How to solve AC humming / vibration / chattering sound in AC solenoid valve?

[Sa-Ro]

Dear all,

I am developing a solenoid valve for 24, 48, 110, 220 V AC (5 VA) and 12, 24, 48, 110 V DC. (5 Watts)

The construction of the valve is Fixed core (SS430FR), Moving core (SS430FR), Core tube (BR 60/40), Shading ring (ETP Copper - 99.9%) Spring - Refer attachment.

The developed prototype is working well for DC voltages.

When testing for AC voltage, I have observed AC humming / vibration / chattering.

We have a reference sample to compare with. So I have replaced a component one by one and found the problem with fixed core.

Studied some theory in internet and gathered some points like shading coil, resultant magnetic flux is always in positive.

Tested the magnetic gauss values and found equal to the reference component.

But still no improvement. Now proceeding for annealing the fixed core and moving core.

Any other suggestion to solve the humming sound?

 

[MagBen]

The Hum seems to lie in magnetostriction from 430. Anneal to improve permeability unlikely fix the problem. 2 solutions: 1. change the mounting/installation to decrease audible humming. 2. change core material with lower magnetostriction. Permalloy 80 can have zero, Si steel has lower striction, but maybe hard to can switch core material.

 

[Sa-Ro]

I have replaced the fixed core with Mild steel and found no humming sound (may be the relative permeability of the mild steel is appox: 5000 - source, google).

Hence the mounting and other arrangements are holds good.

But due to rust, we are unable to use mild steel.

We have to go for Cr 17 - 20% for rust free.

I have studied the magnetostriction and measured the length and diameter of fixed core without and with magnetization (apprx 1000 gauss).

There is no change in length and diameter (digital vernier 0.01 mm resolution)

Do you have any idea about how much improvement in permeability / Coercivity I can expect by annealing process? Like 20%, 30%.

 

[EdStainless]

The improvement will depend on how bad it is to start with.
Often the noise is because the moving core is tight against the end of travel.
You don't want that, you want it to be just off of contact. Maybe a slightly longer of stiffer spring would help, then the spring would be absorbing the vibration.

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P.E. Metallurgy

 

[Sa-Ro]

Kindly refer the attachment in original post. Already s spring is provided for reset.

 

[EdStainless]

But do you know the position when you get humm? Has it maxed out the spring travel? is the spring too soft? there are a lot of details related to the dynamics.
Since you are trying to copy an existing device rather than design one you will have to experiment with a lot of these details.

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P.E. Metallurgy

 

[Sa-Ro]

Contact between the fixed core and moving is ensured during humming.

The spring having assembly load of 260 grams and solid length not achieved. Still we can compress the spring.

When we are open the valve and observe during humming, the moving core goes inside and coming out of core tube.

 

[MagBen]

When application is at a high Guess level, possible permeability boost by anneal will not change magnetostriction. if the magnetization level is lower, say 1000Gs, the higher the permeability, the higher the magnetostriction, which will give you more change to hum.
if your core was fully annealed, re-anneal won't gain much of perm. If it was not annealed, it is possible a full anneal can increase perm by 20-30%, but then you could get a more severe hum.
Assuming the saturation magnetostriction of your core material is 20 ppm, your core length is 50mm, you will get a length change of 0.001 mm when applying a saturated magnetic field, a vernier with 0.01 mm resolution cannot tell much of length change. lee alone that, at 1000Gs, the core material is far from saturation, the magnetostricion will be much smaller.

Yes, mild steel of pure iron has less magnetostriction than ferrite stainless steel. that could be the reason you did not experience hum when you replaced SS with mild steel.

 

[Sa-Ro]

@MagBen

The SS430FR manufactures catalog refers to re-annealing is recommended after machining operation to improve the magnetic properties and relieve the internal stress developed during machining. So that I planned to re-anneal the finished component.

Since the working Guass values is (1000 Gs) less and magnetostriction is less, shall I neglect the consideration of magnetostriction?

Note:
Earlier we were used SS430F for the same component. Due to the humming sound we changed the material to SS430FR.

 

[MagBen]

Except for less eddy current losses due to a higher resistivity, 430FR is not expected to perform differently from 430F. are you saying 430F have bigger humming sound than 430F?!

why the working guass level is only 1000Gs while the alloy can be higher than 13,000Gs? is there a magnetic circle design such that, when the two cores are close, the magnetic field can be maximize? if the useful field is only 1KGs, i call this a "criminal" usage of material.

 

[Sa-Ro]

Yes. When we used SS430F for moving core, we observed more humming noise.

After changing the material to SS403FR, the humming sound is eliminated.

The Gauss value (approx: 1000 Gs) is finalized based on reset spring load and air gap between fixed core and moving core.

Reset spring load based on orifice diameter.

If we increase Gauss value, the more power and increasing coil size.

Note:
If we reduce the reset spring load, the humming sound is eliminated. But response time value is increased. So we can not reduce the reset spring load.

Also the same construction with same reset spring is working good with reference fixed core.

Hence I concluded as only the fixed core is to be attended to solve humming sound.

 

[MagBen]

: realized that 1000Gs is probably not the magnetization the core has when it is magnetized by the coil. when testing magnetostriction, you will need to mimic the core when is magnetized by the coil, and the magnetization of the core must be much larger than 1000Gs. 1000Gs seems to be the min B to generate a min force at max air gap to compensate the force from spring.

I do not understand why 430FS has no huming, while 430F has. this may not be a magnetostriction issue. By the Way, does not the shading coil serve to cancel the humming sound?

 

[Compositepro]

Microscopic changes in geometry can change humming problems. I'm sure we have all experienced humming problems that have been fixed by hitting the offending device.

 

[analogkid2digitalman]

It worked for my friends ex...

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"It's the questions that drive us"
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[hacksaw]

The humming is the result of the core material not "latching." It will latch if you're dealing with a square loop material. It has to do with your material properties such as coercivity, saturation magnetization, and the shape of the M-H loops...

 

[Sa-Ro]

We are using shading coil with SS430FR fixed core.

As per the theory (refer attachment in original post - three wave forms), Main flux by core and secondary flux by shading coil will merge and cancel the zero crossing to maintain the flux at peak.

To confirm the theory we have observed the magnetic flux during coil ON condition.

The wave form captured in oscilloscope is Sine waveform and -72 degree phase shift from input AC voltage - no zero crossing.

The maximum gauss is 1000 Gs and minimum gauss is 800 Gs (same as reference sample).

But still humming sound existing with SS430FR fixed core.