Electric heating – Metal heating – Nonatmospheric environment at hot spot
Reexamination Certificate
2000-06-09
2002-04-16
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
Nonatmospheric environment at hot spot
Reexamination Certificate
active
06373019
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to apparatus and methods for processing a submerged work surface and particularly relates to apparatus and methods for excluding a liquid from a submerged work surface thereby affording a local dry area around a processing apparatus such as a welding torch, heating device or stress-relieving device.
Processing applications such as welding, thermal stressing and the like in an underwater or submerged environment 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 welding underwater, 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 highs and lows of 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 processing area is best achieved at low 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 large 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 gas flow direction outward 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.
More particularly, existing water exclusion devices are inherently inefficient for use over grooves in the surface of substrates since there is no provision either to limit the flow clearance between the device and the lowest portion of the groove as it is filled or, in the case of “flow curtain” types of devices, to provide a differential flow over the groove which is greater than the needed amount away from the groove. As a result, the ability of known devices to exclude water using an internal flow rate below that which disturbs the processing, for example, welding, is limited at best or is ineffective at worst. In addition, the effectiveness of these devices to exclude water from within deep grooves is limited. Even when used within the depth limit of the ability of these devices to exclude water in grooves, they are wasteful of purge fluid since the flow occurring in areas away from the groove is greater than required in order to have sufficient flow over the groove itself. In the worst case, they are totally ineffective to exclude water from deeper grooves.
BRIEF SUMMARY OF THE INVENTION
In accordance with a preferred embodiment of the present invention, there is provided apparatus and methods for excluding liquid, e.g., water, from within a shallow or deep groove formed in submerged substrate materials without excessively high gas flow from within the device. Such high gas flows disturb processing, for example, welding, by chilling or displacing the molten metal pool, or are wasteful of the inert gas commonly used to provide the liquid/gas boundary position at the perimeter of the device. The gas flow must be sufficiently low so as not to disturb the process being applied, yet sufficiently high to effectively displace the surrounding liquid in the gap between the exclusion device and the work surface. Excess liquid vapor must also be prevented from entering the processing zone, which vapor would likely react with the hot or liquid metal and cause weld defects.
To accomplish the foregoing, in a preferred embodiment of the present invention, there is provided a plurality of thin, flat fingers extending parallel to and lying at opposite ends of an exclusion device which is movable along a work surface area such as a groove in the direction of the groove and parallel to the fingers whereby the fingers maintain a differential geometry corresponding to the geometry of the groove adjacent the leading and trailing edges of the exclusion device. Preferably, the thin, flat fingers lie side-by-side at each of the opposite ends of the device and are spring-biased at one end for pivoting movement to an extended position. Consequently, the free or distal ends of each of the fingers is biased in a direction contacting the work surface forming a seal substantially excluding fluid from within the exclusion device. The sides of the device likewise form a seal with the surface straddling the work area or groove. By forming a substantial radius on the distal ends of the fingers, the finger ends will follow the surface contour of the groove under the bias of the springs to form a sufficient mechanical seal with the work s
Bourbour Siamak
Bowen William F.
Chavez Bryan K.
Ninomiya Ron B.
Offer Henry P.
General Electric Company
Nixon & Vanderhye
Shaw Clifford C.
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