US3730501A

US3730501A - Apparatus for treatment of metal products

Info

Publication number: US3730501A
Application number: US00098673A
Authority: US
Inventors: A Gueussier; R Tricot; M Lacoude
Original assignee: Ugine Aciers SA
Current assignee: Ugine Aciers SA
Priority date: 1967-08-01
Filing date: 1970-12-16
Publication date: 1973-05-01
Anticipated expiration: 1990-05-01
Also published as: LU56589A1; FR1555588A; BE717757A; AT279997B; GB1238047A; SE344340B; DE1758666B1; NL6810931A

Abstract

Apparatus for heat treating and descaling metal without harmful superficial decarburization of the shapes. The apparatus comprises a furnace chamber wherein reducing atmospheres, temperatures between 700* and 1,200* C and vacuums between 100 and 0.01 torr may be maintained. A barometric lock enables steel shapes to be introduced and removed from the furnace chamber without disturbing the vacuum.

Description

United States Patent [191 Gueussier et a1.

APPARATUS FOR TREATMENT OF METAL PRODUCTS Inventors: Andre Gueus sier; Roland Tricot;

Michel Lacoude, all of 73 Albertville, France Assignee: Ugine Aciers, Paris, France Filed: Dec. 16, 1970 Appl. No.: 98,673

Related US. Application Data Continuation-impart of Ser. No. 748,291, July 29, 1968, abandoned.

Foreign Application Priority Data Aug. 1, 1967 France ..67116523 US. Cl. ..266/4 A, 214/17 13', 214/23 Int. Cl. ..C2ld 1/62 Field of Search ..266/4 A, 4 R, 5 R,

May 1, 1973 266/4 E, 4 B; 214/17 B [56] References Cited UNITED STATES PATENTS 1,634,319 7/1927 Callaghan ..266/4 B 3,360,252 12/1967 Westeren 266/4 R Primary ExaminerR. Spencer Annear Attorney-Webb, Burden, Robinson & Webb [5 7 ABSTRACT Apparatus for heat treating and descaling metal without harmful superficial decarburization of the shapes. The apparatus comprises a furnace chamber wherein reducing atmospheres, temperatures between 700 and 1,200 C and vacuums between 100 and 0.01 torr may be maintained. A barometric lock enables steel shapes to be introduced and removed from the furnace chamber without disturbing the vacuum.

5 Claims, 4 Drawing Figures PATENTED W 1 sum 2 OF 4.

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' INVENTORS ANDRE GUEUSSIER ROLAND TRICOI- MICHEL LACOUDE' wmwm wwiww APPARATUS FOR TREATMENT OF METAL PRODUCTS RELATED APPLICATION This is a continuation-in-part of application Ser. No. 748,291, filed July 29, 1968, entitled Process and Apparatus for- Treatment of Metal Products which claimed priority under 35 U.S.C. paragraph 119 to French Pat. application No. PV 116,523, filed Aug. 1, 1967. Application Ser. No. 748,291 has now been abandoned in favor of continuation application Ser. No. 132,593, filed Apr. 8, 1971.

In the metallurgical industry, products formed by the conventional hot shaping processes such as forging, rolling or stamping have an oxidized surface referred to as scale and a structure, particularly hardness, which makes them unsuitable for subsequent cold deforma tion and shaping operations. In order to continue operations in the cold state, it is necessary as a rule to perform an annealing heat treatment followed by a scouring operation to eliminate the surface oxides.

In one commercial process currently used, the shapes are heated electrically or with liquid or gaseous fuels and mostfrequently in oxidizing atmospheres. Thereafter, the surface oxides are removed in a twostage operation. In the first stage, the shapes are mechanically scoured by sanding or shot-blasting, or the shapes are chemically scoured or pickled by immersing them in baths of molten salts. In the second stage, the shapes are scoured or pickled in an acid bath. According to another process, the shapes are heat treated, for example in a bath of molten salts, followed by acid stripping or pickling. In yet another process, the heat treatment is under vacuum followed by acid stripping or pickling.

The industrial methods which consist of heating in a nonoxidizing atmosphere have the important advantage of not causing additional oxidation on the metal surface. This is also the case when the annealing or tempering treatment is under vacuum as described in the French Pat. No. 1,205,079 of Nov. 3, 1958. According to the teachings of that patent, the oxidized steel shapes are heated in a vacuum at a temperature of approximately l,0OO to 1,100 C. Thereafter, the shapes are cooled in the presence of a protective gas. The rate of cooling of the shapes in the gas excludes any possibility of fast quenching. in the case of austenitic stainless steels, the process comprises the steps of first heating oxidized shapes in a closed container kept under vacuum close to 0.1 torr at a temperature of approximately l,050 C for several hours, passing a protective nitrogen atmosphere into the container, transferring the shapes exposed to the atmosphere to a quenching bath, and finally pickling the shapes in an acid bath to eliminate the porous layer of residual oxide. This process is burdensome and costly. It causes superficial decarburization of the steel shapes treated. Finally, this process does not avoid the necessity ofsubsequent scouring or pickling.

In our copcnding application referred to above we described a process for heat treatment and descaling of metals or of oxidized metal shapes without causing harmful superficial decarburization. Shapes treated according to that invention usually do not require subsequent acid pickling to remove the scale.

According to our invention described in our copending application, the oxidized shapes are placed in an enclosure containing a reducing atmosphere under a pressure between and 0.01 torr, and heated to temperatures between 700 and 1,200 C, in contact with a carbonaceous reducing agent, after which they are cooled in a nonoxidizing environment.

The carbonaceous reducing agent may be gaseous and may also provide the required reducing atmosphere. It may also consist of a thin liquid or solid layer, for example of a hydrocarbon or of a fine suspension of a solid reducing agent, such as graphite in a liquid deposited on the treated metal. The total quantity of specific carbonaceous reducing agent should be sufficient in each case for all the surface oxides of the metal to be reduced, without exerting an action on the metal itself.

The reducing atmosphere may be generated by injection of a gaseous reducing agent into the enclosure. It may also be generated by injection of a liquid or solid reducing agent, at least partially gasified under the temperature and pressure conditions prevailing in the enclosure. ln particular, it may be generated by partial gasification of a thin layer of liquid hydrocarbons deposited on the shapes to be processed.

In this application we describe and claim an apparatus for the practice of the process described above.

Briefly, according to this invention, a heat treatment furnace is provided, which essentially comprises a sealed enclosure with pumping devices and heating devices, whereby the required pressure and temperature may be reached and maintained; devices for communication between the surroundings and the enclosure allowing the insertion and withdrawal of the shapes to be descaled without reducing the vacuum and without permitting air to enter the enclosure; means of injection and/or coating the shapes with a carbonaceous reducing agent; and means for cooling the products in a neutral atmosphere before emerging into the atmosphere.

According to a preferred embodiment, the furnace is isolated from the surrounding atmosphere by means of at least one barometric lock. A barometric lock may be fomied in a U-shaped well or elbow filled with the carbonaceous reducing liquid. One of the branches of the bend is in communication with the furnace. The other is connected to the surrounding atmosphere.

The two branches of the bend or well are equipped with lowering and lifting mechanisms which render it possible to insert the shapes to be processed through the liquid in the well. It is plain that the outlet of the furnace may be equipped with another U-shaped well filled with any appropriate liquid.

This combination of equipment provides the following results and advantages: the shapes processed according to our invention are inserted into the furnace and removed from this furnace without breaking the vacuum seal. They are coated with the carbonaceous reducing agent at the same time. The nature of the liquid present in the well or wells does not affect the atmosphere of the furnace. The components subjected to the treatment according to our invention may be quenched during their extraction from the furnace, in a liquid, without being in contact with air.

Further features and other objects and advantages of this invention will become clear from the following detailed description made with reference to the. drawings in which: I

FIG. 1 is a schematic section view of a furnace according to this invention;

FIG. 2 is a detailed section through a barometric charging and discharging joint useful in this invention;

FIG. 3 is a plan view of the elevator system in one of the legs of the barometric joint; and,

FIG. 4 is a plan view of the elevator mechanism of both legs of the joint.

One embodiment of this invention, diagrammatically illustrated in a section in FIG. 1-, consists of providing the processing furnace 1 with a toroidal shape having one orifice 2 in communication with a barometric well or lock 3. The lock 3 is in the shape of a U whose two branches are marked 4 and 5. The lock simultaneously serves for inserting the shapes (incorporated coating) and of extracting them (with quenching). It contains an oil, for example, a quenching oil. In operation, the levels of oil 6 in the two branches 4 and have the positions shown. The shapes under treatment travel in a definite direction in the furnace. The raising and lowering mechanisms (shown schematically as a movable hydraulic piston and cylinder 19, but which could be any other suitable raising and lowering device) take the shape to be treated, 7, lower it to 8 at the bottom of branch 4 below the separation level 9, cause it to pass to 10 at the bottom of branch 5 and raise it to 11 up to the orifice 2. The product enters the furnace at 12 and is carried in a definite direction around the toroidalshaped furnace. A shape which has already passed through the furnace is then placed on the raising and lowering mechanisms. The shape is subjected to quenching in the oil of the well before moving out into the atmosphere. A continuously operating furnace is thus obtained, the vacuum pipe being marked 14 and a hydrocarbon injector 13. The injection of the carbonaceous reducing agent occurs through one or more adjustable valves or through any other analogous device. The number and location of such devices corresponds to the thermal cycle selected, to the desirable vacuum, and to the capacity of the furnace. The heating system is comprised of graphite elements 20, for example.

According to an alternate mode of practicing our invention, the outlet of furnace l is a cooling lock 15 having doors l6 and 17. Means 18 are provided to maintain the atmosphere in the cooling lock inert. I

The joint of FIG. 2 is a U-shaped shaft made up of two cylindrical sleeves connected with one another at the base. Leg of the U is connected to the furnace interior 26 in a tight manner. The other leg 27, which opens into the open air, is sufficiently set off to allow ready access to the articles that are to be put into the furnace or to the articles that have been removed from the furnace. This U-shaped shaft is partially filled with a liquid whose level is established in each sleeve as a function of the pressure existing above each free surface. This means particularly that the level of the liquid can be the same in the two legs when the lock chamber is at atmospheric pressure. This may. be the case when the furnace chamber is under atmospheric pressure. This liquid which is suitable for coating the products that are to be treated according to the method of the invention (and possibly for tempering) fulfills the function of the hydraulic joint, thereby assuring isolation of the lock chamber from the atmosphere.

For the purpose of being introduced into the furnace, the articles that are to be treated are brought at 28 by means of any fixed or autonomous device to the charging elevator (shown in broken lines in the raised position at 29) and the elevator is then made to descend to the bottom position.

This elevator is composed of a frame 31 (FIG. 3) equipped with two sets of guide rollers such as 32 and 33 (FIGS. 2 and 3) which roll on vertical rails such as 34 (FIGS. 2 and 3) in such a manner that the vertical movement will be strictly rectilinear. This frame is coupled to at least one endless chain 35 (FIG.-2) which is guided over its entire elevation and is wound, on the one hand, over a control wheel 36 (FIGS. 2 and 4) moved by a set of motor reducers 37 (FIG. 4), and on the other hand, over a slidably mounted wheel 38 (FIG. 2) for regulating the tension of the chain. Each chain executes a back and forth (ascending-descending) motion whose extreme positions are governed by two endof-the-stroke devices, the one for travel at low speed before stopping, the other for stopping.

When this elevator has been brought to the bottom position 30 (FIG. 2) the immersed charge is pushed by gliding on rails 40 (FIG. 2) toward the elevator 39 (FIGS. 2 and 4) of the lock chamber in its low position. The device used here for pushing the charge is a rack bar pusher 41 (FIG. 4) having a pusher 42 (FIGS. 2 and 4) provided in front with a suitably shaped shield and on its lower portion with a rack bar having a control pinion whose movement is assured by a set of motor reducers 43 (FIG. 4) outside of the chamber through a tight rotary joint 44 (FIG. 4). The positions of end-ofstroke and stop-on-return are controlled by an end-ofstroke selector likewise positioned outside of the chamber and actuated by the entry shaft of the rotary joint.

When the charge is on the lock chamber side of the leg of the shaft, with a construction similar to the atmosphere side of the leg, it is hoisted to the lock chamber and returned by the transfer device and then by the furnace charging pusher.

The discharging procedure for the treated product is quite similar. The travel from the elevator platform on the lock chamber side of the shaft to the elevator platform on the atmosphere side is assured by another rack bar pusher 45 (FIGS. 2 and 4).,

In order to facilitate maintenance and repair, the shaft has a tight cover 46 (FIG. 2) on its upper portion which permits access. It also has a sliding trap door 47 (FIG. 2) which makes it possible to isolate the furnace chamber and to reach the corresponding elevator without being obliged to rupture the vacuum or to change the atmosphere of the lock chamber. This trap door, generally concealed in a protuberance, is controlled by an external set of motor reducers which act upon a rack bar hinged to the trap door. The upper portion of the trap door has a joint which cooperates with a mechanical bearing surface, the closing being assured by jacks.

Finally, the lock chamber includes devices for feeding the liquid, for controlling the level, for cooling, and recirculating the liquid 50.

In the foregoing, the entry and discharge of the products are made through the same shaft. It is also possible to provide a shaft specialized in one operation at each extremity of the lock chamber. Then simultaneous maneuvers may be carried out in both shafts which may, moreover, be filled with different liquids.

Having thus described the invention with the detail and particularity as required by'the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.

We claim:

1. A furnace for heat treating and descaling metal shapes consisting of a wall forming a sealed furnace enclosure, means for maintaining a subatmospheric pressure within said furnace enclosure, means for heating the shapes within the furnace enclosure, means for maintaining a reducing atmosphere within the furnace enclosure, and means for inserting and extracting the shapes in said enclosure, said inserting and extruding means comprising a U-shaped tube having two upright legs containing a carbonaceous reducing liquid for coating the shapes prior to entry into the sealed furnace enclosure and for forming a barometric lock therewith, one of said upright legs connected directly to and hermetically sealing with said enclosure, said liquid established at different heights in the different legs of the tube means after application of subatmospheric pressures to the enclosure, means for moving the shapes through the tube means so as to coat the shapes with said carbonaceous reducing liquid and then move them into the enclosure.

2. A furnace according to claim 1 in which the extracting means comprises a cooling lock and means for maintaining the atmosphere within the cooling lock in- 811.

3. A furnace according to claim 1 in which the wall means is toroidal in shape.

4. A device for moving shapes to and from an enclosure maintained at subatmospheric pressures comprising a U-shaped tube having spaced upright legs, one leg connected directly to and hermetically sealing with the enclosure and the other communicating with the atmosphere, a carbonaceous reducing liquid in said tube for coating the shapes prior to entry into the sealed furnace enclosure and for forming a barometric lock therewith, said legs sufficiently long to support a barometric column of said fluid, means for raising and lowering the shapes in each leg so as to coat the shapes with said carbonaceous reducing liquid, means for transferring the shapes from one elevating means to another.

5. A device according to claim 4 in which there is provided a means for pumping fluid from the bottom of the U-shaped tube to the top of the leg in communication with the enclosure.

Claims

1. A furnace for heat treating and descaling metal shapes consisting of a wall forming a sealed furnace enclosure, means for maintaining a subatmospheric pressure within said furnace enclosure, means for heating the shapes within the furnace enclosure, means for maintaining a reducing atmosphere within the furnace enclosure, and means for inserting and extracting the shapes in said enclosure, said inserting and extruding means comprising a U-shaped tube having two upright legs containing a carbonaceous reducing liquid for coating the shapes prior to entry into the sealed furnace enclosure and for forming a barometric lock therewith, one of said upright legs connected directly to and hermetically sealing with said enclosure, said liquid established at different heights in the different legs of the tube means after application of subatmospheric pressures to the enclosure, means for moving the shapes through the tube means so as to coat the shapes with said carbonaceous reducing liquid and then move them into the enclosure. 2. A furnace according to claim 1 in which the extracting means comprises a cooling lock and means for maintaining the atmosphere within the cooling lock inert.

3. A furnace according to claim 1 in which the wall means is toroidal in shape.