The Single Chamber Tubes for Heater Cores is the core basic pipe material of the automobile warm air core, mainly made of aluminum alloy substrate, with internal circulation of coolant, and long-term exposure to alternating cold and hot conditions, water vapor, and antifreeze corrosion. The surface condition of the pipe directly affects the corrosion resistance, brazing performance, service life, and defective leakage rate of the core. Reasonable selection of surface treatment processes can meet the requirements of brazing assembly, delay pipe pitting and crevice corrosion, and improve the long-term operational reliability of automotive warm air radiators. This article summarizes the mainstream surface treatment solutions for single chamber tubes used in heater cores, to assist in the comparison of procurement, research and development, and radiator factory selection.
1. Degreasing and degreasing treatment (all pre process basic procedures)
Defatting is the first process of surface treatment, not a functional coating, but essential for subsequent processing. During the extrusion and drawing process, the surface of the pipe will adhere to stretching lubricating oil, metal dust, and demolding residue.
Process principle: Using alkaline degreasing or neutral water-based degreasing agents, combined with spraying, soaking and cleaning, and then rinsing and drying with multi-stage pure water to remove oil stains on the inner and outer walls of the pipe.
Function: Eliminate brazing porosity and virtual welding caused by oil pollution; Prevent oil stains from forming localized corrosion points during long-term use; Ensure uniform adhesion of subsequent passivation and conversion coating.
Applicable scenario: All heater core single chamber tubes must undergo degreasing and cleaning, regardless of whether they are subsequently coated with anti-corrosion coating.
Risk Warning: Incomplete degreasing can cause welding defects at the joint between brazed fins and single chamber tubes, which can lead to coolant leakage in the later stages.
2. Aluminum chemical conversion coating (chromized/chromium free passivation, mainstream anti-corrosion solution)
Aluminum conversion coating is a commonly used surface treatment in the automotive radiator industry, which is divided into traditional chromate passivation and chromium free passivation.
Process principle: The pipe is immersed in a specialized conversion agent, and a chemical reaction occurs on the surface of the aluminum material, generating a dense inorganic film that adheres to the surface of the metal substrate.
Performance advantages:
1. Improve the corrosion resistance of aluminum alloy substrates and resist pitting corrosion caused by antifreeze and water vapor;
2. Enhance the adhesion of the coating as a base coat, facilitating subsequent painting;
3. It does not affect the brazing process and is suitable for brazing production in core furnaces.
Selection differentiation:
Chromium passivation: Stable anti-corrosion performance, but some overseas markets have heavy metal control restrictions;
Chromium free passivation: Compliant with RoHS and REACH environmental regulations, it is currently the preferred choice for exporting automotive parts.
Applicable: Warm air heater cores for passenger cars and commercial vehicles, export radiator projects.
3. Special welding aid pretreatment for brazing (for brazing assembly in the furnace)
The Single Chamber Tubes for Heater Cores needs to be assembled with aluminum fins and collector tubes through vacuum brazing or brazing in CAB furnace, and some pipes will be pre treated with brazing.
Process feature: Remove the natural oxide film on the surface. Aluminum alloys are prone to forming aluminum oxide films at room temperature, with a high melting point of the oxide layer, which hinders the infiltration of solder and can result in virtual welding.
Solution: Controllable acid washing to remove oxide skin, or pre coating with specialized brazing flux. Pre coated thin layer of flux activates the metal surface in a high-temperature brazing environment, promotes the flow of solder, and ensures a tight welding bond between fins and pipes.
Key point: The amount of flux coating needs to be strictly controlled. Excessive residue can form impurities inside the pipeline, block the flow channel, or accelerate internal corrosion.
4. Spray anti-corrosion coating (epoxy resin, organic protective coating)
Part of the customized Single Chamber Tubes for Heater Cores will be coated with organic spray coating, which is commonly used for harsh corrosion conditions, such as heating cores in construction vehicles and machinery.
Process: After the pre-treatment of the pipe is completed, an organic protective film is formed by electrostatic spraying or immersion coating.
Advantages: Isolation from air, water vapor, and corrosive media, with stronger anti-corrosion ability.
Limitations: Ordinary organic coatings are not resistant to high temperatures during brazing and cannot be used for brazing processes in furnaces. They are generally used for non brazed assembly structures.
Applicable: Heat sinks for construction machinery and special equipment, as well as heater core components that have not undergone high-temperature brazing processes.
5. Polishing and finishing treatment (optimization of appearance and surface roughness)
Mechanical finishing and slight polishing are used to optimize the surface roughness of pipes, which belongs to physical surface treatment and does not form a protective film layer.
Function: Reduce surface burrs and scratches, minimize stress concentration and local corrosion sources at scratch locations; Improve surface uniformity and facilitate the uniform formation of the conversion film.
Explanation: Pure polishing does not have anti-corrosion ability, and is generally used together with passivation/conversion film. The inner wall of the pipe can also be polished to reduce burrs and minimize the risk of impurities hanging on the wall.
6. Inner wall cleaning treatment (special treatment for inner walls, easily overlooked by procurement)
The inner wall of the single chamber tube of the heater core comes into contact with antifreeze, and residual metal debris and dust on the inner wall will continue to induce internal corrosion and block the small flow channels of the core.
The special treatment of the inner wall includes high-pressure pure water flushing, compressed air blowing, and ultrasonic cleaning, and the impurity content of the inner wall is controlled after treatment.
Application: High end passenger cars, new energy vehicle air conditioning heater cores, with clear particle size requirements for cleanliness.
Key points for comparing the selection of different surface treatment schemes
1. If the production line adopts furnace brazing: priority degreasing+chromium free conversion film, optional matching brazing assistance pre coating, cannot use organic spraying.
2. Export to European and American markets: Prioritize chromium free passivation to meet REACH and RoHS environmental requirements.
3. Construction machinery and high corrosion conditions: Evaluate organic spraying schemes, provided that they are not brazed.
4. New energy vehicle warm air core: additional clean control of the inner wall is added to strictly control the particles on the inner wall.
Key points of incoming inspection (must see for procurement)
Purchase and inspect the surface treated heater core single chamber tube, with key testing items:
1. Continuity of the film layer, without holidays, spots, or peeling;
2. The thickness of the film layer should be controlled within the specified range of the process;
3. Salt spray test to verify the anti-corrosion ability;
4. Visual inspection of surface oil stains, dust, and scratches;
5. Conduct brazing sample testing to verify the welding infiltration effect (brazing type pipes).
Summary
The surface treatment of the heater core using a single chamber tube is not just about the appearance process, but the core goal is to balance brazing assembly performance and long-term corrosion resistance. The vast majority of aluminum single chamber tubes for car heating cores have a basic process of degreasing and cleaning+chromium free chemical conversion coating; Special working conditions are combined with polishing and inner wall cleaning treatment. When selecting, it is necessary to comprehensively determine the production process (whether it is brazing in the furnace), target market environmental regulations, and vehicle usage environment.
