US1487719A - Process of malleableizing iron - Google Patents

Description

Mach :5, 1924.

T. CHANDLER PROCESS OF MALLEABLEIZING IRON 'i'iled Nov. 14, 1921 Patented Mar. 25, 1924.

HENRY T. CHANDLER, 0F MARYSVILLE, MICHIGAN.

PROCESS OF MALLEAIBLEIZING IRON.

Application filed November 14, 1921.

To all whom it may concern.

Be it known that I, HENRY THOMAS CHANDLER, a citizen of the United States of America, residing at Marysville, in the county of St. Clair and State of Michigan, have invented certain new and useful Improvements in Processes of 'Malleableizing Iron, of which the following is a specifica-.

tion, reference being had therein to the accompanying drawings.

Commercially, the manufacture of malleable iron is conducted in two steps. The first of vthese includes melting, molding, casting and other foundry operations incident to the production of suitable white iron castings. The second step consists in the conversion of these hard, brittle, unmachineable castings, by a suitable thermal treatment, into soft, malleable'and commercially useful products.

This invention relates particularly to this commercial method of annealing.

Metallurgically, white iron, suitable for malleableizing, consists of a mixture of iron carbide, known as cementite, and an alloy of. iron carbide and iron. The properties of these constituents and their distribution within the casting account for the brittleness and other physical characteristics of the metal. This system, in which the carbon all exists in chemical combination, is me tastable; in other words, it is permanent not because actual chemical equilibrium exists, but because further molecular re-arrangement is impossible under the temperature conditions obtaining. It is the purpose of annealing to convert, by the effect of time and temperature, this metastable system of iron carbide and iron into the stable system consisting of iron and free carbon (graphite), accomplishing thereby a change in the nature and re-arrangement of the constitu- Serial No. 514,844.

cuts of the casting resulting in a commercially useful product.

Annealing practice, as usually carried out, consists first in packing the castings together with either an inert or chemically active material, such as mill scale, slag, iron ore and the like, in cast iron or other pots. Various sizes and forms of containers and kinds of packing materials are used, depending largely upon the work to be treated and to some extent upon the nature of the equipment available and personal opinion of the annealer. The purpose of packing is primarily to support the castings while hot and thus prevent sagging or distortion under their own weight or the weight of the cast ings above them. It also serves as a protection for the castings from scaling or other effects of the combustion gases and further, due to mass, has a stabilizing effect upon temperature, preventing rapid changes harmful to this process. Packing has no significant effect upon the graphitizing reactions proper.

The pots containing the castings are then stacked and charged into the annealing ovens. These ovens are usually very simply constructed and hand fired with coal. They .may hold from twenty-five to one hundred stacks of pots; neither extreme, however, is common practice. The doors are sealed and the oven and its contents are brought to a maximum temperature of from about 1500 to 1850 degrees Fahrenheit. heat-ing is chemically unimportant and is limited by the .nature of the oven and the disposition of the charge within.

Temperature is maintained for a period of from a few hours to several days, to effect thorough heating'of the charge and permit the initial reactions within the castings to attain equilibrium. When this is accomplished, firing is stopped and the oven and contents allowed to cool. The cooling rate is important and the ovens are so built that this does not exceed 10 to 15 degrees per hour throughout the critical range. After cooling to from 1000 degrees Fahrenheit to around 200 degrees Fahrenheit, depending largely upon the means available for removing the work, the pots are removed and the The rate of castings cleaned. after which they are ready I i the A,

its large size,- second,

cases, over two weeks. Widevariationsin denecessary to avoid scaling; and third, to the tail are practiced in different foundries, due, mechanical equipment necessary to effect the no doubt, to the fact that the art of producmovement of the charge through the furing malleable iron preceded by over a hunnace. Furnaces of this type can only be dred years an understanding of thechemistry eliicient when constantly operating at full of graphitization. 1 or nearly full capacity, and therefore lack In all instances, however, the complete the flexibility demanded in the usual jobprocess may be divided into the following bing foundry. I fourintervals, the first two of which being In the stationary type of mufile furnace, heating and the last two cooling operations: packing is also either totally or partially 1st, Heating to some temperature above eliminated, and the cooling cycle becomes point. i a question cf furnace control. 2nd. Holding at this temperature for a lVith my improved process, instead of carperiod of time. rylng out the complete operation'in one ag- 3rd. Cooling to below the A point at a paratus, the heating and cooling steps oft 0 slow rate. V 7 treatment are separated and accomplished 4th. Further cooling to permit handling. in different enclosures, the heating being These four parts of the annealing cycle carried on in a furnace which is adapted for are completed in a single furnace or anneal efiiclently carrying "out this operation and ing chamber, substantially as outlined abovei he Work being then transferred to an an- The process, thus conducted, when comparatus constructed to etficiently effect t e pared with analogous metallurgicalo eranecessary cooling cycle. The process is tions, is v ry ineffi i nt This is du fir t. based z first, on the discovery that chemically to the fact that an oven which will have the the rate of heating is immaterial; secon l li h t i ti cessary for the that the higher the initial temperature is successful completion of the process, is not ralsed above the critical point, the more a construction suitable for the eflicient heat rapidly is chemical equilibrium established; ing of the work either as regards time or third, that the rate of coolingis immaterial, fuel economy; second, the oven operates as excepting through a narrow temperature a heating unit during but a small part of the range, and; fourth, that the initial temperatime necessary for the complete cycle; third, ture may be considerably higher than this the extreme range of temperature to which range. 7 the oven is subjected results in rapid de- The conditions being such, the transfer of terioration and heavy upkeep expenses." work to the cooling chamber may be accom- Initial installation, upkeep and overhead plished without detriment to the reactions costs must, therefore, be met on an apparaof graphitization, it being only necessary tus svhich is idle a greater part of the time that the initial temperature should be sufliin performing one of its major functions, ciently high to avoid dropping below this which is subjected to temperature extremes, critical range during transfer. causing rapid deterioration due to expan- The specific form of apparatus required sion and contraction of the brick work, and, forthe carrying out of my improved rocess due to the great length of time necessary to may be varied, but as diagrammatical y repcomplete'the process, is limited in its outresented in the drawings,

ut. The direct result of these conditions is that'only the most simple and cheap conheating furnace; and structions are economically practical, and Figure 2 is a similar view through the more eliicient furnaces and methods of fuel cooling chamber. utilization, through almost universally used As shown, A is a furnace suitably conin allied practice, are here ruled out on the: structed for the eflicient heating of the work basis of cost. r placed 'in thechamber. The furnace may be a More recent development has contemplatof the car type in which the work is placed ed the use of electricity as a source of heat *upon trucks B which are meva-ble into and or the use of mufiie furnaces of either the out from the furnace, or any other cou= stationary or tunnel type, in order to avoid venient means'of transporation may be propacking and thus speed up the process to avided. C is the cooling chamber which dif- Figure lis a cross section through the point where the use of such equipment befers radically in its construction from A so 7 comes of economic value; as to be efficient in the control of the coolin the tunnel furnaces the work is grading of the work. If the work is placed on ually advanced, first passing through a zone trucks, these may be transferred from the in which the proper temperature is reached heating furnace *A to the cooling chamber C and maintained and then through portions and these two parts of the apparatus may at progressively lower temperatures to combe located in any convenient relation to each pletion. Such a type of apparatus is necesother. Cooling may be controlled by the v sariiy initially very expensive, due; first, to use of suitable dampers for the admission of t e mufile construction hot waste gases from the melting furnaces or heating oven, or the use of an individual heating equipment, or combinations of these. In place of cooling of the product of the heating chamber in a single cooling chamber, two or more of these may be used, if desired.

The essential feature of the apparatus is that the cooling chamber shall not interfere with the efiicient functioning of the heating furnace and that the heating furnace shall not interfere with efficient functioning of the cooling chamber.

In operation, the higher the temperature in the heating furnace without detriment to the work, the more rapidly is equilibrium established in the initial reaction, and the shorter the time interval required for this step of the treatment. The work is there fore placed in the heating furnace and permitted to remain for an interval varying with the temperature and with other conditions, such as the analysis of the iron, the manner of packing, etc. The work is then transferred to the annealing furnace and the rate of cooling controlled until the low point of the critical range is reached, after which it maybe removed.

The time required for the complete process as thus carried out is very much less than with the usual practice, as not only is heating effected more rapidly than in usual practice, but also the very slow cooling necessary to the reaction is carried out only within the range in which it is effective.

The economies of the process are many, among which may be cited the following:

First, the heating furnace is operated continuously as a heating unit within a comparatively narrow temperature range, thus varying fuel consumption; I

Second, he cooling chambers are of very simple and cheap construction and are capable of long service, as they are not subjected to either excessive temperature or change of temperature;

Third, due to the resulting shorter time cycle, the output of the annealing equipment is increased and the overhead burden borne by the charge is reduced;

Fourth, installation costs are low when compared either with the usual practice or the use of tunnel and muflle furnaces.

W'hat I claim as my invention is:

1. The method of malleableizing iron which consists in. heating the work in one enclosure and in cooling the work in a separate enclosure.

2. The method of malleableizing iron which consists in heating'the work in a fur nace adapted for the efiicient accomplishment of such operation, in cooling the work .in a separate chamber and in transferring the work from theone to the other while at a temperature above the critical point.

3. The method of malleableizing iron which consists in heating the work in a furnace adapted for eflicient and rapid elevation of temperature to above the critical point for the primary reaction, in maintaining the temperature above such point until the equilibrium of the primary reaction is established, in transferring the work while at a temperature still above said critical range to a separate cooling chamber and in controlling the rate of cooling through the low point of the critical range.

4. The method of malleableizing iron which consists in elevating the temperature of the work rapidly to above the critical point (A,) for initiating the primary reaction, in a furnace adapted for efliciently accomplishing such treatment, in transferring the work while still above the critical temperature to a cooling chamber and in controlling the cooling process at the required rate through thecritical range. v

5. The method of malleableizing iron which consists in heating the work while stationary in one enclosure, in transferring the work to a separate enclosure, and cooling the work while stationary in the latter enclosure.

6. The method of malleableizing iron which consists in heating the work while stationary in a furnace adapted for the eflicientaccomplishment of such operation, in transferring the work while at a temperature above the critical point to a separate chamber adapted for controlling the rate of cooling and cooling the working in said chamber at-a predetermined rate through the low point of the critical range while said work is stationary therein.

7 The method of malleableizing iron which consists in placing the work in a furnace adapted for efiicient and rapid elevation of temperature to above the critical point for the primary reaction, in maintaining the work stationary in said furnace at a temperature above such point until equilibrium of the primary reactionis 'es tablished, in transferring the work while at a temperature still above said critical range to a separate cooling chamber, and in controlling the rate of cooling through the low point'of the critical range while maintaining the work stationary in said chamber.

In testimony whereof I afiix my signaturea HENRY T. CHANDLER.

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