JPH0527796B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a welded bellows and a method for manufacturing the same. [Prior Art] Bellows have long been used in piping systems and the like that require vibration, expansion, and contraction stages. In recent years, with the development of industry, the requirements for piping systems have become more sophisticated, such as high temperature, high pressure, corrosion resistance, and complete prevention of leakage. In addition, in the valves used in these piping, in order to completely prevent leakage from the valve stem penetration part of the valve body, so-called bellows is used, which connects the valve body and the valve body or valve stem via a bellows. Valves are often used. The bellows used for this require particularly high reliability. Traditionally, bellows have mainly been molded bellows made by spinning tubular materials into a pleated cross-sectional shape, but they have a greater degree of freedom in material selection to meet the recently more sophisticated requirements, and improvements in pressure resistance, manufacturability, etc. Since then, welded bellows have become widely used. As shown in Fig. 1, the welded bellows is made by stacking elements 1, which are shaped like disc springs by press punching or press forming from plate materials, so that their concave and convex sides face each other, and the contact part is Welded parts 2 and 3 are formed on the edge side of the outer diameter.
It is assembled by joining by TIG welding or plasma welding. [Problems to be Solved by the Invention] However, in conventional welded bellows, accidents often occur in which cracks occur in the welded portion. As a result of various investigations and experiments regarding the cause of the occurrence of this crack, the present inventor has discovered the following. Various materials are selected for the welded bellows. Precipitation strengthened alloys containing Al are often used for their strength, corrosion resistance, etc. In the welded bellows made of this alloy containing Al, a minute whisker-like crack 4 was discovered from the weld boundary A in the enlarged cross-sectional view of the weld shown in Figure 2, as seen in the microscopic photograph in Figure 4. It was done. That is, long cracks are seen in a zigzag pattern from the overlapping surface of the elements 1. This whisker crack 4 becomes the starting point of stress concentration or fatigue fracture,
Grow into cracks. A film mainly composed of Al ₂ O ₃ is present in the whisker-like cracks 4, causing so-called fusion failure. The cause of this is that Al in the film or material on the surface of element 1 is oxidized with a small amount of oxygen due to its strong affinity for oxygen, resulting in oxides mainly consisting of Al ₂ O ₃ . It was found that the substance did not diffuse into the substance and remained as a film. The present invention achieves the following by improving the welding method etc.
It is an object of the present invention to provide a highly reliable welded bellows that prevents this whisker-like cracking and a method for manufacturing the same. [Means for Solving the Problems] The present invention provides a plurality of elements formed into substantially disc spring shapes, which are arranged one on top of the other so that their concave or convex directions are opposite to each other, and their contact portions are placed on the edge surface. In welded bellows that are welded together from the side,
The element contains Al0.1-5.0% by weight
A welded bellows made of Fe, Ni or Co-based alloy, characterized in that it prevents the occurrence of long whisker-like cracks in the welded part from the overlapping surfaces of the elements in a zigzag manner, and
Made of Fe, NiCo-based alloy containing 0.1~5.0% Al,
Multiple elements shaped like disc springs,
In the manufacturing method of welded bellows, the welded bellows are stacked so that the concave and convex directions are facing each other, and the contact portion is welded from the ^edge side. The production of welded bellows is characterized by TIG welding or plasma welding carried out in an inert gas, reducing gas or a mixture thereof without exposure to air, or by electron beam welding carried out under vacuum. It's a method. [Operation] The surface film of the element can be removed by pickling or the like. Therefore, whisker cracks can be prevented by preventing oxidation during welding. Generally, welding is carried out in a neutral or reducing atmosphere as a method to prevent oxidation during welding. Conventionally, when welding welded bellows, TIG welding or plasma welding using reducing gas as a shielding gas is used. etc. were used. However, as a result of follow-up welding tests, oxygen remained in the recesses of the overlapping parts of the welded bellows, so even if a reducing gas was used as a shielding gas, sufficient oxidation prevention effect could not be obtained, and the above-mentioned It was found that whisker-like cracks occurred. In the present invention, elements are welded in an oxygen-free state. To do this, the element is first evacuated to remove oxygen adsorbed on the surface, and then welded without exposing it to oxygen.
This welding is performed using TIG in an inert or reducing gas.
Welding or plasma welding or electron beam welding in a vacuum are suitable. As mentioned above, the whisker-like cracks are caused by the oxide of Al, and if Al is less than 0.1%, the whisker-like cracks will not occur even without the present invention. Furthermore, the present invention provides Al ₂ O ₃ by cutting off oxygen.
Since this prevents the formation of Al, even if the element material contains a large amount of Al, welding can be performed without generating the above-mentioned whisker cracks. However, since the materials commonly used for welded bellows are FeNi or Co-based alloys that usually contain less than 5% Al, the present invention limits the upper limit of the Al content to 5%.
% of Fe, Ni or Co-based alloys. Furthermore, in the case of TIG welding or plasma welding using an inert gas or reducing shielding gas, the vacuum level must be 10 ^-2 Torr or higher. If the degree of vacuum is less than 10 ^-2 Torr, the evacuation effect will be reduced, and the above-mentioned whisker-like cracks will be more likely to occur. In the present invention, the thickness of the element is not particularly limited. However, the present invention is particularly effective for plate thicknesses in the range of 0.05 to 1.5 mm. If it is less than 0.05 mm, it is difficult to obtain a stable bead, and if it exceeds 1.5 mm, a small amount of oxide will easily diffuse into the molten pool (even with conventional welding methods, the above-mentioned whisker cracks are less likely to occur). . [Example] The table below shows the chemical composition of the prototype welded bellows. First, melt the three types of materials shown in the table in a vacuum melting furnace.
After casting, 3mm by hammer blooming and hot rolling.
It was made of thick plate material. Next, after removing the oxidized scale on the surface by grinding, cold rolling and photo-volatile annealing were repeated to finish the plate to a thickness of 0.25 mm. This plate material was punched and press-molded, and the surface was purified by pickling to obtain an element.

〔Effect of the invention〕

As described above, the present invention has been able to achieve high reliability by preventing the cracking accidents that conventionally occur in welded bellows made of Al-containing alloys, which are difficult to avoid due to strength, corrosion resistance, etc. This has an extremely large effect industrially.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the structure of the welded bellows, Fig. 2 is an enlarged sectional view of the welded part to explain the position of the speculum, and Figs. 3 and 4 are the weld boundaries between the method of the present invention and the conventional method. 3 is a micrograph showing the microstructure of each part. 1... Element, 2, 3... Welding part, 4...
The above-mentioned whisker-like crack, A... welding boundary.

Claims (1)

[Claims] 1. A welded bellows in which a plurality of elements shaped into substantially bellows springs are arranged one on top of the other so that their concave or convex directions face each other, and their contact portions are welded from the edge side. , the element is Fe, Ni containing 0.1 to 5.0% Al by weight ratio.
Alternatively, a welded bellows is made of a Co-based alloy, and is characterized in that long whisker-like cracks extending in a zigzag pattern from the overlapping surfaces of the elements are prevented from occurring in the welded joint. 2. The welded bellows according to claim 1, wherein the element has a thickness of 0.05 to 1.5 mm. 3 Fe, Ni or Ni containing Al0.1 to 5.0% by weight
In a method for manufacturing a welded bellows, a plurality of elements made of a Co-based alloy and formed into a substantially disc spring shape are stacked so that their concave or convex directions are opposite, and the contact portions are welded from the edge side, The welding involves heating the element to 10 ^-2 Torr.
TIG welding or plasma welding is performed in an inert gas, reducing gas, or a mixture of these gases without exposure to air after evacuation to a higher degree of vacuum, or electron beam welding is performed under vacuum. A method for manufacturing a welded bellows characterized by: