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Vacuum brazing of titanium heat exchanger

Titanium alloy has developed into an important structural material in modern advanced aviation and aerospace structures, and the amount of titanium alloy structural material selection has shown a rapidly rising trend. At present, in the advanced American F119 fourth-generation aero-jet engine, the amount of titanium alloy has reached one-third of the total structure. And it is expected that the amount of titanium used in the next generation of turbine engines and aircraft structures will continue to grow. It is known that the titanium alloy brazed structure can be widely used in aircraft large core honeycomb sandwich wings, ribs and rudder reinforcement ribs, life support and protective clothing plate-fin heat exchangers, landing reverse thrust grids, ducts, etc. , Wide-chord hollow fan blades of turbine engines, compressor guides and diffusers, intake guides, etc., and the installation ring of the combustion chamber of the rocket engine. The brazed structure of the new TiAl and TMC materials can be used in low-pressure turbines, combustion chambers and nozzles with an operating temperature of 600C-1000C for advanced turbine engines.
At present, there are basically two types of brazing materials for brazing titanium and titanium alloys. One is low-temperature Al-based and Ag-based brazing filler metal; the other is high-temperature Ti(Zr)-Cu-Ni-based and Cu-based brazing filler metal. material. The shortcomings of the former low-temperature brazing joints are low corrosion resistance and high temperature strength; the latter high-temperature brazing joints have good high-temperature strength and corrosion resistance and are the best brazing materials for titanium brazing. The traditional heat exchanger is mainly a brazed structure made of aluminum, copper or stainless steel, and the new titanium heat exchanger has obvious advantages in weight reduction, corrosion resistance and high temperature strength performance. Aerospace, aerospace and nautical are its applications The best area. The structure of the titanium heat exchanger is complex, with many brazing seams, high brazing rate requirements, and high requirements for the tightness of the brazing seams. Therefore, high requirements are placed on the brazing process.

Brazing method:
Using TA2 material heat exchanger, the structure is shown in the figure. The heat exchanger is composed of two parts, the body and the cover plate. The cover plate is placed in the square groove of the body to form a brazed joint with the rib of the body. After brazing, a sealed structure is formed. The rib width is 2 mm and the cover plate is 1.9 mm thick.

Using solder:
(1) Ti-Zr-Cu-Ni series Ti-based brazing material, brazing temperature range 910-960C, used in the form of powder and 0.05-0.07mm thick quenched amorphous foil;
(2) Pure Cu solder is used in the form of 0.05mm thick cold-rolled foil and 10um plating layer.

Device:
Vacuum brazing adopts the vacuum brazing furnace of Shanghai Gehang Vacuum Technology Co., Ltd., the size of the average temperature zone is Ø300 x 400mm, the use temperature is 1250C, and the thermal vacuum degree is better than 2×10-2Pa.

Brazing process:
After cleaning, the pure Cu brazing foil is spot-welded to the rib of the heat exchanger body with an energy storage welding machine. The cover plate is inserted into the groove of the body, and then the brazing material is added to the brazing gap between the side of the cover plate and the body. The assembly is placed on the brazing fixture to be compressed, so that the brazing material is compressed in the brazing gap, and the predetermined brazing gap of each brazing stroke is guaranteed to obtain a high brazing rate and air tightness. To prevent sticking, the fixture and titanium heat exchanger are separated by solder resist. Due to the large brazed parts, a stainless steel pressure plate with fastening screws is used to press evenly at multiple points.
Brazing process parameters:
Experiments and comparisons have been made on different brazing filler metals and brazing filler metal usage forms, brazing gaps, and different brazing temperatures and times.

Using Cu as the brazing filler metal under the condition of 960C/60min vacuum process plan, brazing the heat exchanger, the brazing joint is dense. The brazing rate is 100%. Brazing is performed at 960C, and the base material manager has grown up. The leak detection and compressive strength of the brazed heat exchanger are combined with the actual use requirements.
Brazing the titanium heat exchanger with Ti-Zr-Ni-Cu brazing material can easily obtain the isothermal solidification brazing structure. With pure Cu solder, the price is low, and dense and beautiful brazed joints can also be obtained, but the plasticity is low.

SIMUWU vacuum brazing furnace:
Vacuum brazing furnace is a large-scale equipment for heat treatment, which can carry out various processes such as vacuum brazing, vacuum annealing, vacuum aging and so on. Multiple different programs can be edited, and hundreds of heat treatment curve points can be controlled and programmed, one-zone temperature control, there are multi-point and single-point temperature recorders and over-temperature protection devices, and the furnace temperature is uniform The performance can be controlled within a constant temperature range (± 5 ℃), and a high-purity nitrogen high-flow strong cooling device is also provided. The equipment has a large furnace load and high efficiency, and does not require supplementary process treatment products for complex parts and parts with special requirements.

Application:
Mainly used for aluminum brazing, copper brazing, stainless steel, titanium alloy, hard alloy, high temperature alloy, non-ferrous metal brazing for aircraft parts, automobile parts, electronic communication parts, household appliances, heat exchangers and various radiators And vacuum tempering of high-speed steel, tool steel, bearing steel, stainless steel and other materials, as well as the aging and annealing treatment of non-ferrous metals and vacuum brazing of stainless steel heat exchangers, oil coolers, stainless steel vacuum cups.

Feature:
1. Use zoned heater arrangement to make the temperature uniformity in the heating zone consistent.
2. Brazed in a vacuum atmosphere to keep the workpiece clean and bright.
3. Heating under vacuum can remove the grease and oxide film on the surface of the workpiece, so the surface brightness of the parts is high, and no flux is required, and there is no need to clean after welding.