Nabertherm is renowned as one of the leading companies in the branch for almost 50 years. 

GERO is established in the market as a manufacturer of technologically sophisticated furnaces with application temperatures of up to 3,000°C.

The sintering process is a major step in the production of technical ceramics. Controlled atmospheres and temperatures are necessary to create homogeneous textures. Tailor made furnace design is essential to manufacture high quality ceramic components.

Nabertherm and GERO offer a range of high temperature furnaces with the following features:

• chamber, hood, shaft and tube furnaces
• temperature range from 300 to 3000°C
• volumes from 1 to 20,000 litres
• gas sweeping (nitrogen, oxygen, argon and hydrogen)
• vacuum systems for as low as 10³ bar
• special furnace insulation for aggressive media
• catalyst to decontaminate exhaust gases
• switchgear from program control to all automatic operation control
• multizone control for temperature gradients of ±1K

The following gives a selection of Nabertherm and GERO sintering furnaces:

1. Chamber Furnace HT 160/16/S3

The chamber furnace HT160/16/S3 (Fig. 1) is designed to manufacture ceramic components at 1,600°C. Gas sweeping allows sintering in controlled atmospheres. A magnetic door lock prevents the furnace from opening while in operation. 2 program controllers operate redundantly. i.e. in case of failure of the main controller, the sintering process is automatically continued by the safety controller.

Fig. 1:  Chamber Furnace HT160/16/S3 (Nabertherm)

2. Hood Furnace HT64/17/LTS

The HT64/17/LTS (Fig. 2) is used for sintering oxide ceramics at a temperature of 1,750°C. Four-sided heating guarantees extremely good temperature distribution. Fast heating and cooling and low heat loss is provided by insulation made of high-quality vacuum thermoformed Al2O3-fibre plates. A thyristor-controlled switchgear guarantees a consistent temperature accuracy of ±2K.

Fig. 2: Hood Furnace, HT 64/17/LTS (Nabertherm)

3. Chamber Furnace HTZ 01/20

Nabertherm is able to offer a chamber furnace for a maximum temperature of 2,000°C in oxidising atmospheres (Fig. 3). The outer chamber is heated by 4 Kanthal-Super elements. The inner chamber with a volume of 1 litre is zirconia insulated and heated by 4 zirconia elements. Both chambers are controlled separately and follow fixed heating and cooling rates.

Fig. 3: Chamber Furnace HTZ01/20 (Nabertherm)

4. Chamber Furnace HT 276/17

The chamber furnace HT276/17 (Fig. 4) is designed to sinter oxide ceramics at 1,700°C. The furnace is equipped with a warm-air inlet (fan and heater) to guarantee excellent temperature distribution and to transport the outgoing binder to the catalyst. The furnace has doors on both sides for easy and comfortable loading.

Fig. 4: Chamber Furnace HT 276/17 (Nabertherm)

5. Hood Furnace HT 180/17/LTS

The furnace is equipped with a moveable hood and two electrically moveable tables (Fig. 5). In a useful volume of 180 litres, oxide ceramics are sintered at a temperature of 1,700°C. Continuous charging and utilisation of stored heat result in economical and efficient production cycles. The switchgear is equipped with a control system to control all electrical movements. Four-sided heating by 23 Kanthal-Super elements provides excellent temperature distribution. To increase the cooling rate, the hood is lifted gradually from 1,100°C on.

Fig. 5: Hood Furnace HT180/17/LTS (Nabertherm)

6. Shuttle Kiln W1260/14/S

The shuttle kiln W1260/14/S (Fig. 6) was designed with the requirement that the charge of thin-walled ceramic tubes should be free from shock or vibration. Therefore, the furnace was designed for moving on rails while the table remains fixed. Production takes place in three similar furnaces of 1260 litres at 1,340°C. Five-sided heating and four-zone regulation guarantee excellent temperature distribution.

Fig. 6  Shuttle Kiln W1260/14/S (Nabertherm)

7. Shuttle Kiln W10800/HS1

Ceramic grinding wheels are manufactured at Slip Naxos of Vastervik/Sweden at a temperature of 1,340°C. The production takes place in six shuttle kilns W10800/HS1 (Fig. 7). Five-zone-regulation provides extremely good temperature distribution in a useful volume of 10,800 litres. A programmable cooling fan in combination with automatically driven vapour vent flaps results in short cooling terms.

Fig. 7  Shuttle Kiln W10800/HS1 (nabertherm)  

8. Hood Furnace HT1010/17/LTS

The HT1010/17/LTS (Fig. 8) is designed to manufacture thin walled tubes made of oxide ceramics. At a temperature of 600°C the binder is burned-out and subjected to catalytic afterburing. The sintering process takes place at a temperature of 1,700°C. 30 Kanthal-Super elements guarantee temperature distribution of ±5K in a volume of 1010 litres. Due to a specially constructed base, the furnace can be charged with a load of as much as 1200 kg/m².

Fig. 8  Hood Furnace HT1010/17/LTS (Nabertherm)  

9. Hood Furnaces N352/AS and HT352/17/LT

The forced-air oven N352/AS and the high temperature furnace HT352/17/LT (Fig. 9) are designed to burn-out the binder of oxide ceramics at 600°C and sinter the material at 1,700°C without unloading the bogie. Four-sided heating guarantees temperature distribution of ±5 K in a useful volume of 352 litres.

The HBO/400 (Fig. 10) can be operated under vacuum or non-oxidising atmospheres at a maximum temperature of 2,000°C. Insulation and heating elements are made of graphite. Charging occurs from above when the hood is raised. Dornier at Immenstaad/Germany uses the HBO/400 for manufacturing fibre reinforced ceramics. The chamber is evacuated and swept with nitrogen twice in order to obtain an inert atmosphere. Temperatures. evacuation, gas sweeping and hood movements are controlled automatically.

Fig. 10:  Hood Furnace HBO/400 (GERO)  

11. Ten Zone Tube Furnace ZZ200-2000

The ZZ200-2000 (Fig. 11) is designed for heat treatment of ceramic superconductor materials. During 3 heating periods of 40 h each, 2000 mm long wires are tempered at 830°C. Due to a ten zone regulation, temperature distribution of ±0.5 K can be attained.

Fig. 11:  Ten Zone Tube Furnace ZZ200-2000 (GERO)

12. Tube Furnace BKZ 20-500/5

Hoechst AG at Frankfurt/Main, Germany uses the BKZ 20-500/5 (Fig. 12) to produce ceramic superconductor materials at a maximum temperature of 1,500°C. The zone melting process requires extreme temperature gradients to ensure that only a small area of the speciment is liquefied. This offers the chance to grow monocrystals without changing the specimen's shape. The plant is fibre insulated and heated by Pt-Rh heating elements. The vertical five-zone tube furnace moves at 1 mm/h over the bar-shaped specimen (10 mm in diameter). The middle heating zone provides a power of 120 W over 20 mm length which leads to a temperature gradient of 140 K/cm.

 
Fig. 12: Tube Furnace BKZ 20-500/5 (GERO)  

13. Hood Furnace HBO 250

The HBO 250 (Fig. 13) is used for tempering ceramic superconductors for 40 h at 800°C in a pure oxygen atmosphere. With assistance of a centric heating section, a temperature gradient of ±1 K is not exceeded even during heating and cooling periods. Due to a mobile, high temperature cone made of heat resisting steel, a cooling time of 4 h can be reached.

 
Fig. 13: Hood Furnace HBO 250 (GERO)  

14. Microwave Sintering Plant

Using microwave for sintering ceramic components is still new: The direct application of energy into the material allows fast and homogeneous heating. Microwave sintering causes smaller grains, bitter material properties and lower sintering temperatures.

GERO is developing, in cooperation with the Institute for Plasma Research (IPF). Stuttgart, a production plant of 500 litres volume for sintering silicon nitride and alumina components. A plant of 40 liter is already in operation at a working frequency of 28 GHz (Fig 14), The production plant will allow a process temperature of up to 1,700°C and can operate at 2.45 or 28 GHz.

 
Fig. 14: Microwave Sintering Plant