Abstract:
A housing for a processing device includes a plurality of independently extendible and retractable fingers for engaging the work surface. Gas pressure supplied within the housing drives the fingers into their extended positions and assists in excluding surrounding water from the work surface within the housing. The fingers may have fixed balls, roller balls or slidable wheels at their distal ends to facilitate movement of the housing along the work surface. Flexible skirts may be provided about the fingers to assist in water exclusion from the work area.

Description:
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 maintaining a controlled minimum distance between the work surface and the sealing fingers is to have each finger operated independently with a small pneumatic or electromagnetic pin driver connected to a servocontroller which extends each finger as required to make contact with the work surface and then to retract the finger a predetermined distance to provide a minimum clearance. With a limited finger clearance, the purged gas will flow outward and the sliding friction of the fingers against the work surface is minimized, while maintaining the processing zone dry. 
     In a preferred embodiment according to the present invention, there is provided apparatus for processing a submerged work surface, comprising a closed housing having an opening and movable relative to the work surface, an array of discrete fingers carried by the housing for movement substantially independently of one another between retracted positions and positions extending from the housing surrounding the opening, the fingers having tips for engaging or lying in close proximity to the submerged surface in the extended positions of the fingers, means for extending the fingers substantially independently of one another enabling the tips of the fingers to follow the work surface as the housing is displaced relative to the surface and a working head carried by the housing and interiorly of the fingers for processing the surface through the opening. 
     In a further preferred embodiment according to the present invention, there is provided an apparatus for processing a submerged work surface having a closed housing, an opening, a working head within the housing and an array of discrete fingers carried for movement substantially independently of one another between retracted positions and positions extending from the housing surrounding the opening, a method for excluding fluid from the work surface, comprising the steps of extending the fingers substantially independently of one another relative to the housing enabling tips of the fingers to engage or lie in close proximity to the submerged surface in the extended positions of the fingers, advancing the housing along the work surface with the fingers following the contour of the work surface and movable independently of one another to substantially exclude fluid from the work surface exposed to the working head within the housing and operating the working head to process the work surface through the opening as the housing is advanced along the work surface. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary perspective view with parts in cross-section of an exclusion device for submerged processing applications constructed in accordance with the present invention; 
     FIG. 2 is a view similar to FIG. 1 illustrating a further embodiment thereof; 
     FIG. 3 is a fragmentary perspective view illustrating the application of the apparatus against a contoured work surface, for example, a welding head for welding metal plates at right angles to one another; 
     FIGS. 4A,  4 B,  4 C and  4 D are fragmentary elevational views with parts in cross-section illustrating further embodiments of the present invention; 
     FIG. 5 is a fragmentary plan view of arrays of the fingers with one array outside of another array; 
     FIG. 6 is a perspective view with parts broken out illustrating a spring-biased telescoping form of the fingers; 
     FIG. 7 is a plan view of a plurality of rolling fingers; 
     FIGS. 8-11 are fragmentary end elevational views of various forms of fingers; 
     FIG. 12 is a side elevational view of a form of finger hereof; 
     FIG. 13 is an elevational view thereof as viewed from left to right in FIG. 12; 
     FIG. 14 is a top plan view of the finger of FIG. 12; 
     FIG. 15 is a side elevational view of a further form of finger hereof; 
     FIG. 16 is an elevational view thereof as viewed from left to right in FIG. 15; 
     FIG. 17 is a top plan view thereof; 
     FIG. 18 is a fragmentary perspective view illustrating the applicator head employing the fingers illustrated in FIGS. 12-14; 
     FIG. 19 and 20 illustrate arrangements of fingers in arrays thereof forming an internal circular configuration in concentric internal and external circular configurations, respectively; and 
     FIG. 21 is an enlarged fragmentary cross-sectional view illustrating the tip of a finger illustrated in the dashed line circle of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, particularly to FIG. 1, there is illustrated an exclusion device for underwater or submerged processing applications, generally designated  10 . It will be appreciated that the underwater apparatus may be employed for a variety of applications, for example, welding, water-jet cleaning, thermal-based surface residual stress improvement and other types of applications. The present description, however, refers to a particular application of the present invention to underwater welding and it will be appreciated that the invention is not, therefore, limited to underwater welding but embraces other applications. 
     The apparatus  10  includes a housing  12  which is closed at its top and sides and has an opening  15  at a lower end thereof. The housing  12  also includes an applicator head  14 , for example, a welding torch. The applicator head  14  extends through the housing  12  such that the tip of the head  14  is in position to process the work surface through the open lower end of the housing  12 , i.e., to weld on the work surface. The housing  12  includes an array of discrete or individually slidable fingers or plungers  16  which are mounted in closely-spaced holes or seats  18  located in an area, e.g., an annulus, between an inner race  20  and a spherical bearing surface  22 . The fingers  16  are movable between extended positions and retracted positions relative to the housing  12  independently of one another. Consequently, each finger  16  is movable independently of an adjacent finger and the extent of travel of each finger is therefore independent of the extent of travel of adjacent fingers. In the illustrated form in FIG. 1, the fingers have a circular cross-section, although it will be appreciated that non-circular cross-sections may be used. Thus, the fingers act similar to plungers in that they can all move in or out of the housing  12  according to the positions they are extended to, i.e., inward by a high spot on the work surface against the pressure in the housing or outward at a work surface low spot. Means are provided for controlling the movement of the fingers. For example, the movement of the fingers  16  can be controlled by any number of a variety of mechanisms, such as gas pressure, springs, magnets and the like. Gas pressure within the housing, however, comprises a preferred mechanism for advancing the fingers from their retracted to their extended positions. 
     To extend the fingers from retracted positions, a gas inlet supply line  24  is provided for supplying gas into the interior of the housing  16 , i.e., into chamber  17 . It will be appreciated that the interior ends or heads  19  of the fingers  16  are exposed to the gas pressure within housing  12 . Consequently, with the gas pressure within the housing applicable against the interior end faces of the fingers, the fingers may be extended from their retracted positions to extended positions limited only by the contact between the fingertips  26  and the work surface. The fingers  16  are retained within the raceways provided by the seat  18  and the inner race  20  by a retaining ring which engages a shoulder, head or flange on each finger at its extended travel limit position. For example, a projection  28  (FIG. 1) may be provided along the inner surface of each finger adjacent the inner end surface forming a stop limiting travel of the finger from the housing, the stop bearing against the inner face of the inner race  20 . It will be appreciated that any other suitable retaining device can be employed to retain the fingers in the housing in their extended travel limit position. 
     Because the gas pressure within the housing acts uniformly on the interior end faces of the fingers, the finger contact force on the work surface will be uniform and primarily a function of the gas pressure. Thus, it will be appreciated that the force of the fingertips on the work surface can be adjusted by adjusting the gas pressure. The welding torch  14  is accompanied in this preferred embodiment of the invention illustrated in FIG. 1 by a tube  28  which houses the wire feed or welding rod  30 . 
     It will be appreciated that the cross-sectional shape of the fingers  16 , while preferably round, may have other shapes as desired, for example, rectangular or multi-sided. For non-circular transverse cross-sectional shapes, such as rectangular shapes, the tip of each finger  16  may have a large radius on two opposing sides facing the adjacent fingers to enable the fingers to readily slide over irregular contours in the work surface and only a small radius on the other opposing edges to improve gas sealing capability. The spacing of the fingers is preferably close to and preferably in contact with one another in order to minimize the gap and corresponding gas flow rate through which the gas purge flows to prevent water intrusion. 
     Preferably, the material of the fingers and their inner and outer raceways  20  and  18 , respectively, are compatible with the work material which are corrosion-resistant when wetted and which have a low friction coefficient with each other. For example, hardened stainless steel bearing fingers may be employed. Insulating surfaces may be applied on the fingers when an electrically sensed (ground potential sensing) AVC-type of pin clearance servo is utilized. 
     As illustrated in the enlarged illustration of the end of the fingers in FIG. 2, the fingers may be hollow to permit gas flow through the fingers and their tips. Consequently, the fingers  16  may have an axial extending passage  32  from within the housing in communication with the gas pressure through the fingertip. The gas thus facilitates drying of the water/gas interface region of the work surface. Also supplying gas through the fingers and through the tips facilitates control of the axial force of the fingers. Moreover, the ends of the fingers located against the work surface are smooth and have radiussed edges to allow smooth sliding over weld bead crowns. Additionally, while the illustrated apparatus has a generally cylindrical configuration, the housing  12  may have any shape or size consistent with the application of the device and/or with the contoured work surfaces. The housing  12  also may be integral with the welding torch housing  14  or the torch housing may be removed from the housing  12  as desired. 
     While the fingers are continuously pressurized to slide out of the housing due to the differential between the gas pressure acting on the finger ends within the housing and the lower water pressure acting on the tips of the fingers, the gas flowing through the passages  32  of the fingers  16  allows the fingers to essentially “float” across the surface during travel of the housing with significantly reduced friction. Because the gas flows at a higher pressure than that of the water, the reaction force of the gas against the work surface will tend to make the tubular fingertip lift off the work surface until the gas can escape into the water without the additional flow restriction of the otherwise contacting solid surface. Consequently, a finger position “equilibrium” is obtained at this offset location with the standoff distance from the work partly controlled by the applied gas pressure. The closer the fingertip gets to the work surface, the greater the reduction in leakage and corresponding increase in pressure, with the result that the escaping gas displaces the finger back from the work surface, allowing it to float slightly. The finger hole size may be predetermined to provide the desired back pressure by increasing the hole size to decrease the outward force or decreasing the hole size to increase the force. Consequently, in this form of the invention, the fingertips lie in close proximity to the work surface. 
     From the foregoing, it will be appreciated that various processing applications are enabled by use of the exclusion apparatus of the present invention. For example, the exclusion apparatus enables a local dry moving zone to be maintained on uneven work surfaces for purposes of thermal spraying, welding, welding with the addition of filler material in its various forms, i.e., wire, powder, ribbon and the like, mechanical or water-jet peening or for changing the residual stress state of the surface by heating and subsequent liquid quenching of the surface in a progressive pattern. It will also be appreciated that the applicator head may be moved along contoured surfaces which are non-uniform and/or irregular. For example, water may be excluded from inside or outside corners employing the applicator head hereof, as will be appreciated from the ensuing description. 
     Referring back to FIG. 1, the spherical bearing joint  22  between the raceway  18  mounting the fingers  16  and the housing  12  affords a self-aligning feature for the sealing tips of the fingers relative to the applicator head, i.e., the welding head  14 , and its supporting mechanism. The effective travel range capability of the housing is thus effectively increased without increasing the travel range of the fingers within their raceways. Instead of a spherical bearing joint, a bellows may interconnect the housing and the raceways for the fingers to provide this self-aligning feature. 
     Referring now to FIG. 2, springs acting on the fingers  16  may be employed in lieu of or in combination with the gas pressure to extend the fingers into contact or close proximity with the work surface. Thus, the springs  40  in FIG. 2 comprise individual helical coil springs  40  acting between the spherical bearing  22  and the interior end faces of the fingers  16 . The springs thus may be coil compression-type springs, or elements of a monolithic spring device, with each spring element located at and pushing against the fingers in the housing. 
     Also as illustrated in FIG. 2, an oscillator  42  may be incorporated in the pressurizing gas stream to cause the device housing and its fingers to vibrate with high-frequency, low-amplitude motion, enabling the fingertips to glide over the work surface with low friction as the head moves along the work surface. The gas supplied the housing is thus in a vibratory mode provided by the oscillator  42 . The finger vibration also ensures that the fingers do not stick in the housing raceways due to side loading which occurs during applicator head travel along the work surface. Thus, the vibrating fingers need only overcome the dynamic friction force to enable movement over the work surface rather than overcoming the static friction force which is typically higher and undesirable. It will be appreciated that other mechanisms may be employed to provide the vibratory motion through the fingers. For example, a secondary fluid flow can be used to actuate the vibratory motion of the fingers. Further, a motor and offset rotating weight may be used to generate the vibration. Still further, the vibrating mechanism may alternately be an electrically driven oscillator such as a piezoelectric crystal or an electromagnetic coil, thereby enabling fully independent and variable adjustment of the vibration frequency and/or amplitude. It may be built within the housing  12  or comprise a separate external component attached to the housing or its support. 
     The optional vibratory motion of the fingers can be adjusted to have the beneficial effect on the surface residual stresses of the workpiece by reducing their normally high tensile value or, depending on the application, reducing them sufficiently to generate a compressive surface residual stress. This benefit may be achieved progressively during welding or other processing since many applications require a multi-pass weld deposit or cleaning treatment. This is similar to the conventional practice for peening surfaces to improve their stresses. However, the vibratory motion of the fingers introduces lower impact forces in order to avoid the detrimental effects of heavy cold-working of the surface which is susceptible to stress corrosion cracking and is performed in the same process step as the welding. Moreover, employing the present mechanical method of stress improvement enables the width of the treated zone to extend well beyond the edge of the weld deposit and makes the needed stress improvement independent of the welding process parameter ranges. 
     An example of the application of the device to exclude water from a weld bead is illustrated in FIG.  3 . In FIG. 3, a pair of plates  50  and  52  are at right angles to one another and welded together by the welding torch  14  with the addition of weld material  30  forming the weld bead  54 . As illustrated, the housing  12  is applied at the juncture of the plates  50  and  52  and at an angle to both plates. It will be appreciated that the fingers  16  thus variably extend from the housing  12  to contact the contoured surfaces, i.e., the right angularly related surfaces of the plate  50  and  52 . With the fingers in contact with one another and with the surface, together with the flow of gas via gas supply line  24  to within the housing and outwardly through any gap between the fingers and the work surfaces, the water is excluded from the area within the fingers. Consequently, welding may proceed as the housing  12  is moved along the joint, for example, in a direction of the arrow  56 . 
     While the preferred embodiment of the housing is circular as illustrated in FIGS. 1-3, the housing may have an eccentric applicator head, e.g., torch location within the body to allow welding or other processing closer to the bulkheads or component edges without interference with the body perimeter. An eccentric applicator head location can also provide desired variations in the delay of water quenching of the heated area for a predetermined housing travel speed. Symmetrical but non-circular shapes can also be of benefit when welding in deeper grooves when the long dimension is oriented parallel to the direction of housing travel. Also, the portion of the housing containing the fingers may have a general shape at its outlet end which conforms to an inside or outside corner or other surface contour variations such as a weld groove. This configuration enables a reduction of the maximum travel range required by the sealing fingers and a reduction of the maximum extension of the fingers beyond the outlet end of the housing. Bending moments and the potential for finger flexing are also reduced with decreased finger extended length. 
     Referring to FIG. 4A, a combination of finger seals and a flexible porous seal mounted on the end of the fingers affords the advantages of each sealing method if used separately. For example, the fingers  16  in FIG. 4A provide greater axial compliance than a solid material substrate. Thus, a porous seal  60  is mounted on the tips of the fingers  16  for movement therewith. Because the fingers provide axial compliance, the porous seal  60  readily follows the surface contour variations as illustrated considerably more readily than in the absence of fingers. The seal  60  may be formed of a porous or non-porous material. For example, a lower heat-resistance non-metallic material such as silicon rubber may be employed as the seal  60  on the external surface of the fingers  16 . 
     Referring now to FIG. 4B, the seal afforded by the fingers  16  may be combined with an exterior flexible skirt or bellows  70 . This non-porous bellows  70  comprises a membrane surrounding the outside of the fingers in their extended positions and is sealed to the housing  12  at its upper end. This generates a tight sealing effect, forcing all of the excess process/purged gas to flow out at the fingertip to work surface interface. The membrane  70  is sufficiently loose about the fingers to allow the fingers to slide in and out of the housing  12  during use with minimal restriction on their motion. The membrane  70  also eliminates the need for a conforming seal located about the portion of the fingers within the housing. 
     In FIG. 4C, the flexible external skirt or bellows  80  is formed of a heavier material which affords additional sealing effect. In FIG. 4C, the heavier bellows or skirt  80  may also mount a flexible porous seal  82  at the end of this bellows or skirt  80  adjacent the work surface (see the right-hand illustration of FIG.  4 C). This combination with the fingers allows a more uniform distribution of the purged gas to escape through the porous seal positioned about the perimeter of the dry area inside the exclusion device. Use of the porous seal also increases the flow resistance of purged gas out of the device, hence improving its capacity to retard water entry. 
     In FIG. 4D, a pre-shaped flexible skirt  84  extends from the housing  12  and surrounds the fingers  16  in their extended positions. The skirt  84  is pre-shaped according to the contours of the work surface, in this instance, two right angularly related plates  86  and  88  being welded to one another. The lower end of skirt  84  may have a rib  89  for bearing against the surfaces  86  and  88 , the fingers lying in extended and partially extended positions depending upon the contours of the work surface. 
     Referring now to FIG. 5, the fingers  16  may be provided in a single continuous array of fingers about the housing  12 . In FIG. 5, however, an additional array of fingers  90  are provided about the fingers  16 . Multiple arrays of fingers closely spaced to one another provide increased water exclusion and sealing. The increased sealing effect is caused by the increased total gas pressure drop across the labyrinth of fingers as compared to that developed across only one row. To maintain finger alignment and position stability, each row or array of fingers is mounted in its own full complementary raceway, where each finger is mounted in a corresponding opening or hole in the housing. 
     The labyrinth effect of the multiple arrays of fingers illustrated in FIG. 5 is of increased benefit when the fingers  16  are individually mounted in tubes  100  as illustrated in FIG.  6 . By employing tubes  100 , the tubes space adjacent fingers an amount equal to twice the wall thickness of the tubes. By additional arrays of fingers, such as an array  90 , the flow resistance through the curtain of fingers surrounding the applicator head is significantly increased. The tubes  100  are thin-walled so that the adjacent surfaces of the fingers are in sufficient close proximity to one another such that the gas flow rate through the gaps can maintain the water boundary outside of the perimeter of the housing. This tubular mounting of the fingers enables a construction of a compact housing and improves alignment and reduces sliding friction of the fingers against their support members. As illustrated in FIG. 6, springs  102  are employed to extend the fingers  16  toward their extended positions. It will be appreciated, however, that the fingers may be biased and extended by gas pressure alone or a combination of gas pressure and springs. 
     Referring to FIGS. 7-12, a variety of non-circular finger shapes may be employed. For example, in FIG. 7, the fingers  104  may have rectangular cross-sectional configurations with the length dimension of each finger lying parallel to the length dimension of every other finger. This facilitates sliding movement of the housing  12  in the direction of the length dimension of the fingers along the work surface. The tips of fingers  104  may be rounded or have rollers as in FIG. 12, described below. 
     In FIG. 8, the transverse cross-sectional area of the fingers  110  may comprise rectangles with the length dimension corresponding to the radial direction of the housing. Because of the rectilinear configuration of the fingers, the circumferential registering sides of the fingers diverge from one another in a radial outward direction. Projections  112  may be provided on the adjoining outer side surfaces to maintain the fingers in divergent relationship to one another. 
     In FIG. 9, the fingers  116  may have a transverse cross-sectional shape having non-parallel sides along the radii of the housing. Thus, the radially inner sides  117  and fingers  116  he a width dimension less than the width dimension of fingers  116  along their radially outer sides  118 . A circular bellows-type arrangement of fingers  120  is illustrated in FIG.  10 . The fingers  120  thus have a transverse cross-sectional shape in the form of a shallow V, with the apex of the V on the radial inner side of the fingers. The outer edges  122  of each V-shaped finger  120  may slidably engage the outer edge of adjacent fingers. In FIG. 11, fingers  124  having a generally rectilinear transverse cross-section are employed in a staggered arrangement. That is, the long axis  126  of the rectangular cross-section of each finger is skewed relative to the radius  128  of the housing with the skew angles a being substantially constant about the entire periphery of the array of fingers. Referring to FIGS. 12-14, the fingers  129  may have a generally rectilinear transverse cross-sectional configuration, with each finger having a groove  130  formed along one side of the finger. A projection  132  is formed along the opposite side of the finger for engaging in the groove  130  of the adjacent finger  129 . The grooves and projections serve as limiting detents to the extension and retraction of adjacent fingers relative to one another. That is, the length of travel of one finger is limited by the length of travel of its projection in the groove  130  of the adjacent finger, coupled with the movement of the adjacent finger relative to other fingers. Thus, the opposite ends of groove  130  form stops  133  for the projection  132  of an adjacent finger. Additionally, each finger may have a standoff or projection  134  similarly as illustrated in FIG.  8 . It will be appreciated that the tongue-and-groove arrangement limits the stroke between adjacent fingers without limiting the total stroke of the finger assembly. 
     Additionally, the tips of the fingers may be provided with a rotatable ball, a fixed ball or a wheel to provide rolling capacity along the work surface, e.g., a wheel  138  pivoted to the finger  129  for rotation about an axis  140 . These features reduce the applied force required to advance the applicator parallel to the work surface during welding or other processing. If ball rollers are utilized, they are fitted in their sockets with controlled clearance to the tubular fingers and would tend to act gas check valves when in contact with the work surface to automatically provide the “floating” finger function described previously. Alternatively, the ball may be fixed to the ends of the fingers. Preferably, the ball would be formed of a material having a reduced coefficient of sliding friction relative to that of the coefficient of friction of the finger material. For example, a dense polished metal carbide or ceramic ball may be used. A ball  27  is illustrated in FIG. 1 at the tips  26  of the fingers  16 . 
     As illustrated in FIG. 12, wheel  138  is pivoted for rotation about the axis  140  normal to the axis of the fingers. The wheel thus projects from the finger for engagement with the work surface. The wheels, similarly as the balls, reduce the friction between the fingers and work surface thereby reducing the force necessary to advance the applicator along the processing path. In FIGS. 15-17, the fingers  142  are similar to the fingers illustrated in FIGS. 12-14, but without the rotatable wheels on the finger tips. The tips of the fingers  142  are radiussed to engage the work surface. Fingers  142  are illustrated in FIG. 18 in the arrangement of the underwater exclusion device  10 . 
     Referring back to FIG. 7, and for specific applications, the fingers may have a non-circular configuration such as the illustrated rectangular configuration. It will be appreciated that in the illustration of FIG. 7, the cross-sectional configuration of the fingers are uniform in size and the circular arrangement of the fingers  104  provides a circular outside diameter to the seal. The fingers  160  may also be uniform in size and arranged to form a circular interior diameter as illustrated in FIG.  19 . Also, fingers  170  of varying sizes, e.g., different rectilinear lengths in transverse cross-section and arranged parallel to one another, may be used to provide an array of fingers having concentric inner and outer diameters as illustrated in FIG.  20 . 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.