Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/12—Electroplating: Baths therefor from solutions of nickel or cobalt
  • C25D3/14—Electroplating: Baths therefor from solutions of nickel or cobalt from baths containing acetylenic or heterocyclic compounds
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/10—Electroplating with more than one layer of the same or of different metals
  • C25D5/12—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium
  • C25D5/14—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium two or more layers being of nickel or chromium, e.g. duplex or triplex layers

Definitions

• Plates of soft chromium provide excellent corrosion resistance and in addition provide attractive surfaces that lend themselves to polishing processes that yield scratchfree and fissureless coatings possessing high lustre.
• Soft chromium plating is the deposition of chromium upon metal substrates (e.g. cast iron) in a coating having a hardness ranging from 50 to 800 DPH Vickers hardness units when measured by the Vickers Diamond-Point Hardness Tester under a 500 gram load. Such hardness has been recognized by industry as yielding scratchless finishes of high lustre by conventional polishing processes.
• the soft chromium as deposited from the plating solutions is matte-gray.
• Another object of this invention is to provide a process and electrolytic bath for the purposes described which are economical to use, easy to control, simple to prepare and which contains relatively inexpensive ingredients.
• the hard-chromium intermediate layers are deposited at temperatures in the range 45 to C. from conventional baths for deposition of hard chromium (i.e. containing in excess of, say, 1% free sulfate ion and about 250 grams CrO /liter). It is believed that the higher bath temperatures required for the deposition of the hard chromium causes activation results in the excellent adherence of the electrolytically 3 deposited hard chromium which can have a Vickers hardness of 1000 to 1100 DPH units. Under the operating temperatures for the deposition of soft chromium according to this invention, it appears that base metals such as cast iron are insufficiently activated to provide proper adherence of the deposited layer.
• the hard-chromium layer can be deposited from electrolytes either containing fluosilicic acid or free from fluosilicic acid as described by P. Morisset et al. in Hard and Decorative Chromium Plating, Centre dInformation du Chrome Dur, 1961, Paris VIII. When the electrolyte does not contain this acid the deposited hard-chromium layer should be subjected either to a pickling in sulfuric acid or to anodization in chromic acid. Where the electrolyte does contain the fluosilicic acid the soft chromium layer can be directly deposited upon the hard chromium layer when the body emerges from the hard-chromium plating bath. Utilizing such an intermediate hard chromium layer permits deposition of soft chromium upon the cast iron base metal in layers of more than 60p. in thickness with excellent adhesion of the layers to base metal.
• the casting is immersed in a soft-chromium plating bath constituted of an alkali-free aqueous solution of 318 grams/liter CrO 32.7 grams/liter C12O3, and 0.67% free sulfate ion, and electrodeposition carried out at a current density of 71.5 amperes/decimeter against a lead electrode to 10 volts) at a temperature of C.
• a current efficiency in excess of about 50% to yield a soft-chromium coating of a thickness of about 25 microns.
• the coating was free from fissures and had a hardness (Vickers DPH) of about 600.
• the coating was rinsed and polished readily by conventional techniques to a high luster. It was found to be strongly adherent, uniform and wear-resistant. When the temperature was reduced to 20 C., the current (plating) efficiency was about 57% although lower temperatures rendered the process uneconomical because of increased plating time and difficulties of controlling the uniformity of plating. A temperature of 56 C. gave a reduced plating efficiency of only 17%.
• a method of chromium-plating a cast-iron body comprising the steps of:
• step (c) depositing a layer of soft chromium upon the treated hard-chromium layer of step (b) at a current density of to amperes per dm. in an alkalifree aqueous electrolyte containing 0.45 to 0.75% free-sulfate ion and 200 to 400 g. of chromium trioxide per liter at a temperature between 20 C. and 40 C. to a thickness of at least 25 microns; and
• step (d) polishing the soft chromium layer deposited in step (c).
• said soft chromium layer has a thickness of at least 60 microns, a hardness of about 600 DPH on the Vickers scale, the soft chromium plating of step (0) being carried out at a temperature of 25 C. to 35 C.
• a method of chromium-plating a cast-iron body comprising the steps of:
• step (c) polishing the soft chromium layer deposited in step (b).
• step (b) 4. The method defined in claim 3 wherein said soft chromium layer has a thickness of at least 60 microns, a hardness of about 600 DPH on the Vickers scale, the soft chromium plating of step (b) being carried out at a temperature of 25 C. to 35 C.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Electroplating Methods And Accessories (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=7553395

Family Applications (1)

Country Status (5)

Cited By (8)

Citations (5)

• 1964
  • 1964-10-28 DE DE19641521040 patent/DE1521040B2/de active Pending
• 1965
  • 1965-03-10 CH CH332565A patent/CH441920A/de unknown
  • 1965-03-24 AT AT266365A patent/AT258074B/de active
  • 1965-07-23 US US475044A patent/US3421986A/en not_active Expired - Lifetime
  • 1965-07-28 GB GB32248/65A patent/GB1086880A/en not_active Expired

Patent Citations (5)

Also Published As

Similar Documents