Abstract:
A reusable pull plug for masking part openings in parts to be coated or otherwise worked upon. The pull plug has particular utility in masking irregular surface portions about the part opening including, without limitation threaded, chamfered, stepped and spot faced surfaces. The pull plug is comprised of a deformable, segmented body including plug, transition and tail body segments. A flange and void volume, or “dimple,” are formed in one plug body end adjacent the plug segment. The pull plug is pulled into the part opening by the tail segment and the plug segment forms a frictional fit with the deformable body tightly sealing the part opening. The flange covers the first thread in threaded part openings and further covers chamfered, stepped and spot faced surfaces protecting those surfaces from contact by the coating or other materials. The void volume facilitates deformation of the flange and plug segment permitting the flange to conform to the surface about the part opening and permitting the pull plug to be withdrawn through the part opening in the same direction as inserted thereby avoiding damage to the applied coating material. The novel design reduces stresses on the pull plug and enables the plug to be reused through repeated coating or operation cycles.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention is related generally to masking apparatus and, more specifically, to masking apparatus for covering openings in parts during coating and other operations.  
         BACKGROUND OF THE INVENTION  
         [0002]    Many types of manufactured parts, such as parts used in fabrication, aerospace and final assemblies must be coated with various materials and substances to adapt those parts for their intended end use. Such coatings are typically selected to impart desired characteristics to the coated part. For example, the coating may impart corrosion resistance to the part or may be selected to impart a selected surface finish or cosmetic appearance to the part.  
           [0003]    As is known, many different types of materials can be applied to the parts during coating operations. These materials include, for example, nylons, polycarbonates, metals and other known materials.  
           [0004]    There are many coating technologies available and the specific coating procedure can be selected based on the specific application. Modern coating operations include, for example, coating by powder coating, anodizing and plating. In all of these coating operations, the external surface portions of the part are completely exposed to the coating substance. For example, in powder coating operations the part to be coated is typically electrostatically charged and heated and then exposed to a fine particulate spray or fluidized bed of oppositely-charged coating particles. The particles are attracted to the surface to be coated and are melted, forming a coating over the part. In anodizing and plating operations, the part to be coated is charged and then dipped into a fluid bath containing the coating material. The coating material is attracted to the part and is deposited onto the exposed surface portions of the part.  
           [0005]    In many applications it is necessary to mask surface portions of the part to be coated in order to prevent the coating material from coming into contact with such surface portions. The surface portions to be masked can include external surface portions as well as surface portions internal to the part. By way of further explanation, parts to be coated are three-dimensional objects which frequently consist of both external and internal surface portions. The external surface portions of these parts often include one or more part openings. During a coating operation, coating materials can migrate through these part openings and come into contact with the internal surface portions of the part. Depending on the specific application for the part, contact between the coating and the internal surface portions of the part can be undesirable and can severely damage the part.  
           [0006]    Complicating the need to mask part openings is the fact that many part openings are threaded with the threads being provided for mating engagement with a threaded fastener or another part. These threads about the part opening pose a particular problem with respect to limiting the migration of coating material into the interior portions of the part. More specifically, the protruding threads interfere with the operator&#39;s ability to form a complete seal over the part opening blocking the flow of coating material into the part. If unsealed, the threads provide a helical passageway directing coating materials to the interior of the part.  
           [0007]    Yet another complication involving threaded openings relates to the fact that the first thread of the threaded opening is typically chamfered and is not flat or smooth. The chamfered edge further interferes with the ability to form a complete seal over the opening. Failure to fully mask the first thread of the chamfered opening may permit coating materials to contact and build up on the threads damaging the threads and preventing engagement with the fastener or other part following completing of the coating or other work process. Unwanted application of coating to the threads can result in costly re-working expenses or loss of the part.  
           [0008]    Parts to be coated may also include cast or machined “countersunk” portions about the part opening. Such countersunk portions could include, for example, a tapered annular portion having a frusto-conical geometry located about the annulus of a cylindrically-shaped part opening. The different surface geometries about the part opening present an obstacle to forming a complete mask over such surfaces.  
           [0009]    The need to mask or otherwise protect the surface of a part opening is not limited to coating operations. For example, in certain manufacturing processes it may be necessary to weld components or otherwise work on the part at locations near the part opening. Care must be taken to avoid contamination of the part and part opening because debris from the welding or work process can become deposited on the part opening near the weldment. As will be readily understood by those of skill in the art, serious contamination of a threaded part opening tapped directly into the part could potentially result in loss of the entire part.  
           [0010]    One illustrative manufacturing process which requires avoidance of work-related contamination of the part opening involves “weld nuts” which are commonly used in industry to secure parts one to the other. A weld nut is secured to the plate or part by welding with the weld nut in coaxial alignment with a hole or opening in the plate. A bolt or other threaded part may then be secured to the plate or part in threaded engagement with the weld nut. During manufacturing of the product, flux and metal contaminants from welding operations near the weld nut can undesirably become attached to the weld nut in or near the weld nut threaded opening. Any such contamination may require costly cleaning or re-working of the threaded opening in the weld nut or may even require removal of the weld nut. Avoidance of such contamination necessitates use of a masking device to protect the weld nut opening from contact by the contaminants. Further, the weld nut opening must be protected from contact with coating materials if the part including the weld nut is to be, for example, powder coated following manufacture.  
           [0011]    Yet a further factor complicating coating and manufacturing processes is the fact that there is an almost infinite variation in the types of part openings that may be encountered. The size, shape and configuration of part openings can vary significantly from part to part. Each different type of part opening potentially represents a unique set of problems with respect to masking of the opening.  
           [0012]    Many products have been developed to mask, or close, part openings in an ongoing effort to prevent coating materials, contaminants and other materials from coming into contact with the internal surface portions of parts and part openings. For example, various plugs are commercially available to mask openings in the part to be coated. Such plugs are available in many sizes and shapes and include configurations ranging from gently tapered annular plug bodies to plug bodies having pronounced conical designs. For instance, some plugs are provided with a tapered outer body. At least a portion of the tapered plug body has an outside diameter which is larger than the inside diameter of the opening. The tapered plug is held firmly in place by the frictional fit between the plug outer body and the walls forming the part opening.  
           [0013]    “Pull plugs” are one specific type of known masking device used to mask part openings. Conventional pull plugs have a solid, continuous body consisting of a plug portion, a tapered transition portion and a tail portion. Such pull plugs are typically made of silicone rubber and have a durometer of about 55+/−5 on the Shore A scale. The pull plug is selected so that the plug portion will form a friction fit with the part opening. The use of higher durometer material requires that the plug be sized to a specific opening size, again limiting use of each pull plug to a narrow range of part opening sizes.  
           [0014]    One advantage of pull plugs is that such plugs may be removed in the same direction in which they are inserted thereby avoiding damage to the applied coating. Following coating, the tail is grasped and the plug is pulled through the opening in the same direction as it was inserted.  
           [0015]    Conventional plugs, including pull plugs, are available in many types of materials including, for example, cork, silicone and EPDM rubber. Conventional plugs are typically configured to the specific shape and size of the opening to be masked. Because thousands of masking devices may be required for a large production run, the operator is required to maintain a large inventory of plugs. As can be readily understood, any requirement to maintain an unnecessarily large inventory of plugs imposes added costs on the operator which could otherwise be avoided.  
           [0016]    A leading supplier of plugs, pull plugs and other masking products is Engineered Products and Services, Inc. of Menominee Falls, Wis. (EPSI). EPSI is the assignee of this patent application.  
           [0017]    While conventional plugs are very effective in masking typical part openings, such plugs are less than fully effective in masking specialized part openings such as threaded openings, countersunk openings and other openings having more unique configurations. For example, conventional plugs, including pull plugs, may form an incomplete seal with the threads surrounding the opening. A less than complete seal may be formed because the more rigid material typically used to make these plugs does not fully seal the helical passageway formed by the threads.  
           [0018]    By way of further example, conventional plugs, including pull plugs, lack structure to shield the chamfered edge of the threaded opening from contact with coating material or contaminants. The plugs which do include such structure have separate disadvantages. For example, “washer plugs” are commonly used to mask the threads of threaded part openings from contact with the coating material. Such washer plugs are made of a rigid silicone rubber material having a durometer of about 55+/−5 on the Shore A scale and have a flange which is provided to cover the first thread. The higher durometer material used in the washer flanges limits the capability of the plug to conform to the irregular surfaces about the part opening. A further disadvantage of washer plugs involves the fact that such plugs must be removed from the part opening in a direction opposite to the direction in which the plug was inserted. Removal of the washer plug in the direction opposite to the direction of insertion can result in an irregular tearing of the applied coating material around the location of the plug damaging the coated part.  
           [0019]    As a further example, conventional plugs, including pull plugs, are also ineffective in masking countersunk portions about the part opening, such as the tapered annular portions located about the annulus of a part opening. Such conventional plugs are not effective in masking the countersunk portion because the plug body is sized to approximate the opening and is not sized sufficiently to mask the larger countersunk region surrounding the opening.  
           [0020]    It would be significant improvement in the art to provide an improved plug which would be useful for masking one or more openings in a part to be coated or otherwise involved in a work process, which would conform to the irregular surface portions about the part opening, which would protect such part opening surface portions from unwanted contact by coatings and other materials, which would be removable in the same direction as inserted, which would prevent passage of liquids and other materials through the part opening and into contact with internal surface portions of the part, which would be simple and easy to use and which would be reusable.  
         OBJECTS OF THE INVENTION  
         [0021]    It is an object of this invention to provide an improved pull plug which overcomes problems and shortcomings of the prior art.  
           [0022]    Another object of this invention is to provide an improved pull plug which masks a part opening, particularly to prevent coatings and other materials from contacting the part opening.  
           [0023]    An additional object of this invention if to provide an improved pull plug which fully masks irregular surfaces about a part opening including, without limitation, chamfered, stepped, spot faced and threaded surfaces.  
           [0024]    Yet another object is to provide an improved pull plug which is simple and easy to use.  
           [0025]    Still another object of this invention is to provide an improved pull plug that can be removed in the same direction in which it was inserted.  
           [0026]    A further object of this invention is to provide an improved pull plug that can mask a range of part opening sizes thereby permitting the operator to maintain a smaller inventory of masking devices.  
           [0027]    An additional object is to provide an improved pull plug which is reusable.  
           [0028]    How these and other objects are accomplished will be apparent from the descriptions of this invention which follow.  
         SUMMARY OF THE INVENTION  
         [0029]    The invention is reusable pull plug useful for masking an opening in a part thereby preventing coating or other materials from coming into contact with the part opening or with interior portions of the part. In general, the pull plug has a body with first and second ends, a body axis and an axial length between the first and second ends. Preferably, the plug body is made of an elastomeric material having a durometer of between about 30-45 on the Shore A scale. A more preferred plug body durometer is between 35-45 on the Shore A scale. Most preferably, the pull plug body is a unitary elastomeric element.  
           [0030]    The preferred plug body is “segmented” in that it consists of defined body portions. These body portions or segments preferably comprise cylindrically-shaped plug and tail segments and a tapered transition segment positioned between the plug and tail segments. A flange is provided in the body first end adjacent the plug segment. Preferably, the flange, plug, transition and tail segments are coaxially aligned with the body axis and are concentric to one another.  
           [0031]    A void volume or small indentation in the form of a “dimple” is provided in the plug body first end. The void volume is provided to permit radially-inward deformation of the flange and plug body segment.  
           [0032]    The pull plug is seated in the part opening so that the plug segment is in frictional engagement with the part opening wall or threads. The plug segment and flange deform to conform to the shape of the part opening. Such deformation is the result of the low-durometer material comprising the plug body and the radially-inward movement of the flange and plug segment permitted by the void volume. The flange covers the edge of the part opening preventing coating or other materials from coming into contact with the first thread or with the part opening. The plug segment masks the part opening and prevents coatings or other material from moving through the opening.  
           [0033]    The pull plug disclosed herein masks a broad range of part openings. The plug structure permits the plug to deform to cover irregular surfaces. Such irregular surfaces can include chamfered, stepped, spot faced and threaded surfaces which are difficult to mask with conventional plugs. The pull plug is removable in the same direction as inserted into the part opening thereby minimizing any potential damage to the coating applied to the part. The pull plug is simple to use and is reusable over many operational cycles. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0034]    [0034]FIG. 1 is a perspective view of an exemplary pull plug according to the invention taken from a position slightly above the plug.  
         [0035]    [0035]FIG. 2 is a perspective view of an exemplary pull plug according to the invention taken from a position slightly below the plug.  
         [0036]    [0036]FIG. 3 is a top view of an exemplary pull plug according to the invention.  
         [0037]    [0037]FIG. 4 is a bottom view of an exemplary pull plug according to the invention.  
         [0038]    [0038]FIG. 5 is a side elevation of an exemplary pull plug according to the invention.  
         [0039]    [0039]FIG. 6 is a cross-sectional view of an exemplary pull plug according to the invention take along section line  6 - 6  of FIG. 5.  
         [0040]    [0040]FIG. 6A is an enlarged partial cross-sectional view of the first end and plug segment of an exemplary pull plug according to the invention taken along section  6 A- 6 A of FIG. 6.  
         [0041]    [0041]FIG. 7 is a side elevation view of an exemplary pull plug according to the invention shown partially inserted into a weld nut secured to a plate.  
         [0042]    [0042]FIG. 7A is a cross-sectional view of the partially-inserted exemplary pull plug of FIG. 7 taken along section line  7 A- 7 A of FIG. 7.  
         [0043]    [0043]FIG. 8 is a top view of the partially-inserted exemplary pull plug of FIG. 7.  
         [0044]    [0044]FIG. 9 is a perspective view of the partially-inserted exemplary pull plug of FIG. 7 taken from a position slightly above the plug.  
         [0045]    [0045]FIG. 10 is a side elevation view of the exemplary pull plug of FIGS.  7 - 9  shown fully inserted into the weld nut secured to the plate.  
         [0046]    [0046]FIG. 10A is an enlarged partial side elevation view of the fully-inserted exemplary plug of FIG. 10 taken along section  10 A- 10 A of FIG. 10.  
         [0047]    [0047]FIG. 11 is a perspective view of the fully-inserted exemplary pull plug of FIG. 10 taken from a position slightly above the plug.  
         [0048]    [0048]FIG. 12 is a cross-sectional view of the exemplary pull plug of FIG. 7A but positioned further within the weld nut to show a manner in which the pull plug deforms to conform to the part opening. 
     
    
     DETAILED DESCRIPTION  
       [0049]    The reusable pull plug will now be described in detail with respect to the drawings, examples and information provided below. The structure of an exemplary pull plug according to the invention will first be described followed by an explanation of how the exemplary plug structure facilitates masking of an illustrative part opening. The preferred embodiments described herein are not intended to be exhaustive or to limit the invention to the precise form disclosed.  
         [0050]    Referring first to FIGS.  1 - 5 , those figures illustrate the main components of exemplary pull plug  10 . Pull plug  10  includes a body  11 , first and second ends  13 ,  15  and a body axis  17  defining an axial length  19  between the first and second ends  13 ,  15 . The preferred plug body  11  is “segmented” (i.e., divided into portions) and includes a plug segment  21 , a transition segment  23  and a tail segment  25 . A flange  27  is provided at plug body first end  13 . In the example shown, segments  21 ,  23  and  25  and flange  27  are coaxially aligned with axis  17  and are concentric to one another. Plug body  11  includes an outer surface  29  along the entire axial length  19  of the plug body  11 , a first end surface  31  along the first end  13  and a second end surface  33  along the plug body second end  15 .  
         [0051]    Referring further to FIGS.  1 - 5  and  6 A, flange  27  is formed between first end  13  and spaced apart flange edge surface  35  and has an axial length  32  between end  13  and edge surface  35 . Flange  27  edge surface  35  may include an annular radius portion  36  at the junction of the flange  27  and the plug segment  21 . The radius portion  36  facilitates removal of the plug  10  from the part opening by reducing shear force on flange  27  during removal of plug  10  from the part opening thereby extending the useful life of pull plug  10 .  
         [0052]    Flange  27  has a cross-sectional shape and area (collectively ref no.  37 ) at first end  13  in the section  38  transverse to axis  17  and bounded by outer surface  29 . As shown in FIGS.  1 - 3  and  8 - 9 , the preferred shape/area  37  is circular and preferred circular flange  27  has a diameter  40 . Preferred flange  27  is coaxial with axis  17 .  
         [0053]    Plug body first end  13  surface  31  extends across flange  27  and defines a void volume  39  along first end  13 . Preferably, void volume  39  is in communication with first end  13  and is coaxial with body axis  17  and concentric to preferred circular flange  27 . The most highly preferred void volume  39  could be characterized as a “dimple” because such preferred void volume  39  has the appearance of a small indentation in the first end  13  and flange  27 . The void volume  39 , or dimple, facilitates radially-inward displacement and deformation of plug body segment  21  and flange  27  to fully mask the desired part surfaces and to facilitate removal of the plug  10  from the part thereby extending the service life of the plug  10 .  
         [0054]    [0054]FIGS. 1, 3,  6 ,  6 A, 7 A- 9  and  11 - 12  illustrate the most highly preferred form of void volume  39  which is in the form of a hemispherical dimple. As shown in FIGS. 3, 6A and  8 , void volume  39  has a circular cross-sectional shape  41  in section  38  and the circular shape has a diameter  43 . As well shown in FIG. 6A, void volume  39  has an axial length  42  between section  38  at first end  13  and surface  31 . The axial length  42  of the most highly preferred hemispherical dimple  39  is a radius. The void volume axial length  42  is preferably between about 0.7-2.0 times the length of flange axial length  32 .  
         [0055]    Referring next to FIGS.  5 - 6  and  7 - 7 A, plug segment  21  has an axial length  45  between plug segment first end  47  (at the junction with flange  27 ) and plug segment second end  49  (at the junction with transition segment  23 ). Plug segment  21  is preferably coaxial with body axis  17 . Plug segment  21  has a first cross-sectional shape and area (collectively ref no.  51 ) at a section  53  transverse to axis  17  at the plug segment first end  47  and a cross-sectional shape and area (collectively ref no.  55 ) at a section  57  also transverse to the axis  17  taken at the plug segment second end  49 . As shown in FIGS.  1 - 2  and  4 , the preferred plug segment cross-sectional shapes/areas  51 ,  55  are circular. (In FIG. 4 the lead lines for reference numbers  51  and  55  appear to point to the same surface due solely to the fact that both spaced apart circular cross-sectional shapes  51 ,  55  taken in respective sections  53 ,  57  lie in the same two dimensional plane presented by the drawing.) Referring to FIGS.  1 - 2 ,  4 - 6  the cross-sectional area in sections  53 ,  57  bounded by outer surface  29  is preferably the same. Preferably, each plug segment  21  section taken transverse to axis  17  between ends  47 ,  49  has the same cross-sectional shape and area providing a plug segment  21  with the cylindrical configuration well shown in FIGS.  1 - 2 ,  5 - 6 ,  7 - 7 A,  9 - 10  and  11 . The cylindrical plug segment  21  has a diameter  59 ,  61  in each cross section  53 ,  57  and the preferred plug segment  21  bounds a volume as well shown particularly in FIGS.  1 - 2  and  9 .  
         [0056]    In the preferred embodiment illustrated, flange  27  protrudes radially outward from plug body  11  and the flange  27  is coaxial with body axis  17 . The flange shape/area  37  defined by section  38  at first end  13  is greater than the shape/area  51 ,  55  of the plug segment  21  defined by sections  53 ,  57 . Further, the void volume diameter  43  is about 0.20-0.60 the length of the flange diameter  40 . Most preferably, the diameter  43  is 0.25 the length of the flange diameter  40 .  
         [0057]    Referring now to FIGS.  1 - 2 ,  5 - 6 ,  7 ,  7 A and  9 - 10 , transition segment  23  is coaxial with body axis  17  and has an axial length  63  between transition segment first end  65  (at the junction with plug segment  23 ) and transition segment second end  67  (at the junction with tail segment  25 ). Transition segment  23  has a first cross-sectional shape and area (collectively ref. no.  69 ) at section  57  at transition segment first end  65 . Transition segment  23  has a further cross-sectional shape and area (collectively ref no.  71 ) at the section  73  transverse to axis  17  taken at the transition segment  23  second end  67 . As shown in FIGS.  1 - 2  and  4 , the preferred transition segment  23  cross-sectional shapes/areas  69 ,  71  are each circular. (In FIG. 4 the lead line for reference number  69  appears to point to the same surfaces as reference numbers  51 ,  55  due again to the two dimensional nature of the drawing.)  
         [0058]    As is apparent from FIGS.  1 - 2 ,  4 - 6  and  10 , the cross-sectional shape/area  69  bounded by outer surface  29  at section  57  is greater than the cross-sectional shape/area  71  bounded by outer surface  29  at section  73 . As a result, the transition segment  23  has a frusto-conical configuration as is well shown in FIGS.  1 - 2 ,  5 - 6 ,  7 ,  7 A and  10 . The frusto-conical or otherwise tapered geometry of the transition segment  23  facilitates removal of the pull plug and reduces stresses between the plug  21  and tail  25  segments which would be present if there were no transition segment  23 , that is if the plug  21  and tail  25  segments had a stepped configuration.  
         [0059]    The tail segment  25  is well shown in FIGS.  1 - 2 ,  4 ,  5 - 6 ,  7 ,  7 A,  9 ,  10  and  11 .  
         [0060]    Tail segment  25  is preferably coaxial with body axis  17  and is provided with an axial length  75  between tail segment first end  77  (at the junction with transition segment  23 ) and plug body second end  15 . It is preferred, but not required, that the plug and tail segment have identical axial lengths  45 ,  75 .  
         [0061]    Tail segment  25  has a first cross-sectional shape and area (collectively ref no.  79 ) at section  73  located at the tail segment first end  77 . Tail segment  25  has a further cross-sectional shape and area (collectively ref no.  81 ) at a section  83  transverse to axis  17  taken at the plug body second end  15 . As shown in FIGS.  1 - 2  and  4 , the preferred tail segment  23  cross-sectional shapes/areas  79 ,  81  are each circular. (As previously noted, FIG. 4 is a two-dimensional drawing and, consequently, the lead lines for reference numbers  79  and  81  appear to point to the same surface—which is not the case as surfaces  79  and  81  are in spaced apart sections  73  and  83  as shown in FIG. 5.) FIGS.  1 - 2 ,  4 - 6  and  10 - 11  show that the cross-sectional shape/area  79 ,  81  bounded by outer surface  29  at sections  73 ,  83  is the same. Further, each section along tail segment  25  transverse to axis  17  between ends  77  and  15  preferably has the same circular shape and area providing a tail segment  25  with the preferred cylindrical shape well shown, particularly in FIGS.  1 - 2 ,  4 - 6 ,  7 ,  7 A,  9 - 10  and  11 - 12 . As is also shown in these figures, the volume bounded by tail segment  25  is preferably less than the volume bounded by the plug segment  21 .  
         [0062]    The tail segment  25  is provided as an element which may be grasped and pulled so that the pull plug  10  can be pulled into the part opening and later removed from the part opening (following the coating or other operation) in the same direction in which the plug  10  was inserted into the part opening. The tail segment  25  typically has a volume less than the volume of the part opening which aids in inserting the plug into the opening. The tail segment  25  further facilitates insertion and removal of the plug  10  into a part opening because the low durometer materials used in the manufacture of plug body  11  will deform when compressed making it difficult to push the plug  10  through the part opening. Removal of the plug  10  in the same direction as inserted advantageously avoids damage to the coating applied over the plug  10  and the coated part. In fact, removal of the plug  10  in the same direction as insertion causes a clean break from the coating with a fine line at the edge of the coating with little or no coating build up and a very clean and appealing aesthetic appearance.  
         [0063]    The plug body  11 , including the flange  27  and plug  21 , transition  23  and tail segments  25 , is preferably a unitary member and is made of a molded elastomeric material. The material used in the manufacture of plug body  11  is selected so that the material has a durometer of between about 30-45 on a Shore A scale. Most preferably the material forming plug body 11 has a durometer of between about 35-45 on the Shore A scale. Materials suitable for use in manufacturing plug body  11  having a durometer within the required range include ethylene propylene (EPDM), butadiene acrylonitrile (NBR), styrene butadiene (SBR), fluorinated hydrocarbons (such as Viton™), polychloroprene (such as Neoprene™) and conductive silicone. Use of such materials to manufacture articles is well known to those of skill in the art.  
         [0064]    The durometers required by the inventive plug body are outside the range of conventional pull plugs which typically have durometers of about 55+/−5 on the Shore A scale. Use of plug body materials with durometers lower than those of conventional plugs permits the outer surface  29  of the plug body  11  of the present invention to conform more closely to the part opening to be masked better shielding the part opening from contact by coatings or other materials. This advantageous result is not possible with conventional masking devices. Further, use of lower durometer materials, in combination with the void volume  39 , permits the plug segment  23  and flange  27  to be displaced radially inward further facilitating conformation of the plug body  11  to the part opening. Close conformation of the plug body  11  to the part opening is of particular importance when seeking to completely mask irregular surfaces (i.e., threads, countersunk portions about the opening, and the like) around the part opening.  
         [0065]    It has been observed that the flange can deform at angles of between about 90-180° to axis  17  permitting the flange to lie across and mask a countersunk opening formed around the part opening. Deformation of flange  27  at an angle of about 180° to axis  17  essentially allows flange  27  to fold fully out of the way of the part during removal of the plug  10  from the part opening facilitating removal of the plug  10  and minimizing stresses on the plug thereby extending the plug service life.  
         [0066]    Variation is possible with respect to the geometry of the plug body  11 . The plug segment  21  may have any configuration based on the specific part opening to be masked. The plug body  11  could include plug and transition segments  21 ,  23  which are other than cylindrical in configuration. For instance, the plug segment  21  need not have a cylindrical shape as shown in FIGS.  1 - 11  and could, instead, comprise a tapered shape in which the first end  47  in section  53  has a larger cross-sectional area than the second end  49  in section  57 . The plug and transition segments  21 ,  23  need not have the same configuration. For example, one or both of the plug and tail segments  21 ,  25  could have a rectangular configuration. While the transition segment  23  must have a tapered configuration joining the plug and tail segments  21 ,  25 , the transition segment  25  is not limited to the precise configuration presented in the drawings and need not have the preferred frusto-conical geometry illustrated in the drawings. Indeed, a separate transition segment  23  is not necessarily required. For example, a tail segment  25  with a tapered geometry could abut plug segment second end  49  and extend therefrom. The transition segment would, in effect, comprise an integral portion of the tail segment  25 .  
         [0067]    Void volume  39  may have a geometry other than the most highly preferred hemispherical, dimpled shape shown in the exemplary plug  10  although the void volume must permit radially-inward displacement of the plug segment  21  and flange  29  to permit the pull plug  10  to conform to the opening and to be removed from the opening. For example, the void volume  39  could have triangular, square, hexagonal or other suitable geometries. The hemispherical geometry shown in FIGS. 1, 3,  6 ,  6 A,  9 ,  11  and  12  is most highly preferred because liquids and coatings are more easily discharged from the smooth surface  31  defining the void volume  39  minimizing the potential of contact between the interior portions of the part and coating in the void volume  39 .  
         [0068]    Referring next to FIGS.  7 - 12 , the exemplary pull plug  10  will now be described in connection with masking of an illustrative part opening  85  in a weld nut  87 . Weld nut  87  has a top surface  89  and side surfaces  91  formed in a hexagonal pattern. Weld nut  87  part opening  85  is defined by annular opening wall  93 . Opening wall  93  includes threads  95  formed therein. As shown in FIGS. 7A and 12, a first thread  97  is formed in the opening annular inner edge surface  99 . Edge  99  is provided with a chamfer, or bevel, which is typically at an angle of about 45° to the wall  93  thereby exposing the first thread  97  along top surface  89 . It is difficult to fully mask edge  99  about opening  85  because it is difficult to conform a masking device to the chamfered edge  99  profile and uniquely irregular surface provided by the first thread  97 .  
         [0069]    Weld nut  87  is attached by a weld  109  to a surface of which plate  101  is exemplary. Opening  93  is in coaxial alignment with opening  103  formed in plate  101 . A threaded fastener, such as a bolt (not shown) may be coupled to the plate  101  by threaded engagement with threads  95  of weld nut  87 .  
         [0070]    Plug  10  is provided to mask part opening  85  so that the wall  93 , threads  95 , first thread  97  and chamfered edge  99  are covered and shielded from contact by coating material applied to plate  101  and weld nut  87 . Alternatively, plug  10  could be used to cover opening  85  to prevent weld flux or other contaminants being deposited along wall  93 , threads  95 , first thread  97  or chamfered edge  99 .  
         [0071]    It should be emphasized that plug  10  is not limited to use in applications such as those illustrated in FIGS.  7 - 12 . Plug  10  is useful to mask any part opening including part openings which are threaded, non-threaded and those part openings which have irregular surfaces. By way of further example, plug  10  may be used with parts having interior surfaces in communication with the part opening. In such applications, plug  10  masks the part opening (such as opening  85 ) to prevent coating or other material from flowing along the opening (or any passageway formed by threads along the wall defining the part opening) and into contact with the interior surfaces of the part. Plug  10  is useful to mask chamfered, stepped, spot faced and threaded surfaces surrounding many different types of part openings.  
         [0072]    Referring then to FIGS.  7 - 9 , tail segment  25  is first inserted partially into opening  85  in the direction of arrow  105 . Plug  10  is sized so that the plug segment  21  is oversized relative to the opening  85  thereby providing a frictional fit between plug outer surface  29  and threads  95  or wall  93  firmly holding plug  10  in place in opening  85 . In the examples shown, plug  10  is to be used to mask a part opening having an annular wall  93  and threads  95  defining the opening  85 . Plug  10  is selected such that the plug section  21  diameter (i.e., diameters  59  and/or  61 ) is equal to or greater than the diameter  107  of the annular opening  85 .  
         [0073]    Referring next to FIGS.  10 - 12 , the plug tail  25  is grasped and pulled further in the direction of arrow  105  until the plug segment  21  is firmly seated against threads  95  or against threads  95  and wall  93 . As shown in FIG. 12, void volume  39  permits substantially uniform partial displacement of plug segment  21  and flange  27  in a radially-inward direction to permit plug  10  to be seated along wall  93  and threads  95 . Also as shown in FIG. 12, the low durometer material forming plug body  11  permits the body  11  (particularly outer surface  29 ) to conform to the profile of threaded inner wall  93  sealing the helical passageway formed by threads  95  thereby preventing coating material from moving along the threads  95 .  
         [0074]    Masking of the part opening  85  is completed by the co-action of the flange  27  and void volume  39 . As shown best in FIGS. 10A and 12, flange  27  edge surface  35  contacts first thread  97  and chamfered edge  99  along top surface  89 . The flange  27  then deforms at an angle of between about 90-180° to axis  17  depending on the extent of movement of pull plug  10  through opening  85  in the direction of arrow  105 . For example and as shown in FIG. 10, if it is desired to mask weld nut top surface  89  to the full extent of the flange shape  37  and area (i.e., the flange  27  footprint), then the pull plug will be pulled through the opening  85  until flange edge surface  35  meets weld nut top surface  89 . In this arrangement shown in FIG. 10A, flange  27  is not deformed and is at an angle of 90° to axis  17 .  
         [0075]    By way of further example and as shown in FIG. 12, if it is desired to mask only the first thread  97 , chamfered edge  99  and opening  85  (and not weld nut top surface  89 ) then the plug  10  is pulled further through opening  85  further in the direction of arrow  105  to the position shown in FIG. 12. Flange  27  will deform at an angle of between about 100-180° to axis  17  with edge surface  35  conforming to first thread  97  and chamfered edge  99  masking those surfaces. The deformation is facilitated by void volume  39  which, as described and shown in FIG. 12, permits displacement of the plug segment in a radial-inward direction. In FIG. 12 the flange is shown deformed at an angle of roughly 135° to axis  17 . Coating or other material can reach those portions of weld nut top surface  89  which are not in contact with flange edge surface  35 . The deformation of flange  27  as shown in FIG. 12 also permits the flange  27  to conform to and mask countersunk portions (not shown) around a part opening.  
         [0076]    Following completion of the coating or other operation the plug  10  is removed by grasping tail segment  25  and by pulling plug  10  through opening  93  again in the direction of arrow  105 . The flange  27  deforms at an angle of about 180° to axis  17  to facilitate full passage of the plug  10  through the opening  85 . Movement of the plug  10  fully through opening  85  is further facilitated by the optional radius portion  36  which decreases shear against the flange  27  as the plug  10  is pulled through opening  85 .  
         [0077]    An important advantage of the inventive plug  10  versus conventional washer plugs is the capability of the pull plug  10  to be removed through part opening  85  in the direction of arrow  105 . Removal of the plug  10  in the same direction as insertion of the plug  10  results in a clean break between the plug  10  and the applied coating improving the appearance of the coated part and reducing defects in the coating.  
       EXAMPLES AND DATA  
     Example 1  
       [0078]    An important advantage of the inventive plug  10  is that a single pull plug  10  can be used to mask a wide range of part openings each having different opening sizes. As a result, an operator need not maintain as great an inventory of plugs for the operator&#39;s coating or other operation. Since thousands of plugs in different sizes may be needed to operate a large scale coating operation, this can result in significant savings in inventory and material for the operator. This advantageous result is possible because of the combination of (1) the void volume  39 ; and (2) the novel plug body  11  made of the highly deformable material having a low durometer value of 35-45 on the Shore A scale. The combination of these elements permits one plug  10  to deform to fit many smaller part openings (such as opening  85 ).  
         [0079]    A comparison of prior art pull plugs and pull plugs of the invention was conducted to determine the range of part openings which could be fully masked with a single size plug. The conventional and inventive plugs each had plug, transition and tail segments. The diameter of the plug segments was 0.217 inches. The conventional plug was not provided with a dimple or flange and was made of silicone rubber having a durometer of 55+/−5.  
         [0080]    The conventional and inventive plugs were inserted in a range of English course threaded template openings to determine their overall fit and application range. The table that follows shows the versatility of the inventive plug over the conventional plug.  
                                     TABLE 1                           Comparison of Range of Part Openings       Capable of Being Masked by One Plug Size                        Plug               Durometer   Void   Segment   Size Range of Part       Pull Plug   (Shore A   Volume   Diameter   Openings Masked       Type   Scale)   Diameter   (Inches)   (Inches)               Conventional   55 +/− 5   None-   0.217   ¼-20 threaded hole               No void       (approximately .205 to               volume       .215″ diameter holes)       Invention   40 +/− 5   .0827   0.217   ¼-20, ¼-28 and                       M6 × 1.00 holes                       (approximately                       .190-.215″                       diameter holes)                  
 
         [0081]    The data shows that the plug of the invention is capable of fully masking a broader range of part openings than the conventional plug.  
       Example 2  
       [0082]    A further important advantage of the inventive plug  10  is that a single pull plug  10  can be repeatedly reused during the course of many coating cycles. The ability to reuse the plug permits an operator to maintain a smaller inventory of plugs for the operator&#39;s coating or other operation. Again, this can result in significant savings in inventory and material for the operator.  
         [0083]    Control and inventive pull plugs having the geometry of the plugs shown in FIGS.  1 - 12  were manufactured. The plugs had identical flanges  27  and plug  21 , transition  23  and tail  25  segments. Both plugs were made of virgin silicone. The plugs differed only in that the control plug lacked a void volume  39  and had a durometer of 55+/−5 on the Shore A scale while the inventive plug included a hemispherical void volume  39  as shown in FIGS.  1 - 12  and had a durometer of 40+/−5 on the Shore A scale.  
         [0084]    The pull plugs were inserted into a ¼-20 threaded opening in a template and were pulled completely through the template in successive cycles until failure of the plug flange was observed. The control plug without the void volume tore along the flange after 3-5 cycles. The inventive plug remained intact through an average of 50 cycles. The data show that the void volume and lower durometer material contribute to an extended service life.  
         [0085]    It is believed that the invention has been described in such detail as to enable those skilled in the art to understand the same and it will be appreciated that variations may be made without departing from the spirit and scope of the invention.