Spring variability Equation

Hello,

When we Design Hangers for Cold Load(C.L.), then this C.L. is the balance load and hence, the variability calculated by C2 is with equation: K*X / Cold Load.
Where as Most of the Spring Vendors still follow the Equation , mentioned in their catalogue:
K*X/ Hot load,
And this is irrespective of noticing what the Balance load is.
Many a times this leads to a variability which is much higher than 25% as per their calculation, which is not the case as per our calculation.

How do you clarify this?
Is the vendor catalogue needs to be updated?
Your opinion.

Deedee,

Have you contact your vendor?
I did have same question for this, and asked few vendors but some of them not replied, and others said it's hot load eventhough you design spring using cold load.
I would very much to see the answer from other vendors.

CAESAR II sets load variation as (K*delta)/(balancing load); where K is the proposed spring stiffness, delta is the "free vertical growth" (from hanger load case 2), and balancing load is the "restrained weight" load (from hanger load case 1). After a spring is collected from the hanger table, that K is used in the load variation check to confirm that the load variation is not exceeded.
A general definition of load variation, as you say, is the change in load divided by the operating load for the spring. For typical hot (operating) load design, the CAESAR II balancing load will be this hot load and everything is in order.
But when the user selects "cold load design", the calculated balancing load is considered the cold load. Since this "cold load" is now the independent variable,the program's calculated load variation will not reference the hot load; it will be (K*delta)/(cold load) instead.

Since:

Cold Load = Hot Load + K*delta

I think we can adjust our load variation for cold load design to this:

Load Variation = (K*delta)/[balance load-(K*delta)]

Comments are welcome.

Dave,

I agree with your equation Above.
But the point still remains that, How this gets conveyed to vendors? Generally Vendor Catalogues do not define 'Balance load' and also they do not consider "Design for Cold Load" thing.

The Variability equation in Catalogue is fixed since ages. In my opinion All the vendors Should modify the catalogue variability equation:

Variability = K*X/(Load Value as per Min. Absolute displacement).

The term "Load Value as per Min. Absolute displacement" is Balance load.

So , while preparing Spring Hanger Specification, this Balance load should be Tabulated against each spring, so as to have correct variability calculation.

Any comments or suggestions Please.

Just to Add to Above discussion, Even MSS-SP 58 defines Variability on basis of Operating Load and this is what is being followed by All Spring Vendors.