Study on High Frequency Brazing Technology of Electric Kettle Heating Plate

- May 05, 2020-

The electric kettle industry towels and heating plates are mainly welded by furnace atmosphere protection welding, high-frequency induction brazing, etc. The high-frequency induction brazing process is a welding method that uses high-frequency induction current as a heat source. When the high-frequency induction brazing machine is working, the brazed part of the part is placed in an alternating magnetic field, and the base material is heated by the resistance heat of the induced current generated in the alternating magnetic field. High frequency induction brazing, the main process factors are solder ratio, solder coating amount, heating power, heating time, etc. Among them, the heating power and heating time determine the amount of heating heat, which directly affects the solder melting state and soldering quality. In order to verify the effect of heating power and heating time on welding quality, we conducted relevant welding experiments and verification on the heating plate of the electric kettle.

1-Experiment preparation:
Experimental sampling: The heating plate is composed of three parts: stainless steel plate, heat conduction plate, and heating tube. The stainless steel plate is made of 304 stainless steel T 0.4mm thick material, the heat conduction plate is aluminum plate Al060 T 1.8mm, and the main body of the heating tube is aluminum A3006. Samples are cleaned by ultrasonic degreasing and dried by a drying furnace. Solder preparation: Al, Si FeO aluminum-based brazing material is used. Brazing material: brazing agent is mixed at a mass ratio of 1.25: 1.

2- Welding experiment process:
Welding equipment: Six-station rotary disc brazing machine, Equipped with two 40kW high-frequency power supplies, the power supply is used for preheating and welding two stations: by adjusting the power knob, setting the heating time for welding heat control
Soldering method: Combine the heat-conducting plate and heating tube coated with solder to the lower surface of the stainless steel plate in turn, and then use the tooling to position and compact to complete the preassembly; place the pre-installed workpiece horizontally to the induction pad of station 1 On the iron, and start the upper air valve switch to press the workpiece; the workpiece rotates to station 2 and station 3 for preheating and welding respectively; the workpiece rotates to station 4, station 5, and station 6 for cooling under pressure; Finally, the workpiece is rotated to the station for cutting and welding is completed.

3- Design of experimental conditions
Brazing temperature test: the melting point of A1 Si FeO anchor brazing filler metal is 570 ℃, and the melting point of aluminum A1060 base metal is 660 ~ C. Therefore, the theoretical brazing temperature is preset to 595 ° C to 6l5 ° C; the heating power and heating time of station 2 and station 3 are set to the same parameters, the heating power is set to 1365kW, the heating time is adjusted to 32s, and 3 samples of station are observed Welding slag and solder are fully overflowing around the part, and the welding seam is full. The temperature of the welding part of the sample measured by the infrared thermometer is 612 ℃. Design of experimental conditions: the workpiece receives heat Q = 6 Pt, except for the power P and time t, the other conditions are the same, so the correction factor 6 is the same. According to the actual welding temperature and experimental parameters, a P-t parameter correlation table is established as shown in Table 1, and the conditions for locking the P * t value in the range of 43360 ~ 44000 are respectively 1355 & 32, 136O & 32, 1365 & 32, 1370 & 32, 1360 & 32. In addition, two groups of 1355 & 29 and 1375 & 35 conditions were selected to carry out experiments simultaneously。

4- Experimental results and analysis
Destruction inspection: tap the weld between the heat pipe and the heat conduction plate (hereinafter referred to as weld I), the weld between the heat conduction plate and the stainless steel plate (hereinafter referred to as weld 2): the heat pipe and the heat conduction plate are both made of aluminum , The weld 1 should not be knocked apart; the heat conducting plate and the stainless steel disc are of different materials, the weld 2 can be knocked apart, but the welding surface should be smooth and smooth: l The sample weld 1 and weld 2 are knocked apart and tested Unqualified: 2 #, 3 #, 5 samples, 6 # samples, the welding seam l can not be knocked apart, the welding seam 2 can be knocked apart, the welding surface is bright silver shiny surface, the welding powder is fully melted, spread evenly, inspection Qualified: 7 # sample welding seam 1 can not be knocked and separated, welding seam 2 can be knocked and separated, the welding surface is distorted, and the inspection is unqualified.
Dry burning pressure test: dry burning the 4 # sample according to 1.15 times the rated power, energized for 15s, water cooled at room temperature ~ [J45s, repeated 200 times, (as shown in Figure 2 (a)), the surface of the heating plate after the test No obvious deformation, no obvious cracks in the brazed joints, no obvious expansion of the heating tube, using a 0.05mm feeler gauge to check the deformation gap is not abnormal: 1250V high voltage is applied to the heating plate, the test time is 60s, the heating tube has no flashover and breakdown phenomenon, The leakage current is 0125mA ~ 0.168mA, the experiment is qualified.
Metallographic experiment: take 4 # sample to intercept the welding seam between the heating tube, the heat conduction plate and the stainless steel plate (as shown in Figure 2 (b)), the welding seam is full, and there is no obvious thick air hole: the heat conduction plate and the heat pipe material are long Large, filled with solder penetration between grain boundaries, good soldering effect.

5 Conclusion
(1) High frequency induction brazing of AI Si FeO aluminum-based solder, when the actual temperature of the heating plate is in the range of 597 "C ~ 625" C, the solder melts and overflows sufficiently, and the welding effect is good: when the actual temperature of the heating plate is near 612 ~ C , The soldering effect is the best, the solder is fully overflowed, but it will not form a weld knob on the outside, and the weld is full.
(2) Heating power and heating time are the key factors of the high-frequency induction brazing process. When the heating time is 32s, the heating power is 1355kW ~ 1375kW, the welding effect is good: when the heating power is 1360kW ~ l370kW, the welding effect is the best, and the welding surface is fully fused , The connection strength is qualified, the performance of the heating plate is qualified, and the metallographic structure changes in an orderly manner.
(3) The same heating time, heating power adjustment, welding effect response is general; the same heating power, heating time adjustment, welding effect response is intense; therefore, the heating time is more sensitive to the welding effect.
(4) Brazing material: the brazing agent is mixed with a mass of 1.25: 1, and a good brazing effect can be obtained