and by "doesn't hold size" you mean? ... that it tends to deform with time? or that its elasticity makes its final size hard to predict?

That it is hard to predict the amount of over bend to get the size you need. That is why most times a miniature spring is more expensive than a normal every day size one.

Could probably give more ideas if I knew what the final project looked like, but then you'd have to kill me, I know. There are other types of springs that aren't metal, like you could use a piece of thin wall rubber tube. A lot of the dies we used were switched to polymer springs from the old metal springs.

 

I made some tension (rotating, not pulling) springs once that needed to fit into a tube when relaxed. A test mandrel was made close to the size, but a little smaller (5% to 10%) like you have, and I then did a simple linear extrapolation to to make the right mandrel size. Tension on the wire is also important as the wire stretches. So try to keep that constant. In a production, setting a 5 or 3 (?) roller straightener is used.

 

I made some tension (rotating, not pulling) springs once

Do you mean what is commonly called a "mouse trap" spring?

 

Do you mean what is commonly called a "mouse trap" spring?

Yes, a spring to apply torque and move an arm/lever. In fact, I had to deal not only with the OD when relaxed, but the ID when "compressed" (torqued) since it ran on a mandrel.

Like you said several posts ago, it is a lot of trial and error. But, it is not too hard with a few SWAGs.

EDIT: As I mentioned awhile back, tension is also important. A single wrap on a piece of round bar opposite to the turn of the spring may help you control it and add just a little bit more of work hardening. It doesn't have to be opposite, but the music wire I was using was quite soft compared to the straightened pieces one can get at hobby shops.

 

... Like you said several posts ago, it is a lot of trial and error.

... mostly error... from what I'm finding out ...

 

Here's a couple of PDFs that may help, the second one is for the machine I linked to earlier.

 

Here's a couple of PDFs that may help, the second one is for the machine I linked to earlier.

Most excellent info, shortbus... especially the sections dealing with passivation and heat treatment.

Many, many thanks

 

@cmartinez I saw this and thought of you.

https://www.instructables.com/id/Sp...chine/?utm_source=newsletter&utm_medium=email

 

@cmartinez I saw this and thought of you.

https://www.instructables.com/id/Sp...chine/?utm_source=newsletter&utm_medium=email

Very interesting design... and the rotor/bending head looks like it was 3d printed! ... look at its surface traces when the video shows a front view.

 

yes it was 3D printed... I believe he is uses an iPrusa...

 

yes it was 3D printed... I believe he is uses an iPrusa...

Yeah... I noticed that after I scrolled down the page and read about the entire project... duh...

 

That was cool, a DIY four-slide simulation. They at one time at work had a whole department doing that kind of wire bending. https://en.wikipedia.org/wiki/Four-slide

 

Ok, here's what I've learned so far about hardened stainless steel:

• Most hardened SS wire is cold-drawn
• All cold-drawn hardened SS is magnetic
• Cut or machined SS will rust underwater if it's not passivated
• Springs made of SS must be heat-treated to eliminate internal stresses that might affect its shape over time and its useful life, and must be passivated after said treatment.

Now, here's a pic of a test I've been doing on SS for the last several months. It's a glass of tap water into which I submerged several different items, just to see what happened to them on the long run. The water has completely evaporated several times already, and I've had to refill it every time I discovered that happened. That explains the calcium flakes visible here and there at the bottom.

​

• Item #1 is a tungsten carbide drill bit. It's been oxidizing very slowly over time, by becoming dark and a few reddish spots here and there. It's an extremely sturdy material, but it's not for underwater use. Tungsten carbide is also slightly magnetic.

• Item #2 is a 0.020" 304 SS hardened wire that was heated with a small torch. The heat changed its bright color to dark, and completely softened the material. It also made it non-magnetic. I'm surprised that no visible oxidation has manifested. That wire has been underwater for at least a couple of months.

• Item #3 is a large needle. It's 2-1/8" long, and has a diameter of 0.053". I chose to test a couple of needles because their SS material is about the hardest I've ever seen. It's also been underwater at least 8 weeks, and it has stayed untarnished all this time. With the very glaring exception of its eye, which has been growing oxide on its inner rim.

• Item #4 is the exact same wire as item #2, but it was not heated with a torch. It's remained virtually undamaged all this time.

• Item #5 is a small 0.033" dia needle whose both extremes I cut using pliers. Notice how both tips have rusted sharply.

• Item #6 is the same wire as #4. There's nothing really special about it. The black band on its right side was painted with a black marker for measurement purposes.

My conclusion is that every SS piece of metal that has been either cut or machined must be passivated if one wants to use it underwater. I'm surprised that the spring wire I experimented with (items # 2, 4 and 6) were unaffected by my experiment. But if I plan to use this material inside a valve with running tap water inside it, one can never be to careful and must protect its internal parts as best as possible. Besides, there's chlorine in said running tap water. And the chlorine in my glass must have evaporated quite quickly and most probably did not have enough time to affect it noticeably.

 

I chose to test a couple of needles because their SS material is about the hardest I've ever seen.

I've always thought traditional sewing needles were chrome-plated non-stainless steel . The rusted ends and eye suggest that too.

 

I've always thought traditional sewing needles were chrome-plated non-stainless steel . The rusted ends and eye suggest that too.

Interesting ... I guess that could be the case! ... But my attention was drawn to the large needle's (#3) tip. Surely chrome-plating must easily fail the rust experiment at that very spot?

 

Maybe change gears...

Plastics were mentioned early on, but little discussion of such composites followed. Apparently there is a plastic "ultem" that can be thermoformed and makes good springs (I suspect you want to avoid injection molding for cost reasons):
https://www.leespring.com/materials-finishes-and-plating#view-field-mat-material-table-column--6
https://www.ptonline.com/products/springs-molded-of-high-heat-thermoplastic
https://www.sabic.com/en/products/specialties/ultem-resins/ultem-resin

Also, has titanium been considered?
http://www.rentoncoilspring.com/whyti.html

John

 

Maybe change gears...

Plastics were mentioned early on, but little discussion of such composites followed. Apparently there is a plastic "ultem" that can be thermoformed and makes good springs (I suspect you want to avoid injection molding for cost reasons):
https://www.leespring.com/materials-finishes-and-plating#view-field-mat-material-table-column--6
https://www.ptonline.com/products/springs-molded-of-high-heat-thermoplastic
https://www.sabic.com/en/products/specialties/ultem-resins/ultem-resin

Also, has titanium been considered?
http://www.rentoncoilspring.com/whyti.html

John

Titanium has definitely been considered. But I haven't found a hardened version of it yet. At least not from someone who would sell it in small quantities. And thanks for the links, I'll take a close look at each of them, I promise.

Also, I wanted to ask you if you knew of a process that could test for how calcium deposits build up inside a valve. An experiment that could possibly be performed by adding said caltrates (or salts, or whatever) to water and then have it circulate through the device using a pump that would be recirculate it from a medium-sized deposit. Say, a standard 200 liter drum.

 

Sorry, I probably know less than you about calcium deposits. They are a PITA.

 

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?

I confess I have not read all the post. I have worked with springs and other stainless parts used in submerged environments including in very hot high pressure systems involving deionized water. Been awhile I since I don't know what I can or can't say you may wish to give this a read. Get to section 4.5.1.3 where they mention:
"The springs in the control rod drive mechanism are made from nickel-chromium-iron alloy (Alloy 750), ordered to Aerospace Material Specification (AMS) 5698 or AMS 5699 with 4. Reactor AP1000 Design Control Document Tier 2 Material 4.5-3 Revision 16 additional restrictions on prohibited materials. Operating experience has shown that springs made of this material are not subject to stress-corrosion cracking in pressurized water reactor primary water environments. Alloy 750 is not used for bolting applications in the control rod drive mechanisms".

Now I also have no clue if a small spring can be manufactured using the cited material but it may be something to think about. The stuff I worked with was not commercial but I have seen some data on commercial control rod drive mechanisms and they are very similar and the commercial stuff should be published somewhere.

Ron

 

I confess I have not read all the post. I have worked with springs and other stainless parts used in submerged environments including in very hot high pressure systems involving deionized water. Been awhile I since I don't know what I can or can't say you may wish to give this a read. Get to section 4.5.1.3 where they mention:
"The springs in the control rod drive mechanism are made from nickel-chromium-iron alloy (Alloy 750), ordered to Aerospace Material Specification (AMS) 5698 or AMS 5699 with 4. Reactor AP1000 Design Control Document Tier 2 Material 4.5-3 Revision 16 additional restrictions on prohibited materials. Operating experience has shown that springs made of this material are not subject to stress-corrosion cracking in pressurized water reactor primary water environments. Alloy 750 is not used for bolting applications in the control rod drive mechanisms".

Now I also have no clue if a small spring can be manufactured using the cited material but it may be something to think about. The stuff I worked with was not commercial but I have seen some data on commercial control rod drive mechanisms and they are very similar and the commercial stuff should be published somewhere.

Ron

That's invaluable info, Ron. Many, many thanks!