US3550920A - Fluidized bed - Google Patents

Description

United States Patent Hans Geipel Oberhausen-Sterkrade;

Eckehard Forster, Oberhausen; Wilfried Heinemann, Duisburg-Hamborn; Kurt 1 Baranowski, Essen-Frintrop, Germany [72] Inventors [21] Appl. No. 821,700

[22] Filed May 5,1969

[45] Patented Dec. 29, 1970 [73] Assignee Huttenwerk Oberhausen A.G.

Oberhausen, Germany a corporation of Germany [32] Priority May 10, 1968 [3 3 1 Germany Continuation-impart of Ser. No. 729,833, Jan. 25, 1968, now Patent No. 3,492,740

[54] FLUIDIZED BED 5 Claims, 1 Drawing Fig.

152 u.s.c1 2 3/21;

511 1m.c1 F27b3/00, F27b15/00 1501 FieldofSearchQ 1. 263/4OA. 2lA.2lC; 165/104; 34/57A.57T

l 56] References Cited] UNITED STATES PATENTS 1,765,026 6/ l 930 Miller 263/21C 2,600,306 6/1952 Lipscomb 263/8X Primary Examiner-John J. Camby Attorney-Karl F. Ross ABSTRACT: In a plant for the heat treatment of workpieces on a continuously moving apertured conveyor, the latter is surrounded by a fluidized bed of solid ceramic particles entrained by a stream of carrier gas within a tunnel whose discharge end contains an oscillatable supporting plate, upwardly inclined toward the outlet, underneath the conveyor to stop the outward movement of solid particles and accumulate them in a nearly stationary pile traversed by the emerging workpieces; escape of particles underneath the second conveyor is prevented by a flexible seal between the tunnel bottom and the oscillating plate.

PATENTE [1 02 9 I970 INVENTORS GEIPEL- HANS ECKEHARD FORSTER WILFRIED HEINEMANN KURT BARANOWSKI ATTORNEY FLUIDIZED BED This application is acontinuation in part of copending application Ser. No. 729,833 filed 25 Jan. 1968, now 11.8. Pat. No. 3,492,740.

ln commonly owned U.S. Pat. No. 3,492,740 there is disclosed a fluidized bed for the heat treatment of workpieces, particularly but not exclusively the cooling of steel wire which is to be patented (i.e. cooled at a controlled rate) for transformation from its austenitic state to a sorbitic pearlite structure as more fully disclosed in commonly owned application Ser. No. 675,522 filed 16 Oct; 1967, now US. Pat. No. 3,525,507.

The term fluidized bed" denotes a mass of solid particles, such as ceramic granules, entrained by a'stream of carrier gas. The particles, which should have an elevated heat transfer coefficient, serve as the principal constituent of the cooling medium whereas the carrier gas playsonly a minor role in the maintenance of the desired discharge temperature. This gas is also used as a vehicle for a continuous recirculation of the particles, generally in the direction of conveyor motion, through a cooling tunnel and through an external cooling chamber where the heat abstracted from the workpieces (e. g. a succession of wire loops) is removed. For most effective heat transfer it is desirable to let these particles accumulate in a nearly stationary pile at the exit end of the tunnel and, preferably, also at the entrance end. At the same time, for

reasons of economy as well as accurate control of the exit temperature, any escape of particles together with the emerging workpieces should be suppressed or at least minimized; thus, in the wirepatenting process of our aforementioned copending application it is essential to complete the. transformation under substantially isothermic conditions, in the absence of a cooling medium other than the surrounding atmosphere, so that all contactwith accompanying solid particles should be positively terminated as soon as the workpieces leave the bed.

The general object of the present invention is to provide a fluidized bed satisfying this requirement for the aforestated purpose and for other types of heat treatment, a term intended to encompass exposure to any contacting medium maintained at a predetermined temperature.

The solution of this problem proposed in US. Pat. No. 3,492,740 resides in the provision of two conveyors within the tunnel, i .e. a principal conveyor which is apertured to facilitate the circulation of heating or cooling medium around the workpieces carried thereon and which extends within the tunnel past the exit end thereof for discharging the heattreated workpieces, and a secondary conveyor located just below the principal conveyor at the exit end, this secondary conveyor moving in a direction opposite that of the principal conveyor so as to arrest outwardly traveling particles which thereby pile up ahead of the tunnel exit.

Although this solution is satisfactory for most purposes, difficulties may arise from the necessity of sealing the region below the returning run of the secondary conveyor against outgoing particles to prevent their escape from the tunnel.

An object of our present improvement, therefore, is to provide an alternate system which, in addition to satisfying the aforestated desiderata, minimizes this problem of leakage.

in accordance with the present improvement, we replace the continuously rotating secondary conveyor by a vibratile support which is upwardly inclined toward thetunnel exit underneath the apertured band referred to hereinabove as the principal conveyor," this support being oscillatable at a sufficiently high frequency to drive any outwardly traveling particles back into the tunnel. With particle sizes on the order of 40 to 160 microns, a suitable vibration frequency may range between approximately and 40 c.p.s.

Since the oscillatory support, apart from its vibrations, remains at a fixed location with reference to the tunnel wall,

the space underneath that support may be readily sealed with the aid of a flexible strip spanning the intervening gap. Having no major longitudinal motion of its own, this support is found to define a sharper and more constant profile for the pile of particles accumulating thereon so that the duration of the heat treatment is more nearly independent of the extent to which the treated wire or other workpiece projects above the supporting surface. We have found, therefore, that with the present improvement the quality of the product can be significantly enhanced.

The invention will be described in greater detail with reference to the accompanying drawing, the sole FIG. of

which is a diagrammatic side-elevational sectional view of a fluidized bed for the cooling of wire in accordance with a preferred embodiment.-

The bed 1 shown in the drawing consists, essentially, of a mass of solid particles (e.g. of magnesia 2) entrained by a stream of gas which flows toward the discharge end 10 of a tunnel 15 traversed by an apertured principal conveyor 5 in the form of an endless belt such as a wire screen or a set of parallel wires. workpieces 6, i.e. a succession of interconnected loops of steel wire. are deposited on conveyor 5 near the tunnel entrance by a dispenser generally indicated as 16. This dispenser comprises a rotating; tubular arm through which the hot steel wire passes so as to beformed into loops by the arm's rotation; more elaborate types of loop formers are known, for example, from US. Pat. Nos. 3,056,433 and Re. 26,052. The dispenser 16 may oscillate transversely with reference to conveyor 5, in the manner disclosed in commonly owned application Ser. No. 675,405 filed 16 Oct. 1967, for the purpose of spreading the loops most effectively over the available conveyor surface. t

A stream of relatively inert carrier gas, e.g. hydrogen or carbon monoxide, is continuously recirculated through the tunnel 15 by way ofan entrance pipe 17 near the dispenser 16 and an exhaust pipe 18 at the exit end 10. A stationary imperforate support plate 7 underlies the upper run of belt 5 just below the inlet 17 so that solid particles entrained by the carrier gas tend to accumulate as shown at 11. Additional gas is admitted via a manifold 3 at a controlled rate through a perforated base 4 on which the particles 2 come to rest. The particles exhausted through outlet 18 and through a further exit port 20 are returned to the inlet 17 after passing through a cooling chamber not shown; reference is made to the aforementioned copending application Ser. No. 675,522 for additional details of a plant of which the illustrated arrangement forms a part.

Conveyor 5 rotates continuously so that its upper run carries the workpieces 6, accompanied by some of the solid particles 2 of the fluidized bed 1, from the entrance end to the exit end of tunnel 15, Le. from left to right: as viewed in the drawing. A supporting plate 8 is inclinedly disposed at this exit end and carried by coil springs 21 on the bottom 22 of tunnel 15. A vibrator, illustrated diagrammatically asa rotating cam 23 acting upon a boss 24 of support 8, oscillates the latter at 'a preferred rate of several tens of c.p.s. as indicated by an arrow A. A rubber strip 13 forms a flexible but tight seal between the tunnel bottom 22 and the underside of plate 8. The interior of this plate may be compartmented, as shown, to form voids 25 to which further carrier gas may be admitted via flexible tubing, not shown, for discharge into the space above plate 8 by way of orifices26.

The vibrations of plate 8 serve to arrest the outfiowing particles entrained by conveyor band 5 which thereby accumulate in pile 12. On emerging from this pile, the workpieces 6 undergo no further forced cooling up to their discharge from the conveyor. The terminal portion of tunnel 15, beyond pile 12, thus may serve for the completion of the austenitic pearlite transformation, under substantially isothermic conditions with inhibition of outward heat radiation by the thermally reflecting tunnel walls, to prevent the formation of bainite, as more fully described in application Ser. No. 675,522 referred to above. As also described there, the temperature of the particles 2 and the speed of conveyor 5 may be regulated to maintain the desired exit temperature for'the workpieces, e.g. by means of a temperature sensor 19 disposed near the exit pile l2; changing the conveyorspeed varies the residence time of length L.

The conveyor 5 may be disposed substantially horizontally or, as shown,may slope slightly upwardly toward the exit end of the tunnel guarded by the vibratile support 8.

Although the supporting plate 8 has been illustrated as vertically oscillatable, this mode of vibration is shown only by way of example and could be replaced by other modes, e.g. a swinging about a horizontal axis.

We claim:

1. A. fluidized bed for the heat treatment of workpieces, comprising an elongated tunnel; an apertured unidirectionally movable conveyor extending within said tunnel past an exit end thereof for discharging treated workpieces; dispenser means at an entrance end of said tunnel for depositing workpieces to be treated on said conveyor; circulation means for blowing a treatment agent through said tunnel, said treatment agent consisting of a gas stream with entrained solid particles; vibratory support means, with an upper surface rising in the direction of conveyor motion, disposed just below said conveyor at said exit end for arresting outwardly traveling particles and accumulating same in a pile within said tunnel; and flexible seal means extending between said support means and the bottom of said tunnel for blocking the escape of particles from said tunnel beneath said support means.

2. A fluidized bed as defined in claim 1 wherein said support means is provided with drive means for oscillating same at a 3. A fluidized bed as defined in claim wherein said support means comprises a hollow plate having its interior connected to said circulation means for receiving part of said gas stream, the upper surface of said plate being apertured for releasing the gas from said interior into the space thereabove.

4. A fluidized bed for the heat treatment of workpieces comprising an elongated tunnel; an apertured unidirectionally movable conveyor extending within said tunnel past an exit end thereof for discharging treated workpieces; dispenser means at an entrance end of said tunnel for depositing workpieces to be treated on said conveyor; circulation means for blowing a treatment agent through said tunnel, said treatment agent consisting of a gas stream with entrained solid particles: and vibratory support means with an upper surface rising in the direction of conveyor motion, disposed just below said conveyor at said exit end for arresting outwardly traveling particles and accumulating same in a pile within said tunnel; said support means comprising a hollow plate having its interior connected to said circulation means for receiving part of said gas stream, the upper surface of said plate being apertured for releasing the gas from said interior into the space thereabove.

5. A fluidized bed as defined in claim 4 wherein said support means is provided with drive means for oscillating same at a frequency of substantially 20 to 40 cycles per second, said particles having a size ranging between substantially 40 and microns.

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