Ergonomic Spray Gun Improves Production Line

Global competition among industrial finishing operations is fierce. As companies strive to keep costs down, comply with environmental restrictions, and improve quality, they are evaluating all components of their finishing lines. Ergonomics, the human science of matching the equipment, the process, and the environment to the worker, is emerging as one of the most effective tools in the battle. In the competitive arena of plastics finishing, Service Plastics, Inc., Elk Grove Village, Illinois, discovered the benefits of making ergonomic changes to its production line when it replaced several of its traditional spray guns with an ergonomically designed gun, according to Gordon Rhoades, production manager.

Service Plastics finishes television frames and cabinets in crossdraft spray booths. Parts are brought in on a conveyor, placed on holders and sprayed. The parts are then hung back on the conveyor, flashed off, and go through a short bake cycle. Much of the spraying is on horizontal surfaces.

Lacquers and paints are currently supplied by IVC, Indianapolis, Indiana. (Paint suppliers are specified by Service Plastics' customers.) Service Plastics uses a water-borne suede paint (38 sec Zahn No. 2), which provides a soft, textured finish designed to cover imperfections in the plastic TV frames. The flow rate is eight oz/min.

Prior to installing the ergonomic guns, the traditional HVLP spray guns required 12-15 psi atomization air to break up the lacquer. At that time, the company used 30-35 gal of paint to finish more than 1,000 units per day.

In addition to the mechanical production line requirements of its finishing operations, operator fatigue had been an ongoing problem. Complaints about tired and sore shoulders, arms, wrists and upper backs, the primary muscle groups used in spray finishing, were common. Considering the potential impact of human factors on the quality and productivity of any manufacturing process, operator comfort can significantly influence to the bottom line.

Spray Gun Ergonomics

Traditionally, ergonomic changes to spray guns have been represented by a small bump on the gun handle or other minor adjustment. The OMX from ITW DeVilbiss, Toledo, Ohio, represents a significant change in the technical design of a spray gun because it is the first gun to take the capabilities of the spray gun operator into consideration along with the critical requirements of spray finishing operations.

The OMX gun incorporates ergonomic components in the spray gun's design. It is the lightest spray gun available, weighing only 12 oz. The grip is ergonomically designed and features a primary trigger that requires less than two lbs of pull force to actuate. The pneumatic trigger requires less than one lb of pull force to actuate. An upper trigger is designed for spraying horizontal surfaces and bottom edges while keeping the operator's wrist in a neutral position. A pattern adjustment knob requires only a quarter turn to go from full fan to round.

Ergonomics and Material Savings

When the gun was first installed at Service Plastics, the company realized that ergonomic benefits were not limited to operator comfort. The company realized significant material savings almost immediately as a direct result of the ergonomic gun design and its impact on worker performance.

"We have seen significant material savings over our old HVLP guns," noted Mr. Rhoades. "We're using only about 20 gal of paint per day, which is about a 33 pct savings. With these savings, we are paying for each gun in about two weeks.

"Our reject rate has been reduced from seven to about 1.5 pct," he continued. "This is because the paint goes on wetter and with less pressure. Also, the fatigue factor for the painter has been reduced over the period of the day. A reduced reject rate means that operators have to repaint fewer parts, which they like."

The gun air-cap pressure is approximately three to four psi. Prior to gun installation, pressure tanks were filled after three hrs of operation. With the ergonomic gun, pressure tanks remain full up to twice as long.

Operator Comfort

Think of spray operators as industrial athletes whose practice sessions are a minimum of eight hours long, five to six days per week. The industrial athlete's season is 50 weeks long and it's career might span 30 years or more. In that environment, the potential impact the individual can have on the production line is significant.

Realizing the importance of the gun's physical effects on the operator, the supplier contracted with the Biodynamics Laboratory at Ohio State University (OSU) to experiment and investigate the musculoskeletal risk associated with the ergonomically designed gun and a traditional metal spray gun. In this study, experienced and inexperienced male and female spray operators painted for four hours with the two different guns to quantify risks associated with wrist deviation, muscle fatigue, trigger activation and perceived discomfort. The sprayed part required 17 strokes and consisted of leading and trailing edges, plus horizontal and vertical surfaces.

The gun significantly reduced radial/ulnar wrist deviation (the position for painting horizontal surfaces) compared to the traditional gun. Use of the gun resulted in up to 50 pct less fatigue in the shoulder muscles, attributed to the gun's lighter weight.

As for triggering, the OSU study found that using the short, pneumatic trigger of the gun required a significantly lower level of exertion and consequently a reduction in force.

All parts of the subjects' bodies experienced lower average discomfort ratings when using the gun. Significant differences between the traditional paint gun and the ergonomic gun were noted in the shoulder, upper back, arm, elbow, forearm, wrist and hand.

Service Plastics realized the ergonomic impact of the gun right away in its industrial application.

"Our operators have become spoiled (with the gun)," said Mr. Rhoades. "We still have a few of our old metal guns on line, and those operators often come up to me and request `the green gun'(the gun is green). They change places with someone else, use it for a while and their problems clear up."

Start to Finish

Service Plastics is convinced that ergonomics is a true cost benefit. Introducing the gun to its production line has been the most revolutionary change to its finishing operation except for changes in coating technology.

Mr. Rhoades points out that in today's competitive climate, anything he can do to reduce costs positions Service Plastics even better with customers. He cites the material savings resulting from the gun use and operator comfort and improved performance as essential factors in the competitive pricing equation.

"I believe in the whole concept of the gun and the way it sprays. It is so much easier to spray with this gun and the results show it," said Mr. Rhoades.