Spring Wire Flexibility Standard / Testing

[TBone12]

Hello all...

We have an issue I was wondering if any of you could help with... We buy bulk spring wire for one of our products and wind compression springs in house on a commercial spring winder. The spring material is 302 Stainless Steel. We have a problem with the wire we get from our supplier whereas sometimes one batch of the wire is more "flexible" than another batch. If we take some of the bulk wire off the wheel and bend it with our hands, we can tell a difference in how "stiff" it is. When the wire is soft and bends easier, it runs through our winder great. When it is stiffer, it causes us problems with the winder.

Our supplier has told us that the wire passes the ASTM Tensile Strength test, and therefore, the wire is good. I am familiar with spring wrap tests, bend tests, and coiling tests, but those all test spring wire to see if they fail or not.

Does anyone know of any kind of "standardized" test that would measure the flexibility (not failure) of the spring wire that we could use to change our spec??

Thanks in advance...

 

[electricpete]

I don't have much knowledge into the area of springs.

When faced with a supplier problem such as this, I would look into the specification used to purchase it to see what requirements and standards are invoked and which one captures the property your are describing. If it's not covered in your purchase specs, your specs need to be changed.

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[svanels]

I would ask the supplier a certificate of quality and proper batch identification, to ensure I am getting the right stuff. If your supplier is ISO or other certified, he should have quality management system in place to track his products.

If we take some of the bulk wire off the wheel and bend it with our hands, we can tell a difference in how "stiff" it is

I would take something better to check if there are no differences in diameter of the wire.

The modulus of a coiled spring (simplified):

k = Gd⁴/(64nR³)

where:
d = diameter of the wire (controled by the supplier)
G = material property, has to do with torsion (supplier)
n = number of coils (controled by your company)
R = radius of the coil

Hope this helps