JPH091283A - Method for reconditioning molding sand and apparatus therefor - Google Patents

Abstract

PURPOSE: To uniformize a mold strength, to reduce a casting defect and to improve the dimensional precision of a cast product by adjusting the adding quantity of water based on molding sand temp. before vacuum kneading to a preset strength target value of reconditioned sand. CONSTITUTION: At the time of completing premixing, an FK sensor 5 measures the temp. and moisture content in the sand in a mixer 1 and these are inputted into a control unit 30. In the control unit 30, the moisture content of the reconditioing sand is set to a preset temp. target value of the reconditioned sand and the water quantity to be added is calculated based on the moisture content detected with the FK sensor 5 and divided into a primary water for kneading and a secondary water for cooling, and a primary water pouring control valve 18 is opened to pour the primary water. The inner part in a mixer 1 is made to a prescribed vacuum degree with a vacuum pump 23 to execute the kneading, and the secondary water for cooling is poured by opening a secondary water pouring control valve 19. At the time of completing the vacuum kneading, the kneading is executed in the atmosphere. The adding water in such a way is controlled to uniformize the mold strength, and the quality of the cast product can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reclaiming foundry sand and an apparatus for reclaiming recovered foundry sand using a vacuum kneading tank.

[0002]

2. Description of the Related Art As is well known, in a green molding line for molding a green mold for casting, a molding sand is kneaded to form a mold, which is then used for casting and then used. The mold is separated to collect the foundry sand, and the recovered foundry sand (hereinafter, simply referred to as recovered sand) is used, or new sand is added if necessary, and the mixture is kneaded again. The modeling is done. Foundry sand is regenerated and used many times through such a series of circulation cycles.

When the recovered sand is reclaimed and used, the recovered sand obtained by separating the mold after casting is kept at a considerably high temperature at the time of recovery, and is obtained by kneading it as it is. The temperature of the reclaimed sand will be too high.
Therefore, conventionally, the recovered sand is cooled to a predetermined temperature (generally about 40 ° C. or lower) by a so-called sand cooler, and the cooled recovered sand is supplied to the kneading tank.

By the way, in recent years, as a kneading tank used in a green molding line, a part of a vacuum kneading tank capable of kneading while maintaining the inside of the tank at a predetermined vacuum degree has been introduced and already used. It's starting. By using this vacuum kneading tank, it becomes possible to rapidly cool high-temperature sand exceeding 40 ° C. (for example, about 40 to 70 ° C.) to a set temperature of 40 ° C. or less in the kneading tank.

That is, when kneading molding sand to form a green mold, usually, high-temperature recovered sand (adding new sand if necessary) is put into a kneading tank and used as a binder for sand grains. The bentonite and the predetermined amount of water are added and kneading is performed in the tank.However, when a vacuum kneading tank is used, the boiling point of the water is lowered by depressurizing the tank to reduce the boiling point of the added water. By evaporating a part (cooling water described below) and removing the latent heat of vaporization from the inside of the tank (that is, from the surrounding sand) at this time, the sand in the tank can be cooled all at once to the set temperature. When this vacuum kneading tank is used, the amount of water added to the tank is basically the same as that for kneading (moisturizing water) to keep the water content of the foundry sand after kneading at a prescribed value, and high temperature during kneading. It is determined as the sum of cooling water (cooling water) for cooling the recovered sand. Of these, the amount that evaporates in the tank during kneading corresponds to the cooling water.

[0006]

When performing the above-described vacuum kneading, the amount of water added to the kneading tank is such that the quality of the sand (regenerated sand) after kneading is ensured and the target sand strength (that is, It is controlled so as to obtain the coercive force of the raw mold formed from recycled sand. In general, it is known that there is a certain correlation between the water content of sand and the coercive pressure if the sand identity is constant, and conventionally, after measuring the water content of the recovered sand, Based on the correlation, the amount of added water is controlled so that the water content of the reclaimed sand after kneading is constant.

By the way, the water contained in the foundry sand (reclaimed sand) after kneading can be divided into adhering water simply adhering to the surface of the sand grains and adsorbing water permeating into the bentonite crystal layer. Of these, the adsorbed water that has penetrated into the bentonite crystal layer is less likely to evaporate and improves the water retention of the foundry sand. Also,
It is considered that this adsorbed water activates bentonite to accelerate the rise of sand strength (that is, raw type coercive pressure) and to increase the strength itself. The applicant of the present invention has conducted extensive studies on the relationship between the water content of the reclaimed sand after kneading, the temperature of the recovered sand, and the coercive pressure of the green mold. It has been found that the coercive pressure of the raw type becomes higher as the temperature of the recovered sand becomes higher even if the water content of the reclaimed sand after kneading is the same, when the coercive pressure is high.

FIG. 5 is a graph showing the results of examining the relationship between the water content of the reclaimed sand after kneading and the coercive pressure of the raw mold, using the temperature of the recovered sand as a parameter. C, and the straight line C shows the case where the temperature of the recovered sand is 25 ° C. In addition, in the straight line B and the straight line C, all other test conditions such as the amount of bentonite added and the degree of vacuum during kneading are set to be the same. As is clear from the graph of FIG. 5, when vacuum kneading, even if the water content of the reclaimed sand is the same, the higher the temperature of the recovered sand, the higher the coercive pressure of the raw mold. This is because the amount of cooling water to be added increases as the temperature of the recovered sand increases, so the amount of water vapor generated in the vacuum kneading tank increases and the amount of adsorbed water that permeates the bentonite crystal layer increases, activating bentonite. It is thought that this is because of the progress. Therefore, if the temperature of the recovered sand is taken in as a control factor when controlling the amount of water added to the vacuum kneading tank, the quality of the reclaimed sand can be made more stable.

Therefore, the present invention provides a method for reclaiming foundry sand and an apparatus therefor, which pays attention to the correlation between the temperature of recovered sand and the strength of reclaimed sand to obtain reclaimed sand of more stable quality. It was made for the purpose of doing.

[0010]

Therefore, in the invention according to claim 1 of the present application (hereinafter referred to as the first invention), the recovered molding sand is put into a vacuum kneading tank, and water and a binder are added. Is a method for reclaiming the molding sand by reclaiming the recovered molding sand by kneading it, wherein a target value of the sand strength of the reclaimed sand is preset, and the target value is the molding sand in the tank before vacuum kneading. The feature is that the amount of water added is adjusted based on the temperature. In addition, when new sand is not added at the time of kneading, the above "casting sand in the tank before vacuum kneading" means "recovered sand". This also applies to the following second and third inventions.

Further, the invention according to claim 2 of the present application (hereinafter referred to as “the invention”)
2nd invention), in the above-mentioned 1st invention, the amount of water added is the relationship data between the water content of the reclaimed sand and the sand strength, the temperature of the foundry sand in the tank before vacuum kneading at the target cooling temperature. And the amount of cooling water added and the water content of the molding sand in the tank before vacuum kneading.

Further, the invention according to claim 3 of the present application (hereinafter referred to as “the invention”)
A third invention) is a vacuum kneading tank capable of kneading while maintaining the inside at a predetermined vacuum degree, and a recovered sand supply device for supplying a predetermined amount of recovered foundry sand into the vacuum kneading tank. , A binder supply device for supplying a predetermined amount of binder into the vacuum kneading tank, a water supply device for supplying a predetermined amount of water into the vacuum kneading tank, and a casting sand in the tank before vacuum kneading The temperature detection means for detecting the temperature and the water content detection means for detecting the water content of the foundry sand in the tank before vacuum kneading are provided, and the relational data between the water content of the reclaimed sand and the sand strength, the target cooling temperature Based on the relational data between the temperature of the molding sand in the tank before vacuum kneading and the amount of cooling water and the water content of the molding sand in the tank before vacuum kneading, the water into the vacuum kneading tank by the water supply device It is characterized in that a control means for controlling the supply amount is provided.

[0013]

According to the first invention of the present application, a target value of the sand strength of reclaimed sand is set, and the temperature of the foundry sand (mainly recovered sand) in the tank before vacuum kneading is set to the target value. Since the amount of water added is adjusted based on this, the temperature of the foundry sand in the tank before vacuum kneading can be taken in as a control factor when adjusting the amount of added water, and the relationship between water content and sand strength can be simply calculated. The quality of the reclaimed sand can be made more stable as compared with the conventional method in which the amount of added water is set based on the above. As a result, the strength of the mold (green mold) can be maintained more uniformly, which can contribute to reduction of defects during casting and improvement of dimensional accuracy of the cast product.

Further, according to the second invention of the present application, basically, the same effect as that of the first invention can be obtained. In particular, specifically, the relational data between the water content of the reclaimed sand and the sand strength, the relational data between the temperature of the molding sand in the tank before vacuum kneading at the target cooling temperature and the amount of cooling water added, and the inside of the tank before vacuum kneading Since the amount of added water is adjusted based on the water content of the foundry sand, the total amount of water to be added and the allocation of this water for kneading and cooling can be optimally adjusted.

Further, according to the third invention of the present application, since the temperature detecting means and the water content detecting means are provided, it is possible to detect the temperature and the water content of the foundry sand in the tank before vacuum kneading, respectively. Further, since the above-mentioned control means is provided, the relational data between the water content of the reclaimed sand and the sand strength, the relational data between the temperature of the molding sand in the tank before the vacuum kneading at the target cooling temperature and the addition amount of the cooling water, and the vacuum kneading. Based on the water content of the foundry sand in the previous tank, the amount of water supplied to the vacuum kneading tank by the water supply device can be controlled. That is, the temperature of the foundry sand in the tank before vacuum kneading can be taken in as a control factor when adjusting the amount of added water, and simply compared with the conventional method in which the amount of added water was set based on the relationship between water content and sand strength. hand,
The quality of recycled sand can be made more stable.
As a result, the strength of the mold (green mold) can be maintained more uniformly, which can contribute to reduction of defects during casting and improvement of dimensional accuracy of the cast product. Further, the total amount of water to be added and the allocation of this water for kneading and cooling can be optimally adjusted.

[0016]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is an explanatory view schematically showing the overall structure of the foundry sand reclamation apparatus according to the present embodiment. As shown in this figure, the reclamation apparatus has a state in which the inside thereof is maintained at a predetermined vacuum degree. Vacuum mixer 1 capable of kneading in
A predetermined amount of recovered sand and a binder (eg bentonite) as an additive to the vacuum mixer 1, and a weighing hopper 2 for adding new sand as necessary, and a predetermined amount of water to the vacuum mixer 1. And a water supply device 10 for supplying water.

Although not specifically shown, the weighing hopper 2 is a collection station for separating the used molds after the completion of casting in the green molding line to collect molding sand, and bentonite (caking binder) as an additive. It is connected to a bentonite supply device for supplying a chemical agent) and a fresh sand supply station for supplying fresh sand via a conveying device such as a conveyor device or a feeder device. The water supply device 10 includes a water meter 11 for measuring the amount of water to be supplied into the vacuum mixer 1, and a supply pump for pumping the water to be supplied from the condenser 13 side to the vacuum mixer 1 side via the supply line Ls. 12 and a circulation pump 14 that causes the water returned into the condenser 13 via the return line Lr to pass through the heat exchanger 15 connected to the cooling tower 16 and then to recirculate into the condenser 13. Water kept at a substantially constant temperature can be supplied into the vacuum mixer 1.

Downstream of the water meter 11, both primary and secondary water injection control valves 18 and 19 are provided. The primary water injection control valve 18 is for injecting moisturizing water for kneading for maintaining the water content of the foundry sand (reclaimed sand) after kneading at a predetermined value into the vacuum mixer 1 as primary water injection, on the other hand,
The secondary water injection control valve 19 is for injecting the cooling water for cooling the high temperature recovered sand at the time of kneading into the vacuum mixer 1 as secondary water injection. It is controlled by both primary and secondary water injection control valves 18, 19.

Further, the vacuum mixer 1 is connected to a vacuum duct 21 having a vacuum cutoff valve 22 provided in the middle thereof, and the vacuum duct 21 is connected to a vacuum pump 23 via the condenser 13. By driving the vacuum pump 23 with the vacuum shutoff valve 22 open,
The inside of the vacuum mixer 1 can be evacuated to a predetermined degree of vacuum via the vacuum duct 21. Further, the vacuum mixer 1 is connected to an atmosphere release valve 26 for introducing atmosphere into the mixer 1, and by opening this atmosphere release valve 26, the vacuum state inside the mixer 1 can be released almost instantly. .

Further, an FK sensor 5 for detecting the temperature and the water content of the sand (mainly recovered sand) charged in the mixer 1 is inserted in the vacuum mixer 1.
As shown in FIG. 2, the FK sensor 5 is electrically connected to a control unit 30 that controls the operation of the reproducing device, and inputs a detection signal to the control unit 30. The control unit 30 is configured by, for example, a microcomputer as a main part, and in addition to the FK sensor 5, a load cell 11a in the water meter 11 and water injection control valves 18 and 19 are connected so that signals can be exchanged. The detection signal of the load cell 11a is input to the control unit 30, and a control signal is output from the control unit 30 to the water injection control valves 18 and 19.
Although not specifically shown, the control unit 3
In addition to the above, 0 is, for example, a detection signal from the load cell of the weighing hopper 2, a supply line Ls of the water supply device 10.
Various signals such as the water temperature detection signal are input respectively, and, for example, valves such as the vacuum shutoff valve 22 and the atmosphere release valve 26, or devices such as pumps such as the supply pump 12 and the vacuum pump 23 are input. , Various control signals are output respectively.

The operation of the foundry sand recycling apparatus having the above-mentioned structure will be described with reference to the time chart of FIG. First, based on a control signal from the control unit 30, a predetermined amount of high-temperature recovered sand is conveyed and introduced into the weighing hopper 2 from the casting sand recovery station (not shown) side. In addition, fresh sand is transported and loaded from a fresh sand supply station (not shown) as needed. Furthermore, a specified amount of bentonite is supplied from a bentonite supply device (not shown).
It is thrown in. Then, these are premixed in the vacuum mixer 1 for a predetermined time. At this time, the inside of the vacuum mixer 1 has not yet been evacuated, and the inside of the mixer 1 is in an atmospheric pressure state.

When this premixing is completed, the FK sensor 5 measures the temperature and water content of the sand (mainly recovered sand) in the mixer 1 and inputs the detection signal to the control unit 30. In the control unit 30, as will be described later in detail, with respect to a preset target value of the sand strength of the reclaimed sand,
The water content of the reclaimed sand is set based on the temperature of the foundry sand in the mixer 1 before vacuum kneading detected by the FK sensor 5, and the set target water content and the before-vacuum kneading detected by the FK sensor 5 are set. Based on the water content of the foundry sand, the amount of water to be added is calculated, and the amount of water is further divided into primary water for kneading and secondary water for cooling. Then, the amount of primary water is determined based on this calculated value, a control signal is output to the primary water injection control valve 18, the valve 18 is opened for a predetermined time, and a predetermined amount of primary water is poured into the mixer 1. To be done.

Next, when the above-mentioned primary water injection is completed, the valves such as the gate valve provided in each path leading to the inside of the vacuum mixer 1 are closed, the vacuum shutoff valve 22 is opened, and the vacuum pump 23 is opened. Is driven, so that the inside of the mixer 1 has a predetermined degree of vacuum (in this embodiment, for example, 74 hp).
Vacuum is drawn up to a (hectopascal). At 74 hpa, the boiling point of water is 40 ° C. When the degree of vacuum reaches this value, vacuum kneading is started. Then, during the vacuum kneading (more preferably, in the first half of the vacuum kneading step), secondary water for cooling is added. That is,
Based on the control signal from the control unit 30, the secondary water injection control valve 19 is opened for a predetermined time, and a predetermined amount of secondary water is poured into the mixer 1. As described above, by evaporating the secondary water, the sand in the mixer 1 is rapidly cooled to the set temperature (for example, 40 ° C. or less in this embodiment).

When the vacuum kneading step is completed, the vacuum shutoff valve 22 is closed and the atmosphere opening valve 26 is opened to bring the inside of the mixer 1 to the atmospheric pressure state. Then, each gate valve that is closed before the vacuum shutoff valve 22 is opened is opened, and kneading is performed for a predetermined time under atmospheric pressure. When this atmospheric pressure kneading is completed, from the outlet 1a of the mixer 1,
Reclaimed foundry sand (reclaimed sand) containing a preset amount of water (and thus of preset sand strength) is discharged,
It is again used for molding. In this way, one cycle (180 seconds in this embodiment) of reproduction processing is performed.

In the present embodiment, as described above, the casting sand (mainly recovered sand) in the mixer 1 before vacuum kneading detected by the FK sensor 5 with respect to the preset target value of the sand strength of the regenerated sand is set. ) Set the water content of the reclaimed sand based on the temperature of
Based on the set target water content and the water content of the molding sand in the mixer 1 before vacuum kneading detected by the FK sensor 5, the water content to be added is calculated, and this water content is used for kneading. The amount of added water is adjusted by distributing the primary water and the secondary water for cooling. Hereinafter, the adjustment of the amount of added water will be described. In this example, during vacuum kneading,
Only the recovered sand was cast into the weighing hopper 2 as the casting sand and kneading was performed without adding new sand.

First, the target value of the sand strength of the recycled sand (that is, the coercive pressure of the green mold formed from the recycled sand) is set in advance. In this embodiment, the target value of the coercive pressure is, for example, 2.0 kgf.
/ Cm ² . Actually, 1.8 Kgf / cm
A coercive pressure of about ² is sufficient for casting. With respect to this target value of the coercive pressure, the water content of the reclaimed sand is set based on the temperature of the foundry sand (recovered sand in this embodiment) in the mixer 1 before vacuum kneading.

That is, as is apparent from the above description with reference to the graph of FIG. 5, when vacuum kneading is performed,
Even if the water content of the reclaimed sand after kneading is the same, the coercive pressure of the green mold becomes higher as the temperature of the foundry sand in the tank before vacuum kneading becomes higher. The temperature of the foundry sand (recovered sand) in the previous tank is variously changed at fixed intervals and collected as basic data, and the FK sensor 5 detects the temperature and compares it with the basic data to detect the temperature. A target value of the water content of the reclaimed sand after kneading can be set according to the temperature.

Then, the target value of the set water content is input to the control unit 30. Instead of this, the basic data is input and stored in advance in the memory of the control unit 30, and the target value of the coercive pressure of the reclaimed sand is input as the target value to be input to the control unit 30. 5
It is also possible to automatically set the target value of the water content of the reclaimed sand in the control unit 30 by contrasting the detected temperature with the basic data. The control unit 30 controls the target value of the water content of the reclaimed sand set as described above and the casting sand (recovered sand) in the tank before vacuum kneading detected by the FK sensor 5.
Then, the total amount of water to be added to the vacuum mixer 1 is calculated from the water content.

By setting the cooling temperature in the vacuum mixer 1 (in other words, by setting the degree of vacuum in the mixer 1 at the time of vacuum kneading), the temperature of the foundry sand (recovered sand) in the tank before vacuum kneading and There is a certain relationship with the addition rate of secondary water (cooling water) to be added for cooling. An example of the relationship between the two is shown in FIG. The graph indicated by the straight line A in FIG. 4 is a case where the cooling temperature in the vacuum mixer 1 is set to 40 ° C. (that is, the degree of vacuum in the vacuum mixer 1 is set to 74 hpa). By changing, a group of graphs parallel to the straight line A is obtained. The calculation formula of the amount of cooling water to be added as secondary water (that is, the energy formula before and after the cooling treatment) is shown below.

P • t + Ms • Cps • T1 + Mw, X1 • C
w ・ T1 + Mw, △ X ・ Cw ・ Tw + Mw, k ・ Cw ・ Tw =
Ms ・ Cps ・ T2 + Mw, X2 ・ Cw ・ T2 + Mw, △ X ・
Cw ・ T2 + Mw, k ・ (Cw ・ Tsa + ΔHv (Ts
a)) + Qab In the above equation, each symbol represents the following items. -Kw: mixer power-P: energy applied to the mixer motor-t: kneading time-M: recovered sand weight-X1: recovered sand moisture value-Ms: recovered sand dry weight [M- (1-X1 / 10
0)]-Cps: Specific heat of sand-T1: Temperature of recovered sand-Mw, X1: Weight of recovered sand moisture [M · X1 / 100] -Cw: Specific heat of water-X2: Target moisture value-Mw, ΔX: Humidification Water weight [X2 / 100 ・ M-Mw, X
1] -Tw: Humidification water temperature-Mw, k: Cooling water weight-T2: Target sand temperature-Tsa: Average evaporation temperature [(T1 + T2) / 2] -Hv: Latent heat of evaporation [function of evaporation temperature] -Qab: Heat dissipation from mixer

Therefore, the amount of cooling water to be added as secondary water can be calculated from the temperature of the recovered sand detected by the FK sensor 5 and the above data. Then, the amount of secondary water to be added for kneading is calculated from the total amount of water to be added and this cooling water amount. In this way, the total amount of water to be added, as well as for kneading this water (primary water) and for cooling (secondary water)
Can be optimally adjusted.

As described above, according to this embodiment, the relational data between the water content of the reclaimed sand and the sand strength, the temperature of the casting sand (recovered sand) in the tank before the vacuum kneading at the target cooling temperature, and It is possible to control the amount of water supplied to the vacuum mixer 1 by the water supply device 10 based on the relational data with the amount of cooling water added and the water content of foundry sand (recovered sand) in the tank before vacuum kneading. it can. That is, the temperature of the foundry sand (recovered sand) in the tank before vacuum kneading can be taken in as a control factor when adjusting the amount of added water, and the amount of added water is simply set based on the relationship between water content and sand strength. In addition, the quality of the reclaimed sand can be made more stable than in the past. As a result, the strength of the mold (green mold) can be maintained more uniformly, which can contribute to reduction of defects during casting and improvement of dimensional accuracy of the cast product. Further, the total amount of water to be added and the allocation of this water for kneading and cooling can be optimally adjusted.

The present invention is not limited to the above-described embodiment, but may be modified without departing from the scope of the invention.
It goes without saying that various improvements or design changes are possible.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an overall configuration of a foundry sand reclamation apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged explanatory diagram showing a vacuum mixer and water supply control of the regeneration device.

FIG. 3 is a time chart for explaining the operation of the playback device.

FIG. 4 is a graph showing the relationship between the temperature of recovered sand and the addition rate of cooling water.

FIG. 5 is a graph showing the relationship between the water content of reclaimed sand and the coercive pressure of green mold.

[Explanation of symbols]

 1 ... Vacuum mixer 5 ... FK sensor 10 ... Water supply device 30 ... Control unit

Claims (3)

[Claims] 1. A method for reclaiming foundry sand by throwing recovered foundry sand into a vacuum kneading tank, adding water and a binder and kneading the reclaimed foundry sand. A method for reclaiming a molding sand, wherein a target value of strength is set in advance, and the amount of water added is adjusted based on the temperature of the molding sand in the tank before vacuum kneading. 2. The amount of water added is the relational data between the water content of the reclaimed sand and the sand strength, the relational data between the temperature of the molding sand in the tank before vacuum kneading at the target cooling temperature and the amount of cooling water added, and The method for reclaiming foundry sand according to claim 1, wherein the method is adjusted based on the water content of the foundry sand in the tank before vacuum kneading. 3. A vacuum kneading tank capable of kneading while maintaining the inside at a predetermined vacuum degree, a recovered sand supply device for supplying a predetermined amount of recovered molding sand into the vacuum kneading tank, and vacuum kneading A binder supply device that supplies a specified amount of binder into the tank, a water supply device that supplies a specified amount of water into the vacuum kneading tank, and the temperature of the foundry sand in the tank before vacuum kneading is detected. Temperature detection means and water content detection means for detecting the water content of the foundry sand in the tank before vacuum kneading, and the relationship data between the water content of the reclaimed sand and the sand strength, before the vacuum kneading at the target cooling temperature Based on the relationship data between the temperature of the molding sand in the tank and the amount of cooling water added and the water content of the molding sand in the tank before vacuum kneading, the amount of water supplied to the vacuum kneading tank by the water supply device was adjusted. A reclaiming device for foundry sand, comprising a control means for controlling.