JB/T 6890-1993 Technical requirements for repair welding of defects in carbon steel castings for fans
Some standard content:
Machinery Industry Standard of the People's Republic of China
Technical Conditions and Scope of Application for Defect Repair Welding of Carbon Steel Castings for Fans
JB/T 6890—93
This standard specifies the carbon steel for fans Technical requirements for repair welding of casting defects, inspection and acceptance, including defects such as pores, blisters, slag inclusions, shrinkage cavities, cracks and other defects that are not allowed to exist when the casting is in a rough state or during machining, as well as the geometric shape and size of the casting. repair. This standard applies to manual arc repair welding of defects in carbon steel castings for fans (hereinafter referred to as castings). Unless there are special provisions in drawings, technical documents or ordering agreements, repair welding of casting defects shall comply with the provisions of this standard. 2 Reference standards
GB150 steel pressure vessels
GB5117 carbon steel welding rods
JB/T6888 Technical conditions for steel castings for fans 3 Defects that do not require repair welding
JB /T6888 allows defects that do not require repair welding 4 Defect repair welding methods
4.1 Who should prepare before repair welding
4.1.1 Drafts are strictly prohibited in the repair welding work site, and the ambient temperature should generally not be lower than 10 5C. 4.1.2 When the defect is a crack, in order to prevent the crack from expanding, crack relief holes of not less than $5 should be drilled at both ends of the crack before shoveling. 4.1.3 Depending on the condition of the defect, you can choose shoveling, filing, grinding, mechanical processing, gas cutting, carbon Arc gouging method is used to clean welding joint defects. On the premise of completely eradicating defects and facilitating welding, the amount of metal removed should be as small as possible. When gas cutting or carbon arc gouging is used, the requirements in Table 1 should be followed for overall or partial preheating before removal. Surface oxide must be removed after shoveling. Table 1
Steel casting grades
ZG 200-400
ZG 230-450
ZG 270-500
ZG310-570||tt| |Preheating temperature, C
100~250
150~250
Yes
No preheating
Ask
Generally do not preheat Heat, preheat when the defects are large and the measurement is large
Note: In addition to considering the composition of the cast steel, the preheating of the casting must also consider the workpiece structure, processing status, defect size, and other factors for reasonable selection. 4.1.4 For non-penetrating defects, the groove can be opened as shown in Figure 1. The form R shown in Figure 2 should not be less than 6mm. When the size of the defect is large, the slope of the groove can be smaller, but it should not be less than 10°; other groove forms are allowed. 4.1.5 The principle of shoveling defects should be to completely remove defects and facilitate welding. The groove formed after shoveling should have smooth transitions in all places, avoid sharp corners, and have no sudden changes in cross-section.
4.1.6 Thoroughly remove all dirt such as sand, oil, rust, scale and other dirt within 20mm around the place to be welded. Approved by the Ministry of Machinery Industry of the People's Republic of China on 1993-07-13 236
Implemented on 1994-07-01
LL
15°~30°www.bzxz.net
Figure 1||tt ||JB/T6890-93
Figure 2
4.1.7 Preheating before welding should be reasonably selected according to the casting grade, thickness, processing status and repair welding conditions, and refer to Table 1. Preheating can be local preheating or overall preheating, and the preheating temperature should not be lower than the required preheating temperature. During the entire repair welding process, the temperature of the repair welding part shall not be lower than the lower limit of the preheating temperature requirement.
4.2 Repair welding
4.2.1 Welders who are responsible for repair welding must pass the welder examination before they can operate. 4.2.2 The repair welding work should be carried out continuously. If it is interrupted as a last resort, heat preservation measures should be taken. The requirements of Article 4.1.7 should be met when the repair welding is repeated. 4.2.3 The principle for selecting welding rod models is the principle of plastic matching. That is, the strength of the welding rod is slightly lower than that of the base metal, but its plasticity is higher than that of the base metal. Repair welding electrodes can be selected according to GB5117,
4.2.4 In order to ensure the quality of repair welding, low hydrogen electrodes should be preferred and should be dried as required before use. 4.2.5 If cracks, lack of fusion, slag inclusions, pores and other defects that affect the quality of the repair welding occur during the repair welding process, they should be completely removed according to 4.1.3. For defects such as cracks, repair welding can only be continued after inspection and confirmation that they are clean. 4.2.6 The number of repair weldings for the same part shall not be more than three times. For castings after quenching and tempering treatment, the number of repair weldings for the same part shall not be more than two times. 4.3 Post-weld heat treatment
4.3.1 For castings that are repaired welded before final heat treatment, final heat treatment should be carried out in time after repair welding, otherwise post-weld tempering treatment should be carried out in time.
4.3.2 Castings that undergo repair welding after final heat treatment should be tempered after repair welding. However, castings with large defects and those that affect performance after repair welding should be heat treated again. 4.3.3 For tempering heat treatment requirements after repair welding, refer to Table 2. Table 2
Steel casting grades
ZG200-400
ZG 230-450
ZG 270-500
ZG 310-570||tt| |ZG 340-640
Tempering overflow
550--650'℃
Request
Request
Generally, tempering is not required, but the defects are large Parts with high iron content should be tempered and slowly cooled after welding, and should be tempered in time
4.3.4 For castings that require tempering after repair welding, when the defects of the repair welding of the casting are small or the overall tempering is not allowed When, local tempering is allowed. Partial tempering can be done by heating the 100mm range near the weld to 600~650°C by gas flame or other means (it should be slightly lower than the final heat treatment tempering temperature). Each 25mm thick repair welding metal should be kept warm for 10 minutes and then slowly cooled. 5 Repair welding inspection and quality acceptance
5.1 Inspectors should clearly mark the defective parts to facilitate repair welding. 5.2 Inspection personnel should inspect the excavation of defects and the opening of grooves in accordance with the provisions of this standard. Repair welding can only be carried out after passing the inspection. 5.3 All important castings should be comprehensively inspected for preheating before repair welding, weld quality, and post-weld heat treatment in accordance with the provisions of this standard. Process discipline must be strict, key parts must have repair welding processes, and repair welding records must be kept. 5.4 Cracks, burn-throughs and dense pores are not allowed after repair welding. The undercut depth of non-processed parts shall not be greater than 1mm, and the length shall not exceed 10% of the total 237
length. Defects are allowed to exist.
JB/T6890—93
5.5 The weld metal should be well fused with the base metal, the weld should be smooth, and the color of the processed weld should be the same or similar to the base metal. 5.6 For casting defects that require a pressure leakage test, a hydraulic test shall be carried out according to GB150 after repair welding. 5.7 After repair welding, the casting shall be inspected and accepted according to the provisions of JB/T6888. 5.8 After the repair welding of important castings has passed the acceptance inspection, welding marks and inspector marks should be marked. Additional notes:
This standard is proposed by the National Technical Committee for Fan Standardization. This standard is drafted and managed by Shenyang Blower Research Institute. The main drafters of this standard: Li Zheng, Chen Mingliang, and Tian Suwen. 238
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