The Name of Wirefab brought back a memory of a critical machining error by our subcontractor on a large gas expander casing. The rough casting was a half-diameter, in a stainless steel alloy (CA6NM), and weighed approximately 4000 lbs. The part measured about 96" long, and 50" wide, on the outside. It was being machined on a vertical boring mill, standing on end. All the diaphragm grooves had been machined, and they were facing the ends. As best as the subcontractor was able to determine, the digital readout had a brain fart, and they machined off .060" too much material. The subcontractor made the decision to send it to Wirefab for flame spraying, and the flame spraying deposited about 1/8", and returned it. When the machine shop began turning the face back to the final dimension, the flame sprayed material began peeling off, and the customer rejected the part. The machining contractor footed the bill for an entire new casting, $30,000+.
The flame spraying process is not a "welding" process recognized by most Industry and Gov't specs, such as ASME, and NAVSEA.
All true welding processes involve complete fusion of the filler material, and base metal. This involves the base metal to become molten, along with the filler metal, to form a complete, homogeneous bond. (Picture pouring a cup of water into a bucket of water). The base metal, in Flame spraying, does not become molten, and the material, introduced into the plasma (the flame), though molten, is simply overlayed.
The flame spray method does have it's place, in static applications, but doesn't stand up to wear.
Building up the hook on a shotgun barrel may have been done in the past by this process, but it's far from the near 'surgical tolerance' of more recently developed welding procedures like TIG, Micro TIG, and now, Laser welding.
Picture the Sistene Chapel being painted with rattle cans, instead of camel hair brushes.
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09-11-2024, 11:41 AM
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