2. A brief classification of welding.

3. Heat treatment of steel: heat the steel to a certain temperature, keep the temperature for a period of time, and then cool it to room temperature at a certain cooling rate. This process is called heat treatment.

4. The commonly used heat treatment methods are annealing, normalizing, quenching and tempering. Annealing can reduce the hardness of steel, refine grains and eliminate internal stress; Normalization can refine the grain of steel and improve its strength and hardness. Quenching makes the steel obtain martensite structure, which improves the hardness and wear resistance of the steel.

5. The mechanical properties of metal materials mainly refer to their mechanical properties, which is an important index to measure metal materials. The mechanical properties of metal materials mainly include tensile properties, bending properties, impact value and hardness.

6. Steel is an iron-carbon alloy with carbon content less than 2%, and it is called cast steel when carbon content is more than 2%. When the carbon content is less than 0.25%, it is called low carbon steel, when the carbon content is 0.25%-0.6%, it is called medium carbon steel, and when the carbon content is greater than 0.6%, it is called high carbon steel, which is classified according to the carbon content of steel. In fact, in addition to the main element iron, steel also contains elements such as carbon, silicon, manganese, sulfur and phosphorus. According to the content of sulfur and phosphorus impurities in steel, steel is divided into ordinary carbon steel, high-quality carbon steel and high-quality carbon steel. Steel can be divided into carbon structural steel, carbon tool steel and special performance steel according to different uses.

7. Representation method of carbon structural steel brand. The first letter Q is the Chinese phonetic alphabet of the word "yield strength", the middle three digits are the lowest value of yield strength, in MPa, the third letter indicates the quality grade, and the fourth letter indicates the smelting method.

8. The brand of high-quality carbon steel is expressed in ten thousand parts of carbon content. For example, 45 # steel refers to high-quality carbon steel with an average carbon content of 0.45%.

9. The representation method of carbon tool steel brand is expressed in one thousandth of carbon content. For example, T 12 steel refers to carbon steel tool steel with an average carbon content of 1.2%, and "T" refers to carbon tool steel.

10. The naming method of special steel is to add a symbol indicating the purpose before or after the original steel number, where G is boiler steel, Q is bridge steel, R is pressure vessel steel and C is marine steel. H stands for welding steel, U stands for track steel and Y stands for free-cutting steel, all of which are marked in front of the original steel grade.

Chapter II: Welding Equipment

1. What is arc welding power supply?

2. External characteristics of power supply.

3. Classification of welding machines: According to different output currents, they can be divided into AC arc welding machines, DC arc welding machines, inverter arc welding machines and pulse welding machines; According to the operation method, it is divided into manual arc welding machine, semi-automatic arc welding machine and automatic arc welding machine; According to the welding method, it is divided into covered electrode arc welding machine, submerged arc welding machine and gas shielded welding machine.

4. Representation method of welding machine model: A stands for arc welding generator, B stands for arc welding transformer, Z stands for arc welding rectifier, X stands for drop characteristics, and the last three digits represent rated current.

5. Hand arc welding machine should have: simple structure, convenient maintenance and good safety; Flexible adjustment of current; Convenient welding operation; Suitable no-load voltage; Good economy, not easy to get hot.

6. During arc welding, it is required that the no-load voltage of the power supply is high and the current is low when the arc is started. The higher the no-load voltage is, the more favorable it is for arc ignition and stable combustion, but the higher the no-load voltage is, the more unfavorable it is for welder's safety and the more energy consumption. At present, the no-load voltage of AC arc welding machine in China is 60-80 volts, and that of DC arc welding machine is 45-70 volts.

7. The output current value of the welding machine is mainly determined by the heating of the welding machine. When the welding machine is seriously heated, it will burn out the welding machine. Therefore, it is stipulated that the maximum temperature of the welding machine should be raised to 60-80℃, depending on the current and load state. Manual arc welding is always in intermittent load state, so the load duration rate in actual operation is lower than 100%. According to the regulations of our country, the load duration rate is calculated in 5 minutes.

8. Precautions for using hand arc welding machine: The welding machine should be placed in a well-ventilated and dry place as smoothly as possible; Welding machine power circuit welding machine reliable grounding; When the welding machine is empty, the sound is abnormal; Do not let the electrode holder contact with the shell to prevent short circuit; Used within the specified technical parameter values; Always keep all parts of the welding machine clean; Always check whether the bolts of each part are loose; When the welding machine stops working, cut off the power supply.

Chapter III: Welding Materials

1. Coated covered electrode: The coated material for manual arc welding melts covered electrode. The coated covered electrode consists of flux-cored wire and other coatings.

2. Deposited metal: welding metal formed entirely by melting filler metal.

3. Basicity: the quantity representing the basicity of slag.

4. Acid covered electrode: The coating content is mainly covered electrode of acid oxides.

5. Alkaline coating covered electrode: The coating component is mainly covered electrode of alkaline oxide.

6. The function of the welding core: conduct the welding current to form an arc and melt it into the filler metal of the weld.

7. The function of the coating: to ensure the weld formation; Improve welding manufacturability; Metallurgical action; Infiltrate the necessary alloy into the weld.

8. covered electrode can be divided into: structural steel covered electrode J; Stainless steel covered electrode A and G; Low temperature steel covered electrode W; Nickel and Nickel Alloy covered electrode; The aluminum alloy covered electrode L is aluminum; Molybdenum and Cr-Mo heat-resistant steel covered electrode; Surfacing covered electrode d; Cast iron welding rod Z; Copper and copper alloy covered electrode T; Special covered electrode Ts.

9. Compilation method of covered electrode model: the letter E indicates covered electrode, the first two digits indicate the minimum tensile strength of deposited metal in MPa, the third digit indicates the applicable position of covered electrode, "0" and "1" indicate that covered electrode is suitable for all positions, "2" indicates that covered electrode is suitable for flat welding and fillet welding, "4" indicates that covered electrode is suitable for vertical welding, and the third and fourth digits.

10. The coating of covered electrode is easy to get wet. When welding with wet covered electrode, it is easy to produce defects such as blowholes and cracks. In order to ensure the welding quality, covered electrode should be baked before welding. Welders should carefully check the model and specification when using covered electrode. When using low hydrogen covered electrode, it should be placed in an insulating cylinder in covered electrode. In general, low hydrogen covered electrode should be dried at room temperature for more than 4 hours. However, the number of re-baking should not exceed three times.

1 1. When structural steel covered electrode is selected, it should be selected according to the principle that the strength is equivalent to that of the parent material. Secondly, choose other covered electrode according to the strength and structure of the weld.

12. When using low hydrogen covered electrode, DC reverse connection should be generally adopted, that is, the workpiece is connected to the negative electrode at the output end of the welder and the electrode holder is connected to the positive electrode.

Chapter Four: Welding Operation Technology

1. What is manual arc welding?

2. Manual arc welding has the characteristics of simple equipment, convenient and flexible operation, strong adaptability, welding under various conditions and wide application.

3. Joints connected by welding are called welded joints. Welded joints include weld, fusion zone and heat affected zone. Welded joints can be divided into butt joints, T-joints, angle joints and lap joints.

4. Weld: Weld is the joint part formed after welding. Welds can be divided into four types according to their spatial position: flat welding, vertical welding, horizontal welding and overhead welding. According to the combination form, it can be divided into butt weld and fillet weld. According to the interruption, it can be divided into three types: continuous weld, intermittent weld and positioning weld.

5. Weld inclination: refers to the included angle between the weld axis and the horizontal plane.

6. Weld corner: refers to the angle between the vertical plane passing through the weld axis and the bisecting plane of the groove.

7. The weld width refers to the distance between two weld toes on the weld surface; Superelevation refers to the maximum height of weld metal beyond the surface of base metal; Weld thickness refers to the distance from the front to the back of the weld on the cross section of the weld.

8. indicate the welding method on the construction drawing, and the symbol of welding form and weld size is called weld symbol; Weld symbols are mainly composed of basic symbols, auxiliary symbols, supplementary symbols, lead-out lines and weld size symbols.

9. Marking principle of weld size symbol: the size of weld cross section is marked on the left side of basic symbol; The weld length dimension is marked on the right side of the basic symbol; The upper or lower side of the basic symbols of groove angle and root clearance mark; Mark the same number of welds at the end of the reference line.

10. Welding process parameters refer to all kinds of process parameters selected to ensure welding quality during welding; The welding process parameters of manual arc welding mainly include covered electrode diameter, welding current, arc voltage, welding speed and welding level.

1 1. covered electrode diameter is selected according to the thickness of weldment, welding position, joint form and welding level; For weldments with large thickness, covered electrode with large diameter should be used for lap joint and T-joint welding, and covered electrode with small diameter should be used for small groove weldments to ensure root penetration. Backing weld generally adopts small-diameter covered electrode. For different welding positions, the covered electrode diameter is different. Generally, the covered electrode diameter of flat welding is slightly larger than the covered electrode diameter of vertical welding, horizontal welding and overhead welding.

12. Welding current is the most important process parameter of manual arc welding, and the selection of welding current directly affects welding quality and labor productivity. The welding current is too small and the arc is unstable, resulting in defects such as slag inclusion and incomplete penetration. When the welding current is too large, it is easy to bite and burn through, which will increase the deformation of weldment and metal splash. Therefore, when selecting welding current, covered electrode type, covered electrode diameter, weldment thickness, joint form, weld position and welding grade should be considered comprehensively. The welding current of manual arc welding carbon steel covered electrode can be calculated according to the empirical formula I = DK, where I is the welding current, D is the covered electrode diameter, K is the empirical coefficient, and the value of K is between 25 and 60.

13. Arc voltage is determined by arc length. The longer the arc, the higher the arc voltage, and vice versa. The arc should not be too long in the welding process, otherwise there will be defects such as unstable arc combustion, large splash, large depth and blowhole. Therefore, short arc should be used as much as possible when welding. Generally, the arc length should not exceed the covered electrode diameter.

14. The weld length per unit time is called welding speed; In the welding process, the welding speed should be uniform and appropriate, that is, to ensure penetration without burning through, and at the same time to make the weld meet the technical requirements. If the welding speed is too fast, the weld will be narrowed, uneven and undercut, while if the welding speed is too slow, the weld will be widened, the residual height will be increased and the power will be reduced.

15. In welding production, thick weldments often need multi-layer welding. For low carbon steel, the weld thickness has little effect on the mechanical properties, but for alloy steel and stainless steel, the thickness of each weld is less than 4-5 mm. According to experience, when the thickness of each weld is equal to 0.8- 1.2 times, the production efficiency is the highest, which is easy to master and operate. General welding grade n = b/MD, where b is the thickness of weldment, d is the diameter of covered electrode coating, and m is 0.8 ~ 1.2.

16. The operation technology of manual arc welding mainly includes four methods: arc starting method, strip feeding method, joint method and arc closing method.

17. The arc striking process of manual arc welding is called arc striking, and the commonly used arc striking methods are direct arc striking method and arc striking method.

18. When arc striking and welding are carried out, there are three basic movements in covered electrode, namely, the feeding movement of covered electrode, the lateral swinging movement of covered electrode and the moving movement of covered electrode towards the weld. Steel bar conveying mode, covered electrode angle and welding speed are the keys of welder's operation technology. How to choose the correct rod feeding method, covered electrode angle and welding speed according to the weld position, joint form, weldment material, covered electrode diameter, welding power supply, weldment thickness and welding level is an important symbol to measure an electric welder's operating skills.

18. When the thickness of the plate exceeds 6mm, the welded joint generally needs a groove, which is to ensure the root penetration and obtain good weld formation. There are four commonly used grooves: V-shaped, U-shaped, X-shaped and K-shaped.