Worldwide, HALDENWANGER is the only manufacturer of rollers for kilns and furnaces able to supply the complete programme of roller materials. With our know-how of producing different mullite and SiC-based materials we offer custom made solutions.
Roller Hearth Kilns and Fast Firing
Roller hearth kilns for fast firing of wall and floor tiles have been used for nearly 25 years. In this type of kiln the products to be fired are transported through the kiln by means of rotating ceramic rollers. Since the beginning HALDENWANGER has supplied the various manufacturers and users of kilns with oxide and non-oxide ceramic rollers. In the past, the diameter of rollers was up to 55 mm with a length of approx. 2000 mm. Because of increased capacity demands, the wall and floor tile industry asked for more efficient kilns. That is the reason why kilns became wider and therefore the rollers became longer. Today there are roller diameters of 30, 33.7, 40, 42, 45 and 50 mm for maximum roller length of approx. 3700 mm. This corresponds to a useable kiln width of approx. 2500 mm.
Roller tolerances have also become much tighter. Today, diameter tolerances of +/- 0,2 to +/- 0,3 mm are typical and roller bending is as small as 1,0 to 1,5 mm which corresponds to a TIR of 2-3 mm. Additionally, the overall length taper specification of no more than 1mm is today a standard requirement.
Production capacity allows us to produce nearly all standard dimensions. The rollers must have good refractory properties to guarantee a perfect operation for a given temperature and load. Furthermore, there is the need to change rollers during kiln operation. In such cases, the high thermal gradients which rollers have to withstand means that a material must be selected having sufficient thermal shock resistance.
Ceramic Roller Materials and Their Applications
Oxide ceramic rollers, these are our materials Sillimantin 60, Sillimantin 65, Sillimantin 60 NG, are used in roller hearth kilns for firing wall and floor tiles. Non-oxide ceramic rollers, these are our materials Halsic-R (RSiC) and Halsic-I (SiSiC), are used in roller hearth kilns for firing sanitary ware and porcelain. These materials are used because of the better creep resistance compared to the oxide ceramic rollers.
Installation of Rollers
Before installing the rollers in the kiln they must be completely dry. This is very important if the rollers are changed during operation. Drying is usually done by storing the rollers on or above the furnaces (utilisation of waste heat).
Reducing Heat Losses by Plugging Open Ends
Heat losses in the kiln arise from the open ends of the roller. By using ceramic fibre plugs the rollers are sealed at both ends. The plugs usually have a maximum length of 100 mm to 200 mm.
Avoiding Bending of Rollers
The oxide ceramic rollers must continue to rotate whilst they are heated up or cooled down. This is very important, for example, if a roller hearth kiln is to be shut down for maintenance or technical reasons.
Stationary oxide ceramic ollers, even for a short time, results in roller bending. The drive to the rollers should never be switched off even at kiln temperatures of 500 °C to 600 °C, as frequently occurs. Stationary rollers subjected to the above-mentioned temperature will be damaged! When the kiln is re-started, considerable breakage is to be expected. The rollers must also be kept rotating even over short breakdown periods.
Application of Haldenwanger Ceramic Rollers
HALDENWANGER ceramic rollers are used for the firing of:
• Wall and floor tiles up to 1300 °C
• Tableware porcelain up to 1420 °C
• Sanitary porcelain up to 1300 °C
• Ferrites up to 1300 °C on supporting setters
• Heat treatments of metals up to 1200 °C.
Ceramic Supporting Rollers for Glass Tempering Furnaces
In glass tempering furnaces the glass is transported on rollers through the furnace. Product is run directly on the rollers, i.e. without supports.
The tempering time can be regulated via the rotational speed of the rollers as well as by applying different heating systems.
All large sized glass plates are subject to this secondary thermal treatment because of new regulations. (single pane safety glass)
Reasons for Tempering Glass
The aim of this process is to cause pre-stressing the glass through heat, so that there are no sharp splinters if the glass breaks. Like safety glass, the pane must break into many harmless particles.
Properties of Ceramic Rollers for Glass Tempering
Because of the sensitivity of the glass surface, the ceramic rollers used must be very smooth and free of the smallest undulation. The bending and the concentricity are very important factors, too.
Furthermore, the ceramic material must have good thermal shock resistance properties in order to withstand changes of temperature occurring in the process.
Materials for Glass Tempering Furnace Rollers
The material used for these rollers is our Fused Silica. In use today are solid as well as hollow fused silica rollers which can be supplied with mounted metal end caps.