GB2080504A

GB2080504A - Heat Treatment Furnace

Info

Publication number: GB2080504A
Application number: GB8121335A
Authority: GB
Original assignee: Pandrol Ltd
Current assignee: Pandrol Ltd
Priority date: 1980-07-14
Filing date: 1981-07-10
Publication date: 1982-02-03

Abstract

A furnace for the heat treatment of elongate metal billets comprises a walking beam arrangement (21, 22) made of refractory material for feeding the billets from a hopper (17) to the furnace chamber, and a feeding roller (19) arranged below the outlet of the hopper (17) to operate in synchronism with the operation of the walking beam arrangement. The hopper includes agitating means 29 for the billets to prevent blockage. The furnace walls are made of ceramic fibre panels. The gas fired furnace chamber (11) has an outlet for discharging treated billets from the chamber and arranged to allow air to be drawn into the chamber, and gas burners (12) positioned near the outlet and arranged to impinge the flame directly on the surface of the billets near the discharge end of the furnace. <IMAGE>

Description

SPECIFICATION Heat Treatment Furnace This invention relates to a heat-treatment furnace for heating elongate metal billets.

It is well known to provide refractory lined furnaces with so-called "walking beams" which serve to feed elongate billets in an ordered manner to the furnace chamber, the billets being moved step-wise in a direction perpendicular to their longitudinal axes. A walking beam arrangement usually comprises a central walking beam, and a pair of static beams which are arranged one on each side of the central beam.

The central walking beam carries out an orbital movement relative to the static beams in order to advance billets step-wise along the length of the walking beam arrangement. The central beam, and the static beams, have in their upper surfaces a series of V or semi-circular-shaped billetholding grooves which are arranged side-by-side, and which extend perpendicular to the longitudinal axes of the beams (and the feeding direction of the billets). During one orbit of movement of the walking beam, an elongate billet is raised by the walking beam from a temporary rest position in aligned grooves of the static beams and is subsequently deposited, one increment further on in the feeding direction, in an adjacent pair of aligned grooves in the static beams.

Thus, the walking beam arrangement serves to convey a successive supply of elongate billets in stepwise manner from a billet feeding station towards, into and through the furnace chamber, in which the required heat treatment is carried out, and then discharges the heated billets from the furnace. The speed of the stepped feed of the billets will be carefully controlled in relation to the length and heating parameter of the particular furnace so as to provide the required heat treatment of the billets.

The billets are usually fed to the walking beam arrangement by "magazines" which are periodically loaded with charges of billets. Bearing in mind that conventional walking beams are often made of metal, considerable problems are encountered in service in attempting to compensate adequately for relative thermal movements of the walking beam arrangement and the magazine. It will be appreciated that the magazine is located some distance away from the furnace chamber, whereas the walking beam arrangement receives differential heating action in that only some of its parts are located wholly within the furnace chamber.

Bearing in mind that the billets are fed along a generally horizontal guide path from the magazine, in a direction perpendicular to their longitudinal axes, to be received by relatively narrow grooves of the walking beam arrangement, feeding problems can occur if the length of the guide path varies during successive operations of the furnace from start-up. It is a matter of practical experience that the length of the guide path (once the furnace has reached its intended operating temperature) can vary from day to day in unpredictable manner, and can result in improper feeding of the billets from the magazine to the grooves of the walking beam arrangement. Evidently, with a continuous heat treatment process, misfeeding problems are highly undesirable and can have a cumulative disruptive effect on the further supply of billets from the magazine to the walking beam arrangement.Furthermore, an improperly fed billet can be carried into the furnace chamber by the grooves of the walking beam arrangement, often in nonparallel relationship to its neighbouring billets, and is then able to have a disruptive (or even blocking) effect within the furnace chamber on the previously ordered stepwise advance of the billets through the chamber.

This is clearly very undesirable in a heat treatment process which requires careful control over the duration of the heat treatment, and it can be very awkward to clear a blockage inside the furnace chamber during operation. Indeed, in case of severe disruption, it is necessary to shut down the furnace and allow it to cool before the disruption can be cleared.

Accordingly, there exists a need, in furnaces of the type discussed above, to improve the manner in which the billets are fed to the furnace chamber.

According to the invention there is provided a furnace for the heat treatment of elongate metal billets and comprising: a furnace chamber; an inlet for admitting billets to the chamber; an outlet for discharging treated billets from the chamber, said outlet in use also allowing air to be drawn into the chamber; a heating means arranged in the furnace chamber; a conveyor device for conveying elongate metal billets, in a direction transverse to their longitudinal axes, to said inlet and into the furnace chamber, said conveyor device comprising engagement means engageable intermittently with the billets in order to advance the billets in step-wise manner from a receiving station to the interior of the furnace chamber, and drive means for operating the engagement means; and a storage device for storing a charge of billets and arranged to supply billets to said receiving station;; in which the storage device is operable in controlled relationship to the operation of said engagement means by the drive means so as to discharge successive charges of billets to the receiving station.

A charge of billets may comprise a single billet, or may comprise two or more billets arranged in a row.

It is preferred that the storage device comprises a hopper which is arranged above the conveyor device and which narrows at its bottom to a discharge opening of width sufficient to allow the discharge of only a single billet or row of billets. Conveniently, a discharge device is mounted below the discharge opening and comprises a roller having a peripheral groove for receiving a billet-charge and arranged to be driven in synchronism with the operation of the drive means whereby a charge of billets is discharged to the billet receiving station each time the billets currentlu on the conveyor device are advanced by one step by the engagement means.

When a very heavy load of billets is provided in the hopper, this will apply a substantial load which is concentrated in the region of the discharge opening and may tend to inhibit orderly movement of the billets to the discharge opening, so that it is preferred that an agitation arrangement is provided in the hopper which is operable so as to prevent jamming-up of the discharge opening by the billets and to provide an orderly delivery of billets to the discharge opening. This will enable large loads of billets to be borne by the hopper so that, for example, the hopper may be charged with a sufficient load to enable completion of an operational shift without interruption.

Conveniently, the hopper is fixed relative to the furnace, and a removable top hopper may be provided which can be periodically replenished and which cooperates with the fixed hopper to supply additional billets thereto.

The agitation arrangement is preferably operated continuously with the operation of the conveyor device, and may comprise a lever arrangement pivotally mounted in the hopper for up and down movement of a free end of the lever arrangement relative to the discharge opening.

Conveniently, the free end moves along an arcuate path which is spaced from an adjacent side wall of the hopper by a distance slightly greater than the thickness of a billet so as to define, with the side wall, a guide passage along which the billets can travel singly to the discharge opening.

The lever arrangement may comprise a pair of levers which are spaced apart by a sufficient distance, relative to the length of a billet, so as to be capable of lifting one or more billets upwardly away from the discharge opening, thereby to agitate the lower, discharge region of the hopper.

The levers may be slightly upturned at their free ends, in order to hold the billet on the levers as they move upwardly.

The discharge roller, having a peripheral groove for receiving a billet-charge, may also be provided with an agitator which applies upward agitation to a line of billets as they approach the discharge opening during each rotation of the roller. The agitator may comprise an agitation piece mounted on the outer periphery of the roller, which preferably takes the form of a small roller rotatable in a peripheral groove in the discharge roller.

By arranging the hopper and the discharge device above the conveyor device, the billet charge can readily fall under gravity to the receiving station, and the risk is misfeeding of the charge is substantially reduced as compared to the conventional arrangements described above.

In order further to minimise the risk of misfeeding of the successive charges of billets, it is preferred that the components of the conveyor device are made of refractory material so as to provide a conveyor device which alters its length by only a very small proportion when it becomes heated during operation of the furnace.

Conveniently, the conveyor device takes the form of any suitable one of the known arrangements of "walking beam" arrangements.

In order to reduce start-up time to reach operating temperatures and to minimise energy losses by heat dissipation, as compared with conventional furnaces which have furnace walls, floor and roof made of refractory material, it is preferred that the side walls and the roof of the furnace chamber are made of ceramic fibre panels, especially those sold under the Trade Name KAOWOOL.

The heating means provided in the furnace chamber may take any conventional form, but the preferred arrangement provides gas fired burners which are arranged near to the outlet from the furnace chamber so that flames impinge directly onto the surface of the billets to provide rapid heating thereof. Conveniently, a flue is arranged in the roof of the furnace chamber near the inlet to the chamber so that the hot exhaust fumes flow through the furnace chamber in counter-current relation to the advance of the billets to provide pre-heating of the billets.

When the furnace is intended for the heat treatment of elongate metal billets in the form of round bar, it is preferred that the conveyor device has a plurality of successive fixed billet holders extending from the billet receiving station to the interior of the furnace chamber, the holders comprising grooves adapted in shape suitably to receive the round bars. The engagement means engage intermittently with the round bars in the holder so as to advance the bars in stepwise manner from holder to holder.

Conveniently, the conveyor device takes the form of a so-called "walking beam arrangement" in which a central walking beam is provided between a pair of adjacent static beams, the walking beam carrying out an orbital movement h in order to engage intermittently with the round t bars to advance the bars from holder to holder along the length of the static beams.

When the furnace is intended to heat treat different types of elongate billet, such as flat bar, different constructions of conveyor device may be provided, as appropriate. Thus, for flat bar, the engagement means may comprise a pusher device which has intermittent engagement with the billets to provide step-wise advance of the billets.

The invention, in a further aspect, is concerned with a heat treatment furnace comprising side, base and roof walls defining a furnace chamber, an inlet to the chamber, and outlet from the chamber, means for conveying articles to be heattreated through said inlet into the furnace chamber, means for discharging treated articles through said outlet, and heating means arranged in the furnace chamber; in which at least some of said walls of the furnace chamber are made of ceramic fibre panels.

Preferably, the furnace according to the further aspect of the invention is provided with a conveyor device and/or a storage device as defined above.

One embodiment of heat treatment furnace according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view of a gas fired heat treatment furnace for use with elongate metal billets in the form of a round bar; Figure 2 is an end view of the furnace shown in Figure 1; Figure 3 is a detail side view of an agitator for use in a billet-feed hopper of the furnace; and Figure 4 is an end view of the hopper and agitator.

Referring now to drawings, the furnace is designated generally by reference numeral 10, and is gas fired. The furnace 10 defines a furnace chamber 11 which is enclosed by a static floor made of pre-cast serrated refractory blocks, and side walls and a roof wall made of insulative low thermal capacity material such as ceramic fibre panels sold under the Trade Name KAOWOOL.

The furnace 10 has an inlet for admission of articles to be heat treated, and an outlet through which heat treated articles are discharged.

Conveniently, the supply to the furnace, and the removal from the furnace is an "in line" arrangement. Heating means is arranged in the furnace chamber 11 and comprises an arrangement of gas burners 1 2 positioned near the outlet from the furnace chamber 11 and arranged to impinge the flames directly on the surface of the articles to be heat treated, near the discharge end of the furnace. This provides for rapid heating of the articles. A flue 1 3 is provided in the roof 14 of the furnace chamber near to the inlet to the chamber so that hot exhaust fumes pass along the furnace chamber in countercurrent relationship to the advance of articles through the chamber, to provide pre-heating of the articles.

The outlet is not shown in detail in the drawings, but conveniently is provided at 1 2a in the floor of the furnace chamber near the burners 1 2 for gravity discharge of treated billets. The outlet also serves, in so-called rapid heating furnace of this type, to allow air to be drawn into the furnace.

The furnace 10 is supported on a framework 15, and a box-section frame 1 6 is mounted in the framework 1 5 in order to support drive mechanisms for operating a storage device and a conveyor device which serve to supply, and deliver articles to the furnace chamber.

The storage device comprises a hopper 1 7 which, in the illustrated case, has been designed to accommodate elongate metal billets in the form of round bar. The hopper 17 narrows to a discharge opening 18, and below the discharge opening 1 8 there is arranged a discharge device in the form of a cam-operated roller 1 9 having a peripheral groove 20 to receive a billet-charge and arranged to be driven in synchronism with the operation of the conveyor device, as described in more detail below.

The conveyor device, in the illustrated arrangement, comprises a walking beam arrangement which is made from pre-cast serrated refractory block sections. The walking beam arrangement comprises a central walking beam 21, and a pair of adjacent static beams 22.

All of the beams 21 and 22 have V-shaped grooves in which the billets can be received, and the walking beam 21 carries out an orbital movement in known manner in order to engage intermittently with the billets held in the grooves in the static beams 22, and to advance the billets in the feeding direction into adjacent grooves.

Thus, the walking beam 21 constitutes engagement means for engaging intermittently with the billets to provide step-wise advance of the billets.

A cam operated drive train 23 is provided in order to impart the required orbital movement to the walking beam 21. The drive train 23 is operated by means of a pulley and belt drive from an electric motor 24 mounted below the box frame 16.

It will be noted also from Figure 1 that the discharge roller 1 9 also is driven in controlled relationship to the operation of the conveyor device via a belt and pulley arrangement which drives its power from the electric motor 24. The arrangement of the drive to the conveyor device and to the storage device is such that successive charges of billets are discharged at a billetreceiving station provided at the end 25 of the walking beam arrangement in synchronism with the step-wise advance of the billets along the length of the static beams 22 by the walking beam 21.

The storage hopper 17 may be arranged so as to discharge billets singly, or if multiple transverse feed of billets is required, then the storage hopper 1 7 may be arranged to discharge a row of billets, in which case suitable modification will be made to the walking beam arrangement to provide stepwise advance of a row of billets.

By arranging the storage hopper 17 and the discharge roller 19 above the walking beam arrangement, charges of billets can readily fall under gravity to the receiving station. Insofar as the walking beam arrangement is made of refractory material, the walking beam arrangement does not undergo any appreciable thermal expansion, so that the risk of misfeeding of the billets to the receiving station are substantially minimised, as compared with conventional arrangements. The risks of misfeeding are further minimised by the coupling together of the operation of the storage discharge roller 1 9 in synchronism with the step-wise advance of the billets by the walking beam arrangement.

The loading device is a cam operated drumtype automatic hopper feed which is directly interlocked to the walking beam arrangement which, in turn, has an infinitely variable electric drive through a single reduction gearbox controlling all motions.

The gas burner arrangement 1 2 is arranged for operation by natural gas and is mounted angularly through the end wall 26 of the furnace to create flame impingement of the billets at the discharge zone.

Thus, the flames are directed slightly downwardly from the horizontal to impinge directly on the billets as they approach the discharge end of the walking beam arrangement.

The flames will also travel generally horizontally over the following billets to provide preheating of the billets. Thetreated billets fall under gravity from the discharge end of the walking beam arrangement and through the outlet 1 2a in the floor of the furnace chamber.

Referring now to Figures 3 and 4 of the drawings, there is shown an agitation arrangement which is provided in the hopper to prevent jamming-up of the discharge opening by the billets, and to provide an orderly delivery of billets to the discharge opening. Corresponding parts of those already described and shown in the previous Figures are designated by the same reference numerals, and will not be described in detail again.

When a very heavy load of billets is provided in the hopper 17, this will apply a substantial load which is concentrated in the lower, discharge end of the hopper, and may tend to inhibit orderly movement of the billets to the discharge opening 1 8. This would be particularly the case when it may be desired to provide a substantial load of billets in the hopper 17, sufficient to enable completion of an operational shift without interruption. However, as will be described in more detail below, the agitation arrangement provides orderly movmement of the billets to the discharge opening 1 8 even when, as is shown in Figure 3, a removable top hopper 27 is provided which can be periodically replenished and which cooperates with the fixed hopper 17 to supply additional billets thereto.

The agitation arrangement is designated generally by reference numeral 28 and is arranged to be operated continuously with the operation of the walking beam arrangement, the arrangement 28 comprising a lever arrangement composed of a pair of levers 29 which are linked together, and which are mounted on a common pivot 30 for up and down movement of their free ends 31 relative to the discharge opening of the hopper 17.

The free ends 31 move along an arcuate path which is spaced from an adjacent side wall 32 of hopper 1 7 by a distance slightly greater than the thickness of a billet so as to define, with the side wall 32 a guide passage along which the billets can travel in a single line to the discharge opening. As will be seen in Figure 3, the discharge opening of the hopper 1 7 is provided at the end of a vertical guide 33 which communicates with a discharge opening 34 at the convergent, lower end of the hopper 17 proper.

The levers 29 are spaced apart by a sufficient distance, relative to the length of a billet, so as to be capable of lifting one or more billets upwardly away from the discharge opening 34, thereby to agitate the lower, discharge region of the hopper 1 7. In addition the levers 29 are slightly upturned at their free ends 31, in order to hold one or more billets on the levers as they move upwardly. As shown in Figure 3, a pair of billets 35 are nesting at the ends of the levers 29, having been raised from dotted positions shown at 35a during an upward agitational movement of the levers 29.

The provision of the agitation arrangement 28 provides periodic agitation of the contents of the hopper, near its lower discharge end, so as to prevent jamming-up, and to promote the orderly discharge of single billets, or single rows of billets to the feeding roller 19. To provide further agitation, the feeding roller 1 9 is provided with an agitation member or piece in the form of a smaller roller 36 which is rotatably mounted in a peripheral groove in the feeding roller 1 9.

Accordingly, for each revolution of the roller 19, the roller 36 will impart an upward, agitational movement to the line of billets contained in the vertical guide 33.

In order that the rotation of the feed roller 1 9 can be synchronized with the drive for the walking beam arrangement, a lever-operated dog arrangement is provided at one end of roller 19, comprising a lever 37 and an axially slidable dog 38. The lever 37 is pivotable between a "driveout" position as shown in full lines and a drive-in position shown in dashed lines. The dog 38 has a projection 40 which is receivable by a registering opening 41 provided in the adjacent end of the roller 1 9 when correct synchronism is achieved.

Although not shown in detail, drive will be transmitted also to the agitation arrangement 28 > so that this also operates in synchronism.

Accordingly, as described above with refernnre to Figures 3 and 4, thers is provided a hopperfeqd arrangement incorporating lifting levers, in which cropped bars are contained in a fixed hopper unit which is mounted on the charge end of the furnace, above which a larger transportable unit is mounted to increase running time without reloading.

Inside the single faced smaller hopper is a pair of linked levers which are driven up and down.

The gap between the lever ends and the adjacent hopper side is such that only one line of bars can pass between them. This allows a continuous stream of material into the hopper mouth under limited loading conditions. This will allow free movement of a single bar, and also alleviate the possibility of jamming or doubling-up. It will also enhance the feeding of a single bar into the discharge or feeding roller for displacement onto the walking beam racking.

The feed roller is provided with one or more agitation pieces in the form of smaller rollers which agitate the stock once during each revolution in order further to inhibit possible jamming.

The feed roller and the lifting levers are synchronised to allow the levers to support the weight of the majority of stock in the hopper, when the slot (20) in the feed roller (19) is facing the hopper mouthm This will allow the stock to enter the feed roller slot under minimal loaded conditions.

The drive for the feeding roller is via a drive shaft 42 through its hollow centre, and is driven through a dog ciutch (28) on the external face of the roller. The dog has an eccentric so as to only allow engagement in one position, to ensure total synchronisation.

The actual driving of drive shaft 42 is carried out directly from a variable speed gearbox (not shown) which drives the moving beam of the walking beam arrangement. This automatically compensates any feed rate alteration, or change in characteristics, and allows for full synchronisation.

Claims

1. A furnace for the heat treatment of elongate metal billets and comprising: a furnace chamber; an inlet for admitting billets to the chamber; an outlet for discharging treated billets from the chamber, said outlet in use also allowing air to be drawn into the chamber; a conveyor device for conveying elongate metal billets, in a direction transverse to their longitudinal axes, to said inlet and into the furnace chamber, said conveyor device comprising engagement means engageable intermittently with the billets in order to advance the billets in stepwise manner from a receiving station to the interior of the furnace chamber, and drive means for operating the engagement means; and a storage device for storing a charge of billets and arranged to supply billets to said receiving station;; in which the storage device is operable in controlled relationship to the operation of said engagement means by the drive means so as to discharge successive charges of billets to the receiving station.

2. A heat treatment furnace comprising side, base and roof walls defining a furnace chamber, an inlet to the chamber, an outlet from the chamber, means for conveying articles to be heattreated through said inlet into the furnace chamber, means for discharging treated articles through said outlet, and heating means arranged in the furance chamber; in which at least some of said walls of the furnace chamber are made of ceramic fibre panels.

3. A furnace according to claim 2, including a conveyor device for conveying elongate metal billets, in a direction transverse to their longitudinal axes, to said inlet and into the furnace chamber, said conveyor device comprising engagement means engageable intermittently with the billets in order to advance the billets in step wise manner from a receiving station to the interior of the furnace chamber, and drive means for operating the engagement means; and a storage device for storing a charge of billets and arranged to supply billets to said receiving station; in which the storage device is operable in controlled relationship to the operation of said engagement means by the drive means so as to discharge successive charges of billets to the receiving station.

4. Afurnace according to claim 1 or 3, in which the storage device comprises a hopper which is arranged above the conveyor device and which narrows at its bottom to a discharge opening of width sufficient to allow the discharge of only a single billet or row of billets.

5. Afurnace according to claim 4, in which a discharge device is mounted below the discharge opening of the hopper and comprises a roller having a peripheral groove for receiving a billetcharge and arranged to be driven in synchronism with the operation of the drive means whereby a charge of billets is discharged to the billet receiving station each time the billets currently on the conveyor device are advanced one step by the engagement means.

6. A furnace according to claim 4 or 5, in which an agitation arrangement is provided in the hopper.

7. A furnace according to claim 6, in which the hopper is fixed relative to the furnace, and a top hopper is removably mounted on the fixed hopper.

8. A furnace according to claim 6 or 7, in which the agitation arrangement is operable continuously with the operation of the drive means.

9. A furnace according to any one of claims 6 to 8, in which the agitation arrangement comprises a lever arrangement pivotally mounted inthe hopper for up and down movement of a free end of the lever arrangement relative to the discharge opening of the hopper.

10. A furnace according to claim 9, in which the free end of the lever arrangement is movable along a path which is spaced from adjacent side wall of the hopper by a distance slightly greater than the thickness of a billet so as to define, with the side wall, a guide passage along which the billets can travel in a single line to the discharge opening of the hopper.

11. A furnace according to claim 10, in which the lever arrangement comprises a pair of levers which are spaced apart by a sufficient distance, relative to the length of a billet, so as to be capable of lifting one or more billets upwardly away from the discharge opening of the hopper.

12. A furnace according to claim 11, in which the levers are slightly upturned at their free ends in order to hold a billet on the levers as they move upwardly.

13. A furnace according to any one of claims 4 to 12, in which an agitation member is provided on said discharge roller for applying upward agitation to a line of billets as they approach the discharge opening, during each rotation of the roller.

14. A furnace according to claim 13, in which the agitation member comprises a small roller rotatable in a peripheral groove in the discharge roller.

1 5. A furnace according to any one of the preceding claims, in which the components of the conveyor device are made of refractory material so as to provide a conveyor device which alters its length by only a very small proportion when it becomes heated during operation of the furnace.

1 6. A furnace according to claim 15, in which the conveyordevice comprises a walking beam arrangementm

17.A furnace according to any one of the preceding claims, in which the side walls and the roof of the furnace chamber are made of ceramic fibre panels.

18. A furnace according to any one of the preceding claims, including gas fired burners arranged near to the outlet from the furnace chamber so that in use flames impinge directly onto the surfaces of the billets to provide rapid heating thereof.

1 9. A furnace according to any one of the preceding claims, including a flue arranged in the roof of the furnace chamber near the inlet to the chamber so that in use the hot exhaust fumes flow through the furnace chamber in counter current relation to the advance of the billets to provide pre-heating of the billets.

20. A furnace according to any one of the preceding claims and adapted for the heat treatment of elongate metal billets in the form of round bar, in which conveyor device has a plurality of successive fixed billet holders extending from the billet receiving station to the interior of the furnace chamber, the holders comprising grooves adapted in shape suitably to receive the round bars, and the engagement " means being engageable intermittently with the round bars in the holders so as to advance the bars in step-wise manner from holder to holder.

21. A furnace according to claim 16, including a central walking beam provided between a pair of adjacent static beams, the walking beam being arranged to carry out an orbital movement in order to engage intermittently with the round bars to advance the bars from holder to holder along the length of the static beams.

22. A furnace according to any one of claims 1 to 20 and adapted to heat-treat fiat bar, in which the engagement means comprises a pusher device arranged to have intermittent engagement with the billets to provide stepwise advance of the billets.

23. A furnace according to claim 1 or 2 and substantially as hereinbefore described with reference to, and as shown in the accompanying drawings.