Miniature, Lightweight, One-Time-Opening Valve
[2008-7-22]
Tag : Nichrome Wire
The prototype valve includes a 1/8-in. (3-mm) aluminum tube, oneend of which is plugged with a solder comprising about 37 weightpercent of lead and 63 weight percent of tin. The tube and thesolder both have a coefficient of thermal expansion of 23micron/m-K at room temperature. Before plugging, the interiorsurface of the plug end of the tube is cleaned with a commercialflux paste developed specifically for preparing aluminum forbonding with lead/tin solder. The solder is then melted into thecleaned end of the tube, forming the plug.
In a test, the plugged tube was pressurized to 1,000 psi (6.9 MPa)with helium and leak-tested. It was then cooled to a temperature of77 K (about –196 °C) and again leak-tested at the samepressure. Finally, at a lower pressure, the plugged end of the tubewas heated to about 200 °C (the melting temperature of thesolder is 183°C), causing the solder plug to be ejected (seefigure). It has been estimated that in a subsequent version of thevalve, the plug could be melted by electrical heating, using anichrome wire having a mass of only 10 g.
The prototype valve includes a 1/8-in. (3-mm) aluminum tube, oneend of which is plugged with a solder comprising about 37 weightpercent of lead and 63 weight percent of tin. The tube and thesolder both have a coefficient of thermal expansion of 23micron/m-K at room temperature. Before plugging, the interiorsurface of the plug end of the tube is cleaned with a commercialflux paste developed specifically for preparing aluminum forbonding with lead/tin solder. The solder is then melted into thecleaned end of the tube, forming the plug.
In a test, the plugged tube was pressurized to 1,000 psi (6.9 MPa)with helium and leak-tested. It was then cooled to a temperature of77 K (about –196 °C) and again leak-tested at the samepressure. Finally, at a lower pressure, the plugged end of the tubewas heated to about 200 °C (the melting temperature of thesolder is 183°C), causing the solder plug to be ejected (seefigure). It has been estimated that in a subsequent version of thevalve, the plug could be melted by electrical heating, using anichrome wire having a mass of only 10 g.
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