Material for high speed Soleniod???

[andrew99]

We have been developing a high speed solenoid valve. We have tested 430F and Carpenters 430FR. The FR performs better than 430F. ( ie greater force ). The problem is it doesn't come close to the material or competition is using. We have had our competitors material tested and it comes back as 440C ( Which we tested ) or 17-7 which we are unable to locate at this point. Can anybody suggest a material that is corosion resistant, produces high levels of force and can be machined using a screw machine?

 

[EdStainless]

Are you working from bar or tubing?
I don't know, is Crucible or Carpenter making 440 bar?
There are a number of source for 17-7 in both bar and tube.

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Rust never sleeps
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[andrew99]

The material is rod stock. The parts are turned on a screw machine.

 

[israelkk]

Are you sure that the magnetic parts of the valve were 440C or 17-7? This is odd and unusual. The best stainless steel for solenoid valve are 430, 430F and 430FR by that order. The reason you had better results with the FR are just luck. Every batch can have different magnetic values. I suspect you tested a minimum value 430F (within the range allowed by the spec) versus a better than minimum value FR (within the range allowed by the spec). There is also a difference in production methods and Carpenter offer those alloys as a "solenoid quality" grade too.

The 17-7 and the 440C are mantensitic steels and will have larger residual magnetic flux which should be as little as possible when you are designing a valve.

From the post I could not understand if the problem is with the solenoid force or the speed.

 

[andrew99]

What we are looking for is more force. The valve is very small and we have no problem with frequencies up to 700hz. The problem is that on the initial opening the valve may not open. We have closed the magnetic circuit as much as we can but we are unable to improve on the initial opening problem. Are there other materials that generate more force with less corrosion resistance? Is there a source for data related to force generated given other data?

 

[TStaples]

Andrew99,

Carpenter makes a couple of "tweener" soft magnetic stainless materials that have decent resistivity, decent corrosion resistance, and have higher saturation flux densities than 430 FR. They are called Chrome Core 8 (CC8) and Chrome Core 12 (CC12.) They are 8% chromium and 12% chromium respectively, compared to about 17% for 430FR. The 8% has a higher saturation flux density than the 12% (more iron, less chrome) but the tradeoff is less corrosion resistance. Both are available in free machining bar grades (CC8-FM, for example.)

Once you get past those, the absolute best material would be a Silicon Core Iron. Silicon Core Iron B-FM (Carpenter) is available in bar form, but has zero natural corrosion resistance. It would be the best option if you are willing to plate it after all machining and annealing.

Remember, you have to anneal all of these ferritic materials to achieve optimum magnetic properties. Otherwise, you will have tremendous piece to piece variations due to variations in bar annealing from the manufacturer, and from machining on your end.



-Tony Staples

http://www.tscombustion.com

 

[TStaples]

Andrew99,

A couple of details I missed:

1) 430FR should not make any appreciably more or less force than 430F. the 'R' is for resistivity. If your two samples, or groups of samples produced different results, it would be for other reasons. (most likely annealing)

2) 440C and/or 17-7 will never outperform 430 for force, if all are properly annealed. They are martensitic, and have approximately the same chrome level. 440C would be useful if your application needed high remnance. However, high speed solenoids generally don't. You need a material with lower chrome, and higher iron content, to make more force with the same cross sectional area, air gap, etc . . ..



-Tony Staples

http://www.tscombustion.com

 

[andrew99]

Should the 430FR be annealed or is it delivered from Carpenter in an annealed state? Is this common process and where could be performed on a small number of 4-40 X 1/2" screw sized parts?

 

[andrew99]

What is the relationship between force generated and iron content? Is it directly proportional?

 

[TStaples]

Andrew99,

All magnetic alloys come from the mill in an ambiguous state of anneal, in terms of magnetic properties. It's optimized for machining rather than for magnetic properties. When you machine it, you induce further cold working of the material. Hence, it needs to have an annealing operation performed, for optimal magnetic properties, after ALL machining/grinding/etc . . ., are completed.

As for annealing, any reasonable heat treatment shop should be able to do vacuum annealing. Carpenter recommends vacuum, or dry hydrogen atmosphere, annealing at 1550/1830°F for two hours, then cool at 100°F/hr, down to 800°F. Below 800°F, it doesn't matter what cooling rate is used.

As for iron content, it's not always so cut and dry. However, for soft magnetic alloys, more iron percentage generally equals higher saturation flux density. As for specifics, magnetic material properties is a subject that a book could be written on (and I'm sure several exist), and is beyond the scope of Eng-Tips. My earlier posts detail recommendations for materials that are commonly used in high speed solenoid products.



-Tony Staples

http://www.tscombustion.com

 

[israelkk]

andrew99

From your last post "What is the relationship between force generated and iron content? Is it directly proportional" I understand that you have no experience and knowledge in high speed valves design. Who is designing the valve? Does he has any experience or you are just trying to re-engineer / copy a competitor valve.

I assume you operate the valve (On-off) at a variable Duty cycles and high frequency to control the pressure in a volume/piston.

There is no simple answer to your question because the magnetic behavior is non-inear and the magnetic flux has a saturation point.

Ususlly a computer program that solves the electric coil current rise time coupled with the magnetic flux generation rise time, flax value, resulting magnetic force and the plunger movement under the generated magnetic force, acceleration, springs, fluid pressure. etc.

FEA program can help design the static condition but to analyse the valve dynamics a computer program is needed.

You have to be aware that the on and off opening time variations for the valve and the delay from command to full opening of the valve can greatly affect the performance. This is crucial for such a high speed valve.

One more issue is that the mechanical opening and closing time of the valve depends on the fluid pressure in the valve. Therefore in high duty cycle command the valve will be slower.

http://israelkk.googlepages.com/home

 

[dgallup]

You can also get soft ferritic stainless steels from Ugitech. Ugiperm 12FM is similar to Carpenter Chrome Core 12FM. They will sell fully annealed grades that MIGHT not need post machining annealing depending on you application and the amount of cold work.

http://www.uginestainless.com/

Carpenter's latest baby is Chrome Core 13FM. It has high silicon content like 430FR so it has good resistivity which definitely helps in high speed valves. It has less chrome than 430(F)(R) so you get higher saturation flux density. They seem to be pushing this grade because they actually keep some in stock unlike most grades where they tell you to take a number and wait 4 months.

If you really want a lot of force you can't beat 50% cobalt/iron alloys. These will hit 2.4 Tesla but they are hard to machine and expensive.

 

[EdStainless]

Actually I know of a number of solinoid applications using aged 17-7.
The saturation is OK, and the resistivity is high.
It wouldn't be my choice, but it is done.

The 12 and 13% Cr alloys are only sort of corrosion resistant. The work well, but be careful.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[andrew99]

Engineering degrees 0 - High speed valve experts 0 - Number of design riped off from other companys 0 - High speed valve designs valves in market 2 - Number of years in business 15
On a more serious note. We have a working prototype that has some 500M operations on it. We are just looking to improve on some of its characteristics. The majority of our expertise is in circuit design and programming. So we looked to this forum for some advice.
Would a simulation program allow for an armature mass as low
as 0.30 grams? Do these simulations allow for liquids various viscosities? Who would we talk to about such a program?
The valve we are working on is used in industrial inkjet and many non-valve related issues determine the success of the design. The valve operates with its sealing surface open to the air. It must perform well with liquids as diverse as water and MEK. It must run liquids containing both salt based dies and titanium pigment.
You can get some idea of what we are using it for at

http://www.ijp.ca

On the material side, I will try some of the suppliers and materials that have been suggested.

Thanks

A

 

[dgallup]

Look in the FAQ section for the various FEA suppliers. We use Infolytica's MagNet with very good results. The magnetic field solution is very good. Armature mass can be any value. However, the external forces are just lumped parameters. Damping, spring loads, bumper coefficient of restitution, etc. will get you close but not exactly model the actual physics of thin fluid films or unconstrained parts with multiple degrees of freedom. As long as you understand the limitations of your models they are extremely useful. But as always, GIGO.

 

[jmark]

You will have two choices for solving solenoid problems using magnetic FEA software:

1) Transient time domain magnetic solution – This considers nonlinear saturation and back-emf effects. In addition, motion induced eddy currents in moving the plunger and diffusion time of fields are considered. Fast acting solenoids (< 1 msec closing) are probably affected by both. These effects tend to slow the operation of the solenoid.

2) Static magnetic solution – This considers only nonlinear saturation and back-emf effects. A series of static magnetic solutions can be exported to a look-up table (flux linkage and force vs. current and position). This table creates a way to couple the electrical and mechanical systems using a magnetic model. The model is imported into a system simulator and solved vs. time. Mechanical elements are added such as mass, spring force, and hydraulic damping. However, induced effects such as eddy currents and diffusion of magnetic fields are neglected.

Some software companies offer both 2D axisymmetric and 3D solvers which are well suited for solenoids.