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Vacuum Brazing Process of EGR Cooler

With the increasing awareness of environmental protection, the restrictions on diesel engine emission indicators are becoming more and more strict. Exhaust gas recirculation (EGR) is currently the preferred technology, which has significant effects on improving emissions, reducing pollution and reducing NOx emissions from internal combustion engines. The principle is that after cooling the quantitative exhaust gas discharged from the engine, it is sent back to the mixer to be mixed with fresh air and then entered into the cylinder, thereby reducing the combustion temperature of the engine and reducing the relative concentration of oxygen, so that the emission of NOx is smaller.

At present, the application of EGR system in automobile engine is quite common. In addition to effectively reducing NOx emissions, EGR system can also effectively reduce fuel consumption. In the operating conditions of the gasoline engine of a car, the engine throttle valve can be enlarged under high load conditions through a well-matched EGR system, which can effectively reduce the engine power loss. The EGR system can reduce the consumption of precious metals in the three-way catalytic converter, and can reduce the cost of meeting the emission standards of gasoline vehicles. In addition, a lean-burn engine can only meet exhaust emissions when the EGR system is used. In recent years, EGR systems have been increasingly used in diesel vehicles.

Vacuum Brazing of EGR

Since the working medium of EGR is acid concentrate, the working temperature is generally around 700 ℃, and the working pressure is relatively large, so the cooler is generally made of stainless steel. The nickel-based solder has excellent anti-oxidation and corrosion resistance, good plasticity and moderate strength, so vacuum brazing with nickel-based solder is the preferred process for manufacturing this cooler.

The main structure is made of stainless steel plate with lap brazing. In order to increase its surface roughness, the brazing surface is polished with silicon carbide emery cloth, and degreasing and dust-removing cleaning is carried out before brazing.

There are many process factors that affect the performance of vacuum brazed joints. There are three main parameters: vacuum brazing temperature, holding time and heating rate. According to the brazing material, the temperature range is 1010~1200℃, the holding time is generally 3~20min, and the heating rate is 5~15℃/min. The process curve is shown in the figure below.

The brazing process is carried out in a RHVB vacuum furnace with a vacuum degree of 1*10-2Pa. The RHVB vacuum brazing furnace produced by SIMUWU is controlled by PLC. After inputting the parameters, it can be fully automatic without the need for personnel to operate it. And the furnace temperature uniformity is good, the process is repeated and reliable, and it is an excellent product for stainless steel vacuum brazing. The parts are vacuum brazed and the surfaces are smooth and the joints look good. In order to ensure the brazing efficiency, a higher furnace temperature can be used, but sometimes a small amount of oxidation occurs on the surface of the stainless steel, but it does not affect the overall performance.

(Process curve diagram, for reference)

A well-welded finished product with a smooth surface and no internal leakage. The brazed joints are tight, strong and able to withstand the pressures generated during operation. After vacuum brazing, samples should be taken for testing to ensure that the products are qualified.

As we all know, the vacuum brazing furnace selected in vacuum brazing is a crucial factor to ensure the quality of brazing. The RHVB vacuum high temperature brazing furnace produced by SIMUWU has the advantages of good temperature control accuracy, excellent vacuum performance and high heating uniformity. It is an excellent product for processing high temperature brazing process. Under the premise of selecting appropriate process parameters, high-quality vacuum brazing can be achieved.