Metal finishing businesses place a strong emphasis on continuous improvement, as well as improving safety and avoiding costly downtime.
Because of that, immersion heating manufacturer Process Technology (Mentor, OH) has made significant innovations in its “SmartOne” immersion heater equipment that offers inherent safety and improved functionality over typical resistance-wire heaters by using technology called “Positive Temperature Coefficient” chips as the heat source.
“PTC chips offer a self-limiting temperature capability previously unavailable, which eliminates the potential for overheating and equipment damage when used properly,” says Edward Dulzer, forecast manager for Process Technology. “This advancement represents a major milestone in wet process heating.”
Electric Heaters Made with Resistance Wire
Dulzer says traditional immersion heaters use resistance wire as the source of heat, which is commonly used in toasters, electric space heaters, electric water heaters and electric ranges and ovens. When voltage is applied to the resistance wire, it heats up.
Industrial heaters are designed to heat water typically at around 900°F (482°C) internally. Dulzer says the heat output is a function of the supply voltage and the heater resistance (Watts = Voltage2/Resistance), and since the heater’s resistance measurement is constant, the heat output will be constant regardless of the surroundings, environment or application.
“When an electric immersion heater using resistance wire is subjected to less than ideal operating conditions—such as being covered by buildup or operation in air due to a liquid level drop—the heat generated by the wire is not able to dissipate quickly enough,” he says. “This results in a rapid increase in surface and internal temperatures that shorten the heater service life and can damage surrounding material such as a plastic tank or piping.”
To protect surrounding materials from high-temperature damage, immersion heaters using resistance wire are required to include a heater sheath over-temperature cutoff device known as a “protector,” which is designed to detect the surface temperature of the heater and trip if the temperature exceeds a predetermined value.
Dulzer says protectors are often wired into the temperature control circuit, but some may be wired directly in series with a low wattage heater operating below 240 volts. If a properly wired protector trips, the heater will shut off and prevent overheating and possibly starting a fire. The downside, he says, is that once the device trips, the heater remains shut down until the protector is replaced.
Electric Heaters Made with PTC chips
Process Technology’s new PTC electric heaters do not use resistance wire as a source of heat. Instead, Dulzer says they use ceramic PTC chips as the heating source, meaning the resistance value of the chips will increase as their temperature increases, and the resistance change is not linear.
“PTC technology has been available for many years as a low-wattage source of electric heat,” says Dulzer. “They are used in common items such as curling irons, heated car seats and some hair dryers, and are manufactured from barium-titanate plus a few key doping materials to provide the desired resistance/temperature characteristics.”
Dulzer said that when electrical voltage is applied to a PTC chip, heat is not generated at a constant rate. Rather, as the PTC chips heat up they reach a designed temperature at which the heat output decreases drastically and prevents the chip from getting hotter. Thus, PTC chips have a designed temperature limit.
“Because the resistance change versus temperature is not linear, the reduction in heat output is not linear,” he says. “If the hot zone of a PTC heater is exposed to air or covered in buildup, the heat output quickly drops by more than 80 percent of its normal rate, while the internal temperature stays at its designed value.”
PTC chips limit the surface temperature of the electric immersion heater, and Dulzer says they do not require a protector. Instead, he says the over-temperature protection is built into the heater core itself, offering key advantages over traditional resistance heaters.
Process Technology says the designed temperature limit of PTC immersion heaters results in a maximum surface temperature of approximately 518°F (270°C), and is independent of the surrounding environment, even if the heater is operated in air. The company says the temperature is also far below the ignition temperatures of materials used in tank and liner construction.
“In fact, PTC heaters operating in air will not ignite tanks made from polyethylene, high-density polyethylene, fiberglass, polypropylene, CPVC or PVC when used correctly,” Dulzer says.
Although it cannot ignite plastic tanks and tank liners, Dulzer says the surface of a PTC heater could get hot enough to melt them in direct contact, and therefore the heaters still require bumpers (minimum ½-inch recommended) to ensure the surface doesn’t touch surrounding materials.
Enhanced Durability/Longer Life
Process Technology points out that a resistance heater will overheat if operated in air or covered by a layer of scale buildup or sludge, but the elevated internal temperature actually shortens the service life of the heater anywhere from a few months to several years. Dulzer says the service life of his company’s PTC heater is not adversely affected by operation in air, scale or sludge buildup because the heat output is reduced in these conditions.
“PTC heaters only generate enough heat to maintain the designed limit temperature,” he says. “To restore the heater to normal operating conditions, users simply clean the insulating material from the surface of the PTC heater or raise the liquid level. This will optimize the operating environment and increase the heat output accordingly.”
Process Technology says its PTC heaters are able to be wired into existing temperature control and power circuits based upon the wattage and voltage ratings. Existing resistance heaters can be directly replaced by PTC heaters, but Dulzer points out that it is always recommended that plant operators carefully inspect heaters regularly to ensure optimum performance. In many cases, he says, the over-temperature protector circuit will need to be modified because PTC heaters do not require a separate protector device.
Reduced Downtime and Cost of Operation
Another advantage Process Technology says its new heaters have is that possible down time caused by a tripped protection device is eliminated since PTC heaters do not require protectors.
“When a tripped protector cannot be immediately replaced because a spare is not kept in stock or is not readily available, the resistance heater must not be used until the replacement protector is installed,” Dulzer says. “An unheated tank may result in longer soak times, slower production throughput on the line, or may even cause the process line to be shut down until the heater is once again operational.”
All of these consequences can impact the cost of operation and profitability of the process line, but Dulzer points out that with PTC heaters this is not a concern.
“In order to improve the methodologies of wet process heating, a ‘smarter’ technology has been developed to heat solutions with additional ease and safety,” says Dulzer. “The concept of PTC heating has been proven with everyday items, and the time has come to use this innovative technology for electric immersion heating.”
For more information on Process Technology products, please call 800-621-1998 or visit Process-Technology.com.