The electrode consists of two parts: the core and the coating. The electrode is coated on the core uniformly and centripetally with the coating (coating) outside the metal core. The welding rods are different depending on the type of electrode. The core of the welding rod is the metal core of the welding rod. In order to ensure the quality and performance of the welding seam, the content of each metal element in the welding core is strictly regulated, especially for the content of harmful impurities (such as sulfur, phosphorus, etc.). The limit is better than the base metal. The composition of the core directly affects the composition and properties of the weld metal, so the harmful elements in the core should be as small as possible, and the amount of C should be less than 0.10%. For example, H08A, containing S is less than or equal to O. 03%, P is less than or equal to 0.03%, and C is less than or equal to 0.1%. Dozer Parts,Bulldozer Spare Parts,Caterpillar Dozer Parts,Aftermarket Dozer Parts JINING SHANTE SONGZHENG CONSTRUCTION MACHINERY CO.LTD , https://www.sdkomatsudozerparts.com
Welded carbon steel and low alloy steel cores are generally selected from low carbon steel as the core, and filled with manganese, silicon, chromium, nickel and other components (see wire national standard GB1300-77 for details). The reason for using low carbon is that the steel wire has good plasticity when the carbon content is low, and the wire drawing is relatively easy. On the other hand, the CO content of the reducing gas can be reduced, the splash or pores can be reduced, and the temperature at which the weld metal is solidified can be increased. It is good for overhead welding. The addition of other alloying elements is mainly to ensure the comprehensive mechanical properties of the weld, and also has a certain effect on the welding process performance and the removal of impurities.
High-alloy steel and other metal materials such as aluminum, copper, cast iron, etc., in addition to the requirements of the metal core of the weld metal, also control the content of impurities, and often add certain alloying elements according to the process requirements.
The electrode is a molten electrode used for electrode arc welding with a coating. It consists of two parts: the coating and the core, as shown in Figure 3-5. There is 45 at the front end of the electrode. The chamfers on the left and right, this is to facilitate the arcing. There is a section of bare core at the end, which accounts for about 1/16 of the total length of the electrode, which facilitates the clamping of the welding tongs and facilitates electrical conduction. The diameter of the electrode is actually the diameter of the core. It is usually 2, 2. 5, 3. 2 or 3, 4, 5 or 6 mm. It is commonly used as small 3. 2, small 4, small 5 The length "L" is generally between 250^-450 mm.
1. Core
The metal core covered by the coating in the electrode is called a core. The core is generally a steel wire of a certain length and diameter. When welding, the core has two functions: one is to conduct welding current, the arc is used to convert electrical energy into heat, and the other is that the core itself is melted as a filler metal to fuse with the liquid base metal to form a weld.
When the electrode is welded, the core metal accounts for a portion of the entire weld metal. Therefore, the chemical composition of the core directly affects the quality of the weld. Therefore, the steel wire used as the electrode core has its own brand and composition. If it is used as a filler metal for submerged arc automatic welding, electroslag welding, gas shielded welding, gas welding, etc., it is called a welding wire.
(1) Effect of alloying elements in the core on welding
1) Carbon (C) carbon is the main alloying element in steel. When the carbon content increases, the strength and hardness of the steel are significantly improved, and the plasticity is lowered. In the welding process, carbon plays a certain deoxidation effect, and cooperates with oxygen in the action of high temperature of arc to generate carbon monoxide and carbon dioxide gas, and removes the arc area and the air around the molten pool to prevent harmful gases such as oxygen and nitrogen in the air. The adverse effects on the molten pool reduce the oxygen and nitrogen content in the weld metal. If the carbon content is too high, the reduction is severe, causing large splashes and pores. 1%。 The carbon content of the low carbon steel core is generally clustered 0.1%, considering the effect of carbon on the hardenability of the steel and the increase in the sensitivity of the crack.
2) Manganese (Mn) manganese is a good alloying agent in steel. As the manganese content increases, its strength and toughness will increase. Manganese is also a good deoxidizer during the welding process, which can reduce the oxygen content in the weld. Manganese and vulcanization form manganese sulfide floating in the slag, thereby reducing the tendency of weld hot cracking. Therefore, the manganese content of the general carbon structural steel core is from 0.30% to 0.55%, and the specific manganese wire is welded to a manganese content of up to 1. 70% to 2.10%.
3) Silicon (Si) silicon is also a good alloying agent. Adding proper amount of silicon to steel can improve the yield strength, elasticity and acid resistance of steel. If the content is too high, it will reduce plasticity and toughness. In the welding process, silicon also has a good deoxidizing ability to form silica with oxygen, but it will increase the viscosity of the slag and easily promote the formation of non-metallic inclusions.
4) Chromium (Cr) chromium can improve the hardness, wear resistance and corrosion resistance of steel. For low carbon steel, chromium is an accidental impurity. The main metallurgical feature of chromium is that it is susceptible to rapid oxidation, forming a refractory oxide of chromium oxide (Cr203), which increases the likelihood of weld metal inclusions. After the transition of chromium trioxide to the slag, the viscosity of the slag is increased and the fluidity is lowered.
5) Nickel (NO nickel has a significant effect on the toughness of steel. When the low temperature impact value is required to be high, some nickel is appropriately incorporated.
6%。 The sulfur (S) sulfur is a harmful impurity, as the sulfur content increases, will increase the hot cracking tendency of the weld, so the sulfur content of the core should not be greater than 0. 04%. The sulphur content of the sulphur content shall not be greater than 0.03%.
7) Phosphorus (P) Phosphorus is also a harmful impurity whose effect is similar to sulfur.
(2) Classification of the core
The welding core is classified according to the national standard "welding steel wire" (GB 1300-77). The special steel wire for welding can be divided into three types: carbon structural steel, alloy structural steel and stainless steel.
2. Medicine
The coating applied to the surface of the core is called a coating. The coating of the electrode plays an extremely important role in the welding process. If the welding rod is welded with no coating, in the welding process, oxygen and nitrogen in the air will invade the molten metal in a large amount, and the metal iron and the beneficial elements carbon, silicon, manganese, etc. are oxidized and nitrided to form various oxides and Nitride, which remains in the weld, causing weld slag or cracks. The gas melted into the molten pool may cause a large number of pores in the weld, which can greatly reduce the mechanical properties (strength, impact value, etc.) of the weld and make the weld brittle. In addition, welding with a light-welding rod, the arc is very unstable, the splash is severe, and the weld is poorly formed.
In practice, it has been found that if a coating made of various minerals or the like is applied on the outside of the light-welding rod, the arc combustion can be stabilized and the quality of the weld be improved. This type of welding rod is called a coating electrode. With the continuous development of industrial technology, people have created high-quality thick coating electrodes that are widely used nowadays.