BeCu extension spring

[JohnPP]

I am working a project : To use BeCu wire to make an extension spring ( gasket ) for EMI shielding . I have asked the spring coil vendor to make the coil for me ( wire diameter is 0.19mm and to form coil diameter 1.0 mm with spring about 140 mm length ) I use BRUSHWELLMAN Alloy 25 with 3/4H , after coil forming , the springs were heat up 600 degree F for 1 hour . The out come is unexpected : The pitch of the coil extended to total length about 200 mm and discoloured .One of BRUSHWELLMAN engineer told me that it is the effect of stree relief .Please advise what were wrong ? The material spec ? The treatment temp and timing ? What will make the finished part with the original colour , with spring effect and not extended ? Thanks

 

[EdStainless]

Why are you post-forming heating the springs?
There is a volume change on aging this alloy, you can't avoid the changes. Do you really need the aging for strength?

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Rust never sleeps
Neither should your protection

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

 

[JohnPP]

Thanks EdStainless ,
The agent of Brushwellman told me to reheat it after the cold work of spring forming ( actually I told our vendor to do the heat treatment process ), although she has no experience of forming BeCu extension spring . The reason she said is that it will release the main advantages and features of using BeCu.
I also have some samples without doing the heat treatment , it really not very flexible as some competitor's samples .
So , what is the more proper procedure to make a BeCu extension spring ?
Thanks

 

[EdStainless]

Normally when someone used BeCu for springs they need the highest strength possible, so yes, they want to age after forming. If pitch/length is critical then you need to adjust hte formed size accrodingly. I have been through the same thing with age hardening Ni alloy grades.
Is length really critical in your application? could you make them short and stretch into palce?
If the springs are clean I wouldn't expect any discoloration at 600F.

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

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

 

[metman]

JohnPP, "...The pitch of the coil extended to total length about 200 mm and discoloured..."

I can picture the discoloration but not change in geometry. Do you mean that the as-formed compressed coils extended thereby increasing the pitch during heat treat to make it look like a compression spring? Or do you mean that the 1.00 mm pitch dia changed or both?

 

[JohnPP]

Hi EdStainless and metman ,
As in the other thread link , I mentioned that I better describe it as I am making a BeCu extension type garter spring fpr EMI gasket purpose , and the pull force needed is not very important and I can use the basic trial and error method to make one with correct length .
So the questions remain are :
(1) At 600 degree F , it discoloured in 15 minutes as I was told . It should not be ?? ( But we heat treated in a tpyical furance ----- or we need to heat it in a oxigen controlled furance ?? )
(2) The total length extended significantly , so that each pitch having bigger space and it appears not good for EMI shielding purpose .
To answer metman , yes ! After heat treament , it looks like a typical compression spring !!! And its diameter didn't change noticablly .
Anyway , its looks " negative pitch idea " may be one of the answer , but I need to know more about it .
Thanks ,

 

[metman]

JhonPP, When you say negative pitch, I guess you mean to wind the coils with a residual compressive stress pushing the coils together with hopes of minimizing the positive pitch effect from relaxation of residual stress during aging.

You might want to try aging in a vacuum furnace but you still might get some discoloration. I don't think Hydrogen atmosphere would help much at 600F. Another option is to bright dip after aging.

 

[JohnPP]

Hi metman ,
What is Bright dip ?
Thanks ,

 

[israelkk]

JohnPP

Added to my posts in the spring engineering forum I would like to ask why did you choose the BeCu alloy? If it is for electrical conductivity, then there are many other copper alloy spring wires which may do the job. Unless you have specific requirement for force/deflection from the garter spring that dictates BeCu alloy I do not see any reason to use it. More than that if the force/deflection requirements are known there is a possibility to use the BeCu wire in the 3/4 hard or full hard without the need for heat treatment.

The spring properties can be calculated, so why are you using trial and error method to make one with correct length. Even if you will succeed you will not have any idea about the stresses, relaxation, life cycle, etc.

If your spring manufacturer can not do the calculations for you why not seek a professional help?

 

[JohnPP]

Hi israelkk ,
Thanks to your advise .
BeCu alloy is the spec that customer want .
I am using BeCu 4/3H and it is less flexible before heat treatment , I mean not much spring effect .
And using this Forums , I find a lot of help and can refreash my engineering knowledge after my graduation 20 years + ago .
Thanks ,

 

[israelkk]

Even with all the metallurgical help you will get you still need to do the spring calculations of force, deflection, stress, etc. to make it "flexible". There is no other way to avoid the risk of loosing "flexibility" due to relaxation under long period of constant stretch (and high stresses).

 

[JohnPP]

Hi israelkk,
Thanks to your advise .
After this project , if I still have time , I will review the calculation matter that may be further interest to me .

 

[metman]

Bright Dip is a liquid chemical treatment performed by dipping the part into the solution. This would probably be an acidic solution. Metals Handbook has a volume devoted to surface finshing of metals or you could go to a vendor and not deal with details. If you get no further detailed answer here, you could take the bright-dip question the Corrosion Engineering forum.

 

[israelkk]

JohnPP

As a wise guy said: "There is always not enough time to do the design job correctly, but there is all the time in the world to (try) to fix a bad designed job".

 

[JohnPP]

Good News !
Our vendor confirm today that they can make it next week .
Thanks to all of you provided help whole heartly .

Thanks again .

JohnPP