Basic knowledge of welding

A basic knowledge 

1. What is welding? 

A: two or more materials (allogeneic or xenogeneic), by heat or pressure or 
both and use, to achieve the bonding between the atom to form The process of permanent connection is called welding. 

2. What is arc? 

Answer: A strong and long-lasting gas discharge phenomenon is called between the two poles, which is supplied by the welding power source. 

<1> According to the type of current, it can be divided into: alternating current arc, direct current arc and pulse arc. 

<2> According to the state of the arc, it can be divided into: a free arc and a compressed arc (such as a plasma arc). 

<3> According to the electrode material, it can be divided into: a melting arc and an infusible arc. 

3. What is the base material? 

A: The metal being welded - called the base metal.　 

4. What is a droplet? 

Answer: The liquid metal droplets , which are melted at the tip of the wire and melted into the molten pool, are called droplets. 

5. What is a molten pool? 

Answer: The part of the liquid metal with a certain geometry formed on the weldment during welding is called the molten pool. 

6. What is a weld? 

A: The joint formed in the weldment after welding. 

7. What is weld metal? 

Answer: The part of the metal formed by the solidification of the molten base metal and filler metal (welding wire, welding rod, etc.). 

8. What is protective gas? 

Answer: The gas used in the welding to protect the metal droplets and the molten pool from the harmful gases (hydrogen, oxygen, nitrogen) invaded. 

9. What is welding technology?

A: The general name of various welding methods, welding materials, welding processes and welding equipment and its basic theory - called welding technology. 

10. What is the welding process? What does it have? 

A: A complete set of process procedures and technical regulations during the welding process. The contents include: welding method, pre-weld preparation, assembly, welding materials, welding equipment, welding sequence, welding operation, welding process parameters and post-weld treatment. 

11. What is CO2 welding? 

A: MIG welding with a purity of > 99.98% CO2 as a shielding gas - called CO2 welding. 

12. What is MAG welding? 

Answer: A gas-shielded gas shielded welding gas with a mixed gas of 75--95% Ar + 25--5 % CO2 (standard ratio: 80% Ar + 20% CO2) is called MAG welding. 

13. What is MIG welding connection? 

Answer: 

<1> Use a high-purity argon Ar ≥ 99.99% as a protective gas to protect the welding of aluminum and aluminum alloys , copper and copper alloys such as non-ferrous metals; 

<2> use 98% Ar + 2% O2 or 95% Ar + 5% CO2 is used as a protective gas for gas metal welding to protect solid stainless steel wire - called MIG welding . 

<3> MIG welding with protection of 氦 + argon inert gas mixture. 

14. What is TIG (Tungsten Arc Welding) welding? 

Answer: Inert gas shielded arc welding with pure tungsten or activated tungsten (tantalum tungsten, tantalum tungsten, zirconium tungsten, tantalum tungsten) as the infusible electrode , referred to as TIG welding .

15. What is SMAW (electrode arc welding) welding? 

A: The arc welding method of welding by manual manipulation of the welding rod. 

16. What is carbon arc gouging ? 

Answer: A surface processing method that uses a carbon rod as an electrode to generate an arc between the workpiece and a compressed air (pressure 0.5-0.7 MPa) to blow the molten metal. Commonly used for weld root removal, planing groove, repair defects, etc. 

Second, welding materials 

1. What is welding material? What is included? 

A: Welding materials include welding rods, welding wire, flux, gas, electrodes, gaskets, etc. 

2. What is welding wire? 

Answer: As a filler metal during welding, it is also used to conduct conductive wire—called wire. Divided into solid wire and flux cored wire . Commonly used solid wire type: ER50-6 (brand: H08Mn2SiA). 

3. Why is the impact toughness of MAG welded joints higher than that of CO2 welded joints? 

Answer: When MAG is welded, the reactive gas is only 20%, the transition coefficient of the alloying elements in the welding wire is high, and the impact toughness of the weld is high. The CO2 welding active gas is 100%, and the manganese and silicon alloy elements in the welding wire are jointly deoxidized. The transition coefficient of the alloy elements is slightly lower, and the impact toughness of the weld is not as high as that of the MAG welding. For example, Tangshan Kobelco MG-51T welding wire (equivalent to ER50-6) its normal temperature impact toughness value: MAG: 160J; CO2: 110J. 

4. What is the flux cored wire? 

Answer: A wire that is drawn from a thin steel strip into a circular steel tube and filled with a certain amount of powder. 

5. Why is the flux-cored wire protected by CO2 gas?

Answer: There are two types of flux cored wire according to the protection method: the core gas shielded welding wire and the core self-protecting welding wire. The core gas shielded welding wire is generally protected by CO2 gas, which belongs to the joint protection form of gas and slag, has good weld formation and high comprehensive mechanical performance. 

6. Why does the surface of the flux-cored wire weld indented? 

Answer: Because the flux-cored wire is a tubular welding wire rolled from a thin steel strip, it belongs to a seamed welding wire; the moisture in the air will invade the core through the gap, and the flux is wet (cannot be dried), causing the weld to have indented pores. 

7. Why are there technical requirements for the purity of CO2 gas? 

Answer: Generally, CO2 gas is a by-product of chemical production. The purity is only about 99.6%. It contains trace impurities and moisture, which will cause defects such as pores in the weld. The important products for welding must use gas with CO2 purity ≥99.8%, less weld porosity, low hydrogen content and good crack resistance. 

8. Why are there higher technical requirements for argon purity? 

A: There are currently three types of argon on the market: argon (purity of about 99.6%), pure argon (purity of about 99.9%), high purity argon (purity of 99.99%), the first two weldable carbon steels and stainless steels; High-purity argon must be used for non-ferrous metals such as aluminum alloy, titanium and titanium alloy; it is not possible to weld the weld and heat-affected zone. 

9. Why are TIG welding nozzles available in various sizes? 

Answer: There are four kinds of nozzles of 4-8#. For welding carbon steel, 4-5# nozzle can be used. For welding stainless steel and aluminum and aluminum alloy, 6-7# large nozzle should be used to strengthen the protection range of weld and heat affected zone. . Welded titanium and titanium alloys and other non-ferrous metals should use 7-8# larger nozzles to prevent oxidation and heat affected zone from being oxidized. 

10. What is an acid electrode? 

A: The electrode contains a large amount of acid oxide electrode, such as junction 422 (E4303), knot 502 (E5003) and other AC and DC welding electrodes. 

11. What is a basic electrode? 

A: The electrode contains a large amount of alkaline oxide and fluoride containing electrode, such as knot 507 (E5015), knot 506 (E5016) and other welding electrodes.

12. What is a cellulose type (for downright welding) electrode? 

A: The electrode contains a large amount of organic electrodes, and the pipe and thin plate structure are used for vertical welding. 

<1> For example, E6010 (equivalent to E4310, J425G) is suitable for bottom welding, heat welding, and filler welding. 

<2> E8010 (equivalent to E5511, J555) is suitable for heat welding, filler welding, and cover welding. 

Generally, the low-hydrogen down-welding electrode is used for surface welding; E7048 (equivalent to J506X) has a neat and beautiful appearance. 

13. Why should the welding rod be strictly dried before welding? 

Answer: The welding rod tends to deteriorate the process performance due to moisture absorption, resulting in unstable arc, increased spatter, and defects such as pores and cracks. Therefore, the electrode must be strictly dried before use. Generally, the drying temperature of the acid electrode is 150-200 ° C, the time is 1 hour; the drying temperature of the alkaline electrode is 350-400 ° C, the time is 1--2 hours, and the incubator is placed at 100--150 ° C after drying. Inside, use it with you. 

Third, welding equipment 

1. What is welding power? 

Answer: In an electric welder, a device that supplies the electrical energy required for welding and has electrical characteristics suitable for welding is called a welding power source. 

2. Why are there special requirements for arc welding power? What are the requirements? 

Answer: In order to ensure stable welding arc welding and adapt to various welding process requirements, arc welding power supply has the following special requirements: 

<1> Static characteristics (or external characteristics) of arc welding power source - that is, steady state output current and output voltage The relationship between the two has a falling characteristic (constant current characteristic) and a flat characteristic (constant voltage characteristic). 

A. The external characteristics of the electrode arc welding, TIG welding and carbon arc gouging power supply are descending (constant current) characteristics; 

B, the external characteristic of the CO2/MAG/MIG arc welding power source is the flat characteristic (constant voltage characteristic). 

<2> Dynamic characteristics of arc welding power source - when the load state changes instantaneously

(eg: short-circuit transition of droplets, particle transition, jet transition, etc.), the relationship between output current and output voltage of arc welding power source and time, used to characterize the ability to respond to load transients (ie, dynamic response capability), referred to as “moving” characteristic". 

<3> No-load voltage - the voltage displayed by the power supply before the arc is triggered. 

<4> Adjustment characteristics - Change the external characteristics of the power supply to meet the requirements of the welding specification. 

3. Why does the arc voltage change when the arc length changes? 

Answer: Depending on the external characteristics of the arc welding power source, the longer the arc, the higher the arc voltage; the shorter the arc, the lower the arc voltage. 

4. Why does the current display value change when the wire extension length changes during CO2 welding? 

Answer: The longer the wire extension length (ie dry elongation), the greater the resistance of the wire, the greater the current consumed by the resistance heat, the smaller the welding current display value, and the smaller the actual welding current. Therefore, the wire extension length is generally set within the range of 12-20 mm. 

5. Why is the welding current and arc voltage strictly matched when welding CO2/MAG/MIG? 

Answer: When welding CO2/MAG/MIG, adjust the welding current—that is, adjust the feeding speed of the welding wire; adjust the arc voltage—that is, adjust the melting speed of the welding wire; obviously, the melting speed and feeding speed of the welding wire must be equal to ensure The arc is stable welded. 

<1> When the welding current is constant, the arc voltage is adjusted to be high, the melting speed of the welding wire is increased, the arc length is increased, and the droplets cannot be normally transitioned. Generally, large particles fly out and the splash increases. 

<2> When the welding current is constant, the adjustment arc voltage is low, the melting speed of the welding wire is reduced, the arc length is shortened, the welding wire is inserted into the molten pool, the splash is large, and the weld bead is poorly formed. 

<3> Best matching effect of welding current and arc voltage: The droplet transfer frequency is high, the splash is minimum, and the weld bead is beautifully formed. 

6. What is arc stiffness? 

Answer: Under the effect of heat shrinkage and magnetic contraction, the arc is straightened along the axial direction of the electrode. 

7. Why is there a partial blow phenomenon in the welding arc?

Answer: During the welding process, the arc center deviates from the electrode axis due to the interference of the airflow, the action of the magnetic field or the eccentricity of the welding rod. 

8. What is magnetic blow? 

Answer: During DC arc welding, the arc is blown due to the electromagnetic force in the welding circuit. By changing the position of the ground line or reducing the welding current and changing the angle of the electrode, the influence of the magnetic bias can be reduced. 

9. What is the self-regulating characteristic of the CO2 power arc system? Why is the fine wire for CO2 welding? 

Answer: Under the constant speed wire feeding system, when the arc length changes, the current and the melting speed change, so that the arc length recovery becomes the self-regulating effect of the power arc system. The finer the wire diameter used, the stronger the self-regulating effect of the arc, the more stable the arc, and the less the splash. This is the principle of fine wire for CO2 welding. Tangshan Panasonic CO2 welding machine through the advanced control technology, the arc's own regulation is the best, the performance is the most stable. 

10. What is the load continuation rate of the welder? 

A: The load continuation rate refers to the ability of the welding power source to work continuously under a certain current. The national standard stipulates that the manual welding rated load duration is 60%, and the automatic or semi-automatic is 60% and 100%. For example, the 500KR2 welder has a rated current of 500A at a rated load continuation rate of 60%, and a maximum welding current ≤ 387A at an actual load continuation rate of 100% (automatic welding). 

Fourth, the welding process 

1. What is the welding condition? What does it have? 

A: The conditions surrounding the welding, including: base material, plate thickness, groove shape, joint form, restraint state, ambient temperature and humidity, cleanliness, and the type and diameter of the wire (or electrode) determined according to the above factors , welding current, voltage, welding speed, welding sequence, welding method, transport gun (or transport) method. 

2. What is a welded joint? How many basic forms are there? 

A: Joints that are joined by soldering. The welded joint includes three parts: weld, fusion zone and heat affected zone. The basic forms of connectors are: butt joints, corner joints, lap joints and T-type joints. 

3. What is the melting depth?

Answer: The depth at which the base metal melts in the cross section of the welded joint. 

4. What is the welding position? How many forms? 

Answer: The position of the weld joint where the weldment is located during welding. There are flat welding, vertical welding, horizontal welding and overhead welding. 

5. What is downward vertical welding and vertical vertical welding? 

Answer: 

<1> When welding vertical, the arc is welded from top to bottom - called vertical welding. Such as: cellulose electrode down vertical welding; CO2 down vertical welding. 

<2> When welding vertical, the arc is welded from the bottom to the top - called upright welding. 

6. What is a welded structure? 

A: The steel structure connected by welding is called a welded structure. 

7. Why do you want to open the weldment? 

Answer: Groove - according to the design or process requirements, the weld to be welded to the weld to a certain geometry, after the assembly of the groove formed. In order to penetrate the weldment section and reduce the fusion ratio; commonly used groove forms are: I, V, Y, X, U, K, J type. 

8. Why do some materials preheat before welding? 

A: In order to slow down the cooling rate of the weldment after welding, prevent cold cracks. 

9. Why do some of the welded components need to be heat treated after welding? 

A: In order to eliminate welding residual stress and improve the microstructure and performance of welded joints. 

10. Why should the welding procedure be formulated before welding? 

A: Ensure that the quality of welding depends on five major control links: people, machines, materials, methods, and rings. 

Human - welder skills and experience of 

the machine - welding equipment performance and stability of the 

materials - high quality welding material 

Method - correct welding procedures and standard operating 

ring - a good welding operation environment 
before welding according to the welding process and welding test assessment, the development of welding procedure is "regulations," Paul is 
an important factor in the quality of the welding certificate.