Vacuum brazing of EGR cooler

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Automobile exhaust EGR cooler (heat exchanger, radiator) is a new environmental protection product. With the rapid increase of car ownership in the world, the pollution of vehicle exhaust to the atmospheric environment is becoming more and more serious. It has become the main source of PM2.5 pollution in urban air. The situation is particularly prominent in densely populated cities. With the increasingly stringent restrictions on vehicle emissions in China, an important direction of vehicle technology development is to improve emissions and reduce pollution. Exhaust gas recirculation technology is the most effective measure to control no emissions, Exhaust gas recirculation (EGR) is a kind of exhaust gas suppression measure that a small part of combustion exhaust gas is introduced from the exhaust pipe into the intake pipe and mixed with fresh air to artificially increase the amount of exhaust gas in the fresh air to reduce the content of nitrogen oxides in the exhaust. It is installed in the automobile EGR system for cooling the return exhaust gas. ERG system (exhaust gas recirculation system) is a kind of technology and method used to reduce the nitrogen oxides in automobile exhaust emissions. It is a product that must be used for automobile exhaust emissions to reach Euro IV and Euro V standards. At present, few domestic companies can mass produce this product.

Principle and function of EGR cooler:

In the process of automobile combustion, a high temperature of about 500 ~ 600 ° C will be produced. If the exhaust gas with high temperature flows back, the emission effect can not be achieved. It is necessary to cool the exhaust gas before it flows back. This process is completed in the cooler. If the EGR gas is not cooled, the hot return exhaust gas will heat the intake air, resulting in a substantial increase in the combustion temperature and pressure in the cylinder, which counteracts the effect of EGR in reducing NOx. In serious cases, it will also damage the structure of the engine block. Therefore, it is necessary to cool the high temperature EGR gas through the cooler.

EGR cooler cooling object is the recirculation exhaust gas, its temperature is high, and requires the heat exchanger to achieve large heat transfer in a small heat exchange area, but also to adapt to the characteristics of engine vibration. Referring to the advanced experience at home and abroad, the shell and tube heat exchanger is researched and developed from various aspects. It is made of 304 stainless steel with excellent thermal conductivity as the carrier, and is brazed by the shell, spiral groove tube, end plate and connecting flange in high vacuum. It is proved by many tests that the structure is reasonable, and the heat dissipation, vibration proof, explosion-proof and other indicators can meet the requirements. It is suitable for high temperature and high pressure environment use.

SIMUWU vacuum furnace manufacturer provides vacuum brazing, vacuum brazing process, vacuum brazing furnace and vacuum brazing process.

At present, the typical structure of car engine EGR cooler is multi tube shell structure, which is suitable for vacuum brazing, and hydrogen nitrogen protection continuous brazing process is not recommended. The dew point temperature of hydrogen and nitrogen can’t be controlled all the time, and the product enters the furnace before it is completely dry. So the qualified rate of brazing is not high. Nickel base solder is used in moding heat energy.

EGR exhaust gas works under high temperature and high pressure, and there are many sulfur and nitrogen oxides in the exhaust gas. When the exhaust gas is cooled, it can form strong oxides, which will cause corrosion to the cooler. This working condition requires the cooler to be high temperature resistant and corrosion resistant. In order to meet the requirements of high temperature resistance and corrosion resistance, all materials are made of 316L (00Cr17Ni14Mo2) stainless steel with a thickness of 1 mm and a thickness of 0.4 mm.

Selection of welding methods

At present, the core of car cooler is of multi tube shell structure. It needs to be heated uniformly and the thermal deformation is small, so the vacuum brazing process is selected. The furnace brazing of stainless steel is mainly carried out in protective atmosphere or vacuum. When brazing in stainless steel furnace, the most commonly used protective atmosphere is dry hydrogen and decomposed ammonia, which are conducive to reducing oxides. Protecting the base metal and promoting the flow of solder, vacuum is an effective protective atmosphere The impurity content of vacuum brazing austenitic stainless steel is much lower than that of the purest inert gas, and the protective effect of vacuum is better than that of any kind of protective gas. Therefore, the most commonly used filler metal for vacuum brazing austenitic stainless steel is Ni based filler metal, which belongs to eutectic composition and has excellent fluidity. It can flow into the joint with close contact. Generally, it can be dissolved The tendency is not great.

Parameter setting of vacuum brazing

The EGR project was started five years ago, but the emission control scheme with EGR cooler was shelved due to the dispute between the main engine plant and the state on the two schemes of vehicle emission control. However, in recent years, the air haze has become more and more serious, the national V emission standard has been issued, some cities have begun to implement the standard, and the national implementation of the national V standard is just around the corner, Strict emission control, so that each diesel engine vehicle must be equipped with at least one EGR cooler, or even two, in order to pass the national five standards. Developed countries in Europe and the United States have used gasoline vehicles, so the project has broad prospects.

Product use:

Diesel engine range: all kinds of commercial transport vehicles (trucks).

Some passenger cars, construction machinery, other professional vehicles, etc.

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