How to Increase Liquid Coating Production
Q. We want to increase our production rate but we cannot increase the length or our existing curing oven. The paint system we use is landlocked in our building. Are there any options?
A. Without the detailed specifications of your particular process, I can only offer a variety of options that would allow you to increase production within your current system. Options include evaluating oven type/design, coating material type, part racking/density and color change process.
Oven Type/Design. Since the length of your oven is fixed, you must ensure that it is operating efficiently. As a first step, I would recommend that you have an oven heat profile run using a data pack that will chart out the heat profile of your oven. Some companies conduct this evaluation on a regular basis themselves or bring in an outside resource. The process involves connecting thermocouples to your part and reading the actual surface temperature of the part through the curing process.
This data can then be compared to the recommended time and temperature for the coating material. If you find that you are exceeding the recommended cycle, you may be able to increase your line speed.
If you do not meet the recommended time at temperature, you could look to add a booster oven in front of or within the entrance of your existing oven. An infrared booster oven can be used to raise the part temperature quicker, reducing the curing cycle, which could then allow you to increase conveyor speed.
Coating Material. Although it may not be easy to make a change in this area, due to your part substrate or performance requirements needed in the coating, it is worth noting. For example, if you are using a traditional material that requires a part temperature of 320°F for 20 minutes to cure (perhaps requiring a total cycle of 30 minutes, depending on how long it takes the part to ramp up to temperature), you could look at some other options. Alternative coating options such as plural component or UV curable coatings can be cured more quickly.
Plural component materials, typically consisting of two components, a resin and a catalyst once mixed, will cure through chemical cross linking. Heat is used to help speed up the curing process. This may allow you to increase your conveyor speed.
UV curable coatings are specially formulated and utilize a photo initiator to cure. Once the coating material is exposed to high-intensity ultraviolet light sources, the coating will cure instantaneously. This drastically reduces the curing cycle; however, it would require an investment in a UV lamp system. There are also hybrid UV curable coatings that will use a combination of traditional curing ovens (convection or IR lamps) in conjunction with the UV light source. The curing cycle is still reduced when compared to traditional coating/curing options.
Part Racking/Density. With regard to improving the productivity of a coating line, an area often overlooked is the part racking and density. I would encourage you to take a look at how you currently hang your parts and present them for the finishing process. Can you hang more parts per rack without compromising coverage? Increasing your rack density will allow you to improve throughput without increasing conveyor speed.
As a rule of thumb, you should space adjoining parts a minimum of 2.5 × the depth. For instance, if you are spraying panels that are 1 inch in depth, you should allow a minimum of 2.5 inches between two neighboring panels. This spacing typically allows for good access to coat the edge with a conventional or electrostatic application.
I recall working with a customer in our lab that was coating the structural end pieces for pallet and store-type racking. These large pieces were hung individually in horizontal orientation. During our lab demonstration, we double hung the parts back-to-back, slightly staggered, and achieved exceptional results very close to the same fluid flow rates. This dual hanging method significantly improved productivity while increasing transfer efficiency.
Color Change Process. How many times per day do you change colors and how long does it take? Some manufacturers have a single or only a few colors and this does not significantly impact their productivity. Other manufacturers change colors frequently, and depending on the amount of time it takes, it can significantly impact their productivity.
How long should it take to change colors? This is normally dictated by the industry and the investment that a company is willing to make in equipment.
Let’s assume there is a general industrial company that changes color 10 times per day and it takes five minutes each time. This is 50 minutes of lost productivity out of 480 minutes in a normal shift or 10.5 percent of the available production time. If this number could be reduced to one minute per color change through the integration of automation, then production could be increased by 40 minutes or 8 percent each shift without ever increasing the conveyor speed.
Automating the color change process starts with a color change manifold assembly located as close as possible to the point of application. This manifold, generally constructed of stainless steel, serves as a central point to feed the desired number of colors from dedicated supplies. Each color is fed to an individual valve, and there is also a dedicated valve for air and cleaning solvent. The valves are opened and closed with a PLC that sequences through a program. The air and solvent are cycled on and off to create a scrubbing action that cleans the fluid lines and equipment much faster and more effectively. An additional benefit to automating the color change process is a drastic reduction in solvent used and paint waste generated, as well as a reduction in the number of defects related to cross contamination of colors.
John Owed is director of MS Powder Business Americas for Carlisle Fluid Technologies. For more information, visit carlisleft.com.
Originally published in the February 2017 issue.
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