US2514793A - Foundry casting - Google Patents

Description

-Pat nted Jul 11, 11150v FOUNDRY CASTING 1111:9111}. :Pletsch and Michael Bock, II, Conneaut,

Ohio, assignors to Exomet Incorporated, Conneaut, Ohio, a corporation of Ohio No Drawing. Application July 19, 1949,

Serial No. 105,673 F 3 Claims. (Cl. 22-215) fested in a material reduction in the riser metal, by better feeding of the casting and better shrinkage control, and by the effective elimination of pipe notwithstanding'the use of short risers. By

"steel we mean carbon and alloy steels, and by exothermic material we mean a mixture of i powdered or finely divided metal oxide including iron oxide, with or without an oxide of an alloy of the casting,-and aluminum, preferably in stoichiometric proportions, with or without added slag-forming constituents.

Extensive investigations have confirmed our conception of certain interrelated conditions and operations which must be observed in the casting of steel with short risers to feed the casting properly and also to prevent pipe. Our invention is advantageously applicable to the production of steel castings having a minimum diameter of three inches. We have discovered an important relationship between the height of the riser and its cross-sectional area as a prerequisite of the use of exothermic material in the riser. The riser height should be from to /2 the riser diameter. We have also discovered a critical relationship between the temperature of the metal in the riser, the timeto apply the exothermic material, and the amount applied. When the metal in the riser has cooled to incipient solidification, i. e., has cooled to a state where the top (exposed surface) of the riser is between a mushy consistency and a solid thin skin, the exothermic material is dumped into the riser. The exothermic material ignites at about 2300 F. creating intense heat (over 4000 F.) remelting the metal in the riser followed by a boiling action. A slag forms on top which insulates and retains heat, thus keeping the top surface of the riser metal hotter than any other portion of the casting, eliminating the pipe.

The following table illustrates conditions and operations which should be observed in a preferred practice of our invention, especially-"with reference to castings having a high feed demand:

Waiting Time' Riser Dl- Lbs. of Ex- Approx. Ht. 'ameter othermic to Pour Normal Cast- Normal Cast- Castings Inches Material Riser, Inches ings Approx. ings Approx. Approx. 0.03 Min. 0.04 Min. 1 0.05 Min.

Basis Basis Basis 6 2 95 it 1 7 13% 2% M 1 1% 8 17% 2% 1 1% 2 9 211-6 3 1% 2 2% 10 27 3% 2 3 3% 11 32 4 2% 3% 4% 12 37 2% 4 65 13 43 4% 3 5 6% i4 60 3 6 7 5 15 57 5 4 7 8% Waiting Time Riser Di- Lbs. of Ex- Approx. Ht.

ameter othermic to Pour Normal Cast- Normal Cast- Castings Inches Material Riser, Inches ings Approx. ings Approx. Approx. 0.03 Min. 0.04 Min. 0.05 Min.

. Basis Basis Basis The foregoing table gives amounts of exothermic material based upon stoichiometric proportions of F8304 and aluminum, and slag-forming materials in addition to the A1203 slag formed in the reaction, such as CaO, SiOz, CaFz, aluminum silicates or glass. We prefer to include such an amount of slag-forming material in the exothermic material that from 15% to 18% more slag will form than can result from the A120: and the amount of exothermic material in the table include such amounts of added slag-forming materials. We have found that the exothermic material must be added in such a minimum amount that it will have a height of at least 3%, inches in the riser. We have found no technological significance to amounts added much in excess of the minimum except in cases of very massive castings Where 4% inches are required for optimum results. Excessive amounts merel result in a waste of expensive exothermic material.

The waiting time expressed in minutes in the table is a close approximation of the actual time which varies some due to differences in the temperature of the metal poured into the mold. As stated above, the application of exothermic material should be delayed until incipient solidification occurs in the riser which can be determined conveniently by feeling with a bar or by visual inspection.

The exothermic material results in an exothermic reaction producing about 0.46 lb. of metal and 0.54 lb. of slag per pound of material. The slag produced has a high aluminum oxide (A1203) content and therefore has a high heat content and low conductivity and thus acts as a heat reservoir as well as an insulating top for the riser. The metal produced as a result of the exothermic reaction of the aforementioned exothermic material is of the usual low carbon steel composition. This metal remains on the top of the riser due to its highly superheated condition. Only when the alloy composition of the casting is appreciably high, such as in 18-8 stainless steel, where a difference in composition in the risers will cause much undue confusion during subsequent remelting, are special alloy exo thermic materials used.

It has been found that, by pouring the risers short, the heat of the reaction is produced near the junction of the riser and the casting where it is desired to have the feeding take place and to prevent pipe. Moreover, the most economical results are obtained in regard to metal yield. As the temperature produced in the risers is very high, the effective feeding area of a given size riser is increased from normal conditions. In addition, we have found that risers can often be reduced in diameter. This method of pouring risers short and then adding the exothermic material, as shown in the table, will produce solid risers and is followed when open conventional risers are used.

The normal gating and risering practices formerly used maybe followed in practicing our invention subject, however, to pouring the castings short, depending on the diameter of the risers. One pound of exothermic material will save from 6 to 14 pounds of steel, depending on the design of the casting, gating, risering, etc. Of course, enough steel must be poured into the riser to take care of the shrinkage in the casting, but this will normally be more than amply provided for, as shown by the figures in the table. Care should be taken when pouring castings with risers at different levels, as the pouring short must be governed by the riser on the high part of the casting. In many cases exothermic material has been used on but one large riser in the casting, leaving the smaller risers untreated, with very successful results. Should a thin layer of an insulating or mildly exothermic type of pipe'eliminator be used immediately after the riser is poured, the skin formation on the top of the riser will be delayed and this will increase the waiting times considerably from those shown in the table as calculated on the 0.03, 0.04 and 0.05 minutes of waiting time per square inch of cross-section of area basis, and this practice is advisable on very large massive castings.

The table shows the approximate amount of exothermic material to use for various size risers ranging from 3 to 40 inches in diameter. In every case, however, the exothermic material should be applied to a depth of at least 3% inches in the riser. The second column shows the amount of exothermic material to use in pounds and the third column shows the approximate height to which the risers should be poured. The columns entitled waiting time" give the approximate number of minutes between the time that the casting is poured and the time that the exothermic material should be added. The fourth column of the table, which is figured on approximate 0.03 minutes of waiting time per square inch of cross-section of area, is recommended for open hearth steel or cold electric furnace steel. The fifth column, figured on a 0.04 minute per square inch of cross-section of area basis, pertains to an average electric furnace steel or hot open hearth steel. The last column is computed on a 0.05 minute basis and pertains to a very hot electric furnace steel or for castings having a very late feed demand, such as die blocks and other massive castings.

The theory governing the waiting time is based on the fact that castings having a late feed demand can utilize heat more emciently at a later stage-in the solidification than castings havingavery early feed demand. If the exothermic material is added too soon after pouring'is completed, a considerable portion of the heat resulting from the exothermic reaction of the material will be dissipated. Thus, in castings having a late feed demand, the temperature increase obtained by the use of exothermic material will be partially lost before the casting requires feed metal. The longer the waiting time which can be tolerated without the skin or crust formation on the top of the riser becoming too thick, the greater the temperature difference between the metal in the riser and the casting, and this will result in the most effective use of exothermic material.

The amounts of exothermic material required,

as shown by the table, can be materially reduced on smaller castings having a very light feed demand. The values in the table are for chunky castings having close to the maximum feed demand for the given size risers. Thus, the amounts of exothermic material, as shown in the table, are only a starting point. If the feed demand in the casting is relatively low, much less material is required. In many cases, the diameter of the risers can also be reduced so that the amount of exothermic material is less and the yield is even further increased.

Gears of all types, locomotive drive wheels and castings of that nature are very advantageously produced according to the invention. Turbine casing castings have been made quite successfully according to the invention with the yields markedly increased. Turbine diaphragm castings, where the stationary blading is cast into the diaphragm, have been extremely successful, and the difliculty of burning off the blade ends has been eliminated. High pressure castings for steam systems, subject to radiographic examination, when made with conventional type open risers work out very well. In general, it has been found that the method of the invention will be most economical and will work out most successfully on castings which must be made sound and free from shrinkage and other defects.

The following is an example of the mesh analysis of the constituents of an exothermic material of the type recommended for carbon steels and steels of low alloy content as used in thetable.

Iron oxide (Fe304) after grinding but before mix- -12 +40 mesh 30%, 40 +100 mesh 30%, -100 +200 mesh 20%, -200 +325 mesh 10%, 325 I Aluminum before mixing:

5%, -12 +40 mesh 20%, -40 +100 mesh 40%, -100 +200 mesh 25%, 200 +325 mesh 10%, -325 Slag-forming material:

20%, --12 +40 mesh 20%, -40 +100 mesh 40%, -100 +200 mesh 10%, 200 +325 mesh 10%, +325 The above materials inthe selected proportions are mixed together, for'example, in a ballmill,

mixture may include green chromium oxide and black nickel oxide. The chromium oxide may be ground to pass through" a 325 mesh screen and the nickel oxide may have anv analysis similar to the iron oxide.

In producing castings containing, say, 5% chromium, the exothermic mixture may contain around 5% of low carbon ferrochrome.

In referring to the amount of exothermic material used, the mass is based upon the most eflicient proportions of iron oxide and aluminum (stoichiometric pro ortions) and from 15% to 18% of added slag-forming material. It is to be understood, of course, that different total amounts will be required where a diiierent iron oxide is used, for example (FezOa), where stoichiometric proportions are not the same, or where different amounts of slag-forming materials are used. Exothermic materials are considered to be the full equivalent of the exothermic material herein described provided they contain aluminum as the metal to be oxidized and the same amount of heat is produced with substantially the same slas effect. In other words, the mass of the exothermic material and its depth or weight, when differing for reasons as aforementioned, must be adjusted on abasis of equivalents.

We claim:

1. In the production of steel castings with risers having a minimum diameter of three inches, the improvement which comprises pouring the steel into the mold until it reaches a height in the riser of approximately one-third to one-half the diameter of the riser, and after the steel in the riser has cooled to a condition varying from a mushy consistency to and including a solid thin skin applying to the riser at least 2 .pounds of exothermic material and to a depth of at least 3% inches, said exothermic material being based upon stoichiometric proportions of FeaO; and aluminum with some added slag-forming material and in a finely divided and intermixed condition.

2. In the production of steel castings with risers having a. minimum diameter of three inches, the improvement which comprises pouring the steel into the mold until it reaches a height in the riser of approximately one-third to one-half the diameter of the riser, and after the steel has cooled to incipient solidification in the riser applying to the riser a mass of exothermic material in an amount exceeding 2 pounds and suflicient to remelt the steel in the riser and raise the temperature thereby feeding the casting and eliminating pipe in the casting, said exothermic material being based upon stoichiometric proportions of R304 and aluminum with some added slag-forming material and in a finely divided and intermixed condition.

3. In the production of steel casting with risers having a minimum diameter of three inches, the improvement which comprises pouring the steel into the mold until it reaches a height in the riser of from A; to V, the diameter of the riser, and after the steel has cooled to incipient solidification in the riser applying to the riser a mass of exothermic material in a minimum amount of 2 pounds and suflicient to form a depth of 3% to 4% inches to reheat the steel in the riser above alumna Q itameltinzpointandtherebyfeedthectstlnzand eliminate pipe in the casting, aid exothermic ma- Um STATE PAW terial being based upon stolchiometric proportions Number Name F 01' M04 and aluminum with some added glag- 1,294,209 Walker Feb. 11, 1919 forming material and in a. nnely divided and me 1. 96.888 Pacz Aug. 24, 1926 fermixed condition. 2,426,849 Udy Sept. 2, 1947 E ilo'nmn REFERENCES 7 American I'bundryman, August'1946, mes 71- REFERENCES CITED m 76, inclusive, "Exothermic Materials" by Lutta,

The following references are or record in the Hickey and v I flle of this patent: