US 3926147 A
Ion-vapor deposition means include a perforated cage-substrate holder, rotatable about a horizontal axis and disposed in a vacuum chamber above a vapor source. A fixed plate means disposed within the cage limits the vertical component of substrate tumbling movement. Means establishing a relatively limited region of glow discharge in the tumbling region.
Description (OCR text may contain errors)
1 Dec. 16, 1975 Steube GLOW DISCHARGE-TUMBLING VAPOR 2.639.269 5/1953 Yube 427/242 x DEPOSITION APPARATUS 3,021,231 2/1962 Samuel et a1. 118/48 x 3,066,044 11/1962 Samuel 118/48 X  Inventor: Kenneth E. stellbe, St. Charles, MO. 3 213,327 10/19 5 J ki v 118/495 3,517,644 6/1970 Baer 1 1 118/49  Asslgnee' iggg gfg Douglas Cormratmn 3,676,350 7/1972 Wright et al 204/165 X  Filed: Nov. 15, 1974 Primary Examiner-M0rris Kaplan [211 AppL NO; 524 365 Attorney, Agent, or Firm-Charles B. Haverstock 52 US. Cl 118/49.1; 118/418  ABSTRACT 51 Int. cl. c230 13/12 Ion-vapor deposition moans include a perforated Cage-  Field of Search 118/4849.1, Substrate holder, rotatable about a horizontal axis and 118/417 413 19; 427/212 213 242 251 disposed in a vacuum chamber above a vapor source. 36 33.41 A fixed plate means disposed within the cage limits the vertical component of substrate tumbling move-  Refer Cit d ment. Means establishing a relatively limited region of UNITED STATES PATENTS glow discharge in the tumbling region.
2,616,391 11/1952 Russell 118/19 14 Claims, 6 Drawing Figures U.S. Patent Dec. 16,197; Sheet 1 of4 3,926,147
US. Patent Dec. 16, 1975 Sheet2of4 3,926,147
U.S. Patent Dec. 16, 1975 Sheet 3 of4 3,926,147
US. Patent Dec.16, 1975 Sheet4of4 3,926,147
FIG 6 GLOW DISCHARGE-TUMBLING v PoR DEPOSITION APPARATUS Many attempts have been made and many devices constructed and techniques used for plating articles and particularly for plating articles which are to be exposed to extreme environmental conditions including high temperature conditions and other hostile environmental conditions such as encountered at high altitudes and in outer space. This becomes especially critical in the construction of parts such as parts used on surfaces of space vehicles, aircraft and other similar devices which may be exposed to environmental conditions which otherwise could damage or destroy the operative effectiveness of such devices and cause costly failures resulting possibly in loss of life or premature flight abortion. It is also highly desirable to be able to accurately and uniformly plate such workpieces without substantially changing their size, shape or dimensions and without weakening them. This is especially important for parts that are made to fit together such as threaded and like parts. There are many known and available plating apparatuses and processes but no known ion vapor deposition or physical or chemical vapor deposition processes so far as known has solved certain of these problems including especially problems of being able to mass plate articles in sufficient quantities to be practical. These shortcomings have limited the usefulness of known processes and made them unsatisfactory especially for high volume operations.
One known prior art construction and process used for this purpose is disclosed in Carpenter et al. US. Pat. No. 3,750,623 which issued Aug. 7, 1973 and is assigned to Applicants assignee. While the process disclosed in the patent produces satisfactory parts for many purposes, a major shortcoming of the patented process is that it requires considerable handling of the parts to be plated, it is a slow process to use because of this, and in the patented process certain portions of each article to be plated are never plated because they are the portions which are required to attach the articles during the plating operation. Furthermore, the patented process plates certain parts of the articles thicker than other portions which may not always be desirable. Hence with the known construction only those surfaces of the articles that are visible to the plating source taking into account the throwing power of the system are plated, and with the known means and process each part must be handled individually and attached in plating position. The known means and method therefore do not lend themselves to economical plating which is an important limiting disadvantage especially when used to plate parts such as fasteners for air and space vehicles which may number in the thousands for each vehicle. Any of the forms of the present apparatus and process as disclosed herein can overcome otherwise difficult problems which have made other plating techniques inadequate such as the problem of hydrogen embrittlement which is a problem encountered in conventional electroplating techniques, the problem of solid-metal embrittlement that can also occur with certain materials notably titanium when highly stressed and in contact with cadmium, and as stated the present apparatus and process can be used in the production of coatings capable of withstanding high temperatures and it can be used to produce coatings which can prevent and protect against exfoliation corrosion of the parts being plated including on hidden or partly hidden surfaces such as countersinks and other cavities and holes including for example holes in highstrength aluminum alloys and other such materials. The present means and process are especially applicable to coating fasteners and other small parts which heretofore have been expensive to plate by any of the named processes because of excessive handling required and other problems.
It is therefore a principal object of the present invention to provide an improved apparatus for plating small articles.
Another object is to minimize handling of articles to be plated.
Another object is to provide plating means which can be operated to batch plate or to plate a continuous supply of articles as they pass through the plating apparatus.
Another object is to reduce the cost of plating articles and to make a plating process more efficient, less expensive and less time consuming. 7
Another object is to provide in a plating apparatus means for tumbling or jiggling articles while they are being plated and in some cases while the articles are maintained in the presence of a glow discharge region.
Another object is to teach the construction and operation of a novel open-mesh barrel construction for use in a plating device.
Another object is to establish an ion glow discharge in a portion only of an open-mesh barrel or other openmesh structure in which parts are tumbled during a plating operation.
Another object is to provide a more efficient mass production apparatus for plating articles using ion vapor deposition techniques.
Another object is to provide a more efficient mass production plating apparatus which is adaptable for use with physical vapor deposition and chemical vapor deposition techniques.
Another object is to provide plating means which can be operated by using many different plating substances including relatively inexpensive plating substances thereby further reducing the cost of plating articles while achieving superior plating characteristics therefor.
Another object is to provide means for more uniformly and accurately plating all surfaces of articles including surfaces on regular as well as on irregularly shaped articles.
Another object is to provide means for plating hidden surfaces including surfaces formed by holes and cavities and the surfaces of threads and other similar type surfaces.
Another object is to be able to mass produce more uniformly plated articles.
Another object is to provide improved means for feeding articles to be plated into plating position and extracting them therefrom.
Another object is to provide an improved bond between substrates and plating layers applied thereto.
Another object is to provide improved means for surface plating metallic as well as non-metallic workpieces.
Another object is to minimize the labor required to plate objects.
These and other objects and advantages of the present invention will become apparent after considering the following detailed specification which discloses plating apparatus constructed according to one embodiment of the present invention;
FIG. 2 is a right side view of the apparatus of FIG. 1;
FIG. 3 is an enlarged fragmentary cross-sectional view taken on line 33of FIG. 2;
FIG. 4 is a cross-sectional view taken through the center of an apparatus constructed according to the present invention;
FIG. 5 is a cross-sectional view showing an embodiment of the subject device specifically designed to plate articles on a continuous feed through basis; and,
FIG. 6 is a sectional view through a plating apparatus according to another embodiment of the present inventron.
Referring to the drawings more particularly by reference numbers, number 10 in FIGS. 1 and 2 refers generally to a plating apparatus constructed according to one embodiment of the present invention. The plating apparatus of FIG. 1 includes an outer housing 12 which is in the nature of a shield supported by spaced support members 14 at the positions shown. The shield 12 is round and opened at the bottom at 16 for reasons which will be described later.
A drum 18 is positioned concentrically inside the housing 12 and is mounted for rotation therein. The drum 18 is a perforated member such as a wire or screen mesh 19 and is the member on which the parts to be plated such as the parts 20 are positioned during plating. As the drum 18 rotates the parts 20 will tumble continuously on the screen 19 seeking a central lower position on the drum 18 as shown in FIG. 2. The drum 18 includes spaced end walls 21 and 22 each of which has radially extending portions 24 which are connected to a rotating shaft structure formed by connected shaft members 26, 28 and 30. The shaft 26 is the only part of the shaft structure formed by the members 26, 28 and 30 that rotates. The rotatable shaft portion 26 is fixedly connected to the drum 18 at the member 21 which may be a weld connection. The opposite end of the drum is mounted for rotatable movement on the stationary member 28 which is preferably an insulator member. The shaft 26 extends to the left as shown in FIG. 3 and passes through journal means 32 and is connected adjacent to its end to a sprocket wheel 34 over which a drive chain 36 extends. The journal 32 is supported on a shaft assembly which includes an upper shaft portion 38, a lower shaft portion 40 and an insulating assembly 42 which includes insulating member 44 positioned between the ends of the shaft portions 38 and 40. The insulating assembly 42 is provided to electrically isolate the shaft 26 and the drum portions connected thereto from certain electrical potentials. Another insulating assembly 45 which may be similar to the assembly 42 is connected in the shaft 26 between the journal 32 and the sprocket 34. The insulating assembly 45 is included to prevent the high voltage applied to the drum 18 from being applied to the member 34 and 36.
The opposite end of the non-rotatable tubular shaft portion 28 receives the non-rotatable shaft portion 30 which extends through a support member 46 located on the opposite side of the device. The member 46, like the journal 32, is electrically insulated from the means which support it by spaced shaft portions 50 and 52, and by an insulating assembly 54 which is similar to the insulating assembly 42.
A first tubular insulator 56 is mounted on the shaft 26 at the location shown and a pair of other tubular insulators 58 and 60 are mounted on the insulator 56 in spaced relationship as clearly shown in FIG. 3. The shaft 26 extends through the insulator 56 and the free end of the shaft 26 is threaded at 26A and receives a threaded nut 62 which holds the insulators 56, 58 and 60 in position thereon. The non-rotatable tubular member 28 cooperates with the end of the shaft 26 which is preferably not threaded to facilitate relative rotation therebetween, and the member 28 extends through an opening 64 formed in the end wall 22 of the drum 18. The tubular member 30 may be constructed of metal or ceramic material as desired and serves as a conduit for an electrical connection 65 to ground .as will be explained. The member 30 extends through and is held in position by the member 46.
An inner shield structure 66 is mounted inside of the rotating drum structure 18 and includes an outer wall 68 which is supported by radially extending leg portions 70 and 72 which extend inwardly therefrom and are connected to central bearing hub portions 74 and 76 which support the shield structure 66 respectively on the tubular members 56 and 28. The drive means including the drive chain 36 and the sprocket 34 are connected to rotate the drum structure 18 during operation of the device. However, the inner shield structure 66 should not rotate or should only rotate slightly during operation and to assure that this is the case the inner shield 66 may be weighted by suitable weighting means such as by weight means 77, and the bearings formed by the means 74 and 76 and the associated supporting portions of the insulators 56 and 28 should be as free as possible for reasons which will become obvious. The insulators 56, 58 and 60 are provided to keep the shield 66 in proper position spaced from the drum 18 and another insulator member 58A is located in the position as shown for similar reasons.
The shield 66 is cylindrical over most of its outer surface portion 68 but the lower portion as best seen in FIGS. 2 and 3 has a flattened or slightly upwardly curved portion 78 and this portions stays at or close to the position shown due to the weight means 77 which limit rotation thereof. A chamber 79 is therefore formed by and between the flat 78 on the member 68 and the adjacent portion of the screen 19 therebelow. The chamber 79 is the chamber in which the parts to be plated are positioned during the plating operation. The shape of the lower portion of the shield 66 not only serves to form the chamber 79 but is also useful to keep the parts being plated from moving or climbing up too high on the screen 19 during operation so that the parts cannot leave the region where the most effective plating takes place. The shape of the shield portion 78 also confines or limits the area where a glow discharge region is formed. The confinement of the glow discharge region when the subject device is used in an ion vapor deposition plating process assures operation within an abnormal glow and causes a more intense ion bombardment of the parts to be plated. This enhances cleaning of the parts by ion bombardment prior to plating and also increases the ionization of the plating substance such as of aluminum vapor during plating. The result is improved adhesion of the coating to the substrate. The shape of the shield66 and particularly the shape of the lower portion 78 is therefore very important to the present invention when used for ion vapor deposition.
In the preferred embodiment of the present construction the inner shield structure 66 is formed of metal and is maintained at ground or near ground potential by means of the electric connection provided by the lead 65 which extends through an opening 84 in the stationary tubular member 28 and through the non-rotatable tubular members 28 and 30 for connection to ground or some other suitable preferably relatively low potential. The drum 18, including the screen 19 and the end walls 21 and 22 on the other hand, is maintained at a relatively high negative potential for ion vapor deposition in the range from about 1000 to 5000 volts by means of another electrical connection provided on lead 85 and wiper 86 which makes sliding or rubbing contact with the end wall 22 of the drum 18.
During operation the entire mechanism including the structures shown in FIGS. 1, 2 and 3 are mounted in a controlled environment such as in a vacuum chamber shown for illustration purposes formed by belljar 90 (FIG. 4). The belljar 90 is mounted on a base structure identified generally by the number 92 and the base structure may include structures and connections similar to those shown in Carpenter et al. US. Pat. No. 3,750,623. For example, the base structure is shown including a vaporizing boat 94 supported by conductive straps 96 and 98 which in turn are connected electrically to an input source of heater voltage 100 by leads 102 and 104. The electrical connections in this case are made through respective metal tubes 106 and 108 which are shown connected by conduits 110 and 112 and 114 and 116 to a supply of coolant (not shown) used to control the temperature of the electrodes 106 and 108. The boat 94 is shown being supplied with a substance to be vaporized in wire form 118 from a spool 120. The wire is drawn from the spool 120 by drive means similar to those disclosed in the patent.
The base portion 92 has a connection to a vacuum pressure source (not shown) through a conduit 122 and valve means 124. Another conduit 126 and valve 128 are provided to communicate the inside of the belljar 90 with a source of some suitable gas which is provided for the purposes described. Various back fill gases can be used depending on the plating technique that is selected. For an ion vapor deposition the gas selected is usually an inert gas such as argon, while for physical vapor deposition a vacuum only is used and for chemical vapor deposition a more active gas such as oxygen may be preferred.
The same motor which drives the wire 118 to feed the substance being evaporated may also be used to drive the wire mesh drum or barrel 18 although some additional gearing may be required to accomplish this. It is also contemplated to use separate drive means for each. Furthermore, the drive means can be internal or external of the controlled environment. If external drive means are used the rotary motion is transferred to the means that are driven through the wall of the belljar 90 or other chamber forming means. This can be done by a conventional vacuum feed through device.
During operation of the subject device the vacuum pump (not show) is used to evacuate the belljar 90 during preparation of the environment. The pump is operated in the first instance to evacuate the inside of the belljar and to produce a near vacuum condition (approximately 1 X mm Hg) therein. Thereafter, gas from the gas source is fed through the conduit 126 and the valve 128 into the belljar to obtain a pressure therein between about 10 and microns which produces an environment that is made up almost entirely of the gas. A dynamic system pressure is maintained by continuing a controlled flow of the gas through the conduit 126 while throttling the vacuum pump using the valve 124. Thereafter a high negative voltage is applied by way of the lead 85 and the wiper 86 to the wire mesh drum 18 and to the articles to be plated which are positioned therein. When this is done it causes a negative glow region to be established in the vicinity of the parts 20 in chamber 79. This glow region is confined to the space below the flattened lower portion 78 of the shield 68 and around the lower portion 19 of the wire mesh screen which forms the drum 18. Since the shield 66 is positioned and weighted to maintain the position as indicated the glow discharge region will confine itself to the space immediately around the articles being plated.
In the negative glow region which characterizes ion vapor deposition the ionized gas particles are attracted to the adjacent portion of the screen 19 and to the workpieces 20 which they bombard from all directions. This bombardment cleans or scrubs and conditions the workpieces so that they are better and more adhesively able to receive a deposit of the evaporated plating substance, In order to produce the negative glow a relatively high negative potential in the range of approximately 1000 to 5000 volts with respect to ground must be applied to the drum 18. The glow discharge established around the workpieces, and the accompanying bombardment by ionized gas particles is maintained throughout the plating process and is important because it substantially improves the adhesion of the plating substance to the workpieces and produces the desired final plating. Between the glow discharge region and the workpieces being plated including the lower screen portion 19 there is also formed a region which is sometimes called the cathode dark space.
Once the glow discharge is established and has been in operation for some time, the boat 94 will be heated by the lower voltage source 100 to a temperature at which the plating substance being fed thereto is to be vaporized. Most of the vaporized substance will be present in the region extending between the boat 94 and the parts being plated and some of this vaporized substance will be ionized by the action of the charged environment and some will remain as neutral particles or atoms.
The pressure of the gas, the electrical potential on the lower screen portion 19, the temperature of the boat 94 the evaporation rate including the feed rate of the plating substance, the temperature of the workpieces, the spacing between the boat 94 and the workpieces, and the position and relative positions of the parts in the belljar are variables which can be adjusted to obtain optimum plating conditions.
It is important to the operation of the present device that during the plating operation the perforated barrel 18 or other means of exposing surfaces of the workpieces continuously rotate while the parts to be plated positioned therein continuously tumble and maintain positions near the bottom of the barrel in relatively close proximity to the vaporizing boat 94. The tumbling action of the parts 20 will also cause the parts to continuously have different sides and surfaces facing the vaporization source 94, and this in turn will cause them to be plated relatively uniformly on all surfaces thereof a condition that has not been true of any known construction used for ion vapor deposition, physical vapor 7 deposition or chemical vapor deposition including the construction shown in US. Pat. No. 3,750,623. Furthermore, in the ion vapor deposition case by confining the glow discharge region to the lower portion of the barrel 18 the lower portion 78 of the shield 66 concentrates the area where the plating takes place and improves the plating efficiency. In this regard, the spacing between the barrel 18 and the shield 66 should be such that the parts cannot move too far away from the region near the bottom of the barrel because the shield itself may strike parts that move too high during rotation of the drum l8 and force them to tumble back to the location where the most intense plating action is occurring.
The cleaning action produced by the inert gas in the case of ion vapor deposition as described above is usually commenced before the temperature of the boat 94 is raised sufficiently to vaporize the plating substance. This prepares the parts to be plated, increases the adhesion characteristics between the vaporized substance and the workpieces and improves the finished parts.
The present apparatus and method of plating have particular application to plating parts which have irregular shapes such as screws, bolts, and other irregular shaped usually relatively small objects, and the present apparatus and method are able to plate such parts relatively uniformly over their entire surfaces in large batches or continuous flow quantities which has not been true of any known means or method using the same or similar techniques, namely the techniques of ion vapor deposition, physical vapor deposition and chemical vapor deposition.
FIG. shows another embodiment 200 of the subject device which is particularly designed and constructed to plate parts or workpieces on a batch or continuous flow through basis wherein each part is subjected to the plating process for approximately the same amount of time and under the same environmental conditions described above. y
In the modified construction 200 an elongated rotating cylindrical wire mesh drum 202 is positioned with its axis slightly tilted with respect to horizontal so that one end 204 is at a higher elevation than the opposite end 206. The drum assembly 202 including an outer shield 208 in the modified structure 200 is mounted on legs 210 inside of a vacuum chamber formed by a housing 212, and the housing 212 is shown supported by suitable support means such as support means 214 and 216. A drive shaft 218 extends through the chamber in the housing 212 and is journaled to the opposite ends of the housing by journal means 220 and 222. The shaft 218 is also journaled to journal means 224 and is driven by sprocket 228 and drive chain 230. The shaft 218 may be connected to the drum assembly 202 in the manner'similar to the shaft 26 in FIG. 3, and the details of this connection will not again be described. Also supported in the drum 202 is an inner shield 232 which is similar in structure to the inner shield 66, and is supported in a relatively non-rotating condition inside of the drum assembly 202 in a manner similar to that already described. This is so that when the wire mesh drum or barrel 202 rotates the inner shield 232 will remain relatively stationary for the purposes already described.
In the modified assembly 200 the parts to be plated are fed into the drum assembly 202 at the more elevated end thereof and during the plating operation the parts are continuously tumbled and in so doing gradu- 8 ally move from the more elevated end 204 of the drum 202 to the less elevated end. The same can also be accomplished even when using a horizontally oriented barrel by providing helical or spiral shaped members located on the inner surface of the drum. It is also contemplated to use a perforated basket or trough shaped member instead of a cylindrical drum to hold the parts in which case some means such as will be discussed later are provided to vibrate the perforated member to cause the parts contained therein to tumble.
The parts introduced at the more elevated end 204 of the structure of FIG. 5 are introduced through controlled valve means to prevent loss of the plating environment. The means for accomplishing this are shown as including a tube 234 which is connected to a valved hopper assembly 236 which is able to be sealably closed at its upper end by means of a cover member 238 which engages sealing means such as the sealing ring 240. Parts to be plated are put into the upper portion of the hopper assembly 236 when the cover 238 is open and they fall onto valve means 244. The cover 238 is then closed and the upper portion of the hopper assembly evacuated by means of conduit 246 and valve 248 which are connected to a vacuum pressure source or the like. The valve means 244 are then opened to permit the parts to fall through and into the lower part of the hopper assembly 236 and from there through the tube 234 which has its lower end positioned to direct the parts onto the end of the wire mesh drum 202. Thereafter as the drum rotates, the parts will gradually move along the drum 202 until they reach the opposite end at which time they will fall off the drum and into an outlet tube 250 which is shown having a funnel shaped upper end 252 to receive the falling pieces. The parts which have been plated fall through the tube 250 and into the upper portion of valved outlet collector assembly 254 which includes another valve 256 similar to the valve 244. When sufficient parts have accumulated above the valve means 256 and while another closure member 258 is sealably closed against seal means 260, a vacuum pressure is drawn in the lower chamber portion of the assembly 254 by vacuum producing means connected thereto through conduit means 262 and valve means 264. As before this is done to prevent contamination of the plating atmosphere in the housing structure 212. When a sufficient vacuum condition is obtained, the valve means 256 are opened to permit the plated articles to fall into the lower portion of the assembly 254, and the valve means 256 are then reclosed and the vacuum producing source turned off so that the closure means 258 can be reopened to obtain the parts.
The structure 200 is basically operated in substantially the same way as the construction shown and described in connection with FIGS. 1-4 except for the fact that the parts being plated can be introduced more or less continuously without reopening the housing 2 12 and having to reestablish the desired plating environment. Also the housing 212 contains a suitable number of spaced vaporizing boats 266 which are located near the undersurface of the drum 202. Each of the boats 266 may have its own electrical connections and its own source of plating material, and these may be similar to the corresponding elements of the structure as shown in FIG. 4. The main advantage of the construction shown in FIG. 5 is that once the plating environment has been established in the housing 212, it can be operated continuously as long as there is a supply of 9 plating substance available and as long as the environmental conditions can be maintained.
FIG. 6 shows a construction 300 whichis similarin some respects to the constructions described above and is useful for ion, physical or chemical deposition. When either physical or chemical vapor deposition techniques are used it is usually not necessary to provide a glow discharge region or to use high voltages.- Instead the plating that occurs takes place mainly because of evaporization and settling of the evaporated substance on the articles being plated; Obviously with either of these techniques the cleaning action obtained by the presence of a charged environment is not available, and depending on the materials involved the quality and attachment of the plating layer may or may not be as good as in the case of ion-vapor deposition.
In the structure shown in FIG. 6 a perforated basket or trough 302 is positioned in a chamber formed by housing 304. The chamber is then evacuated and the plating substance which is fed to'boat 306 is heated until it vaporizes. Some of the vaporized plating substance settles on the parts and plates the parts. In order to uniformly plate all surfaces of the parts the basket 302 is moved or vibrated using means such as vibrator means 308 which are attached thereto.
In the case of physical vapor deposition a vacuum condition is maintained in the plating chamber and in the case of chemical vapor deposition the plating chamber may be backfilled with a gas such as oxygen which reacts chemically with either or with both the vaporized plating substance or with the parts being plated to produce a chemical reaction during the plating process. In all embodiments of the present invention it is necessary to establish a proper plating environment, it is necessary to establish a supply of a vaporized plating substance and it is necessary to tumble or jiggle the parts while they are being plated in order to expose different surfaces to the source so that all surfaces will be plated uniformly.
Thus there has been shown and described novel apparatuses and novel processes for plating articles which apparatuses and processes achieve superior plating results and fulfill all of the other objects and advantages sought therefor. It will be apparent however to those skilled in the art that many changes, modifications, variations and other uses and applications of the subject apparatuses and processes are possible and contemplated and all such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow.
What is claimed is:
1. Means for plating articles comprising means forming an enclosed chamber, means for evacuating the chamber to establish a near vacuum condition therein, other means for introducing a gas into the evacuated chamber to raise the pressure in the chamber to a predetermined level, a source of a plating substance positioned in the chamber including means for evaporating the plating substance, the improvement comprising means for supporting a supply of articles to be plated in spaced relationship relative to the source of vaporized plating substance, said support means including a perforated wall member on which the articles to be plated are positioned, means for rotating the perforated wall member during the plating operation in such a way that the articles supported thereon tumble and present dif- ,ferent surfaces to the source of vapcirizedplating substance, means connecting the perforated wall member to a source ofrelatively high negativeelectric potential, a, relatively non-movable shield structure positioned adjacent to the perforated wall member above the articles to be plated thereon, means to maintain said nonmovable shield structure at a relatively low electric potential, said shield structure having a portion positioned extending relatively closely in spaced relationship above the articles being plated aiid to the adjacent portion of the perforated wall member to define with said adjacent portion of the perforated wall member a chamber in which the articles being plated are located and restricted in the vertical component of tumbling movement'and to define a relatively limited region of glow discharge.
2. The means for plating articles defined in claim 1 wherein the shield structure includes a closed wall member positioned inside of the perforated wall member, and means to prevent rotation of the shield structure during a plating operation.
3. The means for plating articles defined in claim 1 including an outer shield member positioned extending substantially around the perforated wall member, said outer shield member having an opening at a location that is beneath the perforated wall member.
4. The means for plating articles defined in claim 1 wherein the perforated wall member includes an elongated tubular shaped screen member, means for mounting said perforated wall member in the enclosed chamber with the axis thereof oriented at an angle relative to horizontal so that one end of the screen member is more elevated than the other end, means for feeding articles to be plated onto the more elevated end of the screen member, and other means for receiving articles that have been plated as they drop off of the less elevated end of the screen member.
5. The means for plating articles defined in claim 1 wherein the perforated wall member is an elongated tubular shaped screen member, the means for moving the perforated wall member include means for rotating the wall member, and means positioned in the perforated wall member for moving articles positioned therein toward a selected end thereof.
6. Means for plating articles comprising means forming an enclosed chamber, means for evacuating the chamber to establish a near vacuum condition therein, other means for introducing a predetermined quantity of an inert gas into the evacuated chamber to establish a plating environment therein, a source of a plating substance positioned in the chamber including means to vaporize the plating substance, the improvement comprising means for supporting a quantity of objects to be plated in spaced relationship above the source of vaporized plating substance in the chamber, said support means including a perforated wall member in which the objects to be plated are positioned, means for rotating the perforated wall member during a plating operation whereby the object supported therein are repeatedly tumbled so as to present different surfaces thereon in line of sight with the source of vaporized plating substance, means connected to the perforated wall member including a source of relatively high negative electric potential, a closed wall shield structure positioned in the perforated wall member, said shield structure having a surface portion which extends in relatively closely spaced relations above the objects to be plated to define with the portion of the perforated wall member therebelow a chamber portion in which the objects to'be plated are positioned and to restrict the vertical component of tumbling movement, means to substantially prevent rotation of the shield structure, and means to maintain said shield structure at a relatively low electric potential whereby said chamber portion defines a relatively limited glow discharge region.
7. The means for plating objects defined in claim 6 wherein said perforated wall member is a closed wall member, means journaling said wall member for rotation inside of the enclosed chamber, and means to journal said shield structure inside of the perforated wallmember, said shield structure including weight means located thereon to substantially prevent rotation thereof on the journal means.
8. The means for plating objects defined in claim 6 wherein the means forming an enclosed chamber include a housing structure, means communicating the enclosed chamber formed by the housing structure to a vacuum pressure source, and other means operable to selectively communicate the enclosed chamber with a source of inert gas.
9. The means for plating objects defined in claim 6 including means for grounding the shield structure.
10. The means for plating objects defined in claim 6 including means for rotatably supporting the perforated wall member in the enclosed chamber, said support means including means electrically insulating the perforated wall member from the chamber forming means.
11. The means for plating objects defined in claim 6 including motor means, and means operatively connecting said motor means to rotate the perforated wall member.
12. The means for plating objects defined in claim 6 wherein the perforated wall member includes a tubular shaped screen member having spaced end walls connected to extend respectively across opposite ends of the tubular screen member, said screen member and said spaced end walls being formed of conductive material.
13. The means for plating objects defined in claim 6 wherein the potential of the high voltage applied to the perforated wall member from the electric source is between about lOOO and 5000 volts.
14. The means for plating objects defined in claim 6 including means to maintain the pressure in the enclosed chamber between about 10 and about 20 mi-