Low Temperature Kiln Control

Fuel fired periodic kilns are widely used in ceramic firing applications. ?Many products are particularly sensitive to temperature spikes and transients during the initial low temperature portion of the firing cycle. For example, clay based materials may not be thoroughly dried prior to firing, and rapid heating from room temperature can cause mechanically held water to flash to steam, causing fragile parts to crack.. Similarly, complex technical ceramics, with high organic concentrations, often require careful control of the initial heating rate

Even if the product is well dried, water can be reabsorbed while awaiting the firing process. Some products are very sensitive during initial heating, and ?temperature excursion during the first few hundred degrees can cause rejects.

As an example, below is the temperature trace for a conventional periodic kiln with multiple zones of temperature control. The graph (Figure 1) illustrates a typical problem—a very rapid temperature increase at the start of the heating cycle in all zones with nearly all of them exceeding 212°F within a few minutes of burner ignition. Any retained moisture in the product rapidly vaporizes and can create internal fractures within the part, resulting in rejects.

Implementation of LTC

Traditionally, to minimize the initial disparity of temperatures at the start of a cycle, operators light a few burners at a time to reduce the initial heat input. With a few burners now operating, circulation within the kiln is compromised and does not provide adequate homogeneity of temperature within the kiln. Since this is a manual intervention, subsequent lighting of burners is subject to operator variations and is not always ?repeatable, leading to variable rate heating from cycle to cycle.

Swindell Dressler DynaPulse with the Low Temperature Control (LTC) option addresses this problem. Through a combination of software and combustion control, this system is capable of heating the kiln starting at room temperature with programmable heating rates. The curve below (Figure 2) illustrates this extraordinary control.

The LTC system automatically lights all of the burners and manages their output without any further intervention.

This kiln has eight (8) control zones operating with +/-2°F conformity to setpoint with no temperature spikes.

The end result: higher product yields, no operator intervention, and accurate repeatable results!