JPH0513751B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a hot water supply control device for controlling the filling rate of molten metal filling into a mold cavity of a low pressure casting machine.

(Prior Art) Generally, this type of low-pressure casting machine is equipped with a pressurizing chamber that airtightly covers a crucible containing molten metal, and a mold placed above the pressurizing chamber, and air is supplied to the pressurizing chamber. By filling the cavity of a mold with hot water from a crucible through a stalk at low pressure, a cast product such as an aluminum cylinder head for an engine can be cast.

By the way, in this low-pressure casting machine, if the filling speed of hot water into the mold cavity is too fast, air etc. will be drawn into the casting due to the turbulent flow of the hot water, causing blowholes, etc., and conversely, the filling speed of hot water will be slow. If it is too high, there is a problem that casting defects such as early solidification of a part of the hot water during the supply of hot water occur, so it is necessary to keep the filling speed of hot water constant. Therefore, when the level of hot water in the crucible decreases as hot water is supplied into the mold cavity and the height difference between the level and the mold cavity, that is, the head difference increases, the air supply to the pressurizing chamber increases accordingly. Increased pressure is required.

Therefore, in order to meet such demands, conventionally,
For example, as disclosed in Japanese Utility Model Application No. 55-111663, a pressure reducing valve provided in an air supply system is opened in stages as the number of shots to fill a mold cavity with hot water increases. A system has been proposed in which the air pressure in the pressurized chamber is increased in anticipation of a drop in the level of hot water in the crucible.

(Problem to be Solved by the Invention) However, in the conventional method described above, the pressurizing force of air is controlled stepwise and uniformly for each shot, so when the crucible becomes empty, a new one is refilled. There was a problem in that control errors occurred due to variations in the amount of molten metal replenished. Moreover, since the flow rate of pressurized air is constant, even if air leakage occurs due to lack of airtightness of the furnace lid due to the replenishment of molten metal during pressurization, it cannot be corrected, and as a result, It has been difficult to cast high-precision, high-quality cast products.

In addition, since the flow rate of pressurized air is not controlled, there is a problem that the number of hot water shots increases and the level of hot water in the crucible decreases, making the hot water supply time longer and the dispersion of hot water supply time becoming larger. Ta.

The present invention has been made in view of the above, and its purpose is to detect the supply state of pressurized air when hot water rises to the upper part of the stalk during hot water supply in a low-pressure casting machine, and to set it as the optimum condition. By comparing the results and controlling the air pressure and flow rate for filling the mold cavity in an optimal state based on the difference, the flow rate from the top of the stalk is controlled regardless of changes in the amount of hot water in the crucible. The purpose of the present invention is to enable constant and accurate control of the flow rate of hot water filled into a mold cavity, thereby improving the quality of cast products and shortening casting time using a low-pressure casting machine.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an air supply system that communicates with a pressurizing chamber of a low-pressure casting machine and is provided with a flow rate control valve and a pressure control valve. a servo mechanism for controlling the respective opening degrees of both of the control valves, a pressure detector provided in the pressurizing chamber, and a pressure detector provided in the upper part of the cast material stalk at a certain distance in the direction of the passage. A pair of hot water detectors, characteristics that determine the head difference with respect to the pressurizing force when the hot water reaches the upper part of the stalk, volume change characteristics of the pressurizing chamber with respect to the head difference of the hot water in the crucible of the casting machine, and the head difference a memory unit that stores the flow rate change characteristics of the hot water in the stoke relative to the difference; and the values of the pressurizing force of the air, the flow rate, and the flow rate of the hot water when the hot water at a predetermined level in the crucible reaches the upper part of the stoke; The values of the air pressurization force, its flow rate, the volume of the pressurizing chamber, and the hot water flow rate when filling hot water from the top of the stoke into the cavity are set and memorized as a pattern, and when hot water actually reaches the top of the stoke. The difference between the set value of the pattern is calculated based on the output signal from each of the above detectors and the comparison corresponding signal from the comparison section, and hot water is sent to the cavity for both the servo mechanisms according to the difference. The structure includes a control section that outputs signals for pressurizing force and flow rate of air to send the air.

(Function) With the above configuration, in the present invention, the pressurizing force of air to the pressurizing chamber and its flow rate when the hot water in the crucible is filled into the mold cavity at the optimum flow rate are set and memorized as a pattern, and the hot water is stored as a pattern. For each shot in which hot water is filled into a mold, the pressurizing force and flow rate of air when hot water is actually filled into the cavity are corrected based on the set values of the pattern set above. Therefore, even if the level of hot water in the crucible decreases due to an increase in the number of shots, or air leaks occur in the crucible, the filling speed of the hot water into the mold cavity is maintained at the optimum value without being affected by these factors. controlled by.

(Example) Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 shows a hot water supply control device for a low-pressure casting machine according to an embodiment of the present invention, in which 1 is a furnace body of the low-pressure casting machine, and the furnace body 1 is formed in a box shape with an open top surface. Inside, a conductive crucible 2 containing molten metal (molten metal) is placed on a carrier 3 and housed, and on the inner wall surface of the furnace body 1 is a container that heats the molten metal in the crucible 2 to solidify it. Blocking heaters 4, 4,...
...is arranged. Further, the upper opening of the furnace body 1 is hermetically closed by a removable furnace lid 5, so that a sealed pressurized chamber 6 covering the crucible 2 is formed inside the furnace body 1. ing. The pressurizing chamber 6 is communicated with an air supply line 8 having an open/close type air supply valve interposed therebetween, and an air exhaust line 10 having an open/close type exhaust valve 9 interposed therebetween.

A through hole 5a is formed in the center of the furnace lid 5, and a stalk 11 made of a non-conductive material has its upper end flange 11a in contact with the upper surface of the furnace lid 5, and its lower part is connected to the upper surface of the furnace lid 5. It is fitted and immersed in the molten metal in the crucible 2. Further, on the upper surface of the furnace lid 5, a mold 14 consisting of an upper mold 12 and a lower mold 13 is installed at the flange portion 11a of the stalk 11.
The molding surfaces 12a and 13a forming a cavity 15 are provided on the lower surface of the upper mold 12 and the upper surface of the lower mold 13, respectively.
A core C is fitted inside. Further, the cavity 15 has a sprue 1 formed through the lower mold 13.
6 to the upper end opening of the stalk 11, and supplies pressurized air into the pressurizing chamber 6 of the furnace body 1 via the air supply line 8, and the pressurizing force of the air causes the crucible 2 to It is configured to cast a casting by pressurizing the molten metal therein and filling it from the crucible 2 through the stalk 11 into the cavity 15 of the mold 14.

Further, the air supply line 8 on the upstream side of the air supply valve 7 includes a flow control valve 17 for adjusting the flow rate of air flowing through the air supply line 8, and a pressure control valve 18 for adjusting the pressure of the air. The flow control valve 17 is provided with a flow control valve servo mechanism 19 that controls its opening degree, and the pressure control valve 18 is provided with a pressure control valve servo mechanism 20 that similarly controls its opening degree. ing.

On the other hand, a pressure detector 21 for detecting the air pressure inside the pressurizing chamber 6 is attached to the inner surface of the furnace lid 5 facing into the pressurizing chamber 6. Further, in the upper wall of the stalk 11 made of the non-conductive material, there is an upper electrode 2 as a molten metal detector for detecting molten metal at its upper end position, that is, at a position close to the sprue 16 of the mold 14.
2, and a lower electrode 23 serving as a hot metal detector for detecting molten metal at a position spaced a certain distance l below the upper electrode 22 in the travel direction of the stalk 11, respectively, comes into contact with the molten metal flowing inside the stalk 11. Possibly buried.

Furthermore, the pressure detector 21, both electrodes 22, 2
3 and the crucible 2 made of conductive material are connected to a control unit 24 containing a CPU that controls both the servo mechanisms 19 and 20 in response to the output signal of the pressure detector 21 and the molten metal detection signals of the electrodes 22 and 23. ,
The control section 24 is connected to a storage section 30. As shown in FIG. 2, the storage unit 30 stores information when hot water rises in the stalk 11 and reaches the position of the upper electrode 22 by supplying pressurized air into the pressurizing chamber 6 at the Nth shot. , the pressurizing force of the air P _AN
The hot water level in the crucible 2 and the stoke 11 according to changes in
The height difference between the inside and the hot water level, that is, the positional head difference
P _AN when h _N changes = ρh _N (ρ is the density of the molten metal)
The characteristics shown in FIG. 4 when the volume V _AN in the pressurizing chamber 6 changes according to the change in the head difference h _N of the hot water in the crucible 2, and the above head difference h The flow rate of hot water in the stalk 11 depending on the change in _N.
Three characteristics are memorized, including the characteristics shown in FIG. 5 when V _AN changes.

On the other hand, as shown in detail in FIG. 3, the control section 24 includes an amplifier 25 that amplifies the output signal from the pressure detector 21, signals from both the electrodes 22 and 23, and a ground signal from the crucible 2. Based on this, hot water flows inside the stalk 11 from the lower electrode 23 to the upper electrode 22.
Timer 2 measures the passing time _tN until it rises to
6, receives the output from the amplifier 25 and the timer 26 via the input/o27, processes the output signal and the signal from the storage section 30, and outputs the result via the servo mechanism/o28. 19 and 20. Then, after a predetermined shot of molten metal is stored in the crucible 2, when the melt at a predetermined level in the crucible 2 rises and reaches the upper electrode 22 at the top of the stoke 11 for the first shot, After that, the molten _metal rises further and fills the cavity ₁₅ from the upper part of the stoke ₁₁ through the sprue 16 of the mold 14. It has a function of setting and storing patterns of each value of the pressurizing force P _B of the air, its flow rate Q _B , the volume V _O of the pressurizing chamber 6, and the flow velocity V _B of the molten metal. The control unit 24 also stores an output signal emitted from the pressure detector 21 and both electrodes 22, 23 when the hot water actually reaches the position of the upper electrode 22 at the top of the stalk 11, and the output signal into the storage unit. Based on the comparative correspondence signal obtained by relatively corresponding in step 30, the difference from the predetermined value of the set and memorized pattern is determined as a correction amount, and both the servo mechanisms 19 and 20 are adjusted according to the difference. On the other hand, it also has a function of outputting signals of the air pressurizing force P _BN and flow rate Q _BN for sending hot water into the cavity 15.

Next, to explain the operation of the above embodiment,
After a predetermined amount of molten metal is placed in a crucible 2 in a furnace body 1 of a low-pressure casting machine, the furnace body 1 is sealed with a furnace lid 5. In this state, the exhaust valve 9 is closed and the air supply valve 7 is closed.
When the pressurized air is supplied to the pressurized chamber 6 in the furnace body 1, the molten metal in the crucible 2 is moved from the pressurized crucible 2 into the cavity of the mold 14 via the stroke 11. 15 is filled. Then, after a predetermined period of time has passed, the cavity 1
When the molten metal in the pressurizing chamber 5 solidifies while being pressurized, the air supply valve 7 closes and the exhaust valve 9 opens, reducing the pressurizing pressure in the pressurizing chamber 6. Due to this decrease in pressure in the pressurizing chamber 6, the above-mentioned stalk The molten metal in the mold 11 moves downward and returns into the crucible 2, and one shot of casting into the cavity 15 of the mold 14 is thus completed. After that, the same shot as above is repeated,
When the level of the molten metal in the crucible 2 drops to a predetermined level, the furnace lid 5 is opened and a predetermined amount of molten metal is newly replenished into the crucible 2.

In this case, the pressurizing force P _BN and flow rate Q _BN of air to the pressurizing chamber 6 when the cavity 15 of the mold 14 is filled with hot water at the Nth shot are controlled by the control section 24 . The procedure is explained in detail using the flowchart shown in FIG. 6. First, in step _S1 after the start, when the hot water rises to the upper electrode 22 position at the N shot, the pressure detector 21 and the electrodes 22, 23 are detected. The pressure P _AN of the air in the pressure chamber 6 and both electrodes 2 are determined by the output signal of
Input the passing time t _N of the molten metal rising between 2 and 23. After this, in step _S2 , the average flow velocity of the molten metal V _{′ AN =}
After calculating l/t _N , the process moves to step _S3 , where the input pressure P _AN is compared and correlated with each of the three characteristics stored in the storage unit 30, and the head difference h _N is calculated.
= P _AN /ρ, flow rate of hot water V _AN and volume of pressurizing chamber 6
Find _VAN . Next, in step _S4 , the average flow velocity of the hot water determined in steps _S2 and _S3 is calculated.
The pressurizing efficiency η = V' _AN /V _AN , which indicates the state of air relief from the pressurizing chamber 6, is calculated using V' _AN and the flow rate V _AN , and the pressurizing chamber 6 obtained in step S ₃ above is calculated. The volume ratio ξ=V _{AN /} V _O of the gas portion of the pressurizing chamber 6 is calculated from the volume V AN of the pressurizing chamber 6 and the already stored volume V _O of the pressurizing chamber 6. After that, the process moves to step _S5 , and from among the set values of the pattern stored above, the air flow rate Q _B and pressurizing force P _B when filling the hot water cavity 15, and the hot water stalk 1 are determined.
1. Read the pressurizing force P _A of the air when it reaches the upper part, and calculate the filling pressure △P necessary to fill the cavity 15 with hot water based on both pressurizing forces P _A and P _B
Find =P _B −P _A. In the subsequent step _S6 , the volume ratio _ξ =
(V _AN /V _O ), and multiply it by the pressurization efficiency η (=
By dividing by V′ _AN /V _AN ), the air flow rate when the cavity 15 of the mold 14 is filled with hot water at the N shot is calculated: Q _BN = Q _B × (V _AN /V _O ) ÷ (V′ _AN ／
In addition to calculating the air pressure when the hot water reaches _the upper part of the stalk 11 of the Nth shot,
By adding the above filling pressure △P (=P _B - P _A ) to P _AN , the pressurizing force of air when hot water is filled into the cavity 15 at the N shot is P _BN = P _AN + P _B - P _A Calculate. Thereafter, in step S ₇ , _the opening functions f(P _{BN )} and f( _{Q BN} ),
In the next step _S8 , the functions f(P _BN ) and f(Q _BN ) are applied to the pressure control valve servo mechanism 19 and flow control valve servo mechanism 2 of the air supply line 8, respectively.
0, and one cycle of control is thus completed.

Therefore, in this embodiment, the pressurizing force P B of air when the hot water is filled into the cavity 15 of the mold 14 after passing through the upper electrode 22 position on the upper part of the stalk 11 in the first shot after dispensing the hot water _. and flow rate Q _B
is set and stored in the control unit 24 as a pattern, and in subsequent shots, the pressurizing force _PBN and flow rate _QBN of the air when filling the cavity 15 of the mold 14 with hot water are shown in FIG. 7 as an example of the pressurizing force. As shown in , since the filling speed of the hot water into the cavity 15 is corrected to be the same as the first shot, the cavity 15 of the mold 14 is adjusted to be the same as the first shot.
The filling speed of hot water into the interior can be kept constant, and the quality of the cast product can be improved.

In addition, as the number of shots increases, the flow rate Q _BN of air supplied to the pressurizing chamber 6 is corrected to increase, so even if the level of hot water in the crucible 2 changes, the amount of hot water in the crucible 2 is increased regardless of the change in the level of hot water in the crucible 2. The supply time can be kept approximately constant.

(Effects of the Invention) As explained above, according to the present invention, when hot water rises due to pressurized air and hits the upper part of the stalk during hot water supply in a low-pressure casting machine, the supply state of the pressurized air is detected, By comparing this with the optimum conditions and controlling the air pressure and flow rate according to the difference, the mold can be molded regardless of changes in the amount of hot water in the crucible or air leakage from inside the crucible. The filling rate of hot water into the cavity can be maintained accurately and constant, thereby improving the quality of products cast by the low-pressure casting machine and shortening the casting time.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; Fig. 1 is an overall configuration diagram, Fig. 2 is a schematic explanatory diagram when hot water rises to the upper part of the stalk of the casting machine, and Fig. 3 is a block diagram of the control system. Fig. 4 is an explanatory diagram showing the volume change characteristics of the pressurizing chamber with respect to the head difference, Fig. 5 is an explanatory diagram showing the flow rate change characteristic of hot water with respect to the head difference, Fig. 6 is a control flowchart, and Fig. 7 is FIG. 3 is an explanatory diagram showing a change in the pressurization pattern as the number of hot water shots increases. 1...furnace body, 2...crucible, 6...pressurization chamber,
8...Air supply system line, 11...Stoke, 14...
... Mold, 15 ... Cavity, 17 ... Flow rate control valve, 18 ... Pressure control valve, 19, 20 ... Servo mechanism, 21 ... Pressure detector, 22, 23, ... Electrode, 24 ... Control section , 30...Storage section.

Claims (1)

[Claims] 1. In a low-pressure casting machine that supplies air to a pressurized chamber that covers a crucible, and fills hot water from the crucible into the cavity of a mold via a stalk for casting, the pressurized chamber is connected to the pressurized chamber, and a flow rate control valve and a pressure control valve are connected to the pressurized chamber. An air supply line in which a valve is installed, a servo mechanism that controls the opening degrees of the two control valves, a pressure detector installed in the pressurizing chamber, and a pressure sensor installed in the upper part of the stalk that is constant in the direction of the passage. A pair of hot water detectors installed at a distance, a head difference change characteristic with respect to the pressurizing force when the hot water reaches the upper part of the stalk, a volume change characteristic of the pressurizing chamber with respect to the head difference of the hot water in the crucible, and A memory unit that stores the flow rate change characteristics of the hot water in the stoke relative to the head difference, and values of the pressurizing force of the air, its flow rate, and the flow rate of the hot water when the hot water at a predetermined level in the crucible reaches the upper part of the stoke. Also, while setting and memorizing the patterns of each value of the pressurizing force of air, its flow rate, the volume of the pressurizing chamber, and the flow rate of hot water when filling hot water from the upper part of the stalk into the cavity,
Find the difference between the set value of the pattern based on the output signal from each of the detectors when the hot water actually reaches the top of the stalk and the comparison corresponding signal in the storage section,
A hot water supply control device for a low-pressure casting machine, comprising a control section that outputs signals of pressurizing force and flow rate of air for sending hot water into the cavity to both the servo mechanisms according to the difference.