JPS6325863B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method of operation in pressure casting.

Pressure casting is a process in which a shield chamber 3 surrounds a tundish 1 and a mold 2, as shown in Fig. 1, and an inert gas is introduced into the chamber so that the gas pressure P is almost balanced with the total water head H of the molten steel. In this method, the slab 7 is pulled out while being controlled by the gas supply valve 5 and discharge valve 6 so that the gas pressure and the free surface of the molten steel in the mold, that is, the meniscus, reach an equilibrium state during the initial transition period of casting. is the most difficult to control. In the figure, 8 is a stopper.

In other words, in the pressure casting method shown in Fig. 1, the diameter of the tundish nozzle 4 can be changed to
The feature is that it can be made much larger than the
If the slab 7 is pulled out in a state where P≒PH (p is the specific weight of the molten steel, Kg/cm ³ ), the molten steel passing speed in the nozzle can be reduced, and as a result, non-metallic inclusions etc. are prevented from being drawn in. It has the advantage of being able to However, since P = 0 at the initial stage of pouring, the flow rate of molten steel becomes extremely large, and the rate of rise of the molten metal level in the mold becomes large. It may not be possible to stabilize the

As shown in Figure 3, the model for stabilizing the meniscus of the hot water level in the mold is that when the hot water level reaches a certain level, the gas valve is opened (point A) and a predetermined gas pressure is applied to stabilize the meniscus at a certain level. (In the figure, B indicates the upper limit of the mold), but in reality, as shown in Figure 4, the vibration waveform is accompanied by attenuation, and the so-called molten steel overflows from the mold at the peak of the amplitude. Overflow phenomenon C is likely to occur.

For this reason, the stopper 8 may be opened and closed intermittently and controlled as shown in Fig. 5, but it is very difficult to perform this stopper opening and closing operation automatically, and it is necessary to rely on the intuition and experience of an expert. The reality is that we don't get it.

As mentioned above, this pressure casting has the advantage that the diameter of the tundish nozzle 4 can be made sufficiently large, but the rising speed of the molten steel surface in the mold at the initial stage of casting is very fast, and this transient It is essential to stabilize the period, and the present invention relates to an operating method in pressurized casting with the purpose of achieving this stabilization and preventing overflow accidents.

In the present invention, a device for raising and lowering the tundish is provided, and in the early stage of casting, the level of the tundish 1 is lowered to keep it low as shown in FIG. By immediately applying gas pressure P inside the shield chamber, the meniscus is stabilized within the standard level as shown in Figure 6, even in anticipation of the time constant of the control system, and the molten steel water head is also kept at H.
-h, and the balancing gas pressure can be lowered, resulting in smaller pressure fluctuations and easier control.

As described above, in the present invention, transient phenomena can be quickly stabilized by keeping the tundish low at the beginning of casting, reducing the rate of inflow of molten steel from the tundish, and suppressing the rate of rise of the molten metal level in the mold.

The method of the present invention will be explained in more detail using FIGS. 7a and 7b.

Figure 7a shows the state immediately after the start of casting, and a sealing chamber 3 is inserted between the tundish 1 and the mold 2.
The chamber is surrounded by control valves 5 and 6 so that an inert gas can be supplied into the chamber and the pressure can be adjusted. The molten steel 10 is poured from the tundish 1 into the mold 2 through an immersion nozzle 4. The level of the molten steel surface within the mold is detected by a level detection sensor 11. A stopper 8 for starting injection is attached to the tundish 1 (attachment structure not shown). The tundish 1 is provided with a lifting device (not shown), and H can be changed as shown in FIG. 7b. seal chamber 3
has a structure that allows it to expand and contract following the rise and fall of the tundish, and maintains the airtightness between the mold and the tundish. The inert gas pressure inside the chamber is determined by the size of H, but is generally 0.2~
It is ^about 1.0Kg/cm2.

When starting casting, when the stopper 8 of the tundish is opened at the position shown in Fig. 7a, molten steel is injected into the mold 2, connects with the dummy bar head 9, and the molten metal level gradually rises until it reaches the tip of the immersion nozzle 4. is detected by the sensor 11, and the gas supply valve 5 is opened to
(Kg/cm ² ), and when the hot water level reaches the control range, drawing is started while controlling the hot water level to be constant at a pressure close to PH.

When the water level stabilizes, the tundish water is raised,
Casting is continued by keeping the immersion depth of the tundish nozzle at the optimum position for the casting operation at the position shown in Fig. 7b.

An example of a lifting device used in the present invention is shown in FIG.

The tandem tray 1 has two trunnion pins 1.
2 and 12' and placed on a support lever 13.
This lever 13 is a hydraulic cylinder 14, 1 for lifting and lowering.
4'. This cylinder is fixed to a tundish truck 16. An immersion nozzle 4 is attached to the tundish and is immersed in the mold 2. The tandate truck 16 has a support beam 17,
It runs on the rails provided at 17'.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an outline of the pressure casting method, Figure 2 is a diagram showing an outline of a normal casting method, and Figure 3 is a diagram showing an outline of a normal casting method.
The figure shows a meniscus stabilization model in the Figure 1 method, Figures 4 and 5 are diagrams showing the actual meniscus control in the Figure 1 method, and Figure 6 is a diagram showing the state of meniscus control according to the method of the present invention. It is.
FIG. 7 is a diagram schematically showing the method of the present invention, in which a shows the state at the initial stage of casting, and b shows the state when casting reaches a certain level. FIG. 8 is a partially cutaway side view showing an example of the elevating device of the pressure casting apparatus used in the present invention.

Claims (1)

[Claims] 1 In pressure casting, a retractable chamber surrounds the tundish and the mold, inert gas is supplied inside the chamber, and drawing is performed while approximately balancing the pressure and the total water head of the molten steel. The molten steel and the immersion nozzle are brought into contact with each other at a deep position in the mold at the initial stage of injection, the contact level is detected by a sensor, and from the moment the contact level is reached, a gas pressure of less than PH (molten steel specific weight x water head) is applied to the chamber. After the water level has stabilized at the normal level, the gas pressure is set to approximately PH, the tandem tank is raised, and the immersion depth of the immersion nozzle is adjusted to the appropriate position.