Experimentalinvestigation Of Low-vacuum Brazing Of Stainless Steel Oilcooler Using Fe-based Filler Metal With Low Copper Content

This Research roots in the “Low copper stainless steel oil cooler” project fromZhejiang Yinlun Machinery Co., Ltd. Firstly, the failure reason of the stainless steel oilcooler using pure copper brazing filler metal was analyzed according to the requirementof the project. The fact was found that the copper within stainless steel oil cooler woundreact with the sulfur component from engine oil under the running temperature ofengine, resulting in high copper presentation in engine oil. And the reaction productwould precipitate on some key parts of the engine for they did not dissolve in oil,causing the key parts failed by excessive wear. Meanwhile, the source of the copper thatcaused the failure of the stainless steel oil cooler was discovered which was theevaporation deposition layer on the surface of fin.To solve the problem, the trial by changing pure copper for iron-based brazingfiller metal with low copper content was carried out. It was found that the iron-basedbrazing filler metal had excellent wettability on stainless steel, and there was no copperevaporation deposition layer within the stainless steel oil cooler sample using iron-basedbrazing filler metal, reaching the conclusion that there was no erosion between engineoil and copper in the stainless steel oil cooler using iron-based brazing filler metal. Thatwas, the iron-based brazing filler metal with low copper content could be successfullyapplied to the “Low copper stainless steel oil cooler” project. Moreover, the stainlesssteel oil cooler had no leaking and also passed the bursting test, meaning that iron-basedbrazing filler metal used in the manufacture of stainless steel oil cooler is feasible.At the same time, the experimental research and analysis about the mechanism ofthe oxide film removal from the surface of stainless steel were conducted. The wettingand spreading of iron-based brazing filler metal on stainless steel could also take placein low vacuum. Moreover, the liquid iron-based brazing filler metal had the ability todissolve stainless steel with different thickness of oxide film, and the dissolving degreehad something to do with the thickness of oxide film, the viewpoint that the oxide filmwas removed by dissolving into the liquid iron-based brazing filler metal was presentedafter studying various mechanisms of removing the oxide films from the stainless steel in vacuum. The thermodynamic analysis of dissolving react between liquid iron-basedbrazing filler metal and oxide film, combining with the spreading experiment ofiron-based brazing filler metal on06Cr19Ni10stainless steel in air environment verifiedthe conclusion above. In this article, it was considered that the wetting and spreadingbehavior of iron-based brazing filler metal with low copper content belongs to reactivespread, especially dissolve-reactive spread.In addition, reducing the amount of pure copper brazing filler metal by usingcopper foil with0.03mm thickness was also investigated. Using copper foil with0.03mm thickness could ensure the brazing quality of stainless steel oil cooler whenmaking a little adjustment to the craft. Furthermore, through the exploration of thecopper content within the stainless steel oil cooler, it was found that the fillet size of thefin-plate brazing joint and the evaporation deposition layer on the surface of fin hadbeen reduced, and the residue of copper brazing filler metal on the surface of plate hadalso been decreased to a very low level, which is good for lowering the copperpresentation in engine oil and relieving the erosion by engine oil, but yet to be verifiedby hot oil test. However, it can significantly reduce the cost and create considerablebenefits if copper foil with0.03mm thickness has been industrialized.