A new grade of SiC element offers improved performance, longer element life and the ability to operate in more demanding applications.
Silicon carbide (SiC) heating solutions have been available since the 1920s. Back then, only hot zone material could be manufactured, and these sections were held in place using water-cooled electrodes. Over the years, SiC elements have evolved into the one-piece, single-diameter rods used today in furnaces all over the world. However, a demand exists in all industrial sectors for elements with improved performance, longer element life and the ability to operate in more demanding applications.
Recently, a new grade of SiC element-Globar® SD-was introduced to meet these challenges. Specifically designed to replace Kanthal's Hot Rod, Globar LL and Silit ED ranges of silicon carbide rod elements, the new elements combine all the best features of these different elements into a single, versatile heating system.
Figure 1. Comparison of the porosity and grain size of SiC heating elements.
Kanthal's Hot Rod, Globar LL and Silit ED ranges each followed their own manufacturing route. The manufacturing process for the Globar SD elements has been optimized, and in-process quality control ensures repeatable and reliable performance. For end users, improved element reliability equates to less downtime and improved process yield.
Additionally, a resulting feature of the more intricate control of process parameters is a better-looking product. This is particularly noticed by those involved in producing advanced ceramic components and electronic substrate ceramics, whose eyes are sharply focused on a high level of quality consistency and performance reproducibility.
Like its predecessors, the Globar SD elements are made through a process of recrystallization. The element is formed from alpha SiC grain, and particle sizes are optimized to achieve a relatively high density, minimize the body's total surface area, and reduce the rate of reaction with the furnace atmosphere. Globar SD elements have a relatively large grain size and are less porous than Hot Rod, Globar LL and Silit ED (see Figure 1).
Figure 2. Time required to increase resistance by 50%.
These features reduce the surface area that is exposed to the furnace atmosphere, which limits the rate of resistance increase with time and extends the life of the elements. This can be seen in the results of laboratory tests, where Globar SD has a much lower rate of resistance increase compared to Kanthal's existing range of recrystallized elements (see Figure 2).
Figure 3. Resistance vs. temperature profile.
Electrical characteristics have also been improved, as shown in the resistance vs. temperature (R/T) profile in Figure 3. Hot Rod elements have a high cold resistance, while the resistance of Globar LL elements can fall dramatically at around 600øC. These characteristics have been eliminated from the typical Globar SD R/T profile.
The new elements are made to the same sizes and electrical specifications as Hot Rod, Globar LL and Silit ED. To convert to the new elements, the user simply removes the old elements and installs the Globar SD elements. There are no special requirements for handling and installing the new elements, and the same methods recommended by Kanthal for the previous elements should be followed. The electrical equipment used with the previous elements will also be compatible with Globar SD.
Globar SD was officially launched in January 2004; since then, thousands of these new elements have been installed around the world in a variety of industries, including a number of different ceramic applications. For example, in France, the new elements are the chosen power source for furnaces used by a world leader in the manufacture of ceramic powders. In Germany, the elements have been found to provide excellent temperature uniformity in the manufacture of ZrO2
components for the automotive sector; and in Asia, the elements are being used in the high-volume production of piezoceramic materials, where they have replaced locally produced SiC heaters.
The performance of the new elements is being monitored in these and many other applications, and feedback received so far suggests a significant improvement in performance. In many cases, end users are noticing improvements even after just a few months of use.
SiC elements have come a long way over the last few years. What began as a list of desirable features is now a well-established product, installed in furnaces all over the world and providing around 2.5 megawatts of power.
However, the evolution of SiC elements is not yet finished. Development work is continuing in an effort to improve the performance, properties and reliability of Globar SD even further.
For more information about the new heating elements, contact Kanthal Globar, P.O. Box 339, Niagara Falls, NY 14302; (716) 286-7604 or (877) GLOBAR9; fax (716) 286-7601; or visit http://www.kanthal.com .