JP2006082108A - Method for drying gypsum mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for drying a gypsum mold by which the drying work for obtaining the high quality gypsum mold having no crack etc., can efficiently be performed without increasing working man-hours. <P>SOLUTION: In the method for drying the gypsum mold, drying the gypsum mold with a heating temperature rising, composed of a heating process for dehydrating by heating the gypsum mold while raising the heating temperature and a cooling process for transforming the crystal by cooling the gypsum mold while lowering the heating temperature, the heating process is performed by rising the heating temperature step by step and the cooling process is performed by lowering the heating temperature step by step. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for drying a gypsum mold.

  The method for producing a gypsum mold is to first add gypsum to water and stir to make a uniform slurry, then pour this slurry into a casting frame on which a model is set, and after the slurry has hardened, die and dry The gypsum mold is manufactured.

In particular, when producing a casting gypsum mold having excellent casting surface and dimensional accuracy, the most important process is to release moisture in the gypsum and transform the crystals into a stable crystal form.
Since gypsum has a low thermal conductivity, it tends to cause a temperature difference between the surface and the inside of the gypsum.If this temperature difference becomes too large in the heating and drying process, the shrinkage rate due to dehydration differs between the surface and the inside, and cracks occur. May occur.

  For this reason, in the conventional drying process, since the temperature difference between the surface and the inside of the gypsum was not very large, it was heated very slowly and then slowly cooled, so that the drying time was long and inefficient. It was.

Therefore, the gypsum mold is provided with a through hole that communicates with the outside of the gypsum mold, so that heat can be directly applied to the inside and the inside of the gypsum mold through the through hole, thereby eliminating the temperature difference between the surface and the inside and preventing the occurrence of cracks. An example (see Patent Document 1) has been proposed.
Japanese Patent Laid-Open No. 7-256392

  However, this requires a process for forming a through hole in the gypsum mold, which increases the number of work steps, and it may be difficult to form the through hole depending on the shape of the mold.

  The present invention has been made in view of the above points, and the object of the present invention is gypsum that can efficiently perform a drying operation to obtain a high-quality gypsum mold without cracks without increasing the number of work steps. It is in providing a mold drying method.

Means and effects for solving the problem

  In order to achieve the above object, the invention described in claim 1 includes a heating step in which the gypsum mold is heated and dehydrated while increasing the heating temperature, and a cooling in which the gypsum mold is cooled and the crystals are transformed while the heating temperature is decreased. In the gypsum mold drying method comprising the steps of drying the gypsum mold by controlling the heating temperature, the heating process is executed by increasing the heating temperature stepwise, and the cooling process is executed by decreasing the heating temperature stepwise. The gypsum mold drying method was used.

  Since the heating temperature is controlled to raise the heating temperature step by step in the heating process, the temperature difference between the surface of the gypsum mold and the inside can be reduced while maintaining the heating temperature constant, and the surface of the gypsum mold throughout the heating process. Thus, it is possible to efficiently carry out a heating process in which dehydration is sufficiently performed while preventing the occurrence of cracks by avoiding the internal temperature difference from becoming larger than a predetermined temperature.

In addition, since the heating temperature is controlled to lower the heating temperature step by step in the cooling process, the crystal form of the gypsum mold can be efficiently transformed into a more stable crystal form at the stage of maintaining the heating temperature constant, An increase in the temperature difference between the surface and the inside of the gypsum mold can be prevented.
Since both the above heating process and cooling process can be performed efficiently, the working time of the drying process can be shortened.

  According to a second aspect of the present invention, in the gypsum mold drying method according to the first aspect, the predetermined heating temperature is kept constant for at least the minimum maintenance time, and the temperature difference between the surface temperature of the gypsum mold and the internal temperature is predetermined when the minimum maintenance time elapses. When the temperature difference is not less than or equal to the temperature difference, a control for extending the maintenance time until the temperature difference becomes less than or equal to the predetermined temperature difference is performed for each predetermined heating temperature, and the heating temperature is changed stepwise.

  Maintain the specified heating temperature at least at the minimum maintenance time, and extend the maintenance time until the temperature difference between the surface temperature of the gypsum mold and the internal temperature is not less than the specified temperature difference when the minimum maintenance time has elapsed. Therefore, while reliably performing dehydration or crystal transformation work, the temperature difference between the surface temperature of the gypsum mold and the internal temperature is suppressed to a predetermined temperature difference or less at each predetermined heating temperature, and the temperature difference becomes too large and cracks are generated. Therefore, dehydration and crystal transformation are efficiently performed, and a high-quality gypsum mold can be obtained.

  The invention described in claim 3 is the gypsum mold drying method according to claim 2, wherein the predetermined temperature difference is about 10 ° C.

  The temperature difference between the surface temperature of the gypsum mold and the internal temperature is kept below about 10 ° C for each predetermined heating temperature, so the temperature difference does not greatly exceed 10 ° C throughout the drying process, preventing the occurrence of cracks. And can be efficiently dried.

  The invention according to claim 4 is characterized in that in the heating step, the predetermined heating temperature set in stages is about 120 ° C, about 140 ° C, about 160 ° C, about 180 ° C, about 230 ° C. .

By maintaining the heating temperature constant at about 120 ° C in the heating process, expansion deformation due to the discharge of adhering water from the gypsum mold can be mitigated, and by maintaining the heating temperature constant at about 140 ° C, the adhering water can be released. Later shrinkage deformation can be relieved, and by maintaining constant at about 160 ° C, expansion deformation due to the start of release of crystal water in the gypsum mold can be relieved, and by maintaining constant at about 180 ° C In addition, expansion deformation during the release of crystal water can be alleviated, and by maintaining the temperature constant at about 230 ° C., complete release of crystal water can be secured.
In this way, it is possible to obtain a high-quality gypsum mold while avoiding the formation of moisture nests while completing dehydration while preventing deformation of expansion and contraction of the gypsum mold and preventing dry cracking of the mold.

  According to a fifth aspect of the present invention, in the gypsum mold drying method according to any one of the second to fourth aspects, in the cooling step, the predetermined heating temperature set stepwise is about 180 ° C and about 150 ° C. It is characterized by being.

  By maintaining the heating temperature constant at about 180 ° C in the cooling process, the orthorhombic crystal morphology can be efficiently transformed into a more stable hexagonal crystal or cubic crystal, and shrinkage deformation associated with transformation can be mitigated. By maintaining the heating temperature at a constant temperature of about 150 ° C. for a predetermined time, the hexagonal crystal form can be efficiently transformed into a more stable cubic crystal and shrinkage deformation accompanying transformation can be mitigated.

Hereinafter, an embodiment according to the present invention will be described with reference to FIGS.
A gypsum mold 1 according to the present embodiment is a mold for casting a mold made of an aluminum alloy for vulcanizing and molding a tire. A gypsum obtained by curing a slurry in which gypsum is dissolved in water in a casting frame to remove the mold. The mold 1 is dried in a drying furnace 10 shown in FIGS.

The drying furnace 10 includes a carriage 11 on which the plaster mold 1 is placed and a bell-shaped lid member 21 that covers and heats the entire carriage 11.
The carriage 11 has a column 14 erected on a rectangular base 13 having wheels 12 at four corners, and disk-like mounting plates 15 and 16 are located at an appropriate distance in the middle of the column 14. It is fixed.

  The die-cast gypsum mold 1 is placed on each of the upper and lower mounting plates 15 and 16, and each of the mounting plates 15 and 16 is placed at equidistant positions around the column 14 at equal intervals. 1 is placed.

One gypsum mold 1 is provided with temperature sensors 17 and 18 on the surface and inside thereof, so that the surface temperature and the internal temperature of the gypsum mold 1 can be detected.
Signal lines 17 a and 18 a extend from the temperature sensors 17 and 18 and pass through the support column 14 and below the base 13.

On the other hand, the lid member 21 has a heater 23 built in the side wall 22.
The heaters 23 are disposed on the bell-shaped side wall 22 at equal intervals in the radial direction from the central highest portion so that the inside can be heated substantially evenly.
A longitudinally long opening is formed in the side wall 22 between the heaters 23 and 23 arranged at equal intervals, and the opening / closing door 24 can be opened and closed freely.

When the bell-shaped lid member 21 is placed on the carriage 11 and the carriage 11 is entirely covered with the lid member 21 and the heater 23 is operated, a plurality of pieces placed on the placement plates 15 and 16 in the lid member 21 are applied. The gypsum mold 1 can be heated evenly without bias.
Further, when the opening / closing door 24 is opened and the opening of the lid member 21 is opened, the inside can be cooled.

The die-cut gypsum mold 1 is dried by the drying furnace 10 as described above.
FIG. 3 shows the temperature change in the surface and inside of the gypsum mold 1 by the temperature control process in the drying process by the drying furnace 10 and the temperature control in the present embodiment.

In FIG. 3, the solid line indicated by the broken line indicates the heating temperature H by the heater, the one-dot chain line indicates the surface temperature To of the gypsum mold 1, and the two-dot chain line indicates the internal temperature Ti of the gypsum mold 1.
The surface temperature To and the internal temperature Ti of the gypsum mold 1 can be detected by the temperature sensors 17 and 18.

The drying process includes a heating process in which the gypsum mold 1 is heated and dehydrated while increasing the heating temperature, and a cooling process in which the gypsum mold is cooled and the crystals are transformed while the heating temperature is decreased.
In the heating process, the heater set temperature is raised stepwise up to about 230 ° C., but as the heater set temperature H rises, the surface temperature To of the gypsum mold 1 rises with a slight delay.
The increasing change rate of the surface temperature To of the plaster mold 1 is substantially equal to the increasing change rate of the heating temperature.

On the other hand, the internal temperature Ti of the gypsum mold 1 rises later than the surface temperature To because the heat transfer coefficient of gypsum is small.
And since the rate of change of the internal temperature Ti is somewhat smaller than the rate of change of the surface temperature To, when the heating temperature by the heater is increased, the temperature difference ΔT between the surface temperature To of the gypsum mold 1 and the internal temperature Ti is It grows gradually.

Similarly, in the cooling process, the heater set temperature is lowered stepwise, but as the heater set temperature H is lowered, the surface temperature To of the gypsum mold 1 is lowered with a slight delay.
Further, the internal temperature Ti of the gypsum mold 1 decreases with a delay.

  Since the rate of change of the internal temperature Ti is somewhat smaller than the rate of change of the surface temperature To, the temperature difference ΔT between the surface temperature To of the gypsum mold 1 and the internal temperature Ti gradually increases when the heater set temperature is lowered. It gets bigger.

The heating temperature set in stages is five stages of 120 ° C., 140 ° C., 160 ° C., 180 ° C. and 230 ° C. in the heating process, and two stages of 180 ° C. and 150 ° C. in the cooling process.
A minimum maintenance time during which dehydration or crystal transformation can be reliably performed is determined for each set heating temperature, and at least the set minimum maintenance time is controlled to be kept constant.

Gypsum is mainly composed of gypsum crystals and moisture. The crystals have three forms, cubic, hexagonal and orthorhombic, and the stability decreases in the order of cubic, hexagonal and orthorhombic.
Moreover, the water | moisture content contained in gypsum consists of the crystal water taken in in a crystal | crystallization, the adhesion water adhering to a crystal | crystallization surface, and other remaining free water.

  The water contained in the gypsum is dehydrated in the heating process, and the cooling process transforms the crystal form into a more stable form after the dehydration.

First, in the first stage S1 of the heating process, the heating temperature is kept constant at 120 ° C. for at least 2 hours, which is the minimum maintenance time t1.
The adhering water of the gypsum mold is released near the heating temperature of 120 ° C., and by maintaining the temperature constant at 120 ° C., the expansion deformation of the gypsum mold 1 due to the discharge of the adhering water can be reduced.
And by keeping the temperature constant at 120 ° C. for at least 2 hours, it is possible to ensure the necessary discharge of the attached water.

  In the example shown in FIG. 3, the time for maintaining the heating temperature at 120 ° C. in the first stage S1 is more than 2 hours of the minimum maintenance time t1, but this is because the gypsum mold 1 at the time when the minimum maintenance time t1 has elapsed Since the temperature difference ΔT between the surface temperature To and the internal temperature Ti exceeded 10 ° C., the maintenance time was extended until the temperature difference ΔT became 10 ° C. or less.

If the temperature difference ΔT is 10 ° C. or less when the minimum maintenance time t1 has elapsed, the maintenance time is not extended.
Therefore, at the end of the first stage S1, the temperature difference ΔT between the surface temperature To of the gypsum mold 1 and the internal temperature Ti is always 10 ° C. or less.

In the next second stage S2, the heating temperature is maintained constant at 140 ° C. for at least one minimum maintenance time t2.
There is shrinkage deformation after the adhering water of the gypsum mold is released at a heating temperature of around 140 ° C, and by maintaining the temperature constant at 140 ° C, the shrinkage deformation of the gypsum mold can be alleviated.
In the second stage S2 of the example shown in FIG. 3, the temperature difference ΔT after the lapse of 1 hour of the minimum maintenance time t2 is 10 ° C. or less, and the maintenance time is not extended.

In the next third stage S3, the heating temperature is kept constant at 160 ° C. for at least 2 hours of the minimum maintenance time t3.
Discharge of crystal water from the gypsum mold starts near the heating temperature of 160 ° C., and the constant deformation at 160 ° C. can mitigate expansion deformation of the gypsum mold 1 due to the release of crystal water.

Maintaining the temperature at 160 ° C. for at least 2 hours is sufficient for starting the release of crystal water.
In the third step S3 of the example shown in FIG. 3, the temperature difference ΔT when the minimum maintenance time t3 elapses for 2 hours is 10 ° C. or less, and the maintenance time is not extended.

In the next fourth stage S4, the heating temperature is kept constant at 180 ° C. for at least one minimum maintenance time t4.
The discharge of crystal water from the gypsum mold continues at a heating temperature of about 180 ° C., and by maintaining the temperature constant at 180 ° C., expansion deformation of the gypsum mold 1 due to the release of crystal water can be mitigated.

And by keeping the temperature constant at 180 ° C. for at least one hour, necessary release of crystal water can be ensured.
In the fourth stage S4 of the example shown in FIG. 3, the temperature difference ΔT at the time of 1 hour of the minimum maintenance time t4 exceeds 10 ° C., so the maintenance time is extended until the temperature difference ΔT becomes 10 ° C. or less. ing.

Next, in the final fifth stage S5 of the heating process, the heating temperature is kept constant at 230 ° C. for 3 hours of the maintenance time t5.
By maintaining the heating temperature in the vicinity of 230 ° C. for 3 hours at the maintenance time t5, complete discharge of the crystal water of the gypsum mold is ensured.
Note that the maintenance time t5 is not the minimum maintenance time, and if it is 3 hours, the temperature difference ΔT is 10 ° C. or less and is not extended.

  The heating process for dehydrating from the gypsum mold 1 is completed, and then the cooling process is started. The heating temperature is lowered, and the open / close door 24 of the bell-shaped lid member 21 of the drying furnace 10 is opened to reduce the internal heat. Dissipate heat to cool.

First, in the sixth step S6, the heating temperature is kept constant at 180 ° C. for at least one minimum maintenance time t6.
When the heating temperature is lowered to 180 ° C, there is shrinkage deformation due to the primary transformation of the crystal accompanying cooling after the release of crystal water. By maintaining the constant 180 ° C, the primary transformation of the crystal is efficiently performed and Can be relaxed.

This primary crystal transformation transforms the orthorhombic crystal form into a more stable hexagonal or cubic crystal.
In the sixth step S6 of the example shown in FIG. 3, the temperature difference ΔT at the elapse of 1 hour of the minimum maintenance time t6 exceeds 10 ° C., so the maintenance time is extended until the temperature difference ΔT becomes 10 ° C. or less. ing.

In the next seventh stage S7, the heating temperature is kept constant at 150 ° C. for at least one minimum maintenance time t7.
When the heating temperature is lowered to 150 ° C, there is shrinkage deformation due to the secondary transformation of the crystal due to cooling after the crystallization water is released. By maintaining 180 ° C constant, the secondary transformation of the crystal is executed efficiently and this shrinkage deformation is reduced. Can be relaxed.

This crystal secondary transformation transforms the hexagonal crystal form into a more stable cubic crystal.
Thus, the crystal form of the gypsum mold 1 is completely transformed into the most stable cubic crystal, so that the strength of the gypsum mold 1 is maintained high.
In the seventh stage S7 of the example shown in FIG. 3, the temperature difference ΔT after the lapse of 1 hour of the minimum maintenance time t7 is 10 ° C. or less, and the maintenance time is not extended.

Thereafter, it is further cooled to lower the heating temperature, and the gypsum mold 1 is taken out at 120 ° C. or lower.
Preferably, it is good to take out around 70 degreeC.
In addition, from 120 degrees C or less area | region, since a water | moisture content is absorbed into a casting_mold | template according to the humidity in a drying equipment, it is necessary to interrupt | block outside air and to cool.

  As described above, since the heating temperature is increased stepwise in the heating process, the expansion deformation of the gypsum mold 1 accompanying dehydration is alleviated, and the heating temperature is decreased stepwise in the cooling process. Shrinkage deformation of the gypsum mold 1 accompanying transformation can be alleviated, and deformation distortion of the gypsum mold 1 can be prevented.

  Maintain the predetermined heating temperature at least constant for the minimum maintenance time, and if the temperature difference ΔT between the surface temperature To of the gypsum mold 1 and the internal temperature Ti is not less than 10 ° C when the minimum maintenance time has passed, maintain the maintenance time until it becomes 10 ° C or less Since it is extended, the temperature difference ΔT between the surface temperature To of the gypsum mold 1 and the internal temperature Ti is suppressed to 10 ° C. or less at every predetermined heating temperature while reliably performing dehydration or crystal transformation, and the temperature difference becomes too large. Thus, cracks are prevented from occurring, and dehydration and crystal transformation are efficiently performed.

The gypsum mold dried by the gypsum mold drying method according to the present embodiment described above is a high-quality gypsum mold with no cracks and very few casting nests.
Without the above temperature control, if the temperature difference ΔT between the surface temperature To of the gypsum mold 1 and the internal temperature Ti may greatly exceed 10 ° C. at any stage, cracks will occur, and there will be 10 or more casting voids. Many will be formed.

  In the gypsum mold drying method according to the present embodiment, the gypsum mold is not subjected to processing such as through-holes, and the drying operation is efficiently performed without increasing the number of work steps. Therefore, the work time is also shortened.

It is a perspective view of the state where the lid member of the drying furnace concerning one embodiment of the present invention was opened. It is a perspective view of the state where the lid member was closed. It is the graph which showed the process of the heating temperature control of the drying process by the drying furnace in this Embodiment, and the temperature change of the surface of gypsum mold by the same temperature control, and an inside.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Gypsum mold, 10 ... Drying furnace, 11 ... Bogie, 12 ... Wheel, 13 ... Base, 14 ... Post, 15, 16 ... Mounting plate, 17, 18 ... Temperature sensor, 21 ... Lid member, 22 ... Side wall , 23 ... heater, 24 ... open / close door.

Claims (5)

Drying the gypsum mold by drying the gypsum mold by controlling the heating temperature, which consists of a heating process in which the gypsum mold is heated and dehydrated while raising the heating temperature, and a cooling process in which the gypsum mold is cooled to transform the crystals while lowering the heating temperature. In the method
A gypsum mold drying method, wherein a heating step is executed by raising the heating temperature stepwise, and a cooling step is executed by lowering the heating temperature stepwise.   Maintain the specified heating temperature at least at the minimum maintenance time, and extend the maintenance time until the temperature difference between the surface temperature of the gypsum mold and the internal temperature is not less than the specified temperature difference when the minimum maintenance time has elapsed. 2. The gypsum mold drying method according to claim 1, wherein control is performed for each predetermined heating temperature to change the heating temperature stepwise.   The gypsum mold drying method according to claim 2, wherein the predetermined temperature difference is about 10 ° C.   The predetermined heating temperature set stepwise in the heating step is about 120 ° C, about 140 ° C, about 160 ° C, about 180 ° C, or about 230 ° C. Gypsum mold drying method. The gypsum mold drying method according to any one of claims 2 to 4, wherein in the cooling step, the predetermined heating temperature set in stages is about 180 ° C and about 150 ° C.

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