【作者】 付颜红；

【导师】 凌泽民；

【作者基本信息】 重庆大学 ， 材料加工工程， 2010， 硕士

【摘要】 换热器是汽车空调系统的重要组成部分。随着汽车空调产业的不断发展,对换热器外观及性能提出了更严格的要求。如何既要求换热器外形美观,又保证其优异的换热性能,是汽车工业中的重要研究课题之一。钎焊是换热器的主要加工方法,也是影响换热效果的决定因素之一。文章主要从汽车空调冷凝器的实际钎焊质量出发,结合钎焊机理,针对钎焊时产生的“翅片熔蚀”现象做了详细的研究。在钎剂浓度为5%、烘干温度为230℃、最高钎焊温度为615℃、网带速度为1080mm/min、氮气纯度达99.998%的情况下,钎焊后的冷凝器有部分翅片消失,即“翅片熔蚀”现象,严重影响换热。为解决该问题,首先从冷凝器各个结构的化学成分分析着手。集流管和翅片都是复合层材料,钎料层包覆在母材表面。而复合层材料本身就是很复杂的制造过程,由于生产厂家或生产技术的差异,钎料层厚度及均匀度会影响钎焊时的传热与钎料的流动情况,为钎焊工艺带来困难。分析表明,当材料的复合层过厚或者厚度不均时,会造成集流管处过多的钎料流向翅片,钎料和母材相互扩散,母材基体过多的溶解于钎料造成“硅蚀”。为了深入研究此现象机理,针对钎焊接头组织进行实验分析。实验证明,钎焊接头中确实存在“硅蚀”现象。钎焊工艺同样影响熔蚀现象,网带速度过低或钎焊温度过高都会延长钎料的流动时间,使钎料流向翅片区的机会和量增加,“翅片熔蚀”机率和程度随之增加。而且,扁管表面的细微划痕也能加剧“翅片熔蚀”现象。在以上分析和实验的基础上,改善扁管表面质量的同时,运用分组实验的方法改进工艺。首先只考虑温度因素,即网带速度不变,只改变温度。任选已装配好的工件30件分组进行钎焊并检验,将合格率最高的两组继续进行带速设定试验,选出的设定温度固定不变,分别将网带速度设为1090mm/min、1100 mm/min、1110 mm/min同上进行试验,选取最佳钎焊工艺参数。最终将第六温区和第七温区的温度设置为608℃和610℃,网带速度设定为1100mm/min时得到没有“翅片熔蚀”的产品,合格率接近100%。该研究得到了满意的冷凝器外观,提高了产品合格率,降低了生产成本。最终应用于指导生产,也为钎焊熔蚀的进一步探讨提供了理论基础。更多还原

【Abstract】 Heat exchanger is an important part in automotive air-conditioning system. With the continuous development of automotive air conditioning industry, more stringent requirements is proposed to the appearance and performance of heat exchangers. How to get aesthetic appearance and excellent heat transfer performance is one of the important research topics in the automotive industry. Brazing is the main processing methods of heat transfer, and also is a determining factor of affecting the heat transfer effect. This article, to proceed from the actual brazing quality of car air-conditioning condenser, combined with Brazing mechanism, studied on the "fin-erosion" phenomenon after brazed in detail.In the case of concentration in the flux of 5%, drying temperature of 230℃, the maximum brazing temperature 615℃, belt speed of 1080mm/min, nitrogen purity of 99.998% or more, some fins of automotive air-conditioning condenser disappeared after brazed, which called "fin-erosion" phenomenon and affects heat transfer effect severely. In order to solve the problem, first of all, the study from the chemical composition of various structures of the condenser to proceed. Collecting pipe and fin are composite layer material, and the solder coated the base metal. However, the composite layer material itself has a very complicated manufacturing process. As differences in manufacturers or production technology, solder thickness and uniformity will affect the heat transfer during brazing and solder flow, which create difficulties for the brazing process. Analysis shows that, when the composite layer is too thick or uneven thickness, it will cause excess solder flows from collecting pipe to the fin. With the inter-diffusion between the base metal and solder, "Si-erosion" appears as too much base metal dissolves in solder. Experimental analysis for brazing joint microstructure is proceeded in order to study the mechanism of this phenomenon. Experimental results show the existence of the "Si-erosion "phenomenon in brazed joints, because solder layer and the brazing process do not match. Too low belt speed or too high temperature will extend the solder’s flow time, which increase the opportunities and volume of solder from collecting pipe to fin, then the probability and extent of "fin-erosion" increase. Moreover, minor scratches on the surface of the flat tube can intensify the "fin erosion" phenomenon.Based on above analysis and experiments, the surface quality of flat tube is improved, then,select the brigade-laboratory method to improve the brazing process. At first, just considering on the temperature factor, that is, keep the belt speeds constant and just change the temperature. Randomly choose 30 workpieces has been assembled to brazing and make quality inspection in groups, then,the two groups of the highest pass rate will continue to experiment for belt speed set. To remain the selecting set temperature unchanged, respectively set the belt speed to 1090mm / min, 1100 mm / min, 1110 mm / min to conduct experiment ditto. At last, select the optimum brazing parameters. Eventually ,when the temperature of the sixth and seventh temperature is set to 608℃and 610℃, and belt speed is set to 1100 mm/min, there isn’t "fin- erosion" products, nearly 100% pass rate.The study has got satisfactory appearance of the condenser, and improved the passing rate of products, and the production costs is reduced. Ultimately, it is used to guide the production and provides a theoretical basis for the further study on the erosion during brazing.更多还原