Even the most casual cook is familiar with the principles behind infrared by using appliances in their own kitchen. The gas burner or electric resistance heater in your oven functions just like a gas or electric infrared heater. It isn't new in the marketplace. It isn't experimental. Don't be afraid to examine infrared as a potential solution for your heating, drying or curing needs.
Using infrared effectively doesn't have to be guesswork. A few practical ideas can get you prepared to make a better buying decision as well as use an existing oven more effectively.
1. Understand That More Is Not Always Better
More heat does not accelerate curing in some coatings, and it can increase the cooling time or create a need for forced cooling. Especially with air-dry coatings, they do not harden until the excess heat has cooled back out of the part. Until then, the part will be prone to damage and fingerprints. In these cases, it is better to minimize the heat to accelerate the cure process -- don't treat it like a bake enamel. Reaching 350oF (177oC) is not going to help the drying and may change the coating properties or scorch it. For applications such as these, use a medium- or long-wave emitter for the best results. Forced cooling with something as simple as a floor fan can help immensely, too.
2. Realize That Bigger or Longer Is Not Always the Answer
Look at watt density to determine what will work for you. Don't get over- or undersold. Extra oven length takes up valuable floor space that could be put to use for other processes. Ask “Would the process be more efficient if a higher watt density emitter is utilized?” Some materials or coatings will not handle the increased intensity; however, if the product can absorb it, you can save one-third or even one-half of the floor space. Of course, you also can plan for a ceiling-mounted oven, thus utilizing virtually no floor space. This is where an educated buyer would examine all wavelengths to determine the time required and the expected performance of short-, medium- and long-wave emitters.
3. Line Density: Pack It In
When loading products, it is best to go for a high line density. Your elements are creating heat, and it is a “use it or lose it” situation. The more parts that are in the oven to absorb the heat produced, the better. This is especially true of systems that are percentage-timer or SCR controlled with no closed-loop feedback. The heaters will continue to produce heat according to the cycle setting. If no parts are loaded in the oven, radiant heat will be reflected between the oven walls, and convection heat that is not contained will escape the oven cavity.
Different types of emitters will create different balances between the amount of radiant and convection heat that they produce. For example, a T3 lamp has a high efficiency in terms of producing up to 95 percent radiant heat out of the energy applied. Emitters with ceramic materials are less efficient in terms of radiant heat (usually 65 percent to 80 percent); however, most the balance is converted into convection heat. A good oven builder will design the oven to contain this heat and utilize it in the process. An oven design such as this offers some of the advantages of a convection oven with the speed and efficiency of an infrared oven.
It is true that line-of-sight can be a problem, but it is primarily an issue with short-wave emitters. Uniformly shaped parts and a fixed presentation to the emitters will result in very fast cure cycles. Production lines with a wide product mix can be cured with a well-designed medium- or long-wave radiant oven by racking the parts for maximum exposure to infrared, utilizing staggered heating or racking patterns, or rotating the parts as they convey through the oven. The convection produced will cure hidden areas, and the parts also will have a longer cycle, during which the heat can spread through the part via conduction. Experiment with rack designs to find your optimum arrangement. Generally speaking, if you can easily apply the coatings, you should be able to cure it with infrared.
4. Remember That Not All Elements Are Created Equal
Different infrared heater designs deliver heat differently and are therefore better suited to certain applications. As already noted, the way heat is generated can vary even though they are all “infrared emitters.”
Every infrared heating equipment manufacturer has heard prospective customers say, “We've already tried infrared, and it doesn't work.” When asked what kind of infrared was used or the details of the test rig, though, the customer often has no idea. For reputable infrared heating equipment suppliers, that application is a challenge to solve, not a prospect to give up on.
Testing is key when designing an infrared heating system, and your supplier should try several different emitters. Gas, electric, short, medium, long, ceramic, quartz tube, metal sheath and combinations of the above are all options until they are ruled out. Don't let them forget infrared and convection combination ovens, and you may even want to throw in ultraviolet (UV) technology. There is a best way to get the job done, and sometimes you have to forget what the old-timers told you about this newfangled infrared stuff not working. Coatings and materials have changed. Try a different wavelength to put a little different spin on the electrons in your materials.
5. Try Before You Buy
It is always best to take advantage of testing services offered by manufacturers. You wouldn't buy a car without a test drive. Why buy an oven without seeing the results you can expect in your plant? Expect it. Demand it. Above all, don't ignore it. Hopefully by now, you're convinced that the infrared manufacturing wizards can tell you all kinds of things from behind that big curtain. Go see it for yourself.
If your process is one that must be done in your plant, most manufacturers can send a test set to your location. Keep in mind that the results from a test set will not be as good as the final engineered oven. Tests prove feasibility and approximate cure cycles. Your actual production results should be even better.
6. Maintenance: Are You Really Going To Do It?
Maintenance, regardless of how simple it is, is critical for operating an oven at peak efficiency. If you aren't likely to do any maintenance, buy an element that doesn't need much. I have received requests to add an oven to a line where only a little maintenance was needed to cure the problem the new oven was intended to solve. Maintenance is simple to do and usually only required monthly or quarterly, yet most processors don't do anything to their ovens.
If you buy a short-wave oven, expect to keep the area clean and dust free. Dust or fingerprints on the lamps will cause premature element burnouts. Reflectors must be clean or they become re-radiators, thus changing the wavelength produced and the results of the cure. Medium-wave quartz tubes have many of the same maintenance requirements.
Other sorts of medium- and long-wave elements can tolerate less maintenance, but should you neglect maintenance indefinitely, you will pay for it through bottom line operating costs. Gas or electric makes no difference here. Ignoring gas catalytic heaters that need to be repacked is just as costly as dirty reflectors and burnt-out elements.
For most medium-and long-wave ovens, maintenance is not much different than that required for a convection oven.
- Exhausts should be checked for proper operation and filters changed as applicable.
- Reflectors or side walls should be cleaned per the manufacturer's guidelines.
- Tighten all electrical connections that may have loosened due to plant vibrations.
- Replace or repair elements that are not operating at peak efficiency.
- Clean the oven floor and remove any parts that may be in the cavity.Surely you can reserve a little maintenance time to prevent a disaster or emergency later when you are pressed for more production.
7. Don't Over-Engineer Controls
Match the controls to the reaction speed of the heater. If the emitters require 5 min to heat up, controlling them with SCRs is overkill. You won't reap the benefits of SCR control. Likewise, with their fast heatup time, any style of quartz tube heater cannot be controlled with a percentage timer. The thermal shock on the element will cause element failure very quickly, and your parts will not receive proper heat.
PLC controls can be a cost savings if your oven has several zones. They can be used as a time-controlled device, or they also will accept thermocouple inputs. Another benefit is the ability to lock out the controls, so the settings cannot be changed at anyone's whim.
Because infrared emitters respond quickly, adding a phase-down controller can save you money when the line stops for breaks. When the conveyor stops or when the controller is activated, the oven temperature drops to a lower temperature setting. When work resumes or the conveyor starts, normal operating parameters are restored. A phase-down controller also can help prevent part overbaking when parts are left in the oven for longer times than the proper cure cycle.
8. Infrared Can Go Around Corners -- Sort Of
Infrared is not limited to strictly flat parts or those that are rotated. Depending on the amount of convection vs. infrared that is created, heating around corners and into blind spots can be a breeze. As already noted, certain emitters are better for applications that require this than others. Medium- and long-wave emitters produce some convection heat along with the infrared. They also have a bit slower cure cycle, which gives the convection heat time to help cure hidden areas. This convection heat is no different than the heat in a convection oven. Additionally, infrared ovens usually have minimal airflow, which helps to minimize contamination.
9. Make It Flexible
Use zoning, adjustable width or height to operate in the “zone”: Many options can be built into an oven to make it more flexible. Adjustable widths on vertical ovens or adjustable heights on horizontal ovens are common. Both allow you to maintain optimal focal distance for your emitter.
Zone controls allow the operator to use only the portions of the oven that are needed to cover a part. If you are running small parts, there is no reason to turn on the entire oven. Zones can be set up to turn on just the top, bottom or center emitters, or those that best suit your product mix. You also can zone in length, which allows ramping the temperature up or down for optimal curing. The additional money spent on zone controls will have a short payback time if you properly utilize the features. PH
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