GB1578520A - Apparatus for heat treatment of material to be worked on especially of aluminium or magnesium alloys - Google Patents

Abstract

In an arrangement for the heat treatment of elongate workpieces, e.g. cast strands and ingots, comprising a preheating furnace, a holding furnace and a cooling station, means for rotating the individual pieces (1) about their longitudinal axis are provided both in the holding furnace (4) and in the cooling station. These means (44, 45) are formed in such a way that the individual pieces are prevented from sliding on the receiving surface of these means. <IMAGE>

Description

(54) APPARATUS FOR HEAT TREATMENT OF MATERIAL TO BE WORKED ON, ESPECIALLY OF ALUMINIUM OR MAGNESIUM ALLOYS (71) We, PROLIZENZ AG, a company organised under the laws of Switzerland, of Bahnhofstrasse 12, Chur (Canton of Graubunden), Switzerland; and FRIED RICH WILHELM ELHAUS, a German citizen, of Hofkamp 140, 5600 Wuppertal, Federal Republic of Germany do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: Background of the Invention The invention relates to an apparatus for heat treatment of material to be worked on, such as cast strips and billets, as well as ingots, rods, tubes and the like, especially of aluminium or magnesium alloys. The heat treatment is of the general type in which the material is first pre-heated and thereafter is held at a desired heat treatment temperature.

Cast strips, billets and extrusion and rolling products, are customarily subjected to a heat treatment in order to homogenize, heterogenize, or otherwise heat treat the material. For example, continuously cast billets of aluminium alloys are first pre-heated after the casting, then finally annealed at temperatures between 500 and 620"C, and thereafter cooled. During this treatment, the billets receive the structure desired for further working, such as for example extrusion or rolling. An example of such methods is found in U.S. patent No. 2 802 657 (Nesbitt).

If the material is to be passed through the apparatus in a continuous manner or in a flow operation, one normally tries to transport the material at an equal and constant speed through the pre-heating zone and subsequently through the holding heat treatment zone in the furnace.

One may alternatively use separate furnaces for pre-heating and for holding.

The present invention relates to a means for conveying unfinished metal pieces at holding temperature, with a view to avoiding damage to the shape and surface of the pieces.

The present invention concerns apparatus for heat treatment of unfinished metal pieces, in which the individual pieces are held at the heat treatment temperature while being carried by a transport device, and the transport device comprises stationary beams with saw-tooth depressions having oblique surfaces inclined downwards in the direction of transport to receive the pieces, and also lifting beams, movable in the lifting direction, and movable in the transport direction independently of movement in the lifting direction, which lie between the stationary beams, and below them in the rest condition, and have a flat surface for receiving the pieces, and by means of which the pieces can be lifted from the depression and gently lowered in a controlled manner onto the oblique surfaces of the succeeding depressions, whereupon the pieces under their own weight roll into the bottom of the depression while making contact with the lifting beam which continues descending in a controlled manner opposite to the lifting direction.

The invention is preferably embodied in apparatus in which the individual pieces are first carried through a pre-heating furnace, and are there heated, and in which the pieces are thereafter carried by the transport device through a holding furnace, and are there held at the heat treatment temperature, and in which finally the pieces are cooled at a cooling station.

Brief Description of the drawings For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description, taken in connection with the accompanying drawings in which: Figure 1 is as a schematic view of an apparatus according to the invention with a pre-heating furnace and a successively arranged holding or hcat-treatment furnace; Figure 2 is a cross-section through a preheating furnace which is preferably employed in an apparatus according to the instant invention; Figure 3 is a section along the line III-III of Figure 2; Figure 4 is a longitudinal section through a holding furnace which can be employed in the apparatus according to the invention, with a transport device constructed in accor dancc with the invention; Figure 5 is a partial section according to line V-V of Figure 4; Figures 6a to 6e arc transport phases suc ceding one another in time, in transporting the material through the holding furnace' and Figures 7 and 8 arc, respectively, a longitudinal section, and a cross section according to line VIII-VIII of Figure 7, of a cooling station following the holding furnace.

Description of the Preferred Embodiment In the schematic plan view according to Figure 1, bars or billets are indicated by the reference numeral 1. From a supply device or a magazine 2, the billets or bars 1 are automatically transferred individually to a transport device 8, which can supply step-by-step, in the direction of the horizontal arrows, into the prc-hcating prctreatmcnt furnaces 3 arranged to left and right of it, as seen in Figure 1. The billets or bars 1 are brought rapidly to full annealing temperature individually in the pre-heating pretreatment furnaces 3 in stationary condition by direct flame impingement by means of burners.

Thereafter the individually pre-heated billets are taken out again from the respective pre treatment furnace 3, and are transferred individually in succession from the transport device 8 into a holding or heat treatment furnace 4. This holding furnace is formed as a continuous flow furnace, and operates with circulated hot gas, for example hot air. The full annealing temperature is maintained over the length of the holding furnace, or, in the case where the billets at the entry into the holding furnace have not yet entirely attained the full annealing temperature, is reached after a short travel in the holding furnace.

By alteration of the pre-heating time, that is of the period of time in which the billets 1 are held in the preheating furnaces 3, and by control of the burners, the pre-heating temperature can be adjusted finely and over a wide range, which makes it possible that a uniform prc-hcating of the billets is always obtained.

The holding time in the holding or treatment furnace 4 can be varied according to the alloy composition of the billets and the desired structure by altcration of the speed of through travel. The temperature in the holding furnace 4 can be altered, for example by control of the temperature of the hot air or other hot gas.

In the holding furnace 4 devices are provided for rotation of the billets 1 about their longitudinal axes, so that these are completely uniformly heated and warping or curving cannot occur, or the billets are straightened. The billets, plasticised by the annealing, automatically straighten themselves by reason of their own weight.

The billets 1 are transferred from the exit of the holding furnace 4 to a cooling station 6, where the billets passing through are cooled individually with water and/or air. At the cooling station 6 there is arranged, as shown in detail in Figures 7 and 8, a device for turning the billets during cooling, so that also here there is prevented bending or distortion of the billets, due to uniform cooling effect from all sides.

From the cooling station 6 the billets 1 reach a magazine 7, from where they are conveyed to another station for further working.

Figures 2 and 3 show a preferred preheating furnace in detail.

The pre-heating furnace has such a length that a billet of the largest size available in practice (7-8m) fits into it lengthwise. In the preheating furnace 3 there is provided a double strand or strip conveyor chain 13 with carrier devices 12 mounted thereon for the billets 1 to be pre-heated. The carrier devices 12 reach through a longitudinal slot into a cylindrical furnace chamber 15 formed by two furnace shells 14. The furnace shells are each journalled to swing by their lower ends on a carrier rail 16 and are held together above by spacing members 17. Laterally the furnace shells are supported on the furnace wall by radial supporting bars 18. By removal of the spacing members 17 and slight swinging inwards around the supporting points on the carrier rail 16, the furnace shells 14 can be dismantled without difficulty.

The furnace shells 14 have four radially directed rows of openings 22, into which discharge nozzles 21, likewise radially directed, of pre-mixed burners 19, 20. The radially directed rows of burners extend over the entire length of the furnace shells 14. In doing so, the lower rows of burners 20 are arranged close to the supporting devices 12 and directed obliquely upwards, while the two upper rows of burners are offset by about 90C to the corresponding lower rows of burners and directed obliquely downwards. The upper rows of burners 19 can be adjusted with respect to the lower rows of burners 20.

Based on the arrangement of the rows of burners 19, 20, during heating of billets 1 or 1' (of smaller diameter) the surfaces for heat transfer are employed in an optimum man ner, so that a circularly symmetrical temperature distribution over the cross-section of the billets is achieved. The burner nozzles 21 are at this time differently adjusted in their output, so that the temperature distribution desired in each case is attained at the end of the pre-heating period, and also the ends of the billets are slightly raised from the carrier devices 12 at the beginning of the preheating period, so that no excessive horizontal forces can be exerted on the conveyor chain 13 by the increase in length of the billet produced by heating.

The carrier devices 12 for the billets 1 or 1' have, at the place where they penetrate into the slot formed between the two furnace shells 14, a shaft which is rectangular in cross-section, which fills up the slot except for a safety spacing necessary for thermal expansion.

The flue gases leave the furnace cavity 15 upwards through the slot formed by the furnace shells 14 and the spacer members 17, and are, together with fresh air, sucked away through a suction fan along the exhaust duct 26. The outer casing 27 serves in this connection at the same time as an air duct for the fresh air suched in.

The pipes 28 necessary for the mixing and measuring of the combustion gas, as well as a device 29 for measurement of the temperature of the bars 1 or 1', are arranged at the right hand side of the furnace as seen in Figure 2.

For pre-heating, the billets are pushed into the furnace from the transport device 8 and are taken over by the carrier devices which are moved by the double-run conveyor chain 13. The drive for the double-run conveyor chain is controlled by a limit switch not shown, which turns off the drive when a billet 1 runs against an abutment 30 at one end of the furnace shells 14.

Measuring devices, not shown, arranged at uniform spacings over the length of the furnace shells 14 measure the length of the billet inserted at each moment. These measuring devices control the burners 19 and 20 in groups, so that at each moment only a number of burners corresponding to the length of a billet is actuated for pre-heating.

The burners are first turned on, when a corresponding billet 1 has reached the position shown in Figure 3 against the abutment 30.

With shorter billet lengths, it is also possible that the pre-heating furnace 3 is supplied with a plurality of billets.

When the pre-heating furnace shown is used, a continuous flow operation is also attainable. The billets 1 in this operation are preheated in moving condition. The drive is, however, preferably intermittent in this case, so that the necessary matching with the following period of annealing in the holding furnace 4 is achieved.

The holding furnace 4 shown in Figure 4 in longitudinal section is constructed for continuous flow operation and is heated with hot gas, for instance hot air, which is blown by a radial-axial blower 40 against the billets 1 or 1' which are to be kept hot, and is circulated in the furnace.

The billets lie in saw-tooth shape depressions 42 with oblique surfaces 42a of stationary beams 44 extending longitudinally through the furnace space 43. The beams 44 are arranged with spaces in between, at least two of which have a width x (Figure 5). In the intermediate spaces so defined there fit lifting beams 45 extending between and parallel to the beams 44. The lifting beams 45 have horizontal flat surface portions 45' for receiving the billets 1 or 1', and these surface portions 45' are limited by prismatic abutments in the form of angle sections 46 welded onto the flat upper surface of the lifting beam. Adjacent angle sections 46 have a spacing at least approximating to the spacing of adjacent depressions 42, and, in the transport direction A, have a small longitudinal extent k in comparison with the extent 1 of the flat surface portions 45', so that round billets 1, 1' can roll on the flat portions 45'.

The angle sections 46 serve simply as safety abutments, not normally used, if the billets 1, 1' for any reason, e.g. in the raised condition, are found to be turned, for example by reason of a twist received during lifting.

Three lifting pipes 50 of square cross-section engage each lifting beam 45 from below; they are vertically movable but nonrotatingly held in rectangular longitudinal slots 51 on the floor 52 of the heat maintaining furnace. One of these longitudinal slots 51 is shown for better understanding in dotand-dash lines in Figure 5 where the floor 52 is omitted.

One possible construction is shown at the right in Figure 4. Into the lower end of each lifting pipe 50 there is welded a nut 53, which is passed through by a spindle 54 making screw-threaded engagement therewith. Each spindle 54 carries at its lower end a bevel pinion 55 which meshes with a bevel pinion shifted by 90". All bevel pinions 56 are arranged on a common horizontal shaft 57 which is actuable by a drive motor 58 in order to raise the lifting pipes 50 and therewith the lifting beams 45.

The shaft is journalled in housings 47, each associated with a corresponding spindle 54, lifting pipe 50, and bevel pinion pair 55, 56.

The motor 58 and the housing 47 are mounted on a carriage 59 which operates on rollers 60. This carriage is movable, along the ground or on rails 62, by a double-acting fluid cylinder 61 through a horizontal stroke y which corresponds approximately to the horizontal component of the length of the oblique surfaces 42a. The vertical travel z of the lifting beam 45 which is producable via the above described lifting device by the motor 58 is made of such extent that, in lowered condition, the lifting beam 45 with the angle sections 46 can be freely pushed beneath the billets 1, 1', and in the raised condition the billets 1, 1' lying on the lifting beams 45 do not engage on the oblique surfaces 42a of the saw-tooth depressions 42 during horizontal transport.

In a prefcrred second embodiment (illustrated in Figure 4 at the left hand spindle gear), the nut 53 of each spindle gear is movably held in the housing 47 and tightly connected with the lower end of the lifting pipe 50 and not turnable, but vertically movable in the housing 47 and shiftable in its axial direction. All component parts of the spindle gear are in this case lodged and mounted in the housing 47 and the lifting pipe 50 no longer contains any movable parts of the drive gear. This is advantageous for mounting and maintenance.

The transport of the billets 1 by means of the transport device shown in Figures 4 and 5 will now be described with preference to Fig urcs 6a to 6e.

In the rcst position of the lifting beam 45 (Figurcs 4 and 6a). the depressions between the angle profiles 46 arc slightly shifted ahead of the depressions 42. In principle, the transport device would also function without the angle profiles 46, that means with lifting beams having a horizontal flat surface.

As can be seen from Figure 6a, a billet 1 with large diameter lics in the depression 42 with its centre offset against the transport direction A. This ariscs from the slight inclination of the inclined surface 42a in comparison to the opposite surface (which has no preference numeral).

In the rest position according to Figure 6a.

the billets lie in the depressions 42 of the stationary beams 44. The lifting beams 45 lie below the stationary beams. By actuation of the spindle gears, the lifting beams are now moved upwards in lifting direction B, engaging the billets l and lifting these upwards from the depressions 42 through the distance z (Figure 6h).

Aftcr completion of this lifting movement each lifting beam 45 is moved to the right as shown in Figure 6e, by means of the drive cylinder 61, through the distance y in transport direction A. During this movement the billets 1 move to above the oblique surface 42a of the next following depressions 42 in transport direction. In this way one ensurcs that cven bars which are curved before heat treatment can be carried without trouble through the holding furnace.

Aftcr completed advance of the beam in the transport direction A, the spindle gear is again actuated, but now in direction B' which is opposite to the lifting direction B. The speed of this movement Is controlled in such a way that the billets are gently lowered onto the oblique surfaces 42a of the stationary beams (Figure 6d). The billets 1, due to their own weight, now roll from the oblique surfaces 42a into the depressions 42. During this, they turn about an angle a (Figure 6e).

However, this rolling movement is controlled by the lowering movement of the lifting beam in the direction B', that is to say it is braked to such an extent that no impact blow is created on arrival in the depression 42 that would damage the shape and surface of the billets which are annealed to placticity.

The length of the oblique surfaces 42a is so measured that the billets reach the depressions 42 with a sector turned through an angle, and at each next following depression with another sector, so that in each case these other sectors come in contact with the circulated hot gas or the circulated hot air. Thus the billets in all their sectors may be maintained on a very uniform temperature. The rolling of the billets on the oblique surfaces 42a, controlled by the downward movement of the lifting beam 45, leads to the automatic straightening of the billets due to their own weight, for eliminating curvatures that might have occurred for any reasons.

In the manner described, the billets are transported through the heat treatment furnace, avoiding any gripping between the lifting beams 45 and the stationary beams 44, so that the danger of injuring the billets is practically eliminated.

Simultaneously with the lifting movement of the lifting beams 45, the furnace doors 49, 48. are opened for admitting or discharging the billets 1 or 1'. The furnace doors 49, 48 are shown in Figure 4 in broken lines in open position. The loading and emptying of the holding furnace 4 can also take place in the longitudinal direction of the billets 1 by doors provided on one side of the holding furnace, in which case the doors 49, 48 are omitted.

In practice the billets can attain weights of the order of 1 tonne. Hence, according to the number of billets reccived at once in the furnace, between 25 and 40 tonnes must be lifted, lowered and transported, in a controlled manner. This is not possible with a usual combined drive, such as an eccentric drive, and has been attainable for the first time by the separation of lifting and transporting motion. according to the invention.

The cooling station shown in Figures 7 and 8 has a spray chamber 70 on the upper wall 71 of which there is mounted an internal closed water channel comprising several segmcnts 72 aligned in succession in the longitudinal direction. Each segment 72 of the water channel has a separate water supply pipe 73 and in its lower wall is provided with spray holes 74 which are arranged close to one another in a row in the longitudinal direction of the water channel. Below the water channel a shaft 75, aligned axles 76, and a shaft 77 extend through the spray chamber, parallel to one another. The shafts 75, 77 and the axles 76 are all supported in bearing blocks 78, the shafts 75, 77 and the axles 77 being movable in journals 79, 80.

The shaft 75 is driven by a drive motor 81 arranged outside the spray chamber 70 and carries rolls 82 secured on it at regular intervals.

The axles 76 are mounted to rock about the shaft 77 by means of at least two rockers 84. In the normal position shown in Figure 7, the axles 76 lie in the same horizontal lane as the shaft 75 and at a distance from it adjusted to the measurements of the billets 1 and 1' to be handled, which distance is smaller than the billet diameter.

On the axles 76 there are loosely mounted rolls 83 of the same diamter as the rolls 82 of the shaft 75. The rolls 82,83 are associated in pairs, and form a prismatic recess for the billets 1 or 1'. The rockers 84 supporting the axle 76 are rigidly connected to the shaft 77.

This shaft 77 is shiftable by one or two pivoted cylinders 85 and a crank arm 86 fixed to the shaft 77 and pivoted to the piston rod 87 of the cylinder 85. The rocker 84 is shown in rotated position in dot-and-dash lines.

There is furthermore provided at least one transfer arm 88 to feed the bars 1 into the spray device. This arm 88 is shiftable by a cylinder 89 with a piston rod 94, between the two positions shown in full and in dot-anddash lines, about the axis of the shaft 75.

In the lower portion of the spray chamber 70 there is a collecting tub or reservoir 90, from the deepest location of which there issues a discharge pipe 91 directed vertically downwards.

The spray device described operates as follows: A hot billet 1 or 1' coming from the holding furnace is set in motion along a roller conveyer 92 arranged alongside the spray device. The cylinder 89 has been actuated so that the transfer arm 88 lies below the track of the billet 1. When the conveyor 92 stops, the cylinder 89 is extended, and hence the transfer arm 88 is lifted, raising the billet 1 from the position shown in dot-dash lines, so that the billet may roll along the flat surface 93 of the transfer arm 88, which is now slightly sloping towards the rolls 82, 83 and thereby may reach the prismatic recess between the rolls 82, 83. In order that the billets 1 do not, during transfer, fall into the prismatic recess between the rolls 82, 83, and thus become damaged, the cylinder 85 is actuated with the cylinder 89, or is still in the actuated condition from the previous working cycle, in which the rockers 84 assume the raised position shown in broken lines. In this position the roll 83 engages gently the billet 1 rolling along the transfer arm, without danger of damage to the billet surface. Thereafter the cylinder 85 is actuated further, so that the rocker 84 arrives in a controlled manner in the lowered position shown in full lines, so that the billet is laid gently into the prismatic recess. Thereafter, the driving motor 81 begins to rotate the shaft 75, and thus the rolls 82, clockwise as seen in Figure 8, so that the billet in the prismatic recess formed by the rolls 82, 83 is set into continuous anticlockwise rotation about its longitudinal axis.

The rockers 84 with the axle 76 and rolls 83 are supported resiliently in the lower position by the residual column of air still present in the cylinder 85 in the lowered condition, so that any impacts which may arise during the rotation of the billet 1 are yieldingly resisted, and the danger of surface damage or bending of the billet by such impacts is avoided. Now water is sprayed through the spray holes 74 onto the billet 1 or 1'. As the spray holes 74 are arranged over the whole length of the billet, at small distances from one another, a very uniform cooling of the billet is achieved. For discharging the cooled billet, the piston rod 87 of the cylinder 85 is extended, after previous retraction of the cylinder 89 and consequent shifting of the transfer arm 88 into the power position shown in full lines, so that the rockers 84 and the axles 76 move from the full-line position into the dot-dash-line position. This moves the billet out of the prismatic recess between the rolls 82, 83 onto the now outwardly sloping surface 93 of the transfer arm, from which it rolls down onto the roller conveyor 92 for further handling so that the piston rod 94 of the cylinder 89 is totally withdrawn and the transfer arm 93 is consequently carried into the lowest position shown in solid lines.

Rotary brushes may be provided for cleaning the billet.

In the example shown in Figures 2 and 3, the pre-heating furnace employs direct flame impingement for heating. Alternatively, the billet in the pre-heating furnace may be heated by streams of hot gas. As yet another alternative, the pre-heating furnace may be heated electrically. The holding furnace 4 shown in Figure 4 is heated with hot gas.

Alternatively it may be heated electrically.

WHAT WE CLAIM IS: 1. Apparatus for heat treatment of unfinished metal pieces, in which the individual pieces are held at the heat treatment temperature while being carried by a transport device, and the transport device comprises stationary beams with saw-tooth depressions having oblique surfaces inclined downwards in the direction of transport to receive the pieces, and also lifting beams, movable in the lifting direction, and movable in the transport direction independently of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (13)

**WARNING** start of CLMS field may overlap end of DESC **. one another in a row in the longitudinal direction of the water channel. Below the water channel a shaft 75, aligned axles 76, and a shaft 77 extend through the spray chamber, parallel to one another. The shafts 75, 77 and the axles 76 are all supported in bearing blocks 78, the shafts 75, 77 and the axles 77 being movable in journals 79, 80. The shaft 75 is driven by a drive motor 81 arranged outside the spray chamber 70 and carries rolls 82 secured on it at regular intervals. The axles 76 are mounted to rock about the shaft 77 by means of at least two rockers 84. In the normal position shown in Figure 7, the axles 76 lie in the same horizontal lane as the shaft 75 and at a distance from it adjusted to the measurements of the billets 1 and 1' to be handled, which distance is smaller than the billet diameter. On the axles 76 there are loosely mounted rolls 83 of the same diamter as the rolls 82 of the shaft 75. The rolls 82,83 are associated in pairs, and form a prismatic recess for the billets 1 or 1'. The rockers 84 supporting the axle 76 are rigidly connected to the shaft 77. This shaft 77 is shiftable by one or two pivoted cylinders 85 and a crank arm 86 fixed to the shaft 77 and pivoted to the piston rod 87 of the cylinder 85. The rocker 84 is shown in rotated position in dot-and-dash lines. There is furthermore provided at least one transfer arm 88 to feed the bars 1 into the spray device. This arm 88 is shiftable by a cylinder 89 with a piston rod 94, between the two positions shown in full and in dot-anddash lines, about the axis of the shaft 75. In the lower portion of the spray chamber 70 there is a collecting tub or reservoir 90, from the deepest location of which there issues a discharge pipe 91 directed vertically downwards. The spray device described operates as follows: A hot billet 1 or 1' coming from the holding furnace is set in motion along a roller conveyer 92 arranged alongside the spray device. The cylinder 89 has been actuated so that the transfer arm 88 lies below the track of the billet 1. When the conveyor 92 stops, the cylinder 89 is extended, and hence the transfer arm 88 is lifted, raising the billet 1 from the position shown in dot-dash lines, so that the billet may roll along the flat surface 93 of the transfer arm 88, which is now slightly sloping towards the rolls 82, 83 and thereby may reach the prismatic recess between the rolls 82, 83. In order that the billets

1 do not, during transfer, fall into the prismatic recess between the rolls 82, 83, and thus become damaged, the cylinder 85 is actuated with the cylinder 89, or is still in the actuated condition from the previous working cycle, in which the rockers 84 assume the raised position shown in broken lines. In this position the roll 83 engages gently the billet 1 rolling along the transfer arm, without danger of damage to the billet surface. Thereafter the cylinder 85 is actuated further, so that the rocker 84 arrives in a controlled manner in the lowered position shown in full lines, so that the billet is laid gently into the prismatic recess. Thereafter, the driving motor 81 begins to rotate the shaft 75, and thus the rolls 82, clockwise as seen in Figure 8, so that the billet in the prismatic recess formed by the rolls 82, 83 is set into continuous anticlockwise rotation about its longitudinal axis.

The rockers 84 with the axle 76 and rolls 83 are supported resiliently in the lower position by the residual column of air still present in the cylinder 85 in the lowered condition, so that any impacts which may arise during the rotation of the billet 1 are yieldingly resisted, and the danger of surface damage or bending of the billet by such impacts is avoided. Now water is sprayed through the spray holes 74 onto the billet 1 or 1'. As the spray holes 74 are arranged over the whole length of the billet, at small distances from one another, a very uniform cooling of the billet is achieved. For discharging the cooled billet, the piston rod 87 of the cylinder 85 is extended, after previous retraction of the cylinder 89 and consequent shifting of the transfer arm 88 into the power position shown in full lines, so that the rockers 84 and the axles 76 move from the full-line position into the dot-dash-line position. This moves the billet out of the prismatic recess between the rolls 82, 83 onto the now outwardly sloping surface 93 of the transfer arm, from which it rolls down onto the roller conveyor 92 for further handling so that the piston rod 94 of the cylinder 89 is totally withdrawn and the transfer arm 93 is consequently carried into the lowest position shown in solid lines.

Rotary brushes may be provided for cleaning the billet.

In the example shown in Figures 2 and 3, the pre-heating furnace employs direct flame impingement for heating. Alternatively, the billet in the pre-heating furnace may be heated by streams of hot gas. As yet another alternative, the pre-heating furnace may be heated electrically. The holding furnace 4 shown in Figure 4 is heated with hot gas.

Alternatively it may be heated electrically.

WHAT WE CLAIM IS: 1. Apparatus for heat treatment of unfinished metal pieces, in which the individual pieces are held at the heat treatment temperature while being carried by a transport device, and the transport device comprises stationary beams with saw-tooth depressions having oblique surfaces inclined downwards in the direction of transport to receive the pieces, and also lifting beams, movable in the lifting direction, and movable in the transport direction independently of

movement in the lifting direction. which lie between the stationary beams, and below them in the rcst condition,;lnd have a flat surface for receiving the pieces, and by means of which the pieces can be lifted from the depression and gently lowered in a controlled manner onto the oblique surfaces of the succeeding depressions. whereupon the pieces under their own weight roll into the bottom of the depression while making contact with the lifting beam which continues descending in a controlled manner opposite to the lifting direction.

2. Apparatus according to claim 1 characterised in that the oblique surfaces have a longitudinal dimension different from the circumferential dimension of the pieces.

3. Apparatus according to claim 1 or 2, in which the lifting beams carry prismatic abutmcnts having the form of angled sections, the dimcnsion of which in the transport direction is small in rclation to the dimcnsion in the transport direction of the flat portion of the lifting beam lying between them, so that the pieces can each roll through a controllcd circumfcrcntial distance on the flat portion.

4. Apparatus according to any of claims 1 to 3, in which all the lifting means are supported hy lifting devices which can be operated simultaneousl in the lifting direction, and the lifting devices in turn are supported on a common carriage. which can be shifted horizontally in the transport direction.

5. Apparatus according to any of claims 1 to 4 in which the lifting means or the carriage are movable in the transport direction. and in the opposite direction. by means of a double-acting fluid cylinder.

6. Apparatus according to any of claims 1 to 5. in which the lifting beams are movable in the lifting direction, and in the opposite direction. by means of screw drives.

7. Apparatus according to any of claims I to 6. in which the individual pieces are first carried through a prc-hcating furnace. and are there heated. and in which the pieces are thereafter carried by the transport device through a holding furnace. and are there held at the heat trcatincnt temperature. and in which finally the pieces are cooled at a cooling rotation.

8. Apparatus according to claim 7, in which the pieces are heated in the preheating furnace hn streams of hot gas.

9. Apparatus according to claim 7 or claim 8. characterised in that the means for rotation of the pieces in the cooling station comprises pairs of rollers. the two rollers of which constitute a prismatic recess for supporting the pieces

10. Apparatus according to claim 9, chiracterised in thit ot least one of the two rollers of each pair can be driven.

11. Apparatus according to claim 9 or claim 10, in which one of the two rollers of each pair is journalled on a lifting and lowering device movable relatively to the other roller. for inserting and discharging the piece.

12. Apparatus according to any of claims 9 to 11, characterised in that there is arranged at the cooling station, above the means for rotation, a water channel running along the piece to be treated, which has a plurality of water outlet openings in its lower wall arranged in the longitudinal direction of the piece.

13. Apparatus according to any of claims 7 to 12, in which rotary brushes for cleaning the piece are provided.