Causes and avoidance of firing-related damagePart 1: Diffusion-dependent reactions in the heating-up zone up to 500° C

This multi-part contribution summarizes the raw material-dependent reactions that can cause damage to products during the firing process. Thermally induced physical changes in the developing body and the evolution of reaction gases in the course of heating are investigated with regard to their effects on quality impairing processes.

As anticipated, the nature and intensity of such reactions are largely determined by the raw material composition and the targeted type of product. During the heat-up process, a highly porous, energy-rich body for vertically perforated bricks will produce reactions different to those elicited by a dense-firing, highly argillaceous clinker brick body. Due to the diversity of individual reactions, the processes are arranged according to certain temperature ranges to facilitate their detailed description. The technical contributions are therefore subdivided according to temperature, i.e., up to 500° C, 500° C to 800° C and above 800° C. Information on the causes and avoidance of damage is offered to interested readers for case-by-case application to the operational tunnel kiln process.

1 General

The firing of heavy clay products is subject to a number of such limiting factors as expansion and contraction processes, endothermic and exothermic reactions, reaction gas evolution and the conversion and neoformation of mineral phases. These processes are rate-determining for the firing of any heavy clay product. In the brick and tile industry, a broad range of products is made from a diversity of raw materials with different mineral compositions, chemical compositions and particle size distributions. Consequently, the firing process must be adjusted to the respective raw materials...

Related articles:

Technical Paper

Causes and avoidance of damage on account of diffusion-dependent reactions in the preheating zone of tunnel kilns

1 Introduction The firing of heavy clay products is subject to a number of such limiting factors as expansion and contraction processes, endothermic and exothermic reactions and the conversion and...

more
Issue 03/2010

Causes and avoidance of damage on account of diffusion-dependent reactions in the preheating zone of tunnel kilns with specific consideration of the pore structure of green bricks

1 Background After they have been dried, green clay bricks enter the preheating zone of the tunnel kiln with a varying residual water content. In this preheating zone, the following processes take...

more
Issue 02/2010

Concepts for reducing the loss of exhaust air from dryers in the clay brick and tile industry

1 Initial situation and problem description More than half of the energy used in the production of clay bricks and tiles is currently used for drying green bricks and tiles. The hot air needed for...

more
Issue 6/2018

New concept for improving heat transfer in tunnel kilns

Ceramic products have to be fired before they can be used, and tunnel kilns are well-suited for the job. To help optimize a kiln‘s energy efficiency, fans can be installed in the preheating and...

more
Issue 6/2015

Avoidance of damage due to strength-reducing reactions in the preheating zone of tunnel kilns

1 Objective Decomposition and transformation reactions taking place at temperatures between 500 and 800°?C (900°?C) provoke a loss of strength in brick green bodies. The purpose of these...

more