Oven, kiln, furnace, ovens, kilns, furnaces for drying, debinding, firing and sintering in the ceramic industry.
Koyo Thermo Systems

Koyo Thermo Systems Co., Ltd. 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 engineering 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 it the firing or sintering process. In this step the ceramic body gets his mechanical strength.

Koyo Thermo Systems is producing different types of furnaces for applications in the ceramic industry like drying, debinding, continuous firing and sintering. Koyo Thermo Systems has a lot of experience in this field and for de-binding and firing applications, Koyo 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. Koyo Thermo Systems can offer different types of ovens and furnaces for this application. Common tools are convection ovens.

Debinding, Decarbonization

Inert gas oven, kilnIn 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.

after burner GMThe 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 MoldathermTM heating elements are used normally for ceramic applications.

Loading can be done manually or automatic. Koyo 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.

conveyer furnace
  • 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.

Firing, Sintering

bottom up kilnsThe 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 engineering ceramics. 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, Koyo Thermo Systems can offer three different types of 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.

Oven Type Max. Temp. Max. Load Power

MU

1000°C

100 - 150 kg

17 - 60 kW

SU

1500°C

30 - 200 kg

17- 27 kW

KU

1700°C

30 - 300 kg

9 - 51 kW

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 a special conveyer furnace for this application.

bottom up ovens    sinter furnace, furnaces


Koyo Thermo Systems and Crystec will be pleased to engineer a cost effective system to satisfy your most demanding and exacting requirements.

Crystec Technology Trading GmbH will be pleased to further discuss details with you.
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