Austrian refractories manufacturer Rath successfully developed the refractory lining of a test roller furnace for the ceramics industry. The furnace was designed by Onejoon GmbH, a German manufacturer of industrial furnaces. It is one of more than 15 projects the two companies have successfully collaborated on since 2020.

Test furnaces offer companies the ideal conditions to test their products, as well as the necessary process conditions in terms of atmospheres, temperature regimes, airflow, process times and more. Based on these factors, subsequently installed production furnaces can be better and more precisely designed. The initial requirement is to meet the customer’s expectations of such test furnaces, which include a high degree of flexibility in application and process control, as well as the ability to carry out tests quickly with meaningful results. Associated with this is, of course, good transferability to production plant design.

Rath, a supplier of refractory technology with seven production sites in Europe and the United States, acted as a full-service provider – supplying engineering, material supply and installation of refractory lining – for a test roller furnace for the ceramics industry. A technically demanding solution was required because this complex test roller furnace, which is ideal for the production of thin-film ceramics has numerous lances, nozzles and openings for gas flushing, extraction and measurement. In addition, separation weirs were installed at very short intervals to allow the temperature curves to be set as accurately as possible.

Fig. 1. The refractory lining of a test roller furnace.

Challenge: 3D Design and Firing Temperature

The most challenging aspects of the refractory lining for this test furnace were the firing temperature of 2552°F (1400°C) and the 3D design.

“While Onejoon provided a precursor to the furnace that included some useful aspects, it only operated at 1832°F (1000°C). So, the material qualities had to be adapted to the required 2552°F (1400°C) and the ceiling design changed to our ALTRA Composite System,” said Alexander Jüttner, managing director ceramics and special furnaces at Rath Group.

Molded fiber parts were used for the refractory lining: Kerform KVS 164, KVS 144 and KVS 121. The 3D design resulted in many individual parts (special and milled) that fit together perfectly to produce the optimal furnace.

Sealing was another particular challenge in this case because roller furnaces don’t have a metallic muffle in which the process takes place and which contributes enormously to the seal.

The gas flow in the furnace chamber was also a challenge because the gas and heat exchange between the individual heating sections should be as low as possible during operation. In addition, the furnace had to meet the customer’s requirements for a variety of firing curves and atmospheres (e.g., N₂, O₂, forming gas) that apply to the thin-film ceramics sector.

In general, when such a roller furnace is manufactured, special attention must be paid to the construction and installation of the rollers and roller guides. They must be at exactly the same level; there must not be any difference in height.

Fig. 2. The refractory lining of a test roller furnace.

Ideal Test Furnace for Production of Thin-Film Ceramics

Onejoon’s customers benefit from this test roller furnace in several ways. Thanks to the roller transport, a very smooth and continuous movement of the material is guaranteed, and the speed and dwell time can be precisely adjusted. Furthermore, exact process control is enabled due to the number of heating zones (14) and good separation of the zones from each other. The gas feed rate can be controlled in each heating zone.

The multi-layer furnace furniture stack (four to five layers) is also advantageous. Additionally, exhaust gases can be discharged in each zone, resulting in a high degree of flexibility of flow control within the furnace. Last but not least, customers benefit from the combination of multiple atmospheres in the furnace and from the fact that different types and sizes of product carriers can be used.

“While this test furnace is ideal for the production of thin-film ceramics, a roller furnace is very flexible in general and goes far beyond its use for ceramic products. It has to be considered on an individual basis whether a product is suitable for testing in this furnace,” explained Martin Creutziger, test center manager at Onejoon.

The test furnace has already been commissioned, and first tests by customers were performed in mid-August 2022. Summarizing the collaboration, Simon Schurr, vice president of advanced materials and processes at Onejoon, said, “Rath is a long-standing and competent partner and has also been a trusted supplier for many years.”

Fig. 3. The refractory lining of a test roller furnace.

Meaningful Results for the Design of Future Production Plants

Before tests are run, the exact key data must be discussed with the customer and the chances of success estimated individually. To carry out the tests, the defined parameters are set in the furnace. It can then take some time until stable conditions are established. If any of the parameters change, it is necessary to wait again until stable conditions are achieved.

The material may have to be prepared in advance (e.g., installing thermocouples). It’s also common to determine the material properties (weight, geometric dimensions, etc.) in order to determine changes caused by the process. Finally, the material is placed in the goods carriers. The passage through the furnace is automatic. Afterward, the goods carrier and the material are removed from the feed station. During the test, the process is monitored by Onejoon staff, who document the progress of the entire process.

For more information: Based in Austria, Rath manufactures refractories from seven production sites in Europe and the United States. The company can be reached at www.rath-group.com or via email at info@rath-group.com.