US3847760A - Method of improving the corrosion protection of decorative chrome plated articles - Google Patents

Abstract

The corrosion protection and surface appearance of a metal or plastic article plated with one or more layers of a conductive metal such as nickel or cobalt and a decorative layer of chromium is improved by contacting the surface of the chromium with sand or other particulate substance with sufficient force to form micropores extending at least part way through the layer of chromium. This is achieved by conveying the particles into contact with the plated surface using suitable vibratory equipment or by suspending the particles in a fluid medium such as a water slurry, a fluidized bed, air stream or the like. The length of the treatment should be sufficient to produce a micropore density of at least 3,000 and preferably at least 40,000 pores per square inch. The individual micropores cannot be visually observed and the treatment does not otherwise alter the bright appearance of the decorative chrome.

Description

United States Patent [191 Malak Nov. 12, 1974 METHOD OF IMPROVING THE CORROSION PROTECTION OF DECORATIVE CHROME PLATED [22] Filed: Jan. 18, 1973 [21] Appl. No.: 324,719

Related US. Application Data [63] Continuation of Ser. No. 150,922, June 8, 1971,

abandoned.

[52] US. Cl 204/35 R, 29/D1G. l2, 29/DIG. 30, 29/DIG. 46, 204/41, 72/54 [51] Int. Cl. C23f 17/00, C23b 5/20 [58] Field of Search 117/9; 29/5272, DIG. 12, 29/DIG. 30, DIG. 46, 33, 25; 72/53, 54;

OTHER PUBLICATIONS Metal Finishing Guidebook, 36th Ed., 1968, Metals & Plastics Publications Inc., pages 140, 142, 150, 152, 158, 159, 160.

Primary ExaminerJohn H. Mack Assistant Examiner-R. L. Andrews Attorney, Agent, or Firm-James -A. Lucas [5 7 ABSTRACT The corrosion protection and surface appearance of a metal or plastic article plated with one or more layers of a conductive metal such as nickel or cobalt and a decorative layer of chromium is improved by contacting the surface of the chromium with sand or other particulate substance with sufficient force to form micropores extending at least part way through the layer of chromium. This is achieved by conveying the particles into contact with the plated surface using suitable vibratory equipment or by suspending the particles in a fluid medium such as a water slurry, a fluidized bed, air stream or the like. The length of the treatment should be sufficient to produce a micropore density of at least 3,000 and preferably at least 40,000 pores per square inch. The individual micropores cannot be visually observed and the treatment does not otherwise alter the bright appearance of the decorative chrome.

7 Claims, No Drawings 1 METHOD OF IMPROVING THE CORROSION PROTECTION OF DECORATIVE CHROME PLATED ARTICLES CROSS REFERENCE TO RELATED APPLICATIONS This application is a-continuation-in-part of U.S. Ser. No. 150,922, filed June 8, 1971 and now abandoned.

BACKGROUND OF THE INVENTION It has recently been discovered that the corrosion protection of a substrate provided by a duplex electrodeposit of chromium over nickel can be improved by developing or creatinga network or pattern of microcracks or micropores in the chromium layer. U.S. Pat. Nos. 3,298,802 and 3,449,223 outline these prior art efforts. The first patent describes a process in which any article receives a continuous bright nickel electrodeposit followed by a thin electrodeposit of metal which contains finely divided non-conductive particles. Thereafter chromium is'electrodeposited over the thin metal layer. The particles in this metal layer impeded the flow ofcurrentduring the electrodeposition of the chromium layer, resulting inthe formation of a microporous chromium electrodeposit. U.S. Pat. No. 3,449,223 describes a process wherein a bright nickel layer containing the non-conductive particles is plated directly onto the substrate thereby eliminating the need for two separate layers.

Another method of improving the corrosion protection of a chromium layer is described in U.S. Pat.- No. 3,563,864 and involves the plating of a nickel layer followed by a chromium layer, one or both ofwhich is de-' posited under high tensile stress. This stress results in the development of a fine network of microcracks in the chromium deposit during or after the electrodeposition of the chromium. These microcrac ks extend through the chromium layer and terminate at the surface of the nickel. This permits the exposed portion of the nickel beneaththese microcracks to undergo preferential or sacrificial corrosion with respect to the substrate thereby enhancing the'protection of the same.

In all of these instances, the microcracks or micropores are formed'by theuse of specially formulated BRIEF DESCRIPTION OF THE INVENTION Among the many objects of the present invention is a method of improving the corrosion protection of an article covered with an electrodeposit of decorative chromium wherein the surface of the chromium is treated, subsequent to the electroplating process, by conveying particles into contact with the chromium surface to form a large number of micropores. These micropores, which can also be referred to as micronicks, extend from the. surface'into the chromium layer. Some terminate within the layer, others go completely through the chromium to the underlying layer of conductive metal and yet others extend a short distance into the underlying layer. This underlying electrodeposited layer may typically be of nickel, nickelcobalt alloys,'or cobalt. Although generally circular when viewed under magnification, some of the micropores may be elongated or oval and others may have the appearance of scratches.

In more detail, finely divided particles of sand or other particulate material are conveyed into contact with the surface of chromium with sufficient energy to form micropores in the chromium layer without penetrating an appreciable distance into the underlying layer of metal. This can be achieved by the use of suitable vibratory equipment, by suspending or dispersing the particles in air, water or other fluid medium or by use of an air nozzle or the like. The intensity of the treatment should be adequate to produce a micropore density of at least3,000 po'res per square inch and preferably between 40,0'00-and 200,000 pores per square inch. These micropores have an average width of less than about 8 microns. When confined within these parameters, the treatment improves the corrosion protection of the electroplatewithout adversely affecting the bright surface finish of the decorative chromium.

PREFERRED EMBODIMENTS or THE INVENTION Thereare several types of vibratoryequipment that aresuitable for-use in the practice of the present invention including tub type vibrators, spindle type vibrators, continuous vibratorsand toroidal type vibrators. Im-

' pi-ngement particles such as" round and jagged sand,

various ceramics, glass beads, walnut shells, silicon carbide, aluminum oxide, and resin bonded media in shapes such as'cones, pyramids and cubes of requisite hardness with or without an abrasive incorporated therein, can be used in these vibrators. ln the use of this type of-equipment, the particulate material is conveyed by the vibratory movement of the equipment into contact with a plated article with sufficient energy to form micropores in'th e chromium layer. Typically, when vibratory'equip'mentis used to simultaneously treat a plurality of plated'articles, contact of the articles with one another duringtr'eatment should be avoided.

and'havingthe ability-to form a micropore in the chro mium layer may be used. Round and jagged sand and glass or plastic beads are typicalexamples. It may be necessary to move or vibrate thearticles in this fluid bed to increasethe impact energy of the particle.

Insteadof using a gas such asair to suspend the particles, water or other liquid medium" can be used. The plated article is immersed in the liquid suspension whereupon the impingement of the particles against the surface of the article results in the formation of the micropores. When using this technique, the impingement can be achieved by any appropriate means such as by conveying the suspension through a nozzle into contact with the plated surface or moving or swirling the article in the suspension.

As another alternative, the particles can be entrained in an airstream, for example by using a pressurized air gun or a cyclone which propels the particles into contact with the plated surface of the article. Particles of sand or solid or hollow glass beads in the size range of 30 to 200 mesh can be used with an air gun operating at a pressure of between 10 and 70 psi. The impingement is carried out for a time period ranging from a few seconds to 2 or 3 minutes with the gun spaced a suitable distance from the surface to develop the micropores without abrading or dulling the decorative surface.

The size, hardness and velocity of the particles are some of the factors which must be considered in determining the technique to be used and the minimum particle energy that is required to form the micropores. For example, smaller particles normally require a higher velocity than larger particles of the same density. Likewise, softer particles will require a higher velocity than harder particles. Jagged particles will require lower kinetic energy than round particles and hard particles will normally be more effective than soft or pliable particles.

The microporosity of the chromium layer is determined by use of the Dubpernell test in which a composite electroplate including the top layer of chromium is made the cathode in an acidic copper sulfate solution, and a current is passed through the solution at a cell potential of about 0.2 0.3 volts. Copper is electrodeposited from the solution into the pores and other imperfections. The pore density and description is observed using a microscope at 100-400 magnification.

In determining the corrosion protection of one or more electrodeposited layers, suitable outdoor exposure and accelerated corrosion tests are used. These include the copper accelerated acetic acid salt spray (CASS) and CORRODKOTE tests.

The CASS test, described in ASTM B-368, is primarily used to rapidly test decorative nickel-chromium coatings on various substrates designed for severe service. ln the test, a plated sample is placed in a fog chamber and is subjected to a continuous atomized spray of a salt solution at 49C for a fixed period of time. The solution is composed of NaCl adjusted to a P 5 9 uu lasstieas h pl i e amined immediately following the test to determine the extent of corrosion, which is recorded as the number of pores per unit area.

The CORRODKOTE test is outlined as ASTM Standard B-380. In this test a slurry containing corrosive salts is applied to a test specimen and is allowed to dry. The specimen is then exposed to high relative humidity for a specific period of time and the degree of corrosion is observed and reported in terms of pore density.

When corrosion tests are made, two types of corrosive attack are generally noted, basis metal corrosion and surface pitting of the coating. With a conventional duplex nickel-chromium coating of l-l .5 mil thickness, 2-4 cycles (40-80 hours) of accelerated corrosion may be necessary to cause pore penetration to the substrate and concomitant pin hole or base metal rusting. In the meantime, surface pits, easily visible to the unaided eye, form on the surface of the nickel. when using the teachings of the present invention however, the time required for basis metal corrosion to occur is at least doubled and very fine non-disfiguring surface pits are formed where pores or imperfections had been -formed in the chromium. Slight staining by the nickel corrosion products will occur but this can be removed by washing.

The following examples illustrate the practice of the present invention.

EXAMPLE I Flate area Recess area (Bottom) Semi Bright Nickel 0.5 mil 0.2 mil Bright Nickel 0.3 mil 0.l mil Chromium l4 millionths 4 millionths These panels were placed in a semi-cylindrical plastic lined tub of a ViBrader Model No. COF9, a commercially available vibrator sold by the Rampe Mfg. Co., Cleveland, Ohio. The tub is mounted on a motor driven eccentric arm which vibrates the tub, giving it a circular motion. The vibration of the tub can be varied between 900 and 1800 orbits per minute. The steel panel placed in the tub moves in a circular motion while embedded in the sand. Table I shows the results obtained by treating the panels at different vibration rates and for different lengths of time.

TABLE I Rust Spot Count PANEL VIBRATION TUMBLING NO. RATE TlME DUBPERNELL 36 hrs. CASS- 52 hrs. CASS- (Orbits/min) (SECONDS) TEST RECESS FLAT SURFACE l 1800 45 Uniform 100 5 Med. Porosity 2 1800 Uniform 100 9 Med. Porosity 3 1800 Uniform Fine 3] 0 Microporosity 4 I800 75 Uniform Fine 49 t) Microporosity 5 900 Slight Mud. 5 Porosity 6 I800 90 Uniform Fine l4 0 Microporosity TABLE I Continued In most instances it was noted that improved corrosion m protection was obtained, particularly on the flat surface, without any dulling of the chromium plate. At the higher vibration rates (l800/min) and greater lengths of time (90 sec), however, some haze was noted in the deposit.

EXAMPLE II Panels simlar to those plated in Example I were electroplated as follows:

Recess Bottom Flat area Semibright Nickel .5 mil .2 mil Bright Nickel .3 mil .1 mil Chromium 5 millionths l7 millionths TABLE II Rust Spot Count I PANEL 48 hrs CASS 60 hrs CASS NO. TREATMENT Recess Flat Recess Flat l2 Silica treated 12 l 50 2 l3 0. 33 l00 I 14 Control 200 I7 200 22 EXAMPLE Ill Additional steel panels of the type used in Examples 1 and II were electroplated to deposit 0.4 mils semibright nickel; 0.2 mils bright nickel and 15 millionths of an inch of chromium on the flat areas with a correspondingly thinner deposit in recess areas. Two panels were treated by immersing each of them for minutes in a fluidized sand-bed. The air pressure beneath the bed was sufficient to impart gentle motion to the sand and cause impingement of the sand against the panels. The treated panels showed fine microporosity and improved corrosion protection as shown in Table Ill below.

0.4/0.2 mils duplex nickel and 0.015 mil chromium w l after which they were suspended vertically in a 3 liter tank containing 2 liters of water and 400 ml of Ottawa sand. The sand was swirled around in the water using a 1/30 HP, 2 bladed mixer. Table IV shows the improvement obtained ona panel treated for 4 minutes and another treated for 9 minutes, compared to 2 untreated panels.

TABLE IV Rust Spot Count PANEL l6 hr. 32 hr. 20 hr.

NO. TREATMENT CASS CASS CORROD- KOTE 19 Sand 4 min. 1 1 l 1 20 Control I 3 14 2I Sand 9 min.- 0 O 0 22 Control 2 3 34 EXAMPLE V A plurality of 4 inch X 6 inch panels each with a rounded recess similar to that of the panels used in Examples I through III were plated with 1 mil of nickel and .015 mil chromium and were subjected in pairs to impingement by particles selected from one of the following groups:

a. 30 mesh jagged edge sand b. 30 mesh solid glass beads c. mesh solid glass beads d. 200 mesh solid glassbeads e. 60 mesh hollow glass beads using an air gun held 12 inches from the panel, operatedat a pressure of 10, 40 or psi and for a period of time of between 20 and 140 seconds.

One panel of each pair was Cass tested for 32 hours and the other was Corrodkote tested for 20 hours. The results are shown in Table V,.with R representing recess and S denoting the flat surface of the panel.

From these results it is readily observed that, applied at a pressure of at least 40 psi, the 200 mesh solid glass beads, give the best overall results without any loss in brightness of the deposit. Although improved proteci n. w e se vhta ns wit .lersstaesebs ds 0 TABLE III Rust S ot Count-CASS Panel 16 hr. 52 hr. ZS hr.

No. Treatment Flat Recess Flat Recess Flat Recess 15 Fluidized Bed 0 1 o 7 o 9 17 Control 2 l8 2 75 4 l00 18 do. 2 9 2 6l 4 mesh sand, this, improvement wasgenerally accompa- EXAMPLE IV I nied by the development of a haze on the surface of the "I TABLE V Although Examples l-Vl demonstrate the improved results obtained on substrates of relatively simple configuration, it should also be noted that this novel process is likewise applicable to complex designs. Articles such as steel bumper guards, steel and zinc die cast CASS RESULTS Blast- 30 Mesh Sand 30 Mesh Solid 60 Mesh Solid 60 Mesh Hollow 200 Mesh Solid Glass Beads ing Glass Beads Glass Beads Glass Beads Press- 20 40 20 40 2O 4O 20 40 20 40 80 I40 ure sec. sec. sec. sec. sec. sec. sec. sec. sec. sec. sec. sec.

10 R 3 R-S R l R l00 R l00 R l00 R l00 R l00 R l00 R l00 R l00 R-l psi -0 5-0 8-1 S-l 3-0 5-0 S-5 5-7 5-0 5-0 -SO S-0 40 R-0 R-4 R l00 R-l2 R-l5 R-S R l00 R l00 R-4 R 100 R 2 psi 5-0 5-0 S-l -l 5-0 5-0 8-0 5-0 5-0 5-0 3-0 70 R-9 R-l2 R l00 R l00 R-4 R-2 R l00 R l00 R- R-ZO R-2 psi 5-0 5-2 5-0 S-4 S-O S-() 5-0 5-2 5-0 5-0 5-0 Con- R S trol CASS l00 22 'W EfizifibibTikiSUfiS M Blast- Mesh Sand 30 Mesh Solid 60 Mesh Solid 60 Mesh Hollow 200 Mesh Solid Glass Beads ing Glass Beads Glass Beads Glass Beads Press- 20 40 20 40 2 40 20 40 20 40 80 M0 ure sec. sec. sec. sec. sec sec. sec. sec. sec. sec. sec. sec.

10 R-2 R-l R-O R- R-30 R- R- R-9 R-lO R-0 R-O R-2 psi 5-0 8-0 8-0 5-0 S 0 8-0 8-0 5-0 S-0 5-0 5-0 5-0 40 R-40 R-2 R-O R l00 R-l R-l R-' R-l R-O R-O R0 psi 8-0 8-0 S-O 8-0 8-0 5-0 8-0 5-0 8-0 8-0 8-0 R-4 R-SO R l00 R l00 R 0 R-O R-4 R-7 R-l R-O R-O psi 5-0 8-0 8-0 8-0 5-0 8-0 5-0 S-O 8-0 8-0 8-0 Con- R S trol CORRODKOTE 2 EXAMPLE Vi headlaniiifiaiiies and piasiiaray 'iiavesn eased by 40 this technique with improved results.

A pair of 4 inch X 6 inch flat steel panels was plated with a cyanide copper flash followed by a 0.8 mil deposition of copper from a bright acid copper bath. A 0.4- mil layer of bright cobalt was electrodeposited on the copper from a bath containing cobalt sulfate, cobalt chloride, boric acid and an acetylenic brightener after which a 0.01 mil layer of chromium was deposited from an electroplating bath containing 250 g/l of chromic acid and 2.5 g/l of sulfate ion.

Silicon carbide (30+l00 mesh US.) was used to treat one of the panels by particle impingement. The silicon carbide was entrained in an air stream and was blown through a nozzle toward the panel. The distance between the nozzle and the panel was l8 inches. Impingement of the panel was carried out for a period of 30 seconds at an impact density of 5 pounds per square foot of treated surface.

The treated and untreated panels were subjected to 8 cycles of CASS (16 hours) and CORRODKOTE (20 hours) testing and were then visually examined. Although neither panel exhibited any corrosion of the. base steel, the untreated panel contained large blisters and pitting with substantial exposure of the underlying bright copper layer. On the treated panel, the blisters were substantially smaller ,in size, resulting in very fine surface attack with uniform exposure of the copper layer.

As previously mentioned, a preferred upper limit on microporosity, as determined by the Dubpernell test, is about 200,000 pores per square inch. This test, however, appears to mask or obscure many of the pores. Thus, the count from this test may be below the actual number of micropores that are developed. In fact, if a treated surface that has not been Dubpernell tested is examined under a microscope, between 1 and 6 pores per lineal mil are observed. Thus, the pore count could be considerably higher than 200,000 per square inch and might be in excess of 1 million per square inch.

There are many modifications that can be made in carrying out the practice of the present invention without departing from the scope thereof. For example, a

suitable friction reducing material may be added to the fluid medium to reduce the energy loss of the particles and increase their efficiency in developing the micropores, thereby reducing treatment time. As another alternative, a rust-preventative may be added with the sand or other particulate material to improve the corrosion resistance of the electroplate or further enhance the protection provided to the substrate. Other methods may be used to propel or convey the particles into contact with the plated article, including mechanical propulsion devices, electrostatic guns and the like. The use of these methods and equipment has several advantages over merely dropping the sand on to the surface ,of the article including the space requirements, efficiency and uniformity of the application andthe ability to treat complex articles containing recesses, projections and multiple angles and curves.

In outdoor exposure tests as well as accelerated corrosion tests, the results clearly indicate that the microporous deposit produced by the teachings of the present invention provides substantially greater protection for the substrate than that given by an untreated deposit. Furthermore, the protection approaches the degree of improvement provided by a microcracked surface of the type previously described and covered by the aforementioned patents.

This treatment is applicable to the protection of any metallic or non-metallic substrate that is covered with a duplex electroplate of chromium over a conductive layer such as nickel, cobalt, brass, copper or bronze. Furthermore, it can be used on decorative chromium layers, typically having a thickness between and 50 millionth of an inch, deposited on the conductive metal layer, with or without additional layers of copper or other metal interposed between the top two layers and the metal or non-metal substrate. Thus, the treatment can be applied to an electroplate of, for example, chromium over bright nickel over semi-bright nickel or chromium over bright nickel over copper. Other variations can be made without departing from the present invention which is covered by the following claims in which I claim:

I claim:

l. The process of developing micropores in a layer of decorative chromium overlying a layer of conductive metal electrodeposited over a metallic or non-metallic article comprising a. placing the article in a bed of solid particulate material, and

b. causing the particles in the bed to.contact the surface of the chromium layer so as to develop at least 3000 micropores per square inch in said layer without causing appreciable visible dulling of the chromium.

2. The process of claim 1 wherein the particles are caused to contact the surface of the chromium layer by rapidly vibrating the bed.

3. The process of claim 2 wherein the particulate material is composed of sand and the bed is vibrated at a rate of at least 900 cycles per minute.

4. The process of claim 1 wherein the micropores have an average width of less than about 8 microns.

5. The process of claim 1 wherein the particles in the bed are caused to contact the surface by fluidizing the bed with a fluidizing medium.

6. The process of claim 5 wherein the fluidizing medium is air.

7. The process of claim 5 wherein the fluidizing medium is a liquid and the particulate material is made into a slurry therewith.

Claims (7)

1. THE PROCESS OF DEVELOPING MICROPORES IN A LAYER OF DECORATIVE CHROMIUM OVERLYING A LAYER OF CONDUCTIVE METAL ELECTRODEPOSITED OVER A METALLIC OR NON-METALLIC ARTICLE COMPRISING A. PLACING THE ARTICLE IN A BED OF SOLID PARTICULATE MATERIAL, AND B. CAUSING THE PARTICLES IN THE BED TO CONTACT THE SURFACE OF THE CHROMIUM LAYER SO AS TO DEVELOP AT LEAST 3000 MICROPORES PER SQUARE INCH IN SAID LAYER WITHOUT CAUSING APPRECIABLE VISIBLE DULLING OF THE CHROMIUM.

2. The process of claim 1 wherein the particles are caused to contact the surface of the chromium layer by rapidly vibrating the bed.

3. The process of claim 2 wherein the particulate material is composed of sand and the bed is vibrated at a rate of at least 900 cycles per minute.

4. The process of claim 1 wherein the micropores have an average width of less than about 8 microns.

5. The process of claim 1 wherein the particles in the bed are caused to contact the surface by fluidizing the bed with a fluidizing medium.

6. The process of claim 5 wherein the fluidizing medium is air.

7. The process of claim 5 wherein the fluidizing medium is a liquid and the particulate material is made into a slurry therewith.