Plaster

Type

Water consistency (%)

Mixing time (min.)
Initial

Mixing time (min.)
Final

Expansion ratio (%)

Dry compressive
strength
(㎏f/㎠)

Dry shrink
ratio
(%)

C-1000 

40

5-7

50

0.2

45

0.2

While casting with gypsum models produces good surface quality and precision, air ventilation is poor,
thus requiring a pressurized or de-pressurized casting facility.
01. Pressurization Method
      Please apply pressure of about 0.3~0.7 kg/cm2 to a cast to get a high-quality surface.
02. Depressurization Method
      The depressurization level should be between 20 and 30 cm Hg, usually for about two to three minutes.

01. Hasty out-casting when producing a gypsum model can cause the model's surface to be irritated, which will result in a rough cast surface.
02. A sudden change of temperature while drying or cooling a gypsum model can cause a rupture or crevice.
03. When casting, setting the temperature at a low level can make the gypsum model absorb moisture, which can cause it to fail.
04. When casting, pinholes appearing on the surface of the gypsum model due to boiling or breakage of the model is most likely due to poor handling during the process of drying or cooling the gypsum model.

01. Preparing for an Original Form

Gypsum, silicon rubber, wood or plastic is used to make an original form. If gypsum or wood has absorptiveness, please apply the agent for surface processing two or three times. It is also advisable to use silicon rubber if the original form is complex.

02. Mold Lubricant

Cari soap liquid), stearic acid + Gerotin, Vaseline + Gerotin, and Sam Woo Separator

03. Mixing

Accurately measure the amount of water to be mixed with the gypsum being used. Put the gypsum into the water and after it settles, mix them thoroughly to get an even slurry. It is best to use the vacuum mixing method. The mixture's consistency may vary depending on the mixing method used. Insufficient mixing may cause the gypsum and the water to separate, which may result in a decrease in the strength of the cast or crevices.

04. Injection

After mixing is completed, inject the mixture into the side of the model while shaking it slightly, until the mixture reaches up to the edge of the model.

05. Casting out

Casting out should be done when the calorification temperature is highest. Based on the shape of the model, the time it is cast out may be delayed.

06. Drying

After the model is cast out, it must be kept inside and then dried with an electronic heater once it has fully recovered. Since there may be differences according to the size of the model or the structure of the electronic heater, the drying process must be performed after a thorough examination. Usually, the model is dried for two hours from room temperature to 100°C, and then from 100°C to 200°C for one hour, and finally, from 200°C to 300°C, also for one hour. Later, the model is kept dried for 15 hours at 300°C for heat treatment. If the size of the cast is more than 30 cm, however, the abovementioned process must be performed until the temperature hits 400°C, after which the model is kept for 15 hours to fully remove the remaining moisture.

07. Casting

After the heat treatment is finished, the model is kept inside the electronic heater while the temperature is slowly going down, to cool it down. During the casting process, the temperature of the model should be between 120 and 200°C. Suddenly lowering the temperature can cause crevices on the surface of the gypsum model.