How to prevent welder from biting edge?

(1) Knowledge mastery point 1. Be familiar with relevant welding engineering terms and understand the basic knowledge of commonly used welding materials; 2. Through training, the basic process knowledge of welding is preliminarily obtained; 3, master the basic concepts of welding production process, understand the practical knowledge of welding technology, and lay the foundation for future courses; 4, understand the welding safety technical knowledge, do safety training; (2) The ability training point trains students' welding process analysis ability and hands-on operation ability by welding simple workpieces, laying a solid foundation for future production and technical work. (3) Quality training points 1. Through training, students can establish a scientific attitude of integrating economic viewpoint, quality viewpoint and theory with practice; 2. Educate students in their ideological style, so that they can observe discipline in productive labor and take good care of state property; Second, the focus of the outline, learning difficulties and solutions (II) Learning difficulties 1. Composition of welding arc and composition of molten pool; 2. Selection of welding specifications; (such as welding current, welding speed, arc length and covered electrode angle) 3. Common welding defects and their causes. (III) Solutions to Difficulties 1. Explain some basic concepts carefully and emphatically; 2. Explain the situations that are not easy to observe and pay attention to by drawing some schematic diagrams; 3. Through practical operation, theory and practice are organically combined. Third, the teaching plan unit teaching form main content goal planning time remarks 1 classroom teaching the significance, application and classification of welding 1 minutes examples 2 classroom teaching manual electric arc welding familiar with mastering 6 minutes drawing simple demonstration 3 classroom teaching the joint form of weld, Understand the spatial position and groove for 15 minutes. Draw pictures in class 4. Teach common welding defects and their causes for 15 minutes. Draw pictures in class 5. Teach the safety technology of arc welding for 1 minutes. Example 6. Operate and demonstrate the current adjustment of manual arc welding. Familiar with the welding methods such as arc striking, arc extinguishing, bar conveying, flat welding and surfacing welding, and master the actual operation for 2 minutes. 7 Students' operation is the same as above. 1. First, teach the basic concept, application and classification of welding, so that students can understand what welding is, the classification method and specific form of welding. It is pointed out that hand arc welding is the most widely used at present, and it is also the basis of other kinds of welding methods. 2, focusing on teaching the characteristics of manual arc welding, equipment and tools, composition and classification of covered electrode, wiring method of electric welding machine, arc ignition, bar transportation and bar transportation methods. 3. To understand some basic knowledge of manual arc welding in theory, we also need to know how to choose common welding specifications such as covered electrode diameter, welding current, arc voltage, covered electrode angle and welding speed. 4. Make students know the basic knowledge of weld by drawing. (such as joint form, spatial position, groove and defects) 5. Safety comes first in any work. By teaching safety technology, students can understand that if they don't follow the safety operation rules, they may cause accidents such as electric shock, burns, fires, explosions and poisoning. 6. The above five units are the basic theoretical knowledge taught in class. Starting from Unit 6, the practical operation should be made clear before the operation, such as the safe and economical use of covered electrode, weldments and organizational discipline, so that the demonstration operation can be carried out later. During the demonstration operation, students should pay attention to observing and guiding the teacher how to choose the welding specification when welding. (such as welding current and "three degrees", etc.) 7. When students operate, they should start with imitation to guide the teacher's welding action, and use their brains to find out their own shortcomings in welding and correct them next time. Fourth, material preparation (in groups) 1. Equipment: 1 BX1-3-1 welding machine; 2. Tools: one electrode holder, two masks and one planer. 3. Material: 2 kg of E433 Ф3.2 welding electrode and 2 pieces of low-carbon steel plates with specifications of 18×12×1. 4. Teaching AIDS: standard teaching materials, chalk, wall charts, etc. Introduction of teaching process unit 1-6 Manual arc welding (theoretical part): Manual arc welding is the basis of other welding methods, and it is the focus of this teaching program because it needs to be practiced in our three-day internship. The time schedule is about 2 hours (mainly in class). Unit 1, Significance, Application and Classification of Welding Welding is a processing method to connect two metals with or without filler metal by heating or pressurizing, or heating and pressurizing. Welding is an indispensable advanced manufacturing technology in modern industrial production. With the development of science and technology, welding technology has attracted more and more attention from all walks of life and is widely used in institutions, metallurgy, electric power, boilers and pressure vessels. Production departments such as buildings, bridges, ships, automobiles, electronics, aerospace, military industry and military equipment. There are many classification methods of welding. According to the different states of metals in the welding process, welding methods can be divided into three categories: fusion welding, pressure welding and brazing, and each category includes many welding methods. Fusion welding is a welding method in which the welded joint is heated to a melting state without pressure during welding. Such as gas welding and manual arc welding. Pressure welding is a method of applying pressure (heating or not) to the weldment to complete the welding process. Such as resistance welding and friction welding. Brazing is a method to connect weldments by using a metal material with a lower melting point than the base metal as the brazing filler metal, heating the weldments and brazing filler metal to a temperature higher than the brazing filler metal but lower than the melting point of the base metal, wetting the base metal with liquid brazing filler metal, filling the joint gap and diffusing with the base metal. Such as soldering (heating temperature below 45 degrees? Soldering) brazing (heating temperature above 45 degrees? Brazing). Among them, manual arc welding is the most widely used at present, and it is also the basis of other kinds of welding methods. Unit 2, Manual Arc Welding (I) Characteristics of Arc Welding Manual arc welding is an arc welding method using manual manipulation of covered electrode, which is referred to as manual arc welding. Its characteristics: 1. Simple equipment. 2. Flexible and convenient operation. 3, can carry out all-position welding and is suitable for welding various materials. 4. The disadvantage is that the production efficiency is low and the labor intensity is high. What is an arc? The strong and lasting discharge phenomenon in the gas medium between two electrodes is called arc. When arc discharges, on the one hand, it produces high temperature and strong light at the same time. Manual arc welding is to use the high temperature generated by arc to melt covered electrode and weldment, so that two separated metals can be fused together, thus obtaining a firm joint. Manual arc welding takes covered electrode and weldment as two electrodes, and the welded metal is called weldment or parent metal. When welding, the weldment is partially melted due to the high temperature of the arc and the blowing force. An oval pit filled with liquid metal is formed on the welded metal, and this pit is called molten pool. With the movement of covered electrode, the molten pool cools and solidifies to form a weld. A layer of slag shell covering the weld surface is called slag. The distance from the melting end of covered electrode to the surface of molten pool is called arc length. The distance from the surface of weldment to the bottom of molten pool is called penetration depth. As shown in Figure 1. Fig. 1 Schematic diagram of manual electric arc welding How to distinguish molten pool from slag during welding? When welding, the brightest part directly under the covered electrode is the molten pool, while the dark red liquid with good fluidity is the slag, so it should be noted that the slag should not lead. (2) Equipment and tools used for hand arc welding Question: What are the main equipment for hand arc welding? 1. Equipment The main equipment for manual arc welding is an electric welding machine. The electric welding machine used in arc welding is actually an arc welding power supply. According to the types of generated current, this power supply can be divided into arc welding transformers (AC), DC arc welding generators and arc welding rectifiers (DC). 1) Arc welding transformer: It is actually a special step-down transformer. It reduces the power supply voltage of 22 volts or 38 volts to 6-8 volts (that is, the no-load voltage of the welding machine) to meet the needs of arc ignition. When welding, the voltage will automatically drop to the voltage (3-4 volts) required for the normal operation of the arc. The output current ranges from tens of amperes to hundreds of amperes, and the current can be adjusted as needed. Arc welding transformer has the advantages of simple structure, low price, low working noise, reliable use, convenient maintenance and wide application. The disadvantage is that the arc is unstable during welding. DC arc welding generator: It is composed of an AC motor and a DC generator. The motor drives the generator to rotate, and generates DC power meeting the welding requirements. The welding quality of DC arc welding generator is good, but the structure is complex, the noise is high, the price is high and it is not easy to maintain. Therefore, it is only used in situations where current is required. In addition, this kind of motor-driven arc welding generator is no longer produced in China because of the large consumption of consumables and electricity. Arc welding rectifier: In recent years, arc welding rectifier has also been widely used. It converts alternating current into direct current through rectifier. It not only makes up for the shortcoming of poor arc stability of AC welding machine, but also has simpler structure, easier maintenance and less noise than the general DC arc welding generator. When welding with DC arc welding power supply, there are two methods: positive connection and negative connection because of the different heat on the positive electrode and negative electrode. As shown in figure 2. Connecting the covered electrode to the negative electrode is called positive connection; Conversely, it is called negative connection. When welding thick plates, the direct current connection method is generally adopted, at this time, most of the heat in the arc is concentrated on the weldment, which is conducive to accelerating the melting of the weldment and ensuring sufficient penetration. When welding thin plates, in order to prevent burning through, reverse connection is often used. The model of manual arc welding machine is compiled according to the unified regulations, and it is expressed by Chinese phonetic alphabet and Arabic numerals. The compiling sequence and meaning of models are shown in Figure 3 and Table 1. Table 1 The model of electric welding machine represents letters and numbers, categories, subcategories, basic specifications, names, codes, names, codes, welding generator A, descending characteristics, flat characteristics and multi-characteristics X P D rated current (a) Welding transformer B, descending characteristics, flat characteristics, X P, welding rectifier Z, descending characteristics, flat characteristics and multi-characteristics X P D Question: 1. BX1? -What are the meanings of letters and numbers of model 3-1 electric welding machine? 2. Tool 1) Welding cable: It is a special welding cable made of red copper, which requires a certain cross-sectional area, good conductivity, insulation and flexibility. The function is to conduct current. Electrode holder: Its function is to clamp covered electrode and conduct current. Mask: Its function is to protect eyes and face from being burned by arc light. Planing hammer; Used to remove welding slag covering the weld. (III) Welding electrode 1. Composition and function of covered electrode covered electrode consists of welding core (metal core) and coating 1) Welding core is a special metal wire for welding, which is the main material of weld metal. The main functions of welding core are as follows: first, it acts as an electrode to conduct current and ignite arc. Second, after melting, it is used as a filler metal to form a weld with the melted base metal. In order to ensure the quality of weld, there are strict requirements on the chemical composition of weld metal. Therefore, the welding cores are specially smelted, with low carbon and silicon content and little sulfur and phosphorus content. The diameter of covered electrode is expressed by the diameter of the welding core, and the specifications of covered electrode diameter are φ 1.6, φ 2.5, φ 3.2, φ 4, φ 5 and φ 6 mm, with the length ranging from 2 to 55 mm. And our practice covered electrode is φ 3.2 mm in diameter and 35 mm in length. 2) The main functions of the coating in the covered electrode during manual arc welding are: ① Mechanical protection: the gas released after the coating is melted and the slag formed are used to isolate the air and prevent harmful gas from invading the molten metal. (2) Metallurgical treatment: removing harmful impurities (such as oxygen, hydrogen, sulfur and phosphorus) and adding beneficial alloying elements, so that the weld can meet the required chemical composition and mechanical requirements. ③ Improve the welding process performance: make the arc combustion stable, less spatter, good weld formation, easy deslagging, etc. 2. Classification of welding electrodes 1) According to the different properties of covered electrode coating, covered electrode can be divided into two categories: acidic covered electrode and alkaline covered electrode. Covered electrode with a large amount of acidic oxides (TiO2 _ 2, SiO2 _ 2, etc.) in the coating is called acidic covered electrode. The coating containing a large amount of basic oxides (CaO, Na2O, etc.) is called alkaline covered electrode. Acid covered electrode can be used for both AC and DC, and its welding process performance is good, but its mechanical properties, especially impact toughness, are poor. It is suitable for welding general low-carbon steel and low-alloy structural steel with low strength, and it is the most widely used covered electrode. Alkaline covered electrode has strong desulfurization and dephosphorization ability, and the coating has the effect of dehydrogenation. The hydrogen content of welded joint is very low, so it is also called low hydrogen covered electrode. The weld seam of alkaline covered electrode has good crack resistance and mechanical properties, but poor process performance. Generally, it is welded by DC power supply, which is mainly used for welding important structures (such as boilers, pressure vessels and alloy structural steel). 2) According to the different uses of covered electrode, covered electrode can be divided into structural steel covered electrode (carbon steel covered electrode and low-alloy covered electrode), stainless steel covered electrode, cast iron electrode, heat-resistant steel electrode, low-temperature electrode, surfacing covered electrode, copper and copper alloy, nickel and nickel alloy, aluminum and aluminum alloy covered electrode, etc., among which structural steel electrode is the most widely used. 3. Compilation of carbon steel covered electrode The model of carbon steel covered electrode consists of four digits of the letter "E". The letter "e" stands for covered electrode; The first two digits indicate the minimum tensile strength of deposited metal, and the carbon steel covered electrode is divided into two series: E43 (deposited metal tensile strength ≥42Mpa) and E5 (deposited metal tensile strength ≥49Mpa). The third digit indicates the welding position of covered electrode, "" and "1" indicate that covered electrode is suitable for all-position welding (flat, vertical, vertical and horizontal welding), "2" indicates that covered electrode is suitable for flat welding and flat angle welding, and "4" indicates that covered electrode is suitable for vertical welding. The combination of the third and fourth digits indicates the type of welding current and coating, as shown in Table 2. Table 2 Types of welding power supply and coating type Digital coating type Welding power supply type and polarity Special type AC or DC reverse connection 1 ilmenite type AC or DC reverse connection 3 titanium calcium type AC or DC reverse connection 8 graphite type AC or DC reverse connection 1 high cellulose sodium type DC reverse connection 11 high cellulose sodium type AC or DC reverse connection. Connect 12 high titanium sodium type AC or DC direct connection 13 high titanium potassium type AC or DC direct connection 14 iron powder titanium type AC or DC direct connection 15 low sodium hydrogen type DC direct connection 16 low potassium hydrogen type AC or DC direct connection 18 iron powder low hydrogen type AC or DC direct connection 2 iron oxide type AC or DC direct connection 22 iron oxide type AC or DC. Reverse connection of 23 iron powder titanium calcium type AC or DC reverse connection of 24 iron powder titanium type AC or DC reverse connection of 27 iron powder iron oxide type AC or DC direct connection of 28 iron powder low hydrogen type AC or DC reverse connection Question: 2. What does covered electrode of E433 and E4315 mean? (IV) Manual arc welding technology 1. The wiring method of electric welding machine is shown in Figure 4. 2, the ignition method of electric arc welding.