Electric heating – Metal heating – Nonatmospheric environment at hot spot
Reexamination Certificate
2000-01-14
2001-07-03
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
Nonatmospheric environment at hot spot
Reexamination Certificate
active
06255616
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to apparatus and methods for submerged processing of a work surface and particularly relates to apparatus and methods for excluding a liquid from a work surface thereby affording a local dry area around a processing apparatus such as a welding torch, heating device or stress-relieving device.
Submerged or underwater processing applications such as welding, thermal stressing and the like require a local dry area around the processing head in order that water can be excluded from the work surface to be processed. For example, in submerged welding, the water must be excluded from the molten metal and nearby heated zone to prevent excessive oxidation, premature cooling and other defects. Inert gas is typically used to displace the water locally around the welding head and to provide a chemically inert atmosphere for the molten metal pool. The work surface in many underwater applications, however, is not smooth or regular, particularly after new or unground weld passes have been applied to a work surface. In these cases, a water exclusion device must have sufficient displacement range to fully comply with the relatively high or low and often abrupt changes in the work surface contour.
For welding applications, water displacement around the weld torch and steam displacement from the heated or cold process area is best achieved at lower gas flow rates to avoid known problems at higher flow rates which may be costly to provide, obscure visibility due to excessive bubble formation or disturb the liquid metal pool or other controlled conditions within the local dry zone. However, for greater surface contour changes, a higher gas flow rate must be used to maintain sufficient water exclusion if the limited compliance seal has insufficient range and lifts off of the work surface for a portion of its perimeter, or if an annular gas flow only design without a compliant seal is used to displace the water from within the torch inert gas cup. In both cases, the higher flow rate is needed to maintain the minimum required gas velocity across the increased gap, which maintains the minimum pressure differential across the gap to keep the flow direction outward with gas flowing into the water, rather than inward with water or mixed phases counterflowing into the welding processing zone. A design combining the benefits of a compliant seal and a gas flow gap may desirably have an increased compliant range relative to either design type alone, however, the combined design will still retain similar problems as each of these design types has individually.
Existing designs for water or other liquid exclusion devices for underwater applications have three basic principles of operation: (1) mechanically sealing the gap between the work surface and the applicator head, e.g., in a welding environment, a cup-shaped gas-filled component around the torch end; (2) flowing gas across the relatively small controlled width gap between the work surface and the applicator head; or (3) providing diverging water/gas cone flowing across a controlled gap to displace water within the contact area of the cone against the work surface. Design variations combining these principles include a gas-permeable compliant seal for multiple concentric flowing water or gas cones. The designs relying on a compliant seal have an inherently limited practical working range because an elastic element is deformed to provide compliance and this element has a limited strain range (before it deforms plastically or is fully compressed), as well as a significantly increasing force requirement for increasing displacement which must be overcome by applicator head manipulation to maintain the desired position along the contoured surface. The force requirement and high displacements may be reduced somewhat by employing thinner or softer deflecting seal elements. However, these thinner elements are increasingly prone to mechanical damage due to inadvertent overloading during use or by tearing during handling operations or while sliding over work surface asperities and discontinuities.
Designs relying on positive water or gas flow through a gap have the limitation that local contour changes or tilting of the applicator head typically generate a differential gap, resulting in the expected differential gas flow around the perimeter of the gap. When the gap is greater in one area, the flow rate and flow velocity of gases, particularly in the case of welding, also becomes greater at the expense of the flow rate and velocity in the remaining areas of the perimeter having a lesser gap. As the flow is reduced in the areas having a lesser gap, the flow rate falls below the minimum required to hold back the water without surging of the water/gas interface or, catastrophically, reverse flow of the water toward the dry welding or process zone within the applicator head housing occurs. Accordingly, there is a need to provide a water exclusion device for submerged processing with a substantially increased compliance range without significantly increased seal application force requirements or increased inert purge gas flow rate requirements.
BRIEF SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, there is provided a liquid exclusion apparatus surrounding an applicator head such as a welding torch or material processing device which has significant capability to reliably follow extreme work surface contour changes without allowing liquid such as water to enter the dry area around the applicator head or work surface being processed. A tightly spaced pattern of slidable fingers or plungers are carried by a housing surrounding the applicator head and follow the surface contours by bridging the variable gap between the housing and the contoured work surface. The fingers are continuously pressed against the work surface by gas pressure within the moving device and/or by mechanical means such as springs or may lie in very close proximity to the work surface without flow of gas maintaining the seal between the fingertips and the work surface. The apparatus does not rely on precisely maintaining a controlled or fixed gap between the work surface and a moving rigid applicator head with sufficient gas flowing across the controlled gap to displace water as in the prior art. It also does not require the use of a limited compliance deformable seal to bridge the gap between the work surface and the applicator as in the prior art. As a result, the apparatus has significantly improved mechanical durability and increased work contour variation operating range for underwater applications such as welding, water-jet peening or thermal-based surface residual stress improvement.
The apparatus solves the inherent problems of limited compliance range availability and high purge gas flow rate requirements for welding, cladding, heat treating or mechanical processing such as shot or water-jet peening in a submerged environment, especially on highly contoured work surfaces, e.g., on weld buildups which are not essentially flush with the work surface. The present invention also increases the durability of the sealing components by using strong sliding seal material contacting the work surface and enables a greater rotational misalignment between the work surface plane and the applicator head axis by incorporating an optional, freely turning spherical bearing to support the sliding element assembly. Moreover, the present invention enables movement of the applicator head with a predetermined force applied to the work surface regardless of the surface contour variations, while maintaining improved water sealing between the work surface and the applicator head. The constant force is generated by the constant gas pressure within the apparatus housing that acts on the cross-sectional area of the fingers. The gas pressure within the housing flows continuously out against the ambient water pressure which is at a relatively constant pressure for a given water depth.
An alternative to maintaini
General Electric Company
Nixon & Vanderhye
Shaw Clifford C.
LandOfFree
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