US3514388A

US3514388A - Ion metal plating of multiple parts

Info

Publication number: US3514388A
Application number: US713709A
Authority: US
Inventors: Robert C Brumfield; John T Naff; Alonzo T W Robinson
Original assignee: Automatic Fire Control Inc
Current assignee: Automatic Fire Control Inc
Priority date: 1968-03-18
Filing date: 1968-03-18
Publication date: 1970-05-26
Anticipated expiration: 1987-05-26

Description

May 26, 1970 R. c. BRUMFIELD ETAI- 3,514,383

ION METAL PLTING OF MULTIPLE PARTS Filed March 18, 1968 2 Sheets-Sheet 1 52% j. I y

l 5 /Z /I Z6 7 INVENTORS. t ,.or c. @ez/MH@ A 'F56' JOHA/ r/V//FF Bmw/v50' mx fom/Mv May 26', 1970 R. c. BRUMFIELD ETAL 3,514,383

ION METAL PLATING 0F MULTIPLE PARTS 2 Sheets-Sheet 2 Filed March 18, 1968 .p w Q w www W M W W w A Q w L QW www@ W i w www? v fn/V 1r/m M w// WA 2 i UW/ lolM/w/d W 5 -W n, M. ad F e United States Patent O 3,514,388 ION METAL PLATING F MULTIPLE PARTS Robert C. Brumtield, Emerald Bay, John T. Natf, Costa Mesa, and Alonzo T. W. Robinson, Huntington Beach, Calif., assignors to Automatic Fire Control Inc., South El Monte, Calif., a corporation of California Filed Mar. 18, 1968, Ser. No. 713,709 Int. Cl. C23c 15/00 U.S. Cl. 204-192 8 Claims ABSTRACT OF THE DISCLOSURE This invention teaches a process and apparatus useful in simultaneously metal plating alarge number of metal and non-metal parts with a metal coating by ion metal plating, typically in a low pressure argon atmosphere with ,a high voltage, abnormal glow discharge, rotating the parts while they are physicaly intermixed with void illing conductive particulates.

BACKGROUND OF THE INVENTION This invention related to an improved process for ion metal plating a multiplicity of metal and non-metal parts in a single plating operation, utilizing improved apparatus for the plating process. Conventionally, metal parts have been previously ion metal plated by separately and individually placing each part in an evacuable apparatus, wherein the low pressure, high voltage argon gas abnormal glow discharge is generated between the fixed position heated plating metal anode structure and the xed position cathode structure having one or more parts to be plated electrically conductively secured thereto. This process is disclosed in Mattox, U.S. 3,329,601.

The above conventional process is characterized by high labor costs, in terms of individually placing each part to be plated in electrical contact with the cathode, and removing the part after each plating operation. The process also leaves undesirable rack or cathode structure marks on the plated part, due to non-uniform electrical iield strength shadow zones present during the metal deposition step.

SUMMARY OF THE INVENTION This invention teaches a process and apparatus suitable for simultaneous metal plating of a large number of metal and non-metal parts of varying sizes in a single ion plating operation, utilizing a typical low pressure argon gas, high voltage abnormal glow discharge. In this improved ion metal plating apparatus, a fixed position, electrically grounded, vacuum tight, exterior drum container is located with the cylindrical axis of symmetry horizontal, and there is a vacuum tight removable closure on an end of the drum. An electrically insulated, mixing, interior drum shell slowly rotates axially concentrically inside the fixed exterior drum and is open to the gas pressure inside the exterior drum.

The interior rotating drum shell has mixing bailles located therein, to promote tumbling and mixing of objects placed in the interior drum. The metal and non-metal parts to lbe plated are located in the bottom half of the interior drum shell together with an amount of discretely sized particulates of the same metal as the plating metal, the particulate balls or other small sized irregularly shaped pieces are sized to tit in the interstices between the metal and non-metal parts to be plated and to ll the parts interstices to a high volume percentage. A xed position anode structure is located concentric with the rotating interior shell drum axis of rotation and the interior shell metal rotating drum is the cathode of the low argon gas pressure, high DC voltage abnormal glow discharge system.

rice

The discretely sized, metal balls or other small sized, irregularly shaped particulates of the plating metal serve to lluidize or buoy up the parts to be plated, supply multiple electrical contacts between these parts and the rotating drum shell cathode, and minimize the electrical eld strength shadows which can produce uneven metal plating on the rotating metal parts.

Included in the objects of this invention are:

First, to provide an improved ion metal plating process for simultaneously ion metal plating a large number of metal and non-metal parts in a single plating operation, without individually attaching each part to a xed position cathode.

Second, to provide an improved ion metal plating process for simultaneously metal plating a large number of metal and non-metal parts, eliminating plating imperfections due to electrical eld strength inequalities in the ion plating step.

Third, to provide good low temperature control of the parts plated in an ion metal plating, low gas pressure, high voltage abnormal glow discharge.

Fourth, to provide a rotating drum plating apparatus for simultaneously metal plating multiple parts in a loW gas pressure, high voltage abnormal glow discharge.

Fifth, to provide a process for simultaneously ion metal plating multiple metal and non-metal parts, concurrently burnishing the metal parts and minimizing the number of nicks or scratches formed on the metal parts.

Sixth, to provide means for greatly reducing the labor required to ion metal plate a large number of relatively small metal and non-metal parts.

Other objects and advantages of this invention are taught in the following description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS The description of this invention is to be read in conjunction with the following drawings:

FIG. l is an elevational partial sectional, partial perspective drawing of the rotating drum ion plating apparatus useful in simultaneously metal plating multiple metal parts in a low gas pressure, high voltage, abnormal glow discharge.

FIG. 2 is a View through 2-2 of FIG. l.

FIG. 3 is a detailed partial plan view of a commercial anode filament source of plating metal, in series-parallel electrical connections.

FIG. 4 is a side elevational view of the anode filament source of FIG. 3.

FIG. 5` is a perspective elevational view of another anode plating metal source.

FIG. 6 is an elevational view through 6-6 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. l in detail, the ion plating evacuable apparatus 1 of this invention is shown in an elevational view. A fixed position, vacuum tight, cylindrical, exterior metal drum 2 is disposed with the drum cylindrical axis of symmetry 3 located horizontally, and the drum 2 grounded at 4. A vacuum-tight, removable, swinging hinged door closure 5 seals the drum 2 at the drum opening 6, with suitable gasket seals 7 or the like in the ange pair 8. An electrically conductive and grounded, interior mixing drum 9 also has the horizontally disposed cylindrical axis of symmetry 3. The axes of cylindrical sym- =metry of exterior drum 2 and interior mixing drum 9 are not required to coincide, but it is convenient to do so. The interior mixing drum 9 is supported by the hollow shaft 10, which is located in the vacuum-tight bearing shaft gland 11 secured to the exterior drum '2. The bearing and seal combination 12 provide a vacuum-tight rotational seal, upon which the shaft can be supported and the shaft 10 is supplied with rotative power. The hollow shaft 10 has an opening 13 into the drum 2, which can be used as an argon gas inlet. The bearing and seal combination 12 is bathed in a stream of argon gas 14 at 1.1 atmosphere pressure, providing a pressure gradient preventing air leaks into the exterior drum 2. The interior mixing drum 9 is also electrically grounded through shaft 10 to ground 4.

The water cooling means 15 is thermally conductively secured to the interior mixing drum 9, providing a means to absorb and conduct heat away from the interior mixing drum 9. Although a spirally wound metal tubing 15 is shown welded to the exterior of the interior mixing drum 9 and is the water cooling means 15 in this modification, a conventional jacketed shell around the drum 9 can be an equivalent water cooling means 15, as well as conventional spiral continuous openings cast in the wall of the interior mixing drum 9. The water cooling stream exits from the apparatus through a standard rotative sealing device.

The bafile mixing blades 16 are interiorly located on the walls of the interior mixing drum 9, and are radially aligned toward the axis of symmetry 3, so as to provide a mixing and tumbling action for the metal or non-metal parts 17 and the electrically conductive void iilling means 18 which are co-mingled in the lower half of the interior mixing drum 9.

The co-mingled metal and non-metal parts 17 and electrically conductive void filling means 18 are held in the interior mixing drum by the removable closure 19, having the coaxial opening 20 therein, the opening 20 being coaxial with the axis of symmetry 3.

An anode plating metal source 21 is coaxially disposed along the axis of symmetry 3, and the source 21 is electrically insulated from the exterior metal drum 2 by the pair of insulators 22. Further details of the metal source 21 are illustrated in FIGS. 4-6. A sheet metal electrostatic shield 23 is disposed in a non-rotating, xed position within interior mixing drum 9, spaced within one cathode dark space of drum 9, forming a semi-cylindrical metal shield around the axis of symmetry 3 and is mechanically secured to and electrically insulated from shaft 10. The electrostatic shield 23 is electrically isolated in the apparatus, being substantially at the anode potential.

The interior mixing drum 9 functions as the cathode in the low pressure, abnormal glow discharge ion metal plating apparatus. The potential drop between the high voltage anode source 21 and the interior mixing drum cathode 9 can vary from 1500 to 5000 v. DC, and the potential is supplied by the power source 24. The anode plating metal source is supplied low voltage power by the power source 25.

A pipe opening 26 extends from the exterior metal drum 2, and opening 26 Vents into evacuation pump means 27, having gas regulation means adapted to maintain the interior of drum 2 at an argon gas pressure range of 5 to 100 microns.

FIG. 2 illustrates the concentric circular construction of the apparatus 1. The exterior metal drum 2 concentrically encloses the interior mixing drum 9. The internally projecting radial baille mixing blades 16 are secured to the interior of the drum 9, and the water cooling tubing 15 is circumferentially welded to the exterior of drum 9. The anode plating metal source 21 is shown located coaxially on the axis of symmetry 3, and the opening 13 of the hollow shaft 10 provides an argon gas inlet.

FIGS. 3 and 4 together illustrate one modification of an anode plating metal source 21, utilizing tungsten, tantalum or molybdenum coiled wire ilaments 28. The multiple wire filaments 28 are disposed and secured in parallel array between the electrically conducting bus bars 29, by clamping or the like. The bus bars 29 are mechanically disposed 0n and secured to mounting electrical insulators 4 30, and the insulators 30 are secured to and disposed in spaced position along the thermal and electrical insulator support plates 31.

As illustrated in FIGS. 3 and 4, multiple parallel wire filaments can be connected in an array across a pair of bus bars 29, and then the array connected in series with other multiple arrays to form a parallel-series array of anode wire filaments. The filaments 28 can 4be heated to vaporization temperature of the plating metal coating 32 on the filaments 28, by an AC power source of up to volts or the like, applied at the bus tabs 33. In this anode plating metal source 21, the plating metal coating 32 or plating metal clips are applied to the wire filaments 28 by known technique.

FIGS. 5 and 6 together illustrate another modification of anode plating metal source 34 which can be disposed coaxially along the axis of symmetry 3 of FIGS. 1 and 2. The anode plating metal source 34 is equivalent to the anode plating metal source 21. The rectangular boat 35 may be an inter-metallic composite of boron, titanium, silicon nitrides, and has a rectangular cavity 36 shaped therein. The cavity 36 is lled with substantial amounts of the plating metal 37 in bulk form. A vapor dellector shield 38 is coplanarly disposed adjacently above the boat 35 as shown in FIGS. 5 and 6, the width 39 of the shield 38 being wider than the width 40 of the boat 35. The rectangular cavity 41 of the detlector shield 38 is adjacently opposed to the boat cavity 36. The vapor deflector shield 38 serves to deilect downward the hot metal vapors of the plating metal 37. The rectangular boat 35 and the vapor deflection shield 38 are clamped together, electrically resistively heated and physically supported along the axis of symmetry 3, by the pair of metal clamps 42 which serve as the electrical power conductors to the anode source 34.

The electrically conductive void filling means 18 provides the base of the important inventive advance in the ion plating art. The void filling means 18 can be electrically conductive parts to be metal plated or an electrically conductive, bulk volume filler structure. In operation, the metal or non-metal parts 17 to be plated are randomly disposed in the lower half of the interior mixing drum 9, and the void volume in between the parts 17 are filled with electrically conductive void filling means 18 which are carefully sized in a multiple series of graded volume sizes and shapes to provide as nearly maximum filling of the void volume between the parts 17. Thus, the parts 17 statistically always remain in electrically conductive contact with the cathode interior drum 9 and the potential electrical field strength shadow zones are reduced to a minimum. The slow speed rotation of the interior mixing drum 9 insures the parts 17 are statistically uniformly exposed to the metal ions vaporized from the'anode plating

metal sources

21 and 34, in the electrical field potential between the anode and cathode with a statistical minimum of field strength shadow.

Economically it is an advantage to co-mingle large and small volume parts 17 in a series of graded sizes in the mixing drum 9, a parts diameter ratio of 10:1, or the like, being suitable. In this manner, the maximum number of parts are plated in a single plating operation, and a minimum volume of low economic value void filling means 18 is required. It is possible to schedule and comingle parts 17 for the plating operation in a size distribution pattern, requiring almost no low economic value void filling means 18. The low economic value void filling means may be either metal balls, rods or pebbles of the physical shapes used in typical industrial grinding mill operations, but physically sized to fill the voids between the parts 17. Ceramic type balls, rods or pebbles, including quartz sand, may be substituted for metal, as void filling means, for they may be first plated with the plating metal in a preliminary operation, prior to ion plating the parts 17.

The rotational speed of the interior mixing drum 9 must be carefully controlled to avoid nicking and peening the metal parts during the plating operation. Typically a range of 1-10 r.p.m. is suitable.

By controlling the low speed rotation of the mixing drum 9, the size of the metal parts 9 and void filling means 18, the parts 9 are buoyed up and cushioned during the plating operation, as well as burnished.

Typically the size of the interior mixing drum 9, or the like, can range from one having a inch diameter x 24 inch long, to one having a 5 feet diameter x 6 feet long.

In operation, a typical load of bolts and nuts in a range of sizes to provide a minimum of void space in between the parts 17 is placed in the interior mixing drum 9, or the like. The removable closure 19 is shut on drum 9, and the required volume of appropriately sized void filling means 18 is added through the opening 20. The anode plating metal source 21 or the anode source 34 is positioned along the axis of symmetry 3 and Wired to the power source 25. The swinging door closure 5 is sealed vacuum-tight to the exterior drum 2. The vacuum evacuation means 27 removes all air from the interior of drum 2, and an argon gas atmosphere 43 is introduced and maintained in range of 5 to 100 micron pressure.

Typically, during a parts cleaning initial stage the argon atmosphere 43 is held at 10 micron pressure. During a four hour period of degassing and cleaning of parts, the potential range between the anode source 21 and the metal parts 17-interior mixing drum 9-void filling means 18 forming combination cathode 44 can be from 1500 to 3000 volts DC, and 2000 volts is a typical potential, and is supplied by power source 24. A current density at the frontal area 45 of the tumbling metal parts 17 and void ll means 18 is regulated over a range of 0.05 to 0.5 ma./cm.2, and is typically 0.15 ma./cm.2.

During the cleaning step as well as the following ion plating step, cooling water is circulated through the water cooling tubes 15, or the like, providing heat transfer out of the ion plating apparatus 1, thus maximizing the allowable cathode current density and shortening the cleaning or degassing time 3 to 5 fold over the standard rack type plating procedure of Mattox.

Immediately following the cleaning step, the unopened apparatus 1 is switched to the ion metal plating step. The argon gas atmosphere 43 is now held at 15 micron pressure, the potential gradient between anode source 21 and the cathode combination 44 ranges from 2500 to 5000 volts DC, with 3500 volts typical. The frontal area 45 of the metal parts 17 and void filling means 18 has a cathode current density range of 0.1 to 1.0 ma./cm.Z with 0.4 ma./cm.2 being typical. The anode plating

metal sources

21 and 34, and the like, are operated at the required power input from the low voltage power source 25, providing a resistively heated

metal plating source

21 or 34 Which has a metal vapor pressure approximately equal to the argon gas pressure, typically 10 microns. The plating metal temperatures for the

sources

21 and 34 correspond to the temperatures illustrated in Table I.

Continuing the rotation of the interior mixing drum 9 and its contents while also Water cooling drum 9, the metal atoms vaporized from the

sources

21 or 34, are largely directed toward the frontal area 45 of the parts 17 and the void filling means 18, and the metal vapor atoms are deposited on the parts 17 and the means 18, the electrostatic shield 23 tending to repel the metal atoms. As generally explained by Mattox, a large portion of the metal atom vapor is ionized in the argon gas discharge and -these ionized atoms are accelerated to the pre-cleaned parts surfaces, along with other metal atoms in the vapor having only thermal energy. The pre-cleaned parts surfaces Which have been subjected to prior argon ion bombardment have surfaces which provide very adherent metal plating layers in the final plating step.

A typical cleaning step requires about four hours for a load of 1/2 inch `diameter bolts in a 30 inch diameter inner mixing drum 9. The cleaning time is a function of parts 17 size, as the parts 17 are tumbled in the drum 9 and intermittently exposed at the frontal area 45. The larger the parts 17, the shorter the cleaning time. The time required to ion plate the parts 17 with metal plate 32, or the like, is about 11/2 hours for a 0.0005 inch thick coating of aluminum.

The process and apparatus of this invention provide superior means of ion metal plating non-metal parts. The non-metal parts 17 in the comingled parts 17-void filling means 18 are continuously drained of their electron charges by the electrically conductive void filling means 18 which are in contact with the grounded interior drum 9. Thus electrically insulated parts 17 can be ion plated in this process and apparatus.

A wide range of plating

metal

32 and 37 may be applied to parts 17. Preliminary to the ion plating process, the parts 17, or the like, are first cleaned if necessary in -the conventional steps required prior to high quality metal plating by any standard plating process, e.g., removing metal scale, washing, pickling and drying. Important plating metals which may be applied by this ion metal plating process and in the ion metal plating apparatus taught in this invention, are listed in Table II. Typically plating metals of Group A, such as aluminum, chromium, cadmium and copper may be coated on substrate parts of Group B made of steel, titanium, nickel-copper alloy, magnesium, gold, silver or the like in Table II. Non-metal parts of Group B may typically be coated with all the `plating metals of Group A as listed in Table III, and the 9. Then the heated anode metal plating source means 214 or 34 is operated as in the standard metal evaporation process, at low argon gas pressure, to provide a thin electrically conductive coating of the

metal coating

32 or 37 on the ceramic shapes. f

The plating process and apparatus taught herein provide a means for simultaneously ion metal plating a large number of metal and non-metal parts with a very low unit of labor time per metal part plated. Therefore, this invention is a very important advance over the prior art in contributing to the commercial utilization of ion lmetal plating. The slow speed rotation of the metal parts contributes to a polishing action on the parts and to electrical field strength uniformity which eliminates parts rack marks and the like.

Obviously many modifications and variations of this improvement in ion metal plating process and apparatus are possible in the light of the above teachings. It is therefore understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

TAB LE III Part Substrate (Group B) Glass Pyroceram Carbon Methyl methaerylate polymer Polyvinyl chloride Chloropolyvinyl chloride Aluminum oxide Anodized aluminum Epoxy resin castings Plating Metal (Group A) Aluminum Gold Copper We claim:

1. An ion metal plating apparatus comprising in combination:

(a) a fixed position, vacuum-tight cylindrical, exterior drum, having a horizontally disposed cylindrical axis of symmetry and a vacuum tight, removable closure secured to one drum end,

(b) a slowly rotatable, electrically conductive, interior drum 'having a horizontally disposed cylindrical axis of symmetry, said interior drum being located completely within said exterior drum, said interior drum end adjacent said exterior drum removable closure having a removable closure with a coaxial opening therein,

(c) an anode plating metal source disposed coaxially along the axis of rotation of said interior drum, electrically insulated from said interior drum and from said exterior drum, being mechanically secured to and supported by said exterior drum,

(d) a cathode source electrically secured to said interior drum,

(e) water cooling means thermally conductively secured to said interior drum,

(f) a gas injector inlet disposed coaxially along the axis of rotation of said interior drum, having gas flow regulating means attached to said inlet,

(g) electrically conductive void lling means, located in the lower half of said rotatable interior drum, said void filling means being multiple sized to provide volume filing of the interstices formed between the metal parts to be plated in said interior drum,

(h) a source of argon gas conductively secured to said gas injector inlet,

(i) evacuation means conductively secured to the interior of said exterior drum, having gas pressure regulating means adapted to regulate the gas pressure inside said exterior drum,

(j) a direct current, high voltage power means, having a voltage range of 2000 to 5000 volts, electrically connected to said anode and said cathode for supplying a cathode current density up to 2 milliamperes/cm?, as measured on the cathode surface confronting the anode, and

(k) a low voltage power supply for heating said anode metal plating source to the required metal volatilization temperature.

2. The ion metal plating apparatus of claim 1 in which said electrically conductive void filling means is a multiple sized, spheroid type shaped particulate, having a metal composition equivalent to the plating metal, and having a multiple particle size distribution substantially reducing the free volume between the metal parts being plated.

3. The ion metal plating apparatus of claim 1 in which said electrically conductive void filling means is a multiple sized, spheroid type shaped, particulate ceramic type composition, having a complete exterior coating of the plating metal, and having a multiple particle size distribution substantially reducing the free volume between the metal parts being plated.

4. The ion metal plating apparatus of claim 1 in which said interior drum is concentrically located within said exterior drum, both said interior drum and said exterior drum being disposed along a common horizontal cylindrical axis of symmetry, said interior drum having a rotatable shaft coaxially secured to one end of said interior drum, and said rotatable shaft extending through a gas tight bearing support coaxially secured between adjacent ends of said exterior drum and said interior drum.

5. The ion metal plating apparatus of claim 1 in which said interior drum has a multiplicity of baiiie mixing blades located inside said interior drum, so aligned and secured as to promote mixing and stirring of said metal parts and said electrically conductive void filling means.

6. The process of ion plating in the apparatus of claim 1, comprising:

(a) placing the cleaned, degreased metal parts to be plated in said interior drum, in a volume amount regulated to provide a minimum anode-cathode distance greater than the cathode dark space distance,

(b) filling the interstices between said metal parts with said electrically conductive void filling means,

(c) rotating said interior drum at a rotative speed below which said metal parts and said electrically conductive void filling means are injected into the interior drum volume above the mixing said metal parts and said void filling means,

(d) maintaining an argon gas atmosphere in the exterior drum in the range of l0 to 100 microns Hg pressure,

(e) applying a DC electrical field potential range of 2000 to 5000 volts between said anode and said cathode and applying a cathode current density of 0.1 ma./cm.2 to 1.0 ma./cm.2 of confronting rotating cathode frontal area, for a period of time required t0 clean the metal parts by glow discharge,

(f) then immediately thereafter applying low voltage, not to exceed volts, to the metal plating anode vapor source, to deposit metal plating atoms on said metal parts and said void filling means.

7. The process of claim 6 wherein said plating metal is selected from the group consisting of copper, silver, gold, zinc, cadmium, aluminum, tin, lead, chromium, iron, nickel and platinum.

8. The process of claim 16, in which said bearing support is bathed in a stream of argon gas injected at a higher ambient pressure than the argon gas pressure -in the operating argon gas pressure in the interior of the exterior drum.

References Cited UNITED STATES PATENTS 3,329,601 7/ 1967 Mattox 204--192 3,282,814 1l/l966 Berghaus 204-192 HOWARD S. WILLIAMS, Primary Examiner S. S. KANTER, Assistant Examiner U.S. Cl. X.R. 117-106; 204--298