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Memory Wire and Corrosion Resistance

11/02/2009 5:31 AM

Due to impending redundancy I am considering starting a cottage industry sideline building some small electrical actuators for a hobbyist market. These will use memory wire to produce a smooth linear movement. These are intended for permanent outdoor use. Rather than try to seal the enclosures I will make the innards inherently waterproof so they are still capable of working while immersed. They are not intended for permanent immersion or use in salt water, but must cope with the salty atmosphere in coastal regions (I live in one!).

Flexinol or Nitinol memory wire is described in the data sheets as having excellent corrosion resistance, does anyone have experience of their long term corrosion resistance, either of the wire or the electrolytic corrosion between the wire and its clamps or crimps? I realise I may have to use ac drive to reduce electrolytic effects.

I am beginning experiments to determine the corrosion resistance in real world environments, but I can't wait 10-30 years to bring a product to market so I would appreciate any experience you can offer.

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#1

Re: Memory wire corrosion resistance

11/02/2009 11:18 AM

Nitinol was originally developed by the navy as a corrosion resistant material for use in making underwater tools. It was successful in that application, and you can probably get some of their results by googling Nitinol development. The memory fearture was found accidentally during that program.

Many years back I was involved in the development of a Nitinol motor for use in the process control industry. We fastened the ends with stainless steel clamps, and heated it electrically with a toroidal transformer. The Nitinol went through the center of the toroid and was a one turn secondary. We never had any problem with corrosion.

You obviously can't operate with the wire immersed, as you won't be able to heat it. Your description of the enclosure wasn't that clear on whether the wire would be immersed or not.

As you probably know, Nitinol has to be "trained" to operte at a fixed force level. If not properly "trained", it will continually stretch until it no longer operates correctly. It can stretch over 100% of it's original length.

Good luck with your project.

DaveR

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#2
In reply to #1

Re: Memory wire corrosion resistance

11/02/2009 5:02 PM

Thank you Dave for your helpful comments. I have read up on training the wire.

Forgive me for not describing the whole system and its application in a public forum until I have it on the market. I would prefer to be the first to fill this particular niche in the market!

The actuator will be mechanically latched in position as it is important that it does not move if the power is removed. It will be controlled with a small microcontroller which will be able to sense the operating point and compensate for the ambient temperature.

I think it is too difficult to hermetically seal a low cost enclosure for a decade or more, especially with a linear actuator passing through. Instead I am aiming at IP65 rating on the enclosure with a vent or drain. By potting the electronics I hope to make it equivalent to IP67. I was hoping to be able to operate the wire immersed if necessary although this is would not be the normal mode.

I see two approaches to operating the memory wire while immersed.

  1. A short high current burst that heats the wire faster than the water can conduct the heat away. With current sensing and temperature compensation this may be possible.
  2. Sleeving the wire to thermally insulate it.
  3. or a combination of the above. I will experiment soon.

I am encouraged by what I have learnt about its corrosion resistance. I had not realised its marine background.

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Guru
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#3

Re: Memory Wire and Corrosion Resistance

11/03/2009 11:34 PM

Hi Chankley,

Please read this below with reference as to the uses of both Flexinol and Nitinol.

Nitinol is not suitable for Actuators!

Latest News:
I have received an email from Jeff Brown of Dynalloy, (one of the manufacturers of Nitinol and Flexinol).
He asks me to point out that Flexinol is used in actuators.
Nitinol is not suitable for actuators.
Nitinol and Flexinol are also available as rod, tube, sheet as well as many other shapes and you should read the information on the company-website before making any decisions.
The number of applications for this type of product are enormous.
Here are some interesting links:
About Flexinol
About Nitinol

------------------------------------------------------------------

I hope one of these will give the definative answer you request.

Take care.

__________________
Take it easy, bb. >"HEAR & you FORGET<>SEE & you REMEMBER<>DO & you UNDERSTAND"<=$=|O|=$=>"Common Sense is Genius dressed in its Working Clothes"<>[Ralph Waldo Emerson]
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#4
In reply to #3

Re: Memory Wire and Corrosion Resistance

11/04/2009 5:34 AM

Again more useful information - thanks. Interestingly the Experimental study of Memory Metals looks at heating an immersed actuator - very relevant to what I have in mind.

It is really refereshing to belong to a forum with people who know what they are talking about!

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Guru
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#5
In reply to #4

Re: Memory Wire and Corrosion Resistance

11/04/2009 6:18 AM

Hi Chankley,

You can just call me Genius if you want! LOL! But a little thought and some luck in choosing the search field make things seem easy, you know?

Take care

__________________
Take it easy, bb. >"HEAR & you FORGET<>SEE & you REMEMBER<>DO & you UNDERSTAND"<=$=|O|=$=>"Common Sense is Genius dressed in its Working Clothes"<>[Ralph Waldo Emerson]
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