Structural bricks provide greater insulation, more protection from the elements, and the appeal and durability that have always made clay brick a desirable building material. The manufacturing of large structural clay brick presents challenges to brick makers in two of the critical processes involved in brick making, extrusion and drying. In this blog we will focus on the drying part of the process.
Before bricks can be fired, water needs to be removed from the clay product. Although water does not have to be taken out 100%, any moisture left will be removed very quickly in the kiln causing issues and losses in the brick production. This is why safe drying is a key part of the structural brick manufacturing process.
The characteristics of the brick body being dried can contribute to successful drying or cracking. The characteristics of the brick body include the type of clay minerals, the particle size distribution, the use of non-plastics, and the amount of moisture in the body. Large structural clay brick are formed with thick shells designed to provide sufficient compressive strength in the fired, finished product. These thick shells can have a tendency to crack during the drying process. The tendency of the shells to crack can be overcome through an understanding of drying and what may be done to overcome the tendency to crack.
- The particle size distribution of a clay body can vary greatly depending on the clay minerals, grinding system, addition of additional materials, and the ratios of the materials being mixed. Particles can be separated into sand, silt, and clay sizes. The ratio of these particle sizes in a clay body will have an effect on extrusion, drying firing, appearance, etc. Clay sized particles will tighten a body and slow the drying process while sand sized particles will open a clay body and allow for increased capillary flow. Increased clay particles can help with the adhesion of the brick body during drying while increased sand sized particles can result in decreased adhesion. Clay conditioners may be added to clay bodies to increase adhesion during drying while allowing the percentage of sand sized particles to be high enough for increased capillary flow. Particle size distribution can be tested through screening methods, sedimentation methods, and laser scattering. Some testing can be performed in house while laser scattering can be performed by outside laboratories.
- Drying is defined as the removal of moisture from the brick body. The moisture added to the clay mix in the pug mill is meant to make the clay more workable and easy to extrude. Normally reducing the additional water can result in problems extruding or a reduction in the plasticity of the clay. Clay conditioners can be used to help reduce the amount of water necessary to make the clay workable and plastic enough to be extruded and textured.
There are other ways of controlling and optimizing the drying of bricks during the production process. Maybe you will like this blog we wrote about how to optimize brick production through faster drying.
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