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Text version of the page
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| | unique source for ONE-PIECE FORGED VALVES UP TO 24" (600 mm) | | ||||||||||||||||||
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 | WHY FORGINGS? When compared with castings, forged valve bodies offer the advantages of more uniform structure, greater density, higher strength integrity, enhanced dimensional characteristics and closer dimensional tolerances. | RELIABILITY The ability of forgings to meet design requirements consistently is one of the most important advantages and takes into account all the preceding characteristics to some degree. QUALITY ASSURANCE OF FORGINGS Through the use of forgings, with their uniformity and high quality, the radiographic requirement for comparable Class 1 cast components is eliminated. Recognizing this, the United States Navy regularly specifies forgings for valves and other components for nuclear submarines and aircraft carriers. All that is required by the ASME Code for forgings is ultrasonic examination and magnetic particle or liquid penetrant testing in the finished condition. Rejections of forgings for inherent deficiencies found by U.T., M.T., or PT methods are rare. | ||||||||||||||||||
| The directional structure (flowlines) is superior from an overall strength and stress standpoint against castings. (see Figure 1 below) HIGH STRENGTH Hot forgings promote recrystallization and grain refine-ment allowing the material to develop maximum possible strength and uniformity with a minimum variation from piece to piece. The grain flow closely follows the outline of the body and continuous flow lines decrease the susceptibility for fatigue or common failures. STRUCTURAL INTEGRITY Forging éliminâtes internai flaws and produces a cohérent and uniform metallurgical structure assuring optimum performance. Where stress and intergranular corrosion are a problem, a forging will significantly increase the probability of longer life and trouble-free service. DIMENSIONAL & METALLURGICAL UNIFORMITY Dimensional uniformity of closed-die forgings results in positive control of critical wall thickness, eliminating deficiencies caused by shifted cores in castings. A uniform metallurgical structure without internal flaws is assured by (a) quality, segregation-free billet and (b) high impact forces achieved on 10,000-30,000 ton presses. | ||||||||||||||||||||
| FORGING PROCESS FOR VELAN BODY FORGINGS 12-24" (300-600 mm) | ||||||||||||||||||||
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| | quality of forgings begins with the segregation-free, uniform and pure ingot Special alloys and stainless steels are manu-factured in vacuum induction melt furnaces. Electrodes produced in these furnaces are remelted in vacuum with electrodes pressed directly from chemical powders, resulting in further purification. Solidification is controlled by electronic circuits making possible segregation-free ingots - a task that is difficuly to achieve with castings. Alloy steel heats are vacuum-treated on degassing units to reduce hydrogen content to less than two parts per million and reduce metallic oxides. Teeming (pouring) of ingots is done usually under argon gas shielding. All processes proceed under the watchful eyes of the laboratories using sophisticated monitoring equipment. | |||||||||||||||||||
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| Figure 1: Continuous flow lines in highly stressed crotch area. | ||||||||||||||||||||
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