Tunnel Kiln Q&A;
J.J. Stevenson shares insights regarding Deltech, Inc.'s new small-scale electric tunnel kilns.
What made Deltech decide to begin offering tunnel kilns?
Many, if not most, of our new products over the years have come about after we’ve been approached by a current or potential customer with an application requirement that required some R&D on our part. In this case, an existing customer needed to scale up, but in a way that ensured reproducibility of the outcomes they were getting from their Deltech benchtop furnaces. A small-scale tunnel kiln seemed to offer a good solution.
Is there a practical limit on how small or large electric tunnel kilns can be?
The limit on the small side depends more on what scale makes sense to the customer (i.e., it depends on when they see a need to move from a benchtop unit to a small production furnace). That decision could be based on typical considerations such as expected overall cost savings per piece, ability to meet increased demand, and even superior product quality. Products and processes are sufficiently complex so that furnace size, geometry, and mode of operation can make a huge difference.
An additional consideration is whether a tunnel design makes the most sense, or whether it is better to move to a bottom load or top hat production-size furnace. But one major design consideration is how long the furnace must be to achieve the desired product outcomes. The length must be enough to allow for sufficient soak time in the optimal temperature range.
On the large side, the same considerations apply because at some point the choice must be made between staying with resistance heating and making the change to gas. Doing so is a complicated matter for product outcomes.
Most tunnel kilns are gas fired, brick lined and hundreds of feet long. In addition to being much smaller in scale, what else is different about the Deltech tunnel furnace design?
They are electric fired and fiber lined. They are not meant to compete with gas-fired furnaces, but rather to offer a relatively inexpensive way to scale up without radically changing the process conditions. It is well-known that moving from batch to production-size furnaces can result in changes in product outcomes, even when all the furnace features and firing parameters are maintained.
What information do you need from a potential customer to begin the design process?
Dimensions, weight, and composition of the work product, throughput time, special requirements such as a means to use purge gases, maximum operating temperature and temperature ranges, product load/unload methods, and tolerance for furnace temperature gradients.
What is the maximum operating temperature you offer for these furnaces?
1,800°C. Depending on the specified temperature, we might use ceramic heaters, silicon carbide or molydisilicide heating elements in the design.
These days, many manufacturers have propriety compositions and fabrication methods.
That’s true. We are often asked to execute NDAs (nondisclosure agreements). Being able to freely exchange information is critical to the custom design process.
Do you have to make changes to the control systems for the operating requirements of tunnel kilns? Since the control systems are all certified by Intertek to be UL508A compliant, do different certification requirements apply?
Our certification allows for modifications as long as UL-listed components are used and the UL requirements are met. Most every control system for a custom furnace has unique features, and every tunnel kiln is custom.
Can the existing furnace and control system be modified?
Modifying the control system to incorporate new features or more power is relatively straight forward. Suppose a manufacturer goes from a batch furnace to a small-scale tunnel kiln, and then finds that it needs to change its process for a new product or needs to add length to the kiln (perhaps to increase product volume). In this case, modules can be added. The modification process is simplified if the original unit is designed and fabricated with that possibility in mind.
For more information, visit www.deltechfurnaces.com.