New paint spray line improves work flow, production capacity and finish quality...
Manufacturers of large-sized equipment often face challenges when preparing, painting and curing products. The size and weight of the parts they manufacture make it difficult to achieve smooth, efficient work flow in a reasonable amount of floor space.
This was on the minds of executives at Robinson Helicopter Company, Torrance, California, as they planned a move into a 260,000-sq-ft manufacturing facility that would triple the space of the previous site. Robinson Helicopter is a leading manufacturer of light helicopters for worldwide markets. As the company grew, its existing quarters became too small. Insufficient space and inconvenient location of the paint prep, priming, painting and drying areas had become a real stumbling block to the efficiency and increased production capability it sought for growth.
Before the move, company President Frank Robinson met with Ed Broman, vice president of procurement, and Wayne Walden, vice president of manufacturing, to examine the finishing operation. Mr. Robinson envisioned a new and efficient physical layout to streamline work flow. His goal was to move the helicopter from preparation through final trim painting in as compact an area as possible, reducing the time and labor required for painting and curing.
The Robinson Helicopter team formulated several goals, including faster throughput, reduced labor, and better overall finish quality. Although the company's paint spray process had always been in compliance with California's South Coast Air Quality Management District's (SCAQMD) regulations, it hoped to improve for the future.
Upon further study and analysis, the team decided to completely redesign the finishing process with all new equipment. Citing specific situations that needed streamlining, Mr. Broman noted, "Some inefficiencies were obvious and related to space constraints. For example, each aircraft coming off the manufacturing line had to be wheeled outside for cleaning, sanding and masking. Then it was moved to one building for priming and to another building for painting. There, the craft remained in the paint booth for three hours to dry between coats. Convection heating is used for curing. This excessive maneuvering from location to location slowed production, and the paint spray booth was inoperable while the paint dried."
The team targeted other problems as well. For drying and curing, heated-air supply units were used as heaters to dry the helicopters after painting. Incoming outside air was heated to 120F, introduced into the booth, then exhausted into atmosphere. Improving this time-consuming, expensive and energy-wasting process became a priority.
Armed with a preliminary work flow plan, Robinson Helicopter called on Binks Manufacturing Company, Franklin Park, Illinois.
Bob Hauck, industrial market manager at Binks' Los Angeles office, coordinated the project. The company designed two spray paint systems that would enable Robinson Helicopter to maximize product flow, improve finish quality, meet all SCAQMD requirements and reduce operational costs. The design of the helicopter finishing facility was a total team effort, customizing various technologies to this specific application.
Two spray booth systems, one for priming and one for topcoating, are at the heart of the paint spray systems. The booths are drive-through enclosures, and each is equipped with an adjoining IR tunnel that also incorporates convection heat.
Robinson Helicopter selected cross-draft booths, similar to the units used previously. Each booth has a dedicated air make-up system that supplies filtered, heated air to a supply chamber built into the booth. The new spray booths are quieter, because of mufflers installed in the exhaust stack. In addition, larger door sizes and increased interior lighting for better visibility were added.
Between the two large main booths are two prep booths, where all cleaning, sanding and masking are done. This setup allows the helicopter to be sanded, cleaned and masked in the prep booth; primed, topcoated and trim-painted in the large spray booths; and pushed directly into the infrared section of the oven for curing. It's an efficient configuration that has dramatically improved work flow by eliminating the time and labor needed to transport the craft from one process to the next.
The HVLP spray guns are conventional air spray guns with special modifications and nozzles that allow the gun to operate within SCAQMD VOC emissions regulations. The air passage has a sonic venturi that limits air flow by creating a shock wave in the venturi throat. The air and fluid nozzles allow the gun to atomize the fluid at low air pressures and velocities.
The sonic venturi and gun nozzles interact to limit the air pressure to a maximum of 10 psi at the nozzle. Normal operating pressure at the air nozzle is three to five psi, where Robinson has found it obtains the best transfer efficiency.
The gun uses ambient compressed air from the shop air supply. A five-hp compressor is used to supply the atomizing air. However, compressed air use is low, ranging from 11 to 20 scfm, depending on the operating pressure. The painter controls the atomizing air pressure, fluid flow and spray pattern.
Frank Robinson states that he is satisfied that the new design implements his original vision. He comments: "It is an impressive sight to see the booths and ovens end to end in a space that is just 90 ft long and 50 ft wide.
Infrared curing and monitoring/control technologies were installed in the ovens to meet special requirements. For example, infrared remote surface-temperature-monitoring probes are arranged in the IR oven section of each booth, profiling the entire craft and constantly monitoring surface temperature, to ensure that temperature never exceeds 160F. The craft's plastic windshield would warp at higher temperatures.
A specially designed spray-booth control panel incorporates a silhouette of the ship's profile, illuminated by LED indicator lights that display the actual temperature of the helicopter surface at each probe. If the set point is exceeded at any position, a built-in alarm system warns the operator, and the system shuts down automatically. Operators attest that this custom-tailored system is not only accurate and reliable, but very easy to use.
The IR ovens also combine hot air convection heat with IR radiant heat to provide a flexible and efficient system that gives operators better control of the curing process across a wide range of conditions. Mr. Robinson recommended this combination of heating technologies because of the helicopter's complex configuration. The hot air convection was accomplished using duct heaters and blowers to circulate heated air (120 to 160F) through the oven enclosure, enveloping the aircraft. The heat setting is controlled from a remote thermostat in the control panel. Operators report that, on average, the infrared heat alone is sufficient for fast, high-quality cures. But they have the option of adding convection heat for speedy curing in high humidity, eliminating production delays.
Mr. Broman noted time savings and increased quality are the two major benefits Robinson Helicopter has realized as a direct result of the new drying ovens. He stated, "Since the installation, the paint surface quality of our helicopters has been uniformly excellent, thanks to the combined IR/convection ovens. Equally important is that the time required for curing is now a fraction of what it was, dropping from three hours to about 45 min."
To complete the new finishing operation, Robinson Helicopter also added a small parts line for prime coating and curing of miscellaneous parts. This line includes a waterwash booth, IR oven, and overhead conveyor system that transports parts into the booth where they are sprayed by operators using electrostatic hand guns. Initially, when the supplier recommended a waterwash booth, Robinson Helicopter engineers were hesitant about accepting it, since they had previously used only dry filter booths. However, the "E" style booth included a Centri-Clean™ system, which uses centrifugal force to automatically dewater, compact and discharge paint solids from the spray booth. Once Robinson Helicopter saw the benefits, it agreed to both the waterwash concept and the additional installation expense in order to eliminate the waste disposal expense of dry filters.
Although operators admit that it took time to adjust to the waterwash booth, the results of the choice have been overwhelmingly positive. The new unit eliminates the need to change filters, reducing both maintenance time and labor. Recycling the booth water supply conserves energy. Waste disposal costs have dropped considerably, due to the minimized waste from the Centri-Clean.
With the new system design, Robinson Helicopter has realized its goal of developing a cleaner, more environmentally friendly finishing process. A special filter, approved for eliminating hexavalent chromium emissions, was installed in the exhaust of each of the new spray booths. The filter, known as a "PE Cell," is manufactured by Air Technologies, Inc.
The large main spray booths use a two-stage filter inside the booth, with the final "PE Cell" filter located higher upstream in the exhaust chamber. These filters successfully eliminate all chromate emissions, as specified by SCAQMD regulations. For the same reason, the waterwash booth is also equipped with this type of final filter, located in the exhaust of the wash section, enabling the booths to meet some of the toughest air regulations in the country.
Robinson Helicopter is satisfied that the new finishing system meets all of the stated goals. The company now produces a total of 195 new aircraft each year. Current throughput of the paint production process is six crafts per week, including three four-seat R44s and three two-seat R22s and two overhauls of original equipment.
Frank Robinson concluded: "We've already realized our original objectives, in terms of improved quality, better environmental control and reduced operational process time. However, the most significant advantage of installing the new system is the expansion of our production capabilities. We're better positioned than ever before to meet the light helicopter demands of a global marketplace, now and far into the future."