Steel structure manual arc welding process

1. Construction preparation

1.1 Maerial and main machine and tools:

1.1.1 Welding electrode: The model is selected according to the design requirements and must have a quality certificate.

Bake before the fence welding as required. It is strictly forbidden to use the electrode with the peel off and the rust core. When the design is not specified, E43 series carbon steel structure welding rod should be used when welding Q235 steel; E50 series low full gold structural steel welding rod should be used when welding 16Mn steel; low hydrogen type welding rod (alkaline welding rod) should be used when welding important structure. After baking according to the instructions, put it in a heat preservation bucket and take it with you. Acidic electrode and alkaline electrode are not ready to be mixed.

1.1.2 Arc striking plate: Arc plate is required when connecting with groove. The arc plate material and groove type should be the same as the weldment.

1.1.3 Main machine and tools: electric welding machine (AC, DC), welding wire, welding tongs, mask, small hammer, welding rod oven, welding rod insulation barrel, wire brush, asbestos cloth, thermometer, etc.

1.2Working conditions

1.2.1 Familiar with the drawings and discuss the welding technology.

1.2.2 Welding, the welder's certificate validity period shall be checked, and the welding work that the welder can bear shall be proved.

1.2.3 On-site power supply should meet the welding power requirements.

1.2.4 The environment temperature is below 0C. For preheating and the post-heating temperature should be determined according to the process test.

2. Operating process

2.1 Technological process

2.2 Steel structure arc welding：

2.2.1 Flat welding

A.Select the appropriate welding process, electrode diameter, welding current, welding speed, welding arc length, etc., verified by welding process test.

B.Clean the welding joint: Check whether the groove and assembly clearance meet the requirements before welding, whether the positioning welding is firm, and there should be no dirt or rust around the welding.

C. The baking electrode should meet the specified temperature and time. The electrode removed from the oven should be placed in the electrode barrel and used as needed.

D. Welding current: According to the thickness of the weldment, welding level, welding rod type, diameter, welder proficiency and other factors, choose the appropriate welding current.

E. Arc striking: The over-arc point of the fillet weld should be at the end of the weld, preferably greater than 10mm. It should not be arced casually. After the arc is triggered, the electrode should be pulled away from the weld zone to keep the distance between the electrode and the component in 2-4mm to generate the electrical arc. Butt welds and butt joints and angle joint welds shall be provided with arc runner plates and lead plates at both ends of the weld. They shall be welded to the weld zone after arcing on the arc runner plate, and the fire arc should be made at the joints in the middle which is in front of the weld joint at 15~20mm,After the weldment is preheated, return the electrode to the beginning of the weld. Fill the weld pool to the required thickness, and then continue the welding.

F. Welding speed: Constant speed welding is required to ensure uniform thickness and width of the weld. It is advisable to keep the distance （2~3mm）between the molten iron and the slag in the molten pool (2~3mm) from the inside of the mask.

G. Welding arc length: determined according to the type of welding rod, generally the arc length is stable, the acid electrode is generally 3~4mm, and the alkaline electrode is generally 2~3mm.

H. Welding angle: According to the thickness of the two weldments, the welding angle has two aspects. One is that the angle between the welding rod and the welding advancing direction is 60~70; the other is that there are two cases of the angles between welding rod and the left and right angles of the welding. When the welding thickness is equal, the angle between the electrode and the weldment is 45; when the thickness of the weldment is not equal, the angle between the electrode and the thicker weld is greater than the angle between the electrode and the thinner weld.

I. Arcing: when each weld is welded to the end, firstly fill the arc pit, arcing in the opposite direction of the welding direction, so that the arc pit is inside the weld bead to prevent the arc pit from biting. After the welding is completed, the gas cutting section and the arc extinguishing plate shall be used, and the grinding and smoothing shall be carried out, and it is not allowed to hit with a hammer.

J. Clearing slag: After the whole weld is welded, the slag is removed. After the welder self-test (including appearance and weld size), there is no problem and the welding can be continued at the transfer place.

2.2.2 Vertical welding: The basic operation process is same as that of flat welding, but the following problems should be noted:

A．Under the same conditions, the welding current is 10% to 15% smaller than the flat welding.

B．Short arc welding is used, and the arc length is generally 2~3mm.

C．The electrode angle is determined by the thickness of the weldment. The thickness of the two weldments is equal, and the angle between welding rod and its left and right direction are both 45. When the thickness of the two weldments is not equal, the angle between the welding rod and the side of the thicker weldment should be larger than the angle of the thinner side. The electrode should form a 60℃~80℃ angle with the vertical surface to make the arc slightly upward to the center of the molten pool.

D．Arcing: When welding to the end, the arc is filled by the arcing method, and the arc is moved to the center of the pool and stopped. It is strictly forbidden to make the arc pit aside. In order to prevent biting, the arc should be lowered to change the angle of the electrode so that the electrode is perpendicular to the weldment or slightly blown downward by the arc.

2.2.3 Horizontal welding: basically same as flat welding, the welding current is 10%~15% smaller than the current of flat welding at the same condition, and the arc is 2~4mm.

The angle of the welding rod. the welding rod should be inclined downward during the horizontal welding, the angle is70℃~80℃, to prevent the iron from falling. According to the thickness of the two weldments, the angle of the welding rod can be adjusted appropriately, and the angle between the welding rod and its advance direction is 70~90℃.

2.2.4 Overhead welding：Basically same as vertical welding and horizontal welding,The angle between its welding rod and weldments is related to the thickness of weldments, the angle between the welding rod and weldments is70℃~80℃, the small current and short arc welding will be adopted.

2.3 Low temperature welding in winter：

2.3.1 When performing arc welding under the condition that the ambient temperature is lower than 0℃, in addition to complying with the relevant regulations of normal temperature welding, the welding process parameters should be adjusted to slowly cool the weld and heat affected zone. If the force exceeds level 4, windshield measures shall be taken; joints that are not cooled after welding shall be protected from ice and snow.

2.3.2 In order to prevent welding cracks, the steel structure should be preheated to control the interlayer temperature. When the work site temperature is below 0 ℃, a process test shall be performed to determine the appropriate preheating and postheating temperatures.

3. Quality Standard

3.1 Quality Assurance

①The welding materials shall comply with the design requirements and the related standard regulations. The quality certificate and baking records shall be inspected.

②The welder must pass the examination and the qualification certificate and the date of assessment of the welder's corresponding welding conditions shall be checked.

③Class I and II welds must be inspected by flaw detection and should meet the design requirements and construction and acceptance specifications to check the weld flaw detection report.

③There shall be no defects such as cracks, welds, burn through, craters, etc. on the class I and II welds on welding surface. Class II welds shall not have defects such as surface porosity, slag inclusions, craters, cracks, arc scratches, etc., and Class I welds shall not have defects such as undercuts and underfills.

3.2 Basic Item

①Weld appearance: The weld has a uniform shape, and the transition between the weld bead and the weld bead, the weld bead and the base metal is smooth, and the weld slag and spatter are removed.

②Surface porosity: Class I and Class II welds are not allowed; Class III welds are allowed to have a diameter ≦0.4t in the 50mm length weld; and 2 holes which ≦3mm;and the pore spacing is ≦6 times the pore size.

③Undercut: Class I welds are not allowed.

IClass II weld: undercut depth ≦0.05t, and ≦0.5mm, continuous length ≦100mm, and total length of the undercut on both sides ≦10% weld length

Class III weld: The undercut depth ≦0.1t and ≦1mm.

Note: t is the thinner plate thickness at the joint.

4. Allowable deviation item

Note: b is the weld width, t is the thinner plate thickness at the joint, and hf is the weld angle size.

5. Finished Products Protection

5.1 It is not allowed to hit the joint after welding, and it is not allowed to water the steel that has just been welded. Slow cooling measures should be taken at low temperatures.

5.2 It is not allowed to arbitrarily arc on the base metal outside of the weld.

5.3 Only after the various components have been calibrated can the welding be carried out, and the horn and the fixture should not be moved to prevent the dimensional deviation of the configuration. The weld seam of the concealed part must get through the concealed acceptance procedure before the next concealment process can be carried out.

6. Quality issues that should be noted

6.1 Dimensions exceed the allowable deviation: For the shortage of weld seam length, width, thickness, center line offset, bending and other deviations, the relative position and size of the welded part should be strictly controlled, and the welding should be carried out carefully only after qualified.

6.2 Weld seam cracks: In order to prevent cracks, suitable welding process parameters and fence welding procedures should be selected. The large currents, and sudden extinguish flames should be avoided. Weld joints should be overlapped by 10~15mm. Moving and hitting the weldment during welding is not allowed.

6.3 Surface porosity: The welding and punching is baked according to the specified temperature and time. The welding area must be cleaned. During the welding process, the appropriate welding current is selected to reduce the welding speed and make the gas in the molten pool escaped completely.

6.4 Welded slag: The slag should be removed layer by layers during multi-layer welding. The operation should be carried out correctly and the arc length should be appropriate. Pay attention to the flow direction of the slag. When using the alkaline electrode, the slag must be left behind the slag.

7. Quality record

This process standard shall have the following quality records:

7.1 Certificate of quality of welding materials.

7.2 Welder certificate and serial number.

7.3 Welding process test report.

7.4 Welding quality inspection report and flaw detection report.

7.5 Design change and negotiated records.

7.6 Concealed project acceptance records.

7.7 Other technical documents.