US2793027A

US2793027A - Heat-treatment of metal articles

Info

Publication number: US2793027A
Application number: US560214A
Authority: US
Inventors: Andre M Matthey
Original assignee: METAL ROLLING AND TUBE Co
Current assignee: METAL ROLLING AND TUBE Co; METAL ROLLING AND TUBE Co Pty Ltd
Priority date: 1956-01-19
Filing date: 1956-01-19
Publication date: 1957-05-21
Anticipated expiration: 1974-05-21

Description

May 21, 1957 A. M. MATTHEY HEATTREATMENT oF METAL ARTICLES 5 Sheets-Sheet 2 Filed Jan. 19, 1956 2 m. El

INvENToR Andre M. Mot'rhey BY Mmlzgumfz ATTORNE s May 21, 1957 A. M. MATTHEY 2,793,027

HEAT-TREATMENT OF' METAL ARTICLES Filed Jan. 19, 1956 5 Sheets-Sheet 3 pM,--fmmval AT ToRNEYs NGE United States Patenty HEAT-TREATMENT OF METAL ARTICLES Andre M. Matthey, Johannesburg, Transvaal, Union of South Africa, assignor to Metal Rolling and Tube Company (Proprietary) Limited, Johannesburg, Transvaal, Union of South Africa, a company of the Union of South Africa Application January 19, 1956, Serial No. 560,214

6 Claims; (Cl. 2665) This invention relates to the heat-treatment of metal articles as for annealing the samt or heating them for the purpose of quenching, and incidentally, obtaining thereon clean scale-free surfaces in suitable condition for resisting re-oxdation and/ or for direct treatment such as painting, plating and the like without relatively expensive' pre-treatment being necessary after the heat-treatment. Such annealing or like heat-treatments for their performance involve the use of furnace apparatus within which an atmosphere has to be maintained which inhibits oxidationbut hitherto the maintenance of such an atmosphere has presented considerable difficulties on account, for example, of relatively heavy lossesl of the furnace gases as the articles are introduced into and withdrawn from the furnace, explosion risks arising from the use of certain gases capable of forming explosive mixtures with the air, and other dificulties the avoidance or reduction of which has (as is of particular interest in the present invention) inhibited the obtaining of the heat-treated articles leaving the furnace in the desired surface condition mentioned above.

According to the invention, the articles to be treated are fed in procession at a suitable speed into and out of a furnace space dened at its base by a liquid seal through which the articles are admitted for heating to the required temperature and for the required time and through which also the articles are subsequently removed in cooled condition, the required atmosphere in the furnace being maintained by Vaporisation of the liquid constituting the seal and wetting the admitted articles. and such liquid being selected from` a range of commercial solvents, paint thinners and the like which are oxygen-free and vaporise in the temperature conditions at which it is required to operate the furnace space.

The furnace space is isolated from the atmosphere at its base by the liquid seal and at its upper part by a trap of the selected solvent or like liquid so arranged as, in response to pressure changes occurring in the said space (as between high temperature operative and low temperature inoperative conditions inthe furnace) to control the escape of vapours of said liquid to the atmosphere or to a condenser for subsequent return of the condensate to the sealing liquid container and the induction of nitrogen or other suitable neutral gas into the furnace space when the same is put out of operation, and also to provide for escape of such gas by displacement by the generated vapours when the space is heated for the annealing or like process.

vThe invention also provides for the progressive movement of the articles to be treated in a generally ascending path from the sealing liquid to the upper and hottest` region of the furnace space and for their being returned into the sealing liquid in intimate heat. exchange relationship with the succeeding and ascending articles, so as to eieet general heat economy within the furnace space.

Furthermore, the invention consists in apparatus for operating in accordance with the preceding paragraphs and comprising a generally upright externally heat-insurice lated furnace chamber having an open lower end occurring in an open vessel adapted to contain a quantity of liquid forming a seal over the said lower end, an upwardly converging upper end to the chamber provided with a conduit leading to externally located apparatus, heating means in the upper region of the furnace chamber, endless band or chain or like conveyor means extending within the chamber between the said vessel and the upper region of the chamber by which conveyor means the articles to be treated are traversed in the chamber as aforesaid, and means for feeding the articles through the liquid to the ascending run of the conveyor means and again through the liquid from the descending run.

Preferably, the drive to the conveyor means is applied to its lower end which is submerged in the sealing liquid, i. e. so that the shaft and bearings and like working parts may operate in relatively cool conditions, e. g. only a few degrees above normal atmospheric temperature, and with adequate lubrication from `the said liquid. L

The` aforementioned conduit leading from the upper end of the furnace chamber may comprise or connect with a condenser and a U-shaped arrangement adapted to provide a trap of liquid similar to that used to seal the bottom of the furnace chamber. That limb of the U- shaped tube arrangement which occurs the more remote from the furnace space opens upwardly to the atmosphere and is shaped to provide, or connect with, a chamber for a iloat which is borne on the trapped liquid and operating a non-return valve. The oat is adapted, in response to inequalities in the liquid levels in the respective trap limbs, automatically to close or open the valve, contained in a conduit, to permit condensed sealing liquid to be returned to the sealingV liquid vessel and escape to atmosphere of uncondensed gases.

In order that the present invention may be more clearly understood and carried into practice, reference will now be made to the accompanying sheets of drawings on which like reference numerals refer to like parts throughout the several views.

In the drawings:

Fig. 1 is a diagrammatic transverse cross-section of a heat-treating apparatus for pipes arranged and constructed according to this invention;

Fig. 2 is a diagrammatic horizontal cross-section of the apparatus shown in Fig. l but not showing the extraneous part of the apparatus; and

Fig. 3 is a diagrammatic front elevation of the apparatus shown in Figs. 1 and 2.

Referring to the drawings, reference numeral l denotes f thefurnace structure which essentially comprises spaced outer and

inner shells

2 and 3 between which heat-insulating material 4 is contained. Both said shells Z and 3 provide upwardly converging tops 5 and 6, respectively, from the apexes of which gas conduits or pipes 7 and 8 extend. The outer shell 2 is open in respect of its bottom end and is arranged to dip below the liquid surface 9 contained in a vessel 1i! to form a liquid seal.

Within the furnace space il, formed by the inner shell 3, a vertically disposed endless conveyor l2 is operatively mounted and which conveniently consists of a number of spaced parallel endless chains driven at the same speed from a common driven shaft 13. Said conveyor chains 12. are provided with pluralities of hook-like arms 14 for receiving the articles to be heat-treated. Said articles to be treated in the apparatus shown are pipes i5. The ascending and descending runs of the conveyor chains 12 are preferably arranged as closely together as is practically possible to permit heat exchange between the cooler ascending pipes and the hotter descending pipes.

In the top region of the furnace space 11 and adjacent the top of theV ascending run of conveyor chains 12, l the heating means 16Mis' mounted whereby th..l?ipe's 1.5.5.E

are heated to the desired degree. As sutlicient space is required around the heating means 16, a vertical partition plate 17 is mounted in the furnace space 11 to restrict the space around the ascending and descending runs of the conveyor 12 below the heating means for a maximum concentrated vapour atmosphere to be created around the articles to be treated during their passage within the furnace.

The articles to be heat-treated, e. g. the pipes 15, are carried into the apparatus on parallel spaced conveyor chains 18 onto which such articles are loaded at position 19. Said chains 18 carry said articles over the rim of the vessel and then downwardly into the vessel to a position well below the sealing liquid surface 9. Said chains 18 thereafter elevate the articles and then again lower them onto any suitable transferring device, e. g. spaced wheels providing radial arms, for transferring and placing the articles onto the hook-like arms 14 of the conveyor chains 12. Said chains 1S thereafter pass over sprockets 20 adjacent the vessel bottom and thereafter over elevated sprockets 21` to form a curved run 22 on which the articles are collected after discharge by the hook-like arms 14 of the conveyor chains 12 at the termination of the descending passage through the furnace. The discharge of the articles is below the liquid surface 9 of vessel 10. The heat-treated articles are discharged from the conveyor chains 18 at position 23, exteriorly of the apparatus.

By employing chains for the conveyor 12, heat is enabled to pass freely through it and from the descending runs to the ascending runs. Said conveyors provide for continuous operation of the apparatus as a whole. The conveyor chains 18 are synchronised in respect of their movement speed relative to the speed of the conveyor 12.

The vessel 10 containing the liquid seal may preferably be provided with means, e. g. a cooling water jacket or the like, which may be used in emergency and/ or to maintain the liquid at a general temperature best suited to the temperature and vapour conditions required to be produced and maintained in the furnace.

The pipe 8 is connected to a condenser 24 which is arranged to discharge into the one limb 25 of a U-shaped liquid trap device 26. The other leg 27 conveniently forms a iloat chamber in which float 28 is operatively located and providing a non-return valve 29 permitting entry of lluid into such chamber while reversed flow is prevented. Said leg 27 provides an exit pipe 30 and valve 31 discharging upwardly into the atmosphere as also a second pipe 32 extending from the side of such chamber. Said pipe 32 is provided with a U-formation trap 33 and vallve 34 and is further adapted to discharge into the vesse 10.

The pipe 7 is preferably arranged to discharge into the vessel 10 as is shown in Fig. 1.

The heat-insulation material-containing space between the

shells

2 and 3 is connected to a non-oxidising or neutral gas supply pipe 35 and through valve 36 and a bypass valve 37. The valve 36 is controlled by a float 38 which is operatively located in a chamber 39 which, in turn, is connected by a liquid-containing U-tube 40 to the space between

shells

2 and 3. When the pressure reaches a predetermined high value within said insulation material space the mutual gas supply is automatically cutoff on raising of the tloat 38 due to such elevated pressure. When the pressure drops the float 38 recedes and causes opening of the gas supply. By valve 37, which is manually controlled, the gas may be introduced whenever desired.

A neutral or non-oxidising gas supply is also connected to the liquid trap 26 by vvalve 41. Such gas, e. g. nitrogen, may' be "arranged to ll the furnace space when the furnace is shut down. When the furnace is shut down, the liquid or solvent vapour is condensed and the furnace becomes filled with the neutral or like gas. By such means risks of theikind referred to at the beginningV of this speciiication are avoided and the apparatus as a whole may be rendered substantially fool-proof from the aspects both of ecient operation and safety. When the furnace is brought into use such neutral or like gas is expelled through the nonreturn valve 29 to atmosphere under the action of gravitational displacement.

In order to create a circulation of vapours in the furnace space 11, vertical blowers or fans 42 are operatively mounted in the ends of such furnace space.

In the following description of the performance of the method, the subject of this invention, it may be assumed that the articles to be treated are pipes or tubes 15 destined after annealing to be painted. With the

conveyors

12 and 18 suitably constructed for handling such pipes or tubes and the sealing liquid used being a solvent of such paint as is ultimately to be applied to the article, the operation may be substantially as follows:

As the conveyor 12 slowly advances through its upward and downward paths the tubes 15, being first dipped in the solvent, convey the sealing liquid into the heated chamber where the solvent is vaporised to create the required non-oxidising atmosphere in which also descaling A typical maximum temperature created by the heating means 16 in the upper region of the furnace may be of the order of 1600* F., whereas the temperature as sumed by the solvent constituting the liquid seal may ordinarily be of the relatively low order of 50 F. above atmospheric temperatures.

It is found that the heat-treated or annealed products leaving the liquid seal and cooled are adequately protected from oxidation by a thin coat of the solvent adhering to them, so that they may be stored for considerable periods of time without deterioration such as would interfere with their subsequent painting or other such treatment. In this connection the sealing liquid, which is required to vaporise for the creation of the correct atmospheric conditions within the furnace, may alternatively comprise a commercial oil or the like, but such an oil is undesirable as it calls for degreasing or like treatment which may be avoided as above indicated by a correct choice of the solvent. p

As valready indicated the furnace atmosphere created in the foregoing way possesses strong descaling properties and it is found that even rusty pipes may be cleaned therein to leave the furnace in a perfectly bright condition.

It will be understood, of course, that means may be provided for varying the speed of operation ofthe conveyors 12 and 18 for varying the total time of treatment and therates of heating and cooling which take place` prising a generally upright externally heat-insulated furnace chamber having an open lower end, an open vessel into which the open lower end of the chamber vextends, said vessel being adapted to contain a quantity of liquid forming a seal over said lower end of the furnace chamber, heating meansin the upper region .of the furnace chamber, endless conveyor means extending within the chamber between'the said vessel and upper region of the chamber by which conveyor means the articles to be heat-treated aretraversed inthe chamber from the vessel to the hottest upper region of the chamber and down# wardly'to the vessel, means for feeding the articles to be heat-treated through liquid in the vessel to the ascending run of the conveyor means and again after heat treatment through the liquid in the vessel from the descending run of the conveyor, a condenser located outside the furnace chamber, a vapor-flow conduit leading from the upper portion of the furnace chamber to the condenser, a U- shaped liquid trap, a conduit connecting the discharge of the condenser with one limb of the U-shaped liquid trap, a non-return float valve in the other limb of the U-shaped liquid trap for preventing the flow of liquid from said other limb back into the limb of the trap connected with the condenser, a conduit leading from the upper portion of said other limb of the trap to the atmosphere and having a control valve therein, and a conduit having a control valve therein for conducting liquid from said other limb of the trap to the vessel.

2. An apparatus for heat-treating metal articles as claimed in claim 1, characterized by including a valvecontrolled connection for introducing a neutral or nonoxidizing gas into the space in the furnace chamber through the vapor flow conduit leading from the upper portion of the furnace chamber to lill the furnace space when the furnace is not used, such gas being introduced into the furnace chamber when the furnace is shut down and the vapors therein condense while the gas filling the chamber is expelled through the non-return valve as the furnace is brought into use.

3. An apparatus for heat-treating metal articles comprising a generally upright externally insulated furnace chamber having an open lower end, an open vessel in which is received in spaced relationship said lower open end of the furnace chamber, a liquid contained in said vessel forming a liquid seal for the open lower end of said furnace chamber and which liquid is vaporizable in the temperature conditions at which it is required to operate the furnace space, heating means in the upper region of the furnace chamber, a first endless conveyor means running through the liquid in said vessel for receiving the metal articles to be treated, for conveying such articles into the sealing liquid, for subsequently receiving thc treated articles within the liquid and for the removal of such treated articles from the vessel, a second endless conveyor means extending within the furnace chamber between the said vessel and the upper region of the chambcr for receiving the metal articles carried into the vessel by said first endless conveyor means and for conveying such articles to the hottest upper region of the furnace chamber and then downwardly to the vessel, an upwardly converging upper end to the furnace chamber, an externallydocated condenser, conduit means for conducting vapors from said upper end of the furnace chamber into the condenser, a U-shaped liquid trap of which one upright 'member is connected with the condenser outlet, the other upright member having a valvecontrolled outlet to the atmosphere, a oat borne on the trapped liquid in said last mentioned upright member f the trap, a non-return valve with which said float is associated for preventing liquid from flowing to the upright member of such trap which is connected to the condenser and furnace space, and a conduit having a control valve and leading from said upright member of the U-shaped trap containing the float to the vessel for conducting excess trapped liquid to the vessel.

4. An apparatus for heat-treating metal articles -according to claim 3, including a valved connection for ntroducing a supply of neutral and non-oxidizing gas through the conduit means extending from the upper end of the furnace chamber which is adapted to till the furnace space when the furnace is inoperative, such gas being expelled through the non-return valve of the liquid trap by gravitational displacement as the furnace is brought into use, whereas lling of the furnace with the neutral non-oxidizing gas takes place on condensation of the vapors within the furnace when the furnace is shut down.

5. Apparatus for heat-treating metal articles according to claim 3, wherein the furnace chamber comprises spaced outer and inner metallic shells, heat insulating material lcontained between said shells, both shells being provided with upwardly converging top ends, :a conduit connected into the top end of the outer shell and extending to the liquid-containing vessel for conducting excess vapors expelled from the space between the shells, conduit means provided with a iioat controlled valve for introducing a non-oxidizing neutral gas into the lower region of the space between said shells, and a U-tube containing liquid having one leg connected into the space between said shells while the float of the float controlled valve is responsive to the liquid level in the yother leg of the U- tube, the arrangement being such that when the pressure reaches a predetermined high value within said space between the shells the neutral gas supply is automatically cut olf on raising of the iloat due to such elevated pressure whereas on pressure drop the float recedes andcauses the opening of the float controlled valve for the supply of gas to the space between the shells.

6. An apparatus for heat-treating metal articles, comprising a generally upright furnace chamber having an open lower end, an open vessel in which the open lower end of said furnace chamber is received in spaced relationship, said vessel being adapted to contain a quantity of liquid forming a seal yover said open lower end of the furnace chamber, heating means in the upper region of the furnace chamber, endless conveyor means extending within the chamber between said Vessel and the upper region `of the furnace chamber and by which the articles to be heat treated are moved through the chamber from the vessel to the hottest upper region of the chamber and downwardly again into the vessel, means for feeding the articles to be heat treated through the liquid in the vessel to the ascending run of the endless conveyor means and again after heat treatment through the liquid in the vessel from the descending run of the conveyor means, said furnace chamber being comprised of spaced inner and outer metallic shells, heat insulating material arranged in the space between said shells, said outer `shell extending down to `a point below the liquid level in said vessel, conduit means connected into the space between the inner `and outer shells at the upper portion of the furnace chamber and extending through the lower portion of the outer shell and into the vessel for conducting uid from the space between said shells into the vessel within the outer Shell, a conduit means connected into the upper portion of the furnace chamber for conducting vapors therefrom, and means for delivering a neutral gas into the lower portion of the space between said furnace chamber shells.

References Cited ln the file of this patent UNITED STATES PATENTS 1,738,038 Cope Dec. 3, 1929 1,782,481 Shipley et al. Nov..25, 1930 2,045,392 Kientz June 23, 1936 2,339,192 Roberson Jan. 1l, 1944 2,418,088 Nachtman Mar. 25, 1947 2,458,525 Nachtman Ian. 11, 1949 2,459,674 Nachtman Ian. 18, 1949 2,585,277 Seabold Feb. 12, 1952