Process for overlaying stainless steel sealing face on nodular cast iron valve substrate

Abstract

The invention discloses a process for overlaying a stainless steel sealing face on a nodular cast iron valve substrate. The process comprises the steps that firstly, the valve substrate is cleaned; pulse gas metal arc welding is adopted; full-automatic welding is adopted, pulsed direct currents are adopted, an anode is reversely connected, inert gas shielding is achieved, and flow ranges from 10 L/min to 17 L/min; welding speed ranges from 8 cm/min to 15 cm/min; after welding is completed, the position, to be welded, of the valve substrate is wrapped by a stainless steel overlaying layer of 2 mm to 4 mm; and heat preservation and preheating are omitted. The process has the advantages that the welded sealing face is reliable in strength and stable in performance, the defects of air holes, cracks and the like are overcome, and the utilization rate of materials is high; the process is simple, operation is convenient, and automation can be achieved. Compared with a stainless steel ring spinning, contour welding and embedding process, a plurality of procedures such as line drawing, blanking, plate rolling, butt welding and spinning are omitted, and the process is suitable for automatic welding and volume production.

Description

technical field [0001] The invention relates to a processing technology for a valve sealing surface, in particular to a technology for overlaying a stainless steel sealing surface on a nodular cast iron valve base body. Background technique [0002] The Chinese patent "CN 102785004A" discloses "the process of overlaying stainless steel sealing surface on the ductile iron valve base". After welding, place the valve substrate with the stainless steel sealing layer on the surfacing and heat preservation at 350-400°C for 2 hours; therefore, there are high requirements for welding temperature and preheating time; 2. The protective gas is a mixed gas of argon and carbon dioxide Shielded welding, high welding temperature, large welding spatter caused by carbon dioxide, poor welding surface shape, even if the above insulation measures are adopted during cooling, due to the limitations of the welding process, ductile iron will also appear due to uneven heating and inconsistent coolin...

AI Technical Summary

Problems solved by technology

[0002] Chinese patent "CN 102785004A" discloses the "process of overlaying stainless steel sealing surface on ductile iron valve substrate" in the actual welding process, there are the following problems: 1. Preheat the valve substrate at a temperature of 100-250°C. After welding, place the valve substrate with a stainless steel sealing layer at a temperature of 350-400°C for 2 hours; 2. The protective gas is argon and carbon dioxide mixed gas shielded welding, the welding temperature is high, carbon dioxide causes large welding spatter, and the welding surface is poorly formed. Even if the above insulation measures are adopted during cooling, due to the limitations of the welding process, nodular ink Cast iron will also have cracks due to uneven heating and inconsistent cooling rates of the inner and outer layers; 3. During welding, welds or cracks that are invisible to the naked eye are prone to appear. Even when the product is subjected to a pressure test, the weld or crack cannot be detected. However, when in use, due to the vibration caused by liquid impact, and the toughness of ductile iron is poor, there is stress concentration in the weld, so the cracks hidden in the surfacing layer will continue to expand, resulting in poor sealing, liquid leakage on the sealing surface, and even The welding layer falls off; and in actual operation, there are high requirements for welder technology, welding conditions and other factors, labor intensity is high, the process is complicated, the actual cost rate is low, and multiple repair welding is required, so it is not suitable for large-scale mass production

4. The sealing surface welded by the above process, because it cannot be annealed or normalized, has poor processing performance, slag inclusions, pores, high hardness, and unevenly distributed processing hard spots. When processing with ordinary carbide knives, The roughness of the processing is poor, it is easy to hit the knife, and it is easy to produce accumulated cuts, and the blade needs to be sharpened many times; 5. Carburization and intergranular corrosion occur at the joint between ductile iron and stainless steel, which makes the stainless steel lose its antirust ability. In addition, due to the residual stress Accelerated corrosion due to other reasons