电弧焊基础(Arc-welding-foundation)(共11页).doc

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1、精选优质文档-倾情为你奉上电弧焊基础（Arc welding foundation）A, 1 in the cathode conductive characteristics of cathode functions: accept positive ions and emission cathode electronic institutions: the thermionic emission of cathode surface, field emission, thermal ionization collision local plasma emission cathode. Ho

2、t cathode (tungsten, carbon, etc.) : hot emission cold cathode (iron, aluminum, etc.) : electric field emission collision emission plasma caused the thermal power to leave.The electric conduction characteristic of the arc column is disorganized and the average kinetic energy is increased, resulting

3、in high temperature. The molecules, the atoms, will generate a thermoelectric shock, forming a plasma. The n arc column is electrically neutral (the unit volume is positive and negative with point particlesThe charged particles are directed to move and are essentially free from the repulsive action

4、of the space electric field, so they can transmit a large current under low voltage conditions. N arc column length is arc length, arc column lengthVoltage drop becomes the electric field intensity of arc column. The intensity of electric field in the arc column is low: usually only 5 10v/cm.The rol

5、e of anodes in the conductive characteristic of the 3 anode area: to accept the electron and provide the positive ion to the arc column. The production mechanism of positive ions:? Ionization under the action of the anode field: in the case of small current, the thermal power is difficult to get out

6、. Forming an anode pressure drop?Electron kinetic energy? Collision ionization? Until the anode voltage is stable. ? Thermoelectric current in the anode area: in the case of large current, the anode pressure drop is approximately zero, and the metal evaporates due to high electrode temperature. Ther

7、mal ionization? Does the current not form an anode when it is large enough? The anode pressure drop is also related to the electrode material characteristics, the thermal conductivity is good and the anode pressure drops.2. The forming conditions of cathode spots: 1) the conditions of emission elect

8、ron (field emission and thermal emission) 2) the arc column energy dissipation is minimized by this point. The characteristics of cathode spots: 1) the hot cathode is in the case of small current, while the cold cathode spots the cathode spot in the larger current. 2) to remove oxide film: cathode a

9、rtifacts, automatic search for oxide film (small) work function 3) block drop transition: spot pressure (including metal cations steam flow reaction force and impact force), the dc on melting polar hinder the droplet transition during welding. 4) adhesion characteristics: according to the minimum pr

10、inciple ofThe condition of the anode spot:? Is there any metal evaporation at that point? The arc column at this point consumes the lowest energyCharacteristics of anode spots:? Current density less than cathode spot? Find pure metal, do not have the role of oxidation film? Adhesion? Because the spo

11、t pressure is small, the resistance to the melt drop is small., the welding arc force concrete can be divided into three: the contraction (electromagnetic force) arc arc static pressure dynamic pressure, including the plasma power and spot pressure, impact force, the electromagnetic pressure differe

12、nce, metal evaporation reaction, cathode more stress) explosive force (short circuit transition, the liquid column contraction, resulting in blasting arc space gas expansion, local impact on wire and molten pool result is splash) and fine droplet impact (tiny metal droplet spray transfer, melting, w

13、e were waiting for the ion flow force into molten pool, with the plasma jet force has a great influence on the weld together. Penetration arc center area) the factors influencing arc force 1. Gas medium2. Current and voltage (arc length) 3. Electrode (electrode) diameter 4. Electrode (welding wire)

14、polarity 5. Geometry of the extreme part of tungsten 6. Influence of pulsating currentFour, short circuit transition features: - filaments, short arc, small current, arc arc alternates, (50 hz), 1.6 small 0.8 (130 hz) - the average current, peak current is large, suitable for thin plate and all posi

15、tion welding, small diameter welding wire, electric current density, heat production, welding speed, arc length, welding heating area is small, high quality- process stability - splashBridge transition: non - melting electrode arc welding. Under the action of surface tension, gravity and arc force,

16、the droplet enters the molten pool. ? Forming conditions: non - fusion electrode filaments, gas welding filaments.Droplet excessive: electric arc voltage is high, current is small, coarse drop transition, fine drop transition, reject transition.Spray transfer can be divided into: shoot drops transit

17、ion (drop diameter close to the wire diameter, arc force force from the end of the wire, and quickly through the arc space, in the form of transition to a molten pool. Steel wire pulsed MIG welding, weld wire MIG welding, the current must reach a certain threshold, the transition form will transitio

18、n from shape transition into shot drops), spray transfer (drop are tiny particles, the end of the pencil points along the wire in spray form quickly through arc space transition to a molten pool, in the form of steel wire MIG welding, the pure argon protection, dc reverse connection, high arc pressu

19、re, current must reach a certain threshold), rotating spray transfer (out super-large MIG welding current, welding wire length is larger, the welding current is greater than the critical current, jet length increases, the liquid metal jet fine drops of high-speed jet transition have larger reaction,

20、 once the axis deviation will produce rotating spray transfer, arc instability, molding, splash. Currently used its efficient characteristics, in the narrow gap welding has been applied in production.) , the spray transfer (arc length is shorter, molten droplets, grew up, from formation at the trans

21、ition of molten drops and molten pool short circuit, under the action of electromagnetic contraction force thin neck fracture, complete the transition, arc ignition again. Forming conditions: aluminum alloy weld wire, short arc welding)The transition of slag wall is a kind of transition in welding e

22、lectrode arc welding and submerged arc weldingA transitional form of the molten pool.5. Zone A: the current is very small, the arc voltage is high, the welding wire melts slowly, and the molten droplets are large lumps (big drops), which are not easy to escape from the wire, and can not be obtained

23、continuously when welding. If the arc voltage is reduced in this area, the arc length will be shortened and a solid short circuit will occur. Zone B: small current. Low voltage short-circuit transition specification area, high short circuit frequency, low electric arc voltage (7-21v), melt drop tran

24、sition stability, small splash, suitable for welding thin plate. C area: short circuit transition of high arc pressure and transition zone of particle transition, the ratio of the two is different from that of the parameters, and the splash is larger, but the arc heating efficiency is high. It is of

25、ten used by practical operation. Welding medium thickness workpiece is very deep. Area D: medium current and high arc pressure specification area, a large block transition of molten drop, or rejection transition, welding spatter. E area: large current welding. High arc pressure, the non-axial transi

26、tion of the droplet of fine droplets, the welding depth is large, the splash small is called fine particle transition, suitable for welding thicker workpieces.1) the welding current is small and the welding speed is too high.Or the size of the groove is not suitable, and the center line of the arc i

27、s deviated from the weld, the arc generated by the deflection, and the filament short-circuit transition CO2 welding, which can be easily caused by the small amount of thermal input of the workpiece. In thin plate welding, if the clamp is to the back of the weldThe heat degree is big, also can appea

28、r the lack of penetration, or part of the back part of the weld penetration, incomplete fusion of forming uneven phenomenon, 2) burn through welding current, welding speed is too small or collapse are likely to appear this kind of defect. When the thick plate is welded, the molten pool is too large,

29、 and the surface tension of the solid metal is not enough to absorb the gravity and arc force of molten metal. If in thin plate welding, arc force is too concentrated, or too large gap also can appear welding wear 3) bite edge and the formation of the pit is affected by the molten pool form, corresp

30、onding to the high speed welding arc and pool, due to the fast welding speed, melt on either side of the weld metal is not very good, at the same time, the surface tension of molten metal is easy to gather together and butt weld toe body parts of wettability is bad, easy to form a solid liquid,After

31、 solidification, a bite edge occurs. 4) the molten metal of the welding tumor flows to the unmelted female material in the weld area and gathers into a metal tumor, which is caused by the excessive filling of the metal, or the result of the gravitational effect of the molten pool; N directly aggrega

32、tes into large metal tumors on the weld, mostly due to unstable droplet transitionSeven, splash: in the welding process, most of the nail wire molten metal can transition to the pool, a part of welding wire melting metal (also includes a small amount of the molten pool of metal) fly to the molten po

33、ol outside. This phenomenon is called welding spatter. Measures: 1) correctly select the wire containing the deoxygenation element and limit the C content; 2) adopt multi-element gas protection. 1) correctly select the welding power source, match the appropriate voltage, and avoid the transition for

34、m as much as possible. 2) welding torch Angle is less than 20 , welding torch when vertical splash minimum. 3) limit the drying elongation of the wire. 4) the feeding speed is even. 5) small splash when the power is dc reverse polarity. 6) adopt hybrid gas protection. Power supply: suitable value.Ei

35、ght, submerged arc welding advantages: high efficiency, small heat dissipation, high effective utilization of electric arc, wire less resistance heat, big specification, can be used for large penetration of weld quality working conditions good save metal and electrical faults: hard to all position w

36、elding butt welding assembly requirements before is not suitable for welding sheet/short seam welding materials co., LTD9. Characteristics of melting polar argon arc welding: inert gas protection, high purity of weld, good mechanical properties; Arc combustion stability; The droplet is small and the

37、 transition is stable. Little splash. N and TIG welding ratio: high production efficiency; Welding thickness is greater than the TIG welding, welding current, welding heat input is big, big n and depth of molten SAW than: submerged arc welding seam of H is low, high n and CO2 welding cold cracking r

38、esistance than: arc and droplet transfer stability, weld forming beautiful n using dc reverse welding aluminum and aluminum alloy, with the cathode cleaning action disadvantages: high cost, are sensitive to oil pollutionTen, CO2 arc welding features: wide welding speed (applicable normal low carbon

39、steel of high strength steel cast steel omni-directional welding) welding quality is good, is not sensitive to rust, weld hydrogen content is low, good crack resistance, thermal deformation is small.) Good arc performance (energy concentration, easy to draw arc,Continuous wire feeding arc uninterrup

40、ted. ) Dissolve deepHigh application efficiency. Compared with manual welding: the wind resistance is poor and the equipment is more complex.11. Characteristics of TIG welding: almost all metals or alloys can be soldered? Good welding quality (weld pure, forming good, hot zone small)? Suitable for t

41、hin plate and bottom/full position welding? No spatter defect: low welding efficiency and high cost; ? Strict cleaning requirements before welding; ? Special arcing measures are needed; ? Strong uv and high ozone concentration; ? Resistance to windNoun interpretation:1. Gas discharge: refers to gas

42、ionization. The gas is ionized under the action of the electric field and the thermal field, and the space is formed by the neutral particles such as the cation and the charged particles, the atoms and the molecules. The essence of arc is gas discharge.2, self sustaining discharge: when the current

43、is more than a certain value, gas conduction process itself can produce needed to maintain the conductive charged particles, once discharge starts, cancel and induce measures, discharge process can still continue, the discharge process is called self sustaining discharge.3. Non-self-sustaining disch

44、arge: in a small current interval, the charged particles needed for the conduction of gas cannot be generated by the conducting process itself, and the additional measures are needed to create charged particles. This gas discharge phenomenon is called non - self - sustaining discharge.4. Ionization

45、degree: the ratio of ionized particles in the unit volume to the total number of particles before ionization.5, the cathode spots: when the cathode for cold cathode material, due to thermal emission do not have enough quantity of electrons, cathode will further narrow the conductive area automatical

46、ly, at this time will form at the cathode surface area is smaller, current density larger spots to current flow. This conductive spot is called a cathode spot.6, anode spots: arc burning not covered on the surface of the anode on the whole area of forming uniform current channel, will be formed at t

47、he anode of a local area important channels, most of the electronic through the path to the anode. This conductive spot is called an anode spot.7, arc cathode cleaning action: inert gas in the arc under the condition of the metal plate as cathode, the cathode spots on the metal plate back, removal o

48、f oxide film on metal surface, clean metal surface.8, the principle of minimum voltage, current with the surrounding conditions in a given situation, the arc stable combustion, the radius (or temperature) of the conductive area, should make arc electric field intensity has the smallest value. That i

49、s, the arc has the characteristic of keeping the minimum energy consumption.9, static characteristics: stable state, under a arc length value, under the condition of the stability of shielding gas flow and electrode, the numerical change of arc current, the arc achieved steady combustion state corresponding to the arc voltage.10. Dynamic characteristics: the electric arc voltage of welding current varies with time i