316 ss spring wire for a solenoid

Thread Starter

cmartinez

Joined Jan 17, 2007
6,379
I need to make a spring for a solenoid that will work under water, specifically inside a domestic water pipe. The wire diameter I need is 0.008", and it is my understanding that the 316 alloy is the one that complies with the FDA for applications such as this.

Question, is there any other material out there that could be better suited for this purpose? That is, a material that can withstand being immersed in running water containing a small amount of chlorine.

@shortbus, I've gotta feeling this is right up your alley. Any thoughts?
 

dendad

Joined Feb 20, 2016
2,935
The spring wire would not be insulated so that is a problem for a start. And SS is fairly resistive but it would be water cooled ;)
There are many potted coils than can be used under water, so why not just use them?
More detail please.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
6,379
The spring wire would not be insulated so that is a problem for a start. And SS is fairly resistive but it would be water cooled ;)
There are many potted coils than can be used under water, so why not just use them?
More detail please.
Maybe I didn't explain myself. I need the wire for the solenoid's spring, not for the coil itself. The coil will be made using ordinary magnet wire, and will be completely encapsulated. So it will never be exposed to water.

What I want is to find the appropriate material to build the spring under said conditions. So far, I'm also considering titanium, Incoloy A286, and phosphor bronze, among others. I found an excellent springs material guide. The challenge will be to find a supplier willing to sell small quantities, or a few samples at least.
 

SamR

Joined Mar 19, 2019
1,061
Food Grade SS is 304, not 316. Due to the high nickel content of 304, I don't think it will be good spring material. The nickel content is what gives it the high anti-oxidation qualities needed for food grade. 316 is preferred for marine use due to its impermeability to saltwater corrosion.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
6,379
Food Grade SS is 304, not 316.
I beg to differ, down here it's 316 that's considered food grade. And besides, it's got better corrosion properties than 304. I've already double checked that fact from several sources.

But you've given me extremely valuable info by saying that 316 is used for marine purposes. If it can withstand saltwater, then running domestic water should be a piece of cake.
 

MisterBill2

Joined Jan 23, 2018
3,721
Really, gold would be a far better conductor and it is also OK for use with food, as well.
I am thinking that this is a re-visiting of a thread from a few months back, and the whole concept of a solenoid inside a water pipe seems like a poor choice. I don't recall if the actual purpose was ever described or not, but the whole concept is very unusual.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
6,379
Really, gold would be a far better conductor and it is also OK for use with food, as well.
I am thinking that this is a re-visiting of a thread from a few months back, and the whole concept of a solenoid inside a water pipe seems like a poor choice. I don't recall if the actual purpose was ever described or not, but the whole concept is very unusual.
Thanks. But, again, I'm seeking a material for the spring, and not for the coil. The spring could be made of any material that can withstand being submerged in domestic water.... even plastic, for all I care.
 

MisterBill2

Joined Jan 23, 2018
3,721
Thanks. But, again, I'm seeking a material for the spring, and not for the coil. The spring could be made of any material that can withstand being submerged in domestic water.... even plastic, for all I care.
My suggestion was for use as connecting wires.
As a wire gold would work very well.For the wires there is also teflon insulated wire available in many sizes from a number of sources. The military qualified grades have very good quality insulation. There is also teflon coaxial cable that has silver plated conductors of very pure copper.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
6,379
My suggestion was for use as connecting wires.
As a wire gold would work very well.For the wires there is also teflon insulated wire available in many sizes from a number of sources. The military qualified grades have very good quality insulation. There is also teflon coaxial cable that has silver plated conductors of very pure copper.
I see. Thanks again for the suggestion, but I found a way to route the solenoid's magnet wires through a hole drilled in the valve's wall without them being exposed to the water. The solenoid's coil is completely encapsulated, and the shell in turn is glued to the inside of the pipe. It's inside the glued area that this hole resides, so there's no need for it even to be sealed since the glue itself does that job.

Once outside the pipe, the wires are soldered to small cables that are then connected to a small circuit board. The soldered joints are properly protected using a little sealant and shrink tubes.
 

jpanhalt

Joined Jan 18, 2008
7,697
1) I think your choice of wire is fine. 316/316L is used for sutures and is a little springy. Safety wire is (USA) 302/304 and may be a little more springy. Both are available in fine gauges and will work harden when spooled.
2) What is the solenoid plunger made from?
 

Thread Starter

cmartinez

Joined Jan 17, 2007
6,379
1) I think your choice of wire is fine. 316/316L is used for sutures and is a little springy. Safety wire is (USA) 302/304 and may be a little more springy. Both are available in fine gauges and will work harden when spooled.
Thanks, John. Your opinion in this specific application is very important to me. After some research, I found that 316 wire comes in two different versions, hardened and annealed. The annealed version is very easy to find, whilst the hardened one is not. The thing that concerns me right now, is that I've tested the far more common 302 material and it does rust under water! And not only that, it's quite magnetic and that's a disadvantage (see below)

2) What is the solenoid plunger made from?
The plunger is a small nickel coated neodymium magnet measuring 4 mm dia x 10 mm long. I know that neodymium itself can rust, but the nickel coating is quite uniform and robust. What concerns me is that the plunger is of the retraction type (with a spring in the back), and therefore needs to be somehow constrained so that it doesn't pop out of the assembly. So what I did is place a small piece of wire in front of it which is attached to the plastic casing. But to my surprise, the so called stainless steel wire that I bought from my local supplier is magnetic. And that's a problem because the plunger sticks to it and therefore it becomes harder to retract.
 

jpanhalt

Joined Jan 18, 2008
7,697
I learned something new today:

https://www.mtm-inc.com/ac-20110117-how-nonmagnetic-are-304-and-316-stainless-steels.html#targetText=With its higher nickel composition,"most nonmagnetic" stainless steel.&targetText=The 316N stainless steel alloy,may not be readily available.

Not surprised that welding can make those alloys magnetic but relatively gentle cold forming can too. I took a piece of 302/304 aircraft safety wire 0.020" dia. Totally non-magnetic (didn't stick to a neodymium magnet). Twisted it as one might do as a safety (i.e., not overly tight), and it stuck to the same magnet.

Maybe a plastic spring is a better choice. It doesn't have to be too strong.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
6,379
Maybe a plastic spring is a better choice. It doesn't have to be too strong.
Yes, maybe it is. Then again, the plunger's spring will be inside the coil, and behind the plunger. So its being magnetic could prove to be an advantage. It's the wire acting as a stop at the front of the plunger that has me worried. And space is quite limited, so using plastic for that purpose is more troublesome.

Anyway, I finally found a supplier with reasonable prices and delivery times:

https://stainless-wire.us/hard-wire-piano-wire/coils-o-0-10-to-0-80mm/product/stainless-steel-hard-wire-13545.html


But take a look at these fools... $141.00 dlls for 10 meters of wire!
 

AlbertHall

Joined Jun 4, 2014
8,187
It's the wire acting as a stop at the front of the plunger that has me worried. And space is quite limited, so using plastic for that purpose is more troublesome.
Could you use a piece of fishing line for this? It's definitely not magnetic and will be unaffected by the water.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
6,379
Could you use a piece of fishing line for this? It's definitely not magnetic and will be unaffected by the water.
Already considered it... but it wouldn't work because it's way too soft. At this moment I'm considering titanium and phosphor bronze. And the latter is looking very promising.
 

Thread Starter

cmartinez

Joined Jan 17, 2007
6,379
I learned something new today:

https://www.mtm-inc.com/ac-20110117-how-nonmagnetic-are-304-and-316-stainless-steels.html#targetText=With its higher nickel composition,"most nonmagnetic" stainless steel.&targetText=The 316N stainless steel alloy,may not be readily available.

Not surprised that welding can make those alloys magnetic but relatively gentle cold forming can too. I took a piece of 302/304 aircraft safety wire 0.020" dia. Totally non-magnetic (didn't stick to a neodymium magnet). Twisted it as one might do as a safety (i.e., not overly tight), and it stuck to the same magnet.

Maybe a plastic spring is a better choice. It doesn't have to be too strong.
John, what do you think about phosphor bronze? Would it be suitable for this application? Also, it's a non-toxic material that can have contact with domestic drinking water without side effects, right?

And what about beryllium bronze? It's supposed to be a better material, but my understanding is that beryllium is toxic, right?
 

jpanhalt

Joined Jan 18, 2008
7,697
Phosphor bronze would be OK, I believe, so long as it is lead free. Lead may be added to give a much more machinable material.

Beryllium dust and fumes are quite toxic, but apparently the alloy by itself is safe. Presumably, it would be safe so long as the water concentration doesn't exceed 4 ppb (https://www.who.int/water_sanitation_health/water-quality/guidelines/chemicals/beryllium-background.pdf ; https://safewater.zendesk.com/hc/en-us/articles/212077667-4-What-are-EPA-s-drinking-water-regulations-for-beryllium- ). If that happened, it wouldn't matter much that your device didn't contribute to it. The fact is has beryllium in it might make it guilty by association.
 
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