INCREASE IN THE SERVICE LIFE OF FORMING SURFACES
OF MOLDING UNITS. PART 1. STUDY OF THE IMPROVEMENT
OF MOLDING UNIT FORMING SURFACE MATERIAL QUALITY
E. I. Suzdal’tsev,
D. V. Kharitonov,
and A. A. Anashkina
Translated from Novye Ogneupory, No. 2, pp. 30 – 38, February, 2010.
Original article submitted October 27, 2009.
Materials are reviewed that are used in manufacturing the forming surfaces of molding units. Choice of the op
timum water and gypsum ratio for a gypsum paste is provided and methods are considered for improving gyp
sum mold quality.
Keywords: gypsum, mold porosity, molding unit.
A central component of slip casting of large complexly
shaped ceramic products of the antenna fairing type for guid-
ance rockets is a molding set (Fig. 1) consisting of the fol-
lowing main elements: a body of perforated metal 1, a lower
flange 2, with a connecting pipe for filling the cavity mold
with slip between a core 5 and the active surface of a porous
mold 6, a support flange 3 and replenishing vessels 4. The
configuration of the molding unit presented in Fig. 1 has
been used extensively in practice for preparing objects of
It is generally well known that for the active part of a
molding unit it is possible to use any material from which it
is easy to prepare a mold, answering such requirements as
good reflection of the configuration of the mold, sufficient
strength, capacity to accumulate liquid phase from a slip, ab
sence of chemical reaction with the slip, and endurance. The
most suitable material for these purposes appeared to be gyp
sum, that is used extensively in the ceramic industry in mold
ing preforms from aqueous slips. However, use of gypsum in
molds for slip casting alongside low cost and high technolog
ical efficiency has a series of disadvantages, the main one of
which is the short life of gypsum molds.
On the basis of considerable experience with gypsum
molds it is possible to confirm that currently on average they
serve for 12 castings. With a continuous molding cycle (three
preforms per week) after a month a mold is taken out of ser
vice for retreating the gypsum, that taking account of drying,
lasts one week. Thus, a simple mold constitutes 20%, that in
turn gives rise to a requirement for manufacturing additional
The scatter of the number of defective billets is of inter-
est (having different incomplete feeding, sinks, etc.) obtained
from the same mold with different gypsum reprocessing.
This index varies from 8 to 55%. This considerable scatter
may only be caused by different gypsum properties used for
each of the molds.
Proceeding from this, the aim of the present work is to
increase the service life of the molding surfaces of molding
units and increase the quality of molded preforms. Analysis
made it possible to separate two main areas for resolving the
– studies for improving the quality of molding unit
forming surface material quality;
Refractories and Industrial Ceramics Vol. 51, No. 1, 2010
1083-4877/10/5101-0042 © 2010 Springer Science+Business Media, Inc.
FGUP ONPP Tekhnologiya, Obninsk, Kaluga Region, Russia.
Fig. 1. Fundamental layout of a
molding unit for casting large
complexly shaped ceramic pre
forms foraqueous slips.