Oven, kiln, furnace, ovens, kilns, furnaces for drying, debinding, firing and sintering in the ceramic industry.
JTEKT Thermo Systems is represented in Europe by
Crystec Technology Trading GmbH
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Ceramic Furnaces, Kilns and Ovens
The first step in the manufacturing of technical ceramics is the formation
of a green body. In most cases artificial raw material is used. The green body contains beside the
ceramic powder normally also moisture and organic binders. This green body has to be dried.
Then all organic materials, which are volatile, and can be evaporated or burned have to be removed from
the ceramic green body. The last step is the firing or sintering process.
In this step the ceramic body gets its mechanical strength.
JTEKT Thermo Systems (previously Koyo Thermo Systems) is producing different types of furnaces for applications in the ceramic industry like
drying,
debinding, continuous
firing and
sintering. Jtekt Thermo Systems has a lot
of experience in this field and for de-binding and firing applications,
Jtekt Thermo Systems is the market leader in Japan. We can show a long
reference list to you on request.
Drying
In a formed, moist, ceramic material is still some water
remaining. Connected with the drying process is the shrinkage, a size reduction of
the ceramics. The more water is in the original material, the more
shrinkage happens. Shrinkage is also dependent of grain size, kind of the raw
material, and of the production method. Shrinking can be different in different
dimensions. These so called textures need to be considered by a careful drying
process. Otherwise stress or cracks can be the result. Jtekt Thermo Systems (Koyo) can
offer different types of ovens and furnaces for this application. Common
tools are convection ovens.
Debinding, Decarbonization
In order
to achieve a high green body breaking strength, up to 50 Vol% of organic
additives are added. These have to be removed later. This process is called
debinding or decarbonization. Binder burnout is a very critical process and
requires a carefully selected anneal recipe. This is the more important the
larger the green body is. Temperature profile, pressure, gas atmosphere and
anneal time need to be well balanced. Careless heat treatment of the porous
green bodies could result in defects such as warps and cracks.
Especially in the beginning of the process, slow heat ramping is necessary in
order to avoid sudden evaporation of organic components. The debinding
process starts already at room temperature and is finished normally at
600°C. Oxygen can accelerate the decomposition of the binder and therefore
shorten the debinding process.
There is also the possibility that carbonization happens during the
debinding. Organic components are transformed to carbon residues, which
remain in the structure of the ceramics and have to be fired in another heat
process. Temperatures up to 1000°C are necessary. This method is used for
the manufacturing of silicon carbide.
For debinding, often convection ovens,
circulating the gas in the furnace
chamber, are used in combination with an afterburner. The
INH-type oven is equipped with various gas
inlet circuits so that ceramics debinding can be performed. Several
sizes of this oven are available.
The INH-type
oven is for the use of up to 600°C and can keep the oxygen
concentration below 20 ppm. Targeted adjustment of oxygen as well as
moisturization of the process gas can be achieved by this oven. Oxygen
monitoring
with a ZrO2 sensor is
possible. The oven is also equipped with
a program controller of high capacity as a standard item with 7
patterns
and 140 segments. Operation patterns are shown on a display.
As an option a Stange controller can be ordered with this oven.
In order to remove organic decomposition
compounds from the exhaust gas, an after burner (right picture) is quite often used
in combination with an INH oven. For multiple installation of debinding ovens, one
after-burner can be connected to two symmetrically layed out INH ovens.
It is also possible to use continuous
conveyer furnaces for the debinding process.
Continuous Firing
After drying and debinding or carbonization the structure of the
green body is only kept upright by small adhesion forces. The green body is
very weak and has to be handled with great care during the following process
steps.
Conveyer furnaces
are used for debinding and for continuous firing processes. Conveyer types, using
Moldatherm® heating elements are
used normally for ceramic applications.
Loading can be done manually or automatic.
Jtekt Thermo Systems can provide different loading and unloading systems.
Quite often a nitrogen atmosphere is used.
The oxygen level can be controlled and monitored, using a ZrO2
oxygen analyzer. Different process gases can be used also, like inert gases, forming gas or
hydrogen. Temperature profile and gas flow are very important parameters.
This MT type furnace is equipped with a high-precision temperature controller and a muffle which contribute to higher
attainment of atmosphere stability and repeatability in the furnace.
- As an option a Stange controller can be ordered with
this oven.
- Atmosphere stability is assured by purge chambers at the inlet and at the outlet.
A forced exhaust system is installed
with an ejector that is located at the best burnout position.
- For both side firing of samples special holders can be installed on the metallic chain.
- Temperatures up to 1400 °C are possible.
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Firing, Sintering
The goal of the ceramic technology is to produce bodies with high mechanical
strength. The ceramic bonding and therefore also the body strength can
be reached only by firing at high temperature. The firing conditions
enable the sintering process and the formation of the real ceramics. The
transactions during firing result in hardening and solidification of
the products. Porosity is reduced and the body shrinks. Firing time and
atmosphere influence these properties of the technical ceramic.
The form of the body also influences the selection of the recipe: Thin
and dense parts can be fired faster than large and thick ones.
For sintering, Jtekt Thermo Systems (Koyo) can offer
three different types of small laboratory-style bottom-up furnaces. The ceramic parts are loaded on an elevator which
lifts the parts into the furnace. For further simplification of the loading
procedure, the base plate can be slided to the front. The required recipe is
performed automatically. The furnace atmosphere can be defined. Quite often
nitrogen or forming gas are used. For a quick
removal of air, the furnace chamber can be evacuated. The oxygen content in the oven
can be controlled and monitored, using a ZrO2 oxygen analyzer.
| Furnace Properties |
Oven Type |
Max. Temp. |
Size |
Load |
Power |
MU |
1000°C |
64 - 200 l |
100 - 150 kg |
17 - 60 kW |
SU |
1500°C |
27 - 125 l |
30 - 200 kg |
17- 27 kW |
KU |
1700°C |
15 - 216 l |
30 - 300 kg |
9 - 51 kW |
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For high volume production also large
versions of the bottom-up ovens are available (left picture). Special versions exist for vacuum
sintering (right picture).
It is also possible to use special conveyer furnaces for this application.
Koyo Thermo Systems and
Crystec will be pleased to engineer a cost effective system to satisfy
your most demanding and exacting requirements.
