USE OF ZINC IN MARINE BOILERS.
Zinc has been used in marine boilers for many years, but it was not until the publication in 1880 of the report of the Admiralty committee that the use of zinc became general. It has been used in various ways: 1.—Virgin spelter, as imported in oblong slabs of various sizes. 2.—Cast, or remelted zinc. 3.—Cast zinc buttons, generally made from virgin spelter or new clean zinc trimmings. 4.—Zinc spheres. 5.—Rolled zinc blocks, generally 12 inches by 6 inches, and thicknesses varying from 1⁄4 inch to 11⁄2 inch, generally with a 13⁄16-inch hole in the centre.
It is desirable that close-grained zinc of uniform structure and free from impurities should be used, and rolled zinc appears to meet this want. The wear is entirely confined to the surface. It does not appear to become distorted or broken up. On the contrary, it gradually wastes away till only a slight shred, a sort of skeleton frame work, remains to indicate what it has been.
The primary object in the use of zinc in boilers is the prevention of corrosion, but it has also some effect in reducing the amount of incrustation, and rendering it softer and less adherent.
Table
Showing Amount of Sediment collecting in a steam boiler when evaporating 6,000 gallons per week, of 58,318 grains each.
| When a gallon of feed water evaporated to dryness at 212 degrees Fahrenheit, leaves of solid matter in grains: | The amount of solid matter collecting in boiler per week will be: | |||
|---|---|---|---|---|
| Grains. | Pounds. | Ounces. | ||
| 1 | 13.714 | |||
| 2 | 1 | 11.428 | ||
| 3 | 2 | 9.143 | ||
| 4 | 3 | 6.857 | ||
| 5 | 4 | 4.571 | ||
| 6 | 5 | 2.285 | ||
| 7 | 6 | |||
| 8 | 6 | 13.714 | ||
| 9 | 7 | 11.428 | ||
| 10 | 8 | 9.142 | ||
| 15 | 12 | 13.713 | ||
| 20 | 17 | 2.284 | ||
| 25 | 21 | 6.855 | ||
| 30 | 25 | 11.426 | ||
| 35 | 30 | |||
| 40 | 34 | 4.571 | ||
| 45 | 38 | 9.143 | ||
| 50 | 42 | 13.714 | ||
| 55 | 47 | 2.285 | ||
| 60 | 51 | 6.857 | ||
| 65 | 55 | 11.428 | ||
| 70 | 60 | |||
| 75 | 64 | 4.571 | ||
| 80 | 68 | 9.143 | ||
| 85 | 72 | 13.714 | ||
| 90 | 77 | 2.285 | ||
| 95 | 81 | 6.857 | ||
| 100 | 85 | 11.428 | ||
| 110 | 94 | 4.571 | ||
| 120 | 102 | 13.714 | ||
| 130 | 111 | 6.857 | ||
| 140 | 120 | |||
| 150 | 128 | 9.142 | ||
| 160 | 137 | 2.285 | ||
| 170 | 145 | 11.428 | ||
| 180 | 154 | 4.571 | ||