Articles

July 22, 2019 (Process Heating Magazine)

With industrial heating processes that require some type of heating, drying or curing, several reasons are commonly cited for process improvements. Typical drivers for improvements include:

• Trying to achieve a boost in productivity through an increase in system line speed.
• A significant reduction in energy costs.
• A decrease in maintenance costs.
• A decrease in downtime.
• An improvement in product quality (thereby reducing rejects and rework).
• A reduction of labor costs.
• A reduction in floor-space requirements.
• A new product introduction.
• A change in business owner or management.
• The desire to keep up with competition.
• Electric and gas infrared (IR) heat processing are exciting technologies when implemented appropriately, and they may provide some of these benefits. Infrared heating, however, it is not right for every process. Can infrared be used effectively in yours?

If you are looking to increase productivity, infrared is a good technology to consider. Much of the time, adding infrared heating to the beginning of an existing gas-fired or electrically heated hot air convection oven will provide a 30 to 100 percent increase in line speed and, therefore, throughput. Infrared heat is transferred directly to product coatings and product substrates, making heat transfer much faster than convective heating. With infrared, you do not have to heat the air first, and you do not have to move the heated air at a high velocity in order to then heat product coatings and substrates.

It is quite popular today for companies to look for and install process heating technologies and systems that are energy efficient, or “green.” Many states and utilities provide tax breaks, reduced rates and subsidies for doing so. That said, if you are looking to reduce the operating energy costs of an existing gas-fired or electrically heated hot-air convection oven, you maybe be able to save 20 to 50 percent of your operating costs with infrared. Infrared transfers heat directly to the product coatings and substrates with minimal heat loss in air — and without the need to purposely preheat the air before heating a coated or uncoated product. Also, in the case of powder-coating processes, for example, with an infrared preheat or boost at the entrance to an existing convection oven, you are able to also turn up the air velocity in the first oven zone. This increases the efficiency of the existing convection portion of the system as well.

Perhaps reducing maintenance costs and downtime is the goal. In particular, electric infrared systems are simpler to implement than convection ovens. There is no hot air heater house, no gas train and, most of the time, there is no air recirculation blower or air plenums. Therefore, there are fewer components to fail, troubleshoot, preventively maintain and replace. Air temperatures in an infrared oven typically are lower than those in a convection oven, resulting in less wear and tear on the oven structure and enclosure. The lower air temperatures translate into less time to get in and fix a problem. Infrared systems can be built somewhat modularly. If and when heaters fail or are damaged, they can be removed and replaced with a spare to minimize system downtime.

There is a lack of necessity for moving air in most infrared heat zones or ovens. This helps minimize or eliminate the transfer of dirt or previously processed powder coatings to newly coated products being processed. This will help to improve product quality and minimize rework.

Better productivity can result in lower labor costs. Most infrared heating, drying and cure oven systems and combination infrared/convection oven systems provide increased productivity by facilitating the ability to run faster conveyor line speeds as well as greater part density on a production line.

Infrared helps shorten the heated oven dwell-time requirements — often significantly. Whether added as a boost to an existing line or as part of a new system, the shorter dwell time required for an infrared or infrared/convection combination system will result in the use of less floor space than a convection oven alone would require. In web applications, for example on papers and film webs, drying or curing surface coatings by adding infrared or infrared with air heaters can allow a manufacturer to run faster or completely replace a convection oven with a comparable process heating solution in a much smaller footprint.

As companies develop, grow and look to introduce new products, the new requirements often push the limits of an existing industrial oven system’s capabilities. It is not uncommon for an oven’s work opening or a conveyor turn radius to be too small, becoming a limiting factor for a paint finishing or other automated production system that utilizes industrial ovens. In many cases, these constraints can be addressed by adding infrared to provide more heated height, length, etc. (If desired, the additional heat can be controlled with a photo-eye process, permitting the system to turn on the additional heat only when needed for specific parts or work packages.) Infrared may allow the overall heated dwell-time requirement to be reduced to the point that a multi-pass oven configuration can be changed to a straight-pass oven configuration, so you can process longer parts than was previously possible. Infrared’s modularity, flexibility and ability to provide fast response is critical to overcome production challenges.

Changes in management or ownership may alter a company’s production philosophies. Suppose your company has historically processed products to stock and distribute, but now it prefers a just-in-time processing, packaging and shipping operation. Or, perhaps all of your products have been processed in one main system, but now they will be produced in smaller, product-specific, just-right manufacturing systems. Using infrared to provide a time savings and a much smaller footprint can help your company evolve to meet these needs.

In many applications, infrared will be useful in helping your company keep up with the competition in a constantly changing marketplace.

Methods of implementing electric and gas infrared can include:

• Infrared heating as a boost to quickly raise the temperature of coated product in front of or in the first zone of an existing hot-air convection oven.
• Enough heated dwell in an infrared oven that the heat/dry/cure process can take advantage of product substrate conductivity.
• The introduction of non-purposely heated, recirculated air movement to assist in drying and curing in the hidden or recessed areas of parts.
• The introduction of true convection (purposely heating air) to help finish the drying and curing of coatings on products, either in a following zone or in the infrared oven zone.
• Product rotation through the heated oven zone.
• Multiple temperature control zones vertically, horizontally and in the direction of the conveyor or machine travel, as needed, to effectively handle different part mixes.

Properly employing such infrared oven design techniques will allow your company to meet process requirements in a cost-effective, energy-efficient, reduced footprint way that will result in a successful equipment installation.

It is important to note that if you are considering using infrared heating, testing is usually necessary. It is highly recommended that testing be done in a realistic way to determine whether infrared is a good fit and, if so, the time it takes to do the job properly. Both criteria are necessary in order to determine whether an infrared process heating system will be a successful solution. There are many variables in terms of product dimensions, how products will be presented to an oven, what types of coatings are applied and their specific dry/cure specifications, etc.

At the same time, there are many different types of electric and gas infrared heaters from which to choose. Heater strengths and weakness include: required input energy and the amount of energy used, response time required to turn on, turn off and change temperatures, longevity, maintenance needs, ease of use and capital cost.