Electric soldering iron--classification, principle and application knowledge of commonly used brazing methods
A welding method in which a metal material with a lower melting point than the base metal is used as the solder, and the liquid solder is used to wet the base metal and fill the interface gap between the workpiece and make it diffuse with the base metal. The brazing deformation is small, and the joint is smooth and beautiful. It is suitable for welding precision, complex and components composed of different materials, such as honeycomb structure plates, turbine blades, hard alloy tools and printed circuit boards. Before brazing, the workpiece must be carefully processed and strictly cleaned to remove oil stains and excessively thick oxide films to ensure the assembly clearance of the interface. The gap is generally required to be between 0.01 and 0.1 mm.
Types Depending on the welding temperature, brazing can be divided into two categories. If the welding heating temperature is lower than 450°C, it is called soft soldering, and if it is higher than 450°C, it is called hard brazing.
Soldering is mostly used for welding conductive, airtight and watertight devices in the electronics and food industries. Soldering with tin-lead alloy as solder is most commonly used. Solder generally needs to use flux to remove the oxide film and improve the wettability of the solder. There are many types of flux, and rosin alcohol solution is often used for soldering in the electronics industry. The residue after flux welding has no corrosive effect on the workpiece, which is called non-corrosive flux. The flux used for welding copper, iron and other materials is composed of zinc chloride, ammonium chloride and petroleum jelly. When welding aluminum, fluoride and fluoroborate are used as fluxes, and hydrochloric acid plus zinc chloride is used as fluxes. These residues after flux welding are corrosive, called corrosive flux, and must be cleaned after welding.
Brazed joints have high strength and some can work at high temperatures. There are many kinds of solders for brazing, and the solders based on aluminum, silver, copper, manganese and nickel are the most widely used. Aluminum-based solder is often used for brazing aluminum products. Silver-based and copper-based solders are often used for brazing of copper and iron parts. Manganese-based and nickel-based solders are mostly used to weld parts such as stainless steel, heat-resistant steel and high-temperature alloys that work at high temperatures. Palladium-based, zirconium-based and titanium-based solders are commonly used for welding refractory metals such as beryllium, titanium, and zirconium, graphite, and ceramics. The characteristics of the base metal and the performance requirements of the joint should be considered when selecting the solder. Brazing flux is usually composed of chlorides and fluorides of alkali metals and heavy metals, or borax, boric acid, fluoroborate, etc., and can be made into powder, paste and liquid. Lithium, boron and phosphorus are also added to some solders to enhance their ability to remove oxide films and wetting. Flux residue after welding is cleaned with warm water, citric acid or oxalic acid.
Methods There are many techniques commonly used in brazing, which are mainly distinguished according to the equipment used and the working principle. For example, according to the heat source, there are infrared, electron beam, laser, plasma, glow discharge brazing, etc.; according to the working process, there are contact reaction brazing and diffusion brazing. Contact reaction brazing is to use the solder to react with the base metal to generate a liquid phase to fill the joint gap. Diffusion brazing is to increase the heat preservation and diffusion time, so that the weld and the base metal are fully homogenized, so as to obtain a joint with the same properties as the base metal. The table below shows typical brazed joint styles.
