GB2127338A - Scarfing method and apparatus - Google Patents

Abstract

In the method and apparatus for scarfing the end face of a cylindrical ingot W, a torch 18 is disposed adjacent, and radially of the end face and relative rotation between the ingot and the torch is carried out at constant speed so that, a relatively smooth surface X results and, due to the variation of angular velocity between the centre and the periphery, the depth of cut l increases from the periphery towards the centre where most segregation occurs. <IMAGE>

Description

SPECIFICATION Scarfing apparatus and method This invention relates to a scarfing apparatus and method for use in a method of casting and working a cylindrical body.

Attention is drawn to co-pending application No. 82278475, from which the present application is divided.

For producing steel ingots for annular forgings, there is known, for example as shown in Figure 1, a long ingot method of casting a long cylindrical steel ingot LI by bottom casting method and then cutting the ingot into round slices on a lathe or the like to provide steel ingots to be rolled, on a cheese ingot method (not shown) of casting molten steel into moulds arranged in series below a ladle by a top casting method, shifting the ladle.

In the former long ingot method, however, a lot of cut-off portions in dead head, centre runner, sprue runner, cutting allowance, etc. are lost by cutting the steel ingot into round slices and further a lot of heat is lost by cutting the steel ingot after cooling. In the latter, cheese ingot method, if the "ratio of height to diameter" of the steel ingot is more than 1.0, problems of quality in that cavities and defective portions remain in the interior of the steel ingot, are encountered. In addition, problems are encountered with variable quality and further the long casting time is unsuitable for mass casting.

When the steel ingot cast by the above-mentioned method is further subjected to scarfing work, in conventional method, a torch travels in various directions, A,B,C,D,E,... passing through the centre of hand scarfed surface of steel ingot work W and dividing the circumference at equal intervals as shown in Figure 2(a) so that the centre portion of working surface of work W which has generally more segregation is scarfed more often.

However, in such a method, the hand scarfing is carried out so that the section of the ingot after the scarfing work is formed radially with several corrugated irregular surfaces to defectively damage smoothness as shown in Figure 2(b). In addition, problems are encountered in that a long scarfing time is required and a scarfed surface having uniform desirable conical section cannot be provided.

An object of the present invention is to provide a scarfing apparatus in which a hot steel ingot is automatically subjected to rotary scarfing by use of the change in circumferential speed of radial points on the steel ingot to particularly remove the central segregated portion for effectively providing a smooth scarfed surface.

The present invention provides a scarfing apparatus for use in a method of casting and working a cylindrical body, comprising a torch disposed in use radially opposite a steel ingot to be scarfed, and rotatable relative to the steel ingot so that the circumferential speed of each point on the torch in the radial direction of the steel ingot is utilized for the scarfing.

The invention will be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is an explanatory drawing of the conventional long ingot method; Figure 2(a) is an explanatory drawing of conventional hand scarfing work; Figure 2fbJ is a sectional view of an ingot scarfed by the method illustrated in Figure 2(a); Figure 3 is a schematic view showing a working process for carrying out a casting and working method.

Figure 4 is a partially sectional enlarged view showing casting and working apparatus.

Figure is a partially sectional side view showing main portions of casting apparatus similar to Figure 4; Figure 6(a) is a schematic representation showing scarfing apparatus forming an embodiment of the present invention; Figure 6(b) is a sectional view of a scarfed ingot; and Figure 7 is a graph showing the depth of scarf given by scarfing apparatus of the present invention.

Figure 3 shows a line showing working processes for working of the present invention, in which a mold setting section A, casting section B and mold drawing section C are sequentially arranged in the form of a plain rectangular endless loop as shown in the drawing, for example, and from the mold drawing section C are branched and extended working lines for conveying cast steel ingots to the following process, i.e.

scarfing section D, heating furnace E and then rolling section F.

As shown in Figure 4, a plurality of molds 2 are arranged and set in series at predetermined positions on a carrier truck 1 in the mold setting section A so as to be conveyed to the following casting section B.

As shown in Figures 4 and 5, molten steel required for a work unit of casting ingot is cast into the mold 2 in the casting section B on a weighing machine 3 capable of measuring the weight of mould 2 before and during casting and a molten steel take-out device 4 for passing a necessary amount of molten steel into the mold 2 through a calculating control circuit (computer) 5 interlocked with the weighing machine.

The weighing machine 3 comprises a hydraulic cylinder 6 for supporting and moving vertically the mold 2 with a rod 6' and a load cell 7 mounted on the base of the hydraulic cylinder 6 which is provided to raise the mold 2 from the conveying position up to a position on which the molten steel can be poured. The load cell 7 functions to measure the weight of the mold 2 before casting (tare weight before casting), to apply the measured value and the change in the weight at the beginning of molten steel pouring and during casting sequentially to the input of the calculating control circuit 5.

The molten steel take-out device 4 comprises a dipped nozzle 10 projecting downward from a pouring port 9 of a ladle 8 located above the mold 2, a stopper 11 capable of opening and closing the pouring port 9 and a hydraulic cylinder 12 operated by the calculating control circuit 5 to move vertically the stopper 11.

The calculating control circuit 5 receives the input value from the load cell 7 to calculate an amount of molten steel to be poured into the mold 2 and required for casting a work unit of the ingot and supplies the required output to the hydraulic cylinder 12.

The base end (upper end) of the dipped nozzle 10 is mounted on the pouring port 9 of the intermediate ladle 8, and further a cylindrical cover 13 opened at the lower end is provided around the outer periphery of the point of said nozzle to prevent splash in pouring molten steel. Also, coating 14 for covering the surface of the molten steel W is put into the mold 2.

Further, after casting, exothermic heat insulating agent or a heat insulating plate (plate-shaped heat insulating agent) 15 is put onto the upper surface of the molten steel W to carry out exothermic heat insulation in the conveyance of the molten steel.

A speed control unit 16 for controlling speed with which the molten steel is conveyed along a conveying path after casting is provided to convey the mold 2' to the following mold drawing section C with minimum speed to avoid abrupt conveyance and swaying the surface of the molten steel W.

In the casting section B thus constituted, the weight of the unit steel ingot to be directly rolled, including tare weight, is previously applied and set to the calculating unit 5 shown in Figure 4. Then, the mold 2 located in the casting section B on the line is raised toward the puring port 9 of the intermediate ladle 8 by the lifting cylinder 6 to cast the molten steel into the mold 2. Then, the tar weight of the mold is measured by the load cell 7 to be applied to the input of the calculating unit 5. The input value of the calculating unit is converted into the height of the mold 2 to the intermediate ladle 8 so that the output of the calculating unit is applied to the hydraulic cylinder 12 which lifts the stopper 11 directly connected thereto in the intermediate ladle 8. The pointed end of the stopper is raised higher than the pouring port 9 to start pouring into the mold 2'.When the surface of the molten steel W in the mold 2' is sequentially raised, the load cell 7 attached to the lower cylinder 6 detects the change in the weight of molten steel to lower gradually the position of the mold 2'.

Accordingly, the capacity of the molten steel W is gradually increased without changing the position of the surface of molten steel shown in the drawing, until it provides a predetermined amount of molten steel (amount necessary for an work unit of steel ingot). Meanwhile, the load cell 7 continues to apply the weight change to the input of the calculating unit 5 to measure the predetermined weight so that the hydraulic cylinder 12 lowers the stopper 11 and closes the pouring port 9. The stopper may be subjected to multi-stage control to improve the accuracy of taking out the molten steel. Thus, the predetermined steel ingot (steel slab) with the unit weight is casted.

The casting section B, thus constituted, can weigh individually the molds, take out a necessary amount of molten steel through the calculating control circuit, and at the same time cast a plurality of steel ingots with high quality automatically and rapidly (see Table 1). Also, since top pouring using the dipped nozzle and cylindrical cover are employed, splashing can be prevented to improve the casting skin of the steel ingot.

TABLE 1 Casting Number Average Standard Casting division of casting unit weight deviation time (Fig. 5) (P) (Kg) y(Kg) (Min.) 75 75 440.3 2.7 36min/75p 76 76 440.0 2.6 36min/76p Further, the molten steel coating cover 14 is attached to the outside of the cylindrical cover provided on the pointed end of the nozzle 10 before casting above the upper surface of the molten steel W cast into the mold 2' in said casting section B. After casting, as shown in the drawing, the cover 14 covers the upper surface of the molten steel with the heat insulating agent 15 to keep the surface of the molten steel from swaying and retain heat while the molten steel is conveyed.Also, the molten steel, after casting, is prevented from rapid conveyance by the speed control unit 16 which holds the minimum conveying speed. Thus, during the conveyance, heat is sufficiently maintained while the steel ingot is sent to the scarfing section D while it is hot without sway so that the inner quality of the ingot changes little and the smooth surface is maintained.

Next, though not shown in the drawing, in the mold drawing section C, the mold is laid down and the steel ingot is drawn out of the mold as it is hot to be sent to the following scarfing section D.

In the scarfing section D, as shown in Figure 4, the steel ingot, i.e., work W, is placed on a pair of rollers 17 to be rotated thereon in the direction of arrow shown in the drawing. A torch 18 is provided opposite the scarf surface of the work W and directed radially of the work W. The nozzle is provided with an oxygen jetting port and gas jetting ports dotted and opened around said oxygen jetting port. Further, one of the rollers 17 for rotating the work W is a drive roller and the other a driven roller, the rotational speed of the rollers being adjustable in any degree by a speed adjusting mechanism not shown in the drawing.

Also, in another embodiment of this method, the position of the work W is fixed, contrary to the first method, and the torch 18 opposed to the work is rotated, along a circular rail provided on the outer periphery of the work W for example, to carry out similar scarfing. Further, the torch 18 is adapted to move radially toward and away from the center of the work W.

When the intended scarfing is carried out by the use of the above-mentioned embodiments, the nozzles of the torch 18 are arranged directed from the outer periphery of the rotatable work W toward the center, one side nozzle being opposed to the center of the work W and remaining ones being opposed to corresponding outer portions of the work W, being displaced bit by bit until they approach successively the outer periphery so that the circumferential speed relative to the work W varies as the outer periphery is approached.

Thus, when the scarfing is carried out according to the difference between the respective circumferential speeds of nozzles, the corresponding points on the work W are formed with approximately V-shaped (conical) scarf grooves X as shown in Figure 6(b). In other words, in the steel ingot (2'), scarf depth e of defective portions in the center section having the most of segregation will be cut off the most deeply and furthermore, the cut V-shaped scarf groove X is formed with smooth surfaces different from the irregular surfaces cut by conventional hand scarfing as shown in Figure 2(b).

In the case of scarfing the end surfaces of a 500 ~ m/m steel slab (1) Work temperature: Room temperature (2) Torch: 250t nozzle torch (with acetylene and oxygen) (3) Work material: SU material (4) Rotational frequency of work: 7 RPM (5) Scarfing time: 8.6/second When the scarfing is thus carried out once, the scarf depth as shown by the solid line in Figure 7 is obtained. Further the broken line shows the scarf depth provided by the second scarfing.

Thus, instead of conventional hand scarfing the scarfing apparatus according to the present invention scarfs the steel ingot by the use of the difference between the circumferential speeds of respective points in the radial direction of the work while the work is rotated relative to the torch, so that the center portion of the work is formed with the deeply scarfed surfaces and the outer portions are formed with successively shallower scarfed surfaces as they approach the outer periphery and not only regular and smooth surfaces of scarfed grooves are obtained, but also the scarfing can be automatically carried out in a very short time to display a remarkable action and effect of dispensing with conventional skilled technology.

Also, the scarfing apparatus according to the present invention can scarf a wider extent of the steel ingot compared with conventional hand scarfing and use a large-sized torch for large-sized works so that efficient scarfing and substantial reduction is processing time can be realized.

Further in this embodiment, whilst the large-sized torch is shown as an oxygen jetting port with gas jetting ports therearound as shown in Figure 6(b), a plurality of single-port torches may be used in an array.

Next will be shown a concrete embodiment which scarfs the steel ingot to provide results shown on Tables 2 and 3 under the following conditions; fConditionsl (1) Material of dipped nozzle: Molten silicon, inside diameter 40 p Jetting port: Two horizontal ports x 25 x 2525 ~ x 2 (2) Amount of coating (12) to be used: 2K/T Component: SiO245%; Co 0.8%, A4202 20%; C 16% (3) Amount of heat insulating agent (99) to be used: 4K/T Component: MoA# 15%; At203 40%; SiO2 20% (4) Steel ingot: Unit weight 440 Kg, profile 500a x 285H (5) Mold: Unit weight 1400 kg (mold, bedplate) (6) Kind of steel: C 0.60; Si 0.25; Mn 0.60 (7) Casting speed: 15Kg/sec.

(8) Dimension of steel ingot: (Height/diameter) less than 1.0 (9) Scarf: Height of flux end (outer peripheral portion). more than 10 m/m (10 m/m is the minimum thickness of segregation) TABLE 2 Casting Scarfing Test No. Number of Average Standard Casting Weight Scarfing casting unit weight deviation time of scarf time (Kg) cr(Kg) (min) (Kg) (sec/D) First 150 439.4 2.4 72 14.2 33 Second 149 438.7 2.7 70 15.1 34 Third 149 441.5 2.9 71 14.3 33 Fourth 150 440.0 2.1 72 14.4 33 TABLE 3 Quality Test No.Percentage defective Percentage of wheel of wheel conditioning of wheel (%) (%) First 0 0 Second 0 0 Third 0 0 Fourth 0 0 As is apparent from the above, the following advantages are obtained; (1) Homongenous steel ingots without dispersion of quality, as hot lumps, can be cast and scarfed rapidly in the continuous process from the casting process to the scarfing one and then sent to the following rolling process so that rapid mass production can be obtained.

(2) A plurality of steel ingots can be substantially cast by weighing individually the molds and taking out a necessary amount of molten steel through the calculating control circuit so that high quality steel ingots can be automatically rapidly cast (see Table 1). Also, the top casting using the dipped nozzle and the cylindrical cover are utilized so that the occurrence of splash can be prevented to improve the casting skin of the steel ingot.

(3) Since the scarfing which has been conventionally carried out by hand scarfing is performed by the relative rotation between the torch and the work to utilize the difference between the circumferential speeds of the respective points in the radial direction of the work, the center portion of the work can be formed with deeper scarfed surfaces and the other portions with successively shallower ones as the portions approach the outer periphery. Also, not only regular and smooth scarfed surfaces are obtained, but also the scarfing can be automatically carried out for a very short time so that a remarkable action and effect of dispensing with any conventional skilled technology or the like can be displayed.

Also, compared with conventional hand scarfing, a wider extent of the steel ingot can be scarfed so that a large-sized torch can be used even for large-sized works to realize efficient scarfing and substantial reduction of processing time.

(4) Since the molten steel is conveyed to the following process by reducing the moving speed so as not to sway the surface of the molten steel after casting during the conveyance, the internal quality and smoothness of surface of the molten steel can be maintained during the conveyance thereof.

Claims (12)

1. Scarfing apparatus for use in a method of casting and working a cylindrical body, comprising a torch disposed in use radially opposite a steel ingot to be scarfed, and rotatable relative to the steel ingot so that the circumferential speed of each point on the torch in the radial direction of the steel ingot is utilized for the scarfing.

2. Scarfing apparatus as claimed in claim 1, wherein the torch is fixed and the steel ingot is rotated with rollers.

3. Scarfing apparatus as claimed in claim 2, wherein the steel ingot is fixed, and the torch is rotated along a circular rail.

4. Scarfing apparatus as claimed in claim 1, 2 or 3, wherein the torch is provided with a plurality of nozzles in the radial direction of the steel ingot.

5. Scarfing apparatus as claimed in any one of 2 to 4, wherein the body to be scarfed has a circular cross-section.

6. Scarfing apparatus substantially as hereinbefore described with reference to Figures 6 and 7 of the accompanying drawings.

7. A method of scarfing a steel ingot, which comprises rotating a torch substantially circularly over a surface of the ingot, to provide an increasing depth of scarf with decreasing distance from the centre of rotation for a constant angular speed.

8. A method as claimed in claim 7, wherein the torch comprises a nozzle or array of nozzles extending radially.

9. A method as claimed in claim 7 or 8, wherein the torch is stationary and the ingot is rotated.

10. A method as claimed in claim 7 or 8, wherein the ingot is stationary and the torch is rotated over the surface.

11. A method as claimed in any one of claims 7 to 10, wherein the torch is moved radially during scarfing.

12. A method of scarfing, substantially as hereinbefore described with reference to Figures 6 and 7 of the accompanying drawings.