compression spring torque calculation

[imagineers]

Ok so I can design a spring in solidworks and add a force to one side of the spring and measure deflection. A similar setup can be found here...

http://www.xbitlabs.com/articles/coolers/display/thermalright-true-copper-u120x_5.html

I guess my question is, how do I determine the torque needed to compress the spring a given distance? Another possibly related question is how could I tell the force that each mounting point exerts on the mother board?

 

[hydtools]

So you were able to create an image, not design, of a spring but don't know its spring rate. Knowing the spring rate will allow you to calculate the force to cause a deflection.

I will assume the torque you are seeking is that of the screw to compress the spring some amount. Is that correct?

Ted

 

[imagineers]

To be technical yes I created an image of a spring with approximate 9mm OD that has SS 302 wire thickness of 1.3mm with approximate 4 revolutions. The screw is an m4 that will be screwing into a backplate. I am interested in how to calculate the torque required to compress that spring a certain distance with a driver. Like I said I can bring this in solidworks and add a linear inch/lb force and get a compression distance but that's not really what happens, it is the torque of the screw that compresses the spring

 

[dhengr]

Please do be ‘technically correct’ when you present a question on these forums, there is a big difference between creating an image with a CAD program and actually designing something which actual does something as prescribed, in a simple clean fashion; and a big difference in knowing, and understanding, and not misrepresenting the difference between the two.

It is not “the torque of the screw that compresses the spring.” The fact is that with that particular spring you probably would have trouble measuring torque or torque change before the spring went solid or buckled. To compress the spring a certain distance, what you really want to know is the lead angle of the thread of the screw, in effect, the amount the screw advances per revolution.

 

[hydtools]

Roughly this:

http://www.engineersedge.com/torque.htm

Knowing the spring rate, lb/in, and the spring deflection you can calculate the spring force = screw tension

The torque will be small.

As implied by dhengr, you may get better results by compressing the spring to a desired length to achieve the desired spring force rather than trying to control screw torque.

Ted

 

[desertfox]

Hi imagimneers

Firstly as others have said you need to design the spring and thats important for two reasons:-

1/ you can get your springrate and hence force at deflection

2/ You can also calculate the stress in the spring for
a given deflecton and avoid the spring being overstressed
and taken a permanent set.

Whilst you may not notice that the spring is over stressed it will lose pre-load and your relationship between bolt torque and spring force won't be reliable.
Once your spring is sorted yu can use the formula given in hydtools link above.
For formula on spring design see this site:-

http://www.roymech.co.uk/Useful_Tables/Springs/Springs_helical.html#Compression

desertfox

 

[imagineers]

Thanks for all the information everyone I will have closer look when I revisit my spring design

 

[unclesyd]

Will everyone else was working on the spring I took a look at your cooling arrangement. Here is something you might want to keep in mind for future designs. It is simpler and generally carries a smaller footprint

http://microcooling.com/pdfs/MicroCool General Presentation.pdf

 

[Cockroach]

Computation of the torque on the Nut is quite easy.

Given the Spring geometry, you can compute the load required to bring that spring into solid height. From that load, you can find the torque by noting the screw geometry. So essentially the torque is that load required to bring the spring to solid height times half the major screw diameter.

Pretty much this is it. By the way, I recently did this dynamically using SolidWorks and Motion. Pretty cool.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada