm

The seal bars should be stored in dry, dust-free containers. Aluminum chips and dust accumulated in corner grooves should be removed again before assembly.

2. Cleaning and Drying

Because a closed frame can easily retain oil, dust, and moisture, thorough cleaning is essential.

A typical cleaning sequence is:

Alkaline degreasing → pure-water rinsing → steam degreasing → hot-air drying

The recommended drying condition is 60°C for at least 5 minutes.

A 40 dyn/cm dyne pen test can be used to check the brazing surface. The marking should remain uniform without shrinkage or beading.

After cleaning and drying, assembly should normally be completed within 24 hours. For vacuum brazing, moisture removal must be particularly thorough. For NOCOLOK atmosphere brazing, flux should cover both inner and outer frame surfaces, including corner areas.

3. Core Stacking and Frame Assembly

Assembly accuracy directly determines the final brazing gap.

• Separator-to-seal-bar gap: ≤0.02 mm
• Fin-to-inner-frame clearance: 3–5 mm
• Core perimeter height difference after stacking: ≤1 mm
• Long/short seal bar joint gap: ≤0.15 mm

The frame should remain level and evenly aligned. Assembly fixtures should provide sufficient rigidity, while multiple tie rods should be tightened symmetrically to prevent local gaps or frame distortion.

For vacuum brazing, foil filler metal should be positioned along the upper and lower frame contact surfaces. Additional filler metal may be required at the four corners because these areas are more prone to incomplete filling.

4. Vacuum Brazing Process

Stable furnace conditions are critical for frame seal bar brazing.

The vacuum level during heating should reach ≥1×10⁻³ Pa and remain stable during the brazing stage.

A controlled heating profile can include:

• 200–260°C: Degassing stage
• 380–400°C: Intermediate stress-relief holding stage
• 597–605°C: Brazing temperature
• 15–25 min: Typical holding time depending on core thickness

Insufficient degassing may cause porosity, while insufficient holding time can result in incomplete brazing. Excessive holding may cause filler-metal overflow, flow-channel blockage, or material distortion.

During furnace loading, cores should be positioned evenly without excessive stacking pressure. Large cores may require auxiliary weighting around the frame area.

After brazing, gradual cooling is recommended. Rapid air cooling above 500°C should be avoided because thermal stress can contribute to joint cracking and leakage.

5. Post-Brazing Straightening and Machining

After brazing, frame deformation should be corrected through controlled cold straightening. Excessive hammering should be avoided because it may damage brazed joints.

If drilling or tapping is required around the frame:

• Remove all aluminum chips and cutting fluid.
• Clean the internal flow channels thoroughly.
• Reinspect brazing joints around machined holes.
• Check corner welds for possible microcracks.
• Dry the core again after machining.

These controls help prevent machining residues and vibration-related defects from becoming future leakage sources.

6. Final Inspection and Leak Testing

A complete inspection should include visual, dimensional, and leak testing.

Visual Inspection

The frame weld should be continuous and free from:

• Broken joints
• Visible holes or porosity
• Excessive filler-metal flow
• Flow-channel blockage
• Oxidized or cracked corners
• Significant frame deformation

The four corners should receive particular attention because they are common areas for incomplete brazing.

Leak Testing

For critical applications, 100% leak inspection is recommended.

• Low-pressure air testing: Rapid detection of major leakage.
• Helium mass spectrometer testing: Suitable for high-pressure water-cooling and new-energy thermal management applications.
• Hydrostatic pressure testing: Verify that the frame weld remains free from seepage under the product's design pressure.

The frame length, width, diagonals, and height should also be rechecked after brazing.

7. Common Defects and Prevention

Conclusion

Reliable frame seal bar radiator production requires consistent control from material preparation and cleaning to core assembly, vacuum brazing, machining, and leak testing.

For radiator manufacturers, suitable production equipment is equally important. SUNHOPE supplies radiator core assembly machines, fin forming machines, aluminum vacuum brazing furnaces, leak testing equipment, and radiator and condenser components, with technical support for complete radiator manufacturing projects.

By combining accurate assembly, stable brazing conditions, and reliable inspection, manufacturers can reduce leakage, distortion, and brazing defects while improving overall core quality.