SU1214313A1 - Method of drying moulds produced from lost patterns - Google Patents

Description

eleven

The invention relates to the manufacture of castings on produced models.

The purpose of the invention is to reduce the duration of the process, drying the forms and simplify it.

Figure 1 and 2 shows the dependence of the drying time on the moisture content of the form.

EXAMPLE 1. The forms, after coating them, are placed in a sealed drying chamber, equipped with an electric heater and a fan, and dried by convective heating. Drying temperature (limited by model material used). After reaching a relative humidity of 75% in the chamber, a rapid vacuum (vacuum impulse) to a vacuum of 34 KPa (255 mm Hg) is created. The period of convective heating and pulsed evacuation is one cycle. At the end of the first cycle of the mold, it should be again subjected to convective drying until the relative humidity in the chamber reaches 75%, and then again create a vacuum impulse. The cycles must be repeated before the molds dry - they achieve a residual moisture content of 0.5%. The kinetics of the proposed drying process is presented in FIG. 1, from which it follows that as the forms are dried, the time required for a relative humidity of 75% in the chamber increases. Therefore, the duration of the period of convective heating is variable — it increases from cycle to cycle. The total duration of the drying process is 250 minutes.

Examples 2-5. The drying of the molds is carried out in a manner analogous to Example 1, but other values of the relative humidity in the chamber are selected at which the convection drying period ends. The values of moisture, as well as the total duration of the drying process are given in the table.

As follows from the table, the relative humidity in the chamber at the end of the period of convective heating ts in the range of 70-80% is optimal, and the optimality of these values of relative humidity is preserved at any load of the drying chamber with forms and at any humidity.

32

PRI me R 6. (Prototype). The molds, after applying a layer of coating to them, are placed on the same drying chamber. The drying temperature, blowing speed, and the vacuum value during vacuum are similar to Example 1. The kinetics of the drying process according to the prototype is presented in Fig. 2.

The duration of the convective heating period is constant and is 10 mino throughout the entire process. The convective heating period is followed by a vacuum pulse, after which the cycle repeats. As the molds dry, the relative humidity in the chamber to the end of the 10-minute convective drying period decreases. The total drying time of the molds is 380 minutes. An increase in the drying process time as compared to the proposed drying method occurs due to over-drying of the chamber atmosphere at the beginning of the process and insufficient saturation with moisture at the end of the drying process.

Thus, the proposed method of drying the molds as compared with the prototype makes it possible to reduce the duration of the drying process by 20-25%. In addition, there is no need to adjust the technological mode depending on the loading of the chamber with the molds and the moisture content of the molds, which simplifies the drying process.

five

2

3

4 5

75

 70 80

65

85

250

275 285

325 360

50

6 (prototype) Variable 380

The increase in the number of cycles due to incomplete evaporation of moisture, which is fed to the surface of the mold 55 during vacuuming

  An extension of the period of convective heating due to a drop in the drying rate at the end of this period.

SO120

FIG. 2

2ttO300 HUM

Drying time

Editor S. Lisin

Compiled by V.Ivanov

Tehred T. Dubinchak Proofreader V. But ha

Order 825/16 Circulation 757Subscription

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Branch PPP Patent, Uzhgorod, Projected St.,

Claims (1)

METHOD FOR DRYING THE FORMS OBTAINED BY CLEARING MODELS, including repeating convective heating of molds and subsequent pulsed evacuation, characterized in that, in order to reduce the duration of the drying process and simplify it, the evacuation pulse in each drying cycle is carried out when the relative humidity in the chamber 70- 80% > 1,121