Dip Coating at OKAY Industries
A Pollution Prevention Case Study
In a period of approximately one year OKAY Industries dramatically reduced their air emissions from a highly specialized coating line by switching from a spraying to a dipping process. As a direct result of this change, they have doubled the coating line throughput and improved quality while cutting costs in half and decreasing worker exposures.
By switching from traditional spraying to dip process and reformulating the "extreme performance" coating, they have decreased the Volatile Organic Compounds (VOC’s) content from 6.6 to 2.0 pounds per gallon and are well positioned to maintain compliance with their air emissions permit for this operation. They have also eliminated the generation of all hazardous wastes from this coating operation.
Okay Industries, Inc. is a privately held metal stamping manufacturer doing business in New Britain since 1911. Their facility encompasses approximately 100,000 square feet and has approximately 80 employees running two shifts per day, five days per week.
They specialize in high-volume, high-quality metal components produced on progressive dies, which are designed and built by their own staff. In recent years, they have developed shorter tooling lead times and prototyping capability with improved engineering software and CAD/CAM. They produce components from all types of carbon, stainless, and alloy steels as well as copper, brass, and aluminum. They have automatic presses up to 400 tons capacity, which allow them to work with metals up to 0.250" thick.
As part of their quality initiative, they became ISO 9002 certified in 1996, and are on target to achieve QS 9000 in 2000. Their served markets are automotive (especially engine-related applications), medical/surgical, electronics, general industrial and the military.
Opportunity for Pollution Prevention
A particular military product has been in production since the 1960’s. One of the final manufacturing steps is the application of a specially developed solvent-borne molybdenum di-sulfide coating to ensure continued reliable operation under a wide range of operating conditions. This Military Specification (Mil-Spec) coating was applied with standard air powered spray guns.
As a result of efficiency limitations of this type of spraying equipment and due to part geometry, over half of the coating purchased was actually wasted as over-spray. The process required extensive operator handling for multiple fixturing and spraying steps on each part which resulted in quality problems.
The spray process also was not capable of consistent coverage on the interior of this part. This resulted in a 6-8% reject rate with subsequent rework to re-coat the part.
The process generated hazardous wastes in the form of spent paint filters, waste thinner (Toluol) and overspray which had to be periodically scraped off the paint booths and floors. The levels of solvent vapors in the ambient air of the work area were also of concern for worker safety.
The coating (as sprayed) contained approximately 6.6 pounds of Volatile Organic Compounds (VOC) per gallon. In addition the spray equipment was cleaned with virtually 100% VOC containing solvents after each production run and at the end of each shift.
Because Connecticut has a serious air quality problem, of which VOC’s are a major contributor, the air pollution regulations required the company to obtain a permit for this coating process. The permit would limit emission rates (hourly and daily) and amounts (monthly) associated with the process. This would have the effect of placing a limit on their production rates on a daily and monthly basis. In addition, there was the potential that if Connecticut’s air quality situation worsened, the environmental regulations could become more restrictive.
In 1991, when the present owner took control of OKAY, the company was cited by the DEP for not having a permit for air emissions from the coating line. They responded in a timely manner (by May 1992) to come into full compliance, so no legal action was ultimately taken by the DEP. It must be pointed out that the present owner had already made the commitment to improve or eliminate any operations that were not environmentally sound. They specifically targeted hazardous wastes and VOC producing processes for improvement or elimination. This coating line was one of four areas targeted under this strategy.
OKAY’s Technical Support Manager requested the sole-source supplier to provide a re-formulated spray coating having most of the solvents replaced with water. When that effort met with little success they decided to take a completely new approach and create a water-borne dip coating. Unfortunately, their supplier was unwilling to invest the necessary resources to do this.
A new supplier, however, was willing to undertake the project. The goal was to create a new water-borne formula that would give consistent coverage, dry quickly with under 2.0 pounds VOC’s per gallon and meet the military’s performance requirements.
They set up a pilot dip line for test pieces adjacent to the existing spray line. Several trials were run with various formulations supplied by the new coating manufacturer. Once they felt they had a viable process, their supplier submitted samples of the coating to the military for testing and approval. After several trials, the final approval came in the form of a new Military Specification that made allowances for this new coating and put more emphasis on performance, rather than the coating chemistry or application method.
In order to prepare for the change to a dip coating, they had been investigating vendors of the necessary equipment. OKAY discovered that there was no single vendor who could provide a complete system needed to hang the parts, dip them into the coating tank, remove any drips and then dry the coating. This left them to design a system and specify suitable equipment using in-house engineering expertise.
As soon as the military gave approval for the new coating, OKAY cut purchase orders to obtain the equipment necessary to construct the dip process coating line. Their new system consists of a standard overhead conveyor, dip tank, electrostatic de-tearing grid and an infrared-drying tunnel. They then had to fine-tune the new line to get all the different pieces to operate smoothly. This process took a period of about four weeks.
The workers had to be trained to operate the new equipment. This turned out to be fairly easy, as both the number of operations needed to coat each piece and the required skill level decreased. The parts are now loaded from the existing containers of the prior operation onto the dip line conveyor and are removed at an adjacent station onto an oven curing rack. The subsequent oven curing operation remained essentially the same. This new system changed the coating process from a batch to a continuous operation.
New Process Evaluation
The number of racking steps decreased from six to two for each piece processed through the line and the requirement for manual spraying was eliminated. This allows the workers to process parts at double the previous rate.
The change decreased coating losses by approximately 50% due to the increased transfer efficiency of dip coating versus spray coating. The parts are now consistently coated uniformly over exterior and interior surfaces in one step.
The infrared drying tunnel dries the newly applied coating enough for the parts to be removed without requiring special handling procedures to prevent defects.
Solvent vapors in the coating work area are decreased with the new dip process to the point where personal protective equipment is no longer required. Along with this, the operators perceive a healthier work environment so complaints and absenteeism have dropped.
Hazardous wastes for this operation were eliminated due to the lack of solvent use in the new coating. No solvents are used for thinning or cleanup. Any waste coating (such as due to spills) is not classified as hazardous waste.
OKAY reports that the investment to change over to the new process had a payback period of approximately six months. A table comparing the former (spray) process with the new (dip) process is shown on the following page.
The air emissions permit obtained from the DEP allows OKAY to operate the dip coating line using the low VOC coating as long as they do not exceed specified VOC emissions ceilings and maximum exhaust stack concentrations. The company must also keep records for this process, including their coating usage and not exceed a cap consistent with the overall VOC emissions allowance.
These limits are not expected to impact production under any foreseeable expansion of production levels.
OKAY Industries has benefited greatly from top management commitment to process improvement and pollution prevention. They have reduced costs and improved product quality, while eliminating hazardous waste generation and dramatically reducing air emissions from a specialized coating operation. They accomplished this through a commitment to improving any processes with significant environmental impacts. They worked with their suppliers and cultivated new ones as well as using in-house engineering expertise.
|Labor hours per 1000 pieces||20.96||11.67||
|Rejects per 1000 pieces||60 - 80||0||
|Pounds VOC per 1000 pieces||36||1.6||
|Coating cost per gallon||$61.75||$52.37||
|Yearly Emissions (Pounds VOC)||65,881||736||
Pollution Prevention Works!
The information in this case study is provided solely as a service to Connecticut businesses. This information may not include all available services and suppliers, and does not constitute an endorsement by the DEP or OKAY Industries, Inc. Use of this information does not in any way lessen your responsibilities for compliance with applicable state and federal laws.
Prepared by the Connecticut Department of Environmental Protection. For more information, contact: the CT DEP Office of Pollution Prevention at (860) 424-3297 or John Bigley of OKAY Industries, Inc. at (860) 225-8707 or www.okayind.com
Content Last Updated on December 12, 2006