will nickel coating metal springs increase the stiffness? 2

[GogiBOB]

Hi,

My boss is getting nickel coatings on metal springs with the thickness of 5 mils.
This is only 0.005". My boss thinks getting nickel plate coating on springs will increase the stiffness.
However, I am not so sure if 0.005" of nickel coating will have any significant impact on the spring stiffness.
The springs are only 1.7" tall and have 1.1" outer diameter.

Can anyone give me thoughts on this?

 

[cloa]

By the way what's the spring material and geometry?

 

[dgallup]

What is the wire diameter? .005" is a lot of plating.

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[MintJulep]

It won't do much of anything for stiffness, but if you're lucky you will get hydrogen embrittlement and all the springs will fail in short order.

 

[GogiBOB]

the wire diameter is 0.1620". is 5 mil alot for coating? im new to all these coating stuff im working on and still learning.

 

[TVP]

No, the nickel plating will not affect the stiffness. The variation in wire diameter will be more meaningful.

 

[EdStainless]

The only way to increase the stiffness of a coil spring is to use heavier gage wire.
I would suspect that your Ni plating is more like 0.0005".

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[NickE]

Ed- I noticed significant stiffness increases in my prior work with reed valves, although we were coating with TiN, and around .0005"-.001" on .005-.020" reed valve steels. However this is a much greater % of the total thickness, and the modulus of TiN is much greater than steel.

I suspect that you are right about the coating thickness, and it's a relatively low percent of the overall diameter.

if it was .005" per side, or a .010" larger diameter I suspect that you would see an increase in the stiffness, but only from diametrical increase, since steel and nickel have very similar moduli.

to the OP: What is your coating thickness? .005" 5mils (.000005") or 5"tenths" (.0005")

One way to tell would be to measure the spring rate, if it's significant you should see the difference right away.

Reasonable?

Nick

 

[GogiBOB]

5 mils is 0.005 inch from what i know. i suppose changing the thickness from 0.1620" to 0.1670" must have some impact on the stiffness.
we;ll be getting coated springs on friday and it should be interesting to compare the test result once we get them.
thanks everyone for comments,

 

[swall]

Yes, 5 mils is .005".

 

[dgallup]

.162 + .005 per side = .172

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[NickE]

tool and die measure things differently, since they work in "thousandth's" (.001) thereby making a "tenth" (.0001) and a "hundreth" (.00001) making a "mill" (.000001).

That's why I don't like industry jargon for forum posts.

There's another point, I've always measured and spec'ed coating thicknesses in single side measurements, while we've no indication of how this coating is spec'ed.

so will the wire end-up .005" thicker, or .010" thicker?





Nick

 

[EdStainless]

Putting a ceramic on a reed valve will surely stiffen it.

Putting a metal on a metal part, not so much.
There is a small dimensional change, but the modulus of the material is very similar.

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[israelkk]

GogiBOB (Mechanical)

Changing the thickness from 0.1620" to 0.1670" raises the spring rate by ~3%. The commercial tolerances on the spring rate are normally +/-10%. Therefore, from measuring the spring rate there is no way to deduct anything. If the bare spring batch rate is below the maximum allowable rate then the resulted coated spring may still be within the +10% range. To be sure for future batches, the bare spring must be tested before coating too to make sure no spring is above the +7% or below the -13%. On the other hand there is the risk (happened before) that the manufacturer will use a smaller wire diameter to compensate for the raised rate, resulting in a spring that may be over stressed. Therefore, the bare wire diameter must be checked too to make sure that the spring wire diameter before coating is according to the design specifications.

 

[israelkk]

Sorry, my mistake, it will change the rate by +/-12.9%. But this makes the issue of checking the bare spring rate and wire diameter more important. The nickel coating of 0.005" seems too high. Even if it is an electroless nickel coating the recommended coating for maximum corrosion protection is 0.0015".

See: MIL-C-26074E MILITARY SPECIFICATION COATINGS, ELECTROLESS NICKEL REQUIREMENTS FOR, para. 3.3.2

3.3.2 Thickness. Unless otherwise specified, minimum thickness of the nickel coating shall be 0.0010 inch (0.026 mm) (grade A) for aluminum based alloys, 0.0005 inch (0.01 3 mm) (grade B) for copper, nickel, cobalt, titanium and beryllium alloys, and 0.0015 inch (0.039 mm) (grade C) for iron-based alloys.

 

[GogiBOB]

Hi,
I received the springs today. I thought we were getting 5 mil coating but it turned out that is was actually 5 microns thick which is 0.000196850394 inches according to google.

The wire thickness hasn't changed much but it increased by 0.001" and I think it is because of my caliper.

Anyhow I found out that getting nickel coating actually increased the stiffness of the spring after some testing.
I don't understand how? It contradicts my expectation and what everyone was commenting... does anyone have any thought on this???

Thank you!

 

[EdStainless]

What is the actual plating? is this electroless Ni-P? If so then you have coated the springs with an inter-metallic compound with a significantly higher modulus (and one that is very crack prone).
The high mod would explain the increased stiffness, but what happens when it starts cracking?

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