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What is the difference between no. of coils and active coils?
In most of the springs, some of the coils are inactive. The count varies with the spring end configuration. With the help of the formula below, we can calculate the total no. of active.
Na= N-2 (For closed ground or unground ends)
Na= N – 1 (For Open Unground ends)
Na= N (For Open ground ends)
What is the difference between closed and closed ground ends?
Springs can be coiled with a variety of end configurations. If the space between the coils is reduced to the point where the wire at the tips makes contact with the next coil, the end is said to be closed. If there is no reduction in pitch at the end coils, the end is referred to as open.
Sometimes a operation called Grinding is applied to any of the end configurations listed above. Grinding removes material for the spring end coils to create a flat surface perpendicular to the spring axis. This could be done due to any of the reasons like to distribute uniformly the load on the spring or could be due to improved ease of assembly since the spring is more likely to stand upright unassisted.
The springs with end grinding operation done are known as grounded springs.
The figure below shows schematics of both open and closed ends in both the ground and unground conditions.
How to choose the material?
Spring material depends upon the application and the working environment of the springs.
Several coatings are available which can provide corrosion resistance for the wires that themselves would not resist corrosion. These coatings include Powder coating, Electroplating, Phosphating.
The coated spring produced by this type of material is generally cheaper than the spring produced from Stainless Steel wire. When the application is such that the coated spring will not meet the requirements of the environment, then the focus turns on Stainless Steel wire. Generally Grade 302 is used that provides very high resistance to corrosion and also is good for high temperature applications.
What is Free Length?
For a compression spring it is the length of the spring from one end to other when no load is applied.
For a Tension spring length between two hooks of the spring from inside when no load is applied is known as free length
How to differentiate between right hand coiling and left hand coiling?
As you look at the spring from top, Starting from the end of the spring, curl your finger along with the coil, If the direction of the curl is clockwise, it is said to be Right hand coiling and if the direction of the curl is anticlockwise, it is said to be Left Hand Coiling.
If we stack two springs, will the spring rate remain same?
Stacking springs will definitely change the rate of spring. The rate of the stack will be less than the softest spring in the stack. The effective rate of the spring will be calculated as below:
What is initial tension?
The term initial tension is generally associated with Extension springs. In case of extension springs, they are designed in such a manner that requires certain amount of force to be applied before the deflection can be realized. This minimum force is known as Initial Tension.