Operation of Gas tungsten arc welding II
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- Category: Tungsten Information
- Published on Monday, 13 May 2013 16:30
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An alternate way to initiate the arc is the "scratch start". Scratching the electrode against the work with the power on also serves to strike an arc, in the same way as SMAW ("stick") arc welding. However, scratch starting can cause contamination of the weld and electrode. Some GTAW equipment is capable of a mode called "touch start" or "lift arc"; here the equipment reduces the voltage on the electrode to only a few volts, with a current limit of one or two amps (well below the limit that causes metal to transfer and contamination of the weld or electrode). When the GTAW equipment detects that the electrode has left the surface and a spark is present, it immediately (within microseconds) increases power, converting the spark to a full arc.
Once the arc is struck, the welder moves the torch in a small circle to create a welding pool, the size of which depends on the size of the electrode and the amount of current. While maintaining a constant separation between the electrode and the workpiece, the operator then moves the torch back slightly and tilts it backward about 10–15 degrees from vertical. Filler metal is added manually to the front end of the weld pool as it is needed.
Welders often develop a technique of rapidly alternating between moving the torch forward (to advance the weld pool) and adding filler metal. The filler rod is withdrawn from the weld pool each time the electrode advances, but it is never removed from the gas shield to prevent oxidation of its surface and contamination of the weld. Filler rods composed of metals with low melting temperature, such as aluminum, require that the operator maintain some distance from the arc while staying inside the gas shield. If held too close to the arc, the filler rod can melt before it makes contact with the weld puddle. As the weld nears completion, the arc current is often gradually reduced to allow the weld crater to solidify and prevent the formation of crater cracks at the end of the weld.
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Operation of Gas tungsten arc welding I
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- Category: Tungsten Information
- Published on Monday, 13 May 2013 16:25
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Manual gas tungsten arc welding is often considered the most difficult of all the welding processes commonly used in industry. Because the welder must maintain a short arc length, great care and skill are required to prevent contact between the electrode and the workpiece. Similar to torch welding, GTAW normally requires two hands, since most applications require that the welder manually feed a filler metal into the weld area with one hand while manipulating the welding torch in the other. However, some welds combining thin materials (known as autogenous or fusion welds) can be accomplished without filler metal; most notably edge, corner, and butt joints.
To strike the welding arc, a high frequency generator (similar to a Tesla coil) provides an electric spark; this spark is a conductive path for the welding current through the shielding gas and allows the arc to be initiated while the electrode and the workpiece are separated, typically about 1.5–3 mm (0.06–0.12 in) apart. This high voltage, high frequency burst can be damaging to some vehicle electrical systems and electronics, because induced voltages on vehicle wiring can also cause small conductive sparks in the vehicle wiring or within semiconductor packaging. Vehicle 12V power may conduct across these ionized paths, driven by the high-current 12V vehicle battery. These currents can be sufficiently destructive as to disable the vehicle; thus the warning to disconnect the vehicle battery power from both +12 and ground before using welding equipment on vehicles.
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Description of Wave Soldering
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- Category: Tungsten Information
- Published on Monday, 13 May 2013 16:12
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Wave soldering is a large-scale soldering process by which electronic components are soldered to a printed circuit board (PCB) to form an electronic assembly. The name is derived from the use of waves of molten solder to attach metal components to the PCB. The process uses a tank to hold a quantity of molten solder; the components are inserted into or placed on the PCB and the loaded PCB is passed across a pumped wave or waterfall of solder. The solder wets the exposed metallic areas of the board (those not protected with solder mask, a protective coating that prevents the solder from bridging between connections), creating a reliable mechanical and electrical connection. The process is much faster than manual soldering of components.
Wave soldering is used for both through-hole printed circuit assemblies, and surface mount. In the latter case, the components are glued by the placement equipment onto the printed circuit board surface before being run through the molten solder wave.
As through-hole components have been largely replaced by surface mount components, wave soldering has been supplanted by reflow soldering methods in many large-scale electronics applications. However, there is still significant wave soldering where SMT is not suitable (e.g., large power devices and high pin count connectors), or where simple through-hole technology prevails (certain major appliances).
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The process of Wave Solder
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- Published on Monday, 13 May 2013 16:17
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There are many types of wave solder machines, however the basic components and principles of these machines are the same. A standard wave solder machine consists of three zones: the preheating zone, the fluxing zone, and the soldering zone. An additional fourth zone, cleaning, is used depending on the type of flux applied. The basic equipment used during the process is a conveyor that moves the PCB through the different zones, a pan of solder used in the soldering process, a pump that produces the actual wave, the sprayer for the flux and the preheating pad. The solder is usually a mixture of metals.
A typical solder has the chemical makeup of 50% tin, 49.5% lead, and 0.5% antimony.[citation needed] There are three types of waves: normal wave, a medium speed, long leads used for horizontal soldering; cascade wave, high speed, short leads, used for inclined soldering; and flat wave with extenders; medium to high speeds, long leads that is used for horizontal soldering.
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Advantages of Brazing and Soldering Over Fusion Welding
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- Published on Monday, 13 May 2013 16:04
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1.Substrate remains solid throughout, therefore less heat energy is required
2.Less of the substrate is affected metallurgically by the application of heat
3.The process is less expensive because it requires less energy
Soldering can be differentiated from brazing because of the lower melting temperature of the filler material. Typically solder constitutes primarily of a tin/lead* alloy with alternative alloy components or percentage changes being introduced and varied to increase/decrease the melting temperature. The cut off between soldering and brazing is generally recognized as being above or below 450C.
A melting point below 450C is typically considered to be soldering and above 450C it is typically considered to be brazing, although silver soldering or hard soldering is normally above 450C and consequently should be considered to be the first level of brazing even though it is never really referred to as brazing and nearly always as soldering.
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