Torsion Spring Calculation?

[titancad]

I am trying to calculate what size torsion spring I need to move a 40 lb load. If you look at the following link you can see the application.

http://mysite.verizon.net/tabarr/images/springquote.jpg

I have used the Eng Edge calculator but am not sure if I used it correctly. I have 35 degrees to push using a 180 degree torsion spring. The cutting head weighs 40 lb. The moment is 2". This gives me a spring constant of 2.2857 (lb-in/deg) "K".
Is this "K" value equal to the "torque in/lb" found in a spring catalogue? If not, how do I equate this "K" value to that torque rating.
Thanks in advance,

Todd

 

[israelkk]

Yes, if the arm (which the Eng Edge calculator wrongly calls "torque") is 2" long and the force/weighs acting on it is 40 lbf then the torque is 80 lbf-in. Dividing it to the 35 degrees deflection gives the 2.2857 (lb-in/deg) which is the spring rate.

However, usually a spring designed for 35 degrees deflection during work is preloaded to some torque before it goes the 35 degrees. Is your spring preloaded or the torque changes between zero to 80 lbf-in during the 35 degrees deflection?

Added to other many factors when you select/calculate a torsion spring you have to take into account how many times it will have to endure the 80 lb-inch torque (fatigue analysis).

http://www.webspawner.com/users/israelkk/

 

[israelkk]

After looking at a spring catalog such as the catalog of Century springs

http://www.centuryspring.com

, it appears that the largest spring they carry is 10 times weaker than your spring. I think you will have to design a custom made spring that will have to fit the given space in you assembly.

http://www.webspawner.com/users/israelkk/

 

[titancad]

I am looking at this spring by McMaster Carr (p/n 92877k99) which has a torque rating of 5.150 in-lbs. I would assume this would be enough torque? The application requires the head to expand after coming out of a pipe, so it will be preloaded in the pipe (35 degrees) and the spring will fully expand after coming out of the pipe.

http://www.mcmaster.com/ctlg/DisplC...gPgNbr=3518&ScreenWidth=1280&McMMainWidth=918

Any response is greatly appreciated.

Todd

 

[israelkk]

The strongest spring in the web page has 42.86 lb-in torque. You need 80 lb-in. Those spring were designed to give the torque at 90, 180, 270 or 360 degrees of deflection. You miss read the data. The 5.5 lb-in is not the rate but the torque after deflection of 360 degrees.

Pay attention that the 42.86 lb-in springs (p/n 9287k105 for example) are more than 1.1" outside diameter and approximately 1.5" long. So your spring will be even larger.

http://www.webspawner.com/users/israelkk/

 

[alr]

A free spring calculator is available here

http://www.southernsprings.co.uk/download-frame.htm

Tony R