Torsion Spring Cycle Life

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mkl8687 Participant Join Date: Aug 2016 Posts: 1	Torsion Spring Cycle Life 08/08/2016 10:39 AM
	Hi, I am currently building a worksheet to calculate the cycle life and spring length (or number of coils) for a garage door. The torque, number of winds, and inside diameter are given. The wire diameter is based on a life cycle of at least 25k and spring length of at least 8". I was able to calculate the number of coils using: k = (Ed^4)/(10.8DN) T = k(number of winds) Bending Stress from torsion calculated using: S = (32T)/(pid^3) Now I am having trouble finding a formula to calculate the cycle life based on the stress. Can anyone point me in the right direction? Thanks.
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#1 Re: Torsion Spring Cycle Life 08/08/2016 11:00 AM
	The second thing that is needed is the state of corrosion of the spring, where the corroded material no longer forms part of the flexibility of the spring. A third thing would be a factor to base a reduction of life owing to impact damage from the vehicles entering and leaving the building. It is for that reason that motor vehicles in the UK, once they get over three years from new, are subject to annual inspections and verification of road-worthiness, because it simply isn't possible to calculate the rate of deterioration. How much is a replacement spring, BTW? __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#2 Re: Torsion Spring Cycle Life 08/08/2016 11:22 AM
	Everything in this world cannot be determined by a calculation. Sometimes, some actual work may be required. As PWSlack pointed out, a calculation will yield a number, a number only, with no variation to take into account the thousands of variations possible. Establish a baseline using actual data, or test data, then add to that data as information is gathered. A spread sheet will suffice. Do some research to see if data exists already, then get on with it.
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SolarEagle Guru Join Date: Mar 2007 Location: by the beach in Florida Posts: 33392 Good Answers: 1817	#3 Re: Torsion Spring Cycle Life 08/08/2016 12:26 PM
	You might find something you can use here.... http://www.acxesspring.com/torsion-spring-calculator-instructions.html ..."The standard cycle life in the garage door industry is 10,000 cycles. Spring under 10,000 cycles are considered overstressed and are not recommended for use. If you would like to have more than 10,000 spring cycles, your new torsion springs will need to have a larger wire size. The larger the wire, the longer it will take for the spring to break as thicker steel requires more bending before it breaks. If you increase the wire size of your springs, you will also need to increase the length to keep the same lift and torque rating. On narrower, heavier doors it may also be necessary to increase the inside diameter to provide enough space on the shaft for the springs to fit."... http://ddmgaragedoors.com/springs/standard-torsion-springs.php http://ddmgaragedoors.com/diy-instructions/how-to-measure-torsion-springs.php __________________ All living things seek to control their own destiny....this is the purpose of life
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James Stewart Guru Join Date: Mar 2011 Location: Lubbock, Texas Posts: 14331 Good Answers: 162	#4 In reply to #3 Re: Torsion Spring Cycle Life 08/08/2016 4:14 PM
	You should listen to what was written by Solar Eagle, his comments are usually pretty good, and this time completely spot on. __________________ If it ain't broke, don't fix it. Just build a better one.
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Jpfalt Guru Join Date: May 2016 Posts: 1746 Good Answers: 87	#5 Re: Torsion Spring Cycle Life 08/09/2016 11:26 AM
	You need to find a fatigue life curve for the spring material and calculate fatigue life. This may help: https://www.efatigue.com/constantamplitude/stresslife/#a You will be estimating the fatigue life of the spring based on a probable likelihood of failure.
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James Stewart (1); Jpfalt (1); lyn (1); PWSlack (1); SolarEagle (1)

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