JP3358038B2 - Low pressure casting machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a low-pressure casting machine.

[0002]

2. Description of the Related Art A general structure of a low-pressure casting machine will be described with reference to FIG. 2. In the figure, a crucible 3 capable of filling a molten metal 2 is disposed below a die base 1, and a crucible 3 is provided at the center of the crucible 3. The stalk 4 is immersed in the molten metal 2 and is disposed in a manner hanging down from the die base 1. The upper end of the stalk 4 is connected to a cavity 6 inside a mold 5 composed of an upper die and a lower die.

In the low-pressure casting machine as described above, after the molten metal 2 is injected into the crucible 3 from the hot water supply port 7, pressurized air is supplied into the crucible 3 using the same hot water supply port, and a pressure is applied to the upper surface of the molten metal 2. And the molten metal is injected into the cavity 6 through the stalk 4. The pressure of the pressurized air in such a casting step is controlled by control means (not shown) in accordance with each step of the casting.

FIG. 3 shows a conventional set boosting curve.
A curve A in the figure represents a set boosting curve in the first shot. In the curve A, the pressure rises steeply to a point a where the molten metal 2 reaches the cavity 6 after the start of casting, and then gradually rises at a point b until the molten metal is filled in the cavity 6, and then to a point c. It rises on a steep slope until it reaches the bottom. After the point c, the pressure is kept constant for a predetermined time (T), after which the air is exhausted and the pressure returns to zero. The molten metal in the cavity 6 is cooled and hardened within the evacuation time, and then the casting is taken out of the cavity 6 to complete the first shot. Here, when the first shot is completed, the level of the molten metal 2 in the crucible 3 drops,
Then, as shown in FIG. 2, as the number of shots increases, the level is 10 for 10 shots, the level is 20 for 20 shots, the level is 30 for 30 shots, and so on.
The level of the water drops further. Therefore, in the shots after the first shot, a run-up defect of the casting occurs in the boosting curve such as the curve A. For this reason, conventionally, the curve B (the 10th shot), the curve C (the 20th shot), and the curve D (3
As shown by (0th shot), every time the number of shots increases, a pressure correction method has been adopted in which a pressure corresponding to the decrease in the molten metal level is added to the previous set pressure to obtain a set pressure increase curve.

[0005]

In the conventional pressure correction method, since the pressure is simply increased for each shot, each of the points a, b and c where the pressure changes in any of the curves B, C and D. Is the same as that of the curve A. However, as described above, the level of the molten metal decreases as the number of shots increases, so that the rise time of the molten metal from the level of the molten metal into the cavity 6 naturally increases with each increase in the number of shots. Even if the increase is made, the pressure change timing does not match the rise timing of the molten metal surface and the timing to be considered in each of the subsequent stages, and such a timing mismatch becomes remarkable as the number of shots increases and becomes stable. There was a drawback that a product could not be obtained.

[0006]

In order to solve the above-mentioned problems, a low-pressure casting machine according to the present invention is characterized in that, as the number of shots increases, the set pressure curve of the first shot corresponds to a decrease in the molten metal level. The first shot is defined as a delay time corresponding to a delay in the rise time of the molten metal from the molten metal surface into the cavity of the mold due to the decrease in the molten metal surface. Pressure gradient at the start of injection
Calculated from the correction pressure for each shot obtained by manual boosting
And then move them in parallel along the time axis to draw
Prepare multiple preset boost curves for each shot
To approach the target boost pressure setting curve for each shot
In this manner, the pressure of the molten metal is controlled for each shot .

[0007]

Next, one embodiment of the present invention will be described with reference to FIG. This embodiment is applied to a low-pressure casting machine similar to that described with reference to the prior art with reference to FIG.

The pressure control according to the present embodiment is performed according to the time-pressure characteristic diagram shown in FIG. 1, and a curve A1 in the figure represents a set pressure rising curve in the first shot.
The curve A1 is similar to the curve A in FIG. 3, and the pressure rises steeply to a point a where the molten metal 2 reaches the cavity 6 after the start of casting, and then the cavity 6 is filled with the molten metal at a point b. The pressure rises gently to the point c, and then rises steeply until reaching the point c. After the point c, the pressure is kept constant for a predetermined time (T), and then the air is exhausted and the pressure becomes zero. Return to The molten metal in the cavity 6 is cooled and hardened within the evacuation time, and then the casting is taken out of the cavity 6 to complete the first shot.

Next, a curve B1 shows a set boosting curve at the tenth shot. The timings of the points a1, b1 and c1 corresponding to the points a, b and c of the curve A1 correspond to the points a, b and c. On the other hand, the pressure is shifted to the right side in the drawing, that is, the rear side by t1, and the pressures at these points are represented by a curve A1.
Are higher by P1 than the pressures at points a, b and c, respectively.

The curve C1 shows the set boosting curve at the 20th shot. The timing of the points a2, b2 and c2 corresponding to the points a, b and c of the curve A1 is represented by the curve B1.
Are shifted to the right side, that is, rearward in the figure by t2 with respect to the points a1, b1 and c1, respectively, and the pressures at these points are each higher than the pressures at the points a1, b1 and c1 by P2 in the curve B1. I have.

The curve D1 shows the set boosting curve at the 30th shot. The timing of the points a3, b3 and c3 corresponding to the points a, b and c of the curve A1 is represented by the curve C1.
Are shifted to the right side, that is, the rear side, in the figure by t3 with respect to the points a2, b2, and c2, respectively, and the pressure at each point is higher than the pressure at the points a2, b2, and c2 by P3 in the curve C1. I have.

As is apparent from the figure, each of the curves A1 to D1
Is a point a where the molten metal 2 reaches the cavity 6 after the start of casting.
Up to a1, a2, and a3 (the straight line portion indicated by X in the figure), the pressure rises with a similar gradient from zero, and the above-mentioned times t1, t2, and t3 are from the surface of the molten metal due to the decrease of the surface of the molten metal. The time is set by a time corresponding to a delay of the rising time of the molten metal into the cavity 6. Note that the delay time of each shot after the first shot with respect to the first shot (for example, t1 in B1 and t1 + t2 in C1) is the first shot.
This is calculated from the pressure gradient at the start of shot injection and the correction pressure (obtained by manual boosting) for each shot. The pressure gradient of X is due to the fact that no change was found in all shots.

In this embodiment, the time t1,
t2 and t3 and the pressures P1, P2 and P3 are equal to each other. The set curves of the shots other than those shown in the drawing are also drawn by translating the curve A1 in the time axis and pressure axis directions based on the delay time calculated from the same correction pressure as described above.

That is, in this embodiment, not only the pressure of the set pressure rising curve is increased as the number of shots is increased, but also the timing of the pressure change is delayed at each stage. It is possible to ideally set the relationship between the rising timing and the pressure, the period during which the molten metal fills the cavity 6, and the pressure during the period, and the relationship between the pressurizing water holding time and the pressure during the period. Further, in the present embodiment, since the delay time in an arbitrary shot can be calculated from the pressure gradient at the start of injection of the first shot and the correction pressure in the shot at that time, a set curve can be drawn. There is an advantage that the set boosting curve for the first shot and thereafter can be easily obtained by using the curved line.

[0015]

According to the low pressure casting machine of the present invention , the first shot
Each time the number of shots increases with respect to the set boost curve,
Apply the pressure corresponding to the surface drop to the pressure axis direction
In parallel with the surface of the molten metal
Of the molten metal in the mold cavity
Delay time at the start of the injection of the first shot
Correction for each shot obtained by pressure gradient and manual pressure increase
Calculated from the pressure and added , respectively, and translated in the time axis direction
Move multiple drawn boost curves for each shot
Prepare the preset boost curve for each target shot
Control the pressure of the molten metal for each shot so that
Therefore , regardless of the increase in the number of shots, the relationship between the pressure change timing and the pressure at each stage of the shot can be ideally set, so that there is an advantage that a stable product can be manufactured over all shots.

[Brief description of the drawings]

FIG. 1 is a time-pressure characteristic diagram for each shot in a low-pressure casting machine according to one embodiment of the present invention.

FIG. 2 is a view showing a schematic structure of a low-pressure casting machine.

FIG. 3 is a time-pressure characteristic diagram for each shot in a conventional low-pressure casting machine.

[Explanation of symbols]

 2 Melt 5 Mold 6 Cavity A1, B1, C1, D1 Setting pressure rise curve t1, t2, t3 Time P1, P2, P3 Pressure

Claims (1)

(57) [Claims] 1. Each time the number of shots is increased, a pressure corresponding to a decrease in the level of the molten metal is applied to the set pressure rising curve of the first shot, and the molten metal is moved in parallel in the pressure axis direction, and
The delay time corresponding to the delay of the rise time of the molten metal from the surface of the molten metal into the cavity of the mold due to the decrease of the surface of the molten metal is defined as a first time .
Obtained by pressure gradient and manual pressure increase at the start of shot injection
Was calculated from the corrected pressure in each shot, it
Each shot is drawn with a parallel translation in the time axis direction.
A plurality of set boost curves are prepared in advance for each
Each shot so that it approaches the set boost curve for each shot.
Low pressure characterized by controlling the riser pressure of molten metal for each unit
Casting machine .