Welding requirements for plug valve of casting valve

The welding method is manual arc welding, welding material grade tgs-9cb, welding rod diameter 3.2 mm, welding current 90-120 a, welding voltage 20-24 v.

The whole valve body is preheated by crawler type flexible ceramic resistance heater, and the preheating temperature is (200 ~ 250) ℃.

The bottom welding, filling and capping shall adopt the welding rod with the specification of φ 3.2 mm, multi-layer and multi pass welding method, so as to reduce the welding heat input as far as possible, and reduce the welding stress according to the principle of symmetrical and segmented welding.

The thickness of the backing layer shall not be less than 3 mm, and the sub layer welding shall be carried out in time after the completion. The thickness of the single layer of other welding passes shall not be greater than the diameter of the welding rod plus 2 mm (about 4-5 mm); the swing width of the single pass welding shall not be greater than 4 times of the diameter of the welding rod; during the welding process, the coating and spatter shall be cleaned up after each welding layer, and the defects shall be carefully checked; If there are defects, the next layer of welding shall be carried out after the removal.

During welding, attention should be paid to the operation method to prevent slag inclusion and porosity defects, and connect with the body smoothly. For each welding rod of 1-2, stop welding and remove slag. With a sharp round head shovel, first knock off the coating of the weld, and then hammer the weld three times to release the welding stress. In addition to the bottom layer without hammering, the other layers need to be hammered after slag cleaning; When using the air pick, the air pressure of the air pick is generally 0.25-0.45 MPa, and the hammer mark should be compact and neat to avoid repetition. When hammering, first hammer the middle of the weld bead, then hammer the weld bead boundary, and then weld the next layer after hammering.

Multi layer and multi pass staggered welding is adopted, that is, the direction of each weld is alternately reversed, so that the superimposed stress can be partially offset; the weld bead does not swing or has a small swing range, and special attention should be paid to the arc crater filling at the arc stop to prevent the generation of arc crater cracks; the interlayer temperature is not lower than the lower limit of preheating temperature; the cover layer weld is slightly higher than the blank surface to ensure grinding allowance.

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