US2132276A - Metal mold - Google Patents

Description

Patented Oct. 4, 1938 UNITED STATES PATENT OFFICE to The American Brass Company,

Conm, a corporation Waterbury, of Connecticut No Drawing. Application December 29, 1937, I

Serial No. 182,304.

2 Claims.

This invention relates to cast iron molds for casting various metals into bars, slabs, ingots, etc. or any desired shapes, and has for an object to provide cast iron molds in which the tendency 5 to develop cracks in the surfaces of the mold cavity caused by contact with the molten metal is greatly reduced, thus prolonging the life of the mold and producing better castings for longer periods with the same mold.

In cast iron molds for casting various metals, including the non-ferrous metals and alloys, such for example as copper, nickel, aluminum, zinc and their alloys, steel, cast iron and other metals or alloys, the molds usually fail by what are called heat cracks or checks. These are cracks which form in the surface of the mold cavity. Apparently they are due to the hot metal poured into the mold causing sudden and uneven expansion and contraction of the metal of the mold, particularly on the surfaces of the mold cavity, which causes the cracks in these surfaces. The mold must be discarded when these cracks on the surfaces of the cavity get too numerous or when they open up and become sufiiciently large to make fins on the casting to give a rough surface. to the casting, to cause sticking or hanging of the casting in the mold thus making it difficult to remove it from the mold, and causes cracking of the castmg.

I have found that the addition of a suitable amount of copper to the cast iron mixture from which the molds are made is beneficial to the life of the molds used in the casting of metals. The increase in life has been found from tests in actual practice to be 45 percent or more over similar molds not containing the copper, the range of copper being from about 0.25 percent to about 6 percent, although the preferred amount of copper is about 1.50 percent. Cast iron is composed principally of iron and carbon, the carbon being mostly in the form of graphite. The copper in the cast iron has a refining influence on the graphite. The copper does not reduce the graphite content but makes it come out in finer flakes and more evenly distributed or dispersed throughout the iron. It is thought it is this effect of the copper which retards the formation of the fine surface or heat cracks, and it also retards their development and growth after they start to form in the surface. of the mold in contact with the casting. The copper hardens the iron slightly but does not interfere with the machinability.

The cast iron ordinarily used for molds has an average composition of about 3.30 percent for the total carbon, of which about percent is combined carbon and 2.70 percent is graphite. It also contains about 0.70 percent manganese with 5 silicon about 1.50 percent, and balance principally iron, and with such cast iron I prefer to use about 1.50 percent copper, although the copper may be varied within the range specified. These proportions of the elements may vary. The composition 10 ranges that would ordinarily be used for molds is substantially as follows:

Per cent Total carbon 2.50 to 3.80 Combined carbon 0.40 to 0.80 16 Graphite 2. 10 to 3.00 Manganese 0. 40 to 1.00 Silicon 1.00 to 2.00 Phosphorus .25 max. Sulphur .08 max. 20 Copper 0. 25 to 6.00

With balance iron.

These ranges, however, are What are ordinarily used, but I am not confined thereto as other composition ranges of the cast iron may be used if found desirable for particular metals. Special cast irons containing additional elements such as nickel, chromium, molybdenum or vanadium are sometimes used for making molds. Copper may also be added to these alloy cast irons for the purpose of improving mold life in a manner similar to the above.

Having thus set forth the tion, what I claim is: v 1. A mold for casting metals characterized by improved resistance to formation of small cracks in the mold surface, comprising cast iron containing from 2.50% to 3.80% total carbon of which from 0.40% to 0.80% is combined carbon and 2.10% to 3.00% is graphite, 0.25% to 6% copper, and silicon and manganese in the usual amounts.

2 A mold for casting metals characterized by improved resistance to formation of small cracks in the mold surface, comprising cast iron con,- taining about 3.30% total carbon of which about 0.60% is combined carbon and 2.70% is graphite, silicon and manganese in usual amounts, and about 1.50% copper.

SAMUEL C. SPALDING.

nature of my inven-