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Spray Oct 2014

Coster rotary gassing equipment. 32 Spray March 2014 machine turns a partial vacuum of about 18 to 22" Hg. is first drawn. This is optional. Then the valve mounting cup is mechanically lifted slightly and propellant is added. Finally, the cup is pressed down quite forcefully (download pressure) and the hermetic crimp is performed. These operations contrast with those of the TTV gasser, where the can is first either atmospherically or (partial) vacuum crimped on a separate machine, after which it travels to the gasser for propellant injection. The cost and complexity of the UTC gasser have limited its use in aerosol lines outside the U.S. and Canada. It also leaves a “valve cup full” of liquid propellant when the can is exited. This 3mL or so of propellant instantly evaporates with a unique hissing noise, causing a barely visible cloud of gas to slowly drift downward, where it is captured by the laminar air ventilation system and safely discharged. This may seem insignificant at first, but for a high-speed line producing 100,000 cans per shift, the gas house loss would amount to about 82.2 U.S. gallons. An early advantage of the UTC process is that the propellant is injected around the valve cup, so that the flow rate is not impeded by valve orifice size. To overcome this deficiency for TTV gassers, male valves and adapters were modified so that valves could be gassed both through and around the stem. This by-passed the stem orifice, but left the body tailpiece and any vapor-tap orifices still in play. Nevertheless, it was a significant step forward and probably led to the sale of more TTV gassers. During the 1980s, Precision developed a unique valve called “The Super 90” where the top of the nylon body was crenelated (multi-notched or indented— “crowned”). When under about 600 psi-g. of liquistatic pressure in the gasser, special stem gaskets bend downward into these small channels, allowing the propellant to quickly flow over the temporarily deformed gasket and into the can. This development was copied by other valve suppliers and has effectively removed the last flow rate obstacle to the use of TTV gassers. These comparatively simple machines have low maintenance, can operate with Buttons on Valve with small actuators, lose relatively little propellant in the aftermath of gassing and have the ability to be operated in unoccupied (TV monitored) gas houses. For both UTC and TTV gassers, when using dimethylether (DME), the hoses must be metal lined or metal mesh covered to prevent static charge buildups and the gaskets must be DuPont’s Kalrez for continuous service. The gassing of carbon dioxide at high speeds has posed some challenges. One marketer fills their hydroalcoholic product by first making a solution of about 10% carbon dioxide and 90% ethanol in a pressure-resistant mixing tank. This mixture, with a pressure of about 200 psi-g. at 70°F, is used as the propellant portion. In about 1995, the Kartridg-Pak firm (now R.A Jones & Co.) developed a nine-head oscillating gasser-shaker capable of dissolving carbon dioxide into unusually viscous liquids and even flowable pastes. Today, however, most high-speed methods include the IIG process. This process, developed in about 1980, initially used a UTC gasser to very rapidly inject carbon dioxide, under pressures of about 460 to 680 psi-g, into low viscosity aerosol concentrates. The gas would then explode the liquid into millions of tiny particles, providing a huge surface area, and thus enabling the concentrate to rapidly adsorb the gas. If all went well the cans would leave the gasser with carbon dioxide pressure only 10 to 15% higher than the final equilibrium pressure, which would be attained after a day or so of aging. Each filler has preferred operational parameters, but some guidelines can be given. There should be at least a 25 to 30% volume headspace for good particulation. The carbon dioxide should be tempered to about 100° to 106°F. The concentrate should be equilibrated to about 60°F. Adapters should be used to permit unimpeded (thus instantaneous) flow of gas into the can. Island depressors may be needed to restrain flat cup valves from flexing upward slightly under unusual conditions, as with tall 211x709 cans of water-based insect sprays. While TTV gassers have been used for IIG, sometimes, with a can shaking machine immediately afterward to reduce non-equilibrium over-pressures, they can be troublesome unless process conditions are ideal. They must be used with the “Super 90” type valve, but even here the rate of gas injection is thought to be slightly slower than that of UTC gassers. If the gas pressure is a bit too low, then the special rubber stem gasket may not depress fully into the body channels, impeding flow rate and causing reduced particulation of the product. Special stem gaskets with slightly reduced Durometers may be more tolerant of lower injection pressures. Island depressors are recommended to prevent the possible slight upward flexing of flat cup valves, but are not needed for conical cup valves. Spray Editor's Note: Images are for illustrative purposes only. See a complete list of aerosol equipment manufacturers in the SPRAY Annual Buyers Guide in the July issue or at www.spraytm.com. 46 Spray October 2014


Spray Oct 2014
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