Abstract: Electric iron is an essential tool for electronic production and electrical maintenance. Its main purpose is to weld components and wires. According to the structure of electric iron, it can be divided into internal heating type electric iron and external heating type electric iron. According to the function, it can be divided into welding electricity. Soldering iron and soldering iron are divided into high-power electric soldering iron and low-power electric soldering iron according to different purposes.
The structure of electric iron is the role of electric iron rosin
Structure introduction
The soldering iron is divided into two types: external heat type and internal heat type:
The external heating type soldering iron is composed of a soldering iron head, a soldering iron core, a casing, a wooden handle, a power lead, a plug and the like. Since the tip is mounted inside the iron core, it is called an external heating type soldering iron. The iron core is a key component of the soldering iron. It is formed by winding the heating wire in parallel on a hollow ceramic tube. The mica sheet in the middle is insulated, and two wires are connected to the 220V AC power supply. There are many specifications for external thermal soldering irons, such as 25W, 45W, 75W, 100W, etc. The higher the power, the higher the temperature of the soldering iron.
The internal heat type soldering iron is composed of a handle, a connecting rod, a spring clip, a soldering iron core and a soldering iron head. Since the iron core is installed inside the soldering iron tip, the heat is fast and the heat utilization rate is high, so it is called an internal heat type soldering iron. The common specifications of the internal heating type soldering iron are 20W and 50W. Due to its high thermal efficiency, the 20W internal thermal soldering iron is equivalent to an external thermal soldering iron of about 40W. The rear end of the internal heat type soldering iron is hollow, and is sleeved on the connecting rod and fixed by the spring clip. When the soldering iron head needs to be replaced, the spring clip must be first removed, and the front end of the soldering iron head is clamped with the pliers. Pull out slowly, remember not to use too much force to avoid damaging the connecting rod.
Mechanical principle
These two situations will bring great difficulties to the debugging and overhaul of electronic production. These two situations can only be avoided after a large number of serious welding practices.
When soldering a circuit board, be sure to control the time. Too long, the board will be burnt or cause the copper foil to fall off. When removing components from the board, the soldering iron tip can be attached to the solder joints. After the tin on the solder joints is melted, the components are pulled out. The temperature of the soldering iron has a certain relationship with the size, shape and length of the soldering iron. When the size of the tip is relatively large, the hold time is longer. In addition, in order to meet the requirements of different welds, the shape of the tip is different, and the common ones are tapered, chiseled, round beveled, and the like.
Use the multimeter ohmmeter to measure whether there is an open circuit short circuit at both ends of the plug, and then use Rx1000 or Rx10000 file to measure the resistance between the plug and the outer casing. If the pointer is not moving or the resistance is greater than 2-3MΩ, it can be safely used without leakage. The iron core of the internal heating type soldering iron is made of a relatively thin nickel-chromium electric resistance wire wound on a porcelain tube, and its electric resistance is about 2.5 kΩ (20 W), and the temperature of the soldering iron is generally about 350 ° C. Since the internal heating type soldering iron has the characteristics of quick heating, light weight, low power consumption, small volume, and high thermal efficiency, it has been applied in general.
After the soldering iron is turned on, it is not hot or too hot. Check whether the power supply voltage is lower than AC210V (normal voltage should be AC220V). If the voltage is too low, the heat may be insufficient and the soldering is difficult. The soldering iron tip is oxidized or the root end of the soldering iron tip and the inner wall of the outer tube are oxidized. In the three-phase four-wire power supply system, the neutral line is grounded and equipotential to the earth. If the bubble is illuminated when tested with a test pencil, it indicates that the neutral line is charged (the potential difference between the neutral line and the ground). The zero line is open, the neutral line grounding resistance is increased, or the grounding down line is open and the phase line is grounded.
The use of soldering iron should pay attention to the soldering iron should be grounded, it is best to use a pointed soldering iron, temperature (260 ° C -300 ° C), you can add some soldering materials (rosin, flux), the surface of the chip should choose the right solder Wire (0.6-0.8), if necessary, you can use a constant temperature soldering iron. Wear an anti-static wristband during the welding process. Pay attention to the direction of the core, which should be consistent with the silk screen. The iron core has different power specifications and its internal resistance is different. The resistance of the 25W soldering iron is about 2kΩ, the resistance of the 45W soldering iron is about 1kΩ, the resistance of the 75W soldering iron is about 0.6kΩ, and the resistance of the 100W soldering iron is about 0.5kΩ. The soldering iron tip is made of copper material. Its function is to store heat and conduct heat. Its temperature must be much higher than the temperature to be soldered.
The role of rosin
Rosin acts as a flux in the welding process and acts as a flux. In theory, the melting point of the flux is lower than that of the solder, and the specific gravity, viscosity, and surface tension are smaller than that of the solder. Therefore, when soldering, the flux melts first, and quickly immerses and covers the surface of the solder to prevent the metal from being isolated. Oxidation, and can react with the surface oxide film of the solder and the metal to be welded at the high temperature of the solder to melt and restore the pure metal surface. A suitable solder helps to weld a satisfactory solder joint shape and maintain the surface gloss of the solder joint.
Rosin is the most commonly used flux, it is neutral and does not corrode circuit components and soldering iron tips. If it is a newly printed circuit board, apply a layer of pine perfume to the surface of the copper foil before soldering. If it is a prepared circuit board, it can be soldered directly. In fact, the use of rosin depends on personal habits. Some people will dip the tip of the soldering iron on every rosin after soldering one component. Every time I use the soldering iron tip to be oxidized, it is not convenient to use. Dip some rosin on top. The use of rosin is also very simple. Open the rosin box and dip the energized tip on it. If a solid core solder is used for soldering, it is necessary to add some rosin; if a rosin solder wire is used (the flux is wrapped in the wire core), rosin may not be used.
Since the metal surface is in contact with air, an oxide film is formed. The higher the temperature, the more the oxidation. This layer of oxide film prevents the liquid solder from wetting the metal, just as if the glass is oiled, the water will not be wet. Flux is a special material used to remove oxide film, also known as flux.
Flux has three major functions:
1. Remove the oxide film. The essence is that the substance in the flux undergoes a reduction reaction, thereby removing the oxide film, and the reaction product becomes suspended slag and floats on the surface of the solder.
2. Prevent oxidation. After it melts, it floats on the surface of the solder to form an isolation layer, thereby preventing oxidation of the soldered surface.
3. Reduce surface tension, increase solder flow, and help solder wet weldments. 
Editor in charge: Zhao Hongli
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