JPS63295041A - Drying method for mold - Google Patents

Abstract

PURPOSE:To shorten drying time of a mold, to reduce dispersion of dried condition and to improve strength of the mold by holding the mold under reducing pressure at 300-5 Torr absolute pressure at least for two hours and dehumidifying. CONSTITUTION:In case of exceed 300 Torr of the absolute pressure, the reducing pressure effect is low and the dehumidifying is slow and in the case of <5 Torr the absolute pressure, trouble of deformation or crack in the mold are developed. Therefore, at the time of actual work, the pressure must be changed according to size and shape of the mold, but the reducing condition of the pressure in the range of 300-5 Torr is applied to almost of the molds. Then, as the effective drying ratio is obtd. by holding for two hours under this prescribed pressure, the holding time is to execute at least two hours. Further, in the reducing pressure drying method, as the moisture is vaporized under heat insulating condition, the temp. of the mold is descended, and at the time of taking out the mold to the air after completing drying, the moisture is absorbed in the mold caused by dewing phenomenon. By heating the mold under reducing pressure at least at the temp. of outside, this harmful influence can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for drying a mold in a lost wax precision casting method.

[Conventional technology]

In the mold manufacturing process of lost wax precision casting, the final coating of the mold is completed before dewaxing.
It is necessary to thoroughly dry the mold to improve its strength. Conventionally, the mold has been dried by fan drying for at least 24 hours in a drying room, usually at a humidity of 30% to 50%.

The dried mold is dewaxed and fired at 1000°C for about 1 hour to further improve the strength of the mold before being used for casting.

[Problem that the invention seeks to solve]

Even if a mold is kept in a drying room with constant humidity for a predetermined period of time and dried with a fan, the degree of drying of the mold will vary due to differences in the shape of the product, the direction and strength of the fan's airflow, etc. For this reason, drying for about 24 hours may be insufficient. If this conventional drying method is used to de-wax by raising the temperature without drying sufficiently, the strength of the mold is low and the mold is likely to crack due to thermal expansion of the wax, and this crank will cause burrs to form during casting. There was a problem with inviting people.

Furthermore, since it takes a long time of 24 hours or more to dry the mold, the time spent on mold production increases, and a drying room with a large space must be provided, resulting in an increase in cost.

The purpose of the present invention is to provide a mold drying method that shortens the drying time of the mold, increases the drying rate, reduces drying variation, and improves the strength of the mold.

[Means for solving problems]

The present invention is characterized in that the mold is held under reduced pressure of 300 to 5 Torr absolute for at least 2 hours to dehumidify it,
Furthermore, the method for drying a mold is characterized in that the mold is heated to at least the outside atmospheric temperature.

Although drying methods in which dehumidification is performed by holding the product under reduced pressure for a predetermined period of time have been used in various industrial fields, there has been no example of its application to drying the mold of the lost wax precision casting method according to the present invention. The few attempts made in the past failed because the degree of depressurization was too high, causing mold distortion and cracking.

The present invention is based on the discovery of an optimal method for drying molds through various experiments.

The reason why the absolute pressure of the present invention is set to 300 to 5 Torr is that if it exceeds 300 Torr, the effect of pressure reduction will be small and dehumidification will be slow, and if it is less than 5 Torr, problems such as distortion and cracking will occur in the mold as mentioned above, and Even considering the capacity of the vacuum pump, the equipment cost, etc., a pressure of 5 Torr or less is not necessary. During actual work, it is desirable to change the pressure depending on the size and shape of the mold, but a reduced pressure of around 107 orr can be applied to most molds.

Further, as will be described later, if the film is held under a reduced pressure of 10 Torr for 2 hours, a drying rate of about 130% can be obtained, so the holding time was set to be at least 2 hours.

Furthermore, in the vacuum drying method, moisture evaporates adiabatically, which lowers the temperature of the mold, and when it is taken out into the atmosphere after drying, it absorbs moisture due to condensation. This phenomenon is often seen during the rainy season and summer. This adverse effect can be prevented by heating to at least the outside atmospheric temperature under reduced pressure.

〔Example〕

The present invention will be explained based on examples.

Test pieces coated with six layers were dried by three methods: no-air drying, fan drying, and vacuum drying, and comparative experiments were conducted on the relationship between drying time, drying rate, and flexural strength.

FIG. 1 shows the relationship between drying time and drying rate.

The drying rate was defined as 100% when there was no change in the weight of the mold in conventional fan drying.

As shown in FIG. 1, by performing vacuum drying, the drying rate improved by 30%, reaching a degree of dryness that could not be achieved with fan drying, achieving a drying rate of 130%. In addition, the drying speed is very fast, and a drying rate of 100% is approximately 17% drying compared to windless drying.
7. Fan drying time of about 175 was reached in about 30 minutes.

Further, FIG. 2 shows the relationship between drying rate and mold strength (flexural strength). The strength in this figure shows the as-dried bending strength of molds dried to a drying rate of 60%, 80%, and 100% by conventional fan drying, and molds dried to a drying rate of 120% by vacuum drying.

Furthermore, the firing strength indicates the bending strength after firing this mold at 1000° C. for 1 hour.

According to this figure, the drying rate before firing is 60% and the strength is 140g/
A mold of mm2 has a strength of 270 g/mm" after firing, but a mold with a drying rate of 120% and a strength of 240 g/mm" according to the present invention has a strength of 370 g/mm2 after firing. is clear.

Next, as another experimental example, we will explain an investigation of the difference between molds when a product was actually cast and subjected to vacuum drying and fan drying.

In order to cast a product having the shape of 24 slits shown in Figure 3, the mold of the present invention was vacuum dried for 3 hours at a pressure of 10 Torr after the final coating, and the mold was dried for 24 hours with a fan as usual. Ninety molds were used for each. After casting, the number of slits where flash was generated was counted and the results are shown in the table. According to the wood chart, it is clear that the number of slits in which burrs were generated has been significantly reduced, and the number of molds in which no burrs have been generated has been significantly increased. In addition, in the conventional method, 24
There were 35 molds in which burrs were generated in 12 or more of the slits, but with the method of the present invention, this can be completely eliminated, and more than 50% of the molds had burrs in 6 or less slits. Became.

Table [Effects of the Invention] As described above, according to the present invention, it is possible to shorten the mold drying time from 24 hours or more to 2 to 3 hours, and at the same time, the drying rate and mold strength are significantly improved. improve,
This invention is industrially very effective because it can reduce the occurrence of casting burrs.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between drying time and drying rate in no-air drying, fan drying, and vacuum drying of a mold according to the present invention;
FIG. 2 is a diagram showing the influence of the drying rate on the bending strength of the mold in its raw state before firing and after firing, and FIG. 3 is a diagram showing the shape of the product tested for the effects of the present invention. Figure 1 Drying time (minutes) Drying rate before firing (0 mm) Figure 3

Claims (1)

[Claims] In a method of drying a mold, the mold is placed in a pressure reducer and dried for about 1 hour.
This method of drying a mold is characterized by holding the mold under a reduced pressure of 0 Torr for 2 to 3 hours. 1. A mold drying method, which comprises holding the mold under reduced pressure of 300 to 5 Torr absolute for at least 2 hours and dehumidifying it. 2. The mold drying method according to claim 1, characterized in that the mold is heated to at least the outside atmospheric temperature.