Electric iron power selection electric iron power difference

In the process of electrical repair, the soldering iron is an indispensable tool, but many maintenance personnel who have just touched the soldering iron do not know the power of the soldering iron according to the standard in the welding process, and it is often a soldering iron to go to the world. The most direct consequence is that the welding effect is not satisfactory due to the inability to pay attention to the power of the soldering iron.

The power of the soldering iron used is too large, and it is easy to burn the components (usually the junction temperature of the diodes and triodes will burn out when the temperature exceeds 200 °C) and the printed wires are detached from the substrate; the power of the soldering iron used is too small, and the solder is not sufficient. When melting, the flux can not be volatilized, the solder joint is not smooth, not strong, and it is easy to produce solder joint. Generally, it is used as a welding integrated circuit, printed circuit board, CMOS circuit, decoration transistor, IC type tape recorder, TV set, for ordinary circuit experiment, generally 20W is suitable, repair vacuum tube machine, such as amplifier, old instrument 35W is suitable, and the external heat type is 45W. The wiring of the welding transformer and the grounding trunk on the metal base plate are 50W of internal heat type and 75W of external heat type. If you want to weld metal materials, you should use an external thermal soldering iron of 100W or more. If conditions permit, amateur radio enthusiasts can be equipped with a 2OW internal heat type, a 35W internal heat or external heat type, and a 150W external heat type soldering iron, which can basically meet the needs of various welding.

The solder we use is generally divided into lead solder and lead-free solder, but the most commonly used is lead solder, which is 63% tin, 37% lead, 183 ° C melting point: the lead-free solder composition is 99% tin. The flux is about 1% and the melting point is 227 °C. The advantages of lead soldering are low melting point, easy soldering and low price, but it is not environmentally friendly. Lead is harmful to the human body. Therefore, after soldering, be sure to wash your hands carefully. During the soldering process, it is best to wear a mask or a bright place to ensure The head is at a certain distance from the weldment. As people's environmental awareness has increased, the machine welding in the factory now uses lead-free solder. Since the melting point of lead-free solder is high, it is not difficult to understand why solder is more difficult to melt when repairing imported electrical appliances.

The soldering iron is an electric heating device that generates a high temperature of about 250 ° C after being energized. In the welding process, the soldering iron is actually a process of heat conduction. When contacting the soldering surface, the heat on the soldering iron head is transferred to the solder. The solder absorbs heat and melts and flows under the surface tension to form a bright and round solder joint. . In the process of solder heat conduction, since the metal is a good conductor of heat, heat transfer is faster. During the melting process of the solder, the temperature of the soldering iron tip is more or less reduced due to the heat loss of the soldering iron. If the soldering point is large, it needs to absorb more heat to make the solder on the soldering point reach the melting point. If the iron tip is small, the stored heat is less, and the temperature drops faster. Because the heat generated by the small iron core is less than the heat that is added, the most obvious phenomenon is that the solder does not melt or melts incompletely. In this case, we have to use a high-power soldering iron for welding. On the contrary, if the welding parts are small, we do not need to use high-power soldering iron; if using high-power soldering iron, we must pay attention to the welding time, otherwise the excessive heat will easily cause the current to flow through the circuit called circuit, circuit board damage. Causes the printed copper foil to fall off. The specific power of the soldering iron is suitable, there is no specific quantitative requirements, the long-term work experience of the maintenance personnel is the best way to choose the soldering iron.

Explain two common problems and let us have a deeper understanding of the weldment principle. First of all, why use flux (such as rosin), in fact, the purpose of using flux is to prevent the phenomenon of soldering, the most direct role of the flux is to make the solder flow easily, it is not difficult to understand that smooth flow of solder will fill each A tiny hole; in addition, the flux also removes the oxide layer on the surface of the weldment. Of course, some fluxes are corrosive (such as solder paste) and should be used with caution. In order to improve the quality of the welding effect, the rosin is added to the finished solder wire, which is convenient to use.

The second question, why do you want to prevent the soldering iron from burning out? The soldering iron is burned to death. The soldering iron is not used because of long-term energization, resulting in a black oxide layer on the soldering iron. This black oxide layer is an oxide product of various metals such as copper and solder, and the metal oxide is a poor conductor of heat, preventing heat conduction. Moreover, since the soldering iron tip is oxidized, no solder is applied, and the contact surface of the soldering iron on the soldering iron tip and the soldering member is reduced, thereby further preventing heat transfer. Therefore, after the soldering iron is burned, the soldering iron soldering function is basically lacking. The only thing left is the heater function. In order to prevent the soldering iron from burning, it is the key to control the soldering iron for a long time. If you do not use the soldering iron for a long time during maintenance work, you should turn off the power to stop the soldering iron. Of course, it is also a good idea to install a control circuit to reduce the temperature when the soldering iron is idle.

Editor in charge: Zhao Hongli