US3372065A - Method for heat treating articles - Google Patents

Description

March 5, 1968 w. R. KEOUGH METHOD FOR HEAT TREATING ARTICLES '5 Sheets-Sheet 2 Filed Oct. l1, 1963 6 m .RM n. O U 5 mw. er WK nw m@ .NNMSJ M4 @a w WM i m. .www

March 5, 1968 w. R. KEouGH 3,372,065

MET-HOD FOR HEAT TREATING ARTICLES Filed Oct. l1, 1963 5 Sheets-Sheet 3 1b je? T10. 5 18 82 wv@ La4 Y 5o -ao INVENTOR,

d/Ljo/vl 557745 2. Cen/G grroeNEx/ s 3,372,065 Patented Mar. 5, 1968 dice 3,372,065 METHOD FR HEAT TREATENG ARTECLES William R. Keough, Birmingham, Mich., assigner of fortyiive percent to Muitifasteuer (Iompany, Detroit, Mich., a partnership Filed Oct. 11, 1963, Ser. No. 315,467 7 Claims. (Cl. 148-13) ABSTRACT UF THE DESCLOSURE A method of heat treating articles by transfer from a heat treatment furnace into a quenching bath. The articies are passed through streams of cooling lluid continuously flowing towards the surface of the bath from a point above the surface of the bath. The downwardly directed streams will eliminate splashing of the quenching liquid into the furnace.

This invention relates to the heat treating of articles, and more particularly to improvements in methods and apparatus for the transfer of heated metal articles from a heat treatment furnace into a quenching bath.

The present invention is especially concerned with that type of heat treatment process wherein metal articles are conveyed through a heat treatment furnace at a rate chosen to achieve the desired exposure of the article to heat during its transit through the furnace and to discharge the article from the conveyor directly into a quenching bath. Because of the high temperatures maintained within the furnace and the continuous exposure of the conveyor to these temperatures, the choice of materials for the conveying belt is limited and most materials which are satisfactory for this purpose are exceedingly expensive. In the machine disclosed in this application, the belt is constructed of stainless steel. Frequently, the liquid in the quenching bath is extremely corrosive and splashing of the bath liquid onto a conveying belt of the furnace materially decreases the useful life of the belt.

Accordingly, it is an object of the present invention to provide a heat treatment installation wherein heated articles may be dropped directly from a heat treatment furnace into a quenching bath in a manner such that splashing created by the entry of the part into the quenching bath is minimized.

It is another object of the invention to provide a quenching bath installation in which quenching fluid is recirculated in a manner which assists in maintaining a constant temperature throughout the bath and at the same time minimizes the splashing of liquid as articles to be quenched are dropped into the bath.

The foregoing, and other objects, are achieved in an installation in which an endless conveyor belt is employed to convey articles through a heat treatment furnace and to discharge the articles by discharging the heated articles into a quenching bath located below the discharge end of the conveyor. The quenching bath is contained in a tank divided into two chambers. An openended vertical tube projects downwardly into a first chamber and articles discharged from the furnace conveyor drop .downwardly through this tube into the quenching bath contained in the rst chamber of the tank. A conveyor is located within the lirst chamber with a carrying run extending below the lower end of the tube and articles are thus conveyed from the quenching bath to the next treatment station.

At a location above the normal level of quenching liquid in the iirst chamber, a pair of conduits place the interior of the tube in communication with the second of the two chambers, the conduits entering the tube at opposed sides of the tube. Pump means are provided to 'continuously recirculate quenching liquid from the first chamber into the second chamber from which the fluid iiows through the conduits and is discharged into the tube in intersecting streams which intersect each other at a location above the level of liquid within the first chamber. The pump means are operated to maintain a generally constant static head in the second chamber which is above the level of the apertures. The rate of liow of liquid into the tube through the apertures is such that the streams of liquid have a substantial downward component at their point of intersection. Articles dropping downwardly into the quenching bath are dropped from a location such that they strike the downwardly converging streams substantially at their point of intersection, thus, splashing of quenching liquid upwardly to a distance such that it could Contact the belt of the furnace conveyor is prevented.

To achieve a constant temperature throughout the bath,

la cooling jacket is mounted on the tube at a location below the apertures and cooling air or other suitable cooling fluid is continuously circulated through the cooling jacket; this particular region representing the highest temperature region of the quenching bath, because this region is that into which the heated parts from the furnace are dropped.

The second chamber partially surrounds the first cha-mber and heating means are located in the second chamber. Operation of the heating and cooling means is coordinated to achieve the desired temperature regulation.

Other objects and features of the invention will become apparent by reference to the following specification and to the drawings.

In the drawings:

FIG. l is a side elevational view, partly in section, of a heat treatment furnace;

FIG. 2 is a transverse cross-sectional View of the furhace of FIG. l taken on line 2 2 of FIG. l;

FIG. 3 is a side elevational view with certain parts 'broken away or shown in section of a quenching 4bath |,tank employed to receive heated articles from the furnace of FIG. l;

FIG. 4 is a top plan View, with certain parts broken away or shown in section, of the tank of FIG. 3;

FIG. 5 is a cross-sectional view of the tank of FIG. 3 taken on the line 5-5 of FIG. 4; and

FIG. 6 is a cross-sectional view, partially taken on line 6-6 of FIG. 4.

Referring first to FIGS. 1 and 2, there is shown a heat treatment furnace of more or less conventional construction which takes the form of a thermally insulated tunnel designated generally 10, through which parts to be heated are conveyed on the upper run of an endless conveyor belt 12. Belt 12 is trained around a drive roller 14 and an opposite end roller 16 and is driven by a motor 18 in a direction such that the upper run of the belt moves from left to right as viewed in FIG. 1.

Articles to be conveyed through the furnace are fed onto the upper run of belt 12 from an infeed conveyor 2t) to a chute 22 which passes through an inlet opening 24 into the interior of tunnel 10. As the parts are conveyed by belt 12 through tunnel 10, they are exposed to the high temperature maintained in the interior of tunnel 1t) by a suitable number of burners 26. The temperature within tunnel 10 and the speed of movement of the articles through the tunnel are cooperatively adjusted to achieve the desired heat exposure of the article during its transit through tunnel 10.

When the parts reach the righthand end of the conveyor, as viewed in FIG. l, they drop freely from the sst/2,055

3 belt downwardly through an outlet opening 28 in the bottom of tunnel and into an open-ended tube 30 which extends downwardly from opening 28 into an open tank designated generally 32.

Tank 32l isv constructed with outer side walls 34, end walls 36 and 38 and a bottom wall 40. A belt conveyor designated generally 42 is suitably mounted to extend longitudinally of the tank, end wall 38 being inclined as best seen in FIG. 3, to accommodate the exit of conveyor 42 from the tank. Conveyor 42 takes the form ot an endless belt and is driven by suitable means, not shown, so that its upper run is driven from left to right as viewed in FIG. 3 to' carry articles dropped throughtube 3i) onto the belt through a bath of quenching liquid contained in tank 32 and to discharge the parts or articles to a suitable receiving means schematically indicated at 44 in FIG. 3.

A series of interior walls divide tank 32 into two chambers. An interior end wall 46 extends upwardly from bottom wall in spaced parallel relationship with tank end wall 36 and apair of interior side walls 48 extend forwardly from interior endv wall 46 at locations spaced inwardly onthe respective outer side walls 34 of the tank.

At the forward portion of tank 32 an interior top wall 50- and an interior front wall 52 extend entirely across the tank between outer side walls 34, while an interior rear wall 54- extends vertically between bottom wall 40 and interior top wall Sil and horizontally between interior sidewalls 48. The space between interior side walls 481 and their adjacent outer side walls 34 is closed by end walls 56 which extend upwardly from' top wall Sti to the top of tank 32.

TheI foregoing construction divides the interior of tank 32v into two separate chambers, one of which extends the .entire width of the tank below plate 50 and between walls 52 and' 54 and extends the entire height of the tank betweeninner and outer side walls 48' and 34 and inner and outer end walls 46 and 36. The second chamber is constituted by the remainder of the interior of the tank. For convenience, these two chambers are identified as first chamber 60 and second chamber 62, conveyor 42 being located in chamber 60, while chamber 62 is that chamber which includes the space between side walls 34 and 48 and beneath interior top wall' Sil;

Quenching liquid contained in tank 32.' is continuously recirculated betweenchambers 6i? and 62 by a pair of pumps designated generally 64 which continuously pump quenching liquid from' chamber 60 downwardly through openings in interior top wall 50 into chamber 62. From beneath topwall 50, the liquid iiows below walls 56 into the space between side walls 34 and 48. From each of side walls 48, a conduit 66 extends to the adjacent side of tube 30 to place chamber 62 in communication with the interior of tube 30 through apertures 68' in the opposed sidewalls of tube 30. Liquid liowing into tube 30 from conduits 66 passes downwardly through tube 3! to return to chamber 60.

Interior rear wall 46 is formed with an opening through the wall as at '70, and a bathe plate 72 is guided for vertical sliding movement to adjustably regulate the size of the opening; A vertical rod 74 coupled to plate '72 is provided with a series of hooks or notches 76 which may be engaged by any suitable stationary `cooperating member 78 to positiony plate '72 vertically relative to opening '70.

When pumps 64 are placed in operation, liquid is continuously pumped from chamber `60 into chamber 62 `and returns from chamber 62 through conduits 66 and tube 30 to chamber 60. In order to achieve the desired ilow through conduits 66, it is necessary to maintain a static head of liquid in chamber 62 which is above that maintained in chamber 60. The desired difference in static head is achieved by lowering plate 72 to completely close opening and operating pumps 64 until the desired difference in head is achieved. Plate '72 is then elevatedV to uncover opening 70 and the size of opening l 7i? is adjusted until the flow of liquid from chamber 60 into chamber 62 induced by pump 64 is equalized by the dow of duid from chamber 62 into chamber 60 via conduits 66 and opening 7 0.

The difference in static head between chambers 62 and 60 is adjusted to be such that bath liquid discharged into tube 36 through apertures 68 is discharged from the opposed sides of tube 33 in streams which intersect each other centrally of the tube at a level below the level from which the streams are discharged. In this manner, at the intersection of the streams within tube 30, both streams have a substantial downward component of velocity.

Because of the extremely high temperature maintained in furnace lil, the most satisfactory material for belt 12 has been found to be stainless steel. Stainless steel belts employed in heat treatment processes of the type under consideration are extremely expensive and the cost of the belt alone can represent a major portion of the cost of the entire installation. Stainless steel belts are entirely satisfactory from the standpoint of withstanding the high temperatures encountered in the furnace. However, in most cases the composition of the liquid in the quenching bath is of an extremely corrosive nature. From the standpoint of efciency of the heat treating operation, it is desirable to quench the heated article in the least possible time after it has passed through the furnace so that the article is quenched before any substantial cooling of the article has occurred.

Thus, from `the standpoint of obtaining properly treated articles, the distance between the quenching bath and the conveying belt should be at a minimum.

In the particular apparatus disclosed in the drawings, the quenching bath liquid is molten salt. Molten salt is extremely corrosive and in the event even a small amount of molten salt should contact belt 12, the belt would shortly be rendered useless.

In order to prevent splashing of molten salt onto belt 12, molten salt Within tank 32 is recirculated in the manner described above. The discharge end of belt l2 is located so that parts dropping from the discharge end of the belt are dropped downwardly through the center of tube 3d so that the articles tirst contact the bath liquid at the point at which the streams of liquid discharged from apertures 63 intersect each other. As described above, the rate `at which the streams are discharged into the tube is so regulated that at the intersection of the streams, both streams have la substantial downward component of velocity. Thus, the relative velocity at which the `article strikes the liquid of the bath is substantially reduced, thereby minimizing and substantially eliminating the upward splash of molten sal't. The normal level of liquid within chamber 60 is such that the surface of the main body Of liquid within chamber 60 is located below the intersecting streams, thus the splash created as the article drops into the main body of quenching liquid is smothered by the streams.

As described above, articles droppingV through tube 39 fall through the liquid bath onto the upper or carrying run of conveyor 42 and are conveyed through and out of the bath to be discharged on the receiving means 44.

When the apparatus disclosed in the drawings is operated .at full capacity, the heat of the articles dropped into the bath may be suicient to maintain the salt bath in molten form. However, because of the relative large volume of tank 32, it is desirable to provide additional heating means so that the temperatureA of the bath can be maintained as uniform as pos-sible through the tank.

To accomplish this, a pair of radiant heaters 80 are mounted in the tank to extend along each side of the tank near the bottom throughout the entire length of the tank. Because of the fact that that portion of the tank surrounding the bottom of tube 30 tends to become the hottest because the continuous dow of heated parts from the furnace enters the bathat this location, it is desirable to provide a means for locally cooling this particular region. To this end, a cooling jacket 82 is mounted on the lower end of tube 30 in surrounding relationship to the tube and provided with an inlet 84. Cooling fluid may be introduced into the interior of jacket 82 as by the schematically illustrated blower and conduit 88 of FIG. 5 and, in the case where air is employed as the cooling fluid, a suitable conduit connection to outlet 86 may be provided to exhaust heated air from the cooling jacket. It will be appreciated that operation of heaters 80 and the cooling jacket will be coordinated as required to achieve the desired effect.

While one embodiment of the invention has been disclosed and described in detail, it will be apparent to those skilled in the art that the disclosed embodiment may be modified. Therefore, the foregoing description is to be considered exemplary ra-ther than limiting, and the true scope of the invention is that defined in the following claims.

I claim:

1. ln a heat treatment process wherein articles to be treated are conveyed through -a heat treatment furnace and discharged into `a quenching bath; the method cornp-rising the steps of continuously recirculating the bath liquid to establish a stream of bath liquid, descending the stream upon the surface of said bath from a point above the surface of said bath, and dropping larticles to be quenched from said furnace into and through said stream at a location where said stream has a substantial downward component of velocity, and thereafter immersing the article into said bath to thereby essentially smother upward splashing cre-ated by entry of the articles into said bath.

2. In a heat treatment process wherein articles to be -treated are conveyed through a heat treatment furnace and discharged into a quenching bath; the method comprising the steps of continuously recirculating a fiow of bath liquid, discharging the flow as ya plurality of streams from locations above the bath ilevel, causing said streams to intersect each other at a region of general common intersection above the level of said bath and below the level from which the streams are discharged, and dropping articles to be quenched into and through said region of common intersection and into said bath to minimize the splash created by the entry of the article into the bath,

3. In a heat treatment process wherein articles to lbe treated are conveyed through ia heat treatment furnace and discharged into a quenching fluid bath; the method comprising the steps of continuously cascading a stream of quenching fluid from above the bath level to pass downwardly upon the surface of a predetermined region of the bath, dropping articles to be quenched through said cascading stream and into the predetermined region to minimize the splash created by the entry of the article into the bath, and circulating a Icooling fiuid about said selected region.

4. In a heat treatment process wherein articles to be treated are deposited from a heat treatment furnace into a quenching bath; the method comprising the steps of confining the quenching bath in an open tank having a first chamber and a second chamber, continuously recirculating the bath liquid between said chambers to maintain the level of the bath in said second chamber at any one of several predeterminable levels above the level of the bath in said first chamber, discharging bath liquid from said second chamber into said first chamber in a plurality of streams intersecting each other in a predetermined region above the level of liquid in said first chamber and below the level from which said streams are discharged, and dropping articles to be quenched into said first chamber through said predetermined region to minimize the splash created by the entry of the article into the bath.

5. In a heat treatment process wherein articles to be treated are conveyed through a heat treatment furnace and discharged into a quenching bath; the method comprising the steps of confining the quenching bath in an open tank having a first reservoir and a second reservoir, continuously recirculating the bath liquid between said reservoirs to maintain the level of the bath in said second reservoir at a predetermined level above the level of the bath in said first reservoir, discharging bath liquid from said second reservo-ir into said first reservoir in a plurality of streams intersecting each other in a predetermined re` gion above the level of liquid in said first reservoir and below the level from which said streams are discharged, dropping articles to be quenched into said first reservoir by passing the articles through said predetermined regions, and circulating a cooling fluid about said predetermined region.

6. In a heat treatment process wherein articles to be treated are heated in a heat treatment furnace and discharged into a quenching bath; the method comprising the steps of recirculating a flow of bath liquid into a predetermined region above the bath surface and out of said region beneath the bath surface, discharging an article from the furnace toward said region and the bath, imparting a substantial velocity flow component at a location above the bath surface in the direction of movement of the article toward the bath, substantially immersing the article in the flow at essentially said location above the bath surface and thereafter immersing the article in the bath to thereby minimize splashing created as the article enters the quenching bath.

7. In a heat treatment process wherein articles to be treated are conveyed through a heat treatment furnace and discharged into a quenching bath; the method com prising the steps of establishing a stream of bath liquid, cascading the stream upon the surface of said bath from a point above the surface of the bath, discharging articles to be quenched from said furnace into and through said cascading stream at the location above the bath surface, and thereafter immersing the articles into said bath to thereby essentially smother upward splashing created by entry of the articles into the bath.

References Cited UNITED STATES PATENTS 2,494,361 1/1950 Scarbrough et al. 266-4 X 2,322,777 6/1943 Purnell 148-143 2,618,284 11/1952 Purnell 134-154 DAVID L. RECK, Primary Examiner.

JAMES H. TAYMAN, IR., HYLAND BIZOT,

RICHARD O. DEAN, Examiners.

I. I. MULLEN, Assistant Examiner.

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