US1536904A - Process of casting iron in metal molds - Google Patents

Description

Patented May 5, .1925.

u'm'rao STATES PATENT OFFICE.

DANIEL HELOCHE, OF DETROIT, MICHIGAN, ASSIGNOR .TO GEORGE E. HOLL'EY, OF

' DETROIT, MICHIGAN.

ZPROCESBDT CASTING IRON-IN METAL MOLDS.=

11o Drawing. Application filed May 8,

To all whom it may concern.

. Be it known that I, DANIEL H. Mnnoorm, a citizen of the United ;State's,'re'siding at 8&50 Fourteenth Street, Detroit,- in the county. of Wayne and State of Michigan, have invented certain new and-useful Impi'ovements in Processes of'Casting Iron in etal Molds, ofwhich theifollowing is a' specification.

The object of this invention is to cast gray iron'in metalmoldsbndto obtain a casting which will be as machinable as that cast in sand and at the same time have the advantages inherent in'the die'castinfi.

Cast iron cast in metal molds has eretofore been less machinable than that cast in sand for this-reason, that if the iron, is of such com osition that the carbon is thrown out of so ution by thesilicon, thatis to: say,

if the iron contains 2 to 3%% of silicon then on casting the iron in a metal mold,

not only is the carbon not completely pres' icon itself is precipitated unless the molten iron is .above 2200 F.- The combinationof precipitated silicon and dissolved carbon produces a casting less-machinable combined carbon correspondingly increases,

than anordinary gray iron cast in a sand mold. If the silicon be reduced so asto avoid thisdifliculty then the percentage of because, as is well known in'the casting art, the'less silicon the more combined carbon.

If the cast iron is hotter'than 2200 the tendency to chill deeper is very pronounced. If this tendency is counteracted, as it may I be, by suitable coating and also by highly heating the metal molds, the coatings here- .erosive action of the fluid cast iron.

tofore in use are unstable, both= volatiliz'ing and decomposing so that they fail to ,protect the surface of the metal-mold from'tiie n extreme'cases the cast ironmay even weld A i to the surface of themold, but as cast iron .is very ;diflicu-ltjto .weldthis is an' unusual The formation of hard spotswithin the casting, when using comparatively cold iron (be1ow\2200 F.' ),.is believed to be due to *the -wellknown phenomenon so character isticof' cast iron, namely :its expansion on setting,'wh1ch expansion corresponds somewhat to the 'recalescence polnts of steel.

- Iron is usually poured in zit-permanent mold cipitated as free carbon, but some of the 1922. Serial No. 559,463.

at the lowest temperature consistent with fluidity. By so doing thesemi-volatile coatmgsnow in use oflt'er sufficient protection so that the'molds are. permanent. The moment the iron is poured in these-molds a skin of iron is formed enclosing within a. certain quantlty of fluid 1ron.:' In an ordinary casting having more or less intricate parts a certain part of the ffluid iron is thus tra ped' in pockets. On removing the castingiiom the mold, which necessarily happens in quantit production whilst the casting 'is still re hot (1600 F.), the pressure created by the expansion of these pockets of liquid iron is due entirely to the shell of the-iron and not due to the confining influence of the mold. Nevertheless the pressure is sufficient .to force the carbon into solution and thereby produce hard, spots of white iron which are characteristic of imperfect castings made in permanent metal molds.

, To a degree these hard spots may be eliminated by protracted annealing at 1450' F.- 1550 F., but the annealing period extends for hours, which increases the eost'of the casting.

To overcome these difliculties I have discovered that by using a suitable coating for the mold and maintaining theface of the mold at a temperature corresponding to 'a dull red heat, namely"1100 F., and pouring iron at a white heat, that is to. say above 2200 F., and ejecting the casting from the mold when the outer skin is set I secure cast- .ings in which the silicon remains in solution and of the carbon is uniformly dis-' tributed at what may best' be described as temper carbon, beingsimilar in appearance and properties to the blackheart core of malleable castings, the carbon remaining -in hundred castings, the castings being poured every two minutes or even more frequently, it is necessaryI find to apply a coating of lamp black between each casting operation.

This coating of lamp black is best applied by means of a smoky acetylene flame, although I have used other smoky flames for the same purpose. This smoky flame may be applied automatically or by hand as the case may be.

The molds are heated before the iron is cast therein, and as the castings are successivel poured in themold the surface of the mold rapidlyincreases in temperature, and when the surface of the mold exceeds 1100 F. I admit cooling air within the molds, which are made hollow for this purpose. The surface temperature of the mold desired is between 1000 F. and 1100 F.

The cupola is so operated as to give metal of substantially the following composition:

Total carbon in excess of 3 The silicon should be under 3% but over 4% The manganese should be over .5% and under .7

The sulphur should be less than .07%, although satisfactory castings can be made somewhat in excess of this figure.

Phosphorus should be less than .7

The coke used in the cupola' should be comparatively free from sulphur, preferably under 1%. Very little soft steel scrap is added, 5% being the usual figure in order to maintain the high percentage of carbon which I have found desirable, and the scrap iron is held down to 10%, but the real secret of successful die casting iron is the control of the temperature by means of the blast so that the iron is discharged at above 2500"- F., for the reasons set forth above. The molds in which the iron is cast are made of somewhat harder iron than the iron cast therein.

The reasons for the successful results obtained by using iron white hot (over 2200 F.) are, I believe, as follows :Ordinarily gray cast iron expands when it sets, but if the cast iron be poured into the molds at a temperature greatly in excess of the setting temperature, the molten iron contained within the skin of iron formed on the surface of the casting when ejected from the ermanent mold is hot iron, that is to say 1t is iron at a temperature-above that of the temperature at which iron sets and as it cools to the temperature of freezing it contracts and thereby counteracts the compression stresses set up during the subsequent expansions of the iron.

The resulting castings, therefore, have substantially the same specific gravity as the castings made in sand molds. Whilst specific gravity in itself is of no importance it indicates whether the carbon in the iron is in the free or the combined state and therefore is a guide to the quality of the casting produced. Of course, where there are blow holes within the casting then this castingis apparently less dense, but of course it is otherwise defective and therefore the density is of value as a criterion only to castings free from blow holes. v

The added advantage of pouring extremely hot iron in heated molds is that the iron being more fluid forms a better surface free from pin holes and those other surface imperfections known as cold shots, which latter are characteristic of castin s produced with comparatively cold iron. l3y cold iron, of course, is meant iron which is slightly above its setting point of approximately 2000 F.

What I claim is:

1. The process of casting ray iron in permanent molds, consisting o pouring the metal while above 2200 deg. F. into a permanent mold having a semi-permanent lining of a metallic oxide which is of low thermal conductivity and which vaporizes at a temperature eater than the white heat of the iron cast t erein.

2. The process of casting gray iron in having a coating of carbon in addition to.

the metallic oxide, said carbon being liberated from the coating when the molten metal enters the mold.

3. The process of casting gray iron in permanent molds, consisting of pouring the metal at atemperatur'e greater than 2200 F. into a permanent metal mold having a semi-permanent lining of metallic oxide which is of low thermal conductivity and which does not materiall vaporize at the temperature, 2200 F., o the molten iron cast therein.

4. The process of casting gray iron in permanent molds, consisting of pouring the metal above 2200? F; into a permanent mold having a semi-permanent lining of a metallic oxide which is of lowthermal conductivity and which does not materially vaporize at the temperature of the molten iron cast therein, said lining having a coating of carbon in addition to the said metallic oxide lining, a portion of said carbon being removed from the coating by each casting operation.

5. The process of casting gray iron inpermanent molds, consistin of pouring the metal while above 2200 eg. F. into highly heated metal molds having a semi-permanent lining of a metallic oxide which is of low thermal conductivity and which vaporizes at a temperature greater than the white heat of the iron cast therein.

6. The process of casting gray iron in permanent molds, consisting of pouring the metal while above 2200 deg. F. into highly heated metal molds having a semi-permanent lining of a metallic oxide which is of low thermal conductivity and which vaporizes at a temperature greater than the temperature of the metal cast therein, such lining having a coating of carbon in addition to the metallic oxide, said carbon being liberated from the coating when the molten metal enters the mold.

' 7. The process of casting gray iron in 15 nent lining of stannic oxide, applying a coating of carbon super-imposed on the lining of stannic oxide, renewing the coating of carbon between each casting operation.

8. The process of continuously casting gray iron at a temperature above 2200 F.

into a series of permanent metal molds, maintaining the temperature of the surface of the metal molds between 900 F. and 1200 F., semi-permanently lining the surface of the metal molds with stannic oxide and applying a coating of lamp black between each casting operation.

In testimony whereof I afiix my signature.

DANIEL H. MELOOHE.