Powder coating with robots

Powder coating with robots

FO C U S 300 popular colours in a variety of effects and textures, in small sample sizes up to 10 lb, covering all of the main chemistries of powder c...

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FO C U S 300 popular colours in a variety of effects and textures, in small sample sizes up to 10 lb, covering all of the main chemistries of powder coating (p 3). This new alliance, under the name TruPak, will allow rapid sampling to coaters seeking new customer approval, or meet requirements for small orders and work that need small amounts of both colours and product types. Supported with a 24 hour technical service, TruPak is bound to increase the sales of TCI Powder Coatings. Another global market survey (p 5) highlights the increasing use of UV curable resins in the Asia/Pacific market where the usage is over half of the total global demand. The largest and fastest growing end usage of UV curable resins is coatings manufacture, an outlet which accounted for over 65% of the total global demand in 2012. UV curable resins are considered to be an attractive alternative to conventional coatings because of their faster curing time and low VOC content. Many indigenous Chinese manufacturing companies already favour powder coatings for in-house finishing operations and UV curable powder coatings are the ideal choice for combining freedom from VOC emissions with the lowest production costs. Many supplier companies are seeking to develop bio-based raw materials, and I think it is difficult to justify the reasoning behind this concerted move away from lower cost alternatives. Their main argument centres on the belief that bio-based products are the only replacement option to the declining use of fossil materials. As global warming continues its relentless effect upon our climatic conditions, it becomes increasingly important to reverse the build-up of carbon dioxide in the atmosphere. This is not scientifically difficult; it merely requires global co-operation to collect this pollutant. The collected gas can then be converted into carbon compounds 2



that will become a lower cost alternative to the currently used fossil-based materials, and certainly much cheaper than bio-based products. Food crops are a more essential future requirement! Sid Harris

TECHNICAL Powder coating with robots The efficient use of robots coupled with dense phase technology is a combination that has made large volume powder coating application the most effective alternative to liquid coating procedures. Modern robots used to control the movement of the powder spray gun are small units that offer more flexibility than fixed axis powder applicators. They can maintain a gun-to-part distance that is more precise and they are able to contour a work-piece and penetrate into difficult to reach areas, ensuring a more uniform coverage of the powder to all surfaces. There are robots available that can sense when a work-piece is misaligned on the conveyor track, and also the type of work-piece and its shape. Part identification instructs the robot motion and it can send information to the powder gun controller to adjust powder flow and electrostatic control. While the use of a robot alone will give a consistent coating that reduces powder waste and minimizes rejected parts and rework, it is possible to achieve even higher levels of productivity when the robots are coupled with dense phase powder delivery and fast colour change. The dense phase delivery pump was developed to replace the venturi pump, which at high line speeds tended to propel the powder past the work-piece. The new pump was designed to deliver more powder at lower

C O AT I N G S velocities by operating as a twochamber metering device with two valves timed to simultaneously pull powder in by vacuum and push it out with pressure. This lower powder velocity allows the powder to be charged more efficiently due to the increased relaxation time of the corona discharge. The overall effect of dense phase delivery is that the gun to work-piece distance becomes shorter. It does not, however, mean that the effective spray fan pattern width is reduced, because there are a wide range of nozzle configurations available to match or improve upon the spray pattern of conventional powder spray guns. As the dense phase technology was applied to 20 second colour changes it also became adaptable to automatic gun setups used for spray-to-waste systems, and also for use in reclaim powder systems. The almost infinite movement and reach of a robot gave the dense phase gun the ability to track very close to the work-piece at a high speed, resulting in exceptional powder uniformity, better film build, reduced overspray, and reduced cycle time. Coupled with current limiting technology by automatic feedback control, this enables the robot to reach into cavities without bounce-back of the low velocity powder. It also avoids the defects caused by high increases in current and voltage, which create back ionization and the Faraday Cage Effect. The dense phase technology is not limited to organic powder coating. It can also be used to pump and spray ceramic powders and is currently being applied to the coating of oven cavities. The versatility of these combined technologies is described in an article entitled ‘Powder Coating with Robots and Dense Phase Technology: A Critical Blend of Advanced Technologies’ by John Binder of Nordson Powder Coating Systems. Original Source: Metal Finishing, Jan-Feb 2012, 110 (1), 31-34 (Website: http://www.sciencedirect.com) © Elsevier Inc 2012

JULY 2014