SU506464A1 - Composition for hardening shell ceramic molds - Google Patents

Description

(54) COMPOSITION FOR STRENGTHENING SHELL CERAMIC CASTING FOILS

This invention relates to the field of foundry, in particular, to the processes of making foundry molds.

A known composition for hardening shell ceramic molds made from melted models on liquid glass and with a hardener, ferrochrome slag.

The disadvantage of this composition is low thermal conductivity and heat resistance, as well as the hygroscopicity of the obtained forms due to the presence of ferrochromic slag in it, which does not allow to pour molds in a cold state and sharply deteriorates the quality of the castings. The presence of quartz sand with liquid glass does not provide a fast heat sink after casting the molds due to the low values of the ten-fold coefficient of these materials, which leads to the formation of shrinkage defects in the castings. In addition, in the temperature range of calcination (900-1100 ° C), quartz forms on liquid glass soften, which can lead to deformation of the form. Upon cooling of the calcined molds below 600 ° C, polymorphic transformations of quartz and shrinking of the s-glass occur, which causes the formation of torshin in the mold.

Also known is a moldable mixture for making ceramic molds and rods for steel on a metal phosphate binder.

Metallic phosphates are used as a binder, for example, phosphates of alkaline earth metals or metals P1 of the periodic system, such KaKMg (n2PO ,,); 2

or AlPO.;. Zirconium silicates, zirconium oxide, mullite, sillimanite, alumina, chamotte, magnesite, and others with a grain size of ~ 4 mm can be used as a refractory ionol-titel.

The disadvantage of such a molding mixture is the need to maintain the floor of the cervical temperature (up to 300 ° C) during the drying process and its considerable duration due to the fact that the room temperature of the stump is not solidified, and this excludes the possibility of using the molding mixture to strengthen the shell forms and output on melted models

In order to increase thermal sth-ykost

and acceleration of hardening in the proposed composition additionally introduced dupto-peridotitozy powder in the following ratio of components, weight. %:

Refractory material 40-60

Dunito-peridotite

powder15-25

Calcium Hydroxide 5--1-3

Orthophosphoric acid 10-20

Dust-like part of the proposed patch:

Ок ;; -: ц} п: 0--0,1 М contains oxides- ;: main: 1,

iron, chromium and calcium, which directly interact with orthophosphoric acid, form a self-hardening refractory binder as a result of the formation of three-substituted salts of magnesium, iron, chromium and calcium, insoluble in water, which eliminates drying of the form at elevated temperatures and speeds up the process of formation.

The pulverized part of the proposed composition was selected on the basis of the conditions of the optimal solidification time under ordinary conditions (10–20 minutes) and the mold destructibility after casting with metal. Calcium hydroxide is introduced into the composition as an additive that improves breakability of the form, since the strengthening composition based only on the dunito-peridotite component and orthophosphoric acid after calcining the form and pouring it has high strength (-900 kg / cm).

The composition for hardening shell-shaped ceramic casting molds is prepared as follows; blowing way.

raw materials are loaded into the mixer. After stirring, orthophosphoric acid is poured in and stirred for 3-4 minutes. The finished composition is poured into the flask (jacket) with two or

three-layer model block and vibrate for .20-30 seconds for better filling. After solidification of the composition, the form enters the installation for melting the model composition and further, in accordance with

accepted technological process of pouring on melted models.

Table I shows five examples of the composition of the hardening solution, wt. %

Table 1

table 2