US3317411A

US3317411A - Process of producing a smooth continuous surface

Info

Publication number: US3317411A
Application number: US336617A
Authority: US
Inventors: Calvin O Letendre
Original assignee: Chromium Corp of America
Current assignee: Chromium Corp of America
Priority date: 1964-01-09
Filing date: 1964-01-09
Publication date: 1967-05-02
Anticipated expiration: 1984-05-02
Also published as: DE1496754C3; GB1096948A; FR1419477A; DE1496754A1; DE1496754B2

Description

8 Claims. (Cl. 204- This invention relates to a method of treating surfaces. More specifically it relates to a process for producing level electrodeposits having a high degree of smoothness.

As is well known to those skilled in the art, there are numerous operations which require that the surface of a basis metal be smooth, i.e. must have a reading as measured by a stylus-type instrument of less than about 125 microinches, root mean square, and typically a reading of -32 R.M.S. microinches. Such a smooth surface may also be preferably characterized by the absence of any discontinuities, including pits, flaws, or irregularities, which may be greater than about three times the R.M.S. microinch measurement of the surface.

Typical of the surfaces which must be smooth, i.e. free of imperfections of the type noted, may be rolls, drums,

castings, or cylinders which may be used in the manufacture of paper, felt, plastics, food, pharmaceuticals, photographic material, adhesive compositions, etc. Since the process of this invention may readily be used to treat rolls, reference may for purpose of convenience, be hereinafter made to rolls. These surfaces may not function satisfactorily unless they are smooth. Furthermore, it is particularly necessary that this be the case if the surface of the roll is to be electroplated during manufacture or during rebuilding.

As is well-known, plating with many metals, e.g. chrmium, nickel, cadmium, tin, copper, etc., is particularly characterized by the fact that the deposited plate follows the depressions, i.e. pits, indentations, discontinuities, or other irregularities of the basis metal. Metal surfaces of basis metals, such as cast iron or steel, on which a smooth, level metal plate is desired may contain numerous pits or surface cavities, typically about 0.15 mm. or less in width. When such a basis metal is plated in an electroplating bath, it may be found that a continuous smooth plate cannot be formed, and the metal plate may also have numerous pits or cavities corresponding to those present in the basis metal.

To produce smoother electrodeposited surfaces, processes for plating certain metals, particularly copper and nickel, have been developed in which the electrodeposited layer is smoother or more level than is the underlying layer. Such levelling electroplating processes have been moderately successful in plating nickel and copper. They have had little or no success in plating chromium and other common surface finishes. The need for providing smooth and level electrodeposited surfaces is present in the manufacture of new products, e.g. rolls, as well as in the rebuilding of used products wherein the surface has been worn in service. In these rebuilding operations, the surface is usually reground and then a new surface is deposited.

It is an object of this invention to provide a process for preparing smooth and level electrodeposited surfaces. It is a further object of this invention to provide a process for preparing a level chromium electrodeposited surface. It is still a further object of this invention to provide a smooth level electrodeposited surface which will serve as a basis metal or underlying layer on which another surface may be electrodeposited. Other objects will be apparent to those skilled in the art on inspection of the following description.

In accordance with certain of its aspects, this invention United States Patent 0 provides a process for producing smooth, continuous metal plate on a basis metal having surface cavities having a width of less than about 0.15 mm. which comprises the steps of degassing the basis metal; grit blasting the surface to be plated thereby forming a saturated matte finish surface; applying to said saturated matte finish surface a hardenable polyester resin; hardening said polyester resin thereby forming a hardened polyester resin coating on said saturated matte finish surface; grinding the hardened polyester resin coating and the saturated matte finish surface to a smooth, level surface in which substantially all of the remaining hardened polyester resin is present in cavities having a width of less than about 0.15 mm. and said remaining hardened polyester resin constitutes less than 1% of the area of said smooth, level surface; and electroplating a metal plate over said smooth, level surface thereby forming a smooth, continuous metal plate.

Typically the basis metal upon which the smooth, level plate is desired may be iron or an alloy thereof, say cast iron or steel, and typically it may be an iron or steel roll having pits or cavities which are less than 0.15 mm., say 0.02 mm. in Width.

The surface of the roll or other basis metal which is to be plated may preferably be blasted with fine grit to produce a saturated matte finish in order to provide a surface having good adhesion properties. The grit employed may be silicon carbide, aluminum oxide, or similar materials, and preferably it may be a No. 40-80 grit. Blasting may be done by means of an air stream, centrifugal impeller, or other blasting apparatus. Preferably, the surface may be uniformly blasted to a saturated matte finish, i.e. until further blasting produces no appreciable change in appearance.

The saturated matte finish may, if desired, be produced directly upon the basis metal. In accordance with certain preferred embodiments of this invention, the basis metal may be plated with a thin deposit of chromium prior to the blasting operation. For example chromium may be plated directly over the basis metal, or a copper-nickel undercoat may be employed. The chromium deposit may be plated from an acid bath containing chromic acid and sulfate ion at a temperature of about 25-50 C. and a current density of about 15-50 amperes per square decimeter. Plating may be continued until a deposit of about 0.02-0.1 mm., preferably 0.05 mm. of chromium is obtained, typically in about 120-200 minutes. The so-produced thin chromium deposit may then be lightly ground to remove gross surface imperfections, nodules, etc., and subjected to the blasting operation hereinbefore described to produce thereon a saturated matte finish.

Prior to further treatment, the basis metal may preferably be degassed by heating or other suitable means. Typically, it may be heated to at least 65 C. and preferably about C. for 3-6, say 4 hours, during which time any adsorbed or trapped gases may be liberated. After degassing, the basis metal may be thoroughly cleaned and degassed with carbon tetrachloride, benzene, trichloroethylene, tetrachloroethylene or the like.

After degassing, degreasing, and cleaning, the saturated matte finish may be coated with a hardenable liquid polyester resin. A hardenable polyester resin is one which may be cured to form a hard solid cured resin. The hardenable polyester resin employed may contain a saturated or unsaturated polyester. Saturated polyesters are those prepared from compounds containing no ethylenic unsaturation, e.g. phthalic anhydride, isophthalic acid, hexahyd-rophthalic anhydride, adipic acid, succinic acid, etc. together with ethylene, glycol, propylene glycol, butylene glycol, diethylene glycol, glycerine, etc. Unsaturated polyesters are those which contain residual ethylenic unsaturation.

They are typically prepared by replacing at least a portion of the saturated dibasic acid with an unsaturated dibasic acid, such as maleic acid, maleic anhydride, fumaric acid, citranconic acid, mesaconic acid, etc.

The liquid hardenable polyester resins may be hardened or cured by heating, by use of a catalyst, etc. The unsaturated polyesters, which may be highly preferred, may be cured by free radical initiators, e.g. methyl ethyl ketone peroxide. Preferably, the unsaturated polyester resins may contain an ethylenically unsaturated monomer which may assist the formation of a cured or hardened resin by forming crosslinks. Ethylenically unsaturated monomers are compounds containing polymerizable carbon-to-carbon double bonds. Typical ethylenically unsaturated monomers which may be used to crosslink the unsaturated polyesters include styrene, diallyl phthallate, vinyl toluene, triallyl cyanurate, acrylic esters, acrylonitrile, etc. Styrene may be a preferred monomer.

Illustrative polyesters which may be employed in the practice of this invention may include the following.

Acid

phthallic acid-maleic acid tetrahydrophthallic acid-fumaric acid phthallic acid maleic acid Alcohol ethylene glycol diethylene glycol butylene glycol propylene glycol The polyester resins may preferably be viscous resins which are liquid at a temperature up to about 40 C. and preferably at 2540 C. Typical preferred viscous polyester resins include phthallic acid-maleic acid--ethylene glycol polyesters in styrene solution, preferably containing about 20-40 parts by Weight styrene and 6080 parts by weight polyester. Resins of this type are available under several trademarks, e.g. Laminac. They are preferably hardened or cured by heating them typically to about 50-100 C. in the presence of a free-radical initiator such as methyl ethyl ketone peroxide and, if desired, an accelerator such as cobalt naphthenate.

The hardenable polyester resins may be applied to the saturated matte finish by troweling, doctoring, spreading, wiping, spraying, etc. Preferably, the polyester may be forced into the depressions of the saturated matte finish to obtain good bonding. Preferably, the amount ap plied may be just sufficient to fill all the depressions of the saturated matte finish, typically about 0.25-0.50, say 0.35 grams of polyester per square centimeter of saturated matte finish.

After the polyester resin is applied to the saturated matte finish it may be hardened, typically by heating to about 50-100 C. say 75 C. for about 10-60 say 20 minutes. Curing time may be regulated by the amount and type of initiator or catalyst employed. Typically, the article coated may be allowed to cool slowly for about 12-24 hours after heating to ensure complete hardening of the polyester resin.

After the polyester has been hardened, the polyester coating and the saturated matte surface may be abraded to a smooth level surface. Abrading may be carried out by grinding, sanding or belting. Preferred means for abrading may be grinding, typically with a line grit abrasive, say No. 320 to No. 180 grit aluminium oxide, silicon carbide, etc. set in grinding stones. Grinding is preferably continued until substantially all of the remaining hardened polyester is present in depressions or cavities having a width of less than about 0.15 mm., say 0.02 mm. Preferably the hardened polyster will constitute less than 1% of the surface area of the smooth level surface and metal will constitute at least 99%, say

99.9%, of said surface area. polished to a high luster.

Following the grinding operation, the smooth level surface may be covered with the desired metal plate, typically by electrodepositing the metal plate from a plating bath. The metal plate which is deposited may be nickel, copper, chromium, etc. Preferably it may be chromium. Typically, chromium may be deposited on the smooth level surface by immersion of the piece, as cathode, in a chromic acid plating bath containing chromic acid, say 250 g./l., and sulfate ion, say 2.5 g./l. at a temperature of about 30-50 C. and a current density of about 1520 amperes per square decimeter for about 3 hours. The chromium plate obtained may have a thickness of about 0.07 mm. and may be particularly characterized by its smooth, level, continuous surface substantially free from pits, depressions, and discontinuities.

Practice of this novel invention may be observed from the following illustrative example.

A cast iron roll having dimensions of 150 cm. in length by cm. in diameter was thoroughly cleaned and degreased. Chromium was deposited on the iron basis metal by electroplating from a bath containing 250 g./ 1. chromic acid and 2.5 g./1. sulfate ion at a temperature of 43-49 C. and a current density of 30 amperes per square decimeter for 90 minutes. The final thickness of the deposit was 0.07 mm. Light grinding was employed to remove nodules and other gross imperfections. The roll was then degassed by heating to C. for 12 hours. It was blasted while warm with No. 240 grit aluminum oxide to a saturated matte finish.

While still warm (about 40 C.) the saturated matte finish was coated with a hardenable polyester resin containing 60% polyester prepared from phthalic acid, maleic acid and propylene glycol together with 40% styrene, 0.5% methyl ethyl ketone peroxide as catalyst and 4% cobalt napthenate as promoter. The polyester resin employed is sold under the trademark Boatex No. 10. Application was made by pouring on the resin and smoothing and pressing it with a wide spatula. Application was sufiicient to fill all of the depressions of the saturated matte surface and to form a thin unifrom coating over the roll. This was about 0.3 grams per square centimeter of roll surface. The coated roll was heated to 75 C. for 20 minutes and allowed to cool slowly over about 12 hours thereby hardening the polyester resin. When the resin had fully hardened, the surface of the roll was ground to a smooth level finish with No. 240 grit The surface may then be grinding stones and a water lubricant. During grinding,

the surface was periodically washed with clear water. Grinding was continued until substantially all of the hardened polyester which remained was present in cavities having a width of less than 0.15 mm. (about 0.05 average) and the smooth, level surface was about 1% by area polyester and 99% by area chromium.

Chromium was electrodeposited over the smooth, level surface by immersing the roll, as cathode in a chromium plating solution containing 250 g./l. chromic acid, 2.5 g./l. sulfate ion, at a temperature of 49 C. and a current density of 30 amperes per square decimeter for minutes. The chromium deposit obtained had a thickness of .15 mm. and was smooth, level and remarkably free from pits, cavities or the like. The surface was uniformly covered having no pits, cavities or other discontinuous surface defects. Inspection of this example illustrates the novel, desirable and highly unexpected results obtainable through practice of this invention.

Although this invention has been illustrated by reference to specific examples, numerous changes and modifications thereof which clearly fall within the scope of the invention will be apparent to those skilled in the art.

I claim:

1. The process for producing smooth, continuous metal plate on a basis metal having surface cavities less than about 0.15 mm. in width which comprises the steps of degassing the basis metal; grit blasting the surface to be plated thereby forming a saturated matte finish surface; applying to said saturated matte finish surface a hardenable polyester resin; hardening said polyester resin thereby forming a hardened polyester resin coating on said saturated matte finish surface; grinding the hardened polyester resin coating and the saturated matte finish surface to a smooth, level surface in which substantially all of the remaining hardened polyester resin is present in cavities having a width of less than about 0.15 mm. and said remaining hardened polyester resin constitutes less than 1% of the area of said smooth, level surface; and electroplating a metal plate over said smooth, level surface thereby forming a smooth, continuous metal plate.

2. The process for producing smooth, continuous metal plate as claimed in claim 1 wherein the hardenable polyester resin is ethylenically unsaturated polyester-styrene resin.

3. The process for producing smooth, continuous metal plate as claimed in claim 1 wherein the metal plate electroplated over said smooth, levelsurface is chromium plate.

4. The process for producing smooth, continuous metal plate on a basis metal having surface cavities less than about 0.15 mm. in width which comprises the steps of forming on said basis metal a thin chromium deposit; degassing the basis metal; grit blasting the surface to be plated thereby forming a saturated matte finish surface; applying to said saturated matte finish surface a hardenable polyester resin; hardening said polyester resin thereby forming a hardened polyester resin coating on said saturated matte finish surface; grinding the hardened polyester resin coating and the saturated matte finish surface to a smooth, level surface in which substantially all of the remaining hardened polyester resin is present in cavities having a width of less than about 0.15 mm. and said remaining hardened polyester resin constitutes less than 1% of the area of said smooth, level surface; and electroplating a metal plate over said smooth, level surface thereby forming a smooth, continuous metal plate.

5. The process for producing smooth, continuous plate as claimed in claim 4 wherein the thin chromium deposit has a thickness of 0.050.1 mm.

6. The process for producing smooth, continuous plate as claimed in claim 4 wherein the hardenable polyester resin is an ethylenioally unsaturated polyester-styrene resin.

7. The process for producing smooth, continuous plate as claimed in claim 4 wherein the metal plated electroplated over said smooth, level surface is chromium plate.

8. The process for producing smooth, continuous chrom-ium metal plate on a basis metal having surface cavities less than about 0.15 mm. in width which comprises the steps of forming on said 'basis metal a chromium deposit having a thickness of 0.05-0.1 mm.; degassing the basis metal; grit blasting the surface to be plated thereby forming a saturated matte finish surface; applying to said saturated matte finish surface a hardenable ethylenically unsaturated polyester-styrene resin in amount suificient to fill the depressions of said saturated matte finish surface; heating said hardenable polyester resin to 100 C. thereby hardening said polyester resin and forming a hardened polyester resin coating on said saturated matte finish surface; grinding the hardened polyester resin coating and the saturated matter finish surface to a smooth, level surface in which substantially all of the remaining hardened polyester resin is present in cavities having a width of less than about 0.15 mm. and said remaining hardened polyester resin constitutes less than 1% of the area of said smooth, level surface; and electroplating a chromium metal plate over said smooth, level surface thereby forming a smooth, continous chromium metal plate.

References Cited by the Examiner FOREIGN PATENTS 216,710 8/1958 Australia. 566,776 1/ 1945 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner. VAN SISE, Assistant Examiner.

Claims

1. THE PROCESS FOR PRODUCING SMOOTH, CONTINUOUS METAL PLATE ON A BASIS METAL HAVING SURFACE CAVITIES LESS THAN ABOUT 0.15 IN WIDTH WHICH COMPRISES THE STEPS OF DEGASSING THE BASIS METAL; GRIT BLASTING THE SURFACE TO BE PLATED THEREBY FORMING A SATURATED MATTE FINISH SURFACE; APPLYING TO SAID SATURATED MATTE FINISH SURFACE A HARDENABLE POLYESTER RESIN; HARDENING SAID POLYESTER RESIN THEREBY FORMING A HARDENED POLYESTER RESIN COATING ON SAID SATURATED MATTE FINISH SURFACE; GRINDING THE HARDENED POLYESTER RESIN COATING AND THE SATURATED MATTE FINISH SURFACE TO A SMOOTH, LEVEL SURFACE IN WHICH SUBSTANTIALLY ALL OF THE REMAINING HARDENED POLYESTER RESIN IS PRESENT IN CAVITIES HAVING A WIDTH OF LESS THAN ABOUT 0.15 MM. AND SAID REMAINING HARDENED POLYESTER RESIN CONSTITUTES LESS THAN 1% OF THE AREA OF SAID SMOOTH, LEVEL SURFACE; AND ELECTROPLATING A METAL PLATE OVER SAID SMOOTH, LEVEL SURFACE THEREBY FORMING A SMOOTH, CONTINUOUS METAL PLATE.