Abstract:
The preferred embodiment of a masking apparatus is adapted to mask the overspray of a coating applied by a spraying device. In another aspect of the present invention, a coated article or part includes a member with an inner surface and at least one opening. The inner surface is sprayed with the coating. In yet another aspect of the present invention, the apparatus includes a deformable masking cup which is operably located adjacent to the opening in the article.

Description:
BACKGROUND OF THE INVENTION 
     This invention is generally related to spraying of articles, and more specifically to an apparatus and method for masking the overspray from a spraying device. 
     The deposition of metal or ceramic coating to a part using a thermal spraying process is well known. Thermal spraying also known as flame spraying, involves the melting or at least heat softening of a heat fusible material such as a metal, and propelling the softened material in particulate form against a properly prepared surface which is to be coated. The heated particles strike the surface where they quench and bond to the surface. In one type of thermal spray gun, a powder of the coating material is fed axially through a low velocity combustion flame. Alternatively, a thermal spray gun can utilize a high intensity arc to heat inert gas in the gun so as to effect a high velocity gas stream or plasma into which the heat fusible material is injected. 
     In another type of conventional thermal spray gun, a wire is fed axially through an oxygen-acetylene (or other fuel gas) flame which melts the wire tip. An annular flow of compressed air atomizes the molten wire tip into small droplets or softened particles. The droplets are propelled against a surface by the compressed air. In still another type of traditional thermal spray gun, two wires converge to where an arc between the wire melts the tips to form molten material. The material is atomized and propelled by compressed air against the surface to be coated. All three types of thermal spray are employed to coat various components. 
     Aluminum alloys are currently being used in automotive components such as internal combustion engine blocks, heads, pistons, bucket tappets and brake rotors to reduce weight and meet governmental fuel economy standards. Other components such as pumps, compressors, transmissions, gear boxes, transfer boxes and axles are also made of aluminum alloys and used in automotive as well as construction, general industry, aerospace and agricultural applications. In addition to aluminum, other materials such as magnesium, zinc, composite metal and polymeric components may be used to reduce cost and improve performance. In most of such applications, there is a need to coat the surfaces of such components in order to withstand thermal-mechanical stresses imposed on them during use. 
     In one application, such as aluminum engine cylinder blocks, the use of a thermally sprayed coating into the bores of the engine block eliminates the need for inserting cast-iron liners to withstand the sliding contract of steel piston rings or the need to use high silicon content aluminum alloys that require special treatment to precipitate hard wear particles in the bores so as to withstand sliding contact. 
     When using the thermal spray process, it has been found necessary to mask certain areas of the parts in order to prevent application of the coating in specific adjacent areas. Reasons for masking parts include preventing the coating from entering apertures in the part, maintaining dimensions within a desired range, weight savings and the like. 
     Three different approaches have been proposed to achieve masking in certain areas. One conventional approach uses a masking tape such as described in U.S. Pat. No. 5,508,097 entitled “Plasma Spray Masking Tape” which issued to Hauser et al. on Apr. 16, 1996. Applying a masking tape to surfaces can be time consuming and labor intensive. Thus, the use of a masking tape in high volume thermal spray operations has not met with great success. 
     Another approach is to control the thermal spray with a spray attenuation member. Examples of the use of such spray attenuation members are shown in U.S. Pat. No. 5,439,714 entitled “Method for Thermal Spraying of an Inner Surface” which issued to Mori et al. on Aug. 8, 1995 and JP 11106891. However, it is difficult to control overspray at the ends of an inner surface of a part and undesirable non-uniform metal layers can be formed on the inner surface to be coated with this approach. 
     The third traditional approach is to use masking jigs. Masking jigs are commonly used because they can be positioned by automated equipment to prevent the thermal overspray into specific areas. An external surface masking jig is described in JP 8302459A2. Masking jigs for coating the inside surface of a part such as an engine block, are described in JP 6-287740 and JP 6-65711. Coating the inside surface of a component is more challenging than coating the external surface because of the geometric constraints of accessibility of the thermal spray device and jig into the interior surface area to be coated. 
     JP 406287740 utilizes a rigid tubular member as a masking jig member. The jig member appears to form a slight gap with the inner diameter of the cylinder bore of an engine block. The masking jig member also appears to move axially in the bore and synchronously with the thermal spray gun as the gun moves in the bore so that substantially all of the overspray is captured in the tubular cavity of the masking member. This unit is complex and requires the tubular jig member to have a slight gap with the surface to be coated to enable the jig to be moved in conjunction with the thermal spray unit. The masking jig must not have a gap that is too large with the inner surface to be coated so as to prevent any substantial overspray past the gap and into masked adjacent areas. However, it may not always be possible to use such a rigid device in cylinder block type applications where the bearing area width-to-bore spacing may limit the size and positioning of such a tubular jig member. Additionally, other geometric constraints at an end of the inner surface of the cylinder bore may prevent forming a slight gap with the inner diameter of the cylinder bore. 
     Furthermore, JP 406065711A appears to employ a two-part rigid masking jig member with a flange and a tubular portion which can be assembled and disassembled repeatedly for a masking jig. The outside diameter of the assembled masking member appears to have a flat flange that is larger than the inside diameter of the bore and the outside diameter of the cylinder. The masking jig member appears to be assembled within the external end faces of the area adjacent to the crank or bearing journals where the flange is pressed against the bottom end face of the cylinder bore. The thermal spray device is introduced into the bore and the flat flange deflects any overspray back into the cylinder bore. This masking jig most likely has a tendency to form a burr at the interface of the flange and the inner diameter of the bore which is not desirable. Furthermore, the need to assemble and disassemble the masking jig each time the jig is used requires complex and expensive assembly mechanisms. 
     All of the conventional masking jigs are rigid and non-conformable, and do not permit the use of a rigid masking jig in applications where the distance between bearing caps is less than the diameter of the bore. Thus, there is a need for a conformable jig member that prevents a substantial portion of the overspray from the thermal spray device from deflecting back into the inner surface of the member to be coated and which can deform or conform to fit between bearing cap spaces that are smaller than the bore size of the surface to be coated by the thermal spray. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the preferred embodiment of a masking apparatus is adapted to mask the overspray of a coating applied by a spraying device. In another aspect of the present invention, a coated article or part includes a member with an inner surface and at least one opening. The inner surface is sprayed with the coating. In yet another aspect of the present invention, the apparatus includes a deformable masking cup which is operably located adjacent to the opening in the article. The masking cup essentially prevents or minimizes overspray from exiting the article past the end of the opening. Another aspect of the present invention provides a method for masking the overspray of a coating. 
     Thus, the masking apparatus of the present invention is advantageous over conventional devices since the present invention provides a deformable masking cup that is both reusable (or single purpose in an alternate embodiment) to encapsulate the end of the article opening, and is simple and easy to operate. Another advantage of the present invention is that the masking cup is conformable in order to fit between a bearing cap spacing that is less than the bore size of a workpiece such as an engine block. These and other advantages and benefits of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic side view showing an engine block transfer line employing the preferred embodiment of a masking apparatus according to the present invention; 
     FIG. 2 is a fragmentary cross sectional view, taken along line  2 — 2  of FIG. 1, showing a thermal spray device employed with the preferred embodiment masking apparatus; 
     FIG. 3A is a fragmentary bottom view showing the engine block with a first alternate embodiment masking apparatus; 
     FIG. 3B is a fragmentary cross sectional view, taken along line  3 B— 3 B of FIG. 3A, showing the engine block with the first alternate embodiment masking apparatus; 
     FIG. 4A is a fragmentary bottom view showing the engine block with the preferred embodiment masking apparatus according to the present invention; 
     FIG. 4B is a fragmentary cross sectional view, taken along line  4 B— 4 B of FIG. 4A, showing the preferred embodiment masking apparatus; 
     FIG. 5 is a fragmentary cross sectional view, like that of FIG. 2 and 90° to FIG. 3B, showing the engine block with the first alternate embodiment masking apparatus; 
     FIG. 6A is a side perspective view showing a mask cup employed in the first alternate embodiment masking apparatus; 
     FIG. 6B is a side perspective view showing a mask cup employed in the preferred embodiment masking apparatus; 
     FIG. 7A is a fragmentary cross sectional view, similar to FIG. 3B, showing a second alternate embodiment masking apparatus according to the present invention; 
     FIG. 7B is an enlarged cross sectional view showing the end of the second alternate embodiment masking apparatus and engine block; and 
     FIG. 8 is a fragmentary cross sectional view showing a mask cup employed in a third alternate embodiment masking apparatus according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment of a masking apparatus or device  100  of the present invention is used in conjunction with an engine block, a thermal spray device  40 , and a masking apparatus  100 . This is shown in FIGS. 1,  2  and  4 B. The practice of the present invention will be described in terms of thermal spray coating of the internal cylinder wall portions of the engine block for a “V” configuration engine. This particular embodiment is selected for illustration purposes only, and it will be appreciated that the practice of the invention is readily adaptable to a number of other components, such as by way of non-limiting examples, pumps, compressors, transmissions, gear boxes, axles, and to other configurations of engine blocks such as V4, V5, V6, V8, V10 and V12 shapes and in-line cylinder designs, as well as other surfaces for automotive and non-automotive workpieces. 
     FIG. 1 shows an engine block transfer line  2 . Transfer line  2  is preferably a power roll conveyor, having multiple rollers automatically driven by one or more electric motors. The engine block is cast from aluminum, a composite or the like, with a plurality of cylinder bores  14  defined by interior surfaces or walls  16 , as an engine block casting  10   a . Engine block casting  10   a  is then placed on transfer line  2  which advances casting  10   a  to a machining station  4 . At station  4 , engine block casting  10   a  is machined to form a semi-finished engine block  10   b . In particular, bores  14  are machined so that they are oversized a few thousandths of an inch to create semi-finished machined bores  14   a . Each cylinder bore  14   a  has a top edge  18 , an interior surface  16  and a bottom edge  19 . Semi-finished engine block  10   b  is suitably cleaned and degreased at station  5 . 
     After cleaning and degreasing, engine block  10   b  is moved from station  5  to masking and spraying station  6  where thermal spray device  40  is inserted into engine block  10   b  as shown in FIG.  2 . To facilitate insertion of spray device  40 , engine block  10   b  is automatically tipped by a hydraulic cylinder  131  which upwardly pushes on one side so that bores  14   a  on one bank of block  10   b  are oriented substantially in a vertical plane, in the embodiment shown. 
     Thermal spray device  40  has a gun head, generally indicated at  42  that creates a molten particle streams  58 . Device  40  may be an electric wire arc spray gun as described in U.S. Pat. No. 5,468,295 entitled “Apparatus and Method for Thermal Spray Coating Interior Surfaces” which issued to Marantz et al. on Nov. 21, 1995, or alternatively device  40  may be a powdered metal spray device as described in U.S. Pat. No. 5,334,235 entitled “Thermal Spray Method for Coating Cylinder Bores for Internal Combustion Engines” which issued to Dorfman et al. on Aug. 2, 1994, both of which are incorporated by reference herein. 
     At least one gun head is mounted on support plate  38  which is movable by a hydraulic lift mechanism (not shown). The lift mechanism includes a stationary support bracket and a hydraulic piston assembly. The hydraulic piston assembly is used to automatically lift and lower thermal spray device  40  into bores  14   a  of engine block  10   b . Gun head  42  has a tubular extension portion extending toward a nozzle and a body portion. For example, in multiple cylinder applications such as a V8 semi-finished engine block  10   b , device  40  includes four tubular extensions, four body portions and four deflecting nozzles which are supported in a parallel spaced relationship on support plate  38  in order to coat the inner surfaces of four adjacent bores at the same time. Gun head  42  reciprocates and is automatically, axially driven into and out of the bore while rotating to fully coat the inside of the bore. 
     A compressed gas source (not shown) delivers compressed gas to the body portion of device  40 . The compressed gas is introduced into the nozzle to direct particle streams  58  and to form a layer of coating material  43  radially outwardly onto interior surface  16  of semi-finished machined bore  14   a . Atomized molten particle streams  58  are generated by each thermal spray device  40  and the gas from the nozzle particle streams  58  from the longitudinally elongated central axis of gun head  42  toward interior surface  16  of semi-finished machined bore  14   a . An electronic controller (not shown) controls various functions of thermal spray device  40  including the flow of gas in the nozzle. The controller also controls the movement of gun head  42 . 
     The operation of thermal spray gun  42  in only one cylinder bore  14   a  will now be described. The nozzle of gun head  42  is initially located at or near top edge  18  of engine block  10   b  prior to the introduction of the nozzle in bore  14   a . Thermal spray gun  42  is operated to direct molten particle streams  58  axially onto surface  16  of bore  14   a . Device  40  is lowered into bore  14   a  by the hydraulic lift and rotated in bore  14   a  until molten particle streams  58  form a layer of coating material  43  on internal surface  16  of cylinder bore  14   a . When the coating process is complete, the apparatus is turned off and lifted out of bore  14   a  by the hydraulic lift for applying a coating to the next cylinder bore  14   a  or the next bank of the engine block. 
     Various coating materials may be utilized to form the layer of material  43 , such as electrically conductive materials. Alternatively, composite materials may also be utilized to coat the bores. Where the engine block is formed of aluminum, for example, the coating material may be a mild steel which is melted and atomized to form a relatively inexpensive wear resistant layer  43  on internal surface  16  of bore  14   a.    
     Masking apparatus  100  of the present invention is used in conjunction with thermal spray coating device  40  to prevent or at least minimize overspray into a crankcase area  20  when a layer of material  43  is sprayed on internal surface  16  of the cylinder bores of any engine block. When coating material  43  is sprayed on the internal surface  16  in bore  14   a  near bottom edge  19 , it has been found necessary to mask crankcase portion  20  of the engine block. If the crankcase portion is not masked, a portion of the overspray of molten particle stream  58  from spray device  40  will deposit on machined bearing surfaces  22  or other high tolerance areas. This is not desirable since it could interfere with the subsequent function of the assembled engine. As shown in FIGS. 4A and 4B, engines are challenging since an axial distance  29  between bearing caps  25  is narrower than inside diameter  12  of bore  14   a.    
     The preferred embodiment of a masking apparatus  100  is shown in FIGS. 4A,  4 B and  6 B. Apparatus  100  preferably includes a deformable cup  62 , and a masking cup insertion device  80 . Masking apparatus  100  is designed to move cup  62  past and through distance  29  between bearing caps  25  and locate cup  62  near bottom edge  19  of bore  14   a  of engine block  10   b.    
     Referring to FIG. 6B, a cup  62  has a normally circular open edge  64 , with an outer diameter  165  that fits into annular relief  11  in engine block  10   b , and a closed bottom  63 . Because the outer diameter of cup  62  is larger than axial distance  29  between bearing caps  25 , masking cup insertion device  80  squeezes or deforms leading, open edge  64  and outer diameter  165  in order to permit the cup to move through axial distance  29  between bearing caps  25 . Thus, a pair of rigid fingers  98  press on outer diameter  165  of cup  62  as the cup passes an area adjacent to bearing caps  25  so as to deform cup  62  diametrically to less than distance  29 . Deformed cup  62  can thus pass through axial distance  29 . After cup  62  is moved past bearing caps  25 , the fluid pressure continues to advance a piston  94  in a piston cylinder cavity  93 ; whereafter the fluid pressure is removed, spring  87  retracts piston  94  and fingers  98  are released so cup  62  returns to its original frusto-conical shape, edge  64  returns to its original circular shape and outer diameter  165  fits into annular relief  11 . Annular relief or groove  11  is formed near bottom edge  19  in block  10   b  in crankcase area  20  to provide a positive location for cup  62 . Annular relief  11  has a diameter  13  that is larger than inner diameter  12  of bore  14   a.    
     As best shown in FIG. 5 for both embodiments, masking cup insertion device  80  includes a strut  82 , a lateral slide guide  84  mounted to top of strut  82 , and a cup holder  90 . A mechanism  351 , having a vertical actuator, is mounted to the floor of a manufacturing plant to provide vertical movement of strut  82 , or alternately, extends to a robotic arm, with vertical and horizontal jointed strut sections, or alternately at an offset angle. Lateral slide guide  84  is automatically moved by an electric motor or hydraulic cylinder (not shown) approximately ⅜ths of an inch (for a typical V8 engine) to align the masking cup with the appropriate cylinder bore since the cylinder bores in the right bank are offset from those in the left bank to accommodate a later installed cylinder connecting rod. Thus, slide  84  allows a fine motion shuttling of the cup between cylinder bores. Slide  84  and the attached strut mechanism assembly further provide a gross motion clearance to an oil pan rail  8  when device  80  is automatically advanced by way of the fluid powered (hydraulic or pneumatic) cylinder or electric motor insertion mechanism  351 , and moved into crankcase area  20 . Guide  84  further has a lateral channel with an undercut to capture a plate  86  therein and permit a slight increment of longitudinal movement relative to the engine block and alignment of cup  162  relative to each bore  14   a.    
     A cup holder  90  is mounted to plate  86 . Cup holder  90  includes a cup supporting cap  91  of a cylindrical housing  89  and the fingers  98  pivotally connected to housing  89 . The internal piston cylinder cavity  93  is disposed in housing  89 . Cup  62  is mounted on cap  91  of housing  89  by way of screws, if the cup is to be removable, or by rivets. A piston rod  99  projects through an aperture in the top wall of housing  89 . Piston rod  99  has tapered distal end  95  that operatively engages fingers  98 . Fingers  98  are pivotally attached to housing  89  by pivot pins. Each of fingers  98  include an elongated portion  96  and an enlarged portion  97  with a chamfered end. Thus, when piston  94  is advanced toward the engine block, end  95  of piston rod  99  engages and outwardly cams the chamfered end of each enlarged portion  97 , thereby inwardly rotating and holding in position each of fingers  98 . Top portion  96  of each finger  98  moves radially inwardly to push on opposite sides of cup  62 . Piston rod  99  has an internal cavity  88  into which a compression spring  87  is disposed. An opposite end of spring  87  is secured within a coaxial channel  92  of housing  89 . Spring  87  is compressed when the fluid advances piston  94 . Thereafter, when the fluid is allowed to exit out of cavity  93  by a valve or port, spring  87  biases piston  94  away from cap  91  of housing  89  so that piston  94  is longitudinally retracted. Thus, as now illustrated in FIG. 4B, retraction of piston  94  allows outward rotation of fingers  98  so cup  62  can return to its normal circular open end view shape. 
     Cup  62  is made from a resilient, compressible or compliable material such as thin sheet metal including aluminum or steel, a polymer such as silicone or a Santoprene® synthetic elastomer from Monsanto Co., a composite material such as a reinforced polymer or a composite aluminum foil laminated to a fiberglass cloth or another polymer. Alternatively, any material that returns to its original shape after being deformed or squeezed by fingers  98  and can withstand the temperature of the droplets from thermal spray device  40  is believed suitable for practicing the invention. 
     Functionally, fingers  98  are actuated to rotate inwardly and squeeze the opposite sides of cup  62 ; this action causes cup  62  to deform from a circular configuration to the somewhat oval configuration thereby permitting open end  64  to fit between bearing caps  25  of the engine block. Thereafter, fingers  98  release cup  62  allowing it to return to its original shape. Cup  62  is then further longitudinally advanced into relief  11  in order to seal on the surface around bore  14   a . Then, when spray device  40  (see FIG. 2) is operated to coat interior walls  16  of semi-finished block  10   b , any coating overspray is essentially prevented from being deposited onto the bearing surfaces in crankcase area  20  by cup  62 . 
     A first alternate embodiment of the present invention is shown in FIGS. 3A,  3 B and  6 A wherein the first alternate masking apparatus is designated by the reference number  200 . The reference numbers will be the same where the elements used in the alternate embodiment are essentially the same as in the preferred embodiment. Deformable cup  162  has a closed, somewhat round end  163  and an oval or elliptical open, wider end  164  in its natural state. Oval open end  164  has a major axis  165  and a minor axis  166 . Minor axis  166  is in alignment with the longitudinal axis of crankshaft. Minor axis  166  is less than axial distance  29  between bearing caps  25 . Furthermore, major axis  165  is larger than an inner diameter  12  of cylinder bore  14   a . During insertion after clearing the bearing caps, oval open end  164  of cup  162  is deformed by fingers  98  to a circular end view shape, thereby permitting cup  162  to fit in and generally seal against annular relief  11  by masking cup insertion device  80 . In all other aspects masking device  200  operates as in the preferred embodiment. 
     A second alternate embodiment of the present invention masking apparatus  300  is shown in FIGS. 7A and 7B. The second alternate embodiment cup  262  is designed with a fluid passage  267  formed around the rim of an open end  263 . A fluid channel or passage  267  is defined as a mostly circular or C-shaped cross-sectional shape by an inwardly turned flange with a gap  268  formed between the wall of cup  262  and edge of passageway  267 . The top edge of passage  267  which corresponds with open end  263  fits into annular relief  11  of engine block  10   b . Fluid  261  is introduced into passageway  267  through a port which is connected by a flexible line or hose  269  to a fluid source including a pump  273  and a tank  275 . Fluid  261  is preferably a liquid but alternately any suitable fluid such as air or a detergent solution may also be used. Gap  268  is nearly closed when fluid  261  is not under pressure. However, gap  268  increases in size when pressurized fluid  261  is introduced into passageway  267 . Pressurized fluid  261  flows through gap  268  and along inner walls  70  of cup  262  and out of an aperture in bottom end  63 . This prevents the thermal spray droplets from adhering to walls  70  of cup  262 . It is also envisioned that the constant gap  268  may be replaced by spaced apart holes in the otherwise closed passage  267 . The fluid is drained through an exit tube adjacent the bottom of the cup. In all other aspects the second alternate embodiment operates the same as in the preferred embodiment. 
     A third alternate embodiment of the present invention masking apparatus  400  is shown in FIG. 8 where cup  362  is the same as any of the other embodiments disclosed herein except that cup  362  has a coating  370  on its inner surface to reduce the adherence of the thermal spray droplets. Coating  370  also facilitates cleaning of inner walls  70 . For example, coating  370  can be a Teflon® material from E.I. DuPont de Nemours and Co. or a mold release such as that disclosed in U.S. Pat. No. 6,291,026 entitled “Method for Forming a Mold-Release Coating” which issued to Hanson et al. on Sep. 18, 2001, and is incorporated by reference herein. Similarly, if cup  362  is made of a polymer such as silicone or a thermoplastic elastomer, cup  362  may be coated with a thin layer of aluminum or lined with an aluminum insert. A spring steel cup  362  with a polymeric lining can be used. In all other aspects, the third alternate embodiment operates the same as in the preferred embodiment. Cups  62 ,  162 ,  262  and  362  may be reusable with periodic cleaning or single purpose wherein the cup is removed and discarded after a number of uses. 
     While the invention has been described with reference to many embodiments, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims. For example, the apparatus and method may also be used in other applications and other materials and part configurations can be substituted for those disclosed. Any automotive, machine tool, aerospace, appliance or other workpiece part having holes or even flat surfaces that must be free of paint or any other coating can employ the present invention masking apparatus. Furthermore, other coating processes, whether thermally sprayed or not, can be used with the masking apparatus of the present invention; for example, the present invention can be used with robotic paint spraying guns. Moreover, it is envisioned that four or more fingers, multiple compressing members of other shapes, and even fingers that linearly rather than rotatably move can be employed. In another alternate arrangement, other mechanical linkages, cams and cables, or electromagnetic driven members can be used to deform the masking cup. It is intended by the following claims to cover these and any other departures from the disclosed embodiments which fall within the true spirit of the present invention.