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PSC inc. has been in business since 1969, serving the ceramic, fiberglass, foam and other industries with radio frequency (RF) ovens and dryers. In 1999, the company was purchased by C.A. Litzler Co., a manufacturer of convection and infrared heating systems, enabling the two companies to work together to provide customers with complete solutions to their heating and drying needs. Last year, PSC invested in upgraded equipment for its laboratory facility that encompasses all three technologies—RF, convection and infrared.
How Combination Systems WorkMaterials with good thermal insulation characteristics, such as ceramics, are often difficult to dry. Traditional drying methods like convection are limited by the dry, insulating layer of material that often forms on the product’s surface. As the convection system moves hot air around the product, this layer acts as a barrier, preventing the heat from traveling into the product and also trapping the moisture inside.
RF technology turns the tables on the traditional methods and avoids this problem. “RF is volumetric heating—it heats uniformly throughout the whole thickness of the product,” explains Ben Wilson, PSC’s sales manager. “It’s heating from within, rather than from the outside in. With RF, we typically heat the middle and push the moisture to the surface.”
This is where the benefits of a combination system come into play. Once the RF technology has heated the product and moved the moisture to the outside of the product, convection is used to remove it from the surface. “For ceramics, typically RF and convection is the best combination system,” says Wilson. “Convection does very well at the surface, but not very well from the inside of the product. RF does very well from the inside, and then pushes the water to the surface where convection can take the surface moisture off. It’s a terrific combination.”
Another benefit involves binder dispersion. “As the product is dried, many times there will be a wicking effect, where the moisture will move to the surface and carry the solids and the binder with it. You get more binder on the outside and less on the inside,” explains Wilson. “Because RF heating is uniform and the water is moving through the product as a vapor, the solids don’t get carried to the surface and the binder dispersion is more uniform.”
For some applications, such as drying or curing coatings, a system that also incorporates infrared technology will provide the best results. While it’s not typically used with RF, infrared can be combined with convection as a pre-heat or temperature boost in the convection zone. “Infrared is a very good technology for high-heat input into the product,” says Wilson. “It’s a surface heating, so it’s typically used on thinner materials and for drying coatings.”
Determining FeasibilityIn order to provide customers with the best solution to their needs, PSC performs feasibility studies. Potential customers are asked to send in a sample, and the staff at PSC and Litzler evaluates both the technical and economic aspects of each customer’s application. “We look at the different heating technologies, based on what the customer is trying to do, and then determine which is going to be the best system for them,” says Wilson. “For ceramic applications, we’re finding that a combination system will typically be most effective for their heating and drying.”
In some cases, though, the most economical drying solution may be a single technology. Infrared can be used effectively for surface heating, convection can be used for effective drying and precise control, and RF can be used for selective heating and for heating from within.
Whether it’s a single technology system, a combination RF-convection system or one that incorporates infrared technology, PSC tailors each project to suit the customer’s needs. Customers can then either purchase the equipment or lease it to test on their process at their own facility. PSC also supplies spare parts and provides phone and field service assistance.
Upgrading the LaboratorySince more customer applications are being developed that benefit from combination technologies, PSC recently upgraded some of the equipment in its laboratory to better address the changing needs of the industry. The company’s RF lab oven was upgraded with a new convection system to improve the control of the temperature and the volume of the hot air used. “Specifically for ceramics, we’ve upgraded our capability to look at both RF and convection at the same time,” says Wilson. A new Allen Bradley PLC control system was also installed. Featuring touch screen controls and data acquisition, the system allows precise control of oven parameters and improves the oven’s process development capabilities.
Additionally, new fiber optic temperature sensing allows for real-time temperature monitoring. “The RF field is not compatible with metals, so you can’t use a typical thermocouple,” explains Wilson. “You can use infrared, but that only measures the surface temperature. The fiber optic temperature sensor measures the internal temperature of the product during the heating and drying. The unit sends a light signal through a fiber optic cable, and the tip of the probe reflects that light back. As the temperature of the product changes, it changes the properties of the tip, and the unit measures the change in reflection of the light.”
Several types of infrared heaters were also added, and a combination convection and infrared unit allows the company to assess the feasibility of this combination.
As the needs of its customers evolve, PSC continually works to meet their diverse demands. “The challenge is, there’s no single perfect technology,” says Wilson. “We look at the benefits and drawbacks of each of the different heating and drying technologies and then combine them to optimize the benefits for each customer.”