Automatic Arc Welding
Automation and mechanization of the arc welding process can be recognized as one of the most important problems of modern welding technology. Manual arc welding is too time consuming, requires large amounts of skilled labor is relatively expensive, and, of course, can not ensure uniformity of product, as well as the subsequent quality control of welding difficult, not reliable and not always feasible, then the confidence in the quality of welding is reduced and deliberately reduced allowable stress for welded joints.
In arc welding automation in recent years achieved such success that now this process is the degree of automation of the basic operations can be considered one of the most advanced and progressive process of metal.
Automation respond well to all the major types of arc welding. By the degree of mechanization and semi-automatic distinction, in the past has maintained a large proportion of manual labor. To implement automatic welding requires a range of machines and devices that make up the automatic setting for arc welding. The device, which produces the ignition of the arc, the electrode feed as providing stable combustion and burning of the arc is called an automatic head for arc welding or arc machine. The most important industrial importance for the automatic welding fusible metal electrode (Fig. 81). Instead of separate short electrodes, used in manual welding, automatic welding is used in the electrode wire of great length, in bundles or coils, and the winds off the machine tool supplied to the zone of the arc as its melting point. wire is fed through the gear and the drive rollers drive a small electric machine . After a drive rolls, and often the correct mechanism, device, and sculpt the curvature of the bay with winds up giving the wire straightness, it enters the mouthpiece of the machine or the current lead, which is pressed against the electrical contacts and slides over it, carrying out welding current, arc power supply. The distance from the current supply to the arc of contact is small (several centimeters), so the machine works as a short continuously renewable electrode. This is an important advantage of the machine, since the wire is reduced Joule heating and creates the possibility of very high current densities in the electrode wire without overheating. Wire feed speed automatically with its melting, so the arc length of the combustion of the wire remains approximately constant. Many machines also automatically produce the ignition of the arc at the beginning of welding and re-ignition of accidental breakage during operation. Regulation of the welding process in the machine can be carried out in various ways. For example, you can link the feed rate of electrode wire with a voltage of the arc and its length. In the normal length of the arc and its normal voltage wire machine supplies at a rate approximately equal to its rate of melting, with a decrease in the length of the arc wire feed speed is reduced, so that the arc length and voltage increase and establish their normal values. In case of accidental increase in the length of the arc flow rate wire increases and the length of the arc, and at the same time the voltage is reduced to the normal set point. When a short circuit when the arc voltage drops almost to zero, the feed direction of the electrodes is changed, ie, the electrode is not applied towards the base metal, and withdraw ago, and the end of the electrode is removed from the base metal. After turning on the machine when the electrode is not concerned products and there is no arc, the voltage between the electrode and the workpiece is equal to the full-load voltage current source. This voltage is above the normal arc voltage, and therefore the electrode is fed forward to the product. When the electrode tip for product and short-circuits the arc gap, there is a reversal of filing e arc ignition. If the separation of the electrode arc does not light up, the above process is repeated. After ignition of the arc starts feeding electrode forward with changes to the product flow rate, respectively, the voltage of the arc. Thus, the arc length is automatically maintained constant with an accuracy that is not available for manual welding. Modern machines maintain the arc voltage up to 0.5 V, which corresponds exactly to maintain the arc length ± 0,2-0,3 mm. arc machine is an automatic control that supports the constant mode of arc welding as far as possible, regardless of the impact of external disturbances and random factors. In the framework of regulation of the arc-melting machine with a metal electrode can be based on different principles. Currently, there are two basic types of machines with arc consumable electrode, different in principle of regulation: 1) Automatic control of electric-ray values, and 2) machines with a constant feed rate of the electrode. In the first type of automatic variable is any value of the electric arc regulating the size - flow rate of the electrode. Controlled quantity can serve as the voltage of the "or arc power, etc. In modern machines for adjustable size usually take the arc voltage. In the welding arc voltage is virtually independent of the strength of the current depends only on the arc length, varying in proportion to changes in length: U = a + bL. If the machine that supports the constant arc voltage, arc length remains constant and the welding process will retain a normal character. Thus, the regulation of constant arc voltage regulation is equivalent to the constancy of its length. For decades, machines for arc consumable electrode constructed with only automatic control of the constancy of the arc voltage. VI Woodpeckers first proposed a new principle of automatic devices arc electrode for supplying a constant rate, independent of the arc voltage or other factors. He first drew attention to the self-arc welding with consumable electrode , investigated this phenomenon and proposed the use of machines in the arc. In some cases, self-regulation of the arc takes place so rapidly that there is no need to use a fairly sophisticated automatic control schemes arc - just constantly apply the electrode in an arc with a constant velocity equal to its melting point. Self-regulation of the arc due to the fact that the rate of melting of the electrode varies with the length of the arc: with increasing length of the arc melting rate decreases with decreasing length of the arc, this rate increases. At a constant feed rate of the electrode arc length of random variation causes a change in the rate of melting of the electrode, aimed at restoring the original length of the arc. At the intensity of self-regulation, among other factors, the most heavily influenced by the density of the welding current to the electrode and the shape of the external characteristics of the welding power source. If there is insufficient self-regulation of current densities flowing so slowly that accidentally started a shortening of the arc has often led to a short circuit, and elongation - to the edge of the arc early in the process of self-regulation than the time to restore the normal length of the arc. with increasing current density rapidly increases the rate of melting of electrode wire and the intensity of self-regulation. For example, the steel electrode wire at low current densities of 15-25 A/mm2, giving the rate melting of electrode wire of 0.5-1 m / min, necessarily requires automatic control of the arc and a constant feed rate of electrode wire can not be used for these modes of machines. At current densities of 30-50 A/mm2 and wire feed speed of 1-2 m / min can be used as automatic control, and a constant feed rate. For current densities of 50-100 A/mm2 and higher wire feed speeds 2-6 m / min all the benefits - at a constant feed rate. In connection with the tendency in modern technique to increase the current densities in automatic welding machines use is growing rapidly with a constant feed rate, and this type of machine is the most common. very important for self-regulation of the arc has a form of external characteristics of a current source feeding the arc. above set forth the performance requirements of current sources, the actual Welding current low densities used in manual or automatic welding. At high current densities and a constant feed rate of self-regulation is most intensive in the flat characteristics of the current source and the best results are obtained with a constant current source voltage, and in some cases it is advisable not falling, and increasing the external characteristics when the voltage increases with increasing current. arc machine supports and feeds the arc electrode wire. For the weld must be moved through an arc welding process. Depending on the method of moving the arc distinguished pendant machines, welding machines and self-propelled tractors. Suspension Automatic has no moving mechanism, it is a separate device. can navigate the product with a fixed machine (as is usually carried out circular joints) or the same machine, mounted on a self-propelled trolley along the product, such as when welding long straight seams. possible and the simultaneous movement of the machine and products convenient when certain curved seams. self-propelled machines have a mechanism for moving, structurally integrated with a gun. self-propelled machine moves on a special track. welding tractor is lightweight, compact self-propelled machine which travels directly to the surface of the workpiece or a portable light rail track to be placed on surface. Welding Tractors are particularly suitable for welding of large size, such as ship hulls, large tanks etc. Here is a brief description of some arc machines. First consider the machine with voltage regulation, and thus the arc length by changing the feed rate of electrode wire. An example of this is enough of a perfect machine of continuous operation can be automatic Td, manufactured by the "Electric".
See also:
Automatic Arc Welding
Automatic ADS
Machines with a Constant Feed Rate of Electrode
Flux Equipment
Settings for Automatic Arc Welding
Automatic Submerged Arc Welding Introduction
Fluxes for Automatic Arc Welding
Processed Fluxes
Ceramic Fused Fluxes
Semi-Automatic Arc Welding
Arc Welding with Flux Cored Wire
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