Gas Catalytic IR: Does It Live Up To The Hype?
The Pros, the Cons, and the Facts about this not-so-new Thermal Process
If you believe the buzz about Gas Catalytic IR, then it can cure your paint and powder, thermoform your plastics, or cure your resin (and even brown your pizza), quicker, better and less expensively than any other thermal process. Sound too good to be true? Let’s find out.
Wouldn’t it be awesome if you could find a thermal process that could carry out its designed tasks quicker, better and cheaper than your current system? Many manufacturers (including Heraeus!) of Gas Catalytic IR systems claim that it can, but how and why? Is this always the case? Why are some system designs better than others? Why do some never live up to the hype?
How to read this article:
If you are just curious about Gas Catalytic IR:
- Feel free to skim and to learn whatever you like
- The key takeaways are in the red and green boxes
If you want to learn more about Gas Catalytic IR, in depth, then read the bits in between the boxes!
Key PointS - About this article
We Will Explore:
- Convection Ovens
- Why Convection Ovens Are Not All that Bad
- What is Gas Catalytic IR?
- How Does IR Work?
- Will IR Work For My Application?
- What Are The Alternatives?
- When To Use Gas Catalytic IR
- Why It Is Not Always The Best Solution?
- Can Convection and IR Be Combined?
Before Gas Catalytic IR - Tried and Trusted Convection Ovens
In the old days, there was only one option. Processes that required heat to dry or cure either paint or powder when applied to a substrate were generally carried out using a convection oven. A convection oven can generally be described as an insulated enclosure with a heat source, usually a gas fired burner, heat ducts for distribution and finally an exhaust duct for combustion by-products.
The hot air heats the parts and the coating up to the temperature that is required for the curing chemistry to be activated. The ovens can be either closed, "batch" ovens or continuous flow ovens where parts pass through, suspended from an over head conveyor or supported on a "chain on edge" conveyor.
The overiding battle with convection ovens is very much a "rear guard" action. The two main battle lines are heat retention and the effects of moving air (powder blow off, dust creation and movement).
Heat retention means having a well insulated enclosure, which impacts initial cost. Also consider the amount of time and energy it takes to bring a convection up to its operating temperature from a cold start. The burner has to provide enough energy to heat the complete internal structure, including walls, ducts and conveyors up to temperature. This process can take up to an hour or more. Also consider workers breaks and the decision to either keep the oven running with nothing going through it or shutting it down.
Studies have shown, that at best the thermal efficiency of a convection oven is very low, at around the 7% level. This means that only 7% of the energy used in a convection oven is used to heat the part sufficiently to cure the coating. Over time, convection ovens became more developed with air curtains, heat recovery and recirculation systems introduced to increase their efficiency and reduce heat losses but advances in thermal efficiency have been very limited. There are, of course, also Gas Radiant and Electric IR Systems to consider.
The Problem With Convection Ovens
The effects of moving air are very much a double edged sword. Dry-off ovens, which use gas burners and high volume airflow, to remove water after a wash process, and before coating are without doubt the most effective solution available. But moving air in a powder coating oven can cause a number of problems.
Powder blow-off is a perennial problem. Much time is spent ensuring an even covering of powder at the right thickness, only to see it blown off when entering the convection oven. Cross contamination is another; two parts with different colors have to be very well spaced apart to ensure powder from one does not blow off onto the other. Lastly, air movement will carry dust which can land on curing parts thus creating a quality control problem. The only preventative measure is either air filtration (added cost) and regular cleaning of the oven.
Lastly, but not least is the issue of pollutants. Burning natural gas produces Nitrogen Oxide (NOX), Sulfur Dioxide (both of which are regulated pollutants), Carbon Monoxide, Carbon Dioxide and particulates.
So, do convection ovens still have a role in todays finishing industry? The answer is emphatically yes, as we will see when we talk about hybrid systems. But be aware that there are serious drawbacks that must be considered.
Key PointS - Convection Ovens
- Lowest initial cost of all technologies
- Works well with all part geometries
- Readily available new & used
- Can be a quick & expedient solution
- Highest operating cost of all technologies
- Not suitable for heat sensitive substrates
- Largest floor area required of all technologies
- Thermally very inefficient
- Produces regulated pollutants
- Not as efficient as Gas Catalytic IR for either curing or drying (dry-off)
Gas Catalytic IR Technology
Gas Catalytic IR Technology uses Infra Red energy waves that are not converted into heat until they hit an object.
The Infra Red (IR) energy is produced by passing natural gas through a pad of special fibres that have been impregnated with Platinum. This creates a true Catalytic reaction (the Platinum remains unchanged) that produces Infra Red energy, Carbon Dioxide and water vapor.
The natural gas is not burnt, as it is with a convection oven, so it does not produce any regulated pollutants.
The main advantage of Infra Red when used in the finishing industry is that it is inherently efficient, as more of the available energy is used to heat the part, not the surrounding air. It does not rely on air movement so the problems of powder blow-off or cross contamination does not exist. When compared to convection ovens, with a thermal efficiency of only 7%, Gas Catalytic IR has an amazing 80% efficiency level. What this means in real terms is that Gas Catalytic IR ovens cost around 50% less to run than a convection oven.
The main technical challenge with Infra Red energy is that it travels in straight lines, so it "heats what it sees", which is why it is not always suitable for all part geometries. This challenge is surmountable in the vast majority of cases by a combination of careful oven design, panel positioning and using natural heat conduction within the part.
For industrial applications the Infra Red emitters are generally panels of various sizes that can be arranged in different configurations to suit the application. The level of Infra Red output can be controlled by regulating the amount of natural gas that is passed through the catalyst. To ensure a continuous catalytic reation, a gas flow equating to 20% of the total available output needs to be maintained. This means that during work breaks and line stoppages, a "stand-by" mode is available which requies less energy usage.
What Does A Gas Catalytic IR Oven Consist Of?
A Gas Catalytic Infra Red oven consists of a series of emitter panels arranged in modules or sections. Because there are a number of individual panels in each oven, they inherently lend themselves to be individually controlled, usually by PLC touch screen controls. The panels can be controlled in groups both vertically and horizontally. This features gives a very close control on the heat profile of the oven from entry to exit. More heat is required on entry to quickly raise the part temperature, but once the cure chemistry has started, less heat is required to maintain the process.
It is important to note that the gaps that occur between the Infra Red panels are filled in with a reflective material. This feature ensures that Infra Red waves that do not hit the parts are reflected back and either re-absorbed into the surface of the panels or redirected onto the part. This is what is called Fully Reflective Technology. Failure to use this will result in IR being wasted adding heat to the surrounding work area, including the back of the oven. This is often seen on "stick built" ovens, i.e. ovens which have Gas Catalytic IR heaters simply bolted on to Unistrut or welded angle iron framework. This leaves gaps between the heaters and presents a fundamental design flaw.
Heat The Part Not The Air
As it is the part instead of the air that is heated by the Infra Red energy, then there is no need for insulated contruction panels anywhere in the oven construction, except in poorly designed ovens that do not use Fully Reflective Technology between the heater panels. In this case Infra Red energy that misses the part escapes via the gaps between the Infra Red panels, out into the general workshop area or is absorbed by the insulated contsruction panels. A good guide to bear in mind is the 3:1 Rule, which says that one minute in a Gas Catalytic IR oven is the equivalent to three minutes in a Convection oven.
There is usually an air extraction facility which operates at a very low CFM (Cubic Feet per Minute). This does not give rise to any significant air movement within the oven, thus reducing any associated problems.
One of the key points about Gas Catalytic IR is that it can be used on heat sensitive substrates such as engineered timber (MDF, Plywood etc.) as well as any type of metallic substrate. Well known Scandinavian furniture manufacturer IKEA are already well advanced in using Gas Catalytic IR technology to cure powder on MDF and thus remove the need for liquid finishes. The reduction in handling costs, by reducing a 3 or 4 coat finish to a single powder coat are staggering. Powder coated MDF products have another huge advantage over liquid finishes in that they can be used in high humidity applications.
Key PointS - Gas Catalytic IR Ovens
- Lowest operating cost of all technologies
- Suitable for heat sensitive substrates (MDF, Plywood etc.)
- Smallest floor area required of all technologies
- Thermally very efficient
- Fast warm up times
- No regulated pollutants created
- Improves quality
- Improves output
- Highest initial cost of all technologies
- Complicated part geometires require careful oven design
What About a Hybrid System - Part Infra Red Oven and Part Convection Oven?
Now that's a sensible question! A very valid option is to place a Gas Catalytic Infra Red oven directly in front of a convection oven.
This form of Gas Catalytic Infra Red oven is commonly known as a Pre Gel Oven.
The main feature of this arrangement is that the parts are brought up to cure temperature very quickly in the Infra Red part of the oven before passing into a convection oven to maintain the temperature during cure completion phase.
The advantages include the overall reduction of the plant footprint when compared to a single convection oven. So, if you are short of space, but want to increase output without the expense of completely replacing your convection oven, then a Pre Gel Oven may be the solution.
Another major advantage is the reduced capital investment. Gas Catalytic IR Pre Gel ovens are smaller and therefore less expensive, so they do provide a big "Bang for your Buck". There will also be a modest reduction in overall operating costs.
It is also useful if parts have complicated geometries, as the convection oven ensures complete curing of hidden areas. Also very useful for parts that have elements with thick cross sections, as they do not need to reach cure temperature internally as they would with convection ovens.
Cross contamination is eliminated allowing closer spacing of parts on the conveyor. Powder "blow off" is also eliminated, thus making powder consumption reductions.
Key PointS - Hybrid (Pre-Gel) & convection ovens
- Provides Flexibility
- Any Part Geometry
- Higher Output From Same Floorspace
- Very Cost Effective
- Not Quite The Full Energy Saving Package
- Not Quite The Full Space Saving Package
- Still Produces Regulated Pollutants
What About ROI (Return On Investment)
Because of the huge savings in operating costs, improved quality and improved output, the ROI for new installations can be 12 months, well below the 2 or 3 years that most corporate accounting rules demand. That experience is just based on Capital Cost v. Operating Costs savings. Delve deeper and there are savings on powder, improved production and a big reduction on the "Total Cost of Quality" and the ROI looks even better.
Gas Catalytic IR - Are There Any Pitfalls?
Yes there are! The most important aspect of moving over to Gas Catalytic IR from Convection, is to ensure that your new IR oven has been correctly designed. The correct design comes from a process of assessing all the part geometires, the cure schedule for the coating and the substrates.
The best way to do this is to ensure that the manufacturer of the Gas Catalytic IR Oven carries out testing. If done correctly this will enable all the above factors to be taken into account, plus build in a contingency for future line speed increases, or other planned changes.
Every now and again, one hears of isolated incidences of Gas Catalytic IR ovens that do not work as intended. Experience has shown that either the technology has been incorrectly applied in the first instance, the oven has been incorrectly designed, or the system has not been built with enough thermal capacity.
Key PointS - Payback & pitfalls
ROI (Return On Investment)
- Generally Very Quick (12 months)
- Don't Forget Savings On:
- Improved Output
- Total Cost of Quality
- Higher Output From Same Floorspace
- Very Cost Effective
- Incorrectly Designed Oven
- Insufficient Thermal Capacity
- Ensure Your Application is Suitable for Gas Catalytic IR
What To Do Next
If you have read this far, you are probably interested in looking at Gas Catalytic IR (or not) as a potential thermal process!
One of the following situations may apply to you:
- Requirement for added capacity from within existing available space
- Requirement to replace old and inefficient existing equipment
- Requirement to reduce the "Total Cost of Quality"
- Requirement to reduce running costs
In reality it will probably be a mix of "all of the above". The best place to start will be to:
- Find out if your application is suitable for Gas Catalytic IR by testing
- Read some Case Studies
- Look at all aspects of your current thermal process and indentify potential areas that could be improved.
- Talk to a designer of Gas Catalytic IR and get a ROM (Rough Order of Magnitude) costing.
- Test your products at one of Heraeus's Application Test Centres (USA, UK & China)
- Proceed to a full quotaion
- Determine the Payback time
Key PointS - does gas catalytic ir live up to the hype?
Well.....It's not all Hype!
- Gas Catalytic IR has very legitimate place alongside other technologies
- Overall, It has huge advantages and minor disadvantages
- Its very well established technology
- It is expensive to buy
- It is consideraby cheaper to run
- It is very eco friendly
- it produces a better product
- Gas Catalytic IR is a valid choice for most thermal processes
- Test before you buy
- Deal with the experts in the field