US1280418A - Heat treatment for centrifugally-cast pipes. - Google Patents

Description

D. S. DE LAVAUD.

HEAT TREATMENT FOR CENTRIFUGALLY CAST PIPES.

APPLICATION FIL EU 1ULY30. |917 Patented Out l, |918.

2 bHEETS-SHEET l /ll/ VEN 720]? D; S. DE LAVAUD.

HEAT TREATMENT FoR cENTmFuGALLY GAST PxPEs.

APPLICATION FILED JULY 30. 1917..

1,280,418. Patentedot. 1, 1918,

2 SHEETS-SHEET 2- mab'ix v- [me y gagne/gu ferrite INVENTOR Y BY r .a "r.

" nrmr'rnr sENsAUD nernvnun, or new Yonne, n. r'.-

HEAT TREATMENT FOR CENTRIFUGALLY-CAST PIPES.

\ Application led July 30, 1917. Serial No. 183,503.

To all wh'om'z't may concern:

Be it known that I, DIMITRI SENSAUD DE -L'AVAUD, a citizen of the United States of cast under the influence of centrifugal force.

The object ofthe invention is to provide an improved heat treatment for centrifugally cast pipes or similar articles, whereby the speed of manufacture of the pipe is increased, and, this latter being the most important object, the quality of the pipes is bettered to a remarkable degree.

In particular, the prime object of the pres- Speciication of Letters Patent.

ent invention is to reduce a cast iron pipe which has a very ne grain, and in which the graphite exists `in iine particles and not in coarse akes as the case is with ordinary cast iron pipes. This I accomplishr bythe follow- 4 ing steps. First, the molten metal of which l advantageously carried out, and a typical the pipe is to be formed iis subjected to the action of centrifugal force, and at the same time rapidly cooled, the metal being preferably cooled within three 'to siX seconds after it has been poured into the mold. The casting, now of awhite cast iron, is with. drawn from the fold immediately after solidification, the casting leaving the mold at substantially 15000 Fahrenheit. The pipe is then superheated by elevatin its temperature to from '1800o to 2000 Fa renheit depending on the composition of the metal. The pipe metal changes over into gra cast iron with graphite in fine particles, andy any brittlegess that vmay have been caused by the sudden cooling is removed. By this process a pipe of exceptionally line rained structure, strength and toughness 1s reduced at a comparatively rapid rate.

he invention will be more clearly understood from the following description when taken in connection with the accompanying drawings illustrating an apparatus by which the process of the present invention may be molecular structure of the gray cast iron product resulting from the process. y

In these drawings, r

Figure 1-shows the apparatus somewhat Patented oet. il, raie.

diagrammatically and partially in section;

and

Figs. 2,. 3 and 4 are pen and ink replicas of microphotographs (450 diameters) of cross sections vthrough a pipe, taken respectively near the outside of the and near the inside.

Referring to Fig. 1,1 is a centrifugal casting machine from which a pipe 2 has been pipe, near the center drawn by the supporting carriage 3. The4 mold of this machine is preferably cooled by admitting water through the'pipe 18. .Means are provided for transferring the pipe to asuperheating oven, which maybe the crane 4, suitably supported in any manner'as from the I-beam 5. The oven may advantageously have a sloping floor 6 resting onsuitable supports 8. The oven lis provided with a Y roof 7, preferably of refractory material Aspaced suitably from the floor to allow of the passage of the pipes therebetween. This roof may have a-n arched portion'9 where the sion of combustible gases through the apertures 10 when they are burned within the oven. ,Thel oven is also provided with a stack 11 which may be tted'with a damper 12 for the regulation of the draft. The stack 11 is preferably placed so that the gases ofq heating is done', which may be by the admiscontaining tar 14. The tar may be. kept in liquid conditionby burning fuel on the grate 17 'A baille or guide 15 is provided for the control of the passage of the pipes through the tar pit, and the pipes as they emerge are received on the platform 16. Y

The operation of the 'apparatus shown,

.mechanically, is briefly as follows:

Molten metal is poured into the casting machine and the pipe cast and withdrawn from the machine in the usual manner. ,The pipe is then raised by the crane 4, revolved ,fthrough a `right angle, and deposited upon the upper end of the floor 6, whence it travels by its ownweight slowly down the incline through the oven, being subjected to the 'heat of the burning gases emerging from the apertures 10. 0n emerging from the oven,

the pipes enter the tar pit 13 and are guided therethrough by the baliie 15,l the Weight of the oncoming pipes being sufficient to cause the pipes to move through and out of the pit.

Thermally considered, the operation of the apparatus used in carrying out the process, is as follows:

The metal in the centrifugal casting machine 1 which is being formed into a pipe 2 is rapidly cooled, as by Water circulation through "fthe pipe 18; the casting being formed and cooled within three to six seconds after the metal has been poured into the. machine l. The manner and rate of cooling is such that when the casting is withdrawn from the mold, immediately after solidification, the casting is at the temperature of 15000 Eahrenheit. The pipe 2 is withdrawn from the machine by the traveling` carriage 3,engaged by the crane 4, and deposited at the right-handy end of the sloping floor 6 of the oven, and passes under the roof 7 and into the zone of the burners 10, with such" celerity, preferably, that the superheating treatment of the pipe commences very soon after the pipe is Withdrawn from the mold, that is, before the pipe cools by contact with the atmosphere to a temperature appreciably lower than 15000 Fahrenheit. During the passage of the pipe through the oven the temperature of \the pipe is elevated from 18000 to 20000 perhaps better be understood if it is ex.

Fahrenheit, depending on the composition of the metal. The process of the present invention will plained that iron cast in sand molds cools very slowly, ordinarily, its latent heat diffusing gradually. The iron being a liquid, it crystallizes as it approaches' the solid state, and the essential ingredients'or impurities, so to speak, separate out and become entrapped or inclosed in the finally solid mass.

The principal constituent or impurity in cast iron is the carbon which exists in the graphitic state-really pure carbon which separates out as the iron cools. It usually exists in flakes or plates, often large-ah' Ways so if the iron cools slowly. But whether the iron cools slowly or rapidly, these Hakes or plates, that is, the lamella structure familiar to metallurgists, persists, at least to a deleterious extent. The carbon in slowly cooled iron is found in larger globules or Hakes than in iron that cools more quickly. Thus, iron cast in a permanent metal mold, whether it revolves or not, contains smaller 'crystals of carbon as well as of all other constituents. And when the iron, so cooled, is removed at once into the air, the cooling or accelerated formation of the crystals is accentuated. So that one of the features of the present invention, or rather one of the steps of the preferred tures are largely empirical, as is also the process, is to cool the metal rapidly as it is being formed into the casting in the centrifugal casting machine, so that the pipe is formed and the casting cooled within three to six seconds after the metalis poured into the rotating mold of the machine. The real essence of the present invention, however, is my discovery, further, that when the casting is solidified in the mold, rapidly cooled in the mold, and rapidly extracted from the mold, preferably at the instant of solidification and when the casting is substantially at 15000 Fahrenheit, the quality of the casting may be improved to a remarkable extent, as compared with any heat treatment heretofore suggested, if the casting is superheated by elevating its temperature to from 18000 to 20000 Fahrenheit depending on the composition of the metal. These latter tempera- 15000, and are therefore not4 intended to be here stated in a limiting way, but merely as illustrative of what actual experiment with various dierent compositions of metals have shown me. With most if not all of these compositions' of metals, the 15000 temperature has been found so far to be ideal at the instant of extraction of the casting-from the mold; but in the case of the superheating temperature, this has varied, so far as noted between 18000 and 19800 Fahrenheit as the ideal superheating temperature, depending on the composition of the metal.

When the pipe iswithdrawn', at the 15000 temperature, it has a chilled outer surface. ln certain cases, of special mixtures, the pipe is chilled throughout. It cannot be led. or drilled by tool steel, and cannot in fact be worked by any instrument whatever. YThechill consists of cementite and pearlite, with a few black spots showing graphite. A layer of pure pearlite may be formed at the surface. rIhe crystals are of needle formation. Near the center of the casting, that is, toward the inner wall of 11o the pipe, white dendrites of Silico-ferrite are found, surrounded by a mass of fine 4 graphite and ferrite. vSometimes the pearlis very line on the outside and inside surfaces, but a little coarser at the center. The absence of coarse graphite plates is noticeable; very marked. The structure is to a certain extent similar to that of a sand casting, but there is much less pearlite.. There 130 are White grains and dendries of silico-ferrite and fine graphite `and `ferrite in the matrix .of pearlite.

I olalm: 1. A process for providing improved iron annulus-type castings, which consists in providing a metal rotary mold, feeding a chargel of molten metal thereto'and rotating the mold to ycompress the molten metal against the metal mold'by centrifugal force, While congealing the molten metal within six seconds after pouring the metal into the mold, extracting the casting thereby formed from the mold after said congealing of themolten' Within six seconds after pquring the meta-l into the mold, extracting the castlng thereby formed from the mold in time to prevent the casting from losing in the mold `more heat't'han the heat Whichthe metal mold labsorbs for the congearling, and afterward subjecting the extractedcasting to a temperature of at least 1800o Fahrenheit, and then permitting the thus superheated casting to cool. 5,

3. A process for providing -improved iron castings of the' annulus-type, which consists in providing a metal rotary mold, feed;

ing a charge of molten metal thereto and' rotating the mold to compress the. molten metal against the metal mold by centrifugal' force, .Whilecongealing the molteny metal Within six seconds after pouring the metal into the mold, extracting the casting .thereby formed from the mold at the instant when the temperature of the casting is substantially 1500 Fahrenheit, then rapidly heating the extracted casting to a temperatilt ture substantially between 18000 and 2000" Fahrenheit, depending on the composition of the metal, and then permitting the casting to cool.

4. A process for providing improved annulus-type iron castings, which consists in feeding a charge of molten metal to a metal rotary mold and rotating the mold to compress the molten metal against the metal mold by centrifugal force, While congealing the molten metal Within six seconds after pouring the metal into the mold, extracting the casting thereby formed from the mold after said congealing of the molten metal as quickly as the machine permits, and after- Ward subjecting the extracted casting to a temperature of at least substantially 500 Fahrenheit less than the fusion temperature of the molten metal employed, and then permittingthe casting to cool. v

5. A casting of gray cast-iron of the annulus-type, having a structure very much similar to that of a sand-casting, but with very much less pearlite; the grain being entirely normal and regular but the grain being very close, that is to say, very small; the absence of coarse plates of graphlte being noticeable, in fact very marked, With the graphite Very fine on the outside and inside surfaces, but a' little coarser at the center; the casting being soft and easily machined 1n all parts; there `being present White grains and dendrites of Silico-ferrite and grains of line graphite and ferrite in a matrix of pearlite.

6. An iron casting of the annulus type having a molecular structure characterized bythe fact that the graphite is very fine on the'outside of the casting and increases in.

coarseness a little from the outside toward. the' center of the casting but in such manner that the outside of the casting may be easily Worked by any tool; there being present dendrites and grains'of Silico-ferrite and grains of ferrite containing tine graphite surrounded by a net Work of pearlite.

In testimony' whereof I have signed my lname to this specification.

DIMITRI SENSAUD DE LAVAUD.

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