Mix together ½ pint of oil of vitriol, 2 ounces of saltpeter, and 3 gallons of clean water. Heat the casting, and plunge it in this solution, keeping it there until cold.
Dayton, O. George E. Hetzler.
Heat to a cherry red, allowing it to lie level in the fire. Then with a pair of cold tongs put on a piece of sulphur a little less than the size hole to be drilled. This will soften the iron entirely through, providing it is not too thick. O. E. Voris.
To successfully case-harden cast iron, the pieces to be hardened should be heated to a red heat, then rolled in a composition of equal parts of prussiate of potash, sal-ammoniac and saltpeter. All pulverized and thoroughly mixed. Every part of the casting must be covered by the composition before plunging (red-hot) into a bath of 2 ounces prussiate of potash and 4 ounces sal-ammoniac to each gallon of cold water. A.
To case-harden cast iron use a pot of suitable size for the piece, packing it in with 2/3 raw bone and 1/3 charcoal ground to about the same size as the bone. Seal the pot cover with fire-clay and place in a furnace and run it about 5 hours. Then take out the work and dip in oil or water.
E. W. Norton.
I have successfully case-hardened cast Iron, using the following receipt: Pulverize and mix together equal weights of saltpeter, prussiate of potash and sal-ammoniac. Make a dipping solution by adding to each quart of cold water 1 ounce prussiate of potash and ½ ounce sal-ammoniac Heat the cast iron pieces till red-hot, roll them in the powder, and then plunge them into the liquid.
Los Angeles. Cal. J. M. Menegus.
To toughen and surface harden small cast iron machine parts, which are subjected to wear, such as small gears, cams, etc., heat to a dull red and quench in a saturated solution of cyanide of potash and water which should be kept as near boiling point as possible. This can be accomplished best by putting the solution in an iron pot near the fire in which the parts are being heated. J. H. V.
To harden cast iron take ½ pint vitriol (sulphuric acid), 1 peck common salt, ½ pound saltpeter, 2 pounds alum, ¼ pound prussiate potash, and ¼ pound cyanide potash, dissolve in 10 gallons of water. Heat iron to a cherry red, dip, repeating until hard enough. W. T. Sears.
The following process can be used for hardening cast iron whether rough or after machining. The casting is first heated to a cherry-red heat; it is then dipped in a bath which consists of a practically anhydrous acid of high heat-conducting power, preferably sulphuric acid of a specific gravity of from 1.8 to 1.9, to which is added a suitable quantity of one or more of the heavy metals or their compounds - such, for example, as arsenic or the like. The preferable ingredients of the bath are sulphuric acid of a specific gravity of approximately 1.84 and red arsenic in the proportions of ¾ pound of red arsenic crystals to 1 gallon of sulphuric acid. The castings may be either suddenly dipped in the aforementioned mixture, and then taken out and cooled in water, or they may be left in the bath until cool. In preparing the bath, when sulphuric acid and red arsenic are used, better results are obtained when the crystals are added to the sulphuric acid and the bath is allowed to stand for about a week before using. O. G.
Iron castings that are too hard to machine or which have hard spots destructive to tools may be nicely annealed by packing closely in covered cast iron boxes with black manganese, and heating to a temperature of 1,500 or 1,600 degrees P., until thoroughly heated through. A large box packed in this manner with a closely-fitted cover luted with fire-clay must be heated for several hours to raise the interior to the annealing temperature. To be sure of getting the interior heated properly, a number of witness wires should be placed in the box, projecting through the cover where they can be conveniently grasped with tongs and pulled out one at a time to show how far the heat has progressed. When the interior has reached a bright red heat the box should be hauled out and covered with ashes so that it will cool slowly. It is claimed that hard spots in gray iron castings can be softened with black manganese by applying the manganese and heating to a dull red, using a blow-torch or any other convenient means of heating. M. E. Canek.