JPS5850166A - Low pressure casting method by holding of residual pressure - Google Patents

Abstract

PURPOSE:To manufacture efficiently castings of high quality under low pressure by dropping the compressed air pressure to bring the molten metal in a stalk slightly lower than the charging port of the stalk upon ending of one shot and charging the molten metal by exerting pressure in the next shot. CONSTITUTION:Air is fed from a compressor to the inside of a low pressure casting furnace 12 through a pressurization control valve 14 and solenoid valve 16a, whereby molten metal is cast under low pressure. Thereafter, the valve 16a is closed, a solenoid valve 16b is opened, and the air is fed through a residual pressure control valve 18 to the inside of the furnace 12. At the same time, the pressure in the furnace 12 is decreased gradually by opening a reducing valve 34. The decrease in the pressure is transmitted to the pressurizing chamber 24 of a differential pressure controller 20, where a diaphragm 22 detects the differential pressure from a residual pressure chamber 26. When the pressures in the chambers 24, 26 balance, a proximity switch is operated to close the valve 34. In this state, the molten metal level in the stalk is held in the position slightly lower than the charging port of the stalk. The valve 16b is closed and the valve 16a is opened to carry out the next pressure casting.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low pressure casting method by maintaining residual pressure.
After completing one shot, the compressed air pressure sent into the crucible is slightly lowered, and the molten metal rising during the stalk is held by only slightly descending from the stalk pouring port, and in the next shot, the pressure is increased again to pour the melt. By doing so, the air flowing into the stalk is minimized to prevent oxidation of the molten metal, and
The present invention relates to a low-pressure casting method by maintaining residual pressure, which suppresses the formation of molten metal in the crucible due to hot water return, and prevents the contamination of precipitated impurities in the molten metal, thereby obtaining a high-quality product.

In the low-pressure casting method, compressed air is sent to the surface of the melt in the crucible, and the pressure causes the molten metal to rise into the stalk, where it is poured into a mold connected to the stalk and solidified.

In the conventional low-pressure casting method, the residual pressure in the crucible after one shot is released, the molten metal rising in the stoke is returned to the surface, and then pressurized again in the next shot.

For this reason, air flows into the stalk each time a shot is completed, oxidizing the molten metal adhering to the inner wall of the stalk, and this oxidized metal mixes into the casting, resulting in a significantly low F quality.

In addition, since the molten metal in the stoke is returned to the surface of the molten metal,
When the level of the hot water is lowered due to continuous pouring, the return head is large, and this impact causes the hot water to be classified into different types, and impurities such as iron and magnesium that have precipitated in the hot region are mixed into the poured hot water, resulting in poor quality. This will lead to a decrease in Therefore, the hot water must be refilled frequently before the hot water level has dropped too much, which not only degrades work efficiency, but also causes the above-mentioned oxides adhering to the inner wall of the stalk to be mixed in during the first two shots when refilling the hot water. Due to the high number of defects, the product must be discarded, resulting in a high defect rate, and in general, the good product rate by conventional low-pressure casting methods is only about 80%.

The present invention has been made to solve the above-mentioned difficulties, and its purpose is to efficiently obtain high quality castings.
This pressure is achieved by blowing compressed air onto the surface of the molten metal in a crucible housed in a sealed furnace.

In the low-pressure casting method in which molten metal is poured into the mold through a stalk connected to the mold, the residual pressure of the compressed air in the furnace after one shot is reduced so that the molten metal surface rising in the stalk is lower than the stalk pouring port. The object of the present invention is to provide a low-pressure casting method by maintaining residual pressure, which is characterized in that the remaining pressure is held at the same position, and at the next shot, the pressure is increased from the reduced residual pressure position and poured.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the apparatus used in the method of the present invention will be explained.

The pressure piping 10 from the compressor is communicated with the inside of the low-pressure casting furnace 12, which is the object of pressurization control, through a pressure control valve consisting of a pressure reducing valve and a residual pressure control valve in parallel in the middle of the pressure pipe 10. . The pressurization control valve is a pressurization control valve 14 that is configured to be programmable, for example, a combination of a swing valve mechanism and a pulse motor that linearly changes the pressurizing force according to the rotation angle of a valve opening/closing handle, and a pressurization control valve 14 configured to be programmable. An electromagnetic on-off valve 16a for pressurization control, which is connected immediately after the control HARTZ 14 and constituted by an electromagnetic valve, is connected in series. The residual pressure control valve is constituted by a residual pressure control valve 18 configured similarly to the pressure control valve 14, and an electromagnetic on-off valve 16b connected immediately after the residual pressure control valve 18 and constituted by an electromagnetic valve. The above electromagnetic on-off valve 16
a and 16b are configured so that when one is on, the other is always off. Low pressure casting furnace 12 and residual pressure control valve 1
A differential pressure controller 20 that detects differential pressure and generates a control signal is provided at a position approximately equidistant from 8.

The differential pressure controller 20 separates the inside of the sealed cylinder via a diaphragm 22 into a pressurizing chamber 24 below the diaphragm and a residual pressure chamber 26 above the diaphragm. A pressure pipe is led out and communicated with the residual pressure chamber 26 from an intermediate position between the residual pressure control valve 18 and the electromagnetic on-off valve 16b. A sliding guide cylinder 28 is provided at the upper center of the residual pressure chamber 26 of the differential pressure controller 20, and a rod 30 that slides inside the sliding guide cylinder 28 is erected and fixed at the center of the upper surface of the diaphragm 22. Sliding guide tube 2
A proximity switch is provided near the rod 8, and a magnet for operating the proximity switch is fixed to the two ends of the rod 30. The lower end of the rod 30 and the residual pressure chamber 26) are connected via a coil spring 32, and the proximity switch is turned on when the pressure in the residual pressure chamber and the pressure in the pressurized chamber are balanced and the pressure difference becomes zero. The elastic force of the coil spring 32 is set so that A pressure reducing pipe for discharging pressurized high temperature gas in the low pressure casting furnace 12 into the atmosphere is connected to the low pressure casting furnace via a pressure reducing valve 34, and a control signal line from the differential pressure controller 20 is connected to the pressure reducing valve 3.
Contact 4.

Next, the method of the present invention will be explained using the above apparatus.

From the compressor to the pressure control valve 14 and the electromagnetic on-off valve 1
6a, air is sent into the low-pressure casting furnace 12, and the pressure is maintained for a certain period of time to perform low-pressure casting (step in FIG. 2). Next, the electromagnetic on-off valve 16a is closed and the electromagnetic on-off valve 16'b is opened.
Air for residual pressure control is sent into the furnace. At the same time, the pressure reducing valve 34 is opened to lower the pressure inside the furnace.
(A in Figure 2). This pressure drop within the furnace body is transmitted to the pressurizing chamber 24 of the differential pressure controller 20 through pressure piping. Since air controlled to a required residual pressure is sent into the residual pressure chamber 26 of the differential pressure controller 20 from the pressure pipe connected immediately after the residual pressure control valve 18, the diaphragm 22 of the differential pressure controller detects the differential pressure. When the falling air pressure in the pressurizing chamber 24 and the required pressure in the residual pressure chamber 26 are completely balanced, the proximity switch is activated and the pressure reducing valve 34 is closed. In this state Gε, gas at a constant pressure can be sent into the furnace from the residual pressure control valve, so the constant pressure can be accurately maintained without being disturbed by gas leaks from the furnace or subtle temperature changes inside the furnace. (Step II in Figure 2). At this point, the molten metal surface rising during the stalk is set to be held at a slightly lower position than the stalk pouring port.

Next, in order to return to the pressurized state, it is only necessary to close the electromagnetic on-off valve 16b, and while the residual pressure is maintained, the pressurization pressure is increased by the necessary amount from the program-controlled pressurization control valve. Pressurized air can be sent into the furnace to perform the next pressurized casting.

Note that in order to prevent product chipping and excessive flaking and to cast products of constant quality with a high yield, it is required to always pour metal into the mold at a constant pressure.

For this purpose, it is necessary to lower the temperature of the hot water level in the crucible by removing the product.
It is also necessary to increase the required amount in response to changes in the area of the hot water level in the crucible (PL, P2O1, in Figure 2). This necessary increase is calculated for each shot and the pressure control valve 1 is
4 is program controlled.

Further, since the residual pressure increases sequentially due to the increase in the pressure of q, the set value of the residual pressure control valve 18, which maintains the reduced pressure, is programmed to increase the pressure sequentially in accordance with the above-mentioned pressure increase. Accurate control of this residual pressure has made it possible to improve the yield rate of small cast products from 80% to 97%, but the pressure change of this residual pressure itself is about 3/1000 K gj/c rn". However, it is extremely difficult to control the pressure using ordinary pressure change measuring means because of the high temperature inside the furnace.

Note that the method of the present invention does not necessarily require the use of the above-mentioned device; for example, it is composed of a pressure control valve 14 and a pressure reduction valve 34, and after one shot is completed, the set pressure of the pressure control valve 14 is reduced and the pressure reduction valve 34 is opened. It is also possible to perform program control such that the pressure inside the furnace is reduced, and then the pressure reduction valve 34 is closed and the pressure control valve 14 is increased in pressure.

In short, any device may be used as long as it can control the pressurization and depressurization curve shown in FIG.

As shown in Figure 1-L, according to the method of the present invention, the residual pressure in the furnace after the completion of one shot is slightly reduced, and the level of the molten metal rising during the stoke is controlled to be slightly lowered from the stoke pouring port. Therefore, the amount of air flowing into the stoke is small, which prevents the oxidation of the molten metal, and prevents the melt from returning to the crucible as in the case of conventional methods, allowing it to settle in the temperature range. This method has the remarkable effect of producing high-quality products that are not contaminated with impurities and are cast with a high yield.

Although the present invention has been variously explained above with reference to preferred embodiments, the present invention is not limited to these embodiments, and it goes without saying that many modifications can be made without departing from the spirit of the invention. It is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an apparatus used in the method of the present invention, and FIG. 2 is an explanatory diagram showing an example of changes in furnace pressure. 10. Pressure piping 12. ,,low pressure casting furnace. 141. , pressurization control valves, 16a, 16b. 8. Electromagnetic on-off valve, 18. ,,Residual pressure control valve, 2”O,,Differential pressure controller, 22゜1.Diaphragm, 24.,Pressurization chamber, 2608
．． Residual pressure chamber, 28. ,, sliding guide tube, 30...
0 tsudo, 32. ,,coil spring. 34, pressure reducing valve. Patent applicant Nissin Kogyo Co., Ltd. Representative Sadao Miyashita

Claims (1)

[Claims] 1. In the low-pressure casting method, compressed air is blown onto the surface of the molten metal in a crucible housed in a sealed furnace, and this pressure is used to pour the metal into the mold through a stalk connected to the mold. The residual pressure of the compressed air inside is reduced to hold the molten metal surface rising during the stalk at a position lower than the stalk pouring port, and at the next shot, the pressure is increased from the reduced residual pressure position and poured. A low-pressure casting method that maintains residual pressure.