GB2152854A - Coating portions of articles - Google Patents

Abstract

In order to protect the sidewalls of cylindrical ceramic spark plug resistors (11) from overspray of hot metal which is flame-sprayed onto the ends of the resistors (11) to provide electrical contacts, the resistors are inserted into openings (12) in a mask (10) made of resilient, elastomeric material with a hardness of 10-50, Shore A Durometer e.g. silicone rubber. Figure 7 shows apparatus for loading the mask with resistors in which a rotatable shaft (23) receives the resistors within cavities (24) from which the resistors are loaded into the mark using press pins (46). The openings (12) in the mask (10) are loaded a row at a time, with the mask being advanced after each loading operation. <IMAGE>

Description

SPECIFICATION Method and apparatus for coating portions of articles BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for preventing overspray during application of a coating to selected surfacesoflongitudinally-extending objects, to a mask useful in the method, and to apparatus useful for inserting the objects into the mask.

2. Description of the PriorArt There have been numerous suggestions of methods and apparatus for selectively coating objects and/or preventing oversprayon surfaces thereof. For example, U.S. Patent No.3,635,730 discloses a method for automatic tape masking of articles; the articles are conveyed through a coating station by a belt and are magnetically lifted into engagement with the mask.

U.S. Patent No.3,082,115 discloses a method and apparatusforapplying a coating to selected middle portions of objects while leaving the ends thereof uncoated. Vacuum is used to remove the objects from a reservoir and to depositthem in recesses of a supporting member. The objects are then clamped between resilient shields of a second support, and the exposed portions are sprayed.

U.S. patent No.2,739,911 discloses a method for depositing an emissive coating on cathode supports.

The supports are inserted into openings in the floor of a resilient container so that the ends thereof protrude above the floor; the openings, which can be cylindrical, are sized to receive the support snugly. A liquid suspension of the coating material is poured into the container and allowed to stand until it settles out and is deposited on the ends ofthe support by gravity. The tight fit between the supports and the containerfloor prevents the application of coating where it is not desired.

U.S. Patent No.3,647,533 describes a method for sheet-masking large scale array substrates. Bonding lumps reformed in a desired pattern by thin film vacuum deposition through a mechanical mask.

SUMMARY OF THE INVENTION The instant invention is based upon the discovery of a methodforpreventing oversprayduring application of a coating to selected surfaces of longitudinally- extending objects. A mask useful in practicing the method has also been discovered, as has apparatus for inserting the objects into the mask.In a preferred embodiment, for preventing oversprayontothe sidewalls of an object which is substantially a right circular cylinder having a height of X, opposed ends, and a diameter of Y, the method involves the use of a mask of a resilient, elastomeric material having a plurality of openings extending therethrough be tweenthemajorsurfaceesthereof; the method comprises the steps of: a) aligning the object with an opening of the mask; b) inserting the object into the opening with which it is aligned, whereby the object is frictionally engaged by the sidewall ofthe opening and the ends ofthe objectdonotextend beyondthemajorsurfacesofthe mask; and c) appplying the coating to the opposed ends of the object.

A mask useful in practicing the method described above can comprise a body of a resilient elastomer having a hardness offrom lotto 50, Shore A Durometer, and having substantially parallel and planar upper and lower major surfaces. An object to be masked can be substantially a right circular cylinder; the mask, in this case, has a plurality of substantially right circular cylindrical openings extending through its body, between the major surfaces thereof; each opening is oriented substantially per pendicularto the major surfaces. With respect to such a cylindrical object having a longitudinal dimension X and a diameter of Y, each opening, preferably, has a longitudinal dimension within the range of 1.026X to 1.1 56X, and most desirably, from 1.040to 1.124X.

The diameter of the opening, in this case, is preferably within the range of from 0.867Yto 0.986Y, most desirably, from 0.894Yto 0.953Y. It is preferred that the material of the elastomeric body ofthe mask have a hardness of from 20 to 30, Shore A Durometer.

The apparatus in accordance with the instant invention for inserting an object into an opening of the above-described mask can comprise, in combination: a) a feederforthe object; b) a receiving and loading means including an escapement shaft having an internal cavity which extends transversely thereth rough for receiving the object; c) means operable to rotatethe escapement shaft between a first position and a second position; d) means fortransferring the objectfrom thefeeder to the internal cavity ofthe escapement shaft when in the first position; e) means for advancing the mask to a plurality of successive positions in each ofwhich one ofthe openings therethrough is aligned with the internal cavity of the escapement shaft when the shaft is in the second position; and f) means operable when the escapement shaft is in the second position for transferring an objectfrom the internal cavity thereof into an aligned opening ofthe mask.

BRIEF DESCRIPTION OF THE DRAWINGS Figure lisa perspective view of a preferred mask according to the invention; an object to be masked is shown suspended in longitudinal alignment with an opening ofthe mask.

Figure 2 is a fragmentary sectional view taken along the line 2-2 of Figure 1.

Figure 3 is a fragmentary sectional view similar to Figure 2, but showing objects whithin the openings of the mask.

Figure 4 is a schematic, front view in perspective of a preferred embodiment of apparatus according to the invention for inserting objects into a mask.

Figure 5 is an enlarged, transverse sectional view of a portion ofthe apparatus of Figure 4taken substantially along the line 5-5 of Figure 4.

Figure 6 is an enlarged, perspective view, partially broken awayto show internal details of construction, of a portion of the apparatus shown in Figures 4 and 5.

Figure7 is aviewsimilarto Figure6 butshowing a partoftheapparatus in a different rotational position.

Figure 8 is an enlarged view, partly in section, taken along the line 8-8 of Figure 5.

DETAILED DESCRIPTION OF THE INVENTION Referring now in more detail to the drawings, and in particularto Figures 1 through 3, a preferred embodi ment of a mask according to the invention is indicated generally at 10. A longitudinally-extending object 11 is shown positioned for insertion in one of a plurality of openings 12 which extend through the mask 10;the object 11 is substantially a right circular cylindrical, ceramic resistor useful in spark plugs or similar ignition devices (not shown) for suppressing radio frequency interference. The openings 12, in the particular embodiment, are generally right circular cylindrical in shape.The mask 10, made of a conventional, resilient silicone rubberelastomer having a hardness of about 25, Shore A Durometer, is rectangular in shape, having substantially planar and parallel upper and lower major surfaces 13 and 14, respectively, and opposed ends 15 and 16. The openings 12, which extend through the mask 10 between the major surfaces 13 and 14 substantially perpendicularly thereto (best seen in Figure 2), are arranged in twenty equally spaced rows of three. The rows are parallel to one another, the axis ofthe center one ofthe openings 12 of each row approximatelythrough the longitudinal center-line of the mask 10.

The mask 10 ofthe instant invention is especially advantageousto preventoversprayduringtheflame- spraying of metal to form electrical contacts upon the ends of the longitudinally-extending ceramic resistors 11, Figure 1. The effectiveness ofthe mask 10 is attributableto such factors as the size of the openings 12 in relation to the size ofthe objects 11, and the hardness of the elastomeric material ofthe mask.It is preferred thatthe elastomeric material comprising the body ofthe mask 10 have a hardness offrom 1 Oto 50, Shore A Durometer, and that each opening 12 have a longitudinal dimension offrom 1 .026Xto 1.1 56X, and a diameter offrom 0.867Yto 0.986Y, whhere Xis the length ofthe object 11 and Y is tha diameterthereof.

Most desirably, the hardness of the material is from 20 to 30, ShoreA Durometer, and each opening has a longitudinal dimension of from 1.040Xto 1.124Xand a diameteroffrom 0.984Yto 0.953Y.

Itwill be appreciated thatthe dimensionsforthe above-described openings 12 of the mask 10 will be, in all embodiments thereof, slightly larger in longitudinal dimensions and slightly smaller in diameterthan the corresponding dimensions ofthe objects 11 being masked. Accordingly, each object 11 to be masked can be inserted into an aligned mask opening 12 so that the objectfrictionally engages the resilientsidewalls ofthe opening along its longitudinal dimension and the opposed ends ofthe object 11 do not extend beyond the major surfaces 13 and 14ofthe mask.

Therefore, in use,the opposed ends of an object 11 will be recessed from the surfaces ofthe mask but exposed to the coating being applied, and, accordingly, the side of the object 11 will be protected from overspray. In addition, it has beenfoundthatthe elastomeric material of which the mask is made aids in the prevention of such coating overspray by not only maintaining frictional engagement with the sidewall oftheobject, butalso byoverlappingslightlythe opposed ends thereof (best shown in Figure 3), thereby enabling a more uniform pattern of deposition of the coating on the ends of the object. The latter feature ofthe mask has been found to be particularly advantageous in the production of ceramic resistors for forming uniform, circular, electric contacts on the ends thereof by flame-spraying of metal thereonto.

The mask 10 can comprise a body of any suitable resilient. elastomeric material, so long as the hardness ofthe material is from 10 to 50, Shore A Durometer.

Whether or not any given resilient, elastomeric material is suitable can depend on the temperature at which the coating material is sprayed on the ends of bodies that have been inserted into the mask. For example, the temperature of a flame-sprayed nickel alloy can be as high as several thousand degrees Fahrenheit, while Wood's metal can be flame-sprayed at a temperature of approximately 160OF. and alumi num alloys can besprayedatintermediatetempera- tures. Silicone rubber is capable of withstanding flame sprayed nickel alloys, without deterioration, and, therefore, is a preferred mask material; its resiliency and hardness are also stable, and molten metal is comparatively non-adherentto its surfaces.Urethane rubbers are deteriorated slightly in ordinary flame spraying of nickel alloys, particularly in localized areas where relatively large masses ofthe molten alloy strike the mask, butwhen kinks in the wire feed enter the metallizing gun, but are operable. Neoprene, polysulfide, butyl and urethane rubbers can all be used for masking objects during the spraying of coatings which are at sufficiently lowtemperatures that the masks are not deteriorated, as can such elastomeric rubbers as isoprenes, styrene-butadienes, nitrile butadienes, ethylene-propylenes, chlorosulfonated polyethylenes,fluoroelastomers, and polyacrylics.

A mask 10 according to the invention can be produced by any conventional procedure, for example, by injection-molding or, particularly in the case of silicone rubber, by forming from a conventional liquid resin/hardener system in a suitable plastic mold.

Referring nowto Figures 4 and 5, preferred mask loading apparatus in accordance with the present invention is indicated generally at 17 (Figure 4). The apparatus 17 comprises a mask loading assembly 18 and a mask carrying and indexing assembly 19, both supported on a common base 20.

The mask loading assembly 18 comprises a plurality of conventional, vibratoryfeed hoppers 21 (only one being shown in Figures 4 and 5), a plurality offeed tubes 22, and an escapement shaft 23. The tubes 22 convey objects 11 (not shown in Figures 4 and 5) from the hoppers 21 into internal cavities 24 (see Figures 5 through 7) in the shaft 23. There arethree cavities 24 (see Figures 6 and 7), extending transversely through the shaft 23, one in the center, one a given distance above and anotherthe given distance below; the cavities 24 are generally right circular cylindrical in shape, and are slightly large in diameterthan the objects 11. As shown in Figure 5, the escapement shaft 23 is supported between a lower pedestal 25 and an overhanging bracket 26.The shaft 23 is mounted for rotation between two positions, one for receiving objects 11 delivered from the hoppers 21 through the tubes 22 andthe otherfor loading objects 11 into the openings 12 ofthe mask 10; the former position is shown in Figure6 whilethe latter is shown in Figure 7.

A rankarm 27 (Figure is fixedly secured to the upper end ofthe shaft 23 and pivotally connected by a link28to one of a longitudinally movable push rod 29.

The push rod 29 is slidably mounted in a pair of spaced pillars 30 and 31 affixed to the base 20. The push rod 29 is urged to the right toward a retracted position by a compression spring 32 and moved to the left to an extended position by a cam follower33 operably associated with an appropriately shaped rotatable plate cam 34. The cam 34 is fixedly mounted on a vertical drive shaft 35 suitablyjournalled as by spaced bearings (not shown) for rotation in a support structure 36 affixed to the base 20. The drive shaft 35 is driven bya pulley 37 fixed to its upper end. As shown in Figure 4, the pulley 37 is driven by a belt 38, a drive pulley 39 driven by a gear reduction box 40 powered bya motor41.

As shown in Figure 6, the apparatus 17 includes a body 43 sutiably positioned and attached to the overhanging bracket 26. The body 43 has an inlet chamber44 in fluid communication with branch ducts 45. The center lines of the branch ducts 45 are aligned with the center lines ofthe cavities 24. When the shaft 23 is in the object receiving position (see Figure 6), the branch ducts 45 are aligned with the openings 24 in the shaft 23. When the shaft 23 is in the object loading position (see Figure 7), press pins 46 are aligned with the cavities 24. The press pins 46 (see, also, Figure 5) are supported by pin guides 47 extending from the overhanging bracket 26. Specifically, the press pins 46 are fixedly mounted in a head 48 which slides on the guides 47 and is connected to a longitudinally movable loading rod 49.The rod 49, which is slidably mounted in the pillars30 and 31, is urged to the rightto a retracted position by a compression spring 50, and is driven to the left toward an extended position by a cam follower 51 operably associated with a cam 52.

The cam 52 is fixedly mounted on the drive shaft 35 for rotation therewith. The cams 52 and 34 are operableto align the cavities 24 with the feed tubes 22 (Figure 6), to apply vacuum (through a line, not illustrated) to the inlet chamber 44, the branch ducts 45, and the cavities 24to seat objects 11 on the cavities 24, to rotate the escapement shaft 23 to the position shown in Figure 7 where the cavities 24 are aligned with the press pins 46 and with the mask openings 12, and finally to drivethe press pins 46 into the cavities 24, forcing the objects 11 into the mask openings 12.

As best shown in Figures 4 and 5, the mask carrying and indexing assembly 19 comprises a longitudinally movable, elongate carrier 53. The carrier 53 is L-shaped in cross-section, having a vertical leg 54 and a horizontal leg 55. The lower edge of the vertical leg 54 has an integral, horizontally projecting lip flange 56. An elongate flange bracket 57 is removably attached by flat head screws 58 to the upper edge of the leg 54. The mask 10 is clamped between the flange 56 and the bracket 57, adjacent the leg 54. Tracks 59 and 59' extend along opposite sides ofthe horizontal leg 55 of the carrier 53. Thefacing edges of the tracks 59 and 59' are V-shaped (see Fiqure 5), supporting the carrier 53 between a plurality of opposed pairs of spaced rollers 60 and 60'. A depending counterweight 61 urgesthe carrier 53 from left to right in Figure 4.The counterweight 61 is attached to an end of the carrier 53 by a cable 62 which extends around an idler pulley 63 that is journalled on the free end of an arm 64 carried by the base 20.

An elongate index bar 65 (see Figure 5) is attached to the bottom ofthe horizontal leg 55 ofthe carrier 53. As best shown in Figure 8, the index bar 65,which cooperates with a translatable pawl mechanism 66, is an elongate tooth memberwhich has spaced teeth 67 and 67' on opposite sides.

Referring specificallyto Figure 8, the pawl mechanism 66 com prises a plate 68, movably transversely of the index bar 65, as indicated by the arrow. The plate 68 carries two aligned, spaced pawls 69 and 69', each pivotally mounted by a cap screw 70, the pawl 69 on one side ofthe bar 65 and the pawl 69' on the other side. The pawl 69 is biased by a hairspring 71 against a stop pin 72 and the pawl 69' is biased by a torsion spring 73 against a stop pin 72'. The pawls 69 and 69' are thus mounted so that they can be rotated away from the teeth 67 and 67' for a purpose which is subsequently explained.

The plate 68 is slidably mounted relative to the base 20. The mounting includes spaced hinge members 74 and 74' (see Figure 8), which comprises pins 75 and 75', bushings 76 and 76', and brackets 77 and 77' which are fixedly mounted relative to the base 20. The pins 75 and 75' are attached to channels 78 and 78' having webs 79 and 79' and sidewalls between which the plate 68 is slidably supported. There is an elongate opening 80 through the plate 68 to enable sliding movementthereofwithout interference bythe lower pedestal 25.

Referring now to Figure 5, the plate 68 is supported by a roller 81 either in an upper position (shown in full lines) orin a lower position (shown in dotted lines).

The roller81 isjournalledto an arm 82 of a member83 which is keyed to a shaft 84. Referring to Figure 4,the shaft 84 journalled between brackets 85 and 85'.

Arms 86 and 86' (FigureS) supportthe member83,the former when the roller81 is in the upper position and the latter when the roller 81 is in the lower position.

The member 83 is rotated between the upper and lower positions by rods 87 and 87' (Figure 4), and attached operating knobs 88 and 88'. A handle 68' facilitates positioning of the plate 68.

The plate 68 is movable relative to the index bar 65 between the position shown in solid lines in Figure 8 and the position shown in broken lines. To this end, a slot 89 of the plate 68 receives a head 90 of a slide rod 91. The rod 91 is slidable relative to the pillars 30 and 31 (see Figure 5); it is urged toward a retracted position by a compression spring 92 and driven to an extended position by the action of a cam follower 93 panda cam 94 mounted on the drive shaft 35 for rotation therewith.

In operation of the apparatus 17, the objects 11 (Figures 1 and 3) are charged to the hoppers 21 (Figure 4), from which they are fed through the tubes 22 and into the cavities 24 ofthe escapement shaft 23, which is then in the object receiving position shown in Figure 6.The shaft 23 isthen rotated to the loading position shown in Figure 7, and the pins 46 are driven to the left to force the objects 11 into the mask openings 12 which previously have been aligned therewith. The pins 46 arethen retracted. The plate 68 is next moved to the other of its two positions, for example from the solid line position of Figure 8 to the broken line position.This movement withdraws either the pawl 69 orthe pawl 69' from engagement with one oftheteeth 67 or 67' and brings the other of the pawls into position for engagement. The weight 61 (Figure 4) then causes the index bar76 to move to the right (Figure 8) until another oftheteeth 67 and 67' engages the other ofthe pawls. The relationships between the mask 10 and the teeth 67 and 67' are such that this movement ofthe index bar 65 advances the mask 10 to bring another row of openings 12 into alignment with the openings 24 of the shaft 23 to receive additional objects 11. This cycle is then repeated until the mask 10 isfully loaded with objects 11, at which time a limit switch 95 (Figure 4) on the arm 64 interrupts the operation.When a given mask 10 is fully loaded with objects 11, it is removed from the apparatus 17 and replaced by an empty mask 10. The carrier 53 is then returned manually to the starting position, this movement causing the pawls 69 and 69' (Figure 8) to rotate awayfrom the teeth 67 and 67'. A scale 96 and a pointer97 on the carrier 53 and the base 20, respectively, indicate the position on the apparatus.

Itwill be appreciated that a specific embodiment of the instant invention has been described, but that various changes and modifications are possible from the specific disclosure hereofwithout departing from the spirit and scope ofthe invention as defined in the following claims. For example, a pluralityofthe masks 10 can be mounted on a wheel (not illustrated) which is advanced periodicaliy in rotation to bring successive rows ofthe openings 12 into alignment with the openings 24 in the shaft 23. Loaded masks 10 can then be removed from the wheel forflamespraying, and replaced by empty masks 10 to be loaded. In addition, the shaft23 can bemountedforrotationabouta horizontal axis between an object-receiving position in which the openings 24 extend vertically and a mask loading position in which the openings24extend horizontally. Such apparatus and the usethereofto load masks 10 constitute the best mode presently contemplated by the inventor.

Claims (14)

1. A method for preventing oversprayduring application of a coating on a right circuiar cylindrical object having opposed ends, a longitudinal dimension of X and a diameter of Y, which method comprisesthe steps of aligning the objectwith an opening in a mask of a resilient, elastomeric material having a hardness offrom lotto 50, Shore A Durometerand having a plurality of right circular cylindrical openings extend- ing thereth rough between major surfaces thereof, each opening having a longitudinal dimension be tween said majorsurfaces of from 1.026X to .156X and a diameteroffrom 0.867to 0.986Y,said mask being sufficiently resistant to destruction bythe coating to enable its repeated use as a mask, inserting the object into the opening with which it is aligned, whereby the object is frictionally engaged by the sidewall ofthe opening and the opposed ends ofthe object do not extend beyond the majorsurfaces ofthe mask, and applying the coating upon the exposed ends ofthe object.

2. A mask for preventing overspray while spraying a coating on a right circular cylindrical object having a longitudinal dimension of X and diameter of Y, said mask comprising a body of resilient, elastomeric material having a hardness of from 10 to 50, Shore A Durometer, and having a plurality of right circular cylindrical openings extending therethrough between major surfaces thereof, each opening having a longitudinal dimension between the major surfaces offrom 1.026X to 1 .1 56X and a diameter of from 0.867Yto 0.986Y, said mask being sufficiently resistant to destruction bythe coating to enable its repeated use as a mask.

3. The mask claimed in claim 2, wherein each opening has a longitudinal dimension offrom 1.040X to 1.1 24X and a diameter of from O.894Yto 0.983Y.

4. The mask claimed in claim 3, wherein the elastomeric material has a hardness offrom 20 to 30, ShoreA Durometer.

5. The maskclaimed in claim 4, wherein the elastomer is selected from the group consisting of silicone, neoprene, polysulfide, butyl and urethane rubbers.

6. Apparatusforinserting an object into a mask having a plurality of openings therethrough for receiving the object, said apparatus comprising, in combination, afeederforthe object, a receiving and loading mechanism operable to receive the object in an internal cavity which extendstherethrough, means for transferring the object from said feederto the internal cavityofsaid receiving and loading mechanism, means for advancing the mask, said mask advancing means being operable so that successive ones of the openings therethrough are sequentially positioned in a predetermined location for receiving the object, means for moving said receiving and loading mechanism between a first postion in which the cavity thereof is aligned to receive an object from said feeder and a second position in which the cavity thereof is aligned with an opening ofthe mask which is positioned in an object-receiving location, and means for transferring an object from the cavity of said receiving and loading mechanism into an opening of the mask when the cavity of said receiving and loading mechanism and the opening are aligned and the opening is in the object-receiving location.

7. The appparatus claimed in claim 6 wherin said transferring means is a flexible tube.

8. The apparatus claimed in claim 7, wherein said means for advancing the mask comprises an indexing mechanism, and said indexing mechanism includes a carrier and a manner which is releasably engageable with said carrier.

9. The apparatus of claim 7, which additionally includes a tooth bar and pawl mechanism, said bar and said pawl mechanism being operatively associated with one another and with the apparatus to control longitudinal movement of said carrier.

10. The apparatus claimed in claim 6, wherein said receiving and loading mechanism and said means for moving said receiving and loading mechanism between the first and second positions comprise an escapement shaft and means for rotating said escapement shaft.

11. The apparatus claimed in claim 10, wherein said means for rotating an objectfrom the cavity of said receiving and loading mechanism into an opening within the mask comprises at least one press pin aligned with the cavity of said receiving and loading mechanism and operable to push the object therefrom into the opening ofthe mask.

12. A method for preventing overspray during application of a coating on a rightcircularcylindrical object, substantially as decribed with reference to, and as illustrated in the accompanying drawings.

13. Amaskforpreventing overspraywhile spraying a coating on a rightcircularcylindrical object, substantially as described with reference to and as illustrated in Figures 1 to 3 ofthe accompanying drawings.

14. Apparatus for inserting an object into a mask having a plurality of openings therethrough for receiving the object, substantially as described with reference to ,and as illustrated in Figures 4to 8 of the accompanying drawings.