Crystec Technology Trading GmbH

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.

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 are available.

The INH furnace can be operated up to temperatures of 600°C. The oxygen content can be reduced to below 20 ppm. Targeted oxygen supply as well as humidification of the gas in the furnace is possible. The oxygen content can be determined with a ZrO₂ sensor. The furnace is controlled by a programmable controller that can store 7 recipes with 140 program steps. The entered steps are displayed on a screen. Optionally this furnace can be supplied with a Stange controller.

An afterburner (photo on the right) is often used to remove organic decomposition products from the exhaust gas. When multiple furnaces are installed, one afterburner can operate two symmetrically arranged furnaces.

The use of continuous through‑furnaces for the debinding process is also possible.

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.

Conveyour-furnaces are used for continuous firing processes. The conveyour-furnaces used in the ceramic sector normally use Moldatherm® heating elements. Loading and unloading of the furnace can be automated. JTEKT Thermo Systems can supply different loading and unloading systems.

Often a nitrogen atmosphere is used. The oxygen content can be measured with a ZrO₂ oxygen analyser. Other process gases such as inert gases, forming gas or hydrogen can also be employed. The temperature profile and gas flow in the furnace critically determine the process result.

The MT furnace shown here is equipped with a highly accurate temperature controller and a muffle designed for high gas stability and reproducibility.

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  As an option a Stange controller can be ordered with this oven.
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  Atmosphere stability is assured by purge chambers at the inlet and at the outlet.
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  A forced exhaust system is installed with an ejector that is located at the best burnout position.
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  For double‑sided firing of samples, these can be fixed on special holders mounted on the metal mesh.
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  Operating temperatures up to 1400 °C are possible.

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. Nitrogen or forming gas is often used. To ensure 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.

For high throughput production large versions of the vertical furnace are available. Special types exist for vacuum sintering.

JTEKT Thermo Systems and Crystec look forward to building a cost‑effective system for you that meets your most demanding requirements.