US3092524A - Heat treating articles wrapped in a metallic envelope - Google Patents

Description

June 4, 1963 J. L. GIOVANNUCCI 3,092,524

HEAT TREATING ARTICLES WRAPPED IN A METALLIC ENVELOPE Filed Aug. 15, 1956 5 Sheets-Sheet 1 INVENTOR. g JUL/U5 L .GIOVANNUCCI ATTORNEIU.

June 4, 1963 J. GIOVANNUCCI 3,092,524

HEAT TREATING ARTICLES WRAPPED IN A METALLIC ENVELOPE Filed Aug. 15. 1956 5 Sheets-Sheet 2 INVENTOR. JUL/U6 LGwvmuucc:

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lm 1963 J. GIOVANNUCCI 3, 4

HEAT TREATING ARTICLES WRAPPED IN A METALLIC ENVELOPE Filed Aug. 15, 1956 5 Sheets-Sheet 3 IN VEN TOR. JuuusLGlol/Amv ucc/ Ian M ATTORNEY- June 4, 1963 J. L. clbvANNuccl 3,092,524

HEAT TREATING ARTICLES WRAPPED IN A METALLIC ENVELOPE Filed Aug. 15, 1956 5 Sheets-Sheet 4 INVENTOR. H JULIU3L.GIOVANNUCCI BY W ATTORNEYS.

J1 1963 J. L. GIOVANNUCC! 3,092,524

HEAT TREATING ARTICLES WRAPPED IN A METALLIC ENVELOPE Filed Aug. 15, 1956 5 Sheets-Sheet 5 T INVENTOR.

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United States Patent HEAT TREATING ARTICLES WRAPPED IN A METALLIC ENVELOPE Julius L. Giovaunucci, Stratiord, Conn., assignor to National Distillers and Chemical Corporation, a corporation of Virginia Filed Aug. 15, 1956, Ser. No. 604,098 11 Claims. (Cl. 148-13) This invention relates to a metal heat treating process and apparatus designed to permit the heat treatment of metal work under either a vacuum or a controlled atmosphere.

Prior art processes and apparatus designed to accomplish the above involve the use of massive and expensive equipment because the prior art has operated on the principle that the enclosure for the metal work must withstand the atmospheric pressure. The evacuation removes the internal atmospheric pressure so that the prior art has thought such massive equipment to be necessary whenever the metal work is heat treated either entirely under a vacuum or by first creating a vacuum and then following this with the introduction of controlled atmospheres of various types.

The use of such massive equipment involves a high initial equipment cost, high operating cost, demands considerable floor space, and with all of these objections still has severe limitations with respect to carrying out heat treating cycles which are metallurgically desirable but incapable of accomplishment because of the slow heating and cooling to which the equipment is limited by its great mass.

One of the objects of the present invention is to overcome or reduce the seriousness of the above objections while at the same time completely or to a considerable extent freeing the heat treatment from the restrictions imposed by the necessarily slow heating and cooling times of the prior art. Other objects may be inferred from the following.

Generally speaking, the invention is based on the concept that by enclosing one or more pieces of the metal work to be heat treated, in a hermetically sealed flexible sheet metal envelope or enclosure, with the latter arranged so that it is either initially or eventually structurally supported by the metal piece or pieces against collapse, it becomes possible to draw even the highest commercially feasible vacuum within the envelope or container without concern about the latters structural strength. Under the atmospheric pressure the envelope or enclosure collapses slightly or substantially to bring its interior surface into contact with the metal piece or pieces being heat treated the latter then bracing the envelope or enclosure against further collapse. Proper design of the envelope or enclosure prevents the necessary seams of the latter from rupturing. Ordinarily these seams will be formed by welding or brazing, the envelope or enclosure being made from sheet steel or other sheet metal. Mechanically closed seams may be possible.

In the above fashion any kind of metal work may be heat treated under vacuum. After evacuation the envelope or enclosure may be purged or flushed with a nonoxidizing gas or other atmosphere, such as a reducing gas, and during the heat treating cycle such a gas may, if desired, be kept flowing through the envelope or enclosure. If such a special atmosphere is maintained at a pressure less than atmospheric the flexible envelope or enclosure continues to hug the piece or pieces being heat treated because of the dilferential pressures involved. The piece or pieces being treated need not necessarily be uniform as to their external contour because the flexible metal envelope or enclosure will mold itself into con- 3,092,524 Patented June 4, 1963 formity with almost any configuration when a high vacuum is drawn within its interior. It is, of course, to be understood that the normal atmospheric pressure exists on the outside of the envelope or container.

Various specific examples or the invention are illustrated by the accompanying drawings in which:

FIG. 1 is a plan view of the envelope or enclosure with the object to be heat treated enclosed therein;

FIG. 2 is a side view of FIG. 1;

FIG. 3 is a cross section taken on the line 3-3 in FIG. 1;

FIG. 4 is the same as FIG. 3 but shows the envelope or enclosure after being collapsed by the evacuation;

PEG. 5 is a view similar to FIG. 1 but shows how a plurality of objects may be heat treated simultaneously;

FIG. 6 is a cross section taken on the line 6-6 in FIG. 5;

FIG. 7 is a view also similar to FIG. 1 but showing a modification in the treatment of a plurality of metal obiects simultaneously;

FIG. 8 is a cross section taken on the line 8-8 in FIG. 7;

FIG. 9 is similar to FIG. 8 but shows in perspective the portion of the envelope or enclosure behind the cross sectioned portion and with the envelope or enclosure collapsed by the atmospheric pressure due to the evacuation;

FIG. 10 is a view similar to FIG. 2 but shows how a plurality of objects of different sizes may be processed, the envelope or enclosure in this case being in its collapsed condition;

FFG. 11 is longitudinal cross section showing the invention applied to the heat treatment of a coil of wide metal strip; and

HG. 12 is a modification showing how a hollow object may he strutted or braced against collapse due to the atmospheric pressure on the enclosing envelope or enclosure.

Referring first to FIGS. 1 through 4, the object to be heat treated is in the form of a hollow tube 1. This tube may be made of metal which reacts very strongly with oxygen or nitrogen. Zirconium is an example of such a metal. Regardless of the expense of prior art vacuum annealing equipment the annealing of such metals has not been entirely satisfactory because of the difficulty of removing all of the air from the large enclosure.

The envelope or enclosure is formed by two metal sheets 2 and 3 within which the tube 1 is placed so that the side edge portions of the sheets 2 and 3 come together. These portions are hermetically sealed together as by electric resistance welding along the broken lines 4 shown in FIG. I. This now fully encloses the tube to form what is in effect a flexible wall package which is very little larger than the tube itself.

The resulting envelope or enclosure has an exhausting outlet in the form of a metal tube 6 which is welded or otherwise hermetically mounted through the envelope wall. as at 7. A generally similar connection is shown at S and 9 but for the moment it may be assumed that either this second connection does not exist or that the tube 8 is closed.

Now by drawing a vacuum through the tube 6 the interior of the envelope or enclosure is exhausted. The exterior is exposed to the atmospheric pressure and the full force of the latter is now applied to the sheets 2 and 3, forming the wall, since the atmospheric pressure is unbalanced by any pressure within the envelope or enclosure.

The sheets 2 and 3 are made of a ductile and malleable metal and they are thin enough to vacuum form about the tube 1 so that their interiors are forced into contact with this tube at every possible location. FIG. 3 shows the condition prior to the evacuation and. FIG. 4 shows the molded condition. In effect the envelope or enclosure is vacuum molded about the tube.

Now it becomes apparent that by maintaining an adequate pressure differential between the inside and outside of the envelope or container, the container wall clings or presses against the tube at all times. Therefore, by applying heat to the outside of the thin sheets 2 and 3 the heating of the tube is effected directly by conduction, the only shielding between the tube and the source of heat being the thin metal wall formed by the two sheets 2 and 3. It is almost as though the tube was exposed directly to the heat yet at the same time with the present invention the tube is fully protected against unwanted gases.

Furthermore, because the object being heat treated functions as a support for the thin sheets 2 and 3 the latter do not need to have the structural strength heretofore thought necessary to resist the atmospheric pressure. Any heating equipment may be used that could be used to heat treat metal work which does not require protection against the atmosphere or the heating medium used. The pressure differential may be maintained continuously by keeping the tube 6 connected to a vacuum source. Therefore, both the protection and the cling of the sheets or wall to the work, which is the tube 1 in this instance, may be maintained throughout not only heat treating but quenching operations as well.

For example, following the practice described, the vacuum packaged tube may be first immersed in a heated liquid bath, such as molten salt or a molten metal, and thereafter transferred into a liquid quenching bath such as an oil bath. The packaged work may, of course, be exposed directly to the air without even a thought of harm to the work regardless of whether or not it is critical to exposure to nitrogen or oxygen. After the heat treatment the tube, or other work, may be unpackaged almost literally by using an ordinary can opener. Of course, in commercial work a suitable shear or the like would be used. Obviously the work is chemically unelfected by any heat treatment, including quenching operations it may have experienced.

In some instances it is desirable to maintain a controlled gaseous atmosphere in contact with the tube or other object during its heat treatment. For example, a hydrogen bath may be desired. The present invention permits this practice because such as gaseous atmosphere may be introduced through the tube 8. By maintaining the pressure of the controlled atmosphere below atmospheric the previously described cling is maintained. If hydrogen is desired it is preferable to first flush the evacuated envelope or container with nitrogen to eliminate the explosion hazard. This can be done prior to heating when the metal tube or other work is, of course, insensitive to any possible tendency to react with the nitrogen. Thereafter the hydrogen may be introduced under subatmospheric pressure and, if desired, kept flowing through the envelope or enclosure during the heat treatment or any part thereof.

By fluctuating the pressure within the envelope or enclosure, it is possible to make the enclosure breathe so that the sheets 2 and 3 are alternately puffed out and sucked in, thus effectively flushing all unwanted gas, such as air from between the interfacing surfaces of the envelope or enclosure and the work. Prior to heat treating the pressure is, of course, reduced to sub-atmospheric as required to effect the cling previously described.

In case the tube 1, or other hollow work, is so thinwalled that it lacks the structural strength to support the atmospheric pressure, it may be internally braced structurally. This modification is shown by FIG. 12 wherein the end of the tube 1 has a thick metal plug 10 inserted within it. This plug is provided with gas passages 11 and may have a flange 12 for limiting its insertion into the tube. If needed, an unflanged ring 13, also having gas passages 14, may be inserted entirely within the tube.

The use of a suitable number of such bracing members or equivalent means may be used whenever the work is so thin-walled as to indicate the need.

In many cases the work will be a solid bar, slab, or other shape and will not require the above bracing precaution. When solid the previously described breathing or pumping action is highly desirable when a controlled atmoshpere is used.

Now it can be seen that the heavy, cumbersome and expensive prior art vacuum heat treating equipment is by the present invention replaced by thin sheet metal and a small piece of welding equipment. This is not only a great cost and time saver but because there is very little mass of metal which must be heated in addition to the work itself, there is both a great saving in heat and an expansion of heat treating cycles into realms which have heretofore been impossible. In other words, extremely rapid heat input and removal with respect to the work itself is now an easy possibility.

It is to be understood that the heat treatment to which this invention relates involves a metallurgical treatment of one kind or another on the part of the object being heat treated. In other words, the temperatures contemplated are sufficient to accomplish annealing as one ex ample of a common heat treatment.

An example of a unique process permitted by the present invention is surface hardening. This may be applied to cam shafts, gears, and the like. These may be packaged cold as described, the envelope or enclosure being evacuated so that only its very thin wall is between the work and the source of heat. This package, with the cling maintained, may be immersed, while cold, in a very hot liquid bath having temperatures ranging around 2000 to 2400 F. Assuming the work to be made is of hardenable metal, which would ordinarily be steel containing adequate carbon, this drastic heating brings only the surface of the work to a temperature high enough to put the carbon or other herdening constituent into solution with the base metal. At that time the package is removed from the liquid bath and quickly quenched in a cold liquid bath. In this way the hardening heating is maintained at the surface of the metal only so that only the surface is hardened. At the same time the finished work is just as bright as it was prior to the treatment, because the work was protected at all times by being in the evacuated envelope or enclosure.

FIGS. 5 and 6 show how a number of objects may be packaged simultaneously in the described manner. In this case five of the tubes 1 are arranged in a series or row with the tubes parallel to each other and laterally spaced from each other. The sheets 2a and 3a correspond to the sheets 2 and 3 and the line of welding 4a corresponds to the line of welding 4. As shown by FIG. 6 the evacuation draws the sheets 2a and 3a together and into direct contact with each other at the 10- cations between the tubes 1 where the sheets are unsupported by the latter. To facilitate the assembly of this package lines of welding 15 may join the sheets 2a and 3a along zones between the interspaced tubes 1.

Of course, the work may comprise a number of solid bars or other objects in this case also.

FIGS. 7 and 8 show how the tubes 1 may be grouped as a bundle or nest with one tube 1a encircled by the others. FIG. 1 shows the appearance after the vacuum molding of the enclosed sheets 2b and 3b. Again the work may comprise bars or other shapes.

The above serves to illustrate a number of things. For example, it shows that by using the atmospheric pressure the outer ring of tubes is pressed against the inner tube tightly by the atmospheric pressure so that the bundle of tubes acquire a heat conductivity from one tube to another which is comparable to a unit piece of work having walls or bodies integrally joined. In other words, although the central tube 1a is remote from the heating medium the heat conductivity path to even this innermost tube is excellent. This example also serves to show how the envelope or enclosure is vacuum molded about an irregularly shaped object. That is to say that the bundle of tubes may be visualized as a single piece of work having an irregular contour. That is to say the envelope or enclosure acts as though it was a skin mounted about the work, intercontact between the skins interior and the work being maintained by the pressure differential previously described. A still further point illustrated by this example is the manner in which a number of pieces or Work which would ordinarily be troublesome and difficult to handle are integrated into a single unit package so that the large number of pieces can be handled as though they were a single larger piece of work.

The adaptability of the present invention to work having a very irregular contour may be accommodated by the present invention. In this case the tubes are bundled as in the case of FIGS. 7 through 9 but the tubes have different lengths. It can be seen that the tubes 1b are much longer than the tubes 10 and that in fact none of the tubes are of equal lengths. In spite of this the sheets and 3c are firmly and tightly mounted about all. This example also serves to show how a single end supporting strut 16 may be used at one end of the package for all the hollow pieces of work while at their other ends the individual elements 10 may be used.

In some cases even very ductile and malleable metal does not deform under the atmospheric pressure enough to completely fill all voids, this condition being shown at 17 in FIG. 10. However, sheet metal normally has enough strength when in short spans not to rupture even when subjected to the full atmospheric pressure. The sheet metal merely draws inwardly somewhat as indicated at the zone 17.

Tubes have been used as a convenient way to illustrate the work pieces. At the same time, as has been indicated, the work may have almost any contour. It may be either regular or irregular in shape. Using the concept of snugly enclosing the work hermetically by a sheet metal skin or wall and then evacuating the resulting envelope or enclosure, a tightly compacted package is effected. This package has the advantages previously de scribed regardless of its relative size.

To illustrate the adaption of the present invention to work of large size, FIG. 11 shows the work 1a in the form of the usual length of wide steel strip as it is delivered by the cold rolling mills in a strip steel plant. This strip is, of course, in the form of a coil and this coil may have a diameter of around 5 feet and may be even longer than its diameter. It must be handled by a crane or the like and usually it is annealed by being placed beneath a huge electrically heated hell with the coil on a very massive base and with the bottom edge of the bell sealed by sand or other means. The equipment is extremely expensive and cumbersome and is not adapted to vacuum annealing. It is flushed with gas of a non-oxidizing or de-oxidizing nature and the annealing and cooling cycle is of very long duration. Usually the coil is protected inside of the bell by a massive cover which greatly retards the transfer of heat from the heating bell to the coil.

According to the present invention one of the sheets 2d is simply wrapped around the outside of the coil, and side seamed. This provides what is in effect the body of a drum, the sheet 2d having a width greater than the length of the coil so that it overhangs the latters ends. Then what are in effect two drumheads 3d are formed with edge flanges So which fit within the overhanging ends of the body or shell 2d. These parts are interseamed so as to effect the air-tight packaging of the coil. The end members, of course, are pressed tightly and molded against the edges of the coil when the vacuum is drawn, and the coil as a whole is bound into the form of an integral unit. The various seams may be made by line t3 welding as previously described. The exhaust tube 6d is sealed at 7d in the center of one of the drumheads While the gas intake 8d, if this is desired, is sealed at 9d at the opposite drumhead. When the vacuum is drawn the unsupported central portions of the two drumheads are merely sucked inwardly providing these heads are made with adequate strength to sustain the atmospheric pressure without rupturing. They will, of course, draw inwardly. If this effect is not desired an internal strut may be used.

In most instances the metal envelope or enclosure may be made from ordinary plain low-carbon sheet steel black plate. The gauge will vary depending on the size and nature of the work being heat treated but in all cases the gauge should be light enough to cause the envelope or enclosure to vacuum mold as previously described. It is also possible to use other sheet metals such as stainless steel. Generally speaking, the least expensive metal that can be used is preferred. Although the package will ordinarily be sealed t csed by the use of resistance welding or by deposited w inst-ti in case of the tube connections, mechanical seams and joints are possible. This expedient might be used where the nature of the work and the metal from which the envelope or enclosure is made suggests the possibility of repeated usage.

I claim:

1. A metal object heat treating process including enclosing said metal object in an enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about said object to a substantial degree by the external atmospheric pressure, and while maintaining said enclosure exhausted, to a degree causing said wall to cling to said object, applying heat treating heat to the latter through said thin metal wall.

2. A metal object heat treating process including enclosing said metal object in an enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about said object to a substantial degree by the external atmospheric pressure, and while maintaining said enclosure exhausted, to a degree causing said wall to cling to said object, applying heat treating heat to the latter through said thin metal wall, and for at least an interval of time during said heat application introducing a gaseous atmosphere to the interior of said enclosure at a pressure sulficicntly below atmospheric pressure to maintain said cling.

3. A metal object heat treating process including enclosing said metal object in an enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about said object to a substantial degree by the external atmospheric pressure, and while maintaining said enclosure exhausted, to a degree causing said wall to cling to said object, applying heat treating heat to the latter through said thin metal wall, said wall being made of ductile and malleable sheet metal.

4. A metal object heat treating process including enclosing said metal object in an enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about said object to a substantial degree by the external atmospheric pressure, and while maintaining said enclosure exhausted, to a degree causing said wall to cling to said object, applying heat treating heat to the latter through said thin metal wall, said heat being applied by immersing said enclosure in hot liquid bath.

5. A metal object heat treating process including enclosing said metal object in an enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about said object to a substantial degree by the external atmospheric pressure, and while maintaining said enclosure exhausted, to a degree causing said Wall to cling to said object, applying heat treating heat to the latter through said thin metal wall, said enclosure being formed by seam welding ductile and malleable sheet metal which forms said wall.

6. A metal object heat treating process including enclosing said metal object in an enclosure having a thin metal wall, exposing said enclosing externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about said object to a substantial degree by the external atmospheric pressure, and while maintaining said enclosure exhausted, to a degree causing said wall to cling to said object, applying heat treating heat to the latter through said thin metal wall, said object being hollow and itself incapable of resisting said pressure, and being internally structurally supported by bracing means prior to said enclosing.

7. A process for heat treating a plurality of metal objects, said process including grouping said objects and enclosing them in a common enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said Wall being thin enough to be molded about said objects to a substantial degree by the atmospheric pressure, and while maintaining said enclosure exhausted to a degree causing said wall to cling to said objects applying heat treating heat to the latter through said thin metal wall.

8. A process for heat treating a plurality of metal objects, said process including grouping said objects and enclosing them in a common enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about said objects to a substantial degree by the atmospheric pressure, and while maintaining said enclosure exhausted to a degree causing said wall to cling to said objects applying heat treating heat to the latter through said thin metal wall, said enclosure being formed by metal sheet and said objects being interspaced so that said sheets collapse into contact with each other between said objects.

9. A metal object heat treating process including enclosing said metal object in an enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about said object to a substantial degree by the external atmospheric pressure, and while maintaining said enclosure exhausted, to a degree causing said wall to cling to said object, applying heat treating heat to the latter through said thin metal wall, said object being a coil of metal strip and said enclosure being formed like a drum with a cylindrical body and heads, all made of thin metal, to form said wall.

10. A metal object heat treating process including enclosing said metal object in an enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about said object to a substantial degree by the external atmospheric pressure, and while maintaining said enclosure exhausted, to a degree causing said wall to cling to said object, applying heat treating heat to the latter through said thin metal wall, and prior to said heating and after said evacuation said enclosure being internally subjected to pressure fluctuations including pressures above atmospheric to flush said enclosure free from the atmosphere it contained initially.

ll. A metal object heat treating process including enclosing said metal object in an enclosure having a thin metal wall, exposing said enclosure externally to atmospheric pressure and exhausting the atmosphere from its interior, said wall being thin enough to be molded about and object to a substantial degree by the external atmospheric pressure, and while maintaining said enclosure exhausted, to a degree causing said wall to cling to said object, applying heat treating heat to the latter through said thin metal wall, and prior to said heating and after said evacuation of said enclosure being internally subjected to pressure fluctuations including pressures above atmospheric to flush said enclosure free from the atmosphere it contained initially, said fluctuating pressure being eflected by introducing a gas to the interior of said enclosure.

Rare Metals Handbook, Reinhold Publishing Co., pp 599, 619; 1954.

Claims (1)

1. A METAL OBJECT HEAT TREATING PROCESS INCLUDING ENCLOSING SAID METAL OBJECT IN AN ENCLUSURE HAVING A THIN METAL WALL, EXPOSING SAID ENCLOSURE EXTERNALLY TO ATMOSPHERIC PRESSURE AND EXHAUSTING THE ATMOSPHERE FROM ITS INTERIOR, SAID WALL BEING THIN ENOUGH TO BE MOLDED ABOUT SAID OBJECT TO A SUBSTANTIAL DEGREE BY THE EXTERNAL ATMOSPHERIC PRESSURE, AND WHILE MAINTAINING SAID ENCLOSURE EXHAUSTED, TO A DEGREE CAUSING SAID WALL TO CLING TO SAID OB-

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