Method for inductively heating steel ingots on a transport shoe and device for carrying out the method

Abstract

A shell (10) acts as a transporting shoe for steel ingots, which are pushed through a preferably tubular induction furnace for inductive heating for the purpose of producing seamless tubes by the extrusion process. The shell (10) is formed in such a way that it partially reaches around the contour of the steel ingot to be heated. The shell is provided at one end leading in the pushing-through direction or transporting direction, with a shoulder (12), which extends at an angle to the transporting direction, against which the steel ingot rests in such a way that the pushed-through steel ingot takes the shell (10) along with it. A method for inductively heating steel ingots uses a shell (10) as described.

Claims

1. A method for inductively heating steel ingots for producing seamless tubes by an extrusion process, comprising the following steps: a) extracting a shell from a shell magazine, wherein the shell is made of a non-magnetizable or non-inductive sheet, and wherein the shell is formed such that it partially reaches around a contour of the steel ingot to be heated, and wherein the shell is provided at one end leading in a transporting direction with a shoulder, which extends at an angle to the transporting direction, against which the steel ingot rests in such a way that the steel ingot being pushed-through takes the shell along with it; b) placing the shell on an insertion device, such that the shoulder comes to rest at the end leading in the transporting direction and points upwards against the force of gravity; c) placing the steel ingot on the shell to form an assembly; d) sliding the assembly of the shell with the steel ingot located thereon into an induction furnace, wherein the assembly of the shell and the steel ingot thereby pushes forward a further steel ingot, if any, already located in the induction furnace on a further shell, e) pulling out the heated steel ingot on the shell and with the shell from the induction furnace; f) separating the heated steel ingot from the shell; and g) repeating the method steps a) to f), wherein the method steps a) to f) are carried out in the order in which they are listed, wherein separating the heated steel ingot from the shell according to method step f) takes place during a horizontal transport movement of the assembly consisting of the heated steel ingot and the shell on a horizontal transport means, wherein the horizontal transport movement of the steel ingot is stopped by a stop or at a stop, wherein the stop acts directly against an end face of the steel ingot leading in the transporting direction of the steel ingot, and wherein the stop is arranged in such a way that it acts as a stripper when the steel ingot is lifted off the shell, and wherein a height of the stop is selected such that lifting the heated steel ingot with an ingot lifting device causes the shell to be stripped from the steel ingot, in case the shell sticks to the steel ingot.

2. The method according to claim 1, wherein the shell is extracted from the shell magazine by a lifting device and is placed on a slide-in roller table, and wherein the steel ingot is subsequently placed on the shell located on the slide-in roller table, and wherein the assembly comprising the shell and the steel ingot is pushed by a hydraulic ram from the slide-in roller table into the induction furnace.

3. The method according to claim 1, wherein the heated steel ingot is pulled by extraction pliers with the shell out of a compensating chamber of the induction furnace onto an extraction roller table.

4. The method according to claim 1, wherein the transport means is an outfeed roller table, and wherein the ingot lifting device lifts the steel ingot vertically off the shell while the shell is on the outfeed roller table.

5. The method according to claim 4, wherein the stop extends over the outfeed roller table in form of a yoke or a bridge.

6. The method according to claim 5, further comprising: transporting the shell on the outfeed roller table to a shell extraction position after separating the ingot.

7. The method according to claim 6, further comprising: returning the shell at the shell extraction position to one of the shell magazines by a shell manipulator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 a shows a schematic cross-section through an induction furnace for preheating cylindrical steel ingots, wherein the induction furnace is lined on the inside with a partially cylindrical sheet strip.

(2) FIG. 1 b schematically illustrates a variant of the induction furnace, in which round steel bars extend on the inside.

(3) FIG. 2 shows a perspective illustration of a shell as a transporting shoe.

(4) FIG. 3 shows a front view of a shell that is loaded with a steel ingot, in its position supported on round steel bars.

(5) FIG. 4 schematically shows the assembly of a plurality of steel ingots, each to be provided with a shell or transport, as the case may be, in an ingot column as it results inside the induction furnace.

(6) FIG. 5 shows a schematic top view of an assembly of induction furnaces on the feed side and the devices for feeding the induction furnaces with cold steel ingots.

(7) FIG. 6 shows a schematic top view of an assembly of induction furnaces on the discharge side and the devices for outfeeding heated steel ingots.

(8) FIG. 7 shows a schematic top view of an assembly of transport devices on the discharge side, on the basis of which the collection of empty shells is illustrated.

(9) FIG. 8 shows a perspective illustration of a heated steel ingot in an ingot extraction position, in which the steel ingot rests against the stop.

DETAILED DESCRIPTION

(10) FIGS. 1a and 1b show a cross-section of an induction furnace 1 for the inductive preheating of cylindrical steel ingots 2, which are to undergo further processing in an extrusion process to produce seamless steel tubes. For this purpose, the steel ingots 2 are preheated to a temperature of approximately 800 C. in a horizontal position in the induction furnace 1. Preheating is performed by a plurality of induction coils 3 arranged in series in the induction furnace 1, which induce eddy currents in the steel ingot 2 concerned, thereby heating it.

(11) The induction furnace 1 has a cylindrical cross-section and comprises an outer steel shell 4 and an inner concrete lining 5, in which the induction coils 3 are cast. The furnace chamber 6 is formed to be hollow-cylindrical, its clear cross-section being only slightly larger than the cross-section of the steel ingots 2 to be heated. The steel ingots 2 to be heated are inserted on the feed side into the tube formed by the induction furnace 1, wherein an ingot column of a plurality of steel ingots 2 arranged one behind the other is formed in the tube, which is up to 8 m long, for example. One steel ingot 2 fed at a time pushes the steel ingots 2 located in the induction furnace 1 further. At the end of the induction furnace 1, there is a compensating chamber 9 (FIG. 6) in which the foremost steel ingot 2 in the ingot column is solution heat treated. To protect the concrete lining 5, it is provided either with a partially cylindrical sheet metal strip 7 arranged at the bottom in the installation position (variant in accordance with FIG. 1 a) or with at least two round steel bars 8 (variant in accordance with FIG. 1 b) also arranged at an angular distance from one another in the bottom in the installation position. Both the sheet metal strip 7 and the round steel bars 8 extend from one end to the respective opposite end of the induction furnace 1. Within the induction furnace 1, the steel ingots 2 experience increasing heating from one end to the opposite end and an associated increasing softening. In the process, the steel ingots 2 slide either on the sheet metal strip 7 or on the round steel bars 8, which would normally result in the shell surface or outer skin, as the case may be, of the steel ingots 2 being damaged.

(12) To prevent such damage, a shell 10 is provided, which is used as a transporting shoe for one steel ingot 2 at a time. The shell 10 is shown in perspective in FIG. 2. The shell 10 forms a base for one steel ingot 2 at a time, which slides over the round steel bars 8 or over the sheet metal strip 7 of the induction furnace 1 with the steel ingot 2 placed on it.

(13) As shown in FIG. 2, the shell 10 is formed as a partially cylindrical, upwardly open trough, whose radius of curvature corresponds approximately to the radius of the shell surface of a steel ingot 2. The shell 10 is provided at an end 11 leading in the transporting direction with a shoulder 12 that extends perpendicularly to the transporting direction and upwards transversely thereto, and rests against an end face of the steel ingot 2 leading in the transporting direction. The shoulder 12, which is formed to be a simple stop, causes a steel ingot 2 resting on the shell 10 to carry the shell 10 along as it is pushed through the induction furnace 1.

(14) The shell 10 is provided with a centering shoulder 13 on each of its longitudinal sides running parallel to the longitudinal axis or axis of symmetry, which, as shown in FIG. 3, cooperates with the round steel bars 8 inside the induction furnace 1 in such a way that it counteracts the rotation of the steel ingot 2 and the shell 10 about the longitudinal axis.

(15) Instead of the centering shoulders 13, the shell 10 can be provided on its underside on the outside, for example, with sliding runners, ribs or beads, which likewise counteract the rotation of the assembly of shell 10 and steel ingot 2 within the induction furnace 1, for example in cooperation with the sheet metal strip 7.

(16) The method is explained below with reference to FIGS. 5 to 8. FIG. 5 shows the feed side of an assembly of two induction furnaces 1. The induction furnaces 1 are arranged side by side and parallel to one another. Cold steel ingots 2 are brought to a loading station 15 via a feed roller table 14. Two slide-in roller tables 16 are also provided. A first shell magazine 17A and a second shell magazine 17B are arranged parallel to the slide-in roller tables 16. For example, a shell 10 is extracted from the first shell magazine 17A by means of a lifting device 18, which is designed as a vacuum lifting device, and placed on a slide-in roller table 16. An ingot loader, not shown, is used to place a steel ingot 2 from the feed roller table 14 onto the shell 10 located on the slide-in roller table 16. The slide-in roller table is arranged in front of an induction furnace 1 such that the relevant steel ingot 2 is aligned with the underlying shell 10 in front of the furnace tube. A hydraulic cylinder assembly 19 (ingot pusher) is then used to push a steel ingot 2 into the relevant induction furnace 1, wherein the ingot column shown in FIG. 3 is displaced within the induction furnace 1. As a result, the steel ingot 2 leading in the ingot column enters the compensating chamber 9 shown schematically in FIG. 6 at the end on the discharge side of the induction furnace 1.

(17) With reference to FIG. 6, the steel ingot 2 is pulled out of the compensating chamber 9 by means of extraction pliers 20 onto an extraction roller table 21. There, another hydraulic cylinder assembly 23 (ingot pusher) pushes the heated steel ingot 2 onto an outfeed roller table 22.

(18) Via the outfeed roller table 22, the steel ingot 2 and the underlying shell 10 travel together to an ingot lifting device 24, which lifts the steel ingot 2 vertically for further processing. The transport movement of the assembly of the shell 10 and the heated steel ingot 2 is stopped by a stop 25 extending over the outfeed roller table 22, which is formed as a yoke or a bridge. The height of the stop 25 is selected such that lifting the heated steel ingot 2 with the ingot lifting device 24 would cause the shell 10 to be stripped from the steel ingot 2, in the event that the shell 10 sticks to the steel ingot 2. The shell 10, which either falls back onto or remains on the outfeed roller table 22, is transported separately from the steel ingot 2 on the outfeed roller table 22 to a shell extraction position 26 (see FIG. 7). The steel ingot 2 and the shell 10 together reach the position at which the stop 25 is located. The steel ingot 2 is lifted and the shell 10 remains in place or is stripped off, if it should adhere to the steel ingot 2. The shell 10 passes under the stop 25 until the steel ingot 2 held above it on the ingot lifting device 24 is free. The outfeed roller table 22 stops and the steel ingot 2 is immediately placed on the outfeed roller table 22. The stop 25 is swiveled upwards such that it clears the way for the steel ingot 2 located on the outfeed roller table 22. The outfeed roller table 22 starts or starts up again, as the case may be, and the shell 10 and the steel ingot 2 move separately to the next position.

(19) At the shell extraction position 26, the shell 10 is returned to one of the shell magazines 17A, 17B by means of a shell manipulator 27.

(20) FIG. 8 shows a perspective view of the assembly comprising a steel ingot 2 with the underlying shell on the outfeed roller table 22, wherein the leading end 11 of the steel ingot 2 rests against the stop 25.

LIST OF REFERENCE SIGNS

(21) 1 Induction furnace 2 Steel ingot 3 Induction coil 4 Steel shell 5 Concrete lining 6 Furnace chamber 7 Sheet metal strip 8 Round steel bars 9 Compensating chamber 10 Shell 11 Leading end of steel ingot 2 12 Shoulder 13 Centering shoulders 14 Feed roller table 15 Loading station 16 Slide-in roller tables 17 A First shell magazine 17 B Second shell magazine 18 Lifting device 19 Cylinder/ram assembly 20 Extraction pliers 21 Extraction roller table 22 Outfeed roller table 23 Cylinder/ram assembly 24 Ingot lifting device 25 Stop 26 Shell extraction position 27 Shell manipulator