The coatings industry, like so many others, has become increasingly concerned with environmental problems and continually seeks methods and materials that are less hazardous and wasteful. Among the concerns are the environmental problems associated with VOCs, which led the U.S. Environmental Protection Agency (EPA) to embark on a program to remove VOC-bearing coating materials from the market as alternatives became available. This effort continues today with increased urgency. Painting contractors facing increasing regulatory pressure in the use and handling of all paints are looking for viable alternatives.

The Xiom1000 system solves the problems of temperature and inconsistent feed rate with a patented gun and powder feeder.

Beginning in the 1960s, electrostatic powder spray process (EPS) became the standard for applying organic polymer coatings. This process is commonly referred to as "powder coating," which means EPS is applied to plastic powder coatings followed by oven curing at approximately 400°F, where melting and film formation take place. In the early to mid 1980s, having little or no VOCs was one of the recognized benefits of factory powder coating.

Other benefits included reduced waste, easier clean-up, good barrier protection, and reclaimable and reusable overspray. However, the materials, methods, equipment, and knowledge of applications still had a long way to go.
Even in the early days, job shop powder coaters and field paint contractors were expressing both the desire and the need to apply powder paint on site. The thermal spray industry attempted to address this need beginning with the flame spraying of thermoplastic powders. But 20 years ago, the results were not too promising.

Two main problems were behind this disappointing beginning. First, the materials available then were limited and not as advanced as now. Second, the thermal spray equipment available was not suitable for low melting point polymers.

The plastic powders being sprayed were the same as those used in the EPS process. No effort was made to modify powder particle size distribution to meet the requirements of thermal spraying. In addition, no effort was made to design new polymer coating formulations for on-site thermal spraying. Coating adhesion, function, and decorative value suffered as a result.

The thermal spray equipment was not suitable for low-melting-point polymers. It had been designed primarily for spraying high-melting-point-metal powders and then adjusted to handle polymer powders. These modifications didn't adequately prevent polymer powders from overheating and burning; therefore, coatings didn't always achieve their intended physical and chemical function.

Pipe being sprayed with the Xiom system.

Flame temperatures designed to melt metals were far too high for powder paint polymer feed stock materials. Propane is a given for the heat source required for these materials because it has a lower flame temperature but higher BTU content than acetylene. In addition, propane hoses can safely be run at longer distances, and historically propane is more economical. Simple propane/air and propane/oxygen mixtures have been tried, but both produced too high a temperature to successfully deposit low melting-point materials.

In addition, existing powder feeders couldn't provide simple, inexpensive, consistent, and reliable feed rates. A consistent feed rate is particularly important for low-melting-point polymer materials because there is a small window between the melting point and ignition. Also, if the feed rate load is too high or is pulsing, polymer materials can act as a fuel source. This was the main problem with previous technology.

Besides having too high a temperature and material feed pulsing, previous technology consumed up to 50% of the coating material and in many cases, even damaged the substrate. The flame measured up to 12 inches long, and the temperature was increased by the ignition of the feedstock material. The increased flame temperature was a further detriment to the coating once it was deposited.

Car part being sprayed by the Xiom system.

Today, as job shop powder coaters face increased competition, many see the on-site market as untouched potential. Recent attempts by the thermal spray industry to provide equipment for field-applied powder coats have had more success than the earlier efforts, but this is mostly due to improved materials. Efforts in equipment development failed for one major reason: plastic powders often act as a fuel source and a short three-inch flame becomes a two- to three-foot flame if the heat source's temperature is too high for the powder material being applied.

Xiom Corp. has solved both problems of temperature and inconsistent feed rate with a patented gun and powder feeder.

The System
In the system, oxygen and propane gas are mixed by means of a chambered double reversing vortex, eliminating the complicated siphon plug of previous systems. This is a simple device that is easy to machine with few parts. Also, the nozzle of the gun provides for a shroud of air between the flame and the feed stock polymer material, which clips and reduces the flame temperature. Additionally, an air distributor cap creates a compression wave, which allows for the rapid transfer of heated air to the material to be melted.

The compression wave is analogous to a pressure cooker; however, it is an open rather than closed system. The gun has a visible one- to three-inch flame and polymer feed stock material is visible as a stream beyond this point. The system does not consume the material and can achieve deposit efficiencies of up to 99%.

Powder Feeder
The other breakthrough of this system is a unique patented powder feeder. This simple and inexpensive feeder provides stable material feed due to its open coupled double venturi. This approach eliminates all pocketing of material in the feed hose. Back pressure surging is virtually non-existent and has no effect on the feed rate.

The flaw of all prior powder feeders is that they have one venturi, which siphons up the material from either a fluid bed or feed screw and then conveys it to the nozzle discharge. However, the material feed rate and material delivery rate are two separate functions and therefore require two separate venturis. The material feed rate must be matched to the available BTUs and system geometry for each separate material. In addition, the material delivery rate must be matched to the dwell time and/or particle velocity required to melt the material.

In existing powder feeders, material builds up in the feed hose, creating a back pressure, which reduces the vacuum of the single venture. The material rate is constantly changing and the delivery of material is constantly pulsing and surging. This problem increases with hose delivery length. The Xiom powder feeder is designed to work with thermal spray equipment and in factory powder paint systems. The total system consists of the powder feeder, console and hoses and weighs just 70 pounds.

Other Developments
Xiom Corp. has also designed a unique line of mixed polymers that are completely free of VOCs. Little or no preheat is required to easily apply the materials to metals, paper, cardboard, plastics, glass, concrete, asphalt roof tiles, fiberglass, duct-board, wood, and canvas as well as other surfaces.

Powder innovation is particularly evident in coating adhesion to various substrates without the need for liquid primers. Surface preparation for most substrates now requires only cleaning and roughing to achieve reliable and reproducible bonding. For instance, Xiom is the first to produce thermal sprayed epoxy/zinc primer/bond coatings delivering very high quantities of zinc to the substrate for corrosion control. These epoxy/zinc primer coatings were designed for secure bonding to steel substrates and to enhance bonding of sprayed plastic coatings by leaving a suitable rough surface for proper adhesion.

Xiom also produces grip and release coatings, coatings for tank linings, concrete and steel structures and anti-microbial coatings for surfaces that come in contact with food and water.

Powder coating—long known for reduction of waste, good barrier protection, ease of cleanup and lack of VOCs—has moved squarely into the new century, both in factories and on site.

For more information, contact Linda Comac at (e-mail) lcomac@xiom-corp.com.