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SprayJuly2014

Hot Water Bath Modern Concepts The venerable hot water bath (or hot tank) dates all the way back to the beginning of the commercial aerosol industry in 1947. Harry Peterson and other pioneers contacted the Interstate Commerce Commission (ICC—a forerunner of the U.S. Dept. of Transportation DOT) to get assurance that the new, lightweight aerosol dispensers could be legally shipped throughout the U.S. ICC advisors, such as Dr. “Bus” Fulton of the Association of American Railroads, became concerned about the ability of the cans to withstand heat during transit without deforming or possibly even bursting. It was suggested that two boxcars filled with aerosols be parked for three days that summer in the Mojave Desert in southern California, with about 200 peripheral cans fitted with thermocouples. The test was completed soon afterward with no cans deformed, and the highest temperature recorded was 126.7°F (52.6°C). A small safety factor was added and this became the basis of the 130°F (54.4°C) testing temperature. At a meeting of the Aerosol Scientific Committee, Chairman Bill Baleu (Bridgeport Brass, Inc.) introduced an executive from the Mojonnier Co., who had brought along a sketch and mechanical drawing of a hot water testing tank. It had two conveyor lanes with magnetic hold-downs and was about 30' (9.2m) long. Dr. Fulton approved it on behalf of the ICC. Several early contract fillers used local machine shops to construct versions of the device, adding protective screens, thermostats, multiple hot water inlets, an air drying accessory and other refinements. Attainment of the 130°F product temperature was confirmed by using short, maximum reading thermometers attached to the valve dip tube by a rubber band. Starting in 1953, the first water-based aerosols were developed and technicians quickly found that these formulas could not be heated to 130°F by one or two minute immersions in a hot tank. In fact, a fairly viscous starch dispersion only rose by about 14°F in temperature. However, the hydrocarbon propellant layer quickly heated up and produced an internal pressure equal to or greater than the pressure generated by immersing the aerosol for an hour or two in a laboratory constant temperature bath set at 130°F. By this time, the ICC had been replaced by the DOT and the loosely-knit aerosol group had become a division of the (then) CSMA. An industry group went to Washington, D.C. and reviewed the situation with the DOT. A convincing technical report was presented and, after a month or so, the agency revised its regulations to require “heating aerosols to their 130°F equilibrium pressure.” Originally, the hot tank was designed to enable the industry to cull out any permanently deformed or exploded cans. However, during those early days about one to three cans per thousand were found to be leakers. In fact, most fillers had a “salvage man” who would collect leakers, store them in a deep freeze, then puncture them to transfer the costly contents into fresh cans that were sealed and put back on the production line. With the advent of water-based formulas and flammable propellants, this practice was discontinued. Leaking cans were collected in small drums at the end of the hot tank. They were then frequently removed to an outside staging area, often for on-site disposal, along with underweight or overweight aerosols and those with dents, marred lithography or other problems. Fortunately, supplier quality today is extremely high; very few defective cans are detected per shift. The European aerosol industry became commercial in 1956. The Dangerous Substances (EEC) Directive that describes pressure testing and pressure resistance of cans states that aerosols must be heated to 122°F (50°C). During the 1990s, the DOT was contacted by the European Aerosol Federation (FEA) and the U.N. concerning the harmonization of its testing regulations with those of Europe, and ultimately the world. They reacted by adding an alternative. Aerosols could be heated to develop their equilibrium pressure to 122°F (50°C), provided the content would not fill more than 95% volume of the dispenser when heated to 130°F (54.4°C). Because of legal and labeling concerns, nearly all U.S. marketers have decided to stay with the original 130°F (54.4°C) regulation, although the energy cost is somewhat higher. The 76 SPRAY July 2014


SprayJuly2014
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