Source: https://insight.rpxcorp.com/pat/US6247521B1
Timestamp: 2020-08-08 07:05:19
Document Index: 563046442

Matched Legal Cases: ['art 14', 'art 14', 'art 14', 'art 14', 'art 116', 'art 116', 'art 116', 'art 116']

Patent US 6,247,521 B1
1. A method of manufacturing a cast product using a casting machine,said casting machine including:
a holding furnace that stores melt;
a mold with a cavity formed in its interior;
a melt duct that interconnects the holding furnace and the cavity; and
a device that generates a pressure difference between the pressure inside the holding furnace and the pressure inside the cavity; and
wherein said cavity is filled by the melt stored in said holding furnace via said melt duct due to the pressure difference, the method comprising the steps of;
providing a pressure difference control program defining a pattern of pressure difference increase rate target values, each pressure difference increase rate target value being associated with a target time period;
applying a first selected pressure difference increase rate target value to the melt stored in the holding furnace for a first target time period;
detecting an actual time period in which the melt moves from a first predetermined level inside the casting machine to a second predetermined level inside the casting machine as a result of applying the first selected pressure difference increase rate target value to the melt; and
replacing the first target time period stored in the control program with the actual time period detected in the detecting step.
A melt filling pressure difference control method controls a pressure difference used to supply melt from a holding furnace to a cavity of a casting machine by generating a pressure difference between an interior space of holding furnace and the cavity formed inside the mold. The method includes the steps of setting up a program pattern comprising time-varying characteristics of pressure difference target values, controlling the pressure difference so as to follow the program pattern that was set up, detecting whether the melt surface has risen to a predetermined level inside the cavity, compensating the program pattern based on the melt surface level when the melt surface has risen to a predetermined level inside cavity, and controlling the pressure difference between space inside the holding furnace and the cavity so as to follow the compensated program pattern.
US 20110101555A1
US 20130062538A1
US 8,710,474 B2
US 8,753,553 B2
US 20180178276A1
US 5,178,009 A
Industrial Engineering Development Incorporated
2. The method of claim 1, wherein the casting machine includes an electrode that is insulated from said mold and exposed to said cavity;
and a device for detecting the electrical resistance between the electrode and the cavity;
wherein the detecting step comprises detecting the timing at which the electrical resistance changes to a set value.
3. The method of claim 2, wherein a strength of said electrode is at least of the same level as a strength of said mold.
6. A method of manufacturing a cast product using a casting machine,said casting machine including:
a mold with a cavity formed in its interior extending vertically from a top end to a bottom end;
a melt duct that interconnects the holding furnace and said bottom end of the cavity; and
wherein said cavity is filled by the melt stored in said holding furnace via said melt duct due to the pressure difference, the method including the steps of;
forcing the melt from the holding furnace and through said melt duct by applying a first rate of pressure difference increase to the melt stored in the holding furnace;
detecting when the melt has reached the bottom end of said cavity;
applying a second rate of pressure difference increase to the melt stored in the holding furnace when the melt has reached the bottom end of said cavity, wherein the second rate of pressure difference increase is less than the first rate of pressure difference increase;
detecting when the melt has reached the top end of said cavity; and
applying a third rate of said pressure difference increase when the melt has reached the top end of said cavity, wherein the third rate of said pressure difference increase is greater than the second rate of pressure difference increase.
7. The method of claim 6, further comprising the step of applying the second rate of pressure difference increase when a set first time period after applying the first rate of pressure difference increase has elapsed, if the melt has not yet reached the bottom end of the cavity.
11. The method of claim 6, wherein said casting machine includes a first electrode, which is insulated from said mold and exposed to said cavity at said bottom end of said cavity;
a first device, which detects a first electrical resistance between the mold and said first electrode;
a second electrode, which is insulated from the mold and exposed to said cavity at said top end of said cavity; and
a second device, which detects a second electrical resistance between the mold and said electrode;
wherein the second timing is detected from the timing at which the second electrical resistance changes to a set value.
12. The method of claim 6, further comprising reducing the pressure difference increase to zero when a set third time period has elapsed after detecting that the melt has reached the top end of said cavity.
setting up a differential pressure control program defining at least a first and second target increasing rates of said differential pressure, the first and second target increasing rates being assigned to a first and second pre-determined time intervals, respectively;
applying said differential pressure at the first target increasing rate during the first pre-determined time interval;
detecting a time when the melt reaches a bottom level inside the mold cavity; and
adjusting the increasing rate of said differential pressure to the second target increasing rate (a) when the first pre-determined time interval has expired or (b) when the melt reaches the first pre-determined level inside the mold cavity if the bottom time interval has not yet expired.
15. The method as in claim 14, wherein the increasing rate of said differential pressure is adjusted from the first target increasing rate to the second target increasing rate prior to the expiration of the first pre-determined time interval when the melt reaches the bottom level inside the mold cavity prior to the expiration of the first pre-determined time interval.
adjusting the increasing rate of said differential pressure to a third target increasing rate assigned to a third pre-determined time interval (c) when the second predetermined time interval has expired or (d) when the melt reaches a top level inside the mold cavity if the second pre-determined time interval has not yet expired.
17. The method as in claim 16, wherein the increasing rate of said differential pressure is adjusted from the second target increasing rate to the third target increasing rate prior to the expiration of the second pre-determined time interval when the melt reaches the top level inside the mold cavity prior to the expiration of the first pre-determined time interval.
setting up a pressure difference control program defining at least a first and second target increase rates of said pressure difference, the first and second target increase rates being assigned to a first and second pre-determined time interval, respectively;
applying the pressure difference at the first target increase rate during the first pre-determined time interval;
shifting the first and second pre-determined time intervals in the pressure difference control program based on a difference between the time detected in said time detecting step and a changing time from the first pre-determined time interval to the second pre-determined time interval in the pressure difference control program.
shifting the predetermined time intervals in the pressure difference control program based on a difference between a time when the melt reaches a top level inside the mold cavity and a changing time from the second pre-determined time interval to a third pre-determined time interval in the pressure difference control program.
20. The method of claim 18, wherein said detecting step comprises detecting a time when electrical resistance between the mold cavity and an electrode disposed within the mold cavity changes to a pre-determined value.
forcing melt from a holding furnace through a melt duct into a mold cavity by adjusting a pressure difference between the holding furnace and the mold cavity, the melt flowing into the mold cavity at a rate proportional to an increase rate of said pressure difference;
detecting when the melt has risen to a bottom end of the mold cavity;
reducing the increase rate of said pressure difference when the melt has reached the bottom end of the mold cavity;
detecting when the melt has risen to a top end of the mold cavity; and
increasing the increase rate of said pressure difference when the melt has reached the top end of the mold cavity.
24. The method of claim 23, wherein the increase rate of said pressure difference is reduced after a first predetermined time interval has expired if the melt has not risen to the bottom end of the mold cavity before the first pre-determined time interval has expired.
setting the pressure difference to a constant value when a third pre-determined time interval has expired.
setting the pressure difference to zero when a fourth pre-determined time interval has expired.
28. The method of claim 23, wherein the melt is forced from the holding furnace to the mold cavity by opening the mold cavity to the atmosphere, sealing the holding furnace and applying pressure to the holding furnace.
generating a differential pressure between a holding furnace and a mold cavity, wherein melt flows from the holding furnace to the mold cavity via a melt duct at a rate proportional to an increasing rate of said differential pressure, wherein during a first pre-determined determined time interval (i) a first constant increasing rate of said pressure differential is applied and (ii) after the first constant increasing rate of said pressure differential is applied, a second constant increasing rate of said differential pressure different from said first constant increasing rate of said pressure differential is applied to force the melt to rise from the holding furnace to a bottom end of the mold cavity;
detecting when the melt reaches the bottom end of the mold cavity;
applying a third constant increasing rate of said differential pressure for a second pre-determined time interval that begins either (a) when the first pre-determined time interval has expired or (b) when the melt reaches the bottom end of the mold cavity if the first pre-determined time has not yet expired, the third constant increasing rate of said differential pressure being less than the first and second constant increasing rates of said differential pressure;
detecting when the melt fills the cavity; and
applying a fourth constant increasing rate of said differential pressure for a third pre-determined time interval that begins either (c) when the second predetermined time interval has expired or (d) when the melt fills the cavity if the second pre-determined time has not yet expired, the fourth constant increasing rate of said differential pressure being greater than the third constant increasing rate of the said differential pressure.
33. A method according to claim 32, further comprising the step of applying a constant differential pressure for a fourth pre-determined time interval after the third pre-determined time interval has expired.
the third constant increasing rate of said differential pressure is applied for the second pre-determined time interval that begins (i) when the melt reaches the bottom end of the mold cavity, and (ii) before the first pre-determined time has expired; and
the fourth constant increasing rate of said differential pressure is applied for the third pre-determined time interval that begins (i) when the melt fills the cavity, and (ii) before the second pre-determined time has expired.
36. A method of making a cast product using a casting apparatus comprising a furnace that stores melt;
a mold cavity disposed above the furnace having a bottom surface, a top surface and a bottom portion;
a melt duct connecting the furnace to the bottom portion of the mold cavity;
means for applying a pressure difference between the melt stored inside the furnace and the pressure inside the mold cavity;
target value storing means for storing a set of target values for controlling pressure differences between the furnace and the mold cavity;
a first melt sensor disposed on the bottom surface of the mold cavity;
a second melt sensor disposed on the top surface of the mold cavity; and
a timer for determining;
(a) a first amount of time from initiating an increase in the pressure difference to force melt from the furnace until detection of the melt by the first melt sensor, and (b) a second amount of time from detection of the melt by the first melt sensor until detection of the melt by the second melt sensor, the method comprising the steps of;
storing an initial set of target values in the target value storing means, the initial set of target values representing;
(1) a first rate of pressure increase, (2) a second rate of pressure increase, (3) a third rate of pressure increase, (4) a first time period for applying the first rate of pressure increase, and (5) a second time period for applying the second rate of pressure increase, wherein the first rate of pressure increase is greater than the second rate of pressure increase, and the second rate of pressure increase is less than the third rate of pressure increase;
applying the first rate of pressure increase to the melt to force the melt up the melt duct and into the mold cavity and simultaneously beginning the first time period for applying the first rate of pressure increase;
using the first melt sensor to detect when the melt has reached the first melt sensor;
using the timer to determine the first amount of time from initiating the first rate of pressure increase to force melt from the furnace until detection of the melt by the first melt sensor;
applying the second rate of pressure increase to the melt at the earlier of (1) expiration of the first time period for applying the first rate of pressure increase, or (2) detection of the melt by the first melt sensor, and simultaneously beginning the second time period for applying the second rate of pressure increase when the second rate of pressure increase is applied to the melt;
wherein, if the first melt sensor detects the melt before the first time period for applying the first rate of pressure increase has expired, replacing the first time period for applying the first rate of pressure increase stored in the target value storing means with the first amount of time from initiating the first rate of pressure increase until detection of the melt by the first melt sensor, and wherein, if the first melt sensor detects the melt after the first time period for applying the first rate of pressure increase has expired, restarting the second time period for applying the second rate of pressure increase when the melt is detected and replacing the first time period for applying the first rate of pressure increase stored in the target value storing means with the first amount of time from initiating the first rate of pressure increase until detection of the melt by the first melt sensor;
using the second melt sensor to detect when the melt reaches the second melt sensor;
using the timer to determine the second amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor; and
applying the third rate of pressure increase to the melt at the earlier of (1) expiration of the second time period for applying the second rate of pressure increase or (2) detection of the melt by the second melt sensor;
wherein, if the second melt sensor detects the melt before or after the second time period for applying the second rate of pressure increase has expired, replacing the second time period for applying the second rate of pressure increase stored in the target value storing means with the second amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor.
37. The method as in claim 36, comprising:
detecting the melt with the first melt sensor before the first time period for applying the first rate of pressure increase has expired; and
replacing the first time period for applying the first rate of pressure increase stored in the target value storing means with the first amount of time from initiating the first rate of pressure increase until detection of the melt by the first melt sensor, wherein the first time period is replaced before the mold cavity is filled with the melt.
38. The method as in claim 36, comprising:
detecting the melt with the first melt sensor after the first time period for applying the first rate of pressure increase has expired;
restarting the second time period for applying the second rate of pressure increase when the melt is detected; and
39. The method as in claim 36, wherein the third rate of pressure increase is applied for a third time period, and the method further comprises applying a constant rate of pressure after the third time period expires.
45. A method of making a cast product using a casting apparatus comprising a furnace that stores melt;
means for storing a set of target values for controlling the pressure difference between the furnace and the mold cavity;
(a) a first amount of time from initiating an increase in the pressure difference to force melt from the furnace until a first time period expires, (b) a second amount of time from expiration of the first time period until detection of the melt by the first melt sensor, and (c) a third amount of time from detection of the melt by the first melt sensor until detection of the melt by the second melt sensor, the method comprising the steps of;
storing an initial set of target values in the target value storing means, the initial set of target values representing (1) a first rate of pressure increase, (2) a second rate of pressure increase, (3) a third rate of pressure increase, (4) a fourth rate of pressure increase, (5) a first time period for applying the first rate of pressure increase, (6) a second time period for applying the second rate of pressure increase, (7) a third time period for applying the third rate of pressure increase, and (8) a fourth time period for applying the fourth rate of pressure increase, wherein the first rate of pressure increase is greater than the second rate of pressure increase, the second rate of pressure increase is greater than the third rate of pressure increase and the third rate of pressure increase is less than the fourth rate of pressure increase;
applying the second rate of pressure increase after the first time period for applying the first rate of pressure increase has expired and simultaneously beginning the second time period for applying the second rate of pressure increase;
using the first melt sensor to detect when the melt reaches the first melt sensor;
using the timer to determine a first actual amount of time between initiating the second rate of pressure increase and detection of the melt by the first melt sensor;
applying the third rate of pressure increase to the melt at the earlier of (1) expiration of the second time period for applying the second rate of pressure increase, or (2) detection of the melt at the first melt sensor, and simultaneously beginning the third time period for applying the third rate of pressure increase;
wherein, if the first melt sensor detects the melt before the second time period for applying the second rate of pressure increase has expired, replacing the second time period for applying the second rate of pressure increase stored in the target value storing means with the first actual amount of time between initiating the second rate of pressure increase and detection of the melt by the first melt sensor, and wherein, if the first melt sensor detects the melt after the second time period for applying the second rate of pressure increase has expired, restarting the third time period for applying the third rate of pressure increase when the melt is detected and replacing the second time period for applying the second rate of pressure increase stored in the target value storing means with the first actual amount of time between initiating the second rate of pressure increase and detection of the melt by the first melt sensor, using the second melt sensor to detect when the melt reaches the second melt sensor;
using the timer to determine a second actual amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor, and applying the fourth rate of pressure increase to the melt at the earlier of (1) expiration of the third time period for applying the third rate of pressure increase, or (2) detection of the melt by the second melt sensor;
wherein, if the second melt sensor detects the melt before or after the third time period for applying the third rate of pressure increase has expired, replacing the third time period for applying the third rate of pressure increase stored in the target value storing means with the second actual amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor.
detecting the melt with the first melt sensor before the second time period for applying the second rate of pressure increase has expired;
replacing the second time period for applying the second rate of pressure increase stored in the target value storing means with the first actual amount of time between initiating the second rate of pressure increase and detection of the melt by the first melt sensor, wherein the second time period is replaced before the mold cavity is filled with the melt.
47. The method as in claim 45, comprising:
detecting the melt with the first melt sensor after the second time period for applying the second rate of pressure increase has expired;
restarting the third time period for applying the third rate of pressure increase when the melt is detected;
48. The method as in claim 45, comprising:
detecting the melt with the second melt sensor before or after the third time period for applying the third rate of pressure increase has expired; and
replacing the third time period for applying the third rate of pressure increase stored in the target value storing means with the second actual amount of time between the detection of the melt by the first melt sensor and the detection of the melt by the second melt sensor.
49. The method as in claim 45, wherein the fourth rate of pressure increase is applied for a fourth time period, and the method further comprises applying a constant pressure after the fourth time period expires.
This low-pressure casting machine 1 is equipped with holding furnace 6 that stores the melt, and mold 3 positioned directly above this holding furnace 6 by fixing plate 2. Cavity 4 is formed in the interior of mold 3. A tubular melt duct 5 is connected to mouth piece 4h of said mold 3, and interconnects cavity 4 formed inside mold 3 with the interior of holding furnace 6. Here, said cavity 4 is released to atmospheric pressure via exhaust ducts (not illustrated), while on the other hand said holding furnace 6 is sealed and compressed air is supplied to the interior thereof by compressor 7. It is thus possible to generate a pressure difference between the pressure inside cavity 4 and the pressure inside holding furnace 6.
That is, in the stage during which the melt is supplied as far as the entrance of cavity 4, solenoid valves 8a and 8b of compressor 7 are opened and a large amount of compressed air flows into holding furnace 6 through pipelines 9a and 9b. Accordingly, the pressure inside holding furnace 6 rises quickly and the melt rises up at high speed inside melt duct 5 to arrive at the entrance of cavity 4. Next, when the pressure in said holding furnace reaches a first prescribed pressure, the melt surface is considered to have risen to the entrance of cavity 4 and solenoid valve 8b is closed. Consequently, compressed air is only supplied to holding furnace 6 through pipeline 9b, and the rate of pressure increase inside holding furnace 6 is relaxed by the drop in the compressed air supply rate. As a result, the melt is slowly filled into cavity 4. Then, when the pressure inside holding furnace 6 reaches a second prescribed pressure, cavity 4 is deemed to have been filled with melt, and solenoid valve 8c is opened. Consequently, compressed air is supplied to holding furnace 6 through pipelines 9b and 9c, and the pressure rises quickly again so that the melt inside cavity 4 is subjected to feeder head pressurizing.
The present invention addresses itself to the technical problem of actually measuring the melt surface inside the cavity and compensating a preset pattern of pressure increase inside the holding furnace based on the result of this measurement, thereby filling the cavity with melt at an appropriate speed and achieving a satisfactory feeder head pressure after filling with melt by applying a suitable pattern of pressure increase inside the holding furnace.
The pressure difference control program, for instance, has a target rate of pressure difference increase of 1 kg/cm2•min until 3 minutes have elapsed after the filling operation is started, and the target rate of pressure difference increase after 3 minutes have elapsed and before 5 minutes have elapsed is defined as 0.5 kg/cm2•min. In general, the target rate of pressure difference increase is controlled according to the elapsed time by the pressure difference control program. This pressure difference control program it set up according to the relationship whereby, under normal conditions, the melt is satisfactorily filled into the cavity. For example, in the example mentioned above, if the pressure is made to rise by 1 kg/cm2 each minute for the first 3 minutes after the filling operation is started, then it is presumed that under normal conditions the melt will have reached the bottom level of the cavity after 3 minutes have elapsed, whereafter the rate of pressure increase per unit time is reduced to a rate of 0.5 kg/cm2•min.
FIG. 1 is an overall cross-section of a low-pressure casting machine used to implement a melt-filling pressure-difference control method relating to an embodiment of the present invention.
A pressure-difference control method for melt filling relating to an embodiment of the present invention is now described based on FIGS. 1 to 3. FIG. 1 is an overall cross-section of a low-pressure casting machine 10 used to implement a melt-filling pressure-difference control method relating to the present embodiment.
Said low-pressure casting machine 10 is provided with holding furnace 16 which stores a molten metal such as aluminum (referred to as the melt hereinafter), and mold 13 positioned directly above this holding furnace 16 by fixing plate 12, and a tubular stalk 15 (melt duct) is connected to mouth part 14h of said mold 13. Said stalk 15 passes through opening 12k formed in the center of said fixing plate 12, and is supported hanging down from fixing plate 12 with its lower end immersed in the melt stored in said holding furnace 16.
Said holding furnace 16 comprises crucible 16r which stores the melt, and casing 16c which houses this crucible 16r and keeps it hot by means of a heater (not illustrated), and the top opening of said crucible 16r is closed off by said fixing plate 12. Also, a melt inlet 18, through which melt is supplied into said crucible 16r, is provided at an inclined angle at the end of said fixing plate 12 (left of center in the figure), and a pressure sensor 18p for detecting the pressure inside crucible 16 is fitted at the position of this melt inlet 18. The pressure signal from said pressure sensor 18p is input to control device 20, which comprises a microprocessor. Note that said melt inlet 18 is closed off by cover 18h after supplying melt into crucible 16r, and thus said pressure sensor 18p is able to accurately measure the pressure inside holding furnace 16.
Also, a pressurizing pipeline 19 for pressurizing the interior of holding furnace 16 is connected to said melt inlet 18. Said pressurizing pipeline 19 is a pipeline for guiding compressed air from a compressor (not illustrated) to the inside of holding furnace 16, and is fitted along the way with reducing valve 19r and flow control valve 19c situated downstream thereof. Here, said flow control valve 19c is remotely operated by means of operating signals from said control device 20 to control the pressure inside holding furnace 16, as mentioned below. Also, an exhaust valve 19b for exhausting the air inside holding furnace 16 is attached downstream of said flow control valve 19c. Note that exhaust valve 19b is normally closed.
Said mold 13 comprises cope 13u and drag 13d, which form cavity 14 when fastened together. Cavity 14 is interconnected with the atmosphere via exhaust ducts (not illustrated). Also, an upper melt level detection sensor 14a is fitted to cope 13u of said mold 13 at the top level of cavity 14, and a lower melt level detection sensor 14b is fitted to drag 13d at the bottom level of cavity 14 (the top level Kb of mouth piece 14h). The melt level detection signals from upper melt level detection sensor 14a and lower melt level detection sensor 14b are input to said control device 20.
Said control device 20 stores a pressure control program that determines the time-varying characteristics of the target rate of pressure increase in order to vary the pressure inside holding furnace 16 with time. This program determines target values for the rate of pressure increase with respect to the elapsed time; an example of a pattern produced by this program is shown by the solid lines (pattern P0) in FIGS. 2 and 3. Note that said pressure control program can be inputted to the control device 20 from an input device (not illustrated), and can be revised. The orifice size of flow control valve 19c is controlled so that the pressure inside holding furnace 16 follows pattern P0 of said pressure control program, That is, the pressure control program defines a rate of pressure increase per unit time corresponding to each elapsed time.
In pattern P0 shown in FIG. 2, point S is the time at which the pressurizing of holding furnace 16 begins, and point a0 is the time at which the pressure inside holding furnace 16 reaches pressure A0, at which it should be possible to bring the melt surface up to the entrance (bottom level) Ka of mouth part 14h of mold 13 (See FIG. 1). Also, point b0 is the time at which said pressure reaches pressure B0, at which it should be possible to bring the melt surface up to the bottom level Kb of cavity 14 inside mold 13. Furthermore, point c0 is the time at which said pressure reaches pressure C0, at which it should be possible to bring the melt surface up to the top level inside cavity 14, point d0 is the time at which it reaches pressure D0 on completion of feeder head pressurizing, and point e0 is the time at which the pressure is dropped prior to opening the mold.
In this basic pattern P0, since the rate of pressure increase from point S to point a0 is large, the melt surface quickly rises to the bottom level Ka of mouth part 14h. In this way, the drop in melt temperature due to stalk 15 is improved to some extent. Also, since the pressure increase from point ao to point bo is slightly smaller, the Tate at which the melt Surface rises between the bottom level Ka of mouth part 14h to the bottom level Kb of cavity 14 is slightly slower. Furthermore, since the rate of pressure increase is gentler from point b0 to point c0, the rate at which the melt surface rises between the bottom level Kb of cavity 14 to the top level of cavity 14 is even gentler. In this way, the mixing of air in with the melt filled into the cavity is prevented. The rate of pressure increase between points c0 and d0 is set large so that the pressure quickly rises, and feeder head pressure is quickly applied to the melt filled into said cavity 14. In this way, the occurrence of pipes and the like is diminished. That is, the rate of pressure increase is made large from the time (tc) at which the melt surface rises up to the top level of the cavity until the third elapsed time has elapsed, the rate of pressure increase is made zero after the third elapsed time has elapsed, and the pressure is made zero after the fourth elapsed time has elapsed. Also, the rate of pressure increase is made smaller after time tb has elapsed from the start of the filling operation, and subsequently the rate of pressure increase is made larger again after the second elapsed time has elapsed (time tc).
First corrected pattern P1 shown by the dashed line in FIG. 2 is the pattern used instead of basic pattern P0 to control the pressure in holding furnace 16 when lower melt surface detection sensor 14b detects that the actual melt surface has risen to the bottom level Kb of the cavity ahead of schedule. That is, in basic pattern P0, the melt surface should rise up to the height of said bottom level Kb at time bo. However, when lower melt surface detection sensor 14b has judged that the actual melt surface has risen to the height of bottom level Kb of the cavity in a shorter period (while pressure control is being performed between points a0 and b0), the control switches from basic pattern P0 to first corrected pattern P1 at this time, and the pressure inside holding furnace 16 is thereafter controlled based on this first corrected pattern P1. Here, point b1 of first corrected pattern P1 is the time at which lower melt level detection sensor 14b detects that the actual melt surface has risen to the height of bottom level Kb of the cavity. Also, the slope from point b1 to point cl is set equal to the slope from point bo to point c0 in said basic pattern P0, and the slope from point c1 to point d1 in first corrected pattern P1 is set equal to the slope from point c0 to point d0 in said basic pattern P0. That is, if point b1 is superimposed on point bo, pattern P1 will map exactly to pattern P0. This pattern correction is achieved by correcting the elapsed time in the pressure control program by the difference in elapsed time between point b0 and point b0.
Also, second corrected pattern P2 shown by the dotted line in FIG. 2 is the pattern used instead of basic pattern P0 to control the pressure in holding furnace 16 when upper melt surface detection sensor 14a detects that the actual melt surface has risen to the top level of the cavity ahead of schedule. That is, in first corrected pattern P1, the melt surface should rise up to the height of the top of cavity 14 at time c1. However, when upper melt surface detection sensor 14a has judged that the actual melt surface has risen to the height of the top of cavity 14 in a shorter period (while pressure control is being performed between points b1 and c1), the control switches from first corrected pattern P1 to second corrected pattern P2 at this time, and the pressure inside holding furnace 16 is thereafter controlled based on this second corrected pattern P2. Here, point c2 of second corrected pattern P2 is the time at which upper melt level detection sensor 14a detects that the actual melt surface has risen to the height of the top of cavity 14. Also, the slope from point c2 to point d2 is set equal to the slope from point c1 to point d1 in the first corrected pattern P1. If points c2, c1 and c0 are all superimposed, patterns P0, P1 and P2 will all map exactly to each other. The above pattern correction process is implemented by correcting the elapsed time in the pressure control program by the difference in elapsed time between points c1 and c2.
Third corrected pattern P3 shown by the dashed line in FIG. 3 is the pattern used instead of basic pattern P0 to control the pressure in holding furnace 16 when lower melt surface detection sensor 14b detects that the actual melt surface has risen to the bottom level Kb of the cavity behind schedule. That is, in basic pattern P0, the melt surface should rise up to the height of said bottom level Kb at time b0 as mentioned above. However, when the actual melt surface rises slowly and lower melt surface detection sensor 14b judges that the melt surface has risen to the height of bottom level Kb of the cavity while pressure control is being performed between points b0 and c0, the c0 ntrol switches from basic pattern P0 to third Corrected pattern P3 at this time, and the pressure inside holding furnace 16 is thereafter controlled based on this third corrected pattern P3. Here, point b3 of third corrected pattern P3 is the time at which lower melt level detection Sensor 14b detects that the melt surface has risen to the height of bottom level Kb of the cavity, and the line from point b3 to point c3 is made by duplicating the line from point b0 to point c0 in basic pattern P0. Also, the slope from point c3 to point d3 is set equal to the slope from point c0 to point d0 in basic pattern P0. As before, if point b3 is superimposed on point b0, pattern P3. Will map exactly to pattern P0. This process is also performed by Correcting the elapsed time in the pressure control program. Note that in FIG. 3, the rate of pressure increase is reduced at point bo. That is, when first elapsed time (tb) has elapsed from the start of the filling operation before the melt surface reaches bottom level Kb of the cavity, the rate of pressure increase is reduced even if the melt surface has not reached bottom level Kb of the cavity. Note that in this specification, the time at which the melt surface reaches level Kb is defined as the first timing.
Fourth corrected pattern P4 shown by the dotted line in FIG. 3 is the pattern used instead of third corrected pattern P3 to control the pressure in holding furnace 16 when upper melt surface detection sensor 14a detects that the actual melt surface has risen to the top level of cavity 14 behind schedule. That is, in third corrected pattern P3, the melt surface should rise up to the height of the top of cavity 14 at time C3. However, when the actual melt surface rises slowly and upper melt surface detection sensor 14a judges that the melt surface has risen to the height of the top level of cavity 14 while pressure control is being performed between points C3 and d3, the control switches from third corrected pattern P3 to fourth corrected pattern P4 at this time. The pressure inside holding furnace 16 is thereafter controlled based on this fourth corrected pattern P4. Here, point C4 of fourth corrected pattern P4 is the time at which upper melt level detection sensor 14a detects that the melt surface has risen to the height of the top of cavity 14, and the line from point C4 to point d4 is made by duplicating the line from point b3 to point C3 in third corrected pattern P3. As above, if points C4, C3 and co are superimposed, patterns P0, P3 and P4 will map to each other. As the relationship between point C3 and point C4 clearly shows, when second elapsed time (from tb to tc) has elapsed from the first timing (b3) before the melt surface reaches the top level of the cavity, the rate of pressure increase is reduced even if the melt surface has not reached the top level of the cavity. Note that in this specification, the time at which the melt surface reaches the top level of the cavity is defined as the second timing.
Here, said basic pattern P0 is switched to first corrected pattern P1 or third corrected pattern P3 based on the program stored in control device 20 by correcting the values of the elapsed times in the control program based on the time at which the melt surface detection signal is input from lower melt surface detection sensor 14b. In the same way, first corrected pattern P1 is switched to second corrected pattern P2 and third corrected pattern P3 is switched to fourth corrected pattern P4 based on the program stored in control device 20 by correcting the values of the elapsed times in the control program based on the time at which the melt surface detection signal is input from upper melt surface detection sensor 14a.
The melt filling pressure difference control method of the casting machine relating to the present invention will now be described.
As shown in FIG. 1, mold 13 is fastened together and set on fixing plate 12, whereupon control of the pressure inside holding furnace 16 is started based on basic pattern P0 shown in FIG. 2 and FIG. 3. As a result, the melt inside crucible 16r rises at high speed through stalk 15 to the height of bottom level Ka of mouth piece 14h, and is supplied into mouth piece 14h relatively slowly from this bottom level Ka. Here, when the melt surface is judged to have risen to the height of bottom level Kb of the cavity by lower melt level detection sensor 14b while pressure control is being performed between point a0 and point b0 of basic pattern P0, the control switches from basic pattern P0 to first corrected pattern P1 at this time, as shown in FIG. 2. The pressure inside holding furnace 16 then continues to be controlled from point b1 based on this first corrected pattern P1, and the melt is slowly supplied into cavity 14. Furthermore, when the melt surface is judged to have risen to the height of the top of cavity 14 by upper melt level detection sensor 14a while pressure control is being performed between point b1 and point c1 of first corrected pattern P1, the control switches from first corrected pattern P1 to second corrected pattern P2 at this time. The pressure inside holding furnace 16 then continues to be controlled from point c2 based on this second corrected pattern P2, and feeder head pressure is applied to the melt filled into said cavity 14. In this way, when the pressure control proceeds to point e2 of second corrected pattern P2, exhaust valve 19b provided on pressurizing pipeline 19 is opened to release the pressure in holding furnace 16, and mold 13 is opened.
Also, when the melt surface is judged to have risen to the height of bottom level Kb of the cavity by lower melt level detection sensor 14b while pressure control is being performed between point b0 and point c0 of basic pattern P0, the control switches from basic pattern P0 to third corrected pattern P3 at this time, as shown in FIG. 3. The pressure inside holding furnace 16 then continues to be controlled from point b3 based on this third corrected pattern P3, and the melt is slowly supplied into cavity 14. Furthermore, when the melt surface is judged to have risen to the height of the top of cavity 14 by upper melt level detection sensor 14a while pressure control is being performed between point c3 and point d3 of third corrected pattern P3, the control switches from third corrected pattern P3 to fourth corrected pattern P4 at this time. The pressure inside holding furnace 16 then continues to be controlled from point C4 based on this fourth corrected pattern P4, and feeder head pressure is applied to the melt filled into said cavity 14. In this way, when the pressure control proceeds to point e4 of fourth corrected pattern P4, exhaust valve 19b provided on pressurizing pipeline 19 is opened to release the pressure in holding furnace 16, and mold 13 is opened.
In this way, the present embodiment is able to detect the actual melt surface at two places—at the bottom Kb of cavity 14 and at the top of cavity 14—and corrects the elapsed times of the initially set pressure pattern based on the times at which the melt level reaches these levels. Thus, the pressure is controlled based on a suitable pressure variation pattern that is matched to the actual circumstances, so that it becomes possible not only to fill the melt into the cavity at a suitable rate, but also to achieve a satisfactory feeder head pressure after filling with melt. Thus there is no incorporation of air into the melt filled inside cavity 14, and it also becomes unlikely that defects such as pipes will occur due to insufficient feeder head pressure. As a result, it is possible to reduce defects such as pressure leaks in pressure-resistant components.
Note that although the present embodiment has described a melt filling control method for a low-pressure casting machine 10, it can—needless to say—also be applied to a low-pressure casting machine wherein the melt is filled into a mold by reducing the pressure inside the cavity.
In the following, a melt surface detection device relating to a first embodiment of the present invention is described based on FIGS. 5 through 7. Here, FIG. 5 is a detailed installation diagram of detection sensor 112 of melt surface detection sensor 14a, and FIG. 6 is a circuit diagram of melt surface detection sensor 14a. Also, FIG. 7 is a cross-section showing the entire mold 13.
Said detection sensor 112 is an upper sensor for detecting whether or not melt is filled into cavity 14, and as shown in FIG. 5 it consists of an electrically conductive electrode 114 fabricated from Fe—Ni steel and a ceramic insulating member 116 that insulates this electrode 114 from mold 13.
Said insulating member 116 is provided with flange part 116f formed into a cylindrical shape at a position in its center, and through-hole 116k along its central axis which houses said electrode 114. Here, said insulating member 116 is a ceramic chiefly consisting of Al2O3, and is joined to said electrode 114 by silver solder after being metallized. Also, when said insulating member 116 and electrode 114 are joined together, the lower end surface of this insulating member 116 and the lower end surface of electrode 114 are positioned in the same plane.
Large-diameter through-hole 102m and small-diameter through-hole 102s are formed coaxially at the top of said mold 13, and a ring-shaped step 102d is formed at the connecting part between through-holes 102m and 102s. Next, the end part 116a and flange part 116f of detection sensor 112 are respectively housed in said small-diameter throughhole 102s and large diameter through-hole 102m. Here, the length of said small-diameter through-hole 102s is set equal to the length of end part 116a of detection sensor 112, so that the lower end surface of this detection sensor 112 is flush with wall surface 4w of cavity 14 when said detection sensor 112 is set in mold 13. That is, the end surface of said detection sensor 112 constitutes a part of the wall surface 4w of cavity 14, and through the use of the above materials, its strength is at least of the same level as that of mold 13.
Said signal output unit 118 is a circuit for outputting a signal that shows whether or not electrode 114 of detection sensor 112 is electrically connected to mold 13 by the melt, and consists of a constant-voltage source 118v and a relay 118r. Constant-voltage source 118v and the coil 118c of said relay 118r are connected in series between terminal T1 and terminal T2. That is, electrode 114 of detection sensor 112, terminal T1, coil 118c, constant voltage source 118v, terminal T2 and mold 13 are all thereby connected in series, so that a fixed current flows in said coil 118c when said electrode 114 and mold 13 are electrically connected by the melt. When a current flows in said coil 118c, the contact point 118s of relay 118r is closed, and this signal is output to the control device (not illustrated) via terminals T3 and T4.
Next, the operation of melt surface detection sensor 14a relating to the present embodiment will be described.
While the melt surface has not yet reached the position of detection sensor 112 in cavity 14, the electrode 114 of this detection sensor 112 is insulated from mold 13 by insulating member 116, so that no current flows through coil 118c of relay 118r shows in FIG. 6. Therefore, the contact point 118s of relay 118r is left open. However, when the melt surface arrives at the position of detection sensor 112, said electrode 114 and mold 13 are electrically connected by the melt, and a fixed current flows through said coil 118c. As a result, relay 118r is operated and contact point 118s is closed, and this signal is output to said control device 20 via terminals T3 and T4.
In this way, with a melt surface detection device 14a relating to the present embodiment, since detection sensor 112 constitutes a part of wall surface 4w of cavity 14, the melt comes into direct contact with this detection sensor 112 and thus there are no time delays or such problems associated with the detection. Also, since electrode 114 of said detection sensor 112 is made of a material having a strength of the same or higher level than the strength of mold 13, and since insulating member 116 is made of ceramic, it has high durability and reliability, and it requires less effort to maintain.
Also, in the present embodiment, detection sensor 112 is fitted at the top of mold 13 (at the uppermost part of cavity 14) and is used to detect whether or not cavity 14 has been filled with melt; however, it is not limited to such a use, and can—needless to say—be used by fitting it at a prescribed level in said cavity 14 and detecting whether or nor the melt surface has reached this position.
Melt surface detection device 220 relating to the present embodiment constitutes an improvement on the electrical Circuit of signal detection unit 118 in melt detection device 14a relating to the first embodiment, and has a configuration wherein it is possible to measure the electrical resistance between mold 13 and electrode 214 of detection sensor 212. Note that the following description is simplified by using the same numbers to signify members that are identical to those used in melt surface detection device 14a of the first embodiment.
FIG. 9 is a graph showing the variation in electrical resistance between mold 13 and electrode 214 between the start (point S) and finish (point D1, D2) of casting. Here, the solid line in the figure shows the variation in resistance when casting is performed with the wall surface 4w of cavity 14 coated with mold paint 203 that is an insulating substance, and the dotted line in the figure shows the variation in resistance when casting is performed without the wall surface 4w of cavity 14 being coated with mold paint 203. As shown in FIG. 1, when mold 13 is positioned directly above holding furnace 16, the inside of holding furnace 16 is pressurized by a compressor (not illustrated), and the melt is pushed up inside cavity 14 via stalk 15. The present embodiment is described for the case where casting is performed after coating with mold paint 203.
Point S in FIG. 9 shows the time at which pressurizing of the interior of holding furnace 16 is started. At the time the pressurizing is started, mold 13 and electrode 214 of detection sensor 212 are electrically insulated by insulating member 216, and as shown in FIG. 8, since the lower end surface of detection sensor 212 is coated with mold paint. 203 which is an insulating substance, the electrical resistance between said electrode 214 and mold 13—i.e., the value of the electrical resistance measured by resistance meter 222—is at its maximum. However, as melt is supplied into cavity 14 and the melt surface rises, the electrical resistance of insulator 216, mold paint 203 and so on gradually decreases due to the heat radiated from the melt, and as shown in FIG. 9, the resistance value of resistance meter 222 gradually decreases. Next, when the melt surface arrives near the top of cavity 14 and the melt starts to come into contact with detection sensor 212 via mold paint 203 (point A1), the resistance value of resistance meter 222 begins to drop sharply. Then, when cavity 14 is filled with melt (point B1), the resistance value of resistance meter 222 becomes equal to the resistance value of mold paint 203 situated between mold 13 and electrode 214 of detection sensor 212. The resistance value attributable to the melt is extremely small.
On the other hand, when casting is performed with mold paint 203 removed from wall surface 4w of cavity 14 (shown by the dotted line in the figure), the measured value of resistance meter 222 is decreased by an amount corresponding to the resistance value of mold paint 203 compared with the case where it is coated with mold paint 203.
Here, the method mentioned above in melt surface detection device 14a relating to the first embodiment is employed, whereby relay 118r detects the state of electrical connection between mold 13 and electrode 114 of detection sensor 112. However, when wall surface 4w of cavity 14 is coated with mold paint 103, the current flowing through coil 118c will be insufficient to drive relay 118r due to the resistance of this mold paint 103, since mold paint 103—which is an insulating substance—is positioned between mold 13 and electrode 114 of detection sensor 112 even when the melt surface reaches the position of detection sensor 112. As a result, there is a limitation in that the melt surface detection device 14a relating to the first embodiment must be used in a state where no mold paint is applied to wall surface 4w of cavity 14.
KABUSHIKI KAISHA ISUZU SEISAKUSHO, Ibaraki Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
Furukawa, Yasutaka, Hirata, Seiji, Kawai, Hiroshi
LIN, ING HOUR
164/457, 164/155.3, 164/63, 164/255, 164/119
Current Assignee: KABUSHIKI KAISHA ISUZU SEISAKUSHO, Ibaraki Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
Sponsoring Entity: KABUSHIKI KAISHA ISUZU SEISAKUSHO, Ibaraki Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)