Guest Editorial -For Plateworld.com
Don Baudrand, Don Baudrand Consulting, e-mail:firstname.lastname@example.org
Quality plating is important all the time. In today’s market, quality is critical to keeping and landing new customers. High quality combined with economical operation is essential to survival. Understanding the best use of nickel plating; deposit distribution, control of the chemistry and addition agents, anodes and racking can reduce the cost and produce the highest quality.
Design for plating is important. Although you rarely have input into the design of parts to be plated, knowledge of how plate distribution is effected by the design factors can be helpful in working with a customer. I strongly recommend using the “Quality Metal Finishing Guides” published by MFSA. These guides can be offered to your customers a guide lines in obtaining the best quality plating by proper attention to the design factors. ASTM standard B-507 is another essential source of information for the customer and for you. These books deal with “significant surfaces’, Design for plating, design for mechanical finishing, design for racking, draining and air entrapment, and design for good distribution of electrodeposits. The Zinc Institute puts out a book on “design features that influence electroplatability.”
Design considerations Mechanical finishing:
“Avoid blind holes, recesses and joint crevices which can retain polishing compounds and metal debris.
Avoid intricate surface patterns which will be blurred in polishing.
Significant surfaces should be exterior, reachable by ordinary polishing wheels or belts.
Avoid sharp edges and protrusions which cause excessive consumption of wheels or belts.”
Design considerations for plating
See table I
The proper design of parts to be plated along with any necessary special racking considerations, bi polar anodes, auxiliary anodes, proper anode spacing, and using the best current density for the best current distribution, will result in using less nickel. Thus reducing costs by plating nickel onto the areas where it is most needed and minimizing nickel thickness on edges, and other potential high current density areas of the parts. In addition, corrosion protection is enhanced.
Throwing power is defined as the ability to deposit significant thickness in recessed areas. Covering power is the ability to plate any metal in recessed areas. Note the difference between these terms.
How to increase throwing power
Reduce the current density
Note. A high nickel chloride, low nickel sulfate solution increases conductivity and can be operated al lower temperatures than the standard Watts solution. (saves heating costs and provides better throwing power) Note also that not all brightener systems will tolerate the high chloride)
Nickel solutions Watts Hi chloride
Nickel sulfate 40 oz/gal 15 oz/gal
Nickel chloride 8 “ 25 “
Boric acid 6 “ 6 “
Nickel is not sacrificial to steel. Since most bright nickel is plated onto steel, there must be either a totally non- porous deposit, or some other means of protection the steel from corrosion. The use of two nickel layers can provide excellent corrosion protection provided that it is done with the right kind of nickel deposits.
1. Plating a layer of a sulfur free semi bright first layer that is about 2/3 of the total thickness, and 1/3 bright nickel has significantly better corrosion protection that the same total thickness of a single layer of bright nickel.
2. To further enhance the corrosion protection, plating a layer of micro discontinuous chrome provides an additional significant increase in corrosion protection.
3. Three layers of nickel: first a layer of semi-bright nickel is plated as in #1, followed by a thin layer of high sulfur bright nickel, followed by a layer of ordinary bright nickel will result in an even further increase in corrosion protection. This increase is also enhanced by using micro discontinuous chrome as the final layer.
Note: Chromium plated from a trivalent chrome solution is inherently microdiscontinuous up to 0.6 micrometers, then it becomes microcracked. Trivalent chrome is less sensitive to burns, white wash, poor throw, and sensitivity to interruptions. Waste treatment is somewhat simplified. Trivalent chrome is not classified a carcinogen, and it is easier to meet emission requirements. The disadvantage is that the trichrome deposit does not look like deposits from hexavalent chrome. The color is slightly different.
Nickel toxicity and health hazards
Nickel is found everywhere in nature. It is the 24th most abundant element in the earth’s crust. In 1962, the estimated dietary intake of nickel in the U. S. ranged from 300-600 micrograms per day. Nickel is an essential nutrient in certain animals and is required at low levels to maintain human life. Nickel is found in many different chemical forms in nature. Some Nickel compounds are toxic, and some are carcinogenic according to some of the Government agencies. The most common health effect of nickel exposure is “nickel itch,” an allergic reaction by some people to exposure to nickel on the skin. Nickel dust is considered to cause lung and nasal cancer. Nickel carbonly is very toxic.
NOISH and ACGHI classify all nickel compounds as carcinogenic.
OSHA dos not list any nickel compounds as carcinogenic.
USEPA regulates nickel dust, nickel subsulfide and nickel carbonyl as human carcinogens but does not regulate the soluble forms of nickel ac carcinogenic. Some offices regard nickel to be carcinogenic by all routs of exposure whereas other offices regulate soluble nickel as non carcinogenic by ingestion. Drinking water is regulated based on preventing noncarcinogenic effects.
Exposure amounts: USEPA (one in a million risk): 0,002Micrograms per cubic meter for nickel subsulfide and 0.004 ug/m3 for nickel dust.
NIOSH REL for elemental nickel is 15 micrograms/square meter. (REL =Recommended exposure limits)
OSHA PEL is 0,1 milligrams per square meter. (PEL= permissible exposure limits)
Even the various government agencies do not agree.
OSHA = Occupational Safety and Health Administration
NIOSH= National Institute for Safety and Health
ACGIH= American Conference of Governmental Industrial Hygienists.
USEPA= United States Environmental Protection Agency
Dealing with risks to workers
Good ventilation, safety glasses with side shields ( soluble nickel compounds in the eye is very irritating) Protective gloves, boots, possibly face shields for those who have been sensitized and developed an allergy to nickel.
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