Bfore the clever inventions of two well-known Americans in the late 19th century, all painting in the United States was done with a brush. Brushes were used to apply paint on buildings, furniture, horse drawn wagons and early horseless carriages. And it took a long time to complete the job, no matter what it was. Imagine painting a 10-foot high by 100-foot long wall with a 4-inch-wide brush. You'd be at it forever.
It was just that daunting task that led Joseph Binks to invent a machine to paint walls. In 1887, Binks was a maintenance supervisor for Marshall Field's Department store in Chicago. Marshall Field's had miles of basement walls that needed to be whitewashed regularly, and when Binks sent a crew down there with brushes and buckets, it was weeks before they finished the walls on a single level of the multi-level basement. In an effort to speed the task, Binks combined a hand-operated pump, a vessel to hold the liquid under pressure and a wand with a nozzle on the end - much like the pump-up garden sprayer you currently use. The whitewash was strained into the tank, pumped under pressure by the hand pump and propelled out the end of the wand.
Binks' cold-water paint spray machine worked great, and the Marshall Field's basement never looked better.
Binks had the opportunity to expand his vision when, in 1893, the Colombian Exposition was held in Chicago - an event on the scale of a World's Fair. People came from all over to see this extravaganza of technology.
But with just days to go before opening, 90 percent of the buildings housing the exhibits were still unpainted. Enter Joe Binks' Paint & Whitewash Spraying Machine. All buildings were sparkling white by the show's opening, and the exposition was referred to admiringly as "The White City" in the press.
Uses for Binks' invention grew steadily. In addition to whitewash, disinfectants and insecticides also lent themselves to spray application, and Binks' unit became a mainstay in agricultural operations around the world in the early part of the century.
Who's the second American to forever change the way painting was done? A doctor trying to cure sore throats.
Open Up and Say, "Aahhhh ... "
In 1888 in Toledo, Ohio, a doctor specializing in treatment for ear, nose and throat disorders had a problem. Dr. Allen DeVilbiss was frustrated with his efforts to medicate his patients' sore throats. If he gave them medication in liquid form, it quickly passed over their throats and was swallowed. To alleviate this, DeVilbiss combined a rubber bulb, some tubing and the base of an oil can to invent the first atomizer. By squeezing the bulb, air was propelled over the top of the tubing, lowering the atmospheric pressure and causing the medication to rush upward to fill the partial vacuum. Once up into the air stream, the tiny atomized particles of liquid medicine rested on the inflamed tissue of the patient's throat long enough to do some good. This is exactly the same principle that siphon (or suction) feed spray guns work on.
In 1907, DeVilbiss' son Thomas expanded on his father's invention and created the first hand-held, air-powered spray gun. By blowing compressed air across the top of a pickup tube submerged in liquid, he created a controllable pattern of atomized material.
The first use for Thomas DeVilbiss' spray gun was in the furniture industry. Just as they would eventually do in automotive finishing years later, spray guns drastically reduced the time required to finish a piece of furniture.
During this period, many manufacturing operations used water to cool parts of their process. Cooling water for re-use fostered the advancement of nozzle technology.
One popular way to cool water was to aerate it into a mist to dissipate the heat. Applying the lessons learned about nozzle hole shapes, sizes and locations enabled Binks to make his pressure sprayers work better, too. And in 1919, Binks introduced his first hand spray gun using compressed air and sold it to a manufacturer to apply carpet dye.
The 1920s: Cycle Time Improvements
Prior to 1924, cars were painted by hand with a brush using shellacs and varnishes. While the earliest assembly-line process enabled the car to be constructed fairly quickly, the paint process took as much as a month (and you thought you had cycle time problems)! By switching to the new air spray guns, completion time per car was shortened to about a week.
The next leap in auto painting speed was a change from shellac to lacquer paints. The DuPont Company introduced nitrocellulose lacquer finishes in the 1920s. Because the solvent (lacquer thinner) evaporated so quickly from the paint film, it couldn't be brushed smooth. The new air spray application was the only option. The 1924 Oakland automobile was painted using DeVilbiss spray guns and DuPont Duco paint, and the cycle time went from a week to two or three days - 10 times faster than the brushed shellac method.
The 1930s: Switching Colors? No Problem
During the 1930s, both DeVilbiss and Binks offered hand spray guns that made changing colors easy. The Binks Model 7 and the DeVilbiss Model MBC were constructed so that the entire spray head assembly, complete with air cap, fluid tip, fluid needle and paint pickup, could be dislodged from the gun body by loosening a single bolt.
It was also pretty easy to switch from painting the cars on your assembly line black to dark blue. The spray head on your pressure feed MBC or Model 7 was connected by a rubber fluid hose to a big barrel of black paint. You just unbolted the entire head, hose and all, and bolted on the new one connected to the drum of dark blue paint.
(HVLP guns were also invented in the 1930s. See "The 1990s: The Advent of HVLP".)
The 1940s: From Cars to Cream Puffs
In the 1940s, spray gun sales took off. Not only were people spraying paint or dyes on every manufactured product, they were spraying cream on cream puffs in bakeries and fabric protectors on clothes at the dry cleaners.
When we went to war, olive green and battleship gray paint were sprayed on literally everything from military vehicles to ships to bomb casings. In fact, many of our industry's future painters learned their craft by spraying for Uncle Sam during World War II. They returned home to find a ready market for new cars and also found money and materials available to refurbish the old ones.
The 1950s: Three Guns to Choose From
During the 1950s when manufacturing shifted into high gear across the country, many manufacturers didn't need the ability to change colors readily because they only painted one color. All toolboxes were red, and all tractors were green. This handle style (one-piece gun body) remains an industry standard today for many kinds of spray guns (excluding the aggressively ergonomic plastic ones, of course).
Three styles of automotive spray gun were (and are) prevalent: siphon feed, gravity feed and pressure feed.
- Siphon feed has the pickup tube pointing down into a cup with a hole in the lid. The hole exists to let in atmospheric pressure (14.7 PSI). When the compressed air passes over the top of the pickup tube, it lowers the atmospheric pressure. The resulting partial vacuum is now less than the pressure entering the cup through the hole on top. The paint in the cup rushes up to fill the vacuum, and the paint gets caught in the rushing air and is blown into small particles by the high-pressure, swirling air.
When this style of gun quits in mid-job, the likely cause is that the top air hole is plugged. Because no replacement air can enter the cup, the paint stops flowing up the pickup tube. It also lacks good transfer efficiency because the paint that exits the front of the gun gets caught in the opposing streams of swirling air in front of the air cap and is blown off target.
- Gravity feed has better transfer efficiency because the paint naturally falls out the front of the gun and doesn't have to be sucked up to the air cap. But the air cap on gravity feed guns still pulls the paint out - that's why the lid to the gravity feed cup has a hole in it, too. One objection American painters make about gravity feed guns is that they can't set them down. Any flat surface will do for a siphon feed cup gun, but gravity guns must hang on hooks or the paint runs out the atmospheric air vent.
- Pressure feed incorporates Binks first invention and has the advantage of pushing the paint up to the air cap. This delivers more paint than the partial vacuum can suck up or that gravity can pull down. By forcing the paint out through a nozzle, some atomization occurs. Add more atomization from the compressed air, and you can put lots of paint on the target, fast.
All hand spraying done on car production lines is pressure feed because of its speed and agility. Agility? Pressure feed still works when you hold the gun upside down. Neither siphon nor gravity will feed paint to the air cap once you tip them over (plus they'll drip paint out the vent hole).
Pressure feeding the paint up to the cap under very high pressure takes Binks' machine another step forward. Called "airless spraying," the paint is pushed up to and through a special atomizing nozzle under huge pressures developed by a multistage pump. First marketed in the 1950s, this advancement made it possible to paint huge surfaces, like entire sides of buildings, in hours. If you're an automotive painter and you've never run an airless gun and pump, rent one and paint your garage. There's nothing like a 5-foot tall paint pattern 3 feet in front of you to give you a feeling of power!
The 1960s: It's Electric!
In the ongoing battle to improve transfer efficiency, thereby saving money and material, electricity was added to the spray gun mix by the 1960s. Electrostatic painting means high voltage (up to 100,000 volts) runs through the part, and the opposite charge runs through the paint. The paint is sprayed through a special gun that not only pumps up the paint to the air cap, but also charges each paint particle as it leaves the gun. When the paint and part get together with their opposite charges, the paint literally leaps onto the part. There's no disruptive compressed air to blow the paint off target.
The 1970s: 2K Systems Bring Consistency
Special guns that blend two-component products established themselves in the '70s and are now used to spray everything from foam insulation to fiberglass boats. Many specialized combinations of material delivery, material temperature, blend ratios, pattern size and coating thickness can be built into these 2K spray systems. Often built onto a robotic arm, these guns ensure repeatable consistency for very complicated paint procedures.
Using robotic painting arms to apply paint serves two purposes: It keeps human painters out of a hazardous and unhealthy atmosphere, and it provides for exact duplication on every painted part.
The 1980s: Powder Power!
Powder painting is an outgrowth of electrostatic technology and though it's been around for decades, it really came into its own during the '80s.
How does the process work? The painted object is grounded, and the powder is positively charged in a special spray gun. Once attached to the part, the powder is then heated until it melts smooth. Transfer efficiency is almost 100 percent because you can just sweep up any powder overspray from the floor and put it back into the hopper for tomorrow.
Because of the electric charge, it's difficult to incorporate metallic reflectants into powdered paint. But new advances are being made with reflective vinyl that will accept a charge much like dried paint does, so we may finally see metallic finishes applied with powder coating.
Clearcoating with powder is already a common practice. In fact, some OEM automobile clears are applied as a powder over a conventionally sprayed base color.
The 1990s: The Advent of HVLP
An important piece of spray gun history is the advent of the high volume, low pressure gun (HVLP) design. Around since the 1930s, HVLP came to the forefront in the '90s as a response to 1987's Rule 1151 in Southern California. Air pollution was the problem, so high transfer guns (65 percent +) were utilized to reduce smog. The same problem was the impetus for the National Rule about VOC content in paint. The result was thicker, more solid paint, requiring smaller fluid tips to spray successfully with any spray guns. HVLP spray guns became a household name not only because of pressure from regulators, but because of their ability to save material cost by actually applying to their target instead of into the air.
HVLP guns were originally an electric carpet vacuum cleaner running backward. The principle is to atomize and propel the paint at low speed and in big droplets to prevent the paint from swirling off target. This HVLP technology can be applied to any of the three spray gun styles.
Siphon feed HVLP still doesn't have very high transfer efficiency because of the crossed air streams necessary to pull the paint up to the air cap. The swirling air shoves the paint particles sideways and away from the target.
Gravity feed HVLP spray guns have a marked improvement in transfer efficiency over regular gravity guns. The combination of Newton's Law and low air pressure keeps the turbulence to a minimum and allows more of the paint to strike the target.
Pressure feed HVLP has the highest transfer efficiency and is what the Southern California regulators had in mind when they passed Rule 1151. Because the paint is forced up to the air cap by pot pressure and then propelled out at low atomization pressure, much more of the paint strikes the target. There's no vent hole necessary in the lid of a pressure feed paint cup, but a check valve (a one-way valve) is required to keep the paint from squirting back out. It lets the pressurized air pass into the cup but won't let the paint pass back out. When your pressure feed gun quits in mid-job, the check valve is likely stuck in the closed position by the gummy paint inside the cup. The moral here might be that successfully using any spray gun and keeping it from quitting mid-job means keeping it clean and well-lubricated.
Ready, Aim ... Paint!
Similar time lines for spray gun development exist in Europe and Asia, and several other long-time spray gun manufacturers had counterparts to Binks and DeVilbiss. Because of all their inventions, today's marketplace is filled with spray guns from around the world, and each of their unique features and resulting benefits might be just what you need.
If you've been painting with the same spray gun for a couple of years, test-drive a few new ones. Just like buying a new car, it seems irresponsible to buy a new spray gun without trying it first. Paint a few jobs with the new gun to see how it operates.
During the test jobs, precisely follow the setup instructions and spray procedures for the gun. After you give the gun a fair test at the recommended settings, feel free to fool with everything until it suits your style.
You like the gun you've been using for the past 10 years, huh? That's great, but if you don't at least take a look at a new gun every few years, how will you know what you're missing? Spray gun technology hasn't changed as quickly as computer technology, but progress is made regularly. For example, if you haven't changed to a smaller diameter fluid tip in your existing gun, you're probably fighting orange peel and overspray all the time. And to accommodate the National-Rule-compliant, high-solids paints used today, you need smaller fluid passages, no matter what style gun you're using.
Ask your jobber to demo the latest spray gun. Have it equipped especially for your paint brand with just the right diameter fluid tip, matching needle and air cap. You might be pleasantly surprised by the results you get - and by the headaches you don't!
Writer Mark Clark, owner of Professional PBE Systems in Waterloo, Iowa, is a well-known industry speaker and consultant. He's been a contributing editor to BodyShop Business since 1988.