Metal treatment – Process of modifying or maintaining internal physical... – With vibration
Reexamination Certificate
1999-04-08
2002-01-15
Wyszomierski, George (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
With vibration
C148S508000, C148S509000, C148S510000, C029S407070, C116S13700R
Reexamination Certificate
active
06338765
ABSTRACT:
TECHNICAL FIELD
This invention relates to methods, apparatus and systems utilizing and benefitting from the energy of pulses, oscillations and impacts on an exterior surface of a solid work product to rearrange the interior product structure, typically by accompanying plastic deformation. Thus, ultrasonic energy is employed for treatment of metallic and plastic bodies with and without welds. Typically bodies of ferromagnetic metal structures are treated on exterior surfaces. More particularly this invention relates to reduction, elimination, redistribution, relaxation of tensile stresses and defective structures such as voids and grain structures weakening the internal body structure including residual welding stresses. Defects tending to cause structural fatigue and failures in metallic structures and welded products are thus treated by the impact of ultrasonic energy applied to the work product external surfaces. Work products, typically product structures and welded products, are nondestructively impacted at exterior surfaces in the vicinity of welding joints when present, e.g. at welding toes, and/or to non-welded surfaces to thereby restructure the work product internal stresses to impart longer life and greater weight bearing strength.
BACKGROUND ART
In the metal forming and welding arts, the initial manufacturing process, the after-manufacture treatment of the product, the encountering of and the magnitude of loads in use and the aging process lead to deterioration of load bearing strength in the product structure, whether unseen without destructive analysis or evidenced by catastrophic failure, such as by appearance of fractures or cracks.
Conventional welded products are made by employment of various welding art technological operation steps before and after the actual welding step in an attempt to improve the working life of the products. Some of these technological operation steps are categorized as: (a) pre-welding preparation of exposed surfaces at welding sites by abrasive or chemical cleaning, (b) post-welding processing of welded seams by cleaning flux and slag and by surface shaping to remove visible sharp projections and contours that identify concentrated stress areas, (c) surface treatment of the welded structure with corrosion resisting coatings, (d) thermal tempering for relaxation of residual stresses and for internally restructuring the metal grain in a manner reducing the influence of stress concentrations, and (e) demagnetizing treatment to protect welding arcs from magnetic interferences during multi-pass welding operations.
There are interactions of the various independent steps typically occurring at various times on metal products, particularly in view of various intricate work product shapes and loading patterns, and the difficulties in detecting defective subsurface base material patterns, such as grain structure and residual stresses in the product that affect fatigue, life and strength, particularly in the presence of stress concentration zones and highly loaded working zones. Thus, efforts in combatting long term fatigue initiated both during initial manufacture and during useful life with various technical operations heretofore available in the prior art have been substantially limited in their effectiveness and/or are unpredictable, thus producing compromised product quality inconsistent with expected and desired performance.
Known vibration and pulsed methods of stress relief include inducing low frequency mechanical vibrations into products such as welded structures to reduce residual stresses, and employing pulsed magnetic fields to relieve stress in ferromagnetic cutting tools.
At this stage of the prior art, a number and variety of interacting technical operations in a series of processing steps in initial production are required to fabricate proper welded metal products with greater load bearing capacity and lower internal residual stresses for longer expected life and higher quality. Simplification and lower cost of the production process as well as improved performance is thus highly desirable.
Welded metal product or structure manufacturing and repair practices require the addition of and/or removal of materials which therefore are consumed in the manufacturing process. For example, overlay welding and beading operations for strengthening weld seams require more initial product metal and require additional technical operations such as mechanical grinding, removal of fluxes and residues, thermal tempering and cosmetic shaping. It has not been feasible to obtain optimum appearance, strength and life in welded products without such steps. On the other hand, such steps increase costs of production and result in more complex fabrication process.
It is conventional to retire and replace aging metal structures such as steel bridgework and load bearing products subject to aging, which encounter stress fatigue corrosion, undesirable internal stress patterns, and the like, causing the presence of either unseen internal damage or observable surface defects. It is therefore desirable to provide improved maintenance and repair technology to extend the useful work product life by restoring or improving initial load bearing strength and reducing residual stresses in maintenance procedures so that current structures may be kept in operation.
In the welding structure arts conventionally in practice, practical technology has not been available which is well adapted for in-use non-destructive and non-deforming repairs to restructure and restore welded products that have become structurally unsound from aging, that have reduced loading capacity because of fatigue and residual stresses, or which have catastrophically failed by cracking, or the like.
For example, the prior art ability to repair visible catastrophic failures of structure, evidenced by cracks or fractures, in most part is limited to the addition of supporting braces, crutches, and other types of overlying structure to bypass damaged zones. Such techniques are not suitable for many metallic structure installations where there is either no accessible place to rework the welded products in-situ, where restrictions in space are imposed or where appearance of such bypassing structure is intolerable such as in bridgework and building structural support infrastructure.
One zone subject to residual stresses which may cause early failure is the junction zone between basic metal material and weld seams that may contain residual grain or stress patterns formed in the welding process. There are prior art techniques for annealing to redistribute and relax the stress patterns. However in general this is not a scientific method but an art dependent upon skills and experience of a few artisans, such as blacksmiths, where access to the work product is available. Such artistic methods have been applied for example in tempering knives or swords. One significant reason that such methods have not been replaced by scientific technology is that the nature of internal structure is difficult to ascertain and stress concentrations are of a diverse nature that defy analysis.
Thus, a serious deficiency with the manufacture and repair of structural and load bearing products is the lack of non-destructive detectors and corresponding automated systems that can both sense the nature of internal defects and correct them in diverse kinds of internal work product structure by restoring structural integrity to produce longer life following original manufacture procedures or renewed life imparted in maintenance procedures that overcome fatigue and internal stress patterns reducing product performance.
Accordingly, a specific objective of this invention is the introduction of novel procedures for sensing the nature of interior body grain and stress patterns, which is particularly important when involving metallic and ferromagnetic product lines either with or without welding seams.
Also detection of internal product structural conditions provides a frontier for novel automation procedures for radically improving the initial
Breiner & Breiner L.L.C.
UIT, L.L.C.
Wyszomierski George
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