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Compression spring selection

Compression spring selection

Compression spring selection

I am looking for a compression spring that has the following specifications:

Initial length: 22-23 mm
The spring will be compressed to a length of 13-14 mm.
The force when the deflection is 5 mm should equal or exceed 150 N (let's say if the initial length is 22 mm, the force at a length of 17 mm should equal or exceed 150 N).
The external diameter should be less or equal to 7.2 mm

These are the specifications that are constraining the design. Any other specification like the internal diameter, force at different lengths, etc are not important for me.

Can anyone help me with finding such spring? If yes, what should the specifications for that spring be in terms of number of coils, wire diemnsions, etc.? I have no problem in going to variable pitch springs. I tried to search many catalogues but I was not able to find any spring that fulfils my requirements.   

RE: Compression spring selection

Some information is missing:
1. Is the spring for static load or for cyclic load (fatigue)?
2. Is it loaded only to one load or deflects extra deflection beyond the 150N during work?
3. Corrosive environement?
4. Application? (Commercial, Military, Aerospace, Naval, etc.)
5. Quantities?

This is classic spring design problem where catalog springs doesn't fit and the space for the spring is limited.



RE: Compression spring selection

The spring is for dynamic loading.

To answer your second question:

The spring is imbedded inside a device that is attached to the ground. In this case, the spring is initially compressed to a length of 12 mm. At this point; the spring force is not an issue. In other words, the spring force is not of any importance at this length.

Then an external force is applied to lift the device; the device is lifted by 5 mm due to this external force. Up to this point, the spring is deflected by 5 mm. then the external force is released and the spring has to push the ground by a force that is around 150 N in order to lift the device (The force is 150 N at an extension of 5 mm).  The force at a length that is above 17.5 mm will be extremely small and of no interest for me.
Therefore, my main concern is the spring force at a deflection of 5 mm, the initial and final length, and the spring diameter.

The environment is not corrosive.

The application is construction.

The quantity depends on the demand but it will be in thousands.

I hope that the answer for question 2 is clear. If not, just let me know.

I really appreciate your prompt response.


RE: Compression spring selection

Dynamic or cyclic, in the world of springs, refers to springs that endure thousands or millions of cycles, like valve springs.  It sounds like your device has to withstand one cycle.

What that cycle comprises is still a mystery to me, with talk about deflection from free state, and the ground and all.

A specification that includes free length as a requirement, not a reference, is unusual, because free length is rarely important to a spring's application, and springmakers often adjust the free length to compensate for small variations in wire size, in order to meet functional requirements, which are usually stated as force length pairs.

Perhaps you could clarify the problem by restating it in terms of a coordinate system with its origin at the end of the spring that isn't deflected.


Mike Halloran
Pembroke Pines, FL, USA

RE: Compression spring selection

Thank you all for your response.

I am sorry if my explanation is not clear enough.

Anyway, the procedure that I described is repeated twice a day and the device should serve for around three years which means more than thousand cycles.

To reiterate, the problem is:
I need a spring that can be compressed to a length of 13 or 14 mm and that can support a force of around 150 N at a length of around 17 mm. The spring should be able to expand to a length of around 23 mm (This is not necessarily the free length; the free length can be higher than 23). The maximum external diameter is 7.2 mm.

RE: Compression spring selection

Why do you need the spring to be able to be compressed to a length of 13 or 14 mm if the 150N force is achieved at a length of 17 mm. Therefore, I have to assume that the actual force that the spring will see will be much larger than 150N. If the 150 N is achieved at a deflection of 5 mm the spring rate is 30N/mm therefore, the force at a length of 14 mm will be 240N and at a length of 13 mm will be 270N.  

RE: Compression spring selection

Thank you. Now I can say that you know exactly what I am looking for.  

Basically, I was looking for a spring with a stiffness of 30 N/mm but I was unable to find it in any of the catalogues. As for me, it seems to be impossible from a scientific point of view to have such spring with a constant pitch. Therefore, I am thinking of a variable pitch spring. The question is that: Is it possible to find a variable pitch spring that can fulfill my requirements? If yes, what are the specifications of the spring in terms of number of coils, variable pitch, etc. Or where can I find a way to design such spring.

Thanks a lot

RE: Compression spring selection

Following a quick check I suspect that a spring that is compressed to 17 mm and gives 150N and then fluctuates between 17 mm and 14 mm (extra deflection of 3 mm) is not possible. The problem is not the constant pitch, it is the high stresses in the spring which are beyond any spring material currently exist.

RE: Compression spring selection

Ok. Thanks. But Can the high stress problem be solved if the force is reduced to 100N instead of 150N at a height of 17mm. Or what is the highest force that can be achieved at a hieght of 17 mm.  

RE: Compression spring selection


Your last question is too broad for a quick answer. In my opinion focusing on the spring alone is not the correct approach. You should see what can be changed in the system too to make more space for the spring and at the same time find/design a spring that will fit. If spring design is beyond your expertise I suggest you seek professional help. selecting a spring involved many aspects such as material and material availability, manufacturing, coatings, cost, and many more. Bad selection of a spring can seriously affect your whole system performance even though a spring looks like a very simple device.

RE: Compression spring selection

Thanks a lot guys. The best thing is to redesign the device so that there is enough space for the springs.

RE: Compression spring selection

Send me your 3d model. We make custom springs and low cost prototypes. We can see if we can make a spring to fit you part.

You can contact me at 847-671-0709

My name is Chris

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