Inherent Damping of a Torsional Spring

Typically from what I have observed there is some 'impact'. You would need a cushion or some type of means to slow down the closing action. it could be frictional or hydraulic.

68torino

A spring has no inherant damping. The friction of the mechanism may slow the action, but a mass on a spring with no stops in a loss free environment while oscilate for all eternity. A spring and mass system behave alot like a pendulum.

If you catch your machanism as the spring slows it, ie at the top of its spwing you get the desired effect but you've created a very precise thingy and I hope you get your money back.

Springs of any type (with the exception noted below) have no inherent damping other than mechanical hysteresis losses in the spring material.

The only spring which offers some damping due to friction is the multiple leaf spring.

BernieK

To add damping to a spring one can add a dashpot. A dashpot is a single-ended cylinder with a loose-fitting piston inside it. The looser the fit, the less the damping, assuming there is some atmosphere to provide some friction.

ok, thanks for the replies.

Now, if this torsion spring is attached to a single-acting rotary vane actuator and the actuator opens the mechanism and the spring closes it, will there be impact on closing. Will the actuator play the role of some sort of a damper?

Regards,

hag

Hi: really, it is possible. Of course, it depend on the characteristics of the actuator and will be a good solution.

Regards,

Gabriel, Buenos Aires, Argentina

That depends on what type of actuator you are using and how you use it.

A pneumatic or hydraulic actuator can have damping if its return port (exhaust) has some type of throttling valve, causing a back pressure. I am assuming this is the case since you describe it as a "vane" actuator, akin to a "vane pump" in reverse.

An electric actuator, like a rotory solenoid or a motor will not have any damping effect once power is cut. If however, power is only reduced during the closing portion of the cycle to provide some minimum torque, it could indeed "dampen" the action of the spring, which exerts less force (and therefore, torque) as it retracts. You could use a variable resistor (potentiometer) to try out various closing "rates" and then substitute a fixed resistor in the final design. But don't forget that motors and solenoids have certain duty cycles which will lessen their force if exceeded.

A standard technique in pneumatic systems is to use a needle valve in the system connected to the valve.

Assume the valve is configured air-to-open, spring-to-close. To slow down opening and closing together, insert a needle valve in the line from the solenoid valve feeding the actuator.

To slow down the closing only, insert a needle valve in the solenoid valve's exhaust port.

To slow the opening only, insert a needle valve in the line from the solenoid valve to the actuator and connect to the actuator via a quick-release valve. Fitting a non-return valve in parallel with the needle valve will also work.

That sounds very much like the ubiquitous 'air strut' so common on hatch-back motor cars. There must be a lot of door closing mechanisms ready made, if our friend searched, he might be able to buy one off the shelf. Probably the least expensive option if it fits the job in hand. Failing that, I was thinking that a pneumatic 'buffer' i.e. a small punctured rubber ball or even a closed cell foamed elastomer insert, might just work? (sadly foams can get lazy and retain a deformed shape if left standing for some length of time) It's a great challenge and has got my grey matter in a spin, of the old "build a better mouse trap" variety. Now there is an instance where we want the spring to come down with a hard slam. My mouse trap is called 'Paddypusscat'

Ah-ah! damping springs. This was exactly what Delaney Galley used to make, as I recall back in the 1960's. Essentially you knit a tube of spring grade stainless steel (annealed of course) then twist the stocking tube into a spring 'Thingy'... (very useful word 'Thingy')....Next you follow the kiln tempering instructions, that come with the annealed stainless steel wire, in the data sheet....Presto...a self damping spring...more of an 'Art' than a 'Science' I fear.

Hi. This is a reply to the torsional spring damping post by Alistair Carnegie. The weaving process described introduces damping by friction between the strands making up the spring, and is not an inherent property of the steel used in making the strands in the first place. In a sense, it is soemwhat the equivalent of the role of friction in multiple leaf spring "damping", if you will.

One additinal consideration involves the fact that 300 series stainlesses and other materials work hardnen over time. If Young's modulus is increased by work hardening, then the damping effect will decrease with age.

BernieK

Berniek, I think you have hit the proverbial nail on the head. Also a very happy New Year.