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Kaolin
In order to serve our customers better we are we are introducing Kaolin and Chamotte of Bulgarian origin from Kaolin AD. Kaolin AD is one of the most well known suppliers of Kaolin and Chamotte in the world for applications in Glazes, Porcelain, Earthenware/Stoneware, Fine Fire Clay and Vitreous China.
In India, Futura is the exclusive agent of all products of Kaolin AD. The following are the specifications of various products offered by Kaolin AD.
To obtain any information or samples or to talk to someone about Kaolin related products please contact kaolin@futuraceramics.com
Website : www.kaolin.bg
CHAMOTTE in PRODUCTION of FIRE CLAY(FC) & FINE FIRE CLAY(FFC)
CHAMOTTE
Chamotte is calcined kaolin (china clay) which fired at 1350 °C in rotary kilns and milled after firing to get controlled thermal expansion and particle size.
Chamotte produced by Kaolin AD is not formed from raw clay, it is formed from refined kaolinwhich has 34-35% Al2O3 content. The refined kaolin is calcined and ground to specified particle size ranges.
Chamotte has a relatively high thermal expansion about 0.4% at 600 °C. This enables the body and glaze expansion to be matched without the need for large amounts of quartz in the body, minimizing the tendency to dunting.
Kaolin AD is a good supplier of chamotte which has 60,000 tons/year production with chamotte specifications for particle size distribution and thermal expansion. Kaolin AD will be able to show quality control data to meet the specification.
FC and FFC
A mixture of chamotte, kaolin, ball clay and quartz is processed to form the body of FFC or FC. Feldspar using is optional to adjust shrinkage. The result after firing is a medium-fine grain mass with a water absorption rate not exceeding 9% for FFC, and a medium-large grain ceramics mass with water absorption is under 13%.
A. Formulation of fireclay bodies
Fire clay or fine fire clay bodies are formulated within the following limits:
Chamotte
25-50%
Kaolin (China Clay)
10-20%
Ball clay
20-35%
Quatz
10-20%
Feldspar and/or other fluxes
0-10%
1.
The most important control elements are the particle size of the chamotte and the thermal expansion. The expansion is controlled by altering the amount of quartz used. For increasing the expansion coefficient, the quartz content in the formulation has to be increased.
2.
Influence of clays-on the water absorption, deformation and mechanical resistance. In the case that the fluxes completely absent, the alkali contained in clays are almost exclusively responsible for the vitrifiction of the body.
3.
The slip FFC is prepared to typical vitreous china slip rheology. Density (specific weight) of slip is generally higher than vitreous china slip. Casting and hardening times are similar to V.C. The big difference is that fine fireclay is porous, about 7-13% and can result in crazing if the glaze expansion is not well balanced to that of the body.
Percentages of components change according to critical target values like total shrinkage, thermal expansion, dry strength and casting rate.
Examples of body formulations are as follows:
I
II
III
IV
Chamotte (-300µ)
33
26
12
34
Chamotte (-125µ)
-
-
12
-
Ball Clay (75-80 kg/cm2)
35
15
27
-
Ball Clay (90-100 kg/cm2)
-
13
-
26
Kaolin
13
20
20
18
Quartz (-45µ/-63µ)
14
17
23
16
Feldspar (-45µ/-63µ)
5
9
6
6
B. Slip control in FFC and FC production
Physical characteristics of a fire or fine fire clay slip.
Fire Clay
Fine fire clay
Specific weight in g/cm3
1900 ÷ 2050
1850 ÷ 1950
Brookfield viscosity in Poise
18 ÷ 20
15 ÷ 18
Content of solids (% in weight)
80 ÷ 78
74 ÷ 76
Gallenkamp viscosity in degrees
180 ÷ 200°
190 ÷ 220°
Gallenkamp thixotropy in degrees
40 ÷ 50°
30 ÷ 50°
Controls carried out on a slip are:
1.
Density (specific weight)
2.
Temperature
3.
Viscosity
4.
Thixotropy
5.
Thickness formation time
All hard materials (chamotte, quartz and feldspar) are powder form and all plastic materials (ball clay ad kaolin) are refined in formulation. It is not recommended using unproccessed materials (noon ground or raw) in body formulation to prevent the big changes of thermal expansion which causes dunting cracks after firing.
C. Engobes used in FFC and FC production
The aims of the engobes are mainly:
1.
To make the thermal expansion coefficient to get equal for both body and glaze.
2.
To make the surface of the glazed unit flat and smooth.
The engobes formation may vary within the following limits:
Unfired and/or fired kaolin
40-50%
Ball clay
0-12%
Quartz
25-33%
Pegmatite
22-50%
The fire sanitary ware engobe is applied before glazing (density of 1550-1650 g/l)
