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I'm looking at using a worm gear for a latching mechanism on a spacecraft that's destined for a LEO trajectory. The mechanism is on the outside of the spacecraft, but the worm gear itself would be in a housing. My general gut feel is to default to aluminum or stainless steel, but worm gears (not the worm) are generally made of a softer material; bronze, brass, plastic.

Does anyone know of any reason not to fly a bronze worm gear (a tin/copper alloy, little or no zinc) with proper precautions taken against cold welding and galvanic corrosion?

Thanks!

uhoh
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D. Hodge
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    As noted at https://en.wikipedia.org/wiki/Materials_for_use_in_vacuum the zinc might be an issue. For Earth-bound vacuum systems one prefers oxygen-free copper to prevent oxygen outgassing as well. So you are left with engineering tradeoffs. If the latch only has to work once shortly after launch vs multiple times over years, possible cross contamination of other adjacent surfaces, etc. – Jon Custer Feb 18 '21 at 18:20
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    @JonCuster bronze typically contains little or no zinc and the question specifically calls out such an alloy. – Christopher James Huff Feb 18 '21 at 18:52
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    @ChristopherJamesHuff - you might be surprised at the amounts in various alloys. Further, if there is the possibility of contaminating nearby surfaces with monolayers it almost doesn't matter since a gear would essentially be an infinite source even at <1 at.% zinc. – Jon Custer Feb 18 '21 at 18:59
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    @JonCuster I've done a fair bit of research into bronze alloys that don't include zinc for entirely different reasons (zinc vapor is somewhat of a health hazard and its volatility makes composition of the resulting alloy harder to control). There's plenty to choose from where zinc is not an intended component, and copper and tin exceeding 99.9% purity are both available (and then there's the aluminum bronzes). If you're concerned about low levels of zinc impurities, that's an issue for any alloy or "pure" metal, it's not specific in any way to bronzes. – Christopher James Huff Feb 18 '21 at 19:39
  • @ChristopherJamesHuff - Sure, just do your homework and get from a reputable supplier (not Amazon). – Jon Custer Feb 18 '21 at 19:46
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    From a few quick searches, it looks like bronze pairs well with stainless steel in this kind of application. Also, bronze can be made in a porous sintered form which could be impregnated with a low vapor pressure lubricant or manufactured containing a dry lubricant, though I don't know if worm gears would be a good application for this. – Christopher James Huff Feb 18 '21 at 19:56
  • Fair enough, thank you both. If/when this flies, I may suggest a corrosion experiment to the program manager since it seems like theres a dearth of info out there for flight heritage of bronze mechanical components. – D. Hodge Feb 18 '21 at 20:25

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