17-7 CH 900 permeability

[dgallup]

I'm designing a helical spring for a solenoid application that has very restricted space requirements. I have always used 302 stainless for these applications as even with extreme cold work the relative permeability is generally under 5. Because of the limited space for this spring, the load & stress requirements, my spring supplier is suggesting I use 17-7 in condition CH 900. The stress & load numbers certainly work out better with 17-7. I know found permeability for condition RH 950 to be 135 max, decreasing to ~50 at higher flux density. Will CH 900 be similar?

 

[israelkk]

I have designed many DC on-off solenoid valves in the range from 6 Volts DC and up to 100 Volts DC and up to 10 Ampers current, for up to 100 Hz with 1.5 msec open and close switching time. Due to very limited space the spring was made off 17-7PH CH900 and was used as the return spring of the plunger. The spring was contained within the solenoid magnetic body. I never had any magnetic issues and problems because of the spring material.

 

[dgallup]

Thanks israelkk. This will be a little faster response than that, we have been running with a weaker spring at 250 Hz. Closing times at typically 0.5 ms. I don't think the 17-7 will affect opening/closing times particularly, more likely it will allow more of the flux to short circuit the air gap, affecting minimum opening voltage.

 

[israelkk]

I assume you either use very high voltage or very short strokes or very light small plunger and/or low low pressure. Otherwise I can not see how you can achive 0.5 msec.

I my case the inlet pressure was 1500-2000 psi and the solenoid force was 80 Newtons with a 0.5 mm stroke.