JP2007222896A - Method for measuring humidity in cavity, and die-casting apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for measuring the humidity in a cavity, having higher accuracy with a simple constitution, in a die casting process. <P>SOLUTION: The method for measuring the humidity in the cavity, is performed as the followings, that is, in the die casting apparatus provided with the cavity constituted in a die and a vacuum generating means for exhausting gas in the cavity, at a prescribed measuring range (24) in a gas exhausting flowing passage (31) communicating the cavity with vacuum-generating means (27, 28), a moisture measuring means (21) for measuring the moisture in the gas passed through the measuring range, a temperature measuring means (22) for measuring the temperature of the gas and a pressure measuring means (23) for measuring the pressure of the gas, are attached; and in this measuring method, a measuring process for obtaining measured wave-form in each measured value at each casting cycle in the die casting apparatus and a calculating process for calculating the ratio of water molecules in the gas passed through the measuring range during the casting cycle, based on the measured wave-form, are performed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cavity humidity measuring method and a die casting apparatus. More specifically, the present invention relates to a cavity humidity measuring method for measuring the humidity in the cavity at the time of molding a cast member for the purpose of quality control in a vacuum die casting process, and a die casting apparatus capable of realizing this humidity measuring method.

  As a method for casting a complex-shaped casting with a thin wall and high accuracy, the air in the cavity is sucked by a vacuum generating means such as a vacuum pump just before the molten metal is injected into the cavity, and a dense work is produced by a smooth hot water flow. Conventionally, a vacuum die casting for forming is known.

  In vacuum die casting, in order to make it easy to take out a workpiece, a mold release agent is sprayed and applied in advance to the inside of the cavity, the mold is closed, and the molten metal is injected after evacuation by vacuum means. This mold release agent is composed mainly of water, and penetrates not only inside the cavity but also into the partition surface of the mold and the clearance of the ejector pins provided on the mold by spraying and coating. For this reason, when a vacuum is generated by the vacuum generating means, the release agent that has permeated into the mold dividing surface is sucked into the cavity, and a large amount of water vapor is brought into contact with the sucked release agent and the injected molten metal. May occur, and internal defects such as blow holes (holes) may be formed. For this reason, various techniques for measuring the humidity in the cavity have been proposed in order to predict the occurrence of internal defects due to water vapor from the release agent.

  For example, in Patent Document 1, when the gas in a cavity is discharged out of a mold by a vacuum pump, a humidity sensor is provided on a pipe that communicates the cavity and the vacuum pump, and the mold side and the vacuum pump side of the humidity sensor. Cavity humidity measurement, characterized in that an open / close valve is provided in each, and the gas discharged from the cavity is collected by appropriately controlling the open / close valve during vacuum suction, and then the humidity of the collected gas is measured. A method is disclosed. By measuring the humidity after holding the collected gas for a predetermined time, it is possible to contact the gas until the reaction time of the humidity sensor elapses without hindering the casting process. Humidity can be measured.

  However, according to this prior art, it is possible to measure the exact humidity of the collected gas, but it is necessary to install an on-off valve and a bypass in the vacuum suction pipe portion in order to collect the gas. There is a problem that it becomes complicated in terms of equipment. Moreover, since the humidity to be measured is relative humidity, the value of humidity will change if the temperature of the pipe portion changes. Therefore, when determining the quality of the cast member based on the measured relative humidity, there is a problem that the temperature in the pipe must be taken into consideration.

  Further, Patent Document 2 is characterized in that a humidity sensor is installed in a mold, and a discharge valve path for discharging gas in the mold and a humidity sensor path communicating with the humidity sensor are provided in parallel. A humidity measurement method is disclosed. The humidity sensor path is provided with a dedicated cooling plate to prevent the intrusion of the molten metal, which stabilizes the gas flow, so that even a general humidity sensor with a slow reaction can be measured. The humidity before and after the molten metal injection can be easily measured.

According to this prior art, there is an advantage that the humidity inside the mold can be constantly measured. Alternatively, it is necessary to remove the humidity sensor every time the mold is replaced, which may complicate the mold and increase the equipment cost. In addition, the humidity in the cavity while the molten metal is filled in the mold greatly affects the occurrence of internal defects in the cast member. It is not useful in managing quality.
JP-A-7-68365 JP 2005-111478 A

  The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide a cavity humidity measuring method with a simpler configuration and higher accuracy than the prior art. A second object of the present invention is to provide a die casting apparatus that can realize a cavity humidity measuring method with high accuracy as described above.

  As described above, in the prior art, the measured value by the humidity sensor after holding for a certain period of time or the maximum value of the humidity in a certain measurement range is defined as the humidity in the cavity. We focused not only on the continuous measurement of temperature and pressure changes, but also on the estimation of the humidity in the cavity during casting using these change waveforms. And it discovered that the influence of the temperature of a measurement area | region (for example, inside piping), vacuum suction conditions, etc. can be excluded by estimating the ratio of the water molecule in the gas which passed the measurement area | region.

  In the present invention, the influence of the temperature of the measurement region and the vacuum suction conditions is excluded for the following reason. In general, humidity represents relative humidity, and this humidity varies greatly depending on temperature and pressure. For example, if the measurement area is 293K and the humidity is 40%, the humidity is about 20% at 303K at the same water vapor partial pressure. (See the relationship between temperature and saturated water vapor pressure in FIG. 2).

  Further, taking the case where the volume of the cavity to be sucked, that is, the volume of the gas that has passed through the measurement region of the exhaust flow path is 1000 cc and 4000 cc, the gas passes through the measurement region within the same time, and When the content ratio of water molecules in the gas is the same ratio, in the case of 4000 cc, many water molecules collide with the detection part of the humidity sensor, and as a result, the humidity measurement value becomes high. That is, with only the measured value of the cavity humidity, various types of determination criteria must be set depending on the size and shape of the cast member and the difference in casting conditions.

  Therefore, in the present invention, the relative value obtained by combining temperature and pressure is used as a criterion for determination, not the absolute value of humidity.

  Specifically, in order to accurately estimate the ratio of water molecules in the gas discharged from the cavity, first, the water vapor partial pressure at each time is calculated from the waveform data of humidity and temperature and the saturated water vapor pressure curve. Then, the degree of the number of water molecules that have passed through the measurement region is estimated by integrating the water vapor partial pressure with the time during one casting cycle. Moreover, the volume of the gas which passed the measurement area | region is calculated by time-integrating the pressure change waveform of a measurement area | region between casting 1 cycle. Then, the ratio between these two values is taken to estimate the number of water molecules per unit volume contained in the gas discharged from the cavity. Although the water vapor partial pressure, gas volume and water molecule number per unit volume obtained as described above are not necessarily physically accurate, they are relative to each casting cycle or judgment value. Any value that can be compared with is acceptable.

  As described above, by processing the measurement data of the humidity sensor, etc., it is possible to estimate the humidity that is not easily affected by the surrounding conditions, and more accurately estimate the ratio of water molecules in the gas discharged from the inside of the cavity. it can.

  That is, the cavity humidity measuring method of the present invention is a die casting apparatus comprising a mold for forming a cavity, a vacuum generating means for discharging the gas in the cavity, and an exhaust passage for communicating the cavity and the vacuum generating means. Cavity humidity measurement method, in which a vacuum suction process for vacuum suction in a cavity and a time change of humidity, temperature, and pressure in a measurement period including at least a vacuum suction process in a measurement region provided in an exhaust passage, respectively A measurement step of measuring and obtaining a time change waveform of each measurement value, and a calculation step of calculating a ratio of water molecules in the gas that has passed through the measurement region during the casting cycle based on these time change waveforms. Features.

In the measurement period in the above measurement process, it is desirable that the opening time of the opening / closing valve provided upstream of the measurement region in the exhaust flow path is a measurement start point, and the closing time of the opening / closing valve is a measurement end point.
Also, the above calculation step includes a first step of obtaining a converted humidity waveform at the reference temperature from the time change waveform of humidity and the time change waveform of temperature, and integrating the converted humidity waveform over the measurement period to obtain the relative number of water molecules. A second step for setting the value (Sh), a third step for integrating the time-varying waveform of the pressure in the measurement period and setting the relative value (Sg) of the number of molecules of the gas that has passed through the measurement region, and measurement during the casting cycle And a fourth step of calculating a ratio (H) of water molecules in the gas that has passed through the region by H = Sh / Sg.

  The die casting apparatus of the present invention includes a mold for forming a cavity, a vacuum generating means for discharging the gas in the cavity, an exhaust flow path communicating the cavity and the vacuum generating means, and a measurement provided in the exhaust flow path. A humidity measuring means for measuring the time variation of the humidity in the measuring area during the casting cycle, a temperature measuring means for measuring the time variation of the temperature in the measuring area during the casting cycle, and in the measuring area during the casting cycle The gas that passed through the measurement area during the casting cycle based on the time change waveform of each measured value obtained by the pressure measuring means, the humidity measuring means, the temperature measuring means, and the pressure measuring means for measuring the time change of the pressure of And an arithmetic means for calculating a ratio of water molecules therein.

  In the die casting apparatus of the present invention, a measurement region is provided in an exhaust passage that communicates a cavity and a vacuum pump, and a humidity measurement unit, a temperature measurement unit, and a pressure measurement unit capable of measuring negative pressure are installed in the measurement region. Yes. Therefore, the time change waveform of the humidity, temperature, and pressure of the gas can be obtained on the same time axis.

  In addition, it is possible to easily estimate the total number of gas molecules and the number of water molecules that have passed through the measurement region by calculation means as relative values rather than absolute values from the time-varying waveforms of the respective measured values obtained. it can. Then, using these two estimated values, the ratio (H) of water molecules in the gas that has passed through the measurement region is estimated.

  Therefore, according to the cavity humidity measuring method and the die casting apparatus of the present invention, it is possible to eliminate the influence of the temperature around the measurement region, vacuum suction conditions, etc., and also in quality control of cast members having different shapes and sizes. Determination can be made using the same determination value (H).

  A preferred embodiment of the present invention will be described with reference to FIGS.

  The die casting apparatus 1 of the present embodiment defines a cavity 18 that is a space by a fixed mold 13 (mold) fixed to the fixed platen 11 and a movable mold 14 (mold) fixed to the movable platen 12. Yes. The lower end side of the cavity 18 communicates with the injection sleeve 16, and a plunger 17 for injecting molten metal is slidably disposed on the inner periphery of the sleeve 16. Reference numeral 29 denotes an extruding mechanism for extruding the cast member solidified after the mold is opened.

  An exhaust valve (also referred to as a vacuum valve) 20 that is driven to open and close by a hydraulic cylinder or the like is installed on the upper end side of the cavity 18, and an exhaust circuit 30 that exhausts the gas in the cavity 18 is connected to the exhaust valve 20. ing. A melt detection sensor 19 for detecting the tip of the melt is embedded in the upper end portion of the cavity 18.

  The exhaust circuit 30 has an exhaust passage 31 that communicates the cavity 18 and the vacuum tank 27, and an opening / closing valve 26 is disposed in the exhaust passage 31, and humidity measuring means 21, downstream of the opening / closing valve 26, A measurement region 24 is provided in which the temperature measurement means 22 and the pressure measurement means 23 are inserted in close proximity. Each measuring means 21, 22, 23 measures the humidity, temperature, and pressure of air or gas (hereinafter referred to as gas) flowing through the measurement region 24 and outputs the measurement result to the controller 25 (calculation means). The controller 25 stores a program for executing a measurement process and a calculation process described later. The vacuum tank 27 communicates with a pump 28, and the inside of the vacuum tank 27 is always depressurized to a predetermined pressure. Here, the vacuum tank 27 and the pump 28 are vacuum generating means.

  In the present invention, the humidity measuring means is not particularly limited, and a commonly used well-known humidity sensor can be used, and a well-known temperature sensor such as a thermocouple can also be used as the temperature measuring means. Moreover, as a pressure measurement means, the well-known pressure sensor which can measure the negative pressure generally used can be used.

  The operation of one cycle of casting (from mold clamping to die casting member removal) of the die casting apparatus 1 configured as described above will be described. The time in parentheses is the time in FIG.

  First, a die plate (not shown) is driven to clamp the fixed mold 13 and the movable mold 14 previously applied with a release agent (ta) to form a cavity 18. Simultaneously with the formation of the cavity 18, the exhaust valve 20 is opened.

Next, a predetermined molten metal is poured into the sleeve 16, and the molten metal is pushed out into the cavity 18 by the plunger 17 at a low speed (tb). When the plunger 17 moves forward and reaches a predetermined stroke, the on-off valve 26 is opened. Thereby, a vacuum suction process is started (arrow t ₀ ).

Simultaneously with the start of vacuum suction (t ₀ ), the forward speed of the plunger 17 is increased to inject the molten metal at a high speed. When the tip of the molten metal reaches the molten metal detection sensor 19, the exhaust valve 20 is closed (tc), the cavity 18 and the vacuum suction circuit (exhaust circuit) 30 are shut off, and the measurement region 24 in which various sensors are arranged in the vacuum tank 27. The pressure is reduced by the pump 28. This completes the vacuum suction process.

When the molten metal filled in the cavity is solidified (tc to td), the fixed mold 13 and the movable mold 14 are opened (te), and the die-cast member cast and solidified is pushed out by the extrusion mechanism 29, and at the same time the on-off valve 26 is closed. (Arrow t ₁ ).

Here, from the start of the vacuum suction by opening the on-off valve 26 at time t _0, a measurement period until the closed-off valve 26 at time t _1. And in this measurement period, the measurement process which measures the time change waveform of humidity, temperature, and pressure is performed.

  An example of each measurement waveform by the humidity measuring means 21, the temperature measuring means 22 and the pressure measuring means 23 during the casting one cycle operation is shown in FIG. FIG. 3 shows each measurement waveform along with the change in injection speed on the same time axis. It can be seen from FIG. 3 that the pressure in the measurement region increases simultaneously with the start of suction, and the gas in the cavity passes through the measurement region. The humidity measurement value obtained by the humidity measuring means 21 rises several seconds later than the pressure measurement value, but this is a problem of the responsiveness of the humidity sensor itself. Further, the temperature in the measurement region remained constant with almost no change during one casting cycle.

  Next, the number of water molecules (relative value) contained in the gas in the cavity 18 discharged via the exhaust valve 20 is obtained by calculation from the time waveform of each measurement value obtained as described above.

  The calculation step includes a first step of converting the obtained humidity measurement waveform into a humidity waveform at a reference temperature, a second step of calculating the relative value (Sh) of the number of water molecules by integrating the converted humidity waveform, A third step of calculating the relative value (Sg) of the number of molecules of the gas passed by integrating the obtained pressure change waveform; and in the gas passed through the measurement region during the casting cycle defined by H = Sh / Sg And a fourth step of calculating the ratio (H) of water molecules.

Here, the relative humidity measurement value (%) at time t (sec) is F _H (t), the channel temperature measurement value (K) is F _T (t), and the channel pressure measurement value (hPa) is F. _P (t), converted humidity calculation value (%) is F ′ _H (t), saturated water vapor pressure (hPa) at temperature T (K) is P (t), and reference temperature (K) for calculating converted humidity is Ts. And

  In step 1, first, the water vapor partial pressure Pt (hPa) at time t is calculated using the following equation (1).

  Next, the apparent water vapor partial pressure Pt ′ at the reference temperature Ts is calculated according to Boyle-Charle's law as shown in equation (2).

From the above result, the converted humidity F ′ _H (t) is calculated using the formula (3).

In the case of stable casting such as the temperature in the region shown in FIG. 3, the temperature change during one cycle is extremely small, and the converted humidity F ′ _H (t) has a waveform substantially similar to the humidity waveform in FIG. However, since the temperature in the region changes greatly even during one cycle at the start of casting or unstable casting, the converted humidity has a waveform different from the measured humidity waveform. An example is conceptually shown in FIG. In FIG. 4A, the thick line A is the relative humidity measurement value (%): F _H (t), and the thin line B is the converted humidity calculation value: F ′ _H (t).

In step 2, the converted humidity waveform F ′ _H (t) is integrated from the valve opening time t ₀ of the on-off valve 26 to the valve closing time t _{1 of the} on-off valve 26 as shown in equation (4), and the area of the converted humidity waveform is obtained. (The shaded area in FIG. 4B), that is, the relative value (Sh) of the number of water molecules is calculated. In this way, the number of water molecules contained in the gas in the cavity 18 discharged via the exhaust valve 20 can be estimated.

Subsequently, in step 3, the pressure change waveform F _P (t) is integrated from the valve opening time t ₀ of the on-off valve 26 to the valve closing time t _{1 of the} on-off valve 26 as shown in equation (5), and the pressure change waveform The area, that is, the relative value (Sg) of the number of molecules of the gas passed through is calculated.

  In step 4, the ratio H of water molecules in the gas that has passed through the measurement region in the exhaust passage during the casting cycle defined by equation (6) is calculated.

  The die casting process of the present invention having the above measurement process and calculation process is combined with a determination and selection process for automatically determining the quality of the cast die cast member, and the value of H obtained for each casting cycle is preliminarily determined. By comparing with the set judgment value, the internal quality control of the cast member becomes possible. According to the present invention, it is possible to make a pass / fail judgment with high accuracy and speed without going through a special inspection process.

  The humidity measuring method of the present invention can be suitably used for internal quality control of vacuum die cast parts.

It is a cross-sectional schematic diagram explaining the vacuum die-casting apparatus which has a humidity measurement mechanism of embodiment. It is a graph which shows the temperature change of saturated water vapor pressure. It is a figure which shows an example of the change waveform of humidity, temperature, and pressure in 1 casting cycle. Conversion humidity Calculated: an example of a graph illustrating _F'H a (t), (a) the relative humidity measured value _(%): shows the relationship between _F H (t), (b) should be calculated The area Sh is shown.

Explanation of symbols

13: Fixed mold (mold) 14: Movable mold (mold) 16: Injection sleeve 17: Plunger 18: Cavity 19: Molten metal detection sensor 20: Exhaust valve (vacuum valve) 21: Humidity measuring means 22: Temperature measuring means 23: Pressure measurement means 24: Measurement area 25: Controller (calculation means) 26: On-off valve 27: Vacuum tank 28: Vacuum pump 30: Exhaust circuit 31: Exhaust flow path

Claims (4)

A cavity humidity measuring method for a die casting apparatus, comprising: a mold that forms a cavity; a vacuum generating means that discharges gas in the cavity; and an exhaust passage that communicates the cavity and the vacuum generating means,
A vacuum suction step of vacuum suction inside the cavity;
In the measurement region provided in the exhaust flow path, a measurement step of measuring time change of humidity and temperature and pressure in a measurement period including at least the vacuum suction step to obtain a time change waveform of each measurement value;
And a calculation step of calculating a ratio of water molecules in the gas that has passed through the measurement region during a casting cycle based on the time change waveform.   2. The cavity according to claim 1, wherein the measurement period is a measurement start point when the on-off valve provided upstream of the measurement region in the exhaust passage is opened, and a measurement end point when the on-off valve is closed. Humidity measurement method. The calculating step includes a first step of obtaining a converted humidity waveform at a reference temperature from the time change waveform of humidity and the time change waveform of temperature;
A second step of integrating the converted humidity waveform in the measurement period to obtain a relative value (Sh) of the number of water molecules;
A third step of integrating the time-varying waveform of pressure over the measurement period to obtain a relative value (Sg) of the number of molecules of the gas that has passed through the measurement region;
The cavity humidity measurement according to claim 1, further comprising a fourth step of calculating a ratio (H) of water molecules in the gas that has passed through the measurement region during the casting cycle by H = Sh / Sg. Method. A mold for forming a cavity;
A vacuum generating means for discharging the gas in the cavity;
An exhaust passage communicating the cavity and the vacuum generating means;
A measurement region provided in the exhaust flow path;
A humidity measuring means for measuring a time change of humidity in the measurement region during a casting cycle;
Temperature measuring means for measuring a temporal change in temperature within the measurement region during a casting cycle;
Pressure measuring means for measuring a time change of pressure in the measurement region during a casting cycle;
Based on the time change waveform of each measurement value obtained by the humidity measuring means, the temperature measuring means, and the pressure measuring means, the ratio of water molecules in the gas that has passed through the measurement region during the casting cycle is calculated. A die-casting device comprising:

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