Vacuum Brazing Process Optimization for Aluminum Plate-Fin Heat Exchangers Under High Humidity Conditions

Vacuum brazing is one of the most important manufacturing processes for aluminum plate-fin heat exchangers, oil coolers, intercoolers, and other high-performance thermal management products.

Compared with traditional welding methods, vacuum brazing provides:

1.Excellent joint strength

2.High thermal conductivity

3.Clean flux-free brazed surfaces

4.Reliable sealing performance

However, during summer seasons, high humidity environments can significantly affect brazing stability.

When workshop relative humidity exceeds 60%RH, moisture can enter the brazing process through components, fixtures, and furnace chambers, resulting in:

For manufacturers producing aluminum plate-fin heat exchangers, optimizing the vacuum brazing process during humid summer conditions is essential for maintaining stable product quality.

This article introduces practical solutions based on six key areas:

1.Workshop humidity control

2.Component pre-treatment

3.Vacuum degassing optimization

4.Heating program adjustment

5.Cooling process improvement

6.Furnace maintenance and material-specific optimization

Environmental control is the first step to achieving stable brazing quality.

The vacuum brazing area should be separated from other production areas and equipped with industrial dehumidification systems.

During rainy seasons or extreme humidity conditions:

Environmental humidity >75%RH

additional mobile industrial dehumidifiers should be used to prevent components from absorbing moisture during transportation.

After machining and cleaning, aluminum alloy components should not be exposed directly to open air.

Recommended requirements:

1.Store components in a temperature-controlled dry cabinet

2.Maintain humidity below 40%RH

3.Complete furnace loading within 2 hours after cleaning

For plate-fin heat exchangers, the narrow channels and dense fin structures can easily retain moisture, making proper storage especially important.

Traditional drying processes may not completely remove moisture under high humidity conditions.

120℃ / 30 minutes

A two-stage drying process is recommended:

Temperature: 80℃
Holding Time: 20 minutes

Purpose:

1.Remove surface moisture slowly

2.Prevent rapid vapor expansion

3.Reduce micro defects caused by trapped water vapor

Temperature: 180℃
Holding Time: 40 minutes

Purpose:

Remove moisture from:

1.Material pores

2.Component gaps

3.Plate-fin structures

After drying:

✓ Cool in a dehumidified area
✓ Complete furnace loading within 15 minutes
✓ Avoid long exposure to humid air

High humidity increases the amount of moisture released inside the vacuum furnace.

Therefore, the vacuum process requires additional degassing steps.

Pump directly to high vacuum

1.Mechanical pump evacuation to 10Pa

2.Extend pumping time by 3–5 minutes

Purpose:

Remove large amounts of humid air inside the furnace chamber.

Parameters:

This allows moisture attached to furnace walls to gradually evaporate and be removed.

Before heating starts:

Water vapor partial pressure should be controlled below 1×10⁻³Pa

to prevent oxidation caused by high-temperature water vapor reactions.

For high humidity production environments, adding low-temperature degassing is one of the most effective improvements.

Function:

Remove absorbed moisture from:

1.Heat exchanger channels

2.Fin gaps

3.Component joints

Function:

1.Remove moisture from hydrated aluminum oxide layers

2.Stabilize furnace vacuum condition

Before entering brazing temperature:

Vacuum fluctuation should be:

< ±2×10⁻³Pa

After degassing, the heating curve should be optimized.

Original heating speed:

8–10℃/min

Optimized heating speed:

5–6℃/min

Benefits:

1.Reduce temperature differences inside components

2.Prevent moisture expansion

3.Avoid brazing cracks and deformation

Recommended adjustments:

These adjustments compensate for reduced filler metal spreading caused by slightly increased oxide thickness under humid conditions.

After brazing:

1.Maintain vacuum cooling until temperature drops below 350℃

2.Start gas cooling afterward

3.Remove products when temperature reaches ≤120℃

High-temperature products exposed directly to humid air may experience:

1.Surface oxidation

2.Dark brazed joints

3.Failed helium leak testing

Finished heat exchangers should be transferred immediately to a dry cooling area.

Regular furnace maintenance helps keep brazing quality stable.

Before production:

1.Close furnace door

2.Perform empty furnace vacuum drying

3.Remove moisture accumulated overnight

Recommended time:

15 minutes

Every 10 cycles:

1.Empty furnace heating

2.Temperature: 500℃

3.High vacuum holding: 1 hour

Purpose:

Remove moisture and contamination from furnace walls.

Summer maintenance:

1.Check diffusion pump oil moisture content every 2 weeks

2.Replace oil immediately if emulsification occurs

3.Inspect cooling water pipelines for leakage

Aluminum plate-fin heat exchangers are highly sensitive to humidity because of their:

1.Large surface area

2.Dense fin structures

3.Internal channels

Recommended parameters:

These improvements help achieve:

✓ Better filler metal flow
✓ Lower porosity rate
✓ Higher leak resistance
✓ More stable thermal performance

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High humidity during summer production can significantly influence vacuum brazing quality. By controlling workshop humidity, improving drying procedures, optimizing vacuum programs, and adjusting brazing parameters, manufacturers can effectively reduce:

1.Brazing porosity

2.Oxidation defects

3.Poor filler spreading

4.Leakage failures

For manufacturers producing aluminum plate-fin heat exchangers, radiators, oil coolers, and intercoolers, a stable vacuum brazing process is the foundation of reliable thermal management products.

SUNHOPE provides professional heat exchanger solutions, including aluminum plate-fin heat exchangers, radiator components, and manufacturing support for global customers.

Contact our engineering team for customized heat exchanger solutions and production support.