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Historical Articles

September, 1953 issue of Plating

 


QUESTION BOX

Readers’ questions of general interest


Q. 164. What is more advisable to use for chroming engraving rolls for textile industries—a vertical or horizontal tank?

A. Rolls or rollers may be chromium plated in either the vertical or the horizontal position, and both positions have their advantages and disadvantages. The advantages of vertical plating are that the rolls are held stationary in simple racks’ and that the ends of hollow rollers or shells can be easily sealed to prevent solution from etching the inside. The disadvantages of vertical plating are that the depth of the tank and the headroom above the tank must exceed the length of the rolls; and that continuous mechanical or air agitation of the solution is required to make the temperature of the solution the same at the bottom of the tank as it is at the top, so that the lower ends of the rolls will not plate heavier.

The advantages of horizontal plating are that an ordinary plating tank with’ ordinary headroom can be used and that no equipment is required to agitate the solution. The disadvantage of horizontal plating is that a motor-driven mechanism is required to keep the rolls continuously oscillating or rotating to’ insure uniform plate. Maintenance costs of horizontal plating are higher and more floor space is required. Most new installations for chromium’ plating engraved rolls for the textile industries are designed to plate the rolls in the vertical position.—J. M. HOSDOWICH.

Q. 165. Do you know of an instrument that will measure the thickness of a non-magnetic metallic coating such as molybdenum or copper on a non-metallic such as glass?

A. There is available a gamma radiation type instrument (name of supplier was furnished) which will measure accurately in the range suggested—(0.005 inch differences plotted across a 10-inch scale)—and appears to be of practical use in this problem.— ANON.

Q. 166. What is the most modern method for quantity production, to 24 karat gold flash (electroplate) zinc permanent mold castings?

A. Gold plating of zinc die castings would involve the same pretreatment as chromium plating the same item. The item would be polished, cleaned and then bright copper and bright nickel plated. After adequate rinsing the work is ready for gold plating.
The size of the gold solution will depend on the size of the item and the volume of production. The size of the nickel plating racks are also a factor if the item is to be gold plated without reracking. Since the time of plating for a flash deposit is short (10 to 30 seconds) the tank is quite small (40 to 100 gallons). The gold control is low (3 to 5 dwt per gallon). It is also best to modify the solution by adding small amounts of base metals.

The general plating conditions are 140-160° F, 3 to 5 volts, 10 to 30 seconds and no agitation. Such solutions using constant temperature, constant current density, automatic timers, duration of plate and ampere-hour meters for replenishment will give trouble free constant-color plating. The larger sources of color change are narrowed down to drag in of nickel and organic contamination. Relatively small amounts of nickel will pale out the gold color. Organic contamination will cause a dead or dull appearance and dark streaks. Such thin deposits would be best lacquered if the item is to be handled considerably or exposed to outdoor corrosion.—EDWARD A. PARKER.

Q. 167. We are interested in obtaining details on the immersion plating of steel with cadmium, zinc or tin. We would appreciate any information you could pass along on plating of this type.

A. Immersion tin coatings on steel are covered in the report on a recent (1-11-52) Swiss Patent No. 284,092 issued to Braunschweizer Huttenwerk. The formulae:
30 g/l stannous chloride
15 g/l cream of tartar with the addition of zinc or
0.35 g/l of stannous chloride and 55 g/l sodium hydroxide

The solution is operated at or above boiling, in the latter case in an autoclave. In contact with, e.g., aluminum, coatings of 0.0001-0.0005 mm are obtained.

Another method for obtaining immersion coatings of tin on steel would be through the use of a preliminary copper plate on the steel followed by immersion tinning in the solution of the following composition:

Sodium cyanide.............6-8 oz/gal
Sodium hydroxide..........4-5 oz/ga]
Stannous chloride..........3 1/4-5 oz/gal
Temperature..................90-100° F
Immerse for 30-60 seconds. Rinse in cold then hot water. Repeat if necessary.

Another method of contact which was worked out in England is based on immersion of the steel part in the conventional sodium stannate-caustic soda solution. When a light alloy contact (2S aluminum wire or braid) is made with the steel, plating of the part takes place as the aluminum dissolves in the solution. The reports from England on this method have been encouraging, but one or two people who have tried it here find that the rate of plating is much less than reported. Evidently it requires a bit of experimenting to get the right conditions of temperature and solution concentration.—A. KORBELAK and R. M. MACINTOSH.




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