Ceramic Heater Questions

Answer: The source should be as close as practically possible to the load. However, the source should be far enough away from the load so that the infrared radiation pattern from each emitter (in a panel) will overlap each other. Some materials are very heat sensitive and if the radiant patterns of the heat source do not overlap at the load, "striping" can occur. The distance from the source to the load is dependent on the spacing between emitters. FT emitters that are spaced 1" apart would require a distance to the load of 8" to achieve even heating of the load.

What are the radiant emission patterns of ceramic emitters?

Answer: The question often arises about the different shapes of ceramic heaters. Ceramic heaters are manufactured with three basic emitter faces: convex as in the FTand HT and flat as in the FF, HF and HS. These different shapes create three different emission patterns.  Radiant energy is emitted from all objects at different levels of intensity. This energy comes off all surfaces at true right angles. The convex shape gives off a "wide area" pattern which is desired in comfort heating or other applications that require dispersed heating. A concave surface will emit a "concentrated" pattern which is highly effective when zone heating is desired as well as radiant heating in general. The flat surface will produce a "uniform" pattern for even heating at a close proximity between the emitter and the material to be heated. Examples of this are sheets of plastic or curing of surfaces.  When dealing with new applications the emission pattern needed is usually easily determined, but in retrofit applications elements should not simply be replaced without questioning whether there has been a change in application.  See page 4 of our Technical Manual for more information.

Can ceramic infrared heaters be used to heat metals?

Answer: If you apply infrared radiation to a polished metal surface, almost all of the incident infrared radiation will be reflected from the metal surface. In this condition the metal will never come up to the temperature required. The only way to effectively heat metals using infrared radiation is to increase the emissivity of the metal surface. Painting the surface of the metal will increase its surface emissivity value to 90%. Now the paint will absorb 90% of the incident infrared radiation and will transfer this heat to the metal via conduction.

Answer: Since the ceramic emitters are relatively slow responding ( 8 minute warm-up time required to achieve operating temperature ) closed loop control with an inexpensive proportional control and contactor will control the heaters typically between +/- 2 ° F. Percentage timers and SCR power controls can also be used very effectively.

A lot has been said about the zoning capability of ceramic heaters. In fact, zone control is one of the biggest advantages to using ceramic elements over other forms of infrared heaters.  Control products are available, and many are stocked at Mor Electric, and can be purchased along with the ceramic elements as well as other accessory products needed to create a "system".

The control of ceramic emitters can be one of two types: non-feedback or feedback. It is important to be able to differentiate between these two control systems in order to best advise your customers on the products available to them.

Non-feedback can control the temperature by two different methods. The first controls by time using a percentage-on/percentage-off duty cycle. When the timer is set for the on/off time cycle, the overall temperature of the emitter will stabilize. This can be done with either a mechanical timer or with a computer control.

The second method of non-feedback is through voltage control. In this application, a manual potentiometer control, or computerized control regulates the amount of voltage the emitters are receiving, thus controlling the temperature.

With Feedback control, a thermocouple is used to either measure the temperature of the element’s coil or, more accurately, the surface temperature of the element. A type K thermocouple is most universally used because of its 0-2000° F. temperature range and because it is able to be cast into the emitter where it measures the actual internal element temperature. If a Type J thermocouple is desired, in the case of low temperature applications, it must be potted into the element after firing, resulting in the measurement of the center of the emitter which is not as accurate. Mor Electric Heating Assoc., Inc. is also the only manufacturer to provide an interchangeable thermocouple in Type J or K. When inserted into a requested thermocouple well, it too will accurately measure surface temperature.

A feedback signal can also be created with a non contact infrared sensor that can sense the emitters or product temperature.

As the temperature of the element changes, the thermocouple creates a millivoltage which is sent back to a temperature controller. The controller then converts the millivoltage into a temperature reading. There are varying ranges of temperature controllers available from a simple on/off, non-indicating controller to a sophisticated digital PID control with ramp soak programming, smart tuning, etc.

Power Switching

HBC - Solid State Relays
DIN Mount. Custom Assemblies
120-240-480Volt
20 Amp, 50 Amp, 90 Amp

Payne Controls Company - SCR Controls
"2 ms" fuses protect power semiconductors against short circuits
120-240-480Volt
Phase Angle or Zero Cross Firing
10 Amps to 1200 Amps

Non-Contact Infrared Sensors

Chromalox 4-20MA or 0-5VAC Feedback
Exergen Type J or K Feedback

Non Feedback Control

Percentage Timers
Chromalox VCF & VCS Series Motor Driven Cycling
120 Volt or 240 Volt
15 second or 30 second time base
Energizes a heater for a chosen percentage (4-100%) of time base
20 Amps

Voltage Control
Infrared TYJ-6219
240 Volt, 13.5 Amps

Feedback Control
Chromalox 1600 Series High/Low Limit Controller
1/16 DIN Electronic, Digital Display
120 Volt or 240 Volt
3 Amp Relay Output or SSR Drive Output

Chromalox 2104 Series Temp. and Process Controller
1/4 DIN Electronic, PID, Digital Display
Smart Tuning / Fuzzy Logic, Ramp Soak
120 Volt or 240 Volt
8 Amp Relay, SSR Drive or 4-20 MA Output

Answer: The ceramic emitter is guaranteed for 1 year against burnout!! Typical life expectancy is in excess of 10,000 hours.

Answer: Like all infrared sources the emitter does not emit one single wavelength but a range of wavelengths. The peak wavelength emitted is dictated by the surface temperature of the emitter which can easily be controlled using closed loop or open loop control. In reference to Planck’s Law, a heater will emit a range of wavelengths which is only dependent on the surface temperature of the emitter.

Answer: As with any electrical heaters there are important warnings to consider:
Hazard of fire: Do not mount emitters/projectors near combustible materials or within a hazardous area.
Hazard of electrical shock: Disconnect power before servicing emitters or projectors. All electrical wiring must be done in accordance with local electrical codes by a qualified service technician.
Hazard of severe burns: Emitters and projectors operate at high temperatures.
Do not operate emitters at voltages in excess of rated voltage or at a surface temperature greater than 1292 °F (700 °C).

Why are ceramic heaters a good choice?

Answer:

	Ceramic heaters are 96% infrared energy efficient, leading all other types of infrared emitters.
	They have an incredibly long life and come with a 1-year warranty, so they make a very good cost effective investment.
	They are the best heaters on the market for zone control. Their small size facilitates complex zoning patterns.
	Watt density can be easily controlled to produce the most gentle heat on the market.
	They are very durable, splash resistant, corrosion resistant, and a clean source of heat.
	They are easy to get. A large stock is immediately available, even for large orders.
	Ceramic infrared heats objects not the air, so they do not waste energy trying to heat the air in an open conveyor type oven, as would convection style heating elements. Also, in an enclosed heating application you would have the benefits of both radiant and convection to heat your product faster.

Can I use ceramic infrared heat for preheating or as a booster?

Answer: Definitely. Due to the nature of infrared heat it’s very easy to have various zones within an oven. A forced air convection oven is almost impossible to zone within the same heating chamber.

How much maintenance is required for a ceramic infrared oven?

Answer: A well built oven is virtually maintenance free. The corrosion resistant elements can be wiped free of any dust or impurities.

General Infrared Questions:

Answer: Water vapor and carbon dioxide particles in the air will absorb infrared radiation. Typically, however, the amount of infrared energy absorbed by the carbon dioxide and water vapor are negligible.

Does short-wavelength infrared penetrate more than medium and long-wavelength?

Answer: This can be true in some cases but not universally. It is important to know the absorption characteristics of the material being heated over the entire Infrared spectrum when selecting the most appropriate type of emitter.

Are IR ovens effective in heating only flat surfaces?

Answer: Flat surfaces are ideally suited to heating by IR radiation. They can be heated rapidly and effectively in an IR oven. However more complex, three dimensional shapes can also be heated in IR ovens. Three-dimensional parts can be rotated so that all sides are evenly exposed to radiation as they pass through the oven. The heating rate can also be varied from zone to zone to allow sufficient soak time to heat internal regions of a part.

Is an electric infrared oven more expensive to operate than a gas fired infrared oven?

Answer: In comparing basic utility costs, an electric infrared oven will be more expensive than gas in most areas. However, the overall efficiency of an IR oven should be measured in terms of production capacity and quality. An electric infrared oven has the capability of producing 37.5 w/in². A gas fired catalytic system can produce only 11.8 w/in². Therefore, an electric infrared oven can produce up to three times the amount of product than a gas fired catalytic system. Also, the flexibility and ease of controlling an electric infrared oven with unlimited zoning capabilities creates an environment continuously and consistently producing quality parts.

What are some of the criteria for evaluating infrared heaters?

Answer: The selection of heaters should be based on a variety of criteria as shown in the chart below:

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