Plant Engineering lllemos Barrel line i s an improvement over basket operations in forming black oxide on steel MEMO:
from Herman Gardner
Chief Chemist, Colson Corp.
plating work includes zinc and 0 cadmium, copper, nickel, and chrome plating applied to steel surUR
faces. The chemical treatments include black oxide coating of steel, black
We thought our volume of black oxide work justified an investigation of a barrel line similar to a plating line. Plastic barrels are generally used in plating, but we desired steel barrels, because hot caustic soda was used in the process. KOstandard bar-
steel surfaces consisted of transferring baskets loaded with work from tank to rels of this kind for this particular proctank until the work was completed. ess were available on the market, so Seither the work nor the solution was we had to design our own barrels, with agitated or moved; a nonuniform careful consideration of the process c.owrnge 01 the >tecl lxirts treatcil \CIS tile i,esult. If t!ie b:iakct \Y:IS Elled \\-it11 too i i i u i h n m k . :I portion \voulcl not re:ict witi: tlie 1il:irliening solution. and a repeat trestinent \vas net.essarJ.. Basket Operations :11so rrsultrtl i n nccumulation of d t in p:irts co~it:~iiiiiig folds and reresses, with sitbxquent ' %.&s@ corrosion. 1
November 1955
steps themselves and the problems that might arise. The salts required for producing a black oxide coating on steel are usually a mixture of caustic soda, sodium nitrite, and sodium nitrate. Operating temperatures are around 300" F. An important criterion for producing uniform work of high quality is proper control of temperatures of the two tanks containing the blackening salts. Preferably the solutions should be automatically maintained a t preset temperatures and the addition of the salts or water should be regulated so that the solution will boil a t those temperatures. This control can be by a bulk-type temperature-indicating controller operating a motorized valve in the water line through a relay. As the solution evaporates and becomes more concentrated, the boiling point rises above control temperature, and the controller signal opens a motorized water-inlet valve, until sufficient water has been added to lower the boiling point. When water level falls below a fixed height, salts are added and the automatic contioller takes care of the added water until the solution l e d is back to normal. Main elements in the formation of the black oxide coating are thoroughly cleaning the work, preferably using a two-tank system with different concentration of blackening salts a t two different automatically controlled temperatures, and finishing mith a rustinhibiting coating. These elements are present whatever system of handling is used. The barrel we designed is hexagonshaped, 273/8 inches long and 15 inches
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INDUSTRIAL AND ENGINEERING CHEMISTRY
101 A
Plant Engineering Memos between the sides of the hexagon, with a volume of 3.1 cubic feet. A 1/2-inch plate serves as the closure a t the drive end of the barrel, with a 1-inch plate a t the other end. The added weight of this thick plate balances the driving units. Stub shafts supporting the barrel a t both ends project sufficiently to fit smoothly into the channel guides welded to the tank. The barrel is hung by heavy steel hanger brackets a t both ends, with a projection of tubing on these brackets acting as a lug to engage the channel guide and align the barrel in the guide. A steel rod welded a t both ends of these hanger brackets aids in placing the barrel in the channel guides and a hoist hook is welded to a horizontal steel bar of the hanger bracket. A large sprocket bolted to the barrel is driven by a sprocket chain connected to a small drive sprocket. This small sprocket connects by a steel shaft riding on a bronze sleeve bearing with a spur gear driven by the reductor spur gear. The drive unit is set to rotate the barrel a t 2.5 r.p.m., a speed which enables excellent coverage of parts with-
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out nicking. The channel guides are made of heavy cold-rolled steel plate welded to the tank, so as to be able to carry the heavy weight of barrel and load, and the barrel shaft rides on a 2-inch pillow block bolted to the guides.
I , YOUR PROCESS DEMANDS
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See Our Booth #I 10, Chemical Exposition For further information, circle numbers 102 A-1, 102 A-2, 102 A-3 on Readers' Service Card, page 111 A
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We decided, after analyzing our requirements, that six steel unlined tanks 24 X 24 X 36 inches (12 cubic feet) and five barrels would ensure continuous operation and more than take care of our present needs. I n operation, work is placed in the open barrel to seven-eighths full. An electric chain hoist picks up the barrel and transfers it to the first, or cleaner tank, which is steam heated. As soon as contact is made through the spur gears, the barrel begins to rotate. The schedule is: Tanh Cleaner Water rinse Pretreat blackening Main blackening Co1.d water rinse Rust-inhibiting coating
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"
Salt Concn., Wt./Gal. Zounces h-one
Temp., F. 180 160
Time, Min. 10 5
7.,5 It..
290
10
10 lb.
305
15
Sone
Room
...
Room
2-3
...
The cover of the barrel is then removed and the work dumped into a handling unit for delivery to the next station. Uniform black coverage is excellent, and size of work is limited only by barrel size. In addition to upgrading costing quality, we have eliminated a labor bottleneck and have substantially reduced costs. The basket operation required two shifts 5 days per week; the barrel line requires only two 8-hour shifts to complete the same amount of work. Cost of blackening has been reduced from 45 to 66% on various representative parts. Elyria, Ohio August 18, 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 11
