Classification: horizontal welding, vertical welding, horizontal welding and overhead welding. With the development of national economy, the output of steel products is increasing year by year, and the proportion of steel pipes in all steel products is increasing, among which the proportion of welded pipes is over 45%. With the progress of welding technology, the welding of welded pipes, especially small and medium diameter steel pipes, has been applied to many manufacturing industries. The welding of horizontal fixed pipe is one of the most commonly used welding technologies of steel pipe, which is widely used. It is usually called hanging welding, that is, hanging the pipe in a horizontal position or near a horizontal position for welding. Including flat, vertical, vertical and other spatial positions, it needs single-sided welding and double-sided molding, which is a difficult welding technology. In operation, the circumferential weld is usually divided into two semicircular welds, with the flat weld and the upturned weld as the boundary. Welding shall be carried out in the order of back-back-flat. The arc extinguishing method (acid covered electrode) or welding and current regulation (alkaline covered electrode) should be used to control the temperature of the molten pool and the penetration degree of the root, so as to achieve the purpose of good positive and negative forming.
Manual arc welding of horizontal fixed pipe
1. 1 Common welding methods for horizontal fixed pipes
There are various welding methods for metal pipes, which are widely used in production practice. For large diameter pipelines, fusion welding methods, such as submerged arc welding and CO2 gas shielded welding, are adopted. Gas welding, manual arc welding, argon arc welding, plasma arc welding, friction welding and resistance welding are mostly used for small and medium diameter pipelines.
1.2 characteristics of manual arc welding
Manual arc welding has low productivity, but its strong applicability is still irreplaceable by other welding methods. It is one of the important methods for welding various metal pipes. Its main characteristics are: the voltage for maintaining arc discharge is low, generally 10V~50V ~ 50V, and the welding current is large, ranging from tens of amperes to thousands of amperes; At the same time, the equipment is simple, the operation is flexible and simple, and ensuring the welding quality mainly depends on the arc welding power supply, the quality of covered electrode, the technical proficiency of the operator and the process construction method.
Manual arc welding operation technology of horizontal fixed pipe
2. 1 technical points of horizontal fixed pipe butt joint operation
Horizontal fixed pipe includes welding in all spaces, including elevation, vertical and horizontal, which is a difficult operation technology. For the welding of medium and small diameter steel pipes, the fixed circumferential seam cannot be welded on both sides. Therefore, it is necessary to ensure the penetration of the first layer from the process, that is, single-sided welding and double-sided molding. Due to the constant change of welding position, the steel bar conveying angle and the height of the operator must adapt to the changing needs. At the same time, under the condition that the welding current cannot be changed, the heat is mainly controlled by the welder swinging the covered electrode.
2.2 Selection of welding process parameters
Before pipeline welding, the oil stain and rust on the 50 mm wide surface on both sides of the groove should be cleaned up. When assembling the pipe, the angle of Y-shaped groove surface is 30-25 degrees, the blunt edge is 1.2-2 mm c, and the clearance is 1.2-2 mrl. The pipe is welded by arc extinguishing method. See table 1-66 for welding process parameters.
Table 1- 1
Covered electrode class covered electrode diameter (mm) welding current (a) arc voltage (v) welding speed (cm/min)
E4303 Floor 3.290 ~14021~ 3010 ~ 30
Middle layer 3.2100 ~160 24 ~ 34 lo ~ 30
Outer layer 4.0130 ~ 220 21~ 3710 ~ 35
Gai 4.0130 ~ 220 21~ 3710 ~ 35
2.3 Distribution of welding defects
Because the welding position changes continuously along the circumference, it requires that the angle of the welder standing and the angle of the bar conveying must meet the needs of the welding position change. In order to control the temperature and shape of the molten pool, in addition to arc-extinguishing welding technology, swing covered electrode is mainly used to control the heat, which requires the welder to have high technology. Because the temperature and shape of the solution pool are difficult to control, the root weld is prone to incomplete penetration, and defects such as flash and edge collapse are common: 1 and 4 are prone to various defects, 2 is prone to edge collapse, and 3 is prone to flash.
2.4 spot welding
The number of tack welds should be selected according to different pipe diameters. When the diameter d of camp is less than or equal to 5 litkrn, choose one point, 5 1≤D≤ 133ram, choose two points at the right time, and choose 3 ~ 4 points when D≥ 133mm; The weld length of tack welding is generally 10 ~ 30 mm, and the height is moderate. If it is too low, it will crack easily. If it is too high, it will bring difficulties to the first level. The tack welding current should be greater than the formal welding current, so that the arc starting point has enough temperature to prevent adhesion. When the arc is closed, the arc pit must be filled. The locating weld is easy to produce defects. If defects are found, they must be re-welded, and slag and spatter should be removed. The two ends of the positioning weld shall be made into a slope shape as far as possible to ensure the weld quality during formal welding.
2.5, welding
Generally speaking, the first layer is called backing weld, the rest is called intermediate bead, and the last layer is called overlay bead. Usually, when welding small and medium pipes, it is divided into two parts with the vertical line at the center of the section as the interface. The first half is called the first half, and the second half is called the second half. When welding, press upward, and the vertical and horizontal welding positions are carried out sequentially from bottom to top, that is, welding starts at the overhead welding position and ends at the horizontal welding position, forming two joints, and one side is realized by low welding.
2.5. 1, the first layer of weld welding.
The welding of the first layer of weld is the key to determine the welding quality, and the first damage is conveyed in a straight line with slight swing. Backing weld on the first floor. According to the different pipe diameters, the arc can be struck at the groove side before the center line of the overhead welding position 10 ~ 20ml (starting from 1). Attention should be paid to avoid arc in groove or counterpart center to avoid defects. After the arc is ignited, preheat the weld root with a long arc for 2-3 seconds, then immediately depress the arc to hold the molten iron and penetrate the weld root with the arc. If the process is normal, continue to weld upwards. If there is a molten hole, you can block the molten hole with a linear reciprocating rod and then continue to weld upwards. When the steel bar is transported to the locating weld, it must be completely fused by electric arc penetrating the root gap. In the welding process, the welding position changes from bottom to top, so the angle of covered electrode must be changed accordingly. The above is the welding of the first half. The operation method of welding seam in the second half is similar to that in the first half, but the upper and lower joints must be connected. When flip-chip welding joints, a part of the weld end (5- 10 mm) to be welded first should be cut by electric arc, which can not only remove possible defects, but also form a gently sloping gap, which is very powerful when welding. When welding the joint, the original weld should be fully melted and a molten hole should be formed to ensure the root penetration.
Second, the middle layer welding
Except for the first layer and the outermost layer, the rest are called the middle layer. Generally, there is an intermediate layer only when the wall thickness is greater than 6mm, and the welding of the intermediate layer is relatively easy. However, due to improper selection of process parameters, there may be defects such as porosity, slag inclusion and incomplete penetration between layers. The welding wave in the middle layer is wide, and crescent-shaped or serrated bars are generally used for continuous welding. The residence time on both sides of the groove is short, and the welding angle changes accordingly.
2.5.3. Welding of the outer layer
The outer weld shall be welded to a certain weld height according to the design requirements, and the appearance of the weld shall be uniform and beautiful, basically consistent along the circumference. Generally, crescent transportation mode is adopted, the swing should be slow and steady, and there should be enough residence time on both sides of the groove. When the groove is wide, multi-pass welding can be used, first welding both sides of the groove, and then welding the middle.
2.5.4, cover surface
Lamp face welding, also called enhanced face welding, not only makes the weld look beautiful, but also reflects its internal quality in essence. When covering the surface, the crescent strip can be used, and the swing should be slow and steady, so that the welding wave is uniform and beautiful. Generally, the width of each side is about 1.5mm wider than the groove. Superelevation is generally 0.5-3 mm for overhead welding parts and 0.5-2.5 mm for other parts. Severe undercut (depth. More than 0.5ram), too high or insufficient superelevation and too high steepness are not allowed. L the shell and workbench of electric welding machine must be well grounded.
2. No-load voltage of electric welding machine should be between 60~90V.
3. The power circuit breaker with live insurance should be used for welding equipment, and it should be installed in a closed box.
4. Before use, the welder must carefully check whether the insulation of the primary and secondary lines is complete and whether the wiring is well insulated.
5. When the welding equipment is connected to the power grid, the human body should not touch the live parts.
6. When welding indoors or in the open air, a hood must be set around to prevent the arc from hurting the eyes of the staff.
7. Welders must be equipped with masks with suitable filter plates, dry canvas overalls, gloves, rubber insulation and white glasses for slag removal protection.
8. The welding insulation cord shall not be less than 5m, and the cord shall not be put on the body during welding, and the grounding wire shall not be trampled.
9. Welding is strictly prohibited when lifting parts.
10. After welding, disconnect the power circuit breaker in time. Manual arc surfacing
Basic information
Title: Manual arc welding
Book number: 243040 1
Reporter: 7- 122
Pricing: 29.0.
ISBN:7 12200494
Author: Wang Xinhong
Publication date: July 0, 20071
Version: 1
Format: 32
brief introduction
This book is one of the series of Welding Skills Reader, which introduces the basic knowledge of manual arc welding, welding materials, welding equipment, manual arc welding operation technology, welding of common metal materials, manual arc surfacing, welding process quality inspection and welding safety and health technology. This paper analyzes the process characteristics of manual arc welding of common metal materials, and strives to improve the welder's understanding and mastery of the basic theory and operation technology of manual arc welding through examples. This book not only introduces the common sense and basic knowledge of manual arc welding, but also introduces the new welding technology, as well as the manual arc welding technology of new welding materials and new structural materials.
This book can be used as a welder's self-study book, a welder's manual arc welding technical training textbook, and a reference for technicians engaged in welding work and teachers and students of related professional research institutes and universities.
catalogue
1 Chapter Basic knowledge of manual arc welding
1. 1 Brief Introduction of Manual Arc Welding Process
1. 1. 1 Overview of welding methods
1. 1.2 manual arc welding.
1. 1.3 characteristics of manual arc welding
1.2 Common terms for manual arc welding
General conditions 1.2. 1
1.2.2 fusion welding terminology
1.2.3 welding material terminology
1.2.4 terminology of welding process equipment and auxiliary appliances
1.3 welded joint
L.3. 1 composition of welded joint
1.3.2 Basic characteristics of welded joints
1.3.3 Basic forms of welded joints
1.3.4 welding position
1.4 weld symbol and weld groove form
1.4. 1 welding symbol
1.4.2 groove form and groove preparation
1.5 Common tools and accessories for manual arc welding
1.5. 1 electrode holder
1.5.2 welding cable joints
1.5.3 welding cable
1. 1. 4 masks and goggles
1.5.5 covered electrode drying and heat preservation equipment
1.5.6 Weld inspection ruler
1.5.7 All-position welding positioner
1.5.8 Protective clothing
1.5.9 welder's gloves, work shoes and foot protectors.
1.5. 10 Other accessories
Chapter 2 covered electrode
2. 1 Composition and classification of coated covered electrode
2. 1. 1 covered electrode component
2. 1.2 Basic requirements of covered electrode
2. 1.3 covered electrode classification
2.2 Commonly used brands and models of covered electrode.
2.2. 1 covered electrode brand
Covered electrode model
2.3 covered electrode's choice
2.3. 1 covered electrode selection point.
2.3.2 Features and uses of commonly used domestic covered electrode.
2.4 the use and management of covered electrode
Use coated covered electrode.
2.4.2 Management of covered electrode
2.5 Special covered electrode
2. 1. 1 Gravity covers covered electrode.
2.5.2 High-efficiency iron powder covered electrode
2.5.3 Vertical dedicated covered electrode.
2. 1.4 covered electrode for pipeline welding.
2. 1.5 Other special covered electrode
Chapter 3 Manual Arc Welding Equipment
3. 1 Basic knowledge of welding machine
3. 1. 1 welder
……
Chapter 4 Manual Arc Welding Technology
Chapter 5 Repair of Common Steels for Manual Arc Welding and Cast Iron Welding
Chapter VI Manual Arc Surfacing Technology
Chapter VII Welding Quality Management
Chapter VIII Safety and Protection of Manual Arc Welding
refer to