Wenger Corporation Saves Over $93,000 by Reducing Powder Paint Use and Rework
Fine-tuning the Automatic Paint Spraying System Process Background
Wenger Corporation supplies equipment and technology for music education and performing arts. Wenger coats nearly 800 different parts with dimensions that range from a few inches to 10 feet.
In 1999, Wenger decided to bring its powder coating in-house to gain greater control over lead time and to reduce costs. The company purchased an automatic powder coat painting system. One of two spray booths are rolled online, depending on whether light or dark colors are being sprayed. Powder reclamation cyclones remove powder from the spray booth and return usable powder to the feed hopper.
Wenger Corporation decreased paint use by increasing transfer efficiency from 75 to 93%, saving over 12,000 pounds of powder and over $81,000 annually. Cost for rework has dropped by an estimated $12,500 annually.
Each automatic booth has two banks of six oscillating guns. Two manual touchup guns are located before the automatics. Painters touch up hard to get areas before the parts pass the automatic guns. The automatic system was designed to powder coat 90 percent of parts without requiring additional touch up. The automatic guns are programmed to adjust the gun-to-part distances according to part dimensions and to trigger when parts move into position.
Incentives for Change
Wenger needed to fine tune its new powder coating system. The automatic spray system was not performing as anticipated and used more powder than projected. Manual touchup and the number of reject parts was higher than Wenger expected. The company wanted to reduce powder use and the cost of waste by 25 percent.
A MnTAP intern reviewed the programming and set up of the automatic spray guns. He investigated other improvements to the painting system as well.
For each major color used, Wenger had purchased a 250-pound capacity main hopper which fluidizes the powder, creating the appropriate consistency for spraying. The automatic level control keeps a constant amount of powder in the hopper to provide continuous powder flow to the spray guns. Virgin and reclaimed powder are fed into the main hopper in a ratio that allows for uniform powder properties.
These large-capacity hoppers were prototypes. The intern discovered that the fluidizing membrane was not supported well and bowed. The bowing caused the air flow holes in the membrane to pinch closed, resulting in the need for higher pressure to fluidize the powder. Because of the bowing, powder was inconsistently fluidized in the hopper leading to puffing and surging when the guns were triggered. Powder would splatter or be too light on the parts, resulting in rejects. The increased pressure also blew out seals on the hoppers, causing loss of powder and compressed air. Line time was lost while repairs were made and the mess was cleaned up.
To help the powder fluidize better, the intern made changes to increase air delivery to the membrane. After this temporary fix, the manufacturer redesigned the membrane supports and the base of the hopper to better suit the large volume of powder. Wenger then purchased hoppers for all colors used in the automatic booths. Now these colors are reclaimed with no spray-to-waste, boosting the total transfer efficiency.
Increased Transfer Efficiency
First pass transfer efficiency
The automatic guns were not functioning correctly so operators disabled their control program, leaving guns to operate with limited movement and without being triggered off as desired. In this mode, distance-to-part was not optimized and powder continued to spray even when parts were not in front of the gun, reducing first pass transfer efficiency. The intern investigated the variables used in programming the automatic guns.
Cyclones control the amount of powder returned to the hopper by sorting out the smaller particles as waste. When cyclone pressure was set at 22 to 25 pounds per square inch (PSI), 25 percent of all powder was going to waste. Each time powder is reclaimed through the system, the fine particle portion is separated and removed from the process by the cyclones. Wastes can also be reduced by improving the first pass transfer efficiency of the system. Waste powder was weighed and its dollar value was tracked.
Cyclone pressure was reduced to 20 PSI. Reprogramming gun movement, distances to the parts and triggering timing, along with reductions in gun pressures, helped achieve a higher first pass transfer efficiency. Powder waste decreased to seven percent, saving over 12,000 pounds of powder and $38,400 annually.
Coating Thickness Testing
Wenger had difficulty achieving a consistent coating, or mil, thickness. The system started out providing inadequate powder coverage. When it was adjusted the powder became too thick on some areas of the part, wasting powder. Manual touchup was done on both the top and bottom of parts. To spray under a part, painters opened the booth doors, affecting the air flow of the spray booths.
To identify the spray variables in need of tweaking, the intern ran a series of 72-inch vertical flat panels through the system. Mil thickness measurements were taken at various points on the panels. Gun variables for spacing between guns, distance to part and up-and-down stroke rate, charge to the powder, as well as powder flow rates were adjusted through eight different tests.
Adjusting the guns greatly improved the consistency of the mil thickness and improved quality. Providing a consistent, even thickness on the part from top to bottom allowed Wenger to reduce overall coating use by 15 percent during the course of the summer. This will result in an annual savings of $25,900.
The panel test also showed that the top and bottom of parts could not be automatically coated to the correct thickness when parts were placed within the top or bottom 12 inches of the operational window. Even when optimal gun settings were used, the tests showed that parts in this top and bottom range were inadequately coated. The oscillators could not overlap at the extreme top and bottom. Parts at the top had the thinnest coating because the powder is affected by gravity and air flow from the opening for the conveyor.
Placing two stationary guns at the top of the booth gave the desired film thickness and eliminated a great deal of manual touchup. Adding two stationary guns at the bottom eliminated the need for painters to go into the booth to paint under a part. The manual touchup openings in the booths could now used as they were designed. Air flow through the booth improved, lessening the amount of paint that escapes and becomes waste. A total of eight additional stationary guns were added between the two booths, costing $36,000.
Equipment ages over time—seals fatigue and gun tips wear out. Moving equipment—like oscillating guns—can cause parts to loosen and change alignment. Testing with flat panels or standard products periodically will help assure that your spray system is operating within the desired parameters or will help you find trouble spots.
Deviating from procedures can impact a system’s efficiency. Operators at Wenger were not cutting powder delivery hoses to the optimal lengths. When they were too long extra pressure was required. Hoses were also routed improperly and not always secured as designed. These errors often caused the hoses to be pinched by the gun movers, restricting air flow or pulling hoses loose, wasting powder. When the air was restricted, powder flow was disrupted, causing defect parts due to sputtering and insufficient coating.
Operators at Wenger thought they were being efficient by quickly cleaning the booths between colors. In their efficiency, they rearranged the order of operations and did not always keep the booth in “run” mode to allow the cyclones to reclaim the most powder possible while the hoses were blown out, guns were blown off, and floor and ceiling swept. Following changeover procedures—in order—can save up to five pounds of powder per color change. For Wenger, this could can save $1,800 a month.
During color changes, powder delivery hoses are changed out with the hoppers. The hoses that are run under the spray booths were suspended by a series of support clips. The intern installed a PVC pipe that operators now simply feed the hoses through, making the process easier and more efficient during changeovers.
With the help of a MnTAP intern, Wenger decreased paint use by increasing transfer efficiency from 75 to 93 percent, saving over 12,000 pounds of powder and over $81,000 annually. Cost for rework has dropped by an estimated $12,500 annually.
Wenger would have improved the performance of its automatic paint spraying system on its own. But with the assistance of a MnTAP intern, the company was able to get a jump on troubleshooting and have its system tweaked much sooner. MnTAP was able to offer Wenger a staff person dedicated to solving this waste-related problem.
New Equipment Reminders
Your purchase contract should document the expectations for the system and the type of technical support that will be provided. The equipment supplier is the expert on any new equipment. Be sure that new equipment purchases include ongoing or follow-up training of operators and their supervisors.
Once in place, most new systems need a little tweaking to ensure they meet operating expectations. Owners and vendors share responsibility in getting the system to run efficiently. Allow time for troubleshooting and be sure to collect data on how the system is operating so adjustments can be made. Systems need the same attention to fine tuning when the product mix changes.