1.Overview
Among the pressure-bearing valves in industrial pipelines, cast steel valves are widely used because of their cost economy and design flexibility. However, due to the casting process by casting size, wall thickness, climate, raw materials and construction operations of the various constraints, the casting will appear trachoma, porosity, cracks, shrinkage, shrinkage and inclusions and other casting defects, especially sand casting alloy Steel castings for more. Because the more alloying elements in the molten steel liquid flow worse, casting defects are more likely to produce. Therefore, it has been a common concern that hot and cold processing of valves should be concerned with determining defects and formulating a reasonable, economical, practical and reliable welding process to ensure that the repaired valves comply with the quality requirements. This article describes several common defects of steel castings repair methods and experience (electrode using the old brand said).
2.defect handling
In the production practice, some casting defects do not allow repair welding, such as through cracks, penetrating defects (through the bottom), cellular pores, can not remove the sand with slag and more than 65 square centimeters of shrinkage, etc., and Other major defects that can not be repaired by welding agreed in the contract between both parties. Before welding repair should determine the type of defect.
3.electrode processing
Repair welding, should first check whether the preheating electrode, the electrode should be generally 150 ~ 250 ℃ drying 1h. After preheating the electrode should be placed in the incubator, so do with the use. Electrode preheating 3 times repeatedly, if the electrode surface coating off, cracking and rust, should not be used.
4.important repair welding
Hydraulic tests Castings with seepage, castings with> 65cm2 weld area, castings with 20% or 25mm wall thickness, ASTMA217 / A217M-2007 are considered as important repairs. For such an important repair welding A217 standards, should be carried out to stress treatment or completely reheat treatment, and this stress-relieving treatment or complete reheating treatment, must be approved by a qualified method, that is important to make welding Repair welding process. ASTMA352 / A352M2006 provides that the important repaired after stress relief or post-weld heat treatment is mandatory. And A217 / A217M corresponding to China's industry standard JB / T5263-2005 will be important in the definition of welding "heavy defects." However, in fact, except that the cast blank can be completely reheated, many defects are often found during finishing and are no longer completely heat-treated. Therefore, in practice, the welder, who usually holds the certificate of pressure vessel welding, is usually solved in the field with effective methods.
