About Infrared Radiation...
The electromagnetic spectrum consists of Gamma rays, X-rays, Ultraviolet rays, visible light, infrared rays, microwave, and radio wave. Infrared radiation is that portion of the spectrum that borders visible light, and microwave. The infrared portion of the spectrum begins at .76um and extends to 1000um. Nearly one half of the energy from the sun is infrared radiation and is visible to the human eye. Infrared is the most efficient form of all forms of radiation in the electromagnetic spectrum where transfer of heat is concerned. Infrared has many of the same properties as visible light. It travels in straight lines from its source, it can be directed into specific patterns by optically designed reflectors and because of the diffusion of its rays, it decreases in intensity as it travels outward from its source.  Infrared is also similar to radio waves in that it is divided into long, medium and short wave.  Today, infrared radiation is used to cure, bond, preheat and dry a variety of materials, and process foods. To examine the properties of infrared radiation in greater depth,

Some Definitions...
What exactly is infrared? Why does it prove to be so much more effective than other forms of heating in many applications? Infrared is not heat. Heat is transferred from an object by one of three methods; Conduction, Convection, and Radiation. Conduction is the transfer of heat by physical contact between the heat source and the object to be heated.  Convection utilises heated air as the transfer medium between the heat source and the object to be heated. Radiation utilises the electromagnetic energy from the heat source to transfer its energy to the object being heated.  Infrared Radiant Energy is not absorbed by air, and does not actually become heat until it is absorbed by an opaque object. Radiant energy may show up in the form of heat as it vibrates and rotates the atoms on the absorbing object which results in a rise in temperature of the object. However, infrared can also appear as a chemical change in the absorbing object- polymerisation and evaporation (drying). 

Properties of Infrared Radiation... 
There are several physical laws that explain the properties of infrared radiation. The first and probably most important of these laws states that there is a positive relationship between radiant efficiency and the temperature of an infrared source. (Radiant efficiency is the percentage of radiant output from a heat source).
The proportion of energy transmitted from a heat source by each of the three heat source methods is dependent on the physical and ambient characteristics surrounding the heat source, and in particular the source’s temperature.

The Stefan-Boltzman Law of Radiation states that as the temperature of a heat source is increased, the radiant output increases to the fourth power of its temperature. The conduction and convection components increase only in direct proportion with the temperature changes. In other words, as the temperature of a heat source is increased, a much greater percentage of the total energy output is converted into radiant energy.
The wavelength of infrared radiation is dependent upon the temperature of the heat source. A source temperature of 3600 degrees F will produce a short-wave of approximately 1um, while a source temperature of 1000 degrees F will produce a long-wave of approximately 3.6um. The wave-length dramatically impacts the intensity of radiation at the subject. 

A critical function of the wavelength of infrared radiation is its ability to penetrate an object. The penetration of infrared energy is a function of its wavelength. The higher the temperature the shorter the wavelength. The shorter the wavelength, the greater its penetrating power. For example, a tungsten filament quartz lamp operating at 4000 degrees F., has a greater ability to penetrate into a product than a nickel chrome filament quartz tube operating at 1800 degrees F. There are certain advantages gained in industrial processing by using the penetrating capabilities of short-wave infrared. For example, short-wave radiation can be effectively used for faster baking of certain paints since the infrared radiation penetrates into the paint surface and flows out solvents from within. Conventional drying methods can form a paint skin and trap solvents. Some other applications of short-wave infrared include heat shrinking, water dry-off, and preheating of objects prior to further processes. 

Colour sensitivity is another characteristic of infrared radiation that is related to source temperature and wavelength. The general rule is the higher the temperature of the source, the higher the rate of heat absorption of darker colours. For example, water and glass (which are colourless) are virtually transparent to short-wave radiation, but are very strong absorbers of long wave radiation above 2. Another characteristic of infrared that is not dependent upon temperature or wavelength is response time. Sources with heavier mass take longer to heat to the desired temperature. For example, a tungsten filament has a very low mass, and achieves 80% radiant efficiency within microseconds. A coiled nickel chrome filament in a quartz tube acquires 80% of its radiant efficiency in approximately 75 seconds and metal sheathed rods require approximately 3 minutes. The rate of response becomes an important consideration especially when applying infrared to delicate and flammable materials.

 Infrared Advantages
There are numerous advantages in using infrared technology including: 

Energy Efficiency 
Most of the energy in properly designed systems is  directed to the surface, acting directly on the coating,  resulting in faster product curing or drying and lower  energy costs. Processing time can be 50-85% faster than convection ovens. 

Time & Space Savings 
Faster heating means shorter ovens, so Infrared equipment occupies less floor  space than convection ovens. Infrared ovens can often be added to an existing  convection oven and production line with little difficulty, and, since they are  modular they can be enlarged or reconfigured as needs change. 

Cleaner & Finer Product Finishes 
Since Infrared heats the coating directly, there is no need to blow hot air. This  often translates into superior surface finish and fewer parts rejects due to surface  blemishes. 

Precise Control 
Electric Infrared emitters respond very quickly and can be controlled by  microprocessors that quickly follow process changes. This is very important where  the coating characteristics change from product to product. 

Low Initial Cost & Maintenance 
Electric Infrared ovens usually cost less than convection ovens. Emitters can be  designed for long life, easy periodic cleaning, and minimal maintenance.

Heating Applications
Infrared heating is used in many applications. The  following will give you an idea of just some of them.  Infrared is used in: 
Heat-setting latex foam to the back of carpets  and heat treating nylon webs used in automobile  seat belts,   Sterilising glass for the drug and pharmaceutical industries, Thermally bonding double-pane glass and safety glass for the automotive  industry, Heat shrinking plastics for shipping protection and heat setting plastic  safety seals over medicine bottles. Infrared also activates or melts hot melt adhesives prior to bonding. And it is used in:  Thermoforming plastic sheet materials,  Cooking pizza, toasting buns, and broiling foods with fast, accurate,  automated control,  Reflowing solder on printed circuit boards.  Tempering glass for many uses,   annealing copper tubing and aluminium cable, Heating titanium alloys to superplastic temperatures for pressure/vacuum  forming, and   Incinerating organic wastes and sintering Teflon tubing. 

Infrared Drying Applications
Infrared technology:  Speeds ink drying in printing and textile dye applications. Dries and dehydrates surface moisture from plastic pellets before injection moulding. Dries adhesives on metallised foil or liquid vinyl in the manufacture of vinyl-clad steel, and   Dries water-based paints.

Curing Applications
Remember that curing is more than merely heating it  involves the chemical transformation of a substance  through oxidation and cross-linking. Infrared-cured  coatings often have higher durability, greater hardness,  and improved chemical resistance. Typical infrared curing applications include: Powder (polyester, epoxy, acrylic, and TGIC) and Teflon coatings on metal  sheets. Ceramic inks on glass, and   Vinyl on fabric-backed wall coverings.

Booster Ovens
A growing use of electric infrared is in booster ovens in  front of existing convection ovens. For example, on  auto body production lines, an Infrared oven at the start of the line rapidly heats the paint and sets the body finish. The car then moves into a forced air convection oven where the under parts are dried and cured more slowly. The initial rapid setting of the topcoat eliminates concerns about dust damage in the convection oven. With a booster oven, conveyor speed can be increased significantly without a significant increase in oven length.  

Infrared Coatings
The colour, thickness, reflectivity, and absorption chemistry of the coating material being treated all affect the amount of infrared heat required. For example, it may take longer to cure an automobile panel if the finish is a highly reflective metallic silver than if it is matte black.  Some organic solvent vapours become explosive at certain concentrations. Thus, with solvents like toluene, hexane, or methanol it's essential that there be adequate air flow in the oven to prevent vapour accumulation. (This applies to any type of oven in which organic are treated, not just Infrared ovens.) The contaminated air must then be properly treated. With water-based coatings, the accumulated water vapour must be removed (usually with an air lance and ventilation.) Infrared can treat coatings on a wide variety of substrates including metals, wood products, most plastics, fabrics, ceramics, glass and paper. 

Infrared Curing
Infrared processing is widely used for curing both water-based and solvent-based paints and inks. In a conventional convection oven, paints must be cured slowly to prevent the formation of a surface skin. If a skin forms before the underlying paint has cured, the remaining carrying agent will produce surface blisters as it evaporates, resulting in a less attractive and less durable finish. Infrared radiation can be designed to pass through the outer surface to dry and cure the paint from the inside out, so skinning isn't a problem. The result is a better-looking, more durable surface, produced in less time and at lower cost. 

Infrared is also ideal for curing powder coatings, which are being used increasingly for consumer products such as venetian blinds and appliances, and for automotive parts like oil filters. In fact, about 90% of all garden and patio items are being powder coated because of their superior finish and durability.   Powder coating consists of spraying an electrostatically-charged powder over the work piece and heating it until the powder melts. The powder flows over the surface and is cured in an even layer. A major problem in convection ovens is that moving air can blow the powder around before it melts, leading to an uneven coating. Infrared curing requires no air flow so this isn't a problem. 

Infrared is the range of electromagnetic energy between visible light and radio waves. Most Infrared emitters are visible to the human eye because of the overlap into the visible light range.
   

Infrared is typically divided into three wavelength categories: short, medium, and long. Selecting the proper emitters requires careful matching of the surface coating and the desired depth of energy penetration. In general, short wavelengths penetrate deeper than long wavelengths. 

Short Wave Emitters
Short wave (high temperature) Infrared emitters are electric only and usually consist of tungsten filaments in gas-filled quartz tubes. Their energy is intense and easy to focus, and penetrates coatings well. These emitters are used where intense directed heat is required, such as in curing thick coatings, or in high speed conveyor lines for curing coatings on steel straps and wood products. 

Medium Wave Emitters
Medium wave emitters are usually nickel-chromium or iron-chromium-aluminium wire elements mounted in tubes, silica or quartz panels, or gas units. They're less intense than short wave emitters, so heating with medium wave emitters takes a little longer, However, this can be an advantage for treating material not tolerant to high heat levels. 

Medium wave infrared is usually used where a lower temperature, more diffuse source of heat is required, such as a drying water from fabric or textiles, metal coatings, adhesives, plastic surfaces or curing inks on paper or screen-printed fabrics. 

Long Wave Emitters
Long wave infrared emitters are usually Pyrex glass radiating panels or vitrified ceramic panels operating just cool enough to avoid visible light emissions. That's why they're called "dark emitters." These produce the shallowest penetration and tend to be more connective than others. However, they're also less colour sensitive so multicoloured products are easier to cure with long wavelength IR. Primary application of long wave is in the preheating of aluminium or drying paper products and films. 

Infrared Reflectors
Emitters radiate in all directions, so reflectors are placed behind them to redirect as much of the radiation as possible onto the product in the desired manner. Appropriately placed reflectors can irradiate the whole product uniformly, or focus radiation on a section that needs extra heating. Reflector materials include ceramics, polished aluminium or stainless steel. Gold is often used in tubes and lamps with built-in reflectors. Dirt severely degrades all infrared performance and can lead to lamp overheating and premature failure, so external reflectors need to be cleaned. Internal reflectors are also available to eliminate this requirement.   Reflectors come in several different forms. Quite often, they're separate panels mounted behind the emitters. However, one emitter design uses a twin bore tube with the filament in one bore and a thin layer of gold plated on the inside of the second bore. Thus, the reflector is an integral part of the emitter. It may be necessary to cool reflectors, lamps, and wiring to prevent premature failure. Usually, air is blown over them (from behind to eliminate blowing dust). The hot air can be recycled to heat other parts of the work area, or to augment a convection oven if the Infrared unit is being used as a booster oven. 
Technical Considerations - Infrared
When tailoring infrared to a specific situation, consider the following: 
The number of emitters required will depend on product size, line speed and exposure time. Since emitters usually come in modular units, it isn't difficult to add or remove them as necessary. 
Electric infrared sources generate radiation by resistance heating an element or filament. 
Gas infrared units burn a mixture of air and gas in either a radiant tube, a perforated fibrous matrix or impingement chamber design. Radiation is generated at various wavelengths (producing primarily short or medium) depending upon the temperature of the element. 

Maintenance of IR systems is limited to cleaning the reflectors regularly and replacing burned out emitters.
Short wave emitters should last 5,000 hours when
operated at full power. Decreasing the power input to 80-90% of maximum (by lowering the voltage) can extend emitter life to more than 30,000 hours. Medium wave emitters last even longer. 
Replacement emitters cost between Rs.3500/-(60US$) and Rs.8000/(160 US$)- for each lamp. Radiant heating panels range between Rs12,000/- (200US$)and Rs.40,000/- (600US$)based upon heating area and other factors. 

Infrared Heating
Infrared is best applied when the majority of the energy input is focused on the surface of an object (unless, of course, the material is highly conductive). It's generally not appropriate for deep heating applications. Very high BTU/square foot heating levels are possible, higher than almost any other method. This results in higher throughput which can reduce work in process inventories. Heat is transferred by a combination of absorption and conduction through the material. For most non-reflective surfaces, reflection and transmission losses are very small. Emitters usually look like and operate similar to lamps; shadowed areas may not receive adequate energy. Conversely, infrared energy can be focused for welding or forming operations, or applied uniformly for paint drying or baking. 

Optical pyrometers can sense surface temperatures and provide rapid and accurate feedback and control to avoid surface over- or under-heating.   Where infrared can be used, it's generally superior to convection ovens, since it offers a cooler plant operating environment, can be turned off when not in use, is easier to maintain, and occupies less floor space. 
 

Special Care Situations 
Infrared Technology Alternatives
Electric infrared drying and curing is competitive with traditional methods, such as air impingement, gas convection ovens, and even with gas IR. 
Other radiation technologies, such as electron beam and ultraviolet, are also used to cure specially-formulated coatings. 
Air-drying, is not only slow but the coated surface is exposed to dust, insects and other airborne contaminants. 
Gas-fired convection ovens are usually more costly to install, slower, and less energy efficient. In a convection oven, a large volume of air is heated and the heat is then transferred to the coating in a slow and difficult-to-control process. Further, when a conveyor stops, the product can be ruined by overheating. 

METHODS OF HEATING
Forced circulation air oven heating is preferred for temperature uniformity and least danger of overheating the sheet. For non-critical forming operations, other heating methods are sometimes used. 
1. AIR OVEN HEATING 
2. INFRARED RADIANT HEATING 
3. STRIP HEATING 
OTHER METHODS OF HEATING
Hot water or atmospheric pressure steam will not heat Chemcast® GP to high enough temperatures for forming. Hot oil can be used, but makes the sheet difficult to handle and necessitates subsequent cleaning. A light mineral oil such as transformer oil is preferred. The oil must be kept clean and must be washed off after forming.

INFRARED RADIANT HEATING 
The principal advantage of radiant heating over air­oven heating is speed of heating. Radiant heating time cycles for 0.125” thick Chemcast® GP heated from one side only may vary from one to three minutes, depending on the type of heater and the distance from the heating surface to the Chemcast® GP, compared with about 10 minutes for air­oven heating.

Temperature uniformity varies with the type of heater used. Heaters with more uniform surface temperatures can be held closer to the Chemcast® GP. Chemcast® GP is opaque to much of the infrared radiant energy and absorbs most of the energy on the surface exposed to the heater. The rest of the sheet is heated largely by conduction from the exposed surface. Thus, radiant heating should not be used for sheets over .125” thickness when heated from one side, or 0.250” thickness when heated from both sides, because the surface exposed to the heater may become overheated before the opposite surface or the centre of the sheet has reached forming temperature.

Infrared heating time is critical and must be controlled within a few seconds because of the high surface temperatures (usually 600°F. to 1,000°F.) of the heaters and the large amount of energy radiated from them. Infrared heaters are usually controlled by a timing switch on a relay circuit, varying the on­off cycle to meet the requirements of particular forming operations. 

Infrared radiant heating is not recommended for heating large areas where the most uniform heating is necessary in order to obtain excellent optical properties in the formed part. With infrared heaters, power required is approximately 10 watts per square inch of sheet area. Methods of Heating Acrylic Sheet  Starline Infrared Ovens Starline Equipments. offers an extremely versatile infrared oven for processing a variety of parts and coatings. It is ideal for job shops. The most flexible oven available just got better by adding Adjustable Height settings. Selected rows of the Adjustable Height oven may tilt upward or downward to accommodate multiple products. 
The standard Adjustable Width oven features varying opposed widths to “focus” the radiant panels at the appropriate distance from the product, zoning in height and length, and a modular design. Minimal floor clearances are required for framing since a “clutter free” overhead design is used. Areas of the oven that are not required for a given part may be turned off independently.  The modular design of Starline infrared ovens make them an excellent capital investment simply by changing the framing and configuration, the same infrared units may be used for many applications throughout your facility. Occasionally, increasing the wattage of the element may be necessary to meet new process specifications. Higher wattage elements will fit in the same housing, however, some control panel modifications may be required. 

BENEFITS OF ACS INFRARED OVENS
Increase Production: Due to faster cure cycles, infrared can increase production. Adding a short infrared booster to an existing convection oven can significantly increase output. Energy Efficiency: Infrared energy passes through the air and is transferred directly to the product, thus the temperature increase occurs in 112 to 1/3 of the convection cycle. Typical energy efficiencies of medium wavelength infrared equipment are between 50-65%, referring to the energy applied that actually affects the part.  Minimal Environmental Impact: Electric IR ovens do not have any large gas operated burners which produce NOx and SOx emissions They also have minimal heat losses and require minimal air make up. These factors impact the overall energy costs related to maintaining the plant environment. 

Flexible: All ACS infrared equipment is modular. As requirements expand or change, units may be added or rearranged. Many flexible oven configurations are also available.  Precise Temperature Control: Electric IR can respond very quickly to new temperature settings. Standard elements react within 3 to 5 minutes. Temperature settings of + or - 2 degrees F can be maintained with standard percentage timer controls. Optional PID closed loop feedback controls, SCRs or PLCs may also be used.  Space Savings: Shorter cure cycles result in less oven to occupy floor space. By ceiling mounting the oven, other equipment or operations may be placed under the oven.

Clean Products: Since IR does not depend on circulating air to heat the product, no dirt or dust is stirred up and allowed to settle in the product. The result is fewer rejects due to contamination. Low Maintenance: Electric IR emitters have a very long life, typically five years, and minimal reflector maintenance is required. Quality control panel components are also selected for longevity.