An inventor in Florida has developed a new processing category for thermoplastic resins: spray-ons. Larry Weidman patented a thermal spray gun - a high-velocity, oxygen fuel device - that he said can apply a coating of conventional plastic resin in thicknesses of 1-40 mils onto almost any substrate.
Weidman, president of Weid-man Co. of Fort Myers, Fla., said in a recent telephone interview that his device does not require solvents and eliminates emissions of volatile organic compounds usually associated with thermoset processing.
The device can process commodity resins, such as high density polyethylene, polypropylene and polystyrene; engineering resins, such as nylons, thermoplastic polyesters or ultrahigh-molecular-weight PE; or high-temperature thermoplastic resins, such as polyetherketone, polyetheretherketone and fluoropolymers, Weidman said.
He said he tested more than 150 formulations of resins, including resins with ultraviolet stabilizers and other additives. Resins with additives are compounded, then ground to a fine powder before they are processed.
The results, depending on the thickness applied, can be similar to coatings of sprayed paint or coatings put on lawn and garden and industrial tools through dip molding, Weidman said.
However, unlike dip molding, Weidman said his process is not limited by the size of a vat. Also, it is highly portable.
Weidman said the U.S. Air Force is testing his device and process as a way to replace conventional paint on aircraft structures. A thermoplastic resin coating on an aircraft would be lighter and tougher, and it could offer less resistance to air flow than conventional paints, he explained.
The Air Force is considering nylon resins as replacements for conventional paints, and also is considering using the process to apply thermoplastic coatings that would absorb radar signals or distort infrared radiation generated by the aircraft, Weidman said.
Separately, Martin Baginski, president of Production Methods Corp. of Austinburg, Ohio, is marketing Weidman's device and process for coating industrial tanks and other equipment with thermoplastics that are resistant to acid, caustic and other noxious chemicals.
Also, Baginski said he is marketing it to seal and protect bridges and other public and private structures from corrosion.
Weidman's device is basically a spray gun with heat.
A vacuum system pumps powdered resins through the gun while oxygen and propylene gases provide a flame to melt the resin. Because the flame is contained completely within the spray gun, the device officially is designated as ``flameless.''
Nitrogen is pumped throughthe gun separately from the oxygen and propylene to act as a shielding gas. The nitrogen prevents the heated resin from burning, Weidman said.
The gases propel the heated resin through the gun and onto the substrate at a speed of 760 mph, which just exceeds the speed of sound, Weidman said. When the resin hits the substrate, it splatters and adheres to the surface, he said.
Weidman said his device differs from other flame spray guns on the market in two basic ways:
First, it does not require that substrates be preheated prior to coating.
Secondly, Weidman said other flame spray devices operate at low velocities and are only suitable for low-performance resins, not engineering thermoplastics.
Weidman said his process does not alter polymer chains within resins.
He said that a pound of plastic typically can cover 100 square feet of substrate at a thickness of 1 mil. The spray gun can be adjusted to provide a spray as wide as 8 inches in a single pass.
Also, he said the system provides a secure bond between the resin and a substrate that has been properly prepared by cleaning and making it rough. The bond resisted delaminating in tests, he said.
Baginski said the system can operate more than 100 feet away from the supply of powdered resin. Resin is supplied to the gun through vacuum hoses.
Weidman said costs for the basic vacuum and applicator equipment start at $140,000.
Separately, Weidman said he expects to introduce a related device in June that will add reinforcing chopped fibers to the sprayed resins. That device will include a pressurized chopper. He said he has tested the chopper with glass, fluoropolymer, nylon and carbon fibers, and that the chopper can cut the fibers in lengths from three-eighths inch to 41/2 inches.