What's the Name of This Type of Actuator?

[sethro5hc]

Can anybody help me out with the name of this thing? I'm just trying to experiment with something and I'm looking for the actuators (may not even be called that) that are used in rear hatches for SUVs and sometimes on screen doors on porches. The kind from the porch that just slowly hisses air out and gently closes the door.

Technicaly, I supposed both are just single acting linear actuators, but online all I can find are heavy duty ones, pneumatic ones and a bunch of fancy stuff. I need cheap, very low weight, low pressure ones like used for these 2 applications. Are they called something specific?

 

[Compositepro]

They are called dampers, dampeners, dashpots, speed controls, or shock absorbers. They can be hydraulic or pneumatic. Actuator is not an appropriate term because they do not provide energy to actuate anything - they absorb energy.

 

[amorrison]

Search Google - Images using "gas strut".

 

[EspElement]

They are very simular to gas springs

 

[sethro5hc]

Thanks guys, I knew it was probably not called an actuator. Man, I've found that the simple stuff is harder to find information about than the serious, expensive, heavy duty applications.

 

[sethro5hc]

If anybody has any suggestions, here's a little more information.

I basically just need something for an application that will slowly lower something a small distance, around 5-7 inches. The lower time should be at 2-3 seconds. The weight it will lower will be between 10-20lbs, and 4 of these dampers will be used total with the weight evenly dispersed. The main issue that many parts may have trouble with is that about 75% of this part will be submerged in oil that could reach up to 500 degrees F.

 

[sethro5hc]

Oh and it can't be pneumatic or anything that requires an outside power source other than a person lifting it and a force compressing it.

 

[sethro5hc]

The part would preferably "self-return" to it's elongated position when no force was applied to it. Just some quick research has me thinking perhaps a spring-return damper could be the right part for this application?

 

[imcjoek]

http://www.mcmaster.com/#about-gas-springs/=5qcyw3

No?

 

[sethro5hc]

I'm pretty sure an affordable compressed gas application could end in disaster under the high temperatures this would encounter. Some of the first things I came across when researching some gas struts were firefighters getting impaled by pistons after gas struts from doors and rear hatches expanded and basically exploded in car fires.

The product would need to be fairly cheap, and the more I'm thinking of it the more I'm thinking that designing one myself may be the best option. Just think a typical cylinder and piston and a very small hole in the bottom. The piston can only compress as fast as the fluid inside the cylinder escapes the hole. If our manufacturer can deal with these tight tolerances then it's just a fluid dynamics problem after that.

 

[MikeHalloran]

Yeah, piston/ cylinder/ orifice and the oil that's already present sounds like a natural solution.

Getting oil to survive at 500F is a separate problem.

Forget any kind of elastomer seal on the piston; maybe a couple of piston rings if blowby is a problem.


Mike Halloran
Pembroke Pines, FL, USA

 

[GregLocock]

If you want a coilspring as the return mechanism the high temp will reduce the allowable stress range.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[EspElement]

It needs to lower at a slow rate? I wonder if you could use something that hangs and acts similar to an oil shock only in reverse.. So the reservoir can be positioned above the surface, and the rod eye or steel clevis and rod is the only thing that lowers into the oil.. Maybe using extension springs to pull it back to the retracted position? Sounds pretty hairy....

 

[lumenharold]

Perhaps something like a passive magnetic spring damper?

Harold
SW2010 SP1.0 OPW2010 SP1.0 Win XP Pro 2002 SP3
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nVidia Quadro FX4600

http://www.lumenflow.com

 

[KENAT]

Um, dumb question, but can all the dampeners, springs and everything be housed well above the hot oil with just a 'tray' or 'basket' that the 20lb object sits on being dropped into the oil?

(Sorry, typed all that before seeing EspElements post)

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[sethro5hc]

Thanks for all the help. We've actually found a way for the design to work now without the damper being in the hot oil. We think we found a way to get it far enough away from the hot oil so we don't have to worry about temperature restrictions. Obviously this opens the door for lots of applications.

For a quick prototype, does anybody have any suggestions for which type of actuator, dashpot, damper, or gas strut would be cheapest, while having a stroke of at least 7" but not more than 10"? It would need to be able to be compressed with a force of about 4lbs, but something that requires a slightly heavier force could work (would have to be less than 10lbs though). Ideally, it would be elongated when no force is applied, like a gas strut is. Does anybody know of any of these which may be cheaply purchased and could fit this description?

 

[EspElement]

Id start searching mc msster as a refrence, see if they got something you could use.. Then from there find the actual manufactures of the springs so ur not paying an arm and a leg