There are two general ways for testing malleable cast iron: (1) by so-called shop tests; and (2) by laboratory tests of bars cast from every heat and annealed with the castings.
The usual shop tests consist of bending occasional castings, as well as of twisting the longer pieces, and also of the making and breaking of test wedges. These wedges are about 6 inches long and 1 inch square for 3 inches of their total length, then tapering down in thickness to nothing for the last 3 inches, but keeping the full inch width; this gives thick iron as well as thin on the same piece. When the test wedges come from the annealing, they should be broken on an anvil by striking them with short light blows, the object being to see how much the thin end of the wedge can be bent before the piece breaks, after which, by holding the two parts together and observing the bend, a very fair idea of the quality of the castings these wedges represent, may be had.
The regulation test bars are rectangular in form and are of two sizes: the 1-inch square bar to represent castings \ inch thick and over; while a 1- by 1/2-inch section bar cares for the lighter castings.
Malleable-iron castings may be made by the open-hearth, air-furnace, or cupola process. Cupola iron, however, is not recommended for heavy or important castings.
Castings for which physical requirements are specified shall not contain over 0.06 per cent of sulphur or over 0.225 per cent of phosphorus.
This bar shall be 1 inch square and 14 inches long, cast without chills and left perfectly free in the mold. Three bars shall be cast in one mold, heavy risers insuring sound bars.
Where the full heat goes into the castings, which are subject to specification, one mold shall be poured 2 minutes after tapping into the first ladle, and another mold shall be poured from the last iron of the heat.
Molds shall be suitably stamped to insure identification of the bars, the bars being annealed with the castings. Where only a partial heat is required for the work in hand, one mold shall be cast from the first ladle used and another after the required iron has been tapped.
(2) Of the three test bars from the two molds required for each heat, one shall be tested for tensile strength and elongation, the other for transverse strength and deflection. The other remaining bar is reserved for either tensile or transverse test, in case of failure of the other two bars to come up to requirements. The halves of the bars broken transversely may also be used for the tensile test.
(3) Failure to reach the required limit for the tensile test with elongation, as also for the transverse test with deflection, on the part of at least one test, rejects the castings from that heat.
The tensile strength of a standard test bar for casting under specification shall not be less than 40,000 pounds per square inch. The elongation measured in 2 inches shall not be less than 2 1/2 per cent.
The transverse strength of a standard test bar on supports 12 inches apart, pressure being applied at the center, shall not be less than 3,000 pounds with deflection at least 1/2 inch.
Castings of special design or special importance may be provided with suitable test lugs at the option of the inspector. At his request, at least one of these lugs shall be left on the casting for his inspection.
(1) Malleable castings shall neither be over- nor under-annealed. They must have received their full heat in the oven at least 60 hours after reaching that temperature.
(2) The saggers shall not be dumped until the contents shall be at least black hot.
Castings shall be true to pattern, free from blemishes, scale, or shrinkage cracks. A variation of 1/16 inch per foot shall be permissible. Founders shall not be held responsible for defects due to irregular cross-sections and unevenly distributed metal.
The inspector representing the purchaser shall have all reasonable facilities given him by the founder to satisfy him that the finished material is furnished in accordance with these specifications. All tests and inspections shall be made prior to shipment.
In general it may be said it is not necessary to have a metal very high in tensile strength but rather one which has high transverse strength and good deflection. This means a soft ductile metal which adjusts itself to conditions more readily than a stiff strong product, for it is very hard to produce a strong and at the same time soft material, especially in the foundry making only the lighter grades of castings.