刚刚看到一篇好文章，之前对于焊接、熔焊一直搞不太懂，这个解释的清晰明了，看到了分享一下。7 `. k5 i7 B! Z) U g$ U' S
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by Chris Woodford. Last updated: August 28, 2017. What is welding?! d' C$ d0 [$ l$ y% t% J
Photo: Although welding and soldering can look similar, they do completely different things. Top: This welded joint mechanically fixes two pieces of metal together in an upside-down T-shape. Photo by Brian Hibben courtesy of US Navy. Bottom: These soldered joints on the back of a printed circuit board make a reliable electrical connection between the components and the tracks on the board that join them together. Photo by explainthatstuff.com. You can't really join metals with adhesive—not with ordinary glue, anyway. But you can join them by melting them together in a process known as welding. The basic idea is simple: you apply a source of heat to melt the two metals so they fuse and form a secure joint. Usually (though not always) you add other materials as you apply the heat: a filler (an extra piece of metal, supplied from something called a welding rod, which seals up any gaps where the main metals meet) and a flux (a nonmetallic chemical that helps to stop the molten metals forming oxides and nitrides with gases in the air, which weakens the joint). As an alternative to using a flux, you can weld in an atmosphere from which the air has been removed (filled with other, nonreactive gases such as argon, for example). Most forms of welding involve joining metals with heat alone. But they differ in where the heat comes from. One common form of welding involves using an oxyacetylene gas torch, which makes an intense flame by burning acetylene (an energy-rich fuel made from a simple hydrocarbon molecule) in a rich supply of oxygen. Although convenient and portable, oxyacetylene torches are relatively expensive to use (because the fuel is supplied in gas cylinders). In factories, it's usually more convenient to weld with electrical power using a technique known as arc welding. Instead of a gas torch, you use a piece of metal called an electrode connected to a high-current power supply (hundreds of times higher than the ones that flow through appliances in your home). As you bring the electrode up to the joint you're welding, it creates a spark or arc that melts the metals together. Arc welding produces both bright visible sparks and discharges of ultraviolet light, both of which can lead to blindness; that's why you'll always see people arc welding behind wraparound protective visors. Other heat sources for precision welding include ultrasonics, lasers, and electron beams. You can also weld materials by forcing them together through sheer pressure, with or without extra heat. This is known aspressure welding; used for many hundreds of years by blacksmiths and other artisans, it's one of the oldest metalworking techniques. The basic process involves heating metals in a forge and then hammering them together so they fuse. One way to make arc welding safer is to get an industrial robot to do it for you. Car bodies have been welded by robots for decades. The first welding robot, theUnimate, made its debut in a General Motors plant in 1961. - A- o& q& w+ s' U6 \0 K% D6 F+ n+ l
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What is soldering?Soldering looks similar to welding—but it's quite different! In welding, you're trying to make a super-strong joint between two pieces of metal. Often a welded joint has to stand up to incredible stresses and strains—for example, if you weld parts of a car body or an airplane fuselage together. So the objective is to make a goodmechanical connection. When you solder, the idea is usually to to make a good electrical connection. Solder looks a bit like an unwrapped paperclip, though it's much softer, and it generally comes in tubes and reels. It's an alloy of different metals that has a relatively low melting point. The solder I use, which is typical, is made of 99.25 percent tin and 0.75 percent copper, though other metals such as zinc, silver, and bismuth are also used. (Lead was once widely used in solders with tin, but has now been largely phased out for health reasons). Solders sometimes also contain fluxes to prevent the formation of oxides.
) c/ c- T! R# a8 f" V! e! T% nWhy do you need to solder? Electronic circuits are made of discrete components: tiny devices such as resistors,capacitors, transistors, and LEDs that do specific jobs. When you put them together in different ways, you can build all kinds of amazing electronic gadgets, from radios and televisions to calculators and computers. The components all have little metal legs—terminals that you use to connect them into the circuits. You could just wire these legs together with electrical cables, but the wires might drop off or wriggle free and the connections wouldn't be reliable, so anything you built this way wouldn't work very well. And that's where solder comes in: it makes a much more effective electrical connection. If you want to make a good soldered joint, you don't solder straight away. First, you clean the components you want to join (for example, by scraping them with a knife to remove any surface oxides). Then you make a goodmechanical connection between them (by wrapping the cable tightly round the component or whatever). Only then do you make a good electrical connection by melting some solder on top.
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发表于 2017-12-15 14:11
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