JPS5928427B2 - Continuous metal casting mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mold for continuous casting of metal.

BACKGROUND ART As a continuous casting method for metals, for example, a continuous casting method for steel, the Jungens-Lodge method, in which a mold is vibrated up and down during casting, is popular.

This method tends to cause wavy undulations, or so-called oscillation marks, on the six sides of the slab, and when casting irregular cross-sections, cracks are likely to occur due to uneven cooling within the mold.

In this type of casting method, the casting capacity is proportional to the product of the casting speed and the cross-sectional area of the slab, but the casting speed has already reached its limit due to the cooling capacity that controls the shell formation rate and the cracking of the slab due to thermal stress. The cross-sectional area of the slab is limited by the cross-sectional dimensions of the finished product after rolling.

In order to improve casting capacity, a method has been proposed in which continuously cast slabs with a width that is an integral multiple of the width required for rolled rough material are cut under pressure using rolling rolls, but center segregation and center porosity are exposed on the cut surface. However, it remains a defect in the final product, and improvements are desired.

A method has also been disclosed in which the thickness of the contact part is thinned in order to remove center segregation and center porontee from the cutting position, but this method has not been put to practical use because of cracks during casting.

The mold of the present invention has light oscillation marks, has a large casting capacity, has a low cracking rate even when casting irregular cross-sections, and has a low cracking rate when casting with a double width and cross-cutting in the later process. The purpose is to prevent defects from being exposed.

When the mold of the present invention continuously casts metal, the gap between the mold and the material to be cast is filled with a cooling medium.

In continuous casting of steel, the material to be cast is the lower two parts of the entire length of the mold.
Since one to two-thirds of the mold is away from the mold and insulated by air, the casting speed is lower, e.g. 1.57
7? ,/Limited to below income.

It is widely known that the faster the casting speed, the more likely cracks and pluck-outs will occur in the slab.

Cracks in slabs occur inside the mold and during the subsequent cooling process, but
Cracks within the mold are mainly caused by uneven cooling in the circumferential direction of the slab.

That is, the lower part of the mold is most affected by variations in the voids that occur between the mold and the slab.

In order to reduce this void, keep variations within a small range, and improve heat exchange between the mold and the slab, a method was adopted in which the mold contact area is slightly tapered and the cross-sectional area decreases toward the exit side. However, if the taper is made larger, the frictional resistance between the mold and the slab increases when the slab is pulled out, causing a breakout in which the slab is torn off and molten steel flows out, which is dangerous.

This phenomenon is noticeable not only in slabs with rectangular cross-sections, blooms with square cross-sections, and blooms with circular cross-sections, but especially in slabs and plumes with irregular cross-sections.

Although the mold of the present invention can be applied to all cross sections, an example of its implementation will be described for the case of casting a slab with an irregular cross section.

1 and 2 are a plan view and an elevation view, respectively, of a mold example of the present invention, in which sieve-like protrusions 2 are formed on opposing inner surfaces of a cylindrical mold 1 along the advancing direction of the metal to be cast. , a roller 3 similar to the inner wall of the mold is disposed on the exit side of the mold 1,
A recessed fitting part 4 is formed on the inner wall of the mold directly above the roller 3, and a supply hole 5 for supplying a cooling medium is provided in the recessed fitting part 4.

The mold is cooled by a cooling water passage 6.

Molten steel is injected into the mold by a submerged nozzle γ, and the upper surface is coated with powder (synthetic slag) 8.

The surface layer of the molten steel 9 solidifies through heat exchange with the mold, forming the outer shell 1.
0, and due to heat shrinkage, a free space is created from the mold wall.

In the mold of the present invention, the gap is filled with a cooling medium supplied from the supply hole 5 to reduce heat transfer resistance.

The cooling medium passes through the recessed fitting portion 4 and is caused to advance in the circumferential direction and upward direction.

As the cooling medium, a gas, liquid, or solid having good thermal conductivity can be used.

As a gas, CnHm has a large absorption heat of thermal dissociation, and as a liquid, a low melting point metal such as Sn, At, Pb, Zn
or their alloys or glass or low melting point synthetic slag,
As the solid, a high melting point synthetic slag powder bed or the like can be used.

The cooling medium that melts on the surface of the material to be cast generally flows between it and the mold.

These cooling media adhere to the surface of the material to be cast along with the main road of the material to be cast, or overflow from between the roller 3 and the material to be cast, so they are constantly replenished under pressure from the cooling medium supply hole 5.

By using the above m-type and using a cooling medium,
Heat exchange between the mold and the cast material is promoted and made uniform in the circumferential direction.

In other words, when using the conventional method to cast a grooved slab as shown in Figure 6, the grooves solidify more rapidly in the upper part of the mold than in other parts, and as a result, the solidification progresses further away from the inner surface of the mold, and the subsequent solidification actually affects other parts. However, in the present invention, the heat exchange in the area away from the inner surface of the mold is large enough to prevent the formation of cracks and the solidification thickness. Non-uniformity in thickness is less likely to occur.

The cooling medium lubricates the space between the mold and the cast material, reduces the occurrence of sagging lane marks, and prevents plect out. It also coats the surface of the cast material to prevent it from oxidizing, and prevents scale from burning into the mold. It is also possible to prevent subsequent seizure of the roller apron and improve the surface quality of the slab.

In addition, the roller 3 on the exit side of the mold prevents eccentricity of the corrugated material, and at the same time, changes the surface friction to rolling friction to reduce the pull-out resistance of the slab, resulting in even better pluck-outs and oscillation marks. .

If the grooved slab shown in Fig. 6 is continuously cast using the mold of the present invention, the center of the slab corresponding to the groove will solidify faster than the other center, and center segregation and center porosity can be eliminated from the contact area. I can do it.

Even when such slabs are cut longitudinally through the groove, no internal defects are exposed on the cut surface, so that the slab can be cast with a width that is an integral multiple of the width required in the subsequent process.

As a feature related to the present invention, the grooves of the continuously cast grooved slab are cut on the casting line after solidification is completed.

In the conventionally disclosed method of clamping and cutting using rolling rolls, rolling is performed at the same speed as the casting speed, so the rolling speed is so slow that the temperature of the rolls in the area in contact with the slab increases significantly, and the rolling speed is too low. The rolling equipment is prone to thermal cracks, and the rolling equipment becomes unnecessarily large due to its structure.
In addition, when changing the cutting position, it is necessary to replace the rolls with rolls that match the groove positions of the slab each time.

The clamping forging method proposed by the present inventors as a longitudinal section method for a partial slab will be described below.

FIG. 3 shows an example of a fully curved continuous casting equipment, in which the mold 11
As shown in FIG. 4, a bottleneck 13 is provided at the pre-cutting position of the slab, and a groove is cast into the slab 12.

The slab 12 is cooled by a secondary cooling zone 15, and then straightened by pinch rolls and a straightener 16 and drawn out.

Subsequently, as shown in FIGS. 5 and 7, the signature knife 20 is simultaneously pushed into the groove 14 of the slab from both sides facing each other by the clamping forging machine 17, and as the slab moves forward, it is longitudinally cut.

In the case of continuous casting of steel, the advancing speed of the slab is about 5 to 30 m/sec, so it is sufficient that the cycle of the sword insertion is about 0.1 to 10 H2, and the amplitude is about 10 to 100 wn.

In addition to the rank press shown in Figure 5, a hydraulic press using a hydraulic cylinder can be used to reciprocate the sword.

If there are two or more cutting positions, the pressing force can be reduced by shifting the pushing timing of adjacent swords as shown in Figure 7, or by shifting the positions of adjacent swords in the direction of slab advancement. .

It is preferable to provide side rolls 21 for positioning the slab 12, as shown in FIG. 6, immediately before the clamping forging machine 17.

At or after the signature position, it is preferable to provide side rolls 21 to prevent the slab 12 from shifting, widening beyond the revised drawing value, or bending, as shown in FIG.

The depth Hl-[2)/Kl of the groove in the slab 9 is desirably 1X4 or more in order to make the cooling rate sufficiently faster than other parts.

After being vertically cut by the compression forging machine 17, the slab is passed through the horizontal cutting machine 1.
8 to cut to desired length.

The transverse cutter 18 is not particularly limited, and a conventionally used gas cutter or shear can be used.

Also, the case where the saw cutting method is adopted as the longitudinal section method of the slab will be explained.

As shown in Fig. 8, the saw blade 29 of the hot saw machine tilts and swings at a certain angle with the slab 12, and stays at a position 30 as far away from the slab as possible for a long time, reducing the thermal load on the saw blade. It is desirable to reduce the

In the case of continuous steel casting, the advancement speed of the slab is 5 to 30 rra.
'rL/sec, the thickness of the cut surface of the slab is 100~400
Since the cutting distance is approximately 100 mm apart, existing hot saws have sufficient cutting capacity.

In other words, the maximum cutting capacity required for this line is 12.
It is about OOcrtrA/sec, but 30.000-7
Heat saws with a cutting capacity of seconds are already in practical use.

FIG. 10 is the B-B cross section of FIG. 8 before thermal sawing.

FIG. 11 shows the same <C-C cross section after hot sawing the side grooves.

FIG. 12 shows the same <D-D cross section after hot sawing the central groove.

In this way, the hot saw can be installed at a different position in the slab advancing direction.

The swinging of the hot saw can be achieved, for example, by connecting the hot saw having a motor 33 and a saw blade 29 to a fixed base 32 using a hydraulic cylinder 34, as shown in FIG.

It is preferable to provide side rolls 21 for positioning the slab 12, as shown in FIG. 10, immediately in front of the hot saw 2γ.

Even after sawing, it is preferable to provide side rolls 21 to prevent the slab from bending as shown in FIG.

The depth of the groove in the slab (Hl-R2) /H1 is desirably 1X4 or more in order to make the cooling rate sufficiently faster than other parts.

After longitudinal cutting with a hot saw, the slab is cut into desired lengths with a horizontal cutting machine.

Since the grooves cut vertically through the grooves of the slab, casting defects are not exposed on the cut surface, and the grooves are thinner than the 1000mm portion, making it easier to cut.

The effects of the present invention can be estimated from measurement data of mold copper plate temperature, mold copper plate temperature, molten metal level fluctuation, solidified shell thickness, slab surface temperature directly under the mold, etc. in continuous casting of steel slabs as follows.

The heat flow rate Q in the mold (Kcat/rr? hr) is expressed by the formula % (1) where Tms: molten steel temperature, Tcw: cooling water temperature, RT:
Overall heat transfer resistance (??Z2・hr −'C/Kca, /,
) However, RT=R1+ R2+R3+ R4+ R5+
R6 (2) Here, R1: Film heat transfer resistance between the cooling water and the surface of the mold copper plate, R2: Heat transfer resistance of the mold copper plate, R3: Heat transfer resistance due to the void generated between the slab and the mold, R4: Heat transfer resistance of powder film, R5: Heat transfer resistance of solidified shell, R6:
The film heat transfer resistance between the molten steel and the solidified shell was calculated based on the measured data for each heat transfer resistance.
) below can be ignored, R3 is the thickest 180 x 1
0-4 (rr?・hr −'C/Kca7Δ−), R4
This is followed by 3.2 x 10-4 (77Z2・hr
-℃/Kcal/rmn), but it is about 1/50 of R3, and R5 is 0.4X 10-4 (??
Z"hr"C/Kc a l/rrun ) is extremely small.

Since the number of voids that can actually occur is thought to be 0.05 to 0.80 times, we will compare the RTs for both cases: leaving the void as it is, filling the void with powder, and filling the void with Sn. This is the same as a man's 1 bale.

However, in this case, it is assumed that there is a powder film with a thickness of 0.48 on the surface of the slab, and the solidified shell thickness is 257.
rrIIL, Sn heat transfer resistance is 0.5X10-4 (
rr? -h r ·'C/KcaUrrgrL).

According to the table, the overall heat transfer resistance RT is significantly large if the void remains, and changes significantly depending on the void thickness.

This calculated the powder film thickness to 0.4rra.
Although it is assumed that the distance n is constant, in reality, it varies greatly locally during work and can range from about 0.0 to 0.8 m, so in the conventional method, RT changes significantly locally.

By filling the void with a cooling medium according to the invention,
Even if the position of the slab is displaced from the mold, the overall heat transfer resistance RT is hardly affected, and the cast material can be cooled uniformly and efficiently over the entire circumference.

[Brief explanation of the drawing]

1 and 2 are respectively a plan view and an elevation view of an example of a mold according to the present invention, FIG. 3 is an equipment arrangement row when implementing the present invention in a fully curved continuous casting equipment, and FIG. 5 is a conceptual diagram of the pressure forging machine, and FIG. 6 is a cross-sectional view taken along line A-A in FIG. 5.
B sectional view, Fig. 7 is a C-C sectional view of Fig. 5, Figs. 8 and 9 are conceptual diagrams of the saw cutter, and Figs. They are BB, CC, and DD cross-sectional views. 1.11... Mold, 2... Annular protrusion, 3... Roller, 4... Recessed fitting part, 5
...... Supply hole, 6... Cooling water passage, 7.
...Immersion nozzle, 8...Powder, 9.
... Molten steel, 10 ... Outer shell, 12 ...
... Slab, 13... Defile, 14... Groove, 15... Cooling zone, 16... Straightening machine, 17... Nipping forging machine, 18... Transverse cutting L19... Center porosity, 20...
...Named sword, 21...Side roll, 27...
...Hot saw machine, 29...Saw blade, 32...
...Fixed stand, 33...Motor, 34...
...Hydraulic cylinder.

Claims (1)

[Claims] 1 Sieve-like protrusions are formed on opposing inner surfaces of a cylindrical mold along the direction of movement of the metal to be cast, and a roller similar to the inner wall of the mold is disposed at the outlet of the mold, and the inner wall of the mold directly above the roller is disposed at the outlet of the mold. A metal continuous casting mold having a recessed part formed therein and a supply hole for supplying a cooling medium to the recessed part.